A Phase-shifted Zero-CM PWM for Circulating Current Reduction in Two Paralleled Inverters with Coupled Inductors

The adoption of two paralleled inverters using magnetically coupled inductors is an emerging and effective way to feed the three-phase load, which can be operated with interleaved or zero-common-mode (CM) pulsewidth modulation (PWM). The zero-CM PWM can significantly reduce the CM current and electromagnetic interference (EMI), but worsen the circulating current as compared to the interleaved method. Preventing the coupled inductor saturation is the main rule of coupled inductor design, which is determined by the peak value of the circulating current. This article presents a detailed analysis of the zero-CM PWM effects on the circulating current. A detailed exploration of the pulse position shift technique is presented, and a novel modified modulation strategy referred to as phase-shifted zero-CM PWM is proposed, which can significantly reduce the peak value of circulating current and therefore lower the saturation flux density of coupled inductors. The phase-shifted zero-CM PWM is discussed with respect to the traditional method, and the specific design of phase shift angle leads to the reduced peak value of the circulating current, which can finally reduce the size of coupled inductors. The theoretical and experimental results are presented to evaluate the performance of the proposed method against the traditional zero-CM PWM.