Harmonic voltage compensation and harmonic current sharing strategy of grid-forming inverter

Abstract

In a multi-inverter parallel system, the harmonic governance control strategy may worsen the system's current circulation problem due to the line impedance difference, which could further affect the stable operation of the system. To solve the problem, the strategy considering both power sharing and harmonic control is proposed in this paper. First, the microgrid system with background harmonics is modeled and analyzed. Based on the modeled system, a comprehensive control strategy for the grid inverter with harmonic voltage compensation and harmonic current sharing is established. In this paper, the output signal is controlled by frequency division. This paper adopts grid-forming control in the fundamental wave domain and employs harmonic voltage compensation control in the harmonic domain. The harmonic voltage is synthesized by collecting the specific harmonic current through the band-pass filter, compensating for the harmonic voltage drop on the line to improve the harmonic voltage quality of the point of common coupling(PCC). Aiming at the sharing problem caused by line impedance difference, virtual impedance control is introduced, harmonic impedance is redesigned according to the adjusted output impedance, and the harmonic output impedance before and after adjustment is measured and compared. The simulation results show that the proposed control strategy can not only reduce the harmonic content of the PCC voltage but also achieve the effect of equal harmonic current division.