Research on midpoint potential balance of three-phase three-level VIENNA rectifier

The problem of unbalanced voltage at the midpoint of the three-phase three-level VIENNA rectifier leads to the unbalanced voltage stress of the two voltage equalizers and the main switching device, resulting in the distortion of the zero-crossing current, which reduces the overall performance of the system. To solve this problem, this paper proposes a novel hybrid medium vector (MMV) space vector modulation strategy, which achieves high algorithm flexibility, low switching loss and low computational burden while ensuring the neutral point voltage (NPV) balance of the full range modulation index and power factor. The proposed strategy introduces six additional virtual MVVs at the positions of the six actual MVVs, which allows the spatial vector distribution to be maintained without modifying the synthesis of the reference voltage vector. A simple verdict scheme is provided to determine whether a virtual MVV or an actual MVV should be used, greatly reducing switching losses while ensuring a always balanced NPV.