Detection and Identification of Power Device Failures Using Discrete Fourier Transform for Fault-Tolerant Operation of Flying Capacitor Multilevel Converters

For a flying capacitor multilevel converter (FCMC), prompt detection of power switch failures is crucial for fault-tolerant operation. This article presents a new technology for identifying and locating faulty cells in FCMC. Mathematical derivation points out that different fault types and locations will present different high-frequency harmonics. The new technology extracts high-frequency harmonics in the switch node voltage and looks up a preestablished table to identify the fault type and location. The discrete Fourier transform (DFT) can be easily performed to analyze the harmonic using the built-in IP core in field-programmable gate array (FPGA). For an FCMC with any number of levels, the new approach requires only one voltage sensor and can accurately locate the faulty cell after one carrier cycle when the fault occurs. Both simulation and experimental results validate the proposed concept on a five-level 100-kHz GaN FET-based FCMC prototype. Furthermore, we have experimentally demonstrated the fault-tolerant operation of the FCMC after a switch short and open fault is detected and identified by the new technique.