Adaptive Damping Control of Subsynchronous Oscillation in DFIG-Based Wind Farms Connected to Series-Compensated Network

The frequency of subsynchronous oscillation (SSO) in doubly-fed induction generator (DFIG)-based wind farms connected to series-compensated networks is determined by system-wide operating conditions, including the wind speed, number of in-service wind turbines, and degree of series-compensation. This paper proposes an adaptive mitigation scheme to damp the SSO for a full range of subsynchronous frequency variations due to different operating conditions. The proposed scheme comprises 1) a subsynchronous frequency estimator (SSFE) and 2) an adaptive subsynchronous damping controller (ASDC). The SSFE detects the SSO mode and tracks its subsynchronous frequency accurately. The ASDC utilizes voltage signals to extract the SSO at the estimated subsynchronous frequency, generates appropriate current signals, and injects them into the grid through a shunt-voltage sourced converter (SVSC). The ASDC behaves like a variable impedance, which essentially reshapes the system's impedance response by adding a positive resistance at the estimated subsynchronous frequency. The parameters of the phase-shifters are computed using Brent's root-finding method such that the desired phase-shift at the estimated subsynchronous frequency is always maintained. The control's adaptiveness and damping performance under different operating scenarios is verified through extensive EMT simulations on a real-world wind power system facing SSO using PSCAD.