Virtual Series Impedance Damping Control for SSR Suppression of MMC-HVDC Interconnected With PMSG-Based Wind Farm

There is a risk of sub-synchronous resonance (SSR) when a permanent magnet synchronous generator-based wind farm is connected to a power grid through a high-voltage direct current (HVDC) system. To study such SSR, the linear model of the integrated system has been established using the state space method firstly. The root locus and modal analysis methods are adopted to study the participation variables and participation factors of SSR. It shows that the variables in the q-axis in both wind farms and MMC with high power levels dominate the resonance. Secondly, the simplified impedance models are derived. The simplified minimum loops L^dd and L^qq are used to carry out the parameter calculations. An active damping control strategy with virtual series impedance is proposed by feeding back AC current into the outer loop of MMC. Thirdly, three types of virtual series impedance are presented, considering the structure of damping controller. In addition, the parameter selection ranges and principles for those damping controllers are presented using analytical calculation methods. Finally, the effectiveness and correctness of proposed methods, as well as the robustness of parameters are verified by simulation models. And the feasible structure of the damping controller is suggested.