新型多频率三端口模块化多电平换流器拓扑及其控制策略

There will be industrial frequency, low frequency and DC frequency in the future power grid; however, traditional 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 function 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 corresponding 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 assistant 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.