A Hybrid DPWM for Vienna Rectifiers Based on the Three-Level to Two-Level Conversion

In view of the large neutral-point (NP) voltage fluctuation and the high low-frequency harmonics in the input current of conventional discontinuous pulse width modulation (DPWM) for the Vienna rectifier, a hybrid DPWM (HDPWM) is proposed on the basis of three-level to two-level conversion. The proposed HDPWM combines the modulation degree of freedom, namely the vector synthesis direction and the equivalent zero vector distribution coefficient. Under the two-level modulation unit, the shift angles that satisfy the predefined NP balance requirement for HDPWM are accurately calculated. Compared with the continuous PWM and conventional DPWM, the proposed HDPWM could effectively suppress the zero-crossing distortion, reduce the NP fluctuation and the switching losses. Simulation and experiment results demonstrate that the proposed HDPWM could reduce the NP voltage fluctuation to 1/2 of the conventional DPWM with reduced input current low-frequency harmonics and no zero-crossing distortion.