Interleaved Operation of Two Neutral-Point-Clamped Inverters with Reduced Circulating Current

Parallel inverters are commonly adopted in high-power applications, for instance wind energy systems, smart transformers, and power conditioners. Meanwhile, interleaved pulse width modulation is usually considered as an optimal approach to reduce the current ripple and harmonics of the parallel inverters. However, in the case of a common dc link, the problem of circulating current emerges and leads to performance degradation. This paper aims at investigating the influence of different modulation techniques on the circulating current of two neutral-point-clamped (NPC) inverters under interleaved operation. Two modulation techniques, phase disposition (PD) and alternative phase opposite disposition (APOD), have been studied and compared in terms of current ripple, spectrum quality, and circulating current. Though the PD modulation was regarded as the optimum solution in most of the single-NPC cases, it offers worse performance in the two parallel NPC applications due to higher circulating current. Simulation and experimental validations are provided and show that the APOD leads to much lower circulating current and similar current ripple as well as spectrum quality compared to the PD.