Stability Analysis and Impedance Reshaping Control of Medium-Frequency Oscillation in a PMSG-based Wind Farm Connected to a VSC-HVDC

It is well known that the permanent magnet synchronous generator (PMSG)-based wind farm may face the sub-synchronous oscillation (SSO) or high frequency oscillation (HFO) issue. However, the medium frequency oscillation (MFO) may also exist in a PMSG-based wind farm when integrated with a voltage source converter based HVDC (VSC-HVDC). In this work, to investigate the mechanism and characteristics of MFO, the impedance model of the interconnected system is derived. Furthermore, the influence of the control parameters of both PMSG and VSC-HVDC on MFO is analysed with an accurate criterion based on the single input single output (SISO) equivalent sequence impedance. And the theoretical analysis is verified by simulation. Finally, an impedance reshaping control for MFO is proposed. The results show that MFO can be suppressed with the appropriate virtual impedance installed in the wind farm VSC (WFVSC) station, which is meaningful for the actual project.