Continuous Commutation Failure Suppression Strategy for Hybrid Multi-infeed HVDC Systems Based on Commutation Area Theory

In order to solve the voltage drop and power interruption caused by the continuous commutation failure of line commutated converters based high voltage direct current(LCC-HVDC) in hybrid multi-infeed DC transmission(HMIDC), a continuous commutation failure suppression strategy suitable for HMIDC is proposed. Firstly, the commutation failure mechanism of LCC-HVDC is analyzed based on the commutation area theory. Then, a dynamic non-linear VDCOL controller is designed by using variable slope function, which limits the growth rate of DC current and reduces the area of commutation demand by changing the slope of VDCOL curve. Meanwhile, the mapping relationship between DC current and MMC output reactive power is established, and a MMC fast reactive power controller with capacity constraints is designed to increase the commutation voltage and commutation supply area by adjusting the reactive power emitted by the MMC inverter. Furthermore, a continuous commutation failure suppression strategy based on commutation area theory is constructed for HMIDC. Finally, the system model is built in PSCAD/EMTDC for comparative analysis, the results show that the proposed control strategy can effectively improve the ability of LCC-HVDC to resist continuous commutation failure.