Adaptive CVCF controller design for an energy storage system considering an operation mode change in a standalone microgrid

Abstract

In South Korea, existing diesel generators are being replaced with photovoltaic (PV) generators in several standalone microgrids. However, their reliability and stability are still not guaranteed owing to PV fluctuations arising from unpredictable environmental changes. To reduce the effects of PV fluctuations, an energy storage system (ESS) with a similar capacity is needed to increase renewable energy sources (RES). A large-capacity ESS can be used as a main power source without a diesel generator when the state of charge is sufficient. In this study, a new method is proposed to mitigate the transients caused by the transition of an ESS to constant voltage constant frequency (CVCF) mode as a diesel generator is disconnected from a standalone microgrid. Existing PI controllers cannot completely suppress transients; hence, an adaptive sliding mode control (ASMC) method is applied to achieve a seamless transition. The transient effects of changing modes are analyzed, and the influencing factors are derived. Case studies on a practical standalone microgrid in South Korea are conducted through a time-domain simulation using DIgSILENT PowerFactory (R) software.