Small-signal dynamics and control parameters optimization of hybrid multi-infeed HVDC system

A small-signal model for a Hybrid Multi-Infeed High Voltage Direct Current (H-MIDC) system, which is composed of Line-Commutated-Converter based HVDC (LCC-HVDC) links and Voltage-Source-Converter based HVDC (VSC-HVDC) links locating in a common receiving AC grid in close proximity, is developed and validated by comparing the time-domain responses from the small-signal model and the detailed electromagnetic transient (EMT) simulation in PSCAD/EMTDC. Based on eigen-analysis, the impact of the Short-Circuit-Ratio (SCR) values of the LCC-HVDC and VSC-HVDC links, and the proximity between LCC and VSC inverter stations on the dynamics of the H-MIDC system is investigated. Then, the dominant mode highly related to the state-variables of AC grid and control system is derived, which may cause instability of the H-MIDC system under weak AC grid due to the improper selection of control parameters. Finally, an optimization tuning algorithm based on the parameter sensitivity analysis is presented to systematically optimize the controller parameters for the H-MIDC system attached to weak AC grid. From the time-domain simulation results in PSCAD/EMTDC, it is obvious that the dynamic performances of the H-MIDC system are significantly improved with the optimized controller parameters.