Novel DPWM Method with Suppression of the Voltage Unbalance in the Neutral-Point for Vienna Rectifier

This paper proposes discontinuous Pulse-Width Modulation (DPWM) method for Vienna rectifier with mitigation of the voltage unbalance in the neutral-point. Vienna rectifier is greatly stable and well-established topology for high power transmission system. However, since Vienna rectifier has the circuit structure that each phase leg and mid-point of dc-link capacitor are connected, DC and AC voltage unbalance can occur at the neutral-point. In the proposed method, fluctuation of the neutral-point voltage is analyzed based on space-vector diagram. Based on the analysis, one of the three-phase reference voltages is selected as clamped phase for suppressing the AC voltage unbalance. Furthermore, DC unbalance can be suppressed by applying the modulation method which considers the difference between dc-link top voltage and bottom voltage. In addition, mathematical prediction of the neutral-point voltage fluctuation is presented for applicating the proposed method regardless of the accuracy of the dc-link voltage sensor. The performance and validity of the proposed method is verified by simulations.