Control Strategy for Three-Phase Bridgeless Rectifier Under Unbalanced Grid Conditions

Owing to the unidirectional conduction characteristics of the diodes, the traditional control strategy which is suitable for three-phase star-connected bidirectional PWM rectifier under unbalanced power grid conditions is not entirely applicable to three-phase star-connected bridgeless rectifier(TBR). For such scenario, this paper presents a hierarchical control strategy for the TBR topology under unbalanced power grid conditions, with the emphasis on discussion for suppressing negative-sequence currents and eliminating three-phase input current zero-crossing distortions. In the proposed algorithm, a new modulation control strategy is adopted to mitigate three-phase input current zero-crossing distortions. Moreover, the proposed modulation control strategy is applicable to all other three-phase three wire unidirectional rectifiers under unbalanced power grid conditions. Furtherly, the mathematical deduction is also conducted to demonstrate the validity and feasibility of the hierarchical control strategy for TBR topology. Meantime, the completed simulation results verify the stable operation of the TBR under unbalanced power grid conditions.