Damping DFIG-associated SSR with subsynchronous suppression filters: A case study on a practical wind farm system

The interaction between the converter controllers of doubly-fed induction generators (DFIGs) and fixed series compensation tends to cause a new type of subsynchronous resonance (SSR), or subsynchronous control interaction. To address this issue, this paper proposes a novel scheme to deactivate such an interaction by embedding subsynchronous suppression filters (SSFs) into DFIG´s converter controllers. Its ability to stabilize SSR is validated by applying it to a practical wind farm system in North China, which has experienced many SSR events. The electromagnetic model incorporating multiple DFIG-based wind farms and series-compensated transmissions is established. Then its SSR characteristics are investigated and used to design SSF´s parameters. Two SSF schemes are developed for the target system. The high-cost scheme has all DFIGs equipped with SSFs while a more cost-effective scheme is also designed, which only needs to add SSFs to an optimized number of DFIGs. Simulation results have verified the effectiveness of both schemes in guaranteeing the stability of SSR under all possible operating conditions. In practice, the latter scheme is preferred because of its low cost and sufficient performance.