Voltage and Power Balance Control Strategy for Power Electronic Transformer under Dual Active Bridge Open-Circuit Fault

A DC-link voltage and power balance control method is proposed in this article to ensure the balance and stability of both voltage and power in a three-phase cascaded H-bridge Power Electronic Transformer (PET) under an open-circuit fault (OCF). To address the inter-phase voltage equalization, a control strategy based on negative sequence current compensation is implemented, effectively achieving the balance of inter-phase voltages. For the issue of inter-bridge voltage imbalance, a modulation strategy combining rank and select algorithm is employed. With the proposed approach, the voltages across the inter-bridge and inter-phase of PET are maintained at their required value. Additionally, the active power transferred to each phase can be balanced with the proposed power balance control method, even in the case of Dual Active Bridge (DAB) failure. Finally, simulation and experimental results under open-circuit faults in the DAB are presented to prove the effectiveness of the proposed control strategies.