The improved LCL filter is used in transformerless three-level photovoltaic inverter system for leakage current suppression. However, the common-mode (CM) resonance circulating current (CMRCC) is generated, which causes inverter-side current oscillation, leakage current increment, and system instability. To overcome these issues, an improved CM circulating current model with detailed analyses of CMRCC is proposed in this paper. Based on above theories, the CMRCC is influenced by filter parameters, zero-sequence duty ratio, and number of switching transitions. To suppress CMRCC, a hybrid control strategy composed of proportional integral (PI) and feedforward control is presented. It is realized by real-time adjusting zero-sequence duty ratio in space vector modulation technique. Compared with the conventional damping resistor techniques, the CMRCC and leakage current are effectively suppressed with the proposed method. Thus, the performance of inverter-side currents and leakage current suppression is greatly improved. Besides, the capacitor-voltage-feedforward control is adopted to eliminate resonance peak in the differential-mode circuit. Simulation and experimental results are given to demonstrate the effectiveness of theoretical analyses and the proposed method.

中文翻译：

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无变压器三电平T型光伏逆变器系统的同时共模谐振环流和漏电流抑制


改进的LCL滤波器用于无变压器三电平光伏逆变器系统中进行漏电流抑制。然而，会产生共模谐振环流（CMRCC），导致逆变侧电流振荡、漏电流增大、系统不稳定。为了克服这些问题，本文提出了一种改进的 CM 环流模型，并对 CMRCC 进行了详细分析。根据上述理论，CMRCC 受滤波器参数、零序占空比和开关转换次数的影响。为了抑制 CMRCC，提出了一种由比例积分（PI）和前馈控制组成的混合控制策略。它是通过空间矢量调制技术中实时调整零序占空比来实现的。与传统的阻尼电阻技术相比，该方法有效地抑制了 CMRCC 和漏电流。从而大大提高了逆变侧电流和漏电流的抑制性能。此外，采用电容电压前馈控制来消除差模电路中的谐振峰值。仿真和实验结果证明了理论分析和所提出方法的有效性。