Startup Strategy Based on Coordinated Energy Balance Method of Series-Connected Hybrid Diode Rectifier for Integrating Offshore Wind Farm

The series-connected hybrid diode rectifier (SCH-DR) based high voltage direct current transmission system (HVdc) for integrating offshore wind farm (OWF) confronts challenges in startup, which comprises of a largecapacity DR and a small-capacity auxiliary modular multilevel converter (A-MMC) in series-connection. To achieve DR’s inputting onto OWF’s grid in zero dc current while maintaining energy balance of offshore system, this study proposes a startup strategy based on coordinated energy balance method. Based on this method, OWF needs to generate certain active power to meet consumption of offshore necessary auxiliary devices. To dissipate the surplus power, the proposed method parallels an energy-consuming resistor on AMMC’s dc side. Hence, through its adjustable dc voltage capability, A-MMC can actively and smoothly regulate the dissipated power, thus realizing the coordinated energy balance. The proposed startup strategy exhibits feasibility and engineering practicality, without much escalating investment cost or space requirements. The effectiveness of the proposed startup strategy is verified in MATLAB/Simulink using a scenario of a 2000 MW/±500 kV SCH-DR-HVdc system.