MMC HVDC Controls for Damping Subsynchronous Interactions With LCC HVDC and Thermal Generator

This paper develops a subsynchronous damping controller (SSDC) on modular multilevel converter (MMC) HVDC with the aim of mitigating three‐way torsional interactions between a line commutated converter (LCC) HVDC, MMC HVDC and a nuclear generator. The test case is based on the French IFA2000 2 GW LCC HVDC and the new 1 GW MMC Eleclink, interacting with 1.12 GVA Gravelines generator. The proposed SSDC consists of washout filter, 4 lead‐lag compensators and a low pass filter, designed using analytical system model. A generalized method of selection of the SSDC control input and output is studied in depth. The eigenvalue study shows that the designed SSDC improves damping of two close torsional modes (at 6.3 Hz and 12 Hz for the test case) while not interfering with normal HVDC controls. Time‐domain simulations on the detailed EMTP model confirm improved torsional mode damping and show good robustness to wide range of AC and DC parameters, while having negligible impact on normal performance. The limits on the supplementary controller are set using heuristic methods as trade‐off considering damping efficiency and good large disturbance recovery.