Discontinuous Modulation of Interleaved Parallel NPC Inverters with Reduced Circulating Current

Parallel inverters are generally used in medium-and high-power applications. The interleaved operation of such topologies lead to reducing the output filter size. In particular, in a 1.6 MVA system consisting of 6 parallel neutral-point clamped (NPC) inverters, considered in this paper, the line filter of each NPC is reduced to 0.05 pu. However, the main drawback of the interleaved inverters with common dc-link bus is the circulating current arising between the inverters. Moreover, the peak-to-peak (PP) value of the circulating current is inversely proportional to the filter inductance and in high-power applications it can reach hundreds of amperes, forcing switching devices and passive components to endure constant stress. This paper investigates the influence of discontinuous pulse-width modulations (DPWM) with different carrier-shift techniques on the circulating current and the common-mode voltage (CMV) of paralleled NPC inverters.