Frequency Regulation and optimization of Microgrid System with Multi PV-VSG using Advanced Droop Controller

Power systems with high renewable energy sources: A review of inertia and frequency control strategies over time

In recent years, interest in integration of renewable energy (RE) sources (particularly Wind Energy Systems - WES) into the electrical grid for sustainable, innovative solutions and a greener future continues to grow exponentially. To date, most RE sources have been connected to the grid through traditional grid-following inverters (GFL). Although this control method promises grid compatibility and lower complexity, the unpredictable variability of these eco-friendly RE sources leads to undesirable effects when taken into account. With the increasing interaction of renewable energy sources in today's grid, new challenges arise—such as voltage/frequency regulation and the reduction of overall system inertia—that cannot be resolved with conventional grid-following inverters (GFL). Therefore, the concept of grid-forming inverters (GFM) has been adopted. The aim of this study is to examine the comparison between grid-forming inverters and traditional grid-following inverters, particularly focusing on droop control, and to regulate the simulated test results with appropriate control systems. For this purpose, the study first compares GFM—based on different control techniques (droop, virtual synchronous generator, and synchronverter control) in the literature—with the conventional GFL technique. The circuit tested in this study involves a 40 kVA-rated inverter supplying relevant loads and the grid, with GFL and GFM control modes analyzed separately. Finally, the potential effects of inverters on load variation and grid outages will be considered.

In recent researches on inverter-based distributed generators, disadvantages of traditional grid-connected current control, such as no grid-forming ability and lack of inertia, have been pointed out. As a result, novel control methods like droop control and virtual synchronous generator (VSG) have been proposed. In both methods, droop characteristics are used to control active and reactive power, and the only difference between them is that VSG has virtual inertia with the emulation of swing equation, whereas droop control has no inertia. In this paper, dynamic characteristics of both control methods are studied, in both stand-alone mode and synchronous-generator-connected mode, to understand the differences caused by swing equation. Small-signal models are built to compare transient responses of frequency during a small loading transition, and state-space models are built to analyze oscillation of output active power. Effects of delays in both controls are also studied, and an inertial droop control method is proposed based on the comparison. The results are verified by simulations and experiments. It is suggested that VSG control and proposed inertial droop control inherits the advantages of droop control, and in addition, provides inertia support for the system.

Power sector exhibits interest in renewable energy sources to meet the ever increasing power requirement. Growth of wind power is outstanding among all renewable energy sources which make essential to provide frequency regulation to the grid from wind turbines. The inertial control and droop control techniques are employed for sharing of wind turbines in grid frequency regulation. This article presents the study of frequency response of DFIG based wind turbine for ARMA model of wind speed. Additionally, it objectives to examine the impact on frequency response with increasing wind power potential in cases of wind power plants operated without frequency control and both inertial and droop controllers. Also, the impression of droop parameter has simulated for different wind power penetration. Novelty of this article derived from the fact that it presents influence of increasing wind power potential without and with frequency regulation techniques along with varying droop parameter in totality. Present cases has simulated with the help of MATLAB/SIMULINK. The simulation results support the beneficial impact of wind turbine equipped with inertial control and droop control.

The conventional synchronous generator (SG) can regulate the active and reactive power for frequency and voltage stability, when the system fluctuates. In renewable energy generation system (RES), the stability problem of RES can be solved by adding virtual inertia and damping in the control strategy of the grid-connected inverter. The grid-connected inverter and renewable energy system with this kind of control strategy, called as virtual synchronous generator (VSG), acts as a synchronous generator. In this paper, the topology of grid-connected PV array and energy storage system is proposed. The VSG used in grid-connected inverter, is modelled as stator and rotor model by stator voltage equation and rotor motion equation, respectively. Meanwhile, the VSG control mechanism, based on droop control and model of VSG, can be divided as active power-frequency and reactive power-voltage control. Besides, the system stability is analyzed based on small signal model, for the design of inertia and damping. The simulation model is designed by MATLAB/Simulink for the implementation of VSG. In simulation, it is compared that the dynamic regulation performance of VSG with different control coefficient, such as virtual inertia, virtual damping, droop coefficient and integral coefficient. The optimization for regulation performance in simulation provides an appropriate selection method of the control coefficient for VSG.

Participation of the wind turbine generators (WTGs) in the frequency regulation service is an appealing issue in order to consider the safe increasing of the wind power generation. The droop and virtual inertia control are the most popular approaches that facilitate the WTGs to provide frequency regulation. However, the intermittent nature of the wind complicates the implementation of these methods and has impacts on the wind turbine stability and may cause violation of the allowed power reserve and minimum turbine rotor speed. Therefore, in this paper, a control approach based on the dynamic de-loading technique is proposed, where the wind turbine operating curve is dynamically adjusted in the response of the frequency deviation throughout controlling the turbine tip-speed ratio which helps the turbine provide steady-state power sharing within the reserved power as well as the transient response within its stability criteria. In addition, the inertial response based on a dynamic gain is suggested. The inertial weighting gain has been formulated where it is continuously regulated in the response of rotor speed and reflects the amount of available kinetic energy in the rotating mass. The effectiveness of the proposed control approaches is verified throughout the comparisons of the results with the fixed inertial gain control and the droop control. The simulation results confirm that the combined control of the proposed tip-speed ratio and dynamic inertia control improve the overall system dynamic behavior in terms of frequency response and turbine stability.

Wind farm–based frequency regulation of the power system has progressively attracted more attention owing to its higher power generation capacity. Among which the step start-up and adaptive inertial droop control of wind turbines with a maximum power point efficiently regulate the system frequency via fully utilizing the rotational kinetic energy. Besides, the coefficients of adaptive droop control and virtual inertial control will facilitate a significant influence on the frequency support performance and operation status of wind turbines for the power grid. To obtain optimal control parameters, a parameter optimization framework of a step start-up adaptive inertial and droop controller combined with the CGO algorithm is proposed, whose effectiveness is verified by a three-area four-terminal VSC-MT-HVDC–based WFs and AC system in MATLAB/Simulink. As a result, a set of parameters with a satisfactory and comprehensive dynamic control performance can be acquired by the proposed method under both 200 MW and 300 WM load increases compared with the trial-and-error approach.

Stochastic flexible transmission operation for coordinated integration of plug-in electric vehicles and renewable energy sources

The integration of renewable energy sources (RESs) has become more attractive to provide electricity to rural and remote areas, which increases the reliability and sustainability of the electrical system, particularly for areas where electricity extension is difficult. Despite this, the integration of hybrid RESs is accompanied by many problems as a result of the intermittent and unstable nature of RESs. The extant literature has discussed the integration of RESs, but it is not comprehensive enough to clarify all the factors that affect the integration of RESs. In this paper, a comprehensive review is made of the integration of RESs. This review includes various combinations of integrated systems, integration schemes, integration requirements, microgrid communication challenges, as well as artificial intelligence used in the integration. In addition, the review comprehensively presents the potential challenges arising from integrating renewable resources with the grid and the control strategies used. The classifications developed in this review facilitate the integration improvement process. This paper also discusses the various optimization techniques used to reduce the total cost of integrated energy sources. In addition, it examines the use of up-to-date methods to improve the performance of the electrical grid. A case study is conducted to analyze the impact of using artificial intelligence when integrating RESs. The results of the case study prove that the use of artificial intelligence helps to improve the accuracy of operation to provide effective and accurate prediction control of the integrated system. Various optimization techniques are combined with ANN to select the best hybrid model. PSO has the fast convergence rate for reaching to the minimum errors as the Normalized Mean Square Error (NMSE) percentage reaches 1.10% in 3367.50 s.

The large-scale deployment of sustainable energy sources has become a mandatory goal to reduce pollution from electricity production. As photovoltaic (PV) plants replace conventional synchronous generators (SGs), their significant inherent rotational inertia characteristics are reduced. The high penetration of PV results in reduced system inertia, leading to system frequency instability. Virtual inertial control (VIC) technology has attracted increasing interest because of its ability to mimic inertia. Adoption of the energy storage system (ESS) is hindered by the high cost, although it can be used to provide virtual inertia. The determined forecast gives PVs the ability to reserve power before shading and compensate the power when a system power drop occurs, which can increase system inertia. Nevertheless, it has forecast errors and energy waste in a stable state. To improve the stability of the microgrid and improve the ESS efficiency, this study proposes an adaptive forecasting-based (AFB) VIC method using probabilistic forecasts. The adaptive power reserve and virtual inertia control are proposed to reduce energy waste and increase system inertia. The simulation results reveal that the proposed method has adaptive system inertia to reduce the reserved power, required ESS power capacity, and battery aging.

Renewable power systems dynamic security using a new coordination of frequency control strategy based on virtual synchronous generator and digital frequency protection

Artificial neural network-based virtual synchronous generator for frequency stability improving of grid integrating distributed generators

The integration of renewable energy sources (RESs) such as solar photovoltaic (PV) and wind energy has become a promising solution as the world shifts toward clean energy. Solar PV and wind resources are increasingly replacing conventional synchronous generators, leading to reduced system inertia and increased vulnerability to frequency instability during disturbances. To address this challenge, this study proposes a novel synthetic inertia provision strategy using a battery energy storage system (BESS) integrated alongside solar PV. The proposed method dynamically compensates for the loss of inertia by considering the variability of solar PV output due to changes in irradiance and temperature. Simulation results obtained in MATLAB/Simulink demonstrate that the proposed strategy significantly improves system stability, with a reduction in the rate of change of frequency (RoCoF) by up to 86.6% and an improvement in frequency nadir by 0.91% under high PV penetration scenarios. These results confirm that incorporating synthetic inertia via BESS enhances the frequency response and resilience of low-inertia power systems with high renewable penetration.

Recently, with the large-scale integration of renewable energy sources into microgrid (μGs) power electronics, distributed energy systems have gained popularity. However, low inertia reduces system frequency stability and anti-disturbance capabilities, exposing power quality to intermittency and uncertainty in photovoltaics or wind turbines. To ensure system stability, the virtual inertia control (VIC) is presented. This paper proposes two solutions to overcome the low inertia problem and the surplus in capacities resulting from renewable energy sources. The first solution employs superconducting magnetic energy storage (SMES), which can be deemed as an efficient solution for damping the frequency oscillations. Therefore, in this work, SMES that is managed by a simple proportional-integral-derivative controller (PID) controller is utilized to overcome the low inertia. In the second solution, the hydrogen storage system is employed to maintain the stability of the microgrid by storing surplus power generated by renewable energy sources (RESs). Power-to-Power is a method of storing excess renewable energy as chemical energy in the form of hydrogen. Hydrogen can be utilized locally or delivered to a consumption node. The proposed μG operation demonstrates that the integration of the photovoltaics (PVs), wind turbines (WTs), diesel engine generator (DEG), electrolyzer, micro gas turbine (μGT), and SMES is adequate to fulfill the load requirements under transient operating circumstances such as a low and high PV output power as well as to adapt to sudden changes in the load demand. The effectiveness of the proposed schemes is confirmed using real irradiance data (Benban City, Egypt) using a MATLAB/SIMULINK environment.

The trend of future power systems is rapidly changing towards renewable energy resources (RESs) due to the depletion of fossil fuels. Meanwhile, the integration of RESs leads to the instability of the power system due to the lack of inertia and frequency instability. In this paper, the virtual synchronous generator (VSG) model is originated from imitating the synchronous generator characteristics. The VSG control approach is systematically researched and studied for different inverter-interfaced systems that include RESs integrated with the power grid. Parallel multi VSG based Photovoltaic (PV) systems are analyzed to validate the frequency response and power stability under high penetration of PV system. An advanced master-slave droop control approach is proposed for frequency regulation. Additionally, three case studies are analyzed under various effects of irradiance and temperature on the PV-VSG based system based on a specific area during a year. Meanwhile, an advanced particle swarm optimization (PSO) technique is utilized which effectively optimized the optimal parameters of droop control of VSG and improved the frequency regulation.