The LCL filter is widely used in grid connected converters for good harmonic mitigation performance. With pulse width modulation strategy, converter terminal voltage contains various sideband harmonic components together with expected components corresponding to the modulation wave, especially under a low switching frequency. Considerable resonant current can be generated if the undesired sideband harmonic voltage is located around the LCL resonant frequency. With the background of a medium voltage three-level wind power converter, where the switching frequency is as low as 1.5 kHz, a resonant current depression strategy is proposed against undesired sideband harmonic voltage under low switching frequency. Additional compensators are adopted in the converter current loop. Depending on the system mathematical model, two solutions, a Butterworth low pass filter and a notch filter, based on phase compensation and amplitude compensation, are proposed in this paper. It is shown that the Butterworth low pass filter exhibits better resonant current depression performance, while the notch filter performance is better in terms of system stability. Simulation and experimental results validated the proposed control method.

中文翻译：

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低开关频率下抗脉宽调制谐波电压的LCL谐振电流抑制控制策略

LCL 滤波器广泛用于并网变流器，具有良好的谐波抑制性能。采用脉宽调制策略，转换器端电压包含各种边带谐波分量以及对应于调制波的预期分量，特别是在低开关频率下。如果不需要的边带谐波电压位于 LCL 谐振频率附近，则会产生相当大的谐振电流。以开关频率低至1.5 kHz的中压三电平风电变流器为背景，提出了一种针对低开关频率下不希望的边带谐波电压的谐振电流抑制策略。转换器电流回路中采用了额外的补偿器。根据系统数学模型，两种解决方案，本文提出了基于相位补偿和幅度补偿的巴特沃斯低通滤波器和陷波滤波器。结果表明，Butterworth 低通滤波器表现出更好的谐振电流抑制性能，而陷波滤波器在系统稳定性方面的性能更好。仿真和实验结果验证了所提出的控制方法。