Enhancing the harmonic current sharing performance of low-switching-frequency inverters though dynamic impedance reshaping

Abstract

In islanded microgrids, harmonic currents of nonlinear loads are expected to be properly shared among parallel inverters, and this is normally achieved by shaping the effective harmonic impedance, i.e., the sum of inverter output impedance and transmission line impedance, through virtual impedance controls. However, for low-frequency inverters, harmonic virtual impedances may not be directly implemented due to the bandwidth limitation of the voltage controller. Besides, line impedances with mismatched magnitudes and angles can lead to inaccurate harmonic current sharing results. To solve these issues, this paper proposes an orthogonal impedance-sharing control, which can dynamically adjust the phase and magnitude of the effective impedance. The proposed method is widely applicable with different line impedances, and its effectiveness is validated though simulation/experimental results.