Fault-tolerant Operation Technology for Three-level Cell Power Electronic Transformer

The power electronic transformer (PET) based on the three-level cell has the advantages of few power modules and high power density, which has broad application prospects in the scenarios of uninterruptible power supplies in data centers, railway power distribution systems and super-charging stations. However, there are many switching devices in PET, and the fault module removal action triggered by the device fault will lead to the loss of system capacity, which can easily lead to system instability, fault expansion and other problems. To address this problem, this paper proposes a fault-tolerant operation technology based on cooperation among fault modules, fault phase and non-fault phase. First, the common fault results of three-level cell H-bridge with different fault types are analyzed by using the switch combination enumeration method, and fault module reconfiguration and fault-tolerant operation are realized based on partial device bypass. Secondly, the in-phase coordinated control strategy is proposed to realize the capacitor voltage stability and equalization of the fault module, and the line voltage balance is achieved through the inter-phase coordinated control, which ensures the normal operation of the circuit. Finally, specific fault-tolerant control methods are proposed for different fault results and the effectiveness of the proposed fault-tolerant methods is verified by simulation. The simulation results prove that the PET can operate stably with fault-tolerant control. © 2023 Automation of Electric Power Systems Press. All rights reserved.