Circulating Current Mitigation Discontinuous Pulse Width Modulation for Two Parallel Connected NPC Inverters

Parallel-connected neutral-point-clamped (NPC) inverters encounter significant challenges in suppressing high frequency circulating currents, which can reduce system efficiency and compromise component reliability. Although previous studies have proposed various pulse width modulation (PWM) methods to address this issue, these approaches often require inherent trade offs among high-frequency circulating current reduction, power losses, and thermal stresses on power devices and DC-link capacitors. This paper proposes a high-frequency circulating current mitigation discontinuous PWM (CCM-DPWM) for parallel-connected NPC inverters. The proposed CCM-DPWM achieves effective mitigation of high-frequency circulating currents and maintains low total harmonic distortion (THD) of output currents through the proposed strategic selection of switching vectors to minimize the differential common-mode voltage between parallel-connected NPC inverters. In addition, the proposed method retains the benefits of conventional DPWM based methods in reducing switching losses and thermal loading of power devices, with better performance with respect to the thermal loading of DC-link capacitors, which is one of the main concerns when applying DPWM. The effectiveness of the proposed CCM-DPWM is verified through the simulations and experiments.