Imbalance Mechanism of Capacitor Voltage and Control Strategy for Hybrid Modular Multilevel Converter with Negative Output

2019 4th Asia Conference on Power and Electrical Engineering

能源学;电工学

Gao, L.^1 ; Ning, L.H.^1 ; Yin, Y.J.^1 ; Wu, D.^1 ; Liu, N.M.^1 ; Teng, H.D.^1

Smart Power Grid Shanxi Key Laboratory, Xi'An Jiaotong University, Xi'an

710049, China^1

关键词: Capacitor voltage balance;    DC transmission systems;    Discharging characteristics;    Modular multilevel converters;    Operating condition;    Optimal control strategy;    PSCAD/EMTDC simulations;    Short-circuit fault;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/486/1/012003/pdf
DOI  :  10.1088/1757-899X/486/1/012003

来源: IOP

【 摘 要 】

In a flexible DC transmission system with a large-capacity overhead line, a hybrid modular multilevel converter (MMC) consisting of the half bridge submodule (HBSM) and the full bridge submodule(FBSM) has become a research hotspot due to its self-cleaning capability of DC short-circuit fault. Under the operating conditions of reducing the DC voltage, due to the different charging and discharging characteristics of the half bridge submodule and the full bridge submodule, a capacitor voltage imbalance may occur between the two submodules. This paper first studies the number configuration of half-bridge submodules and full-bridge sub-modules in modular multilevel converters. Then, the capacitor voltage imbalance mechanism of the hybrid MMC sub-module is analyzed in detail, and the optimal control strategy of the capacitor voltage balance is derived according to the configuration requirements of the two sub-modules. Finally, a hybrid MMC-based flexible DC transmission system is established in the PSCAD/EMTDC simulation environment, low DC voltage operation of the system are simulated to verify the correctness and effectiveness of the control strategy.