Hybrid Modulation Strategy to Avoid Zero Crossing Distortion in the Vienna Rectifier

The three level Vienna rectifier has an inherent problem of current distortion at zero crossings. This can be mitigated by injecting a particular zero sequence so that the reference voltage is clamped to the neutral when the converter reference voltage and current have different signs. However, the converter is at risk of entering into overmodulation while operating at higher modulation indices. In this paper, a hybrid modulation strategy is introduced where a calculated minimal amount of reactive current depending on operating conditions is injected along with the zero sequence, to avoid overmodulation. The reduction in reactive current compared to state-of-the-art solution is significant. With the proposed method, the Vienna rectifier can operate in a wide range of power factors without compromising the quality of the source currents.