Equivalent Model and Stability Enhancement Strategy for Distributed Photovoltaic Grid-Connected Systems Based on Coherency VSGs

In the new power distribution system, multi-distributed photovoltaic (PV) systems often exist in the form of either direct parallel connection or indirect interconnection. The virtual synchronous generator (VSG), as a typical grid-forming distributed PV inverter, exhibits different dynamic characteristics with different combinations of control and circuit parameters under grid fault conditions. Current research often focuses on the stability of a single VSG, with few studies addressing the analysis and control of multiple VSG grid-connected systems. Therefore, this paper proposes a method for discriminating VSGs grid-connected system and establishes an equivalent single VSG model for the coherent VSGs grid-connected system, ensuring that the equivalent single VSG system model has a clear physical meaning and can represent the dynamic characteristics of original system. Then, based on the equivalent model, a method for improving the transient performance of the coherent VSGs grid-connected system is proposed. Finally, the correctness of the theoretical analysis is verified through simulation.