Hybrid Modulation Strategy for the Vienna Rectifier

The Vienna rectifier can produce three voltage levels, however only the neutral point is fully controllable using the bidirectional switches. The positive and negative voltage levels are decided by the current direction. As a result, the input current becomes distorted when the input current and the reference voltage have opposite signs. This can be mitigated by injecting a particular zero sequence so that the reference voltage is clamped to the neutral point during the above period. However, the converter is at risk of entering into overmodulation while operating with high modulation indices. In this paper, a hybrid modulation strategy is introduced where a calculated minimal amount of reactive current depending on the operating conditions is injected, along with the above zero sequence, to avoid overmodulation. The reduction of reactive current required compared to the state-of-the-art solutions is up to 100% in certain operating conditions. With the proposed method, the Vienna rectifier can operate in a wide range of power factors without compromising the quality of the source currents. The concept is verified by both simulation and in a 1kW Vienna rectifier experimental setup.