Implementation of virtual synchronous generator with an Improved Hardware Structure in PV-based microgrids

Frequency stability problem in microgrid attracts much attention with increasing penetration of the intermittent and fluctuating renewable energy. Conventional microgrid control strategy in steady state can balance power difference between sources and loads by storages or robust power grids, and hence grid frequency is maintained stable. However, due to lack of inertia in power electronic converters, characteristics of dynamic response in microgrid is neglected and thus causing problems in power system stability. Therefore, the concept of virtual synchronous generator (VSG) is proposed to solve the problem. In most available schemes of VSG, renewable energy and energy storages are combined and controlled through a dc-dc converter, which are connected to a dc-bus of inverter. The scheme is easy for imitation of synchronous generator (SG) due to their similar hardware structure, but increases complexity of hardware implementation with extra design of combined photovoltaic-storage system and lacks flexibility and reliability. In this paper, a new structure and corresponding control strategy are proposed for implementation of VSG in photovoltaic generation, where photovoltaic arrays and storages are connected to microgrid ac-bus through separate inverters. With the proposed scheme, photovoltaic inverter operates in voltage control mode and the integral system behaves like a SG, which enhances performance of VSG in flexibility and reliability. The proposed strategy is verified in simulation.