Impedance modeling and analysis of voltage-source converter-based high-voltage direct current system for grid-connected wind farm

Oscillation issues of the gird-connected offshore wind farm through the voltage-source converter-based high-voltage direct current (VSC-HVDC) have serios influence on the grid stability. However, in the previous modeling and analysis for the VSC-HVDC system, the receiving-end inverter station is usually considered as a constant voltage source, neglecting the impact of the inverter and AC grid. In addition, the commonly used mitigation method by modifying control parameters usually does not consider its influence on the controller's control performance. To analyze the system stability more rigorously and suppress the oscillation effectively, in this work, we firstly establish a detailed impedance model of VSC-HVDC considering the inverter station and DC transmission line, based on which the stability analysis is also presented. Furthermore, an oscillation suppression method based on intelligent impedance optimization is proposed, which is solved by Particle swarm optimization (PSO) algorithm. The proposed impedance optimization method can achieve the maximum stability margin while the transient dynamic performance is still guaranteed, thereby suppressing the oscillation of the system. Simulations are conducted in PSCAD/EMTDC to validate the accuracy and effectiveness of the proposed modeling and suppression method.