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High-Pass-Filter-Based Virtual Impedance Control for LCL-filtered Inverters Under Weak Grid
Jiangfeng Wang*, Yan Xing*, Li Zhang˘Ó, Haibing Hu*, Tianyu Yang*, and Daorong Lu*
Abstract Voltage feed-forward control (VFFC) is widely used in LCL-type grid-tied inverters due to its advantages in terms of disturbance rejection performance and fast dynamic response. However, VFFC may worsen the stability of inverters under weak grid conditions. It is revealed in this paper that a large phase-lag in the low-frequency range is introduced by VFFC, which reduces the phase margin significantly and leads to instability. To address this problem, a novel virtual-impedance-based control, where a phase-lead is introduced into the low-frequency area to compensate for the phase lag caused by VFFC, is proposed to improve system stability. The proposed control is realized with a high-pass filter, without high-order-derivative components. It features easy implementation and good noise immunity. A detailed design procedure for the virtual impedance control is presented. Both theoretical analysis and experimental results verify the effectiveness of the control proposed.
Keyword Grid-tied inverter, Stability, Virtual impedance, Voltage feed-forward control, Weak grid
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