On the issues of fluctuation in the neutral-point and harmonic pollution caused by unbalanced input voltage, this paper adopts three-phase four-wire VIENNA rectifier based on one cycle control and analyzes its working principle deeply. Input current characteristic which is controlled by traditional single-edge modulation is discussed. The relation among harmonics in the input current, switch frequency and input inductor is revealed. Based on the analyses, this paper proposes a bi-edge modulation with triangular-wave as carrier. The inductance current could be modulated both at leading-edge and trailing-edge. Consequently, the low-frequency odd harmonics of inductance current is reduced, and the quality of the input current is improved. The validity of the theoretical analysis and feasibility of the advanced one cycle control strategy are verified by simulation results.