Considering the time delay introduced by the digital control, it turns out that capacitor current proportional feedback active damping (AD) is equivalent to a frequency-dependent virtual impedance in parallel with the filter capacitor. Unstable open-loop poles will arise due to the presence of virtual negative resistor, which causes that the system stability is highly sensitive to grid-impedance variation. Therefore, this study proposes a novel capacitor current quasi-integral feedback AD method. Theoretical analysis shows the proposed AD method can extend the region of the virtual positive resistor, i.e. damping region to the half of sampling frequency ( f _s /2). Hence, strong robustness against the grid-impedance variation is achieved. Finally, experimental results including the proposed AD method as well as capacitor current proportional feedback AD method are given and compared, which validates the superior damping performance of the proposed scheme.

中文翻译：

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具有电容器电流准积分反馈的LCL型并网逆变器的鲁棒AD

考虑到数字控制引入的时间延迟，事实证明，电容器电流比例反馈有源阻尼（AD）等效于与频率相关的虚拟阻抗，与滤波电容器并联。由于存在虚拟负电阻，将导致不稳定的开环极点，这将导致系统稳定性对电网阻抗变化高度敏感。因此，本研究提出了一种新颖的电容器电流准积分反馈AD方法。理论分析表明，所提出的AD方法可以将虚拟正电阻的区域（即阻尼区域）扩展到采样频率的一半（ F _s / 2）。因此，实现了针对电网阻抗变化的强大鲁棒性。最后，给出并比较了所提出的AD方法以及电容器电流比例反馈AD方法的实验结果，验证了所提出方案的优越阻尼性能。