Highly reliable DC voltage control strategy for modular multilevel converter based-UPFC

The DC bus voltage of the unified power flow controller (UPFC) is closely related to the active power balance between the series and the shunt sides. In this study, a highly reliable modular multilevel converter (MMC)-UPFC DC bus voltage control strategy is proposed to ensure the continuous and stable operation of the MMC-UPFC. The DC voltage coordinated control strategy of dual converters in the shunt side, which combines the constant DC voltage control, droop control and margin control, is based on the topology configuration of the main converter and the standby converter. The DC voltage coordinated control strategy is adopted for different control targets under conditions of small-range adjustment of active power flow, wide-range adjustment, and the shunt-side converter failure, to achieve reliable and stable operation of UPFC under different operating conditions. Finally, a simulation model was established under the MATLAB/Simulink environment to verify the feasibility of this control strategy.