There will be industrial frequency,low frequency and DC frequency in the future power grid;however,tradi-tional converter only realize the energy exchange between AC-AC and AC-DC.In this paper,a new multi-frequency triple-port modular multilevel converter(MFTP-MMC)topology is proposed.The MFTP-MMC topology has simple and symmetrical structure,can directly realize power conversion and frequency control among industrial frequency grid,low frequency grid and DC grid,has no reactive power constraint problem,can output twice the DC voltage,and has the func-tion of DC fault self-blocking.The dynamic mathematical model in dq coordinates is established for MFTP-MMC,and the decoupling of two AC frequency components with DC component of the system is realized.On this basis,the corre-sponding control strategies are proposed,including inner loop current control,circulating current control,submodule voltage balancing control,and outer loop power control.The strategies have clear physical meaning and good control performance.Furthermore,the optimization method of reactive power distribution method between main arm and assis-tant arm is given.According to the topology,the blocking strategy in case of DC-side fault and the soft start strategy are proposed.The validity of MFTP-MMC topology,mathematical model and its control strategies proposed in this paper have been verified on MATLAB/Simulink platform.
关键词
多频率三端口换流器/柔性低频输电系统/直流故障阻断/数学模型/控制策略/桥臂无功分配
Key words
multi-frequency triple-port converter/flexible low frequency transmission system/DC fault blocking/mathematical model/control strategy/arm reactive power distribution
维普
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