摘要
Combining three-phase power converters in parallel is a practical approach to enhance required power ratings in distribution power networks. However, when these converters are not identical, the configuration can lead to circulating currents (CCs) among the converters and challenges in managing undesirable power output under three-phase unbalanced operating conditions. This work proposes a solution for parallel-connected three-phase Neutral Point Clamped (NPC) converters, aiming to mitigate CCs while ensuring precise power sharing. The study begins by examining the impact of pulse width modulation (PWM) on reducing high-frequency zero-sequence circulating currents (ZSCC) and common-mode voltage in multiple parallel three-level NPC converters. Analytical expressions for circulating currents are derived, and two carrier-based modulation (CBM) techniques are evaluated using double Fourier integral analysis. To address low-frequency ZSCC, a comprehensive control scheme is introduced, incorporating proportional-integral-resonant (PIR) current controllers with zero-sequence voltage injection and a feed-forward decoupling mechanism. Additionally, communication-enabled virtual synchronous generator (VSG) control with virtual impedance adjustments is integrated to meet the dynamic requirements of microgrid applications. The effectiveness of the proposed approach is validated through numerical simulations and hardware experiments, demonstrating its capability to achieve stable and efficient operations in parallel-connected NPC converter systems.