Rethinking Current Controller Design for PLL-Synchronized VSCs in Weak Grids

This paper revisits the design of current controller for grid-connected voltage-source converters (VSCs), considering dynamic impacts phase-locked loop (PLL), weak grids, and voltage feedforward (VFF) control. First, a single-input single-output transfer-function-based model is proposed to characterize interactions control loops. It analytically found that proportional gain essentially aggravates instability effect PLL in while cutoff frequency low-pass filter used with VFF has non-monotonic relationship PLL-induced instability. Then, based on these findings, guideline re-designing PLL-synchronized VSCs developed, which enables co-design controller. Lastly, simulation experimental results confirm validity theoretical analyses.