MMC-SST input-level control strategy considering power quality optimization

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    The surge of negative sequence component of current affects the waveform quality of grid side current and endangers the normal operation of the system when the three-phase voltage of solid state transformer (SST) in the distribution network is unbalanced and harmonic pollution occurs. In order to solve this problem,a new dual-sequence control strategy is proposed to effectively suppress the negative sequence component of current at the input level of SST. In this paper,the operation principle and input level mathematical model of modular multilevel converter-solid-state transformer (MMC-SST) are introduced firstly. The positive and negative sequence components of voltage and current signals at grid side are separated and extracted by improved second-order generalized integral-quadrature signal generator (SOGI-QSG). The mathematical model of proportional complex integral (PCI) controller is established by introducing orthogonal intermediate variables. A new dual-sequence control strategy based on PCI is proposed under the positive and negative sequence model in the two-phase static coordinate system (αβ coordinate system) to control the positive and negative sequence components of the current at grid side. Finally,the simulation system of MMC-SST is built in Matlab/Simulink. Compared with traditional proportional integral (PI) control and improved PI dual-sequence control,the results verify the feasibility and superiority of the proposed dual-sequence control strategy.

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  • Received:June 15,2022
  • Revised:September 22,2022
  • Adopted:March 07,2022
  • Online: November 24,2022
  • Published: November 28,2022