Average-Filtering Virtual Oscillator Control for Harmonic Voltage Mitigation

Abstract

Virtual oscillator control (VOC) is a grid-forming control strategy for microgrids, where the inverter is regulated to emulate the behavior of a weak nonlinear oscillator. Compared to droop control, VOC offers a faster transient response due to its time-domain approach. However, the cubic nonlinearity of the Van der Pol oscillator generates harmonic voltages, particularly the third harmonic, which compromises the power supply quality of the inverter. In this paper, an average-filter-based VOC is proposed to mitigate harmonic distortion of the inverter output voltage. By decomposing the Van der Pol oscillator’s output voltage into DC and AC components and leveraging its sinusoidal symmetry, harmonic components are significantly suppressed through single-cycle integration. The proposed VOC’s effectiveness in suppressing harmonics is demonstrated through various simulations and experiments. Compared to the original VOC, the proposed average-filter-based VOC significantly reduces the total harmonic distortion (THD) of the output voltage from 2.6% to 0.99%, with the third harmonic voltage decreasing from 2.28% to 0.18%. The proposed method also features a balanced dynamic response and power quality, which enhances its engineering applicability.