7. Fuzzy Logic Control for Virtual Inertia Synthesis

Currently, renewable energy sources (RESs) and distributed generators (DGs) are highly integrated into power systems regarding energy crisis, environmental concerns, and economic growth. The RESs/DGs penetration brings more complexity to the power system, since its systems are decentralized, and power outputs are intermittent or unpredictable against time-varying. Nevertheless, the RESs/DGs may not participate in stability regulation (e.g., frequency/voltage control), which causes the lack of inertia and damping property to the system, resulting in the weakening of grid stability. This situation can lead to system instability, cascading failures, and power blackouts. To deal with this problem, the system requires high-level (advanced) inertia controllers in tracking various levels of RESs/DGs penetration. Fuzzy logic control can be considered as one of the solution techniques due to the high reliability in nonlinear modeling with the fast processing time. In this chapter, a fuzzy logic technique is integrated into a virtual inertia control loop to enable the self-adaptive ability of  virtual inertia constant against the different levels of RESs/DGs penetration regarding frequency control. As a result, the virtual inertia control unit can automatically adjust itself in emulating different amounts of inertia and damping responding the integrated levels of RESs/DGs at the specific time.  At the beginning, the fundamental of fuzzy logic is discussed, and the recent achievements in fuzzy applications for frequency control problems are briefly reviewed. Then, a decentralized fuzzy controller in scheduling virtual inertia control constant is designed. Lastly, the effectiveness of the proposed control scheme is demonstrated through a nonlinear simulation under wide ranges of critical RESs/DGs penetration regarding system inertia and damping variations.