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In this paper, a hybrid control scheme for three-phase Y-connected multilevel bridgeless rectifier (TMBR) under unbalanced input voltages is presented, based on the mathematical model of the TMBR topology, with the emphasis on the discussion for power fluctuation suppression, dc-link capacitor voltages balancing and input current zero-crossing distortion elimination. With the hybrid control scheme, the power fluctuation can be suppressed and three-phase input currents can flow with a purely sinusoidal waveform, besides, three-phase dc-link capacitor voltages can be controlled to be equal to each other under unbalanced input voltages. Moreover, the proposed hybrid control scheme is applicable to all other threephase three wire multilevel unidirectional rectifiers under unbalanced input voltages. The validity of the proposed control scheme is demonstrated by the mathematical deduction. The simulations and experimental results verify that, with the proposed control scheme, TMBR can stably operate not only under balanced input voltages but also under unbalanced input voltages. INDEX TERMS Three-phase multilevel bridgeless rectifier, hybrid control scheme, unbalanced input voltages.

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In order to improve the power quality, many researchers in the worldwide are committed to investigating the feasibility of integrating reactive power compensation (RPC) and harmonic current compensation (HCC) functionalities for unidirectional rectifier, while the capability of RPC for unidirectional rectifier is very limited. Hence, with the aim of enlarging the capability of RPC for unidirectional rectifier, this article introduces a versatile control strategy for three-phase star-connected unidirectional rectifier. The operating principle and the reasons that limit the capability of RPC for unidirectional rectifier are analysed in detail. On this basis, a novel criterion for judging input current distortion zone is proposed. Furthermore, the additional focus of this article is to quantify the constraint relationship between the degree of input current distortion compensation and input power factor regulating range. Simulations and experimental results are conducted to verify the feasibility and effectiveness of the proposed control strategy, as well as the correctness of the theoretical analysis on the proposed constraints of the input power factor regulation.