Novel Virtual Impedance Compensation Algorithm for Operation Stabilization of 3P4L3L PV-BES Microgrids With Constant Power Loads

A hybrid microgrid system that includes photovoltaic (PV) panels, battery energy storages (BESs), and constant power loads (CPLs) is presented in this article, where three-phase four-leg three-level (3P4L3L) is utilized as the main power interface. As the penetration of CPLs increases significantly, the operational stability of PV-BES Microgrids has become one of the most challenging issues. To tackle this issue, this paper proposes virtual impedance compensation methods to prevent the instability and oscillations caused by CPLs. First, the small-signal model of main power interfaces, especially 3P4L3L converters and CPLs, is built. Then, the stability of the cascaded system is investigated using the Nyquist criterion. Two compensation strategies are proposed based on the derived small-signal model, and the two methods are analyzed and compared in terms of the stability margin. Experiments are performed to prove the feasibility of the proposed strategy, and the results show that the virtual impedance compensation can prevent instability in 3P4L3L PV-BES Microgrids with high penetration of CPLs.