Optimization and Configuration of Control Parameters to Enhance Small Signal Stability of Hybrid LCC-MMC HVDC System

This paper investigates the small-signal stability of the hybrid High Voltage Direct Current (HVDC) transmission system, composed of line commutated converter (LCC) as rectifier and modular multilevel converter (MMC) as inverter, under weak receiving AC grid condition. Firstly, the impact of Short-Circuit-Ratio (SCR) at inverter side on the system stability is studied by eigen-analysis, and the key control parameters which have major impact on the dominant mode are identified by the participation factor and sensitivity analysis. Then, considering the quadratic index and damping ratio characteristic, an objective function to evaluate the system stability is developed, and an optimization and configuration approach for control parameters are presented by utilization of Monte Carlo method. The eigenvalue results and the electromagnetic transient (EMT) simulation results show that, with the optimized control parameters, the small-signal stability and the dynamic responses of the hybrid system is greatly improved, and the overall system can even operate under extremely weak ac grid condition.