Abstract
Power systems are the most complex systems that have been created by men in history. To operate such systems in a stable mode, several control loops are needed. Voltage frequency plays a vital role in power systems which need to be properly controlled. To this end, primary and secondary frequency control loops are used to control the frequency of the voltage in power systems. Secondary frequency control, which is called Load Frequency Control (LFC), is responsible for maintaining the frequency in a desirable level after a disturbance. Likewise, the power exchanges between different control areas are controlled by LFC approaches. In recent decades, many control approaches have been suggested for LFC in power systems. This paper presents a comprehensive literature survey on the topic of LFC. In this survey, the used LFC models for diverse configurations of power systems are firstly investigated and classified for both conventional and future smart power systems. Furthermore, the proposed control strategies for LFC are studied and categorized into different control groups. The paper concludes with highlighting the research gaps and presenting some new research directions in the field of LFC.
Highlights
The Load Frequency Control (LFC) models for two-area power systems considering the effects of voltage control loops in the frequency response are developed in [24,30]
A micro-grid and hybrid system consisting of PV, wind turbine generator (WTG), micro turbine, fuel cell (FC) and aqua electrolyzer (AE) are considered for modeling the LFC [64,126,127,128,129,130,131,132,133,134]
Particle swarm optimization (PSO) is based on population and inspired by the friendly behavior of fish schooling or bird flocking, which is considered as a powerful optimization technique, has been widely used for solving LFC problem in interconnected power systems
Summary
The complexity of power systems is growing due to: (i) increasing the penetration of renewable energy resources; (ii) adopting new concepts such as smart grid; and (iii) digitalization of the power systems control based on unsafe communication systems. With increasing the penetration level of renewable resources such as wind farms and photovoltaic plants in power systems, the uncertainties of active power production is highly increased, determining frequency variations. Such increase in active power fluctuation, beside the demand stochasticity, the frequency of power system would be highly oscillated. Many control approaches have been suggested for LFC in interconnected power systems These approaches can be categorized into four groups: (i) classical control approaches focus on designing proportional-integral-derivative (PID) controllers for controlling the frequency and tie-lines power flows; (ii) modern control approaches including optimal control method, sliding mode control schemes, and adaptive control systems; (iii) intelligent control schemes, such as fuzzy control systems; and (iv) soft computing-based approaches for controllers’ parameter tuning which had a considerable attention from researchers in the last decade
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