Analysis and Mitigation of Inverter Output Impedance Impacts for Distributed Energy Resource Interface

In order to provide reliable electric power, the interfacing voltage source inverters in distributed generation often rely on autonomous droop control method integrated with virtual impedance and inner voltage and current control loops. In general, the droop-controlled inverters can be modeled as a controllable voltage source in series with output impedance. However, stability, dynamic performance, and load adaptability in islanding mode are sensitive to the inverter output impedance. In this paper, the detailed impacts of the inverter output impedance are investigated in different operation modes. Furthermore, an inverter current feedforward control scheme is proposed to mitigate the effects. With the implementation of the proposed control scheme, system reliability and load adaptability in islanding mode are enhanced without additional control complexity and extra sensors. Moreover, a voltage magnitude control loop is added to improve the control accuracy of reactive power flow in grid-connected mode. Finally, the proposed strategy is validated with simulation and experiments based on a 15-kVA prototype.