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The Control Strategy of the Multi-phase Permanent Magnet Synchronous Machine under the Unbalanced Grid

When an unbalanced fault occurs in the power grid, it is not only necessary to suppress the over-voltage and over-current generated at the converter side, prevent excessive voltage changes from damaging the core components of the wind turbine, but also to prevent the impact of large voltage drops on the system. It is necessary to make certain reactive power compensation for the power grid. When a multi-phase high-voltage grid-connected wind turbine with modular multi-level converter(MMC) experiences an unbalanced grid, it is necessary to consider the normal operation of wind turbine from the perspective of the generator system control strategy. Therefore, a grid-connected topology of multiphase permanent magnet synchronous generator(M-PMSG) based on MMC access is designed. For each link in the grid connected system, we have proposed corresponding control strategies. In structure, multiple capacitors of MMC can play a small role in energy storage, and energy consumption devices are added to reduce the energy transmitted on the converter. In the control strategy, the positive and negative sequence voltage oriented positive and negative sequence coordinate axis double current loop control strategy is adopted. And the variable k is introduced to flexibly control the setting of active and reactive currents, so as to achieve the effect of multi-level goal linkage control.