Table1_Resonance suppression and quality improvement control strategy for a three-phase grid-connected voltage-source inverter under weak grid conditions.DOCX

The three-phase voltage-source grid-connected inverters suffer from grid-connected current quality problems due to system resonance caused by the under-damping characteristics of the filter and grid impedance, on the one hand, and the grid-connected current distortion caused by the high content of low harmonics in the grid voltage, on the other hand. To resolve this problem, a current quality improvement control strategy, combining capacitor-current feedforward active damping and harmonic virtual impedance reshaping, is proposed by analyzing the mechanisms of system resonance and grid-connected current distortion. In addition, the proposed control strategy allows determining the virtual impedance parameters by using the root locus method, so as to achieve the purpose of improving the output grid-connected current quality of the three-phase voltage-source grid-connected inverter under weak grid conditions. Finally, the correctness and effectiveness of the proposed control strategy are verified by simulation and experiment.

三相电压型并网逆变器（three-phase voltage-source grid-connected inverters）面临两类并网电流质量问题：一方面是滤波器欠阻尼特性与电网阻抗共同引发系统谐振，另一方面是电网电压中低次谐波含量过高导致并网电流畸变。为解决该类问题，本文通过分析系统谐振与并网电流畸变的作用机理，提出一种融合电容电流前馈有源阻尼（capacitor-current feedforward active damping）与谐波虚拟阻抗整形（harmonic virtual impedance reshaping）的并网电流质量提升控制策略。此外，所提控制策略可通过根轨迹法（root locus method）确定虚拟阻抗参数，以实现弱电网（weak grid）条件下三相电压型并网逆变器输出并网电流质量的优化提升。最后通过仿真与实验验证了所提控制策略的正确性与有效性。