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 an islanded mode. In this article, by analyzing the nonlinear dynamical equations of the oscillator and simplifying its nonlinear current source, a novel VOC for 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.