AC Microgrid System Research Articles

Adaptive type-2 fuzzy PID controller for LFC in AC microgrid

An AC microgrid (MG) system links the distributed generation (DG) based on renewable energy resources and local electrical loads in modern power systems. Intermittent characteristics of wind and solar resources influence not only the availability of energy but also the stability of the entire AC microgrid. This matter as well makes a challenge on the load frequency control (LFC) problem in an islanded MG system, and consequently, the fixed structure controllers are unable to provide a proper performance over a wide range of operating conditions. Therefore, it is required to design a dedicated controller for LFC to ensure the capability of maintaining a generation–load balance by managing the intermittent resources. In this paper, an adaptive type-2 fuzzy PID (T2FPID) controller is suggested for LFC in an AC MG system to enforce the frequency deviation to zero by supplying the load demands. The designed T2FPID controller is a nonlinear controller that can handle the system nonlinearities and uncertainties in the MG system in a better way. Using a Lyapunov function, the stability of the system is evaluated and parameter tuning laws for the T2FPID controller are derived using this function. It has been illustrated that the adaptive parameters are bounded and the frequency deviation reaches to zero properly. The proposed adaptive T2FPID controller has been applied for LFC of a MG system, and the simulation results have been compared with those obtained by type-1 fuzzy (T1F) PI and nonadaptive fuzzy PID controllers, which is the latest research in the problem in hand. The simulation results indicate the efficiency of the proposed adaptive controllers in dealing with intermittent resources and changing in the power system parameters.

Distributed security secondary control for cyber-physical microgrids systems under network DoS attacks

This paper considers the frequency regulation and power-sharing problems for cyber-physical microgrids (MGs) under network denial-of-service (DoS) attacks and time-varying communication delays. Compared to conventional distributed controllers based on a system model with ideal communication, a distributed security control protocol is designed. Benefiting from the developed security control method, the adverse effects of network DoS attacks and communication delays can be resisted. Then, a sufficient condition, which is used to achieve the achieve frequency restoration and power-sharing, is established according to the frequency and duration of DoS attacks. By using the average dwell time method and the Lyapunov stability theory, it is theoretically proved that the proposed control scheme can guarantee the stability of the overall AC microgrid system. In order to illustrate the proposed scheme, simulation studies are carried out based on an islanded AC microgrid system with four distributed generators (DGs) built in the simulation. The results do show its effectiveness and also verify the established theoretical results.

A Robust Controller for Battery Energy Storage System of an Islanded AC Microgrid

A battery energy storage system (BESS) can play a critical role in regulating system frequency and voltage in an islanded microgrid. A <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula> -synthesis-based robust control has been proposed for dc link voltage regulation of BESS for achieving frequency regulation and voltage quality enhancement of islanded microgrid. Variation in the operating condition of ac microgrid affects the operating condition of the BESS’ converter. This controller synthesis accounts for such uncertain variations as parametric uncertainty. The stability and performance of the proposed controller can be guaranteed for bounded parametric variations. The bounds on parameters are selected based on practical limitations of BESS. In this article, the proposed controller's performance is tested on an islanded CIGRE TF C6:04:02 benchmark low voltage ac microgrid system. The importance of dc link voltage regulation is analyzed based on performance comparison with a benchmark controller. The controller performance is also validated using a real-time Typhoon HIL emulator.

Virtual Impedance-based Decentralized Power Sharing Control of an Islanded AC Microgrid

The future of power systems depends on the microgrid (MG) which includes distribution generators utilizing Renewable Energy Resources (RERs) and storage facilities. Decentralized control techniques are more reliable and stable in comparison with centralized controlled techniques. In this paper, a decentralized control strategy is presented for an islanded AC MG system. The control strategy includes improved droop control and virtual impedance. Control strategy with PI controllers to control the voltage and current is implemented to two Voltage Source Inverter (VSI) distribution generation units connected in parallel through a Point of Common Coupling (PCC). Circulating current and power-sharing deviations caused by the mismatched line impedance were taken into account. The proposed control scheme was tested in MATLAB/Simulink. Power-sharing accuracy and circulating current suppression were obtained by implementing the proposed virtual impedance-based decentralized control strategy.

Grid Forming Converters in Renewable Energy Sources Dominated Power Grid: Control Strategy, Stability, Application, and Challenges

The renewable energy sources (RESs) dominated power grid is an envisaged infrastructure of the future power system, where the commonly used grid following (GFL) control for grid-tied converters suffers from lacking grid support capability, low stability, etc. Recently, emerging grid forming (GFM) control methods have been proposed to improve the dynamic performance and stability of grid-tied converters. This paper reviews existing GFM control methods for the grid-tied converters and compares them in terms of control structure, grid support capability, fault current limiting, and stability. Considering the impact of fault current limiting strategies, a comprehensive transient stability analysis is provided. In addition, this paper explores the typical applications of GFM converters, such as AC microgrid and offshore wind farm high-voltage direct current (OWF-HVDC) integration systems. Finally, the challenges to the GFM converters in future applications are discussed.

A comprehensive review of distribution generation integratedDCmicrogrid protection: issues, strategies, and future direction

SummaryThe evolution of small‐scaled distributed generators and emerging power electronic devices opens up a new arena of power generation, distribution, and consumption. Operationally, the DC microgrid has attracted significant attention as it offers considerable safety benefits, cost‐effectiveness, energy efficiency, and reliability as compared to traditional AC microgrid systems. Looking at the protection aspects, the DC microgrid has some serious issues both for low‐voltage and mid‐voltage DC system. It needs to be focused on bidirectional power flow, non‐zero crossing point, detection and mitigation of grounding faults, high value of fault current, etc., for an adequate solution. In recent times, these issues are considered by various researchers to arrive at a robust and reliable approach toward protecting the DC microgrid. But certain important areas are still out of sight for researchers. In a blend of conventional and modern approaches, there are many hindrances in developing a flexible universal protective scheme. This work focuses on the protection aspects parallel with the challenges and tried to unearth the loopholes which open up a wider area of research to develop a more robust protective architecture. An extensive review has been done systematically and chronologically keeping in mind the DC microgrid architecture, standards, protection hurdles, traditional as well as latest protective measures, and suggested some reliable improvements. In addition, the futuristic possibility to invent a novel comprehensive approach based on the best technology and techniques is presented in a more secure, reliable, and efficient protection system to combat the power system faults, keeping in view the different modes of operation and configuration of the microgrid.

Coordinated and adaptive power management of AC microgrid system comprising wind and diesel generation sources and AC stand-alone load

This paper proposes a coordinated control scheme for proper and seamless power management of the study AC microgrid system including wind and diesel generation sources, where the generator at both wind and diesel generation sources is from the doubly-fed induction generator (DFIG) type. In this way, at first step, the wind energy source works in the power control mode and injects available wind power to load AC bus, and diesel generator provides AC voltage with constant magnitude and frequency. But, by using this control approach, the available wind power may go beyond the load power leading to overvoltage at local wind and diesel AC buses. Hence, the diesel generator, for creating the rated AC voltage, may absorb the extra wind power. Therefore, in order to address the issues of overvoltage and power return to the diesel unit, the control loops of the DFIGs in the wind and diesel generation sources are enhanced for proper and seamless power management, where the proposed approach is realized by using local AC bus voltages and without any communication facility. By using the proposed control method, the study system seamlessly tracks the load demand without any transient and switch from one control mode to another.

A Hierarchical Security Control Framework of Nonlinear CPSs Against DoS Attacks With Application to Power Sharing of AC Microgrids.

In this article, we investigate the distributed resilient observers-based decentralized adaptive control problem for cyber-physical systems (CPSs) with time-varying reference trajectory under denial-of-service (DoS) attacks. The considered CPSs are modeled as a class of nonlinear multi-input uncertain multiagent systems, which can be used to model an AC microgrid system consisting of distributed generators. When the communication to a subsystem from one of its neighbors is attacked by a DoS attack, the transmitted information is unavailable and the existing distributed adaptive methods used to estimate the bound of the n th-order derivative of the reference trajectory become nonapplicable. To overcome this difficulty, we first design a new distributed estimator for each subsystem to ensure that the magnitude of the state of the estimator is larger than the bound of the n th-order derivative of the reference trajectory after a finite time. By employing the estimator state, a distributed observer with a switching mechanism is proposed. Then, a new block backstepping-based decentralized adaptive controller is developed. Based on the DoS communication duration property, convex design conditions of observer parameters are derived with the Lebesgue integral theory and the average dwell time method. It is proved that the output tracking errors will approach a compact set with the developed method. Finally, the design method is successfully applied to show the effectiveness of the proposed method to solve the power sharing problem for AC microgrids.

Resilient Networked AC Microgrids Under Unbounded Cyber Attacks

This paper considers a cooperative and adversarial AC microgrid system consisting of cooperative leaders and inverters, as well as adversarial attackers. The attackers aim to destabilize the synchronization dynamics of the AC microgrid by first intercepting the communication channels, penetrating the local state feedback, and pretending to be a cooperative neighbor, and then initiating malicious attacks by launching unbounded injections. A fully distributed resilient control framework is offered for the secondary frequency regulation and voltage containment to ensure system stability and preserve bounded synchronization. In particular, a virtual resilient layer with hidden networks is developed to integrate with the original cyber-physical layer. The proposed resilient control framework is fully distributed without requiring any global information. A modified IEEE 34-bus test feeder benchmark system is emulated in a controller/hardware-in-the-loop environment, where the control objectives are met under different attack scenarios.

Distributed Event-Triggered Control for Frequency Restoration and Active Power Allocation in Microgrids With Varying Communication Time Delays

In this article, the secondary frequency restoration as well as active power allocation problem in an ac microgrid (MG) system subject to bounded varying-time delays are addressed. For each distributed generator, a distributed dynamic event-triggered control law is proposed. Besides, benefiting from using dynamic event-triggered mechanisms, the communication burdens can be measurably reduced. By analyzing the resulting system through a Lyapunov function, a sufficient condition is established to ensure stability and achieve asymptotic frequency restoration and active power sharing. Based on the sufficient condition, an explicit tolerable upper bound of all time delays is obtained. The upper bound can be used for the MG system design guideline in the planning phase, which would enhance real time operating safety. Beisides, no Zeno behavior will exist. To test the proposed control method, the experiments are conducted on the real-time simulator OPAL-RT with DSP controllers. The results demonstrate the effectiveness and performance of the proposed controller.

Robust backstepping output voltage controller for standalone voltage‐sourced converters

This work presents a linear state-feedback controller using a backstepping design approach for output voltage regulation of 3 ϕ voltage-sourced converters feeding to customers' loads in a stand-alone AC microgrid system. Irrespective of load type and its variations, parameter uncertainties, and other disturbances, the controller is robust enough to achieve a regulated voltage magnitude within the prescribed bounds and exact frequency tracking. The criterion for gain selection using Lyapunov analysis is given. With global exponential convergence feature and better coordination among inner current and outer voltage control loops, improved transient response is achieved. Controller features are examined by eigenvalue analysis and extensive simulation studies. Experimental results demonstrate the feasibility of the proposed controller implementation.

MVO optimized hybrid FOFPID-LQG controller for load frequency control of an AC micro-grid system

Purpose This paper aims to implement a maiden methodology for load frequency control of an AC multi micro-grid (MG) by using hybrid fractional order fuzzy PID (FOFPID) controller and linear quadratic Gaussian (LQG). Design/methodology/approach The multi MG system considered is consisting of photovoltaic, wind turbine and a synchronous generator. Different energy storage devices i.e. battery energy storage system and flywheel energy storage system are also integrated to the system. The renewable energy sources suffer from uncertainty and fluctuation from their nominal values, which results in fluctuation of system frequency. Inspired by this difficulty in MG control, this research paper proposes a hybridized FOFPID and LQG controller under random and stochastic environments. Again to confer viability of proposed controller its performances are compared with PID, fuzzy PID and fuzzy PID-LQG controllers. A comparative study among all implemented techniques i.e. proposed multi-verse optimization (MVO) algorithm, particle swarm optimization and genetic algorithm has been done to justify the supremacy of MVO algorithm. To check the robustness of the controller sensitivity analysis is done. Findings The merged concept of fractional calculus and state feedback theory is found to be efficient. The designed controller is found to be capable of rejecting the effect of disturbances present in the system. Originality/value From the study, the authors observed that the proposed hybrid FOPID and LQG controller is robust hence, there is no need to reset the controller parameters with a large change in network parameters.

Hybrid Energy Storage Control Method for Isolated Island AC Micro-grid Based on Consistency theory

In the traditional hybrid energy storage control method of isolated island AC micro-grid, due to the difference between different types of hybrid energy storage in the hybrid energy storage system, the control stability is low. Therefore, a hybrid energy storage control method of isolated island AC micro-grid based on consistency theory is proposed. Based on the consistency theory, the voltage and SOC of the isolated island AC micro-grid hybrid energy storage system are subject to the consistency control. On this basis, the power of the hybrid energy storage system is subject to the consistency control. Thus, the research on the control method of the isolated island AC micro-grid hybrid energy storage based on the consistency theory is completed. The experimental results show that the proposed control method based on consistency theory has better control stability.

Power management system for hybrid AC/DC microgrid based on high frequency isolated interlink converter

The hybrid AC/DC microgrid systems have been popular and being developed as the next generation power systems because of the comprehensive combination of both AC and DC microgrid systems. Power management scheme is one of the most critical operation aspects for hybrid microgrids because the system is operating with various generation sources and loads such as renewable energy sources, energy storage systems and AC and DC loads. Therefore, in this research, control strategies and power management scheme is considered for all possible operation modes of standalone and grid-connected conditions. In the existing microgrid system in Electrical Power Engineering department in Yangon Technological University, rooftop PV plant and battery are cooperating to supply the electricity. The inverter in this system allows the unidirectional power flow from DC to AC and there is no specific power management system for grid-connected and standalone operation mode. To provide bidirectional power flow in the existing system, the configuration of converter and control strategies for power management system are developed in this research. To provide the bidirectional power flow between AC bus and DC bus, the bidirectional interlink power converter with high frequency isolation is applied. The control system including the power balancing between generation and demand, DC link voltage control and AC link voltage and frequency control is considered. By applying droop control method in the developed system, power flow balancing between AC bus and DC bus is maintained. And also, using high frequency isolation transformer in interlink converter provides fast response of the system performance and maintaining continuous power supply within each AC system and DC system during disturbance condition in one subsystem. The performance of the proposed power management system is demonstrated by using MATLAB/Simulink.

Robust Frequency Control of an Islanded AC Micro Grid using BDA Optimized 3DOF Controller under Plug in Electric Vehicle

The article presents the effectiveness of a Binary Dragonfly Algorithm (BDA) based 3-DOF controller for robust frequency control in an islanded AC micro-grid system under different uncertainties. A micro-grid is incorporated with the integration of various renewable energy based distributed generations (DG). The proposed micro-grid system is structured with wind turbine generator (WTG), Photo voltaic (PV) system, Diesel engine generator (DEG), Micro-turbines (MT), Aqua electrolyzer based Fuel Cells(FC) and with few energy storage devices i.e Battery energy storage (BES) and Flywheel energy storage (FES). Moreover a chargeable plug in electric vehicle is effected as load side demand while obtaining frequency control mechanism in micro-grid system. However large dynamics, low inertia and incurred uncertainties of most DG system affects system performance especially on system frequency seriously. In view of this to obtain robust control mechanism in islanded micro-grid system the article proposes a novel Binary Dragonfly Algorithm based 3-DOF controller to ensure servicing of good quality power to remote consumers. The performances of proposed BDA optimized 3-DOF controller is compared with conventional PSO, GA technique based PID and PI controller in order to justify supremacy of proposed approaches. Finally it has been suggested that the proposed BDA optimized 3-DOF controller is more effectiveness over other optimized controllers.

Tidal Energy Integrated Robust Frequency Control of an Islanded AC Microgrid with Improved-MFO Tuned Tilt Controller

In recent electrical energy scenario different renewable energy based distribution generation (DG) systems have been developed to provide electrical power to distant and remote consumers. In view of this current research article presents a Tidal Power Plant (TPP) and its integration with an Islanded AC Microgrid system. The tidal energy based TPP is modelled to generate required electrical power. However the inherent dynamic behaviour of TPP largely affects the microgrid system frequency especially in islanded mode of operation. In regard to this to obtain necessary control mechanism in an islanded AC microgrid system , present research article proposes a tilt multistage TDF/(1+TI) controller and to show effectiveness of proposed tilt controller for microgrid control it has been compared with multistage PDF/1+PI and PID controllers. To obtain optimal gain parameters of above implemented controllers an Improved- Moth Flame Optimization (I-MFO) technique has been proposed for this study. To justify viability of proposed I-MFO algorithm its performances have been compared with original MFO algorithm. Finally it has been noticed that to obtain robust frequency control in an islanded AC microgrid system, proposed I-MFO optimized tilt multistage controller exhibits outstanding performance under wind, solar and tidal energy uncertainties.

MVO-PS Optimized Hybrid FOFPID Controller for Load Frequency Control of an AC Micro-Grid System

This paper proposes a new approach for load frequency control in a multi micro grid system by using hybrid multi verse with pattern search (hMVO-PS) algorithm based Fractional Order Fuzzy PID controller. A multi micro grid system may be molded by some of the renewable resources (RESs) like photovoltaic (PVs), wind (WTGs), energy storage system (ESSs) and loads. The fractional order fuzzy PID (FOFPID) controller parameters are optimized by novel hybrid Multi verse with pattern search (hMVO-PS) technique. The flexibility and robustness of proposed FOFPID controller is inspected under different disturbance like stochastic variations. The superiority of FOFPID structure over conventional Fuzzy PID/PID and hMVO-PS technique over multi verse optimization (MVO), particle swarm optimization (PSO) and genetic algorithm (GA) has been manifested.

Modelling and design of PID controller for voltage control of AC hybrid micro-grid

&lt;span&gt;The growing demand for power that needs to be remotely transported creates a fast and effective solution of Distributed Energy Resources (DERs) integration. Distributed Energy Resources (DERs) can lessen the electrical and physical distance between load loss and generator, transmission and distribution, and the level of carbon emissions. Such challenges can be overcome by using microgrids, which combine various types of DERs without interrupting the grid operation, allowing the power system to detect and control the errors more efficiently, allowing the shedding load and automatic switching through control algorithms so that blackouts and power restoration times are shortened, enabling either a relevant grid or islanded mode operation, and improving system reliability and flexibility via DERs. This work includes modelling of hybrid AC micro-grid as well as presenting an efficient control technique for micro-grid. In the present work the performance of hybrid AC microgrid system is analyzed in the islanded mode. Photovoltaic system and fuel cell stack are used for the development of microgrid. It also includes microgrid control objectives and the most common problems encountered and their solutions. The employed control technique is able to control the output voltage at a desired and standard value. The control strategies of the hybrid AC microgrid are simulated in MATLAB/SIMULINK.&lt;/span&gt;

Improved-salp swarm optimized type-II fuzzy controller in load frequency control of multi area islanded AC microgrid

Abstract The present article deals with load frequency control (LFC) in an islanded two area AC microgrid (MC) system. In this study the proposed two area MG system comprises different micro sources including Micro-turbine (MT), Diesel engine generator (DEG) and Fuel Cells (FC) which are primarily responsible for balancing load and power generation in an interconnected system. MG in grid-connected mode has lower possibility of frequency control problem due to active presence of utility grid. Whereas MG in islanded mode faces huge frequency control problem due to dynamic nature of different renewable energy sources (RES) and different uncertainties like wind power fluctuations, disturbances in solar irradiation power, dynamics in applied load and system parameters (damping coefficient & Inertia constant). In regard to this the present article proposes a robust type-II fuzzy PID controller to create secondary frequency control loop for maintaining both frequency and tie-line power to their nominal values under different uncertainties. For performance study, the proposed type-II fuzzy PID controller performances are compared with type-I fuzzy controller, PID and PI controllers. To obtain optimal gain values of above controllers, a meta-heuristic improved-salp swarm optimization (I-SSO) algorithm has been implemented and proposed I-SSO technique performances are compared with original SSO, Particle swarm optimization (PSO) and Genetic Algorithm (GA) techniques. Finally it is observed from different performance analysis that proposed I-SSO tuned type-II fuzzy controller exhibits superior performances for load frequency control in multi-area islanded AC microgrid system under different uncertainty conditions.

A New Approach to Single Phase AC Microgrid System Using UPQC Device

A New Approach to Single Phase AC Microgrid System Using UPQC Device