A DC Offset Reduction of Neutral Point Voltage Strategy Based on Vector Phase Angle Difference Optimization for Vienna Rectifier With Bipolar DC Bus

When Vienna rectifier operates at light load conditions, small load power difference of bipolar dc bus leads to dc offset of neutral point (NP) voltage due to the limitation of dc-link power, increasing the voltage stress on switching devices. To solve this problem, a dc offset reduction of NP voltage strategy based on the vector phase angle difference (VPAD) optimization is proposed. By analyzing the relationship between the magnitude of zero-sequence component and the duty cycles of voltage vectors, the maximum power difference of the conventional strategy is obtained. The proposed strategy illustrates that VPAD can adjust the NP current based on the contour of the NP current, and the maximum VPAD is limited to satisfy the reference voltage and input current have the same sign. To increase the NP current, the VPAD is optimized by introducing the fluctuating reactive current, and the active current disturbance is injected to regulate the change rate of NP current. Therefore, the proposed strategy can significantly reduce the dc offset of NP voltage under light load conditions at the cost of the input current harmonics and the dc-link voltage fluctuation. Finally, the effectiveness of the proposed strategy is verified on a Vienna rectifier platform.