Open-Circuit Fault Diagnosis and Tolerant Control of Matrix-Type Solid-State Transformer

The solid-state transformer (SST) is expected to play a critical role in modern power systems, serving as a key component for efficient and flexible energy transformation. The reliability of the SST is crucial. However, active switches are prone to failures, which can have severe consequences. For the matrix-type SST (MT-SST), the time-varying dc-link voltage poses challenges for accurate and rapid fault diagnosis. This article proposes a comprehensive fault diagnosis and fault-tolerant control method for the open-circuit (OC) fault of a single switch in MT-SST. By comparing the estimated and measured values of the resonant capacitor voltages, the algorithm identifies the OC fault. Additionally, a reduction in the duty cycle of specific switches is introduced to assist in fault localization through monitoring of voltage changes. However, this method can only identify the OC fault on one side of MT-SST when the direction of power flow remains constant. To ensure fault tolerance, the primary and secondary side full-bridge is reconfigured into a quasi-half-bridge structure. The developed methods have the advantages simplicity and reliability. Finally, a 1.5 kW prototype is built, and the validity and feasibility of the proposed methods are verified.