Suppressing switching frequency circulating current in parallel inverters with Carrier Phase-Shifted SPWM technique

Parallel operation techniques can be applied to inverters, especially in high power applications. This paper proposed a parallel structure of three phase voltage source inverters, which individual modules connected both DC and AC sides directly without additional passive components. The Carrier Phase-Shifted SPWM (CPS-SPWM) technique is used to suppress the output current total harmonic distortion (THD). However, the switching action in each module would be asynchronous due to the CPS-SPWM strategy, and this phenomenon will generate switching frequency circulating current between the parallel inverters. The main objective of this paper is to research the behavior of the switching frequency circulating current, including the harm and impact factors, and try to find appropriate settlement, to realize the combination between harmonic cancellation and switching frequency circulating current suppression. A novel interleaved PWM method has been proposed to solve this problem. Based on the analysis, this PWM method is shown to minimize the amplitude of the switching frequency circulating current by more than 50%, and it doesn´t affect harmonic cancellation in the parallel inverters. Simulation results carried out on a 500-kW paralleled three phase inverters are presented to confirm the analytical results.