A New Virtual Oscillator Control without Third-Harmonics Injection for DC/AC Inverter

Virtual Oscillator Control (VOC) is a type of nonlinear grid-forming controller for DC/AC inverters. Compared with the droop control method, the original VOC has a faster transient response in islanded mode. However, its output voltage always contains a third-order harmonic, resulting in a significant third-harmonic current, especially in the grid-connected mode. In order to eliminate this harmonic, a notch-type filter is typically employed, but it affects the synchronization speed of multiple DC/AC inverters connected in parallel in islanded mode. In this paper, by analyzing the nonlinear dynamical equations of the oscillator and simplifying its nonlinear current source, a novel VOC for four-line three-phase DC/AC inverters is proposed, which can successfully eliminate the third-order harmonic in the output voltage of the oscillator. Further, compared with the traditional VOC with notch filter, the grid-synchronization response of the proposed VOC-based DC/AC inverters can be significantly improved. A 3 kW/3-phase/120 V experimental prototype system designed on the DSPACE DS1202 platform has been developed to verify the feasibility of the proposed control strategy.