A Coordinated Strategy to Suppress Zero-Sequence Circulating Currents and Balance Neutral-Point Potential of Parallel 3L-ANPC Converters

With the increasing demand for high-capacity storage equipment, three-level converters parallel system are widely used by sharing DC bus and AC bus directly, but it can't be ignored that the neutral-point potential (NPP) fluctuation and zero-sequence circulating current (ZSCC) problem may do harm to efficiency and reliability of the system. However, the coupling relationship of NPP and ZSCC is still unclear and there is a challenge to achieve NPP balance and suppress ZSCC simultaneously. In this paper, a detailed model of NPP and ZSCC is analyzed to explain the coupling relationship of them, which is related to the inherent and control aspects. Furthermore, a coordinated control strategy is proposed by adjusting the redundant small vectors' duty cycle with distribution factor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$k$</tex>, which comprises a common-mode component (CMC) for NPP balance and a differential-mode component (DMC) for ZSCC suppression so as to control both of them simultaneously. Even in a low power factor, the adjustment strategy for distribution factors ensures the effectiveness of coordinated control. Simulation results are presented to validate the effectiveness of the proposed strategy.