A Short-Time Transition and Cost Saving Redundancy Scheme for Medium-Voltage Three-Phase Cascaded H-Bridge Electronic Power Transformer

Reliability is one of the major concerns when the electronic power transformer (EPT) is employed in the field, and redundancy is a common approach to improve the reliability. For hot and cold redundancy schemes, the redundancy performance will be degraded due to the small number of power modules (PMs) when the EPT is employed in the medium-voltage power grid. For the three-phase EPT, at least three redundant PMs are needed (one redundant PM per phase), which leads to a high redundancy cost. In this paper, a novel redundancy scheme is proposed. The proposed scheme can accomplish the faulty PM replacement process within tens of microseconds with nearly no transition. And only one PM and a set of switches are needed for the three-phase redundancy, which can effectively save the redundancy cost. The proposed scheme is analyzed and supported by simulations and experimental results.