Experimental Validation of an Active Wideband SSR Damping Scheme for Series-Compensated Networks

Transmission network reinforcements are being undertaken to meet renewable energy targets towards a low carbon transition. High-voltage direct-current (HVDC) links and series-compensated ac lines are frontrunners in these developments. Although series capacitor installations can lead to subsynchronous resonance (SSR), HVDC links based on voltage source converters (VSCs) can be used to effectively damp SSR upon occurrence. An active damping technique to mitigate torsional interactions (TIs), a form of SSR, is presented. The damping scheme considers an active wideband filter to ensure positive damping in a wide range of subsynchronous frequencies. A state-space representation of the system has been formulated and eigenanalyses have been performed to assess the impact of the HVDC link on the TIs. A damping torque study for SSR screening is carried out, with results complemented with time-domain simulations to assess the accuracy of the small-signal models. The test system is implemented in a real-time digital simulator and connected to a VSC-HVDC scaled-down test-rig to validate the damping scheme through hardware-in-the-loop experiments. The presented damping method exhibits a satisfactory performance, with time-domain simulations and laboratory experiments showing a good correlation.