Stability Enhancement Strategy for Islanding Microgrid with Multi-type Inverters Based on Hybrid Impedance Modelling

Because of the different output characteristic of deployed inverters including PQ-controlled and droop-controlled inverters, the system stability analysis and enhancement becomes a key issue for the islanding microgrid with multi-type inverters. This paper proposes an effective stability enhancement strategy for islanding microgrid with multi-type inverter based on the hybrid impedance modelling and deduced impedance-based stability analysis criterion. The proposed strategy provides different virtual impedance design methods for PQ and droop controlled inverters. For the droop-controlled inverter, the dual virtual impedance combining the inner virtual inductance and outer virtual inductance is adopted to ensure the inductive output impedance characteristic in the fundamental frequency to easily achieve the P/f and Q/V control and improve the resistive output impedance in the high frequency to enhance the system damping. For the PQ-controlled inverter, the inner virtual resistance control scheme is used to enhance the damping in the resonant frequency. An islanding microgrid model including multi-type inverters is established in Matlab/Simulink and the simulation results prove the effectiveness of the proposed strategy.