Renewable Power Systems Dynamic Security

In this chapter, a comprehensive literature review on the issue of load frequency control (LFC) in the power system has been highlighted. The various power system model configurations and control techniques/strategies concerned with LFC problems have been discussed in both conventional and renewable power systems. In addition, the suggested LFC control strategies have been researched and classified into various control groups. Finally, the chapter highlights the study gaps and presents some new research directions in the field of LFC.

This chapter presents a coordination of secondary frequency control (i.e., load frequency control) and superconducting magnetic energy storage (SMES) technology using a new optimal PID controller in a real power system (e.g., Egyptian power system (EPS)) considering high wind power penetration (HWPP). This coordination scheme is proposed for compensating the system frequency deviation, preventing the conventional generators from exceeding their power ratings during load disturbances, and mitigating the power fluctuations from wind power plants. The EPS considering HWPP was tested by the MATLAB/Simulink simulation to prove the effectiveness of the proposed coordinated control strategy. The convention plants of the EPS are decomposed into three dynamics subsystems: hydro, reheat, and non-reheat power plants. Moreover, the physical constraints of the governors and turbines such as generation rate constraint (GRC) of power plants and speed governor dead-band are taken into consideration. The results show the superior robustness of the proposed coordination against all scenarios of various load profiles, and system uncertainties in the EPS considering HWPP. Furthermore, the results were verified by comparing it with both the optimal LFC with/without the effect of conventional SMES, which is without modifying the input control signal.

This chapter provides a digital scheme of frequency control and over/underfrequency relay (OUFR) protection for an islanded microgrid (μG) considering high penetration of renewable energy sources (RESs). Reducing system inertia by replacing synchronous generators with a large amount of RESs causes undesirable influence on system frequency stability, leading to weakening of the μG. In addition, sudden changes in load and short circuits cause large frequency fluctuations that threaten the system security. Therefore, this chapter proposes a coordination scheme between the digital frequency controller, which is designed based on Tustin’s technique, and the digital OUFR, which operates for both conditions of over- and underfrequency, to protect the power system against high frequency variations. To evaluate the effectiveness of the proposed digital coordination scheme, the simulation results of the studied islanded μG are executed by MATLAB software. Thus, the obtained results emphasized that the proposed coordination scheme can effectively handle several disturbances and high system uncertainty. Moreover, it can regulate the μG frequency and guarantee robust performance to maintain the dynamic security of low-inertia islanded μG.

Renewable energy sources (RESs) are growing rapidly and highly penetrated in microgrids (μGs). However, there are some impacts resulting from integrating RESs such as power fluctuations caused by the intermittent nature of RESs, and lack of system inertia resulting from replacement of synchronous generators with RESs. Hence, in order to cope with this challenge and benefit from a maximum capacity of the RESs, this chapter presents a new frequency control strategy based on a virtual inertia control to emulate virtual inertia into the μG control loop, thus stabilizing μG frequency during high penetration of RESs. Moreover, the proposed virtual inertia control system based on an optimal proportional–integral (PI) controller is coordinated with digital over/underfrequency relay to improve the frequency stability and maintain the dynamic security of the μG considering high penetration of RESs. The studied system simulation results are conducted using MATLAB/Simulink^® software to validate the efficacy of the proposed coordination scheme. Results endorsed that the proposed coordination scheme can efficiently regulate the μG frequency and ensure robust performance to maintain the dynamic security of μG with high penetration of RESs for various contingencies.

Today’s power systems have a high-level penetration of renewable energy sources (RESs). Therefore, the modern power systems become more susceptible to the system insecurity than conventional power systems due to lack of system inertia that results from replacing the conventional generators with RESs and frequency fluctuations that result from the intermittent nature of the RESs. Hence, this chapter presents a new strategy of frequency control including virtual inertia control based on virtual synchronous generator (VSG), which emulates the behavior of conventional synchronous generator in large power systems, thus adding some inertia to the system control loop virtually and accordingly stabilizing the system frequency during high penetration of RESs. Moreover, this chapter proposes an efficient coordination scheme of frequency control loops including the proposed virtual inertia control system-based VSG and digital over/underfrequency protection for maintaining the dynamic security of the renewable power systems because of the high integration level of the RESs. System modeling and simulation results are carried out using MATLAB/Simulink^® software. Results approved that the proposed coordination scheme can effectively regulate the system frequency and guarantee robust performance to preserve the dynamic security of renewable power systems with high penetration of RESs for different contingencies.

This chapter presents a digital model of decentralized load frequency control (LFC) using an optimal PID controller in a real hybrid power system (e.g., Egyptian power system (EPS)) considering communication delays. The EPS includes both conventional generation sources (i.e., steam, gas, hydraulic power plants) with inherent nonlinearities and wind power, which is extracted from Zafarana wind farm, located in Egypt. Thus, the optimal digital controller-based Tustin’s technique is designed for every subsystem of the EPS separately to guarantee the stability of the overall closed-loop system. The efficiency of the proposed digital model is evaluated and compared with the analog model under variation in loading patterns, loading circumstances, system parameters, wind farm penetration, and communication delays. Results endorsed that the proposed digital model can effectively regulate the system frequency and guarantee robust performance under different conditions. It also provides a reliable performance at large sampling times, meaning a decrease in the cost of execution.

In view of the analysis and investigations presented, the main conclusions can be summarized as follows: