Current zero-crossing distortion suppression in the Vienna rectifier using a direct power control strategy

The Vienna rectifier is widely used in three-phase power conversion systems owing to its advantages such as high efficiency and low harmonic distortion. However, its inherent topology limits its operation exclusively to conditions in which the grid voltage and current remain in phase. When a phase difference exists between the voltage and current, notable distortions arise in the AC current, particularly around the zero-crossing points, which severely affects the power quality and system stability. Such distortion increases total harmonic distortion, introduces electromagnetic interference, and reduces rectifier reliability. Therefore, analyzing the mechanism underlying zero-crossing distortion and developing an effective suppression strategy are essential for improving the performance of Vienna rectifiers in practical applications.

To address the zero-crossing distortion problem in the Vienna rectifier, this study proposes an improved direct power control (DPC) strategy integrated with dual second-order generalized integrators (DSOGIs) for frequency and phase synchronization. The mathematical model of the Vienna rectifier in the αβ coordinate system and the conventional DPC strategy in the same coordinate system are analyzed. The cause of current zero-crossing distortion is examined from a vector perspective, revealing that the distortion primarily arises from the phase mismatch between the grid voltage and the input current during switching transitions. Specifically, the three-level topological structure of the Vienna rectifier imposes inherent constraints on current commutation, aggravating phase asynchrony as the current approaches zero and resulting in irreversible current clamping and waveform distortion. Based on this analysis, a DSOGI-based frequency-locked loop is introduced to accurately track the grid frequency and a DSOGI-based phase-locked loop (PLL) is employed to lock the current phase. The phase adjustment is implemented through the real-time modification of the reference voltage vector in the DPC strategy, in which the phase information obtained from the DSOGI-PLL dynamically corrects the reference voltage angle, ensuring that the input current follows the grid voltage phase with high fidelity. By adjusting the phase relationship between the output voltage and current, the proposed method maintains in-phase operation, thereby reducing the distortion region around the current zero-crossing points. Voltage and current vector diagrams of the Vienna rectifier before and after the improvement are presented, along with the control block diagram of the current zero-crossing distortion suppression strategy for the DPC of the Vienna rectifier.

The proposed DPC-based zero-crossing distortion suppression strategy is validated through detailed simulation studies. The results demonstrate that the method markedly reduces current distortion near the zero-crossing points. The output current quality is considerably enhanced, with a reduction in harmonic components and a more sinusoidal current waveform.

The simulation results verify the effectiveness and robustness of the proposed method, demonstrating its potential for enhancing the performance of Vienna rectifiers in practical power conversion systems. This strategy provides a feasible solution for suppressing zero-crossing distortion while preserving the advantages of traditional DPC, offering valuable insights for further research and application in high-performance rectifier designs.