Passivity-Based Stabilization of LCL-Filtered Grid-Following Inverters for Offshore Wind Farms: A Step-by-Step Design With PCC Voltage Feedforward

초록

This article proposes a passivity-based current control design through a systematic step-by-step procedure for LCL-filtered grid-following (GFL) inverters. Offshore wind farms often encounter weak grid conditions due to long-distance transmission, resulting in low short-circuit ratios (SCR). High impedance at the point of common coupling (PCC) triggers converter-driven instability, restricts control bandwidth, and increases the risk of system failure. To mitigate these issues, the proposed design procedure ensures both internal and external stability of grid-tied inverters with LCL filters. First, the current controller gain is determined to ensure internal stability. Then, a PCC voltage feedforward is incorporated to achieve passivity by reshaping the inverter output admittance. Specifically, a second-order low-pass filter (LPF)-based feedforward extends the phase margin of the inverter output admittance up to the Nyquist frequency. In addition, the proposed method is applicable to parallel inverter systems, where cable-induced interactions can introduce multiple admittance intersections. The proposed passivity-based design maintains sufficient phase margin at these intersections, thereby improving system robustness. The robustness and effectiveness of the passivity-based controller are verified through controller hardware-in-the-loop (C-HIL) simulations.

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