Hassan Bevrani

The primary objective of this research is to mitigate the negative impacts of active power fluctuations in weak power grids using grid-connected converters (GCCs). Weak grids need more infrastructure and stability measures to accommodate the integration of renewable energy sources, such as high levels of solar photovoltaic power. One of the key challenges encountered in such grids is the absence of inertia from converter-based resources, which can lead to grid instability. This thesis proposes a solution to this challenge by employing power electronics grid-forming converters to synthesize additional inertia and damping properties, effectively emulating the behavior of synchronous generators through the use of virtual synchronous generator (VSG)-based converter control strategies. By incorporating these control strategies, the proposed method aims to overcome the limitations of weak. Integrating high levels of solar photovoltaic power into weak grids can lead to local mode oscillations and grid instability. To tackle this issue, the proposed method focuses on suppressing these oscillations by emulating a virtual damper winding (VDE) within the VSG-based GCC. By incorporating virtual inertia and damping properties, mitigating active power fluctuations and enabling the smooth integration of solar photovoltaic power. A genetic algorithm (GA) optimization tool is introduced to optimize the VSG-based GCC’s performance. This tool allows for the optimization of virtual damping and inertia parameters, enabling the VSG-based converter to effectively adapt to the changing conditions of weak grids. Through comprehensive time-domain and frequency-domain analyses, the proposed method is evaluated, and simulation results validate the effectiveness of the optimization technique and implementation procedure. The validity of the proposed method is further confirmed through simulations conducted in the MATLAB/Simulink environment, which encompass various operating scenarios encountered in weak grids. The thesis provides a comprehensive discussion of the approach, optimization tool, and simulation results, emphasizing the efficacy of the proposed method in addressing the challenges associated with weak grids.

-

Microgrids are small-scale power networks comprised of distributed generation resources, energy storage systems, and loads. They can operate in two modes: grid-connected or in islanded mode. In order to meet stability and performance requirements in microgrids, a hierarchical control structure consisting of four levels: primary, secondary, central/emergency, and global control level, has been proposed. The primary control level consists of two main layers: an inner voltage and current control layer and an outer power control layer. In the literature, the inner control layer is often referred to as zero-level control. Proportionalintegral or resonant proportional controllers are typically used for zero-level control. These controllers, despite their popularity due to their simplicity, suffer from long settling times, large overshoots, and lack of robustness to parameter changes. Additionally, they lack axis decoupling and are sensitive to system parameter variations. The bandwidth of the zero-level control is usually large, but the overall bandwidth of the primary control level is determined by the cutoff frequency of the active and reactive power measurement filters. Therefore, the overall bandwidth of the primary level is reduced, which can pose challenges when designing higher-level controllers like the secondary control, as the secondary level has lower bandwidth compared to the uncertain communication network. In the first phase of the thesis, an adaptive unified controller is proposed for controlling the zero-level current in AC microgrids. The main goal of this proposed controller is to regulate the voltage at the common point of coupling to desired values determined by the droop controller. The proposed unified controller has adjustable bandwidth that is tuned systematically and provides stable operation at high and medium frequencies without significant oscillations or overshoots in the output. In AC microgrids, conventional droop control methods are commonly used to active and reactive power sharing among distributed generation resources. As the resistance-toinductance ratio of the feeder increases, the adverse effects of interactions between control loops (frequency-active power and voltage-reactive power) intensify, posing challenges to the performance of droop control. In the second phase of the thesis, an adaptive multi-input multi-output (MIMO) current control structure is proposed to address interaction issues in AC microgrids’ primary control. To evaluate the interactions level between control loops and distributed generation units, relative gain array (RGA) matrix and diagonal dominance concept as numerical and graphical methods are used. The design process of the proposed controller starts by defining a reference model in which desired control objectives such as settling time, steady-state error, and maximum overshoot are formulated. Then, a feedforward-feedback control structure is considered, where control gains are adaptively adjusted based on the stability theory of Lyapunov. In droop-based microgrids, voltage and frequency deviations occur when loads change. The primary control ensures voltage and frequency stabilization but cannot restore them to nominal values. To address this issue, secondary control comes into play. While various control methods have been proposed for regulating frequency to its nominal value in the secondary control level without the need for a communication infrastructure, the challenges of these methods and their ability to simultaneously regulate voltage and frequency in microgrids have not been fully investigated. In the third phase of the thesis, an adaptive MIMO control approach is proposed for restoring voltage and frequency to their nominal values while ensuring appropriate power sharing among distributed generation units in an islanded microgrid. The proposed adaptive controllers are designed based on two approaches: droop-based and inertia-based schemes. Furthermore, the impact of design parameters on system performance is thoroughly examined, demonstrating that these parameters can be tuned to achieve predictable outcomes. The required modeling and simulation are performed using MATLAB/Simulink and SimPowerSystems environments.

By establishing a virtual connection between active power and frequency and reactive power and voltage, frequency and voltage can be used to control the active and reactive power in distributed generation sources implementing inverter converters. Based on the steady-state behavior of the speed control system and the automatic voltage regulator of the synchronous generator, this link can be a virtual ratio. In the active power control channel, this ratio is known as active power-frequency droop, and in the reactive power control channel, it is known as reactive power-voltage droop. In an effort to enhance the load-frequency characteristic of microgrids, the creation of a virtual dynamic link between those mentioned quantities has led to the development of the virtual synchronous generator concept. The simplified model of the synchronous generator exhibits the electromechanical dynamics of the rotor through its first-order dynamics. The swing equation reveals that the virtual synchronous generator is essentially a simple first-order dynamic. The virtual synchronous generator model is not flexible enough in various operating conditions. Microgrid control can be improved by virtually offering and suggesting a flexible dynamics that can improve the load-frequency characteristic for microgrids under various operating conditions. In this study, a flexible and robust controller has been proposed for microgrids in the power control layer, at the primary level of control, which provides better performance in improving the load-frequency characteristic of microgrids than the dynamics of a virtual synchronous generator under different working conditions. In addition, a second flexible controller has been proposed in the internal control layer of the primary level control, which could include voltage and current control of distributed generation sources based on inverter converters and define a simple, decoupled, and flexible model of the closed loop system structure

هنگامی که یک وضعیت جزیره‌ای ناشی از یک خطای ناخواسته در یک شبکه توزیع فعال با تولید پراکنده رخ می‌دهد، پایداری فرکانس و مسائل حفاظتی چالش برانگیز خواهد بود. از این رو، این پایان‌نامه بهبود فرکانس شبکه توزیع فعال با حضور منابع تولید پراکنده را با استفاده از یک روش بارزدایی دو مرحله انجام داده و در ادامه از یک سیستم ژنراتور سنکرون مجازی جهت ایجاد اینرسی مجازی در شبکه و حداقل‌سازی بارزدایی در مسیر رسیدن به پایداری فرکانس تحت شرایط جزیره‌ای ناشی از خطاهای غیرعمدی ارائه می‌شود. کنترل اینرسی مجازی بر مبنای معادله نوسان انجام گرفته است تا اینرسی مجازی را تولید کند و اینرسی سیستم را برای افزایش حاشیه پایداری جبران کند. روش پیشنهادی بوسیله نتایج شبیه‌سازی در نرم‌افزار متلب تأیید و پایداری فرکانس و افزایش کاهش بار بدرستی حاصل می‌گردد. این مطالعه ابتدا در سه سناریو برای بارزدایی دو مرحله‌ای بدون عدم حضور اینرسی مجازی انجام گرفته و در مرحله بعد این سناریوها در حضور اینرسی مجازی مورد ارزیابی قرار می‌گیرند. نتایج شبیه‌سازی نشان می‌دهد که کنترل اینرسی مجازی پیشنهادی می‌تواند به طور موثر فرکانس و پایداری گذرا را در شرایط جزیره‌ای بهبود بخشد، و تعداد بارهای قطع شده را کاهش دهد.

ریزشبکه ساختار جدیدی است که با حضور منابع تولیدپراکنده، منجربه بهروزرسانی شبکه برق میشود. قابلیت کار در حالت جزیرهای یکی از مهمترین مزیتهای اساتفاده از ریزشابکهها اسات، زیرا امکان تداوم تامین توان را در زمان بروز اغتشاش در شبکه اصلی فراهم میکند. تسهیم توان یا بهاشترا گذاری توان در ریزشاابکههادر حالت جزیرهای همواره یک نیاز اساااساای محسااوب میشااود، در واقع تسااهیم توان در بین واحدهای تولید پراکنده یکی از مهمترین چالشهای موجود در ریزشبکه است، چرا که عدم تسهیم مناسب توان در میان آنها منجربه تسهیم بار نابرابر میشود که ممکن است در حالت اتصال به شبکه به مصرفکننده و همچنین شبکه آسیب برساند و اغلب منجربه ناپایداری میشود. ت سهیم توان منا سب باعث بهبود عملکرد ریز شبکه و افزایش کنترلپذیری آن در زمان خطا میشود. در ریزشبکههایی که از چندین منبع تولید پراکنده تشکیل شده است، روش کنترل افتی تکنیکی است که برای ت سهیم توان بهصورت گ سترده مورد ا ستفاده قرار میگیرد. کنترل افتی بهفرکانس و ولتاژ اجازه میدهد تا در مقادیر متفاوتی از مقدار مرجع خود ثابت شاااوند و توان اکتیو و راکتیو را در بین منابع تولید پراکنده به اشترا بگذارند، اما در حالی که توان اکتیو بهطور متناسب با مقدار نامی در بین منابع تولید پراکنده تسهیم میشود، ت سهیم توان راکتیو بهدلیل تفاوت در امپدانس خط و امپدانس خروجی اینورترها، به خطا منجر می شود. جهت تسهیم دقیق توان در ریزشبکه ضمن استفاده از روش کنترل افتی، ضروری است به نحوی تفاوت در امپدانس خط و امپدانس خروجی اینورترها کنترل و جبران شود. رویکرد کنترلی پی شنهادی این پژوهش ا ستفاده از حلقههای دینامیک مجازی به عنوان ترمهای ا صالحگر جهت ت سهیم منا سب توان ا ست. ا ستفاده از حلقههای دینامیک مجازی یک روش مناساب جهت بهبود عملکرد روش کنترل افتی معمولی در تساهیم توان اسااات. در این تحقیق ابتدا با اساااتفاده از حلقه امپدانس مجازی تفاوت در امپدانس خط و امپدانس خروجی اینورترها جبران میشود که موجب بهبود تسهیم توان اکتیو و راکتیو میشود، سپس با اعمال حلقه کنترل م جازی به عنوان جایگزین حل قه ام پدانس م جازی ت فاوت در ام پدانس خط و ام پدانس خروجی اینورترها جبران میشاااود و تساااهیم توان اکتیو و راکتیو بهبود مییابد. حلقه کنترل مجازی شاااامل یک جبرانساز پسفاز است که با ایجاد فاز منفی موجب بهبود تسهیم توان میشود.

حفاظت پشتیبان ناحیه-وسیع مبتنیبر PMU در حضور منابع تجدیدپذیر در سیستم قدرت

Distributed generation based on renewable energies with power electronic interfaces are penetrating the power systems at an alarming rate to replace the conventional generation format. This issue may solve the concern related to energy crisis and air pollution, nevertheless, it creates new challenges in the system. The concept of microgrids as a smaller scale power grid makes it easier to exploit and control these resources in the distribution system. On the other hand, increasing the penetration of renewable energy sources in the power grid reduces the inertia and frequency stability of the power grid. The main reason for reducing inertia is the absence of a rotating mass in renewable energy sources and energy storage systems. In addition, the potential degradation in inertia leads to an increase in the rate of frequency change and the nadir frequency. Flexible power converter that mimics the behavior of conventional synchronous generators are gaining traction as a promising strategy to improve the frequency stability of systems facing high penetration of these sources. Initially, this concept was introduced as virtual inertia and virtual synchronous machine/generator. Nowadays, the idea of virtual inertia in the grid is not enough to stabilize a network with different distributed generation units. To solve these challenges, flexible controlled power converters have been proposed in order to virtualize other dynamic properties in modern power grids. This thesis, in addition to using the concept of virtual inertia, it is tried to use other dynamic properties of power grids such as virtual rotor, virtual primary control, and virtual secondary control as developed virtual synchronous generator in the structure of flexible controlled power converters. The developed virtual synchronous generator controller is applied to an AC microgrid for the purpose of frequency control. Besides, in order to have adaptive performance against disturbances and uncertainties in the studied AC microgrid, an effective solution based on a fuzzy controller is presented to adjust the virtual parameters. In addition, conventional linear control methods suffer from high sensitivity to parameter changes and slow transient response, that is why the developed extended virtual synchronous generator based fuzzy can be a suitable method to maintain microgrid frequency stability. The simulation results for a test system show high performance and desirable responses for different scenarios of load and power output of renewable energy sources. The required modeling and simulations have been done in Simulink, Sim Power Systems, and Fuzzy Logic Toolbox of MATLAB software

Inverter-based Distributed Generations (DGs) have emerged as an efficient solution for the exploitation of renewable energies. In addition to regular power generation in the grid presence, DG systems must be able to supply local loads during main grid outages. Hence, their inverters should be capable of operating in both grid-connected and islanded modes. These systems operate as current sources for the AC grid in grid-connected mode, and as voltage sources for the load to control its voltage and frequency in islanded mode. The transition between operating modes may distort the voltage or current waveforms because of a frequency, phase, or amplitude mismatch between the inverter output voltage and the grid voltage. Therefore, for a smooth transition without abrupt changes and distortions, a comprehensive control method is required to be applied to inverters. The control strategy proposed in this research, entitled “Hybrid Fuzzy-Predictive Control,” provides the adjustment of the predictive control cost function coefficients intelligently by using fuzzy logic, and has the harmonic distortion rejection capability caused by nonlinear loads. This controller leads to improved inverter behavior in transitions, as well as enhanced dynamic response in steady states. This improvement has been measured using various control criteria in the simulations. In addition to mitigating Total Harmonic Distortion (THD), enhancing steady-state error, and reducing the overshoot/undershoot of the inverter time response, the suggested control method increases the efficiency, and is also robust under the parameteric uncertainties. The innovation of this thesis is combining fuzzy and predictive control methods, and applying the hybrid controller to voltage source inverters used in distributed generations

تحت فشارهای محیطی و اقتصادی، سیستم قدرت در بیشتر اوقات با ظرفیت کامل بارگذاری می شود. به همین دلیل میرایی ضعیفی دارد. بنابراین، پایداری سیستم قدرت را می توان عمدتا به عنوان ویژگی یک سیستم قدرت تعریف کرد که به آن اجازه می دهد در شرایط عملیاتی عادی در شرایط پایدار باقی بماند و پس از ایجاد اختلال، حالت تعادل کافی را به دست آورد. پایدارسازهای سیستم قدرت (PSS) باید بتوانند سیگنال های پایداری مناسب را در طیف وسیعی از شرایط عملیاتی و اغتشاشات ارائه کنند. با افزایش تقاضای برق و نیاز به فرمان دهی سریع تر و انعطاف پذیرتر سیستم در شرایط رقابتی، سیستم های قدرت فعلی می توانند به شرایط استرس کمتری نسبت به سال های گذشته دست یابند که دلیل این امر افزایش کنترل-کننده های مختلف در سیستم قدرت است. اغتشاشات ناگهانی باعث می شود که سیستم ناپایدار یا نوسانات ضعیفی را دارا باشد که بیشتر در سیستم های قدرت الکتریکی در سراسر جهان، این اتفاق رخ می دهد. در سال های اخیر، با توجه به توسعه سریع تکونولوژی های کامپیوتری، استفاده از ابزارهای بهینه سازی برای کمک به اجرای کنترل پایداری سیستم قدرت امکان پذیر شده است. علاوه بر PSSها، ادوات انعطاف پذیر سیستم قدرت (FACTs) نیز از عوامل بسیار مهم برای افزایش پایداری سیستم قدرت هستند. در این پروژه به بررسی تنظیم پارامترهای پایدارساز سیستم قدرت و همچنین استفاده از عناصر انعطاف پذیر خطوط انتقال جهت بهبود پایداری و کاهش تلفات و مقایسه آنها با تنظیم پارامترهای پایدارساز سیستم قدرت، انجام می گیرد.

This thesis proposes a novel and comprehensive strategy for coordinating the frequency control of a low-inertia islanded microgrid (MG). The main components of the MG include a wind turbine based on a double-fed induction generator (DFIG), a battery energy storage system (BESS), and synchronous diesel generators (DGs).The proposed control strategy handles the MG frequency stability during load-frequency disturbances under all wind conditions with no need for wind velocity measurement. In the frequency control framework, a novel coordination mechanism between the DFIG and the BESS is developed to handle the responsibility of temporary-fast frequency support and compensate for the deficiencies and shortages of DGs in providing the fast-frequency response during sudden frequency disturbances. The coordination is established by a new factor varied with the DFIG rotor speed. It exploits maximum support energy of the DFIG available in any operational wind condition with considering the operational limitations to minimize the use of BESS energy. Compared with the coordination methods existing in recent researches, which usually use fuzzy logic controllers, the proposed coordination has the advantages of simplicity and comprehensiveness for all operational wind conditions. It addresses and compensates the unreliability and the shortages of the DFIG wind system in the certain frequency support under any wind condition by the coordinated use of BESS, while avoiding the over-deceleration (OD) and overloading (OL) issues of DFIG during the support period. It also avoids the secondary frequency drop issue due to the DFIG rotor speed restoration. In normal conditions, to optimally manage the MG energy efficiency, the BESS exchanged power is set to zero, and the DFIG is controlled at the maximum power point tracking (MPPT) operation.The proposed local controls for the DFIG wind system -including the direct power control and a novel MPPT method- are based on power feedback control. It allow the DFIG system to reduce its speed freely and to release the rotor kinetic energy for the temporary support of the MG frequency through a virtual inertia control. After the temporary-fast frequency support, to come back in high-efficiency pre-disturbance normal conditions, the support powers of the DFIG and BESS are brought back to zero by a secondary frequency control (SFC) applied to the DGs. The SFC action ensures the effective frequency regulation in the rated value. The detailed time-domain simulation models the MG with its components for the accurate evaluation and verification of the raised aspects. The coordinated frequency control strategy is compared with no control, only DFIG inertia control, and only BESS control under various wind conditions. The simulation results verify the effectiveness and superiority of the proposed scheme compared with the other methods in the MG frequency stability improvement.

Increasing the penetration level of distributed generation units as well as power electronic devices increases the complexity and variability of the dynamic behaviour of the micro grids. Micro grids have many challenges, such as being random in their production. As a results, the energy production from distributed generation sources will be constantly fluctuating. Therefore studying the micro grid transient modelling and its signal stability are importance. One of the major disadvantages of most studies on micro grid modelling is their excessive attention to the steady state period and the lack of attention to micro grid performance during the transient period. Also, in most of papers, the behaviour of different micro grid loads has not been studied. One of the mechanisms of power systems stability studies is the application of state space modelling. These stability studies including the development of state space models of various components of the power system and then linearizing them around an equilibrium point. In this paper, a comprehensive method for modelling of islanded inverter-based micro grids with dynamic and static loads is presented. The basic concepts of the proposed method are dq0 transformation and dq0-based models. In order to find a complete and accurate model of islanded inverter-based micro grid, the sub-modules of generation, network and load must be modelled in local dq reference and then transferred to a common reference. The simulation results show the effectiveness of the proposed modelling approach for transient stability studies

In recent years, cyber- attacks on communication links became an interesting research topic in various fields. In general, the aim of these attacks is to disrupt the system by corrupt exchange information, sever communication link, etc. Cyber-attacks could occur on different components in cyber-physical-systems e.g., measurement sensors, control and communication links. Distributed control is an attractive alternative to centralized control, however, this control architecture is vulnerable to cyber-attacks due to exchange information between different units. Since cyber-attacks could cause damages in control systems, the resilient control method against them is necessary. In this thesis, firstly the impact of cyber-attacks on current communication links of different secondary control strategies in DC microgrids are studied. Then, resilient control methods against cyber attacks of theses systems are considered. In the first method, an PI controller with an adjustable gain is employed to eliminate the impact of FDI attack on the communication links. A fuzzy based resilient secondary controller is then proposed to cope with all the well-known cyber attacks in DC microgrids. In this method, the communication weights of the Consensus protocol of the distributed secondary controls of units are adjusted through a fuzzy controller. A DC microgrid test system is employed to verify the proposed methods using numerical simulations.

Traditional centralized power generation has recently lost its attraction due to increasing concerns about environmental pollution and the fossil energy crisis. Distributed generation (DG) may be a promising alternative as it can facilitate the interconnection of renewable energy sources (RESs), such as photovoltaics, wind turbines and hydropower. To increase the reliability, flexibility, power quality and intelligence of DG system, several DG units, together with loads and energy storage systems (ESSs), are integrated into a single controllable entity, known as microgrid. Renewable energy sources are usually connected to a point of common couplling through electronic power based interfaces such as inverters. One of the main problems of these electronic power converters is the creation of voltage harmonics along with nonlinear loads. Therefore, coordinated control of parallel inverters and voltage quality play an essential role in the strong performance of microgrids. In this thesis, the load and/or grid connected to an inverter is modeled as the combination of voltage sources and current sources at harmonic frequencies. As a result, the system can be analyzed at each individual frequency, which avoids the difficulty in defining the reactive power for a system with different frequencies because it is now defined at each individual frequency. Moreover, a droop control strategy is developed for systems delivering power to a constant current source, instead of a constant voltage source. This is then applied to develop a harmonic virtual synchronous generator controller so that the right amount of harmonic voltage is added to the inverter reference voltage to compensate the harmonic voltage dropped on the output impedance due to the harmonic current. This forces the output voltage at the individual harmonic frequency to be close to zero and improves the total harmonic distortion (THD) of the output voltage considerably. To evaluate the effectiveness of its performance, it is compared with a droop controller. MATLAB software is used in SimPowerSystems to evaluate the performance of controllers.

Nowadays, microgrids (MGs) have been introduced as new structures of electrical power systems. These structures include a number of distributed generation units (DGUs), loads, and energy storage systems, which can be operated in either interconnected mode, grid-connected mode, or islanded mode. To appropriate control of these systems hierarchical controls have been proposed, where primary control has to keep the voltage and frequency stability of units, and the secondary control (SC) is focused on power quality issues and voltage and frequency restoration considering appropriate power sharing among units. Communication infrastructure (CI) in microgrids (MGs) allows the application of different control architectures for the secondary control (SC) layer. The use of new SC architectures involving CI is motivated by the need to increase MG resilience and handle the intermittent nature of distributed generation units. The structure of SC is classified into three main categories, including centralized SC (CSC) with a CI, distributed SC (DISC) generally with a low-data-rate CI, and decentralized SC (DESC) with communication-free infrastructure. To meet the MGs’ operational constraints and optimal performance, control and communication must be utilized simultaneously in different control layers. In this thesis, first, we review and classify all types of SC policies from CI-based methods to communication-free policies, including CSC, averaging-based DISC, consensus-based DISC methods, containment pinning consensus, event-triggered DISC, washoutfilter-based DESC, and state-estimationbased DESC. Each structure is scrutinized from the viewpoint of the relevant literature. Challenges such as clock drifts, cyber-security threats, and the advantage of event-triggered approaches are presented. Fully decentralized approaches based on state-estimation and observation methods are also addressed. Although these approaches eliminate the need of any CI for the voltage and frequency restoration, during black start process or other functionalities related to the tertiary layer, a CI is required. Then, a decentralized optimal secondary controller for frequency regulation and accurate active power sharing in autonomous microgrids is presented. This optimal controller does not require any communication network. Unlike most of the existing works, a systematic approach of secondary controller design is introduced based on a quadratic cost function in the form of a linear quadratic regulator (LQR) problem. The design procedure only depends on the cut-off frequency of the power calculation filter. Decentralized behavior, simplicity, optimality based on a quadratic cost function, and straight forward design procedure are the main advantages of this approach. Finally, a decentralized SC based on the active power estimation (APE) is presented, as well. This achievement is realized by employing the unique feature of frequency as a global variable in autonomous AC MGs. The APE is merely based on the droop coefficient of P −ω characteristics. The decentralized SC, utilizing a consensus protocol, restores the MG frequency to the nominal value while maintaining accurate power-sharing of the droop mechanism. The consensus protocol is estimation-based and does not require communication infrastructure. In addition to the proposition of stability analysis method, experimental results with four distributed generation units (DGUs) also verify the effectiveness of the proposed SC structures.

In dc MGs, the distributed sources, energy storage systems and loads with different electrical characteristics are typically interconnected to the main bus through power electronic converters. The existence of interfaced converters creates two major problems: 1) the load-side converters and their associated loads, usually considered as constant power loads (CPLs), introduce destabilizing effects into the system, 2) the source-side converters do not possess any inertia or damping properties but reducing the overall inertia of the system. In this thesis, modeling and stability analysis of low inertia dc MG loaded by CPLs have attracted attention and their operating performance are improved by using the concept of controlled power source and virtual inertia in ac MGs dynamic response. The controlled power source consists of three fundamental components: energy storage system, bidirectional interfaced converter, and proper control mechanism. Thus, each component is considered as a useful solution to improve the dynamic response of the system. For energy storage unit, a supercapacitor is proposed due to the high power density and fast dynamic response. The proposed control scheme is composed of a virtual inertia and a virtual damping. It is implemented in the inner current control loop. The proposed virtual inertia is implemented in series with the derivative feedback of output voltage that decreases the rate of change of voltage immediately after disturbance. Furthermore, the proposed virtual damping decreases negative impact of CPLs on stability by improving damping ratio. The proposed control scheme is not dependent on structure of the intrfaced converter and its performance has been tested on buck and boost converters. In order to study the stability of dc MG with CPLs, a comprehensive smallsignal model of sources, interfaced converters, control system and loads are derived by using state space averaging. The effect of proposed control parameters on stability are investigated and an acceptable range of inertia response parameters is determined by using the system’s root locus analysis. The required modeling and simulations are done in Simulink and SimPowerSystems environments of MATLAB software.

با توجه به روند رو به رشد استفاده از منابع انرژی در سالهای اخیر، کاهش سوخت های فسیلی و آلودگی ناشی از آنها، همچنین نگرانی در مورد تغییرات آب و هوا و هزینه زیاد توسعه شبکه های سنتی، لزوم بهکارگیری هر چه بیشتر منابع تجدیدپذیر انرژی احساس می شود. یکی از راهکارهای پیش رو برای غلبه بر این مشکلات، استفاده از منابع انرژی تولید پراکنده می باشد. راه بهینه استفاده از این منابع، ایجاد ریزشبکه است. مفهوم ریزشبکه برای حل مشکل ادغام منابع تجدیدپذیر انرژی و ژنراتورهای توزیع شده در شبکه قدرت، به وجود آمده است. طبق تعریف؛ ریزشبکه ها مجموعه ای از منابع تجدیدپذیر انرژی مانند انرژی باد و خورشید، دستگاه های ذخیره ساز انرژی و بارهای محلی هستند که به دو صورت متصل به شبکه و جزیره ای می توانند مورد بهره برداری قرار گیرند. ریزشبکه هم مانند دیگر شبکه های الکتریکی در معرض انواع خطاها قرار دارد و برای حفظ امنیت آن، باید روش های حفاظتی مناسب هنگام رخداد خطا به کار گرفته شوند. این روش ها باید توانایی تشخیص خطا در زمان مناسب را داشته باشند به گونهای که کمترین آسیب به سیستم وارد شود. در این پایان نامه یک ریزشبکه ACمتصل به شبکه سراسری در نظر گرفته شده و به آن خطای اتصال کوتاه متقارن اعمال شده است. مهم ترین نوآوری این تحقیق، تشخیص خطاهای احتمالی در ریزشبکه ها با استفاده از روش های مبتنی بر سیگنال است. ضرورت اصلی انجام این تحقیق این است که با تشخیص به موقع خطا در ریزشبکه، امکان جلوگیری از عواقب خطرناک آن با استفاده از روش های مبتنی بر سیگنال فراهم گردد. فرض می شود ریزشبکه در معرض انواع خطاهای احتمالی، اغتشاش و نامعینی قرار دارد و هدف، طراحی سیستمی است که بتواند در کمترین زمان ممکن، خطا را تشخیص داده و محل وقوع آن را تعیین کند. بر این اساس، با استفاده از رویکرد مبتنی بر سیگنال و استخراج شکل موجهای سیگنال های جریان، ولتاژ و توان خروجی منابع تجدیدپذیر انرژی و بارهای ریزشبکه در لحظه وقوع خطا و مقایسه آنها با حالت نامی، وقوع خطا تشخیص داده شده است. برای تعیین مکان خطا، ویژگی های حوزه زمان سیگنال توان استخراج و به عنوان ورودی به الگوریتم ماشین بردار پشتیبان داده می شود و با استفاده از روش طبقه بندی کننده ماشین بردار پشتیبان، مکان خطا نیز تشخیص داده شده است. همچنین به کمک این روش، خطا و اغتشاش در منابع تجدیدپذیر انرژی با هم مقایسه شده اند و این روش به خوبی قادر به تشخیص آنها از یکدیگر است.

In recent years, DC microgrids have received special attention due to their easier control, increasing renewable energy sources with DC output and increasing DC loads. Renewable energy sources are often either no inertia or low inertia; however, DC microgrids in the island state (lack of main grid support) and high penetration of renewable energy sources have very low inertia, which in turn drives and fluctuates. To address this problem, the concept of virtual inertia has recently been introduced. In this study, a virtual controller was used to improve the dynamics of a DC microgrid. A virtual inertial controller is introduced as a virtual controller based on the concept of a virtual synchronous machine. The virtual controller is implemented with a built-in controller and a secondary controller in a buck converter. To optimize the robust performance of the microgrid against perturbations and uncertainties, a new approach based on 𝐻∞ robust control is proposed. In the proposed solution, a small 𝐻∞ robust controller is designed instead of a virtual controller with the help of a small signal network model. Then, the virtual controller parameters are determined based on a proposed algorithm. In the following, the simulated DC microgrid is simulated in Simulink / MATLAB software. Then, to evaluate the performance and performance of the proposed solution, the network underwent various tests. The simulation results not only show the robust and optimal performance of the network in the presence of uncertainties, but also determine the efficiency and flexibility of the virtual controller to improve the inertia and dynamics of the network.

Nowadays, Electrical Microgrids are known as a group of most important players of smart grids, which in the AC, DC, and hybrid types are studied, experimentally implemented, and operated in real cases. These active distribution grids that are formed from a set of distributed generation units and electrical consumers, can be operated in the main grid-connected and isolated/islanded modes. So far, these two operation modes have been taken into account in different aspects, i.e. stability, control, protection, planning and operation. In recent years, the interconnected microgrids as a new operation mode is taken into account. It can be resulted in improvement of generation and consumption felxibility, reliability resiliency, penetration increase of renewable energy sources and load shedding decrease. Although, the mentioned adventages are claimed in the valid references and can intuitively be proved, they should be studied in detail and their challenges should be eliminated. Connecting several relatively extensive systems causes a large scale system, which the modeling method and the analysis of the impact of each component on the system stability and control is an important challenge to be researched. Therefore, In this thesis, modeling, stability analysis, and improvement of interconnected AC microgrids is payed attention. Two types of the interface devices of AC microgrids are considered including circuit breakers and back-to-back converters. Both groups of interconnected AC microgrids through these interface devices are modeled and their small-signal stability is analyzed. Moreover, the reduced-order linear models are proposed using perturbation and aggregation methods in otder to analyze the stability of dominant low-frequency modes and study frequency response. The acceptable ranges for the most important parameters of the microgrids and interfaces to stabilize the system interconnected microgrids are calculated using eigenvalue analysis, participation matrix and sensitivity analysis. Furthermore, the transient stability of the studied system is assessed, which results in limiting the DC link voltage in the case of back-to-back converters. Finally, a generalized droop controller embedded with logical functions is proposed to improve the performance of the interconnected microgrids in the emergency condition. The required modeling and simulations are done in Editor, Simulink and SimPowerSystems environments of MATLAB software, as well as real time in OPAL-RT digital simulator.

امروزه تقاضا برای استفاده از انرژی های تجدیدپذیر در سیستم های قدرت مدرن به دلیل عامل هایی از جمله هزینه سوخت، کاهش تدریجی سوخت های فسیلی و آلودگی های زیست محیطی رو به افزایش می باشد. در شبکه قدرت امروزی ظرفیت تولیدات پراکنده با رابط های اینورتری به سرعت در حال افزایش است. در مقایسه با نیروگاه های بزرگ مرسوم که در آن ماشین سنکرون غالب است، واحدهای متصل شده به شبکه از طریق رابط های اینورتری، فاقد اینرسی بوده و یا دارای مقدار اینرسی ناچیزی هستند. کاهش اینرسی کلی شبکه، منجر به افزایش نرخ تغییرات فرکانس و کاهش حداقل فرکانس در مدت زمان کوتاهی می شود که پایداری سیستم را به خطر می اندازد. برای غلبه بر مسئله کاهش اینرسی شبکه در پاسخ به افزایش نفوذ این منابع جدید، اینرسی مجازی به عنوان راه حلی مناسب معرفی شده و مکانیسم های زیادی برای پیاده سازی آن از طریق رویکرد های مختلف مانند کنترل توان توربین های بادی، ذخیره سازها و کندانسورهای سنکرون پیشنهادشده است. اینرسی مجازی، یا به عبارت دیگر مفهوم ژنراتور سنکرون مجازی، می تواند در شبکه به وسیله سیستم ذخیره ساز انرژی و شیوه کنترلی مناسب ایجاد شود. در واقع، ژنراتور سنکرون مجازی رفتار ژنراتورهای سنکرون واقعی را با استفاده از کنترل منابع مبتنی بر مبدل های الکترونیک قدرت تقلید می کند. درحالی که مطالعات قابل توجهی در زمینه ی چگونگی فراهم کردن اینرسی مجازی از طریق تجهیزات و رویکرد های کنترلی مختلف انجام شده تقریباً اکثر روش های موجود ژنراتور سنکرون مجازی در تقلید معادله نوسان برای ویژگی های اینرسی و میرایی ژنراتور سنکرون واقعی مشترک هستند. بحث کنترل فرکانس در ریزشبکه ها با وجود منابع تولید پراکنده به همراه تجهیزات ذخیره کننده انرژی اهمیت پیدا می کند. با توجه به تغییرات در توان تولیدی تولیدات پراکنده و تغییرات در توان مصرفی بار، فرکانس ریزشبکه تغییرکرده که طراحی کنترل کننده ها جهت بهبود فرکانس ضرورت پیدا می کند. برای ارزیابی راهکار پیشنهادی یک ریزشبکه به عنوان نمونه انتخاب می شود. در این تحقیق، یک ژنراتور سنکرون مجازی پیشنهاد شده است که با تقلید ویژگی های ژنراتور سنکرون واقعی یک اینرسی مجازی ایجاد می نماید که وظیفه کنترل فرکانس در برابر تغییرات بار را بر عهده دارد. بنابراین، به منظور تقویت عملکرد کنترلی ژنراتور سنکرون مجازی درکنترل فرکانس ریزشبکه از یک الگوریتم ژنتیک استفاده شده است. این الگوریتم با بهینه سازی مقادیر پارامتری کنترلی، کنترل فرکانس ریزشبکه را بهبود می بخشد و انحراف فرکانس را به حداقل می رساند. در ادامه، ریزشبکه به همراه کنترل کننده های طراحی شده در محیط جعبه ابزار شبیه سازی سیستم قدرت در نرم افزار متلب پیاده سازی می شود و نتایج حاصل از شبیه سازی تجزیه و تحلیل می شوند.

For economic, technical and environmental reasons, the capacity of distributed generation resources in microgrids is growing rapidly. The distributed generation resources connected to the inverter have a very low inertia. When they are connected to the power grid on a large scale, the overall inertia of the system decreases and the system stability decreases. An effective solution to this challenge is to use a virtual inertia. In this thesis, the inertial response of the virtual synchronous generator based on the renewable energy sources connected to the converter as well as the performance of the active power in transient moments in two modes connected to the grid and disconnected from the AC micro-grids are improved. This improvement is achieved by fuzzy controller as a communication-less control method. First, a nonlinear model of the virtual synchronous generator is presented. Then, using the proposed control loops and the designing of the bang-bang and fuzzy controllers, the system performance is improved with respect to inertial response and transient frequency response. The inertial response and transient frequency of system are improved by using the proposed control loops and designing of bang-bang and fuzzy controllers. In order to highlight the effectiveness of the proposed techniques in this thesis, a comparison has been made between the methods, which presented in the thesis and the techniques based on self-tuning methods. In the next step, a comparison between the enhanced and fuzzy control virtual synchronous generator is done. Important criteria for testing accuracy are frequency and rate of change of frequency (RoCoF). Next, a nonlinear model of virtual synchronous generator is linearized in order to investigate and analyze the parameters affecting system performance. In the mentioned section, we analyze the parameters affecting the system performance in transient mode. In all parts of the thesis, including nonlinear and linear models as well as the proposed control algorithms of the thesis, validation has been carried out. Simulations are performed in MATLAB - Simulink software environment. In addition, the experimental results confirm the results of the present study.

Growing the penetration level of distributed generators and increasing of microgrids lead to born a new style of power grids named interconnected microgrids. Thus, new challenges such as load-frequency control while power is exchanged between microgrids are introduced. First, this study is focused on providing a simplified model for load-frequency control in interconnected microgrids. State-space equations are used for this simplification. The final model describes an interconnected microgrids frequency response structure which is suitable for study on frequency control analysis and synthesis. Finally, a block diagram is obtained for study the frequency response. Preserving the frequency stability of new configurations in smart grids such as interconnected microgrids is a serious challenge. Inertia can act as a significant stability/performance index for frequency regulation in the power grids. Renewable energy sources have low inertia and mostly need special control mechanism to apply their inertia to the system virtually. Hence, in this thesis another frequency response model is introduced for AC interconnected microgrids based on inertia concept. In other hand, considering virtual inertia as an important index for system stability is always done in control point of view. A clear classification has not been done considering the inherent behavior of all distributed generators type yet, which can help researchers to introduce more simple strategies to provide better performance. Therefore, this thesis addresses a new approach for study on inertia and a simple frequency response model for AC interconnected microgrids. Furthermore, an adaptive controller (neural networked controller) is suggested for solving the load-frequency control problem. The control methodology is applied to a two-AC interconnected microgrids which is considered as a simplified frequency response model. The effectiveness of the proposed controller is examined by simulation. The simulation results show that in different conditions, neural network controllers can operate better than the conventional proportional-integral (PI) controllers. Finally, this thesis proposes a different approach for analyzing dynamic effect of special ability of renewable energy sources which is introduced as controllable power sources. Based on this concept a frequency response model for two AC interconnected microgrids is presented in two steps. First, the dynamic effect of back to back converters is introduced. Then, controllable power source is added to the model. Performance of the proposed frequency response model is tested by MATLAB/Simulink platform.

In this thesis, new model-based methods are introduced for fault detection in DC-microgrids. Also, the model-based fault detection methods have many challenges, applying this method for DC-microgrids can increase these challenges. The faults in DC-microgrids are considered on two levels. These levels are DC-bus short circuit and parametric faults, respectively. In this thesis, two new methods are designed for DC-microgrids. The first method is designed for detecting DC-bus short circuit by using artificial neural networks (ANNs). The results are shown that this method can be very effective in identifying complex DC-microgrids. Our main challenge in model-based fault-detection is increasing the sensitivity of the residual signal against fault effects and robustness against disturbance effects. The second part of this study aims to solve this challenge for detecting parametric faults in DC-microgrids. Indeed for solving H_-/H_∞ problem, we used from linear matrix inequalities (LMIs). Finally, the H_-/H_∞ based fault detection is compared with Kalman filter based fault-detection in various scenarios. The results are shown that the H_-/H_∞ based fault detection is more effective for detecting parametric fault.

Static output feedback (SOF) is a simple and economical controller that has been used in many applications. Stabilizing, as the most important controlling goal, is at the top of applications. Here, a robust SOF technique is used to perform the control mechanism of a virtual inertia generator in a microgrid to improve the frequency control performance. Lyapunov and non-Lyapunov based approaches have been used in order to solve the static output feedback stabilizer problem, but almost all of them are in face of some difficulties. These difficulties are the result of using some intermediate functions. In this thesis, a direct method has been proposed in order to solve the stabilizing SOF problem. In fact, in this approach a two-step method is presented that uses the closed-loop system matrix directly and unlike other approaches it does not use intermediate functions. In the first step, the proposed method tries to symmetrize the closed-loop system matrix and then in the second step and after symmetrizing, using linear matrix inequalities the stabilizing gain to be found. Some numerical examples demonstrate the effectiveness and simplicity of the approach.

Over the past few decades, because of the occurrence of global outages around the world, the issue of frequency stability has become one of the most serious concerns of the power system operations. Growth of electrical energy demand, electricity markets and economic and environmental constraints in constructing new transmission lines, have brought power systems closer to their stability limits. In such situations, online analysis and monitoring of stability status is essential in order to ensure a safe and stable operation. With advances in communication systems, it is possible to measure voltage and current phasors synchronously in widearea systems. The online estimation of stability indicators to assess system stability is one of the most important applications of the widearea monitoring system, which helps system operator to perform appropriate control actions to maintain system security. In this thesis, a method for estimating the frequency stability indices, including the Rate of Change of Frequency (RoCoF) and the minimum (maximum) frequency and its occurrence time for a power system is presented. The proposed method only evaluates the behavior of the frequency dynamics of the system using the data measured by the PMU units without any information about the network structure. For this purpose, it is assumed that the PMUs have the ability to send data at a rate of 50 frames per second. The efficiency of the proposed method is shown on a two area power system and a 16-machine system. Simulation results show the high accuracy of the proposed method over a period of time that is less than the time of the occurrence of the desired dynamics.

In recent years, the increase in the penetration of distributed generators (DG) in distribution networks has had a direct impact on the reliability, protection and sustainability of these networks. Therefore, it is necessary to conduct a comprehensive study on the impact of the presence of distributed generators on the distribution network, especially traditional protection plans. In this regard, inverter-based distributed generators are the main challenge in the field of protection and automation of microgrids, which is due to their control structure and their inability to generate sufficient fault current. On the other hand, the flexible distribution of energy resources and storage (FDERS), which is a new concept, increases the controllability and reliability of microgrids, as well as the ability to adjust the interface impedance between distributed generators and loads by adjusting the controller reference voltage. The features described for FDERS have a negative impact on the protection system and cause erroneous performance of the current-based relays. FDERS is provided for island microgrids and provides many benefits such as optimal use of energy resources, increase of system robustness and increase of equipment life. In addition, the FDERS scheme, the controllers of distributed generators has been amended. In this study, it is shown that the implementation of the FDERS plan has a negative impact on the protection plans of the distribution system. In order to solve this problem, in this study, the coordination between the control process and the protective equipment has been done by adding new constraints to the current-based relays. To do this, a new control strategy is introduced that is synchronized with FDERS-based inverter controllers. The protection plan proposed in this work is designed to increase the security and reliability of the protection plan. The evaluation of the control and protection plan presented is done using simulation in MATLAB. The simulation results show that the proposed protection scheme has a reliable and error-free performance and eliminates the negative impact of FDERS on the protection system.

Environmental, technical and economic issues have led power systems to replace conventional synchronous generators with renewable energy sources. In the presence of significant penetration of such sources, which are mainly connected to the network through electronic power interfaces, low inertia levels along with variable generator resource production and continuous load changes can lead to frequency fluctuations. Virtual inertia is known as one of the useful auxiliary services for improving frequency response. While significant studies have been done on how to provide virtual inertia through various control equipment and approaches, only a handful of studies are about the placement of virtual inertia in the network. However, the optimal placement of virtual inertia has a significant impact on system efficiency and effectiveness. One of the reasons for the lack of studies in this up-to-date and new field is the lack of a suitable model for virtual inertia from the perspective of the above network, which is discussed in this dissertation. Due to the widespread use of distributed generation resources in recent years, the use of energy storage systems has received attention. Energy storage systems have different specifications and applications, one of which is to help adjust the frequency and improve the frequency dynamics. The main challenge in using such systems is to determine the optimal size and location of their installation to help improve frequency stability with the least capacity. In this study, a model of equations based on practical results for the energy storage generator of virtual inertia is proposed. Optimal placement of virtual inertia is considered as a technical-economical issue and according to the considerations related to storage systems, including annual costs, lifespan and charge status, and with the aim of improving frequency stability with the least storage capacity. In this regard, considering the two cases of frequency stability indicators, the minimum virtual inertia required for the areas that have violated the indicators within the allowed limits has also been determined. After validating the model by comparing the results of the simulation with the results of the storage systems available in the laboratory, the proposed model and method is linearly applied to the three-zone power system as well as a nonlinear system. Analysis of the results shows the importance of the location and value of the inertia added to the system, and finally the efficiency of the virtual inertia placement method and its optimal value to improve the frequency stability after the disturbance has been determined.

increasing demand for electrical energy, emissions on environmental pollution caused by fossil fuels, reduction of fossil fuel resources, resilience requirements to supply sensitive loads whether in fault occurrence or transient conditions, green energy production, efficiency increasing in power transmission and production (rather than traditional power system and transmission lines) and so on are the main power points of the advent of the microgrid concept. Integration of microgrids and its impacts on main grid introduce some acute challenges to traditional power systems. One of these in islanded microgrids is the variable amount of inertia's value. Moreover, intermittence nature in electric power production by renewable energy resource and overall uncertainty which exists in these systems, highlights emergency situations is islanded microgrids. So, to prevent the microgrids collapse in emergency situations, load shedding has been introduced as a common strategy. Calculation the unbalanced power by the generation-demand index and swing equation are one of the popular solutions in the load shedding strategies. But, the intermittence value of inertia in microgrids introduces basically drawbacks to solve swing equation, while there is no such a problem in solution of swing equation in power systems. Towards, an estimation based algorithm to achieve inertia value and unbalanced power compensation in multi-step load shedding is presented to stabilize microgrids with intermittence-inertia characteristic. Validation of the proposed method is investigated under various scenarios. The location of shredded loads is also studied. Finally, capability and flexibility of the proposed algorithm on the inverter-based microgrids and microgrids without inertia are investigated.

Due to the increasing of renewable energy-based technologies and the many benefits of using them as a source of distributed generation sources of energy, their use to provide energy for local loads has expanded significantly. This large-scale expansion also poses many challenges in controlling and exploiting them in the form of microgrids. The flow harmonics produced by nonlinear loads, the coordination between the distributed generation power units in the microgrids, and the inherent limitations of the fuel cell, such as the lack of required oxygen, are some of these major challenges. Nonlinear loads are able to create a wide range of flow harmonics in the microgrid, which has many negative consequences for the microgrid and causes unstable performance of the fuel cell. In this paper, in order to eliminate the negative effects of using nonlinear loads, a control strategy for allocating power between different units based on the Fourier transformation of total power consumption is presented. The results of the simulations show that the use of Fourier analysis in the allocation of power between different units can be an effective tool to eliminate the destructive effects of current harmonics on the fuel cell. A control method is also provided to control the terminal voltage to eliminate the negative effects of nonlinear load disturbances and DC link voltage fluctuations on the output voltage. The model provided for the DC / AC inverter control loop is able to eliminate the negative effects of nonlinear load disturbances and DC link voltage fluctuations on the output terminal voltage. In the following, a control method is presented using frequency response analysis to coordinate frequency control between different microgrid components in the presence of fuel cell. The results of frequency response analysis show that the regulation of secondary controllers using the proposed method has a significant effect on reducing the frequency fluctuations of AC microgrid in islanded mode. Finally, in order to improve the performance of the fuel cell in the face of changes in the output current, methods and have been used to control the amount of oxygen entering the fuel cell cathode. The results show that the designed resistor controllers have a significant effect on improving the performance of the fuel cell against current changes and changes in system parameters.

Expanding the production and use of electrical appliances has increased the demand for electricity. In recent years, renewable energy sources have been widely welcomed due to economic and environmental constraints. The distributed use of these energy sources adds new protective and control complexities to the electrical grid. Therefore, in order to better control these distributed resources, the concept of microgrid has been introduced. Many researches have been done on voltage and frequency control of microgrids. In this dissertation, these researches is discussed generally. Attempts have also been made to determine the direction of research conducted in recent years. In the primary control layer, some studies have tried to improve the performance of this layer by changing the structure of the blocks that make up this layer. A number of studies have tried to use alternative controllers for this layer. But the common use of droop control in the primary control layer provides the need for secondary control. Secondary control was examined in detail in two approaches: centralized secondary control and distributed secondary control. The features and challenges of each are introduced. In this dissertation, a conventional sample of centralized secondary control in the simulation software environment and its results were extracted. In recent years, with the introduction of the distributed secondary control approach, the simultaneous control of voltage and frequency has become more tangible. In the distributed secondary control chapter, two examples of research in this field have been simulated in the software environment and its results have been reproduced. The two models use the Consensus protocol to recover frequencies and voltages. But the microgrid structure has faster fluctuations than the main grid. The telecommunication platforms used in the microgrid and its delays also complicate the problem. Recent research has tried to introduce robust control approaches to these structural changes and telecommunication delays. For this reason, only a relatively complete study of these researches was conducted. A suitable simulation base was prepared with studies in this field and the results of several successful research samples in this field were reproduced. Required to continue research in this area and provide a new control strategy.

As distributed generators increase in the power grid, new challenges arise: stability issues, voltage fluctuations, voltage control, protection system synchronization, etc. A systematic way to deal with such issues is to consider distribute energy sources and their loads as a subsystem or microgrid. Microgrids consist of a number of generation resources, including renewable energy sources, micro-turbines, and energy storage systems. Each production resource has its own limitations in terms of controllability, capacity, and response time. Loads also are often more dispersed than traditional power grids. Microgrids can operate in both grid-connected and islanded modes. Unlike grid-connected mode, voltage and frequency adjustment, load and generation balance in islanded mode depend solely on local generation units. Therefore, the stable and reliable operation of microgrids in islanded mode requires a coordinated control scheme. Traditionally, this coordination is achieved through active power-frequency and reactive power-voltage droop control plans. The traditional droop method, which is based on the concept of real power-frequency loss in power systems, has little compatibility with resistive nature as well as low inertia of generation units electronic interfaces in microgrids. As a result, it offers features such as slow dynamic response and low power quality due to voltage and frequency fluctuations. This thesis proposes a new control method based on voltage-current droop characteristics to coordinate inverter-based generation units in the microgrid. Droop control schemes in general, and traditional voltage-current control schemes in particular due to voltage changes over the microgrid, are unable to divide the proper current between the generated sources. In order to improve the accuracy of current sharing, a new scheme has been proposed without the use of a link between generation resources and the need for secondary control. In the proposed method, the training-learning optimization algorithm has been used to optimally calculate the resistance and reactance values of the lines connected to the production resources and the slope of the droop. In the following, fuzzy control is used to determine the proportional coefficient of voltage controller, which provides satisfactory results in controlling the division of active and reactive power as well as voltage control.

Concerns about environmental pollution, climate change and declining fossil fuels have increased the need for renewable energy around the world. One of the best uses of renewable resources is the concept of microgrid. A microgrid is a small scale of the power grid that includes renewable energy sources, energy storage sources, and loads that are interconnected. The advancement of power electronic interfaces such as AC / DC and DC / AC in recent decades, and their flexibility in transmitting electrical energy, has led to a desire to design and use more microgrid systems. Power electronic converters and electric motor actuators, which are the main components of DC microgrids, will behave like a constant power load when needed to be tuned precisely. This type of load has a negative impedance characteristic at the input terminal that affects the stability of the system and the quality of the control system. This effect is more pronounced in the case of island microgrids and may even cause system instability; Therefore, the existence of this type of load in DC microgrid is considered as a challenge. In this dissertation, we first model and analyze the stability of a DC microgrid, including a distributed generation unit (DG) that provides the power required for a fixed power load. Then, due to the high penetration of this type of load in DC microgrid and the issue of instability in them, an optimal nonlinear controller, using the state dependent Riccati equation method (SDRE), is presented for the DC bus voltage tracking problem, and compared with other methods. Then, to study the power transmission in these types of systems, the study system is developed and a droop-based model predictive controller (DMPC) is designed to compare its performance efficiency and compared with normal droop control. Simpower/Matlab software is used to evaluate performance and designed controllers. The simulation results for the studied system are given at the end of each chapter.

Creating a balance between power generation and network load demand is a prerequisite for a power system. Due to the uncertainty in renewable energy sources, as well as the load demand by users, creating such a balance is challenging. In this project, the problem of instantaneous equilibrium of load and production in a power system including several microgrids is considered. Considering the uncertainty in production and load resources, establishing power flows between microgrids is examined. In other words, when a microgrid has a power shortage and is unable to provide power to its loads, it can receive power from a microgrid that has more generation than its need by the network operator. It can also send power to the power grid at another time that the generation surpass its need, in this case the probability of all microgrids being cut off is equal. Due to the non-convexity of the problem, it uses two methods of internal point and particle swarm optimization to solve the problem. In this study, using the particle swarm method and the internal point, the probability of network interruption is reduced, the load curve is improved and the reliability of the system is increased. Also, based on the two introduced scenarios, the comparison of optimization methods has been done. During the comparison, it was found that the particle swarm method, due to the use of artificial intelligence in updating the particle position, the minimized probability of interruption in the repetition of the algorithm is not a constant value. On the other hand, the results obtained by repeating the simulation vary within an acceptable range. For the first time in this study, the probability of network disconnection has been determined by considering the uncertainties as Gaussian random variables.

Nowadays, with notice to the high power losses of transmission and distribution networks, increasing of environmental pollutions and decreasing of fossil fuel resources, using of distributed generation to meet the load locally is an appropriate solution. Integration of distributed generations and local loads as microgrids has the technical and economic benefits. Due to the high costs of construction of microgrids, designing and finding the best combination of resources due to weather conditions and the type of loads that must be supplied by the microgrid is very important. Among the topics on the microgrid in recent years, researchers have addressed the issue of optimum design, software and professional investors and academics have been produced using a variety of optimization algorithms have proven the importance of this issue. The main purpose of this Thesis is optimal planning of microgrids considering operation problem and demand response programs. Optimal allocation resources and matching resources to weather conditions microgrid Location with considering the demand response program, is a core objective of this thesis. Simulation is done for 24 hours, 52 weeks and 365 days in year for commercial, residential, and industrial loads and considering the encourage programs for renewable energies. The particle swarm optimization is used to solve the proposed models. The optimal provisional microgrid planning in one of the scenarios has been conducted. After optimization, the consumption pattern associated with the planning and the importance of planning microgrid based on the consumption pattern was observed. The optimal provisional microgrid planning based on data for one day in the year increased penetration of renewable generation increases from 2 percent to 5 percent, which is relatively good. In a weekly scenario, the effect of the increase in grant funding from the Department of Energy studied the influence of the solar system, the grant is increased to 20% Qablnsb solar system. In the case of industrial power supply, the effect of demand response programs overall costs of construction and maintenance microgrid has been examined and it was found that the implementation of demand response programs to reduce costs is 8.9 percent.

A microgrid is a localized system that includes distributed generation units, energy storage devices, and controllable loads that can be operated in two modes; connected to the main grid or independently. The presence of unbalanced and nonlinear loads is one of the most important factors that can affect the quality of microgrid power, especially in island performance conditions. Any disturbance in the distribution systems causes voltage disturbances. On the other hand, due to the low inertia of distributed generation resources and the high speed of power electronic devices, the dynamics of the microgrid is much faster than the dynamics of conventional power systems, and this multiplies the possibility of instability and voltage collapse. As a result, it is necessary to provide an optimal and practical solution for stability and voltage control in microgrids. To do this, we must first know the voltage control methods well and then choose the most appropriate method according to the type of system. Various tools are used to compensate for these disorders on sensitive loads. More specifically, this research uses the dynamic voltage return method which is capable of counteracting the effects of voltage changes on sensitive loads. The main role in this method is played by the voltage source inverter, which is responsible for injecting voltage to the sensitive loads of the microgrid when an error occurs. Each inverter needs a suitable control structure to inject properly and deliver the load voltage to the desired and stable value. The use of a proportional-integral-derivative controller seems to be a better choice than other intelligent control strategies due to its mathematical basis and simplicity in implementation. But the main problem is that the controllable coefficients are constant over time. In order to solve this problem, we have used a fuzzy logic controller to instantly adjust the coefficients. In the following, by applying the error at the load point, we examine the performance of the proposed strategy in reducing voltage drop and switching effects.

Some systems have fractional-order transfer functions, while others that do not have a specific transfer function are better to be modeled with fractional-order transfer functions. On the other hand, it has been shown that fractional-order controllers are able to control fractional-order and natural-order systems better than natural-order controllers, so it is important to consider the fractional calculus and fractional-order controller. Just as among the natural-order controllers, the classic PID controllers have received a lot of attention in terms of importance and application, the same is true for the fractional-order PID controller. That's why in this project we have focused on this particular type of controller. The most common method of implementing and simulating transmission functions with fractional order is to approximate them with the correct order transfer function, and there are several methods that have been used in this dissertation using the Ostallope method. In this research, using a fractional-order controller, two types of direct current converter, buck and boost converter, have been controlled. Also, using the constrained optimization algorithm and the Nelder-mead method, the parameters of the controller are tuned. Hence, the system become stable against load fluctuations, changes in input and etc. and will have far less output voltage fluctuations than other controllers used for converters.

After several decades of the appearance of conventional power systems and use of fossil fuels for power generation, nowadays lack of these fuels has come to turn to renewable energies, despite of economic and environmental benefits, new problems facing engineers in the field of power systems and institutions. microgrids (MGs) in power systems create new problems such as voltage and frequency fluctuations during severe load changes, turning to islanding operating mode due to the economic planning or occurring faults. In islanding operating mode, considering lack of backup power existence, violence and range of these fluctuations is an important problem. Meanwhile, considering low inertia of DGs and also high switching rate of power electronic devices, the MGs dynamic is much faster than the conventional power systems. Therefore, existence of an effective control structure with fast dynamic against large disturbances/faults is highly needed. As MG turning to island mode is usual and so there are uncertainties in the generation of distributed generation sources has caused emergency conditions be a very probable in MGs. The design of efficient algorithms for emergency conditions and load shedding is important. In this thesis has been tried to achieve this. Microgrid structure has been studied and power sharing rewritten for microgrid and the effect of active / reactive power on voltage / frequency parameters was investigated in emergency conditions. Importune of reactive power in emergency control as well as in this study is shown.

According to the environmental concerns, the utility of renewable energy is rapidly growing up. Recently, wind energy has had a significant proportion in renewable power resources, although its stochastic nature causes several challenges in power system operation and control. As wind power penetration increases, power industry tends to replace conventional generation units with the wind power resources. The continuous increase of wind power penetration leads to more and more retirement of conventional generations. Modern wind energy conversion machines are not able to participate in frequency response since the machines are decoupled from the grid by back-to-back voltage-based converters. In spite of providing the ability for wind generation to contribute in frequency regulation, the effect of this contribution is not entirely perceived especially at different wind power penetration levels. This thesis, investigates the impact of inertia, primary frequency response (PFR) and combination of those control procedures provided by wind turbines on the power system frequency response. The control method is based on electrically voltage-based converter control that provides fast primary control for wind turbines. The new control method for coordination inertial response of wind farms and conventional power plants is proposed. Also the coordination of inertia, the PFR and combined inertia-PFR between wind farms and conventional generators are evaluated. The comparison between effect of temporarily frequency support from wind farms and wind-conventional power resources coordination is done. The effect of wind power participation methodologies on the performance of secondary frequency control with classical PI controllers, are also evaluated. The simulation results on updated IEEE-39 bus power system show that by applying the coordination control, the frequency performance is enhanced more than the wind farms frequency support. The simulation is performed by Matlab's SimPowerSystems block set.

Over the past few decades, with the growing trend of industrialization, population growth, and the consequent increase in household electricity consumption, the need for more electricity generation has increased. On the other hand, declining fossil fuels, rising pollution, and rising fuel prices have created the need to use new sources of electricity. In addition, due to the increase in greenhouse gases by traditional energy sources, the Kyoto Protocol provides for a global reduction in greenhouse gas emissions with the aim of reducing dependence on these resources. Renewable energy sources have received much attention as new sources of electricity generation due to their cleanliness and unlimited nature. However, the changing nature of these resources, their low inertia and disturbances makes new challenges in power systems. The entry of new uncertainties into the system, such as changes in wind speed or solar radiation, greatly affects system control. In addition, due to the increasing penetration of these resources, including increasing the influence of wind power on power systems, the impact of these powers on frequency control has become very important, because due to the low inertia of these resources, a small disturbance have impact on important parameters such as frequency. Therefore, new control strategies must be adopted to maintain the frequency within a certain range. Control performance standards are indicators for evaluating frequency control performance in power systems. These indicators are important criteria for determining the quality of frequency control performance and distribution of frequency control responsibility among control areas. Each control area is required to follow these standards, following these standards will increase reliability, reduce equipment exhaustion, increase their life, and thus reduce fuel costs. Failure to follow any of these control indicators will result in excessive penalties. Increasing the influence of renewable energy sources due to their variable nature may reduce the compliance of control zones with control performance standards. In this study, the impact of wind turbines as the most pervasive renewable source on control performance standards is first examined. Then, frequency control in the presence of these resources was performed in several different ways.

Up to now, the electromechanical synchronous machine rules the domain of electrical power generation devices. Its specific characteristics guarantee the stable highly parallel grid operation, automatic power balancing. The frequency of the voltage is stabilized by a combination of the rotational inertia (rotating mass) of synchronous power generators in the grid and a control algorithm acting on the rotational speed of a number of major synchronous power generators. When in future small nonsynchronous generation units replace a significant part of the synchronous power generation capacity, the total rotational inertia of the synchronous generators is decreased significantly. This causes large frequency variations that can end up in an unstable grid. A way to stabilize the frequency of the non-synchronous generators is combined power electronics with synchronous machine behavior. In this project, inverters are controlled in such a way as to exhibit a virtual synchronous generator towards the grid, in order to limit grid frequency variations in grids containing a high share of inverter-connected distributed energy resources (DER). As the use of an inverter allows flexible control of the power exchanged with the grid as well as of the waveforms of the voltage and current, it is possible to adapt the inverter control in such a way as to emulate the behavior of a synchronous generator. In order to do this, some energy storage must be connected to the inverter (either directly to the DC-link, through a DC-DC converter or through a rectifier). The control scheme determines the exchange of active power between the inverter and the grid, allowing to emulate the behavior of a synchronous machine. An inverter with energy storage being controlled in this manner is called a virtual synchronous generator (VSG). In this research, a virtual synchronous generator with the function of active power control and frequency control in micro-grid is proposed, and some VSG frequency controllers (virtual inertial control, virtual rotor control, virtual primary control and virtual secondary control) are investigated and shown in this research, the VSG suppresses grid disturbances effectively.

Recently, by expanding technologies related to the power industry and increasing need for electrical energy, specifically in regions that increasing size of conventional system is impossible or is not costly and enviromentally effective, leads to fast growing and most widely utilizing of distributed generation (DGs) units and renewable sources. Thus, entrance of microgrids (MGs) that comprises different types of DGs, attracts particular attentions. Due to increasing number of microgrids (MGs) in power systems, variable inherent of renewable energy sources, low inertia and nonlinearities, if a mismatch between load and power generation occurre in the MG system, the MG frequency and voltage deviation from nominal value is unavoidable, even it may lead to the MG blackout. In industrial environments, PI/PID controllers due to low-cost, reliability and simplicity in design are more popular; but in new power systems, these controllers may not provide desirable performance. Therefore, the applicable powerful control strategies that have robust nature in the presence of environmental condition and load deviation, are needed to achieve a reliable performance in the MGs. Susch as conventional power systems, several hierarchical control approaches are proposed. Local/primary controls, secondary control and global/tertiary control are known as the most important control levels. Frequency stability in microgrids under islanded operation mode is one of the most important control problems in new power system design. MGs control in an islanded mode is more difficult than grid-connected mode, because the main utility grid supports voltage and frequency regulation of the MGs in grid-connected mode. In this thesis, intelligent and robust control methods are designed. In the second chapter, supervisory fuzzy logic controller is proposed with two main goals: holding of structure simplicity that is desirable in industrial environment and implementable capability without opening the existing conventional PI control loops. In the third chapter, H∞ and µ-synthesis robust control techniques are used to develop the MG secondary frequency control loop. The DEG, MT and FC microsources are responsible units in secondary control loop to balance the MG’s load and power generation. Also a generalized method for energy management as well as frequency control of microgrid (MG) to determine the optimal operating set points and cost minimization of microsources (MS). Artificial neural network (ANN) scheme through microgrid central controller (MGCC) is applied to obtain set points in an efficient economical way. It has the on-line capability to adjust the active reserve power generation, economically to demand in islanded mode. To improve the secondary frequency control issue based on optimized set points, an adaptive neuro fuzzy inference system (ANFIS) for PI parameters tuning is proposed.

One of the most important concerns of electricity generators in recent years is the problems caused by traditional production units (large production units and mainly fossil fuels). Reducing fossil fuels and the high cost of building power plants and transmission lines in the network have led to more use of distributed generation resources (DG). These sources of production use mainly clean and renewable energy sources such as wind and solar. The high penetration of these small production units into the network, in addition to its many advantages such as: proximity of energy production to consumers and high flexibility of the network due to its performance, whether connected to the distribution network or islanded; Creates challenges for network control and management. These challenges include increasing the complexity of electrical networks, disrupting the balance and symmetry of the network, and disrupting network security coordination. In order to analyze the electrical networks in the presence of distributed generation resources, the concept of microgrids has been used. Following a major disturbance in the main grid, emergency control measures must be taken to prevent blackouts. Voltage and frequency are important decision-making tools that are frequently used in emergency control strategies. Despite the challenges posed by microgrids, designing efficient controllers on these networks is inevitable. The basis of control design in microgrids should be such that they can feed local loads in both islanded and grid-connected modes. Load-shedding is one of the most common methods of emergency control on the load side and is related to times when existing production is not able to feed the load. This dissertation presents a comprehensive algorithm in which both voltage and frequency indicators are used depending on the system being studied. In small networks, due to the low inertia of the system, the rate of frequency change (voltage) fluctuates a lot, so they are not a good factor for decision making. Therefore, in this dissertation a new factor named the average drop in frequency (voltage) changes is presented. Based on this factor the amount and time of load-shedding is measured.

In this thesis, performance of intelligent fuzzy-based coordinated control for Automatic Voltage Regulator (AVR) and Power System Stabilizer (PSS) to prevent losing synchronism after a major sudden fault and to achieve appropriate post-fault voltage level is presented in multi-machine power systems. The AVR and PSS gains can adaptively change to guarantee the power system stability after faults. To change in AVR and PSS gains, at least one significant generator in each area is equipped with a fuzzy logic unit. The fuzzy logic unit accepts normalized deviations of terminal voltage and phase difference as inputs and generates the desirable gains for AVR and PSS. The construction of appropriate fuzzy membership functions and rules for best tuning of gains is described. The proposed fuzzy control methodology is applied to 11-bus and 39-bus power systems. Simulation results illustrate the effectiveness and robustness of the proposed fuzzy-based coordinated control strategy. In other section of this research, using the fuzzy controller and Static Var Compensator (SVC), the transient stability of multi-machine power system is enhanced in different levels of FSIG-based wind turbines penetration. Fixed Speed Induction Generator (FSIG)-based wind turbines are disconnected from the grid by their protection systems in severe fault situations. The disconnection can affect the power system as a disturbance and it is a menace for transient stability of the system with attention to reduction in active power. Simulation results show that, the transient stability of the considered power system in this research can be improved with the fuzzy coordinator and without any application of SVCs until 50 MW generation rating of wind power in the system. This is a small level of penetration for wind power in multimachine power systems. For more generation of wind power, SVC controller must be used to compensate the reactive power requirement of FSIGs in fault situations. It is also seen that for upper levels of penetration with wind power, the gain of SVC should be increased to ensure the performance of the fuzzy coordinator.

The set of hidden system dynamics that keep the output at zero is called the system's zero dynamics. These dynamics are inherent in the system. The study of zero dynamics plays a very important role in control issues. The algorithms offered for calculating these dynamics in high order systems seem to not be very operational. Techniques have been proposed to stabilize systems with unstable zero dynamics, but there is still no systematic solution to this problem. In addition, sometimes not all system states are available. There are two ways to deal with such a problem: 1- Using an observer, add dynamics to the system. 2- Use the output feedback. Of course, the second method is simpler, cheaper, safer and more flexible. In general, designing static controllers is not easy because there are no specific rules for designing such controllers. Therefore, it may be possible for systems with unstable zero dynamics to first design a dynamic controller, then turn it into a static controller.

In many industrial applications, it is necessary to convert a DC source with a constant voltage to a DC source with a variable voltage. A DC chopper is a device that directly converts DC to DC and is also known as a DC to DC converter. The chopper can be considered the DC equivalent of an AC transformer with a continuously variable loop ratio. Similar to a transformer, a chopper can be used to increase or decrease the DC source voltage step. Choppers are widely used to control the engine in electric cars, forklifts, mining, etc. Their specifications include precise acceleration control, high efficiency and fast dynamic response. Choppers are also used in DC voltage regulators and are used in conjunction with an inductor to generate a DC current source, especially used for a current source inverter. With the expansion of the use of DC regulators and the need for higher voltage levels, cascade converters have been considered. Cascade converters require a more complex control structure. Classic controllers are designed based on nominal operating conditions. Typically, the converter is subject to disturbance, non-uniformity of the input source, sudden changes in output load, and other uncertainties that alter the nominal operation point of the converter. Classic controllers can't have the right solution for multiple operation points; So more robust and efficient controllers are needed. In this dissertation, the robust control structure, efficient and at the same time simple control is examined. Kharitanov's robust control theory is used to design and conceptualize stability to regulate the controller. The efficiency of this control method has been investigated by simulation in time domain on the sample system.

Renewable energy sources such as wind, solar, and hydrogen play important roles in keeping the air clean, reducing distribution and transmission costs, and increasing energy efficiency in future power systems. As a solution to expand the use of these resources, small energy systems called microgrids have emerged that form a special type of low- and medium-voltage electrical system. Following the presence of sources with different production specifications than in conventional systems, the role of power electronic interfaces in the structure of microgrids has been highlighted. The simultaneous presence of several energy sources with variable nature, low microgrid inertia due to the presence of power electronic interfaces and the ability to function in both connected and disconnected modes from the main network have increased attention to issues such as security, efficiency and stability in microgrids. Therefore, re-evaluating control and protection structures in microgrids are issues that arise with the presence of these resources and their interfaces. Controlling and operating a microgrid is especially challenging in islanded mode and when the microgrid is isolated from the main network. In this dissertation, first, some considerations are given about distributed generations. Then, a control method is provided for both connected and disconnected modes, so that the microgrid can feed the local loads in both the grid-connected and islanded modes. Also, a load shedding algorithm is proposed as one of the emergency control methods following severe disturbances. The proposed algorithm is realized using both voltage and frequency indicators. Frequency and its rate of change are used as a factor in initiating the algorithm and preventing unnecessary load shedding. The amount of load shedding is determined based on the voltage drop and a table called the reference table. Also, it has been shown that the place of load shedding can affect the amount of load shedding.

Nature has provided a variety of wide vision systems. The capabilities of this type of vision increase the processing power of computers and reduce the cost of video equipment. Machine vision (MV) is the technology and methods used to provide imaging-based automatic inspection and analysis for such applications as automatic inspection, process control, and robot guidance, usually in industry. Machine vision refers to many technologies, software and hardware products, integrated systems, actions, methods and expertise. Machine vision as a systems engineering discipline can be considered distinct from computer vision, a form of computer science. It attempts to integrate existing technologies in new ways and apply them to solve real world problems. The term is the prevalent one for these functions in industrial automation environments but is also used for these functions in other environments such as security and vehicle guidance.

The basis of control design in microgrids should be such that they can connect local loads in both connected and disconnected state networks. Therefore, it is necessary to have a number of local and central controllers between the microgrid and the global network. In the conventional case, these controllers are set to a certain value and placed in the system for once, based on the nominal operating conditions and the comfort of the power system. But due to the oscillating nature of microgrid energy sources and the low inertia of these networks, classic integral-proportional controllers (PIs) cannot maintain their proper response over a wide range of workstations. Because in these networks, common power system disturbances can easily change the comfort and working point, so more efficient and intelligent control methods are needed more than before. Accordingly, in this dissertation, the stability of frequency and voltage of microgrids using robust control and intelligent control methods have been investigated. Artificial neural networks and fuzzy logic, along with the Particle Concentration Algorithm 1, have been used to control the frequency of microgrids in order to adjust the time of the classical controllers. Resistant control theories, such as the Kharitanov 2 theory and the concept of field stability 3, have also been used to adjust the voltage controller in microgrids. In each of these methods, the more optimal performance and performance of the proposed control methods than the conventional methods have been investigated by simulating the time domain on separate test systems.

The presence of distributed generation resources and microgrids in the power system, despite the many economic and environmental benefits, have added new problems to the power system. These problems include voltage and frequency fluctuations during possible events such as severe load changes or power system errors. In islanded mode, due to the lack of backup power, the intensity and amplitude of these fluctuations and the possibility of instability and collapse of the microgrid are much higher. In addition, due to the low inertia of the distributed generation resources in the microgrid and the high switching speed of the power electronic devices, the dynamics of an islanded microgrid is much faster than conventional power systems. Therefore, it is necessary to have an efficient control structure with fast performance when there is a disturbance in the system. In this study, several intelligent methods are applied to primary voltage and frequency control structures as well as secondary frequency control structure. In the primary control method (droop control), a criterion is presented that uses the line parameters under extreme load changes to coordinate between voltage control and frequency simultaneously. The proposed structure is then improved using powerful tools such as particle swarm optimization algorithms and fuzzy-neural controllers. Then, by adding a transient mode control loop to the proposed method, the output current of the distributed inverter-based sources is limited when an error occurs in the distribution system (errors inside and outside the microgrid), which leads to transient stability of the microgrid. Due to the use of renewable energy sources as well as the low inertia of microgrids, with the slightest disturbance, the basic parameters such as frequency will be affected. In practice, frequency control is performed by secondary proportional-integral controllers. Although these controllers are economical and easy to use, they are not always the best choice for the reasons mentioned. A possible solution that can use both these controllers and overcome their problems is to correct the control coefficients of these controllers, depending on the changes in the system. In the final chapter of this study, using artificial neural networks, the parameters of a proportional-integral controller are adjusted based on the changes in the system.

In recent years, much attention has been paid to renewable energy for electricity generation. One of the most important and widely used types of these energies is wind energy. Recent studies have shown that increasing the use of wind energy creates challenges for the system. One of these challenges is frequency control. In the last ten years, studies have been conducted on the participation of wind farms in system inertia response as well as primary frequency control. However, no serious work has been done in the field of participation of wind power plants in load-frequency control. In this project, first by adding a control loop to the control structure of doubly-fed variable speed wind units, the ability of these units to control the secondary frequency on a system similar to the 9 bus standard IEEE system structure is examined. In the following, the increase of wind power on load-frequency control of the system is investigated and an attempt is made to compensate for the adverse effects of high wind power injection on load-frequency control. Today, proportional-integral (PI) controllers are used to control the load-frequency of the power system. However, with the increase in wind power units, due to the output fluctuations of these units, it is difficult and inaccurate to adjust the parameters of these controllers by trial and error. In this project, a new intelligent algorithm called colonial competition algorithm is used to adjust the parameters of load-frequency controllers and to create coordination between wind units and units with synchronous generators. To test the performance of this intelligent algorithm, a system with a similar structure to the standard IEEE 39 bus system was used.

With the advent of automatic voltage regulators in power systems, a new type of instability called oscillation instability or small signal appeared in power systems. Power system stabilizers have been added to power systems to eliminate low frequency fluctuations and thus improve the small signal stability. Given the discrepancy between the behavior of the two controllers, coordination between the two is essential to maintaining stability under different working conditions. Today, the use of wind energy is more important than other renewable energy sources and is expanding. The entry of wind turbines into power systems and the significant effects of these turbines on system dynamics as well as increasing system uncertainties, the need for a comprehensive dynamic analysis as well as appropriate and independent criteria from the type of error and the system under study to coordinate among these controllers in large power systems, is even more important. This study provides a new control method and criterion for the stable coordination of the power system and the automatic voltage regulator in large-scale power systems. Criteria provided using system behavior after fault occurrence and how the system moves on the generator rotor angle change (phase) - generator terminal voltage changes (portrait of system mode space) plate, a powerful and independent tool from the coordination of studied system is introduced. The criterion is obtained by the mathematical equations governing the power system and used to design a robust controller. The control algorithm provided by combining the two strategies of switching and negative feedback provides a robust way against load/generation changes. The switching strategy used in this study, in contrast to fixed-time switching methods, using system behavior and based on the angle between voltage changes and phase changes, helps to improve the performance of the system based on any possible errors. The robust and efficient performance of the controller provided in terms of generation and load changes in the standard IEEE 68 bus system is confirmed by mathematical calculations.

In recent decades, there has been a strong desire to use new energy due to limited energy resources such as fossil fuels and uranium and their adverse effects on the environment. From the set of new energies, the use of wind energy has grown faster. As the use of these power plants increases, it has become more important to examine their effects on dynamics and control of power systems and to find solutions to improve their performance. In this dissertation, with the introduction of wind energy converter systems, the statistics of wind energy use in different countries are mentioned and while explaining the dynamic models and control loops related to different technologies of wind turbines; Sustainability and dynamic problems of the power system with the presence of wind farms is investigated. Also, the electricity transmission network of Kurdistan province is selected as the model system to be studied and an analytical approach is presented to evaluate the potential of installing wind farms and conducting preliminary economic studies. Furthermore, the effect of high power from wind farms on the dynamics and performance of the power system in terms of various technologies of wind turbines, including constant speed, variable speed and equipped with doubly-fed induction generator is studied. The stability of the power system is analyzed by connecting wind farms, and the need to improve common controls and performance standards is emphasized. Finally, a new control scheme is proposed to improve the stability of the system using static compensators and energy storage devices. The results show that Kurdistan province has the potential to install wind power plants, and dynamic compensator is very effective in improving the transient stability of the province's power transmission network connected to wind power plants and repelling voltage fluctuations due to power plant injection fluctuations. The simulation results also show the validity of the proposed control design for the combination of static compensator and battery in order to delete voltage and frequency fluctuations.

With the dramatic rise in wind power and the emergence of new sources of electricity in the last two decades, frequency control is becoming more and more important as one of the most important challenges in interconnected power systems. The widespread presence of wind turbines in modern power systems affects the dynamic behavior of the system, increasing the complexity and uncertainty in the behavior of the system. On the other hand, the variable and uncontrollable nature of the output power of wind turbines imposes a double imbalance on the system and causes the frequency deviation from its nominal value. Therefore, with the expansion of the presence of wind turbines in power systems, the study of their impact on performance and frequency control of these systems is considered. This study, by emphasizing the frequency of power systems, examines the effect of wind turbines on load-frequency control performance and introduces some of the challenges ahead to increase their presence in power systems. Due to the inability of conventional proportional-integral controllers to achieve optimal results in the presence of wind turbines, two decentralized fuzzy controllers to minimize frequency deviation and exchange power changes between control areas simultaneously that are the main targets of load-frequency control in power systems consist of interconnected, designed and supplied. Also, in order to achieve optimal performance, the particle swarm optimization algorithm is used to determine the parameters of fuzzy controller membership functions. Physical and engineering considerations are taken into account in the design process, and a simulation of the time domain of the 39-bus power system is used to evaluate the performance of the proposed controllers. Finally, the results are compared with the results of a classical controller in response to a load disturbance.

Re-evaluation of emergency control and protection schemes for distribution and transmission networks are one of the main problems posed by wind turbines in power systems. Change of operational conditions and dynamic characteristics influence the requirements to control and protection parameters. Introducing a significant wind power into power systems leads to new undesirable oscillations. The local and inter-modal oscillations during large disturbances can cause frequency and voltage relays to measure a quantity at a location that is different to the actual underlying system voltage and frequency gradient. From an operational point of view, this issue is important for those networks that use the protective voltage and frequency relays to re-evaluate their tuning strategies. In this dissertation first, an overview of the key issues in the use of high wind power penetration in power system emergency control is presented. The impact of wind power fluctuation on system frequency, voltage and frequency gradient is analyzed. The need for the revising of tuning strategies for frequency protective relays, automatic under-frequency load shedding (UFLS) and under-voltage load shedding (UVLS) relays are also emphasized. In the present dissertation, necessity of considering both system frequency and voltage indices to design an effective power system emergency control plan is shown. Then, an intelligent artificial neural network (ANN) based emergency control scheme considering the dynamic impacts of wind turbines is proposed. In the developed algorithm, following an event, the related contingency is determined by an appropriate ANN using the online measured tie-line powers. A comprehensive voltage stability analysis in the presence of the wind turbines is presented. Another intelligent ANN is used to examine the stability margin by estimating the system powervoltage (P-V) curves. The system frequency gradient and stability information are properly used by an effective load shed

In this dissertation, intelligent controllers are used, in the structure of which, control performance standards are used in order to follow these standards in addition to proper load-frequency control. The results showed that by applying performance standards in the controller structure, the controller performance improved in meeting control objectives such as reduced settling time and overshoot. In this dissertation, in addition to the use of classical algorithms, a controller based on multi-agent systems was used, taking into account performance standards to both reduce the exhaustion of Governor equipment and follow NERC performance standards to increase reliability. The results show that controllers that follow NERC standards perform better and their frequency response improves.