Tracking Differentiator Based Approximate Zero-Impedance Control for Three-Phase Grid-Forming Inverter

In conventional voltage control of grid-forming (GFM) inverter, the load current feedforward is often employed to reshape the output impedance and improve control performance. To further enhance this capability, an approximate zero-impedance control for three-phase GFM inverter is proposed in this paper. The core idea is to achieve zero impedance in the continuous domain by introducing a differential term into the load current feedforward path. A discrete-time optimal control (DTOC)-based tracking differentiator (TD) is utilized its excellent noise-suppression characteristics. The proposed approach is general-purpose and applicable across various control structures (e.g., conventional dual-loop or state-space) and reference frames (dq or αβ). Owing to the unique features of the method, the state-feedback parameters become decoupled from the impedance design, which significantly simplifies controller tuning. Finally, experimental results verify the effectiveness and robustness of the proposed strategy.