Interleaved operation of parallel neutral-point clamped inverters with reduced circulating current

Parallel inverters are commonly adopted in high power applications, for instance wind energy system, smart transformer, and power conditioners. Meanwhile, interleaved PWM is usually considered as an optimal approach to reduce the current ripple and harmonics of the parallel inverters. However, in 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 parallel 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 single NPC cases, it offers worse performance in the parallel NPC application 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.


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