Multi-Mode Fault-Tolerant Operation Strategy of Semi-Dual Active Bridge Converter Considering Open-Circuit Fault of the Secondary Side Switch

Semi-dual active bridge (S-DAB) converter is widely applied for scenarios requiring unidirectional power flow, such as electric vehicle charging and PV generation. Considering that the secondary side switch open-circuit fault of the S-DAB converter may threaten the normal operation of the system, the S-DAB converter should be able to maintain uninterrupted operation after a fault. This paper presents a fault diagnosis and fault-tolerant method for the S-DAB converter under open-circuit fault. When an open-circuit fault occurs in the secondary side switch of the S-DAB converter, the current flow path is changed, leading to an abnormal state of the circuit, including a DC bias generated by the transformer current and a significant change in the periodic average of the AC voltage on the secondary side bridge at the moment of an open-circuit fault. Therefore, a fault diagnosis system based on voltage measurement is designed. The proposed strategy requires only one additional voltage sensor to identify the location of the fault switch, improving the reliability of the S-DAB converter at a low cost. According to the previous analysis, the circuit topology is no longer symmetrical when an open-circuit fault occurs in the secondary side switch of the S-DAB converter, causing DC bias of leakage current. To eliminate DC bias, a fault-tolerant single active bridge (SAB) operation method is proposed. Specifically, after an open-circuit fault occurs in any switch on the secondary side of the S-DAB converter, the driving signal of the other switch is blocked. As a result, the secondary bridge is transformed into a diode bridge, forming a symmetrical circuit structure. Based on the proposed fault-tolerant SAB mode, the DC component of the leakage current caused by the fault switch can be eliminated. The potential damage caused by excessive current can be avoided, effectively ensuring the safe operation of the switch, capacitor, and inductor components of the circuit. Furthermore, the S-DAB converter still has a specific power transfer capability after the fault-tolerant operation. An experimental prototype is built. The normal operation, open-circuit fault operation, and fault-tolerant operation of the S-DAB converter are experimentally verified. According to the experimental results, the proposed fault diagnosis strategy and fault-tolerant method can accurately locate and remove open-circuit faults within four cycles and promote the reliability tolerance of the S-DAB converter. © 2024 China Machine Press. All rights reserved.