Adaptive Harmonic Virtual Impedance Control for Improving Voltage Quality of Microgrids

The influence of nonlinear loads on the voltage quality is an emerging concern for islanded microgrids. Existing research mainly focuses on harmonic power sharing among multiple inverters, which ignores the diversity of different inverters to mitigate harmonics from nonlinear loads. As a result, the voltage quality of the microgrid cannot be effectively improved. In view of the above, this paper proposes a novel harmonic power allocation strategy which gives priority to the voltage quality of the microgrid. The core idea is to maximize harmonic power absorption by shaping lowest output impedances of inverters, on the premise that all inverters are not overloaded. To achieve this, the stability domain of the harmonic virtual impedance is carefully defined first and then a fuzzy controller is designed to adjust the harmonic virtual impedance of each inverter based on its operating condition. In addition, a Monto-carlo harmonic power flow based evaluation process is designed to indicate the performance of the method in practice. Finally, comparative studies and control-in-the-loop experiments are conducted.