A Modified PBC Method with Stability Improvement Through Full-Frequency Range Impedance Reshaping for Grid-Tied Inverter

The passivity-based control (PBC) combined with disturbance-observer (DOB) can offer an alternative tracking control scheme with stronger robustness and anti-interference ability for the grid-tied inverter (GTI). However, due to variations in grid impedance, the traditional DOB-PBC method may result in the negative real part of the GTI’s output impedance in both high-frequency and low-frequency ranges, leading to potential harmonic resonance or even system collapse. To improve the stability of the system, a full-frequency range impedance reshaping (FFRIR) method is proposed, which significantly reduces the negative impedance regions. In the proposed FFRIR method, the capacitor voltage feedforward and feedback links are respectively added to reshape the phase of the low-frequency range of the d-axis and q-axis output impedance; the capacitor current feedforward is designed to regulate the phase of the high-frequency range of output impedance. Finally, the three-phase GTI system that has been presented exhibits stable operation even when subjected to fluctuating grid impedance conditions, as evidenced by both simulation and experimental findings.