A Partial Impedance Decoupling Control Method for PMSG-Based Wind Farms Connected to a Weak Grid

Under weak grid conditions, the coupling between the grid-connected converter and the grid impedance tends to bring in harmonic instability in the permanent-magnet synchronous generators (PMSGs)-based wind farm system. Although the symmetrical phase-locked loop (SPLL) can decouple the converter from the grid, it exerts an impact on the system stability. To address this issue, this paper proposes a partial impedance decoupling control method based on the SPLL. Based on a small-signal impedance model, the grid-GSC impedance decoupling mechanism of the SPLL and its adverse impact on system stability are analytically revealed. Furthermore, a partial impedance decoupling method is realized that incorporates adjustment coefficients and symmetric compensation to achieve a trade-off between damping enhancement and coupling mitigation, thus expanding the stable operating range of the PMSG-based wind farm system. Both simulation and experimental results demonstrate that the proposed strategy significantly improves system stability and maintains stable operation under grid conditions with a 10% reduction in short-circuit ratio (SCR).