Sinusoidal Modulation Compensation Strategy of Hybrid DC Chopper Based on Half-bridge Submodules

Hybrid DC chopper is a key device for fault ride through of VSC-HVDC system connected with offshore wind power. In order to solve the problem that negative values appear in the sinusoidal modulation voltage of the chopper valve when the surplus power is large,which facilitates the half-bridge submodule no longer applicable, an AC-DC component compensation strategy of the sinusoidal modulation voltage is proposed. On the premise of ensuring the non-negativity of the modulation voltage, the lack of voltage reverse discharge process of the submodule capacitor is compensated by increasing the submodule capacitor’s external discharge power when the current of the chopper branch is reversed; in the meantime, by extending the maximum power consumption time of the chopper resistor in unit cycle, the chopper resistor’s average power can still be equivalent to the system’s surplus power when its peak power is limited. The simulation verification was carried out based on a surplus power simulation system and a VSC-HVDC system connected with offshore wind power. Results show that the AC-DC component compensation strategy of the sinusoidal modulation voltage can enable the half-bridge-submodules-based hybrid DC chopper to achieve power balance control under a full series of surplus power conditions and ensure the smooth ride-through of the VSC-HVDC system under AC faults at the receiving end. © 2023 Science Press. All rights reserved.