Parallel three-level inverters have attracted considerable attention due to the advantages to increase the power rating and the flexibility of power conversion systems. However, this type of configuration requires to suppress the zero-sequence circulating current (ZSCC) through either modulation or active control strategies, to avoid overloading problems of a single three-level inverter. For the operation of paralleled three-level T-type inverters, another requirement is to reduce the common mode voltage (CMV) associated with a pulsewidth modulation method. To better solve these problems simultaneously, an optimized zero-sequence voltage injection method is proposed to both reduce CMV and eliminate ZSCC for multiparallel-connected three-level inverters. A generalized CMV reduction strategy is developed, which can reduce the magnitude of CMV to one half of the value using the conventional space vector modulation. The highlight of the method is that ZSCC is eliminated by adding an optimal compensation value to the reference duty signals with lower CMV. This compensation value is calculated simply by ZSCC, duty cycles, and filter parameters. The better ZSCC suppression performance can be obtained in both steady and transient states with the proposed scheme, thus, improving the quality of currents.

中文翻译：

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并联三电平变换器消除环流、降低共模电压的优化零序电压注入方法


并联三电平逆变器由于具有提高额定功率和电源转换系统灵活性的优点而引起了广泛的关注。然而，这种类型的配置需要通过调制或主动控制策略来抑制零序环流（ZSCC），以避免单个三电平逆变器的过载问题。对于并联三电平T型逆变器的操作，另一个要求是降低与脉宽调制方法相关的共模电压（CMV）。为了更好地同时解决这些问题，针对多并联三电平逆变器，提出了一种优化的零序电压注入方法，以降低CMV并消除ZSCC。提出了一种广义的 CMV 降低策略，可以将 CMV 的幅度降低到传统空间矢量调制的一半。该方法的亮点在于通过向具有较低CMV的参考占空比信号添加最佳补偿值来消除ZSCC。该补偿值可通过 ZSCC、占空比和滤波器参数简单计算得出。该方案在稳态和瞬态下都能获得更好的 ZSCC 抑制性能，从而提高电流质量。