Study on start-up control strategies for HVDC-Flexible system based on MMC

Pre-charging dynamic process and mathematical model of MMC are analyzed in this paper. The procedure is divided into uncontrollable and controllable stage. To restrain pulse current and stack its adverse impact, the minimum current-limiting resistor is proposed. End point setting of voltage is lower than its theoretical value, which averts rising voltage from the tardy course during late uncontrollable stage. Current control, voltage control and sub-module (SM) balance control in controllable stage are presented based on carrier phase shifted modulation (CPSM), in order to achieve reliable and efficient pre-charging. Seen from the comparisons of simulation results of five-level models built in Matlab/Simulink respectively by formal control and novel control, the start-up method mentioned above possesses excellent rapidity and stability.