Omskifterindretning-fejldetektionssystem og fremgangsmåde til flerniveauomformere

A multilevel converter includes a plurality of phase legs (40) each having at least two inner switching devices (44, 46), at least two outer switching devices (42, 48), at least two clamping diodes (50, 52), a split DC link (53) and a switching device failure detection circuit (70). The switching device failure detection circuit includes a logic module (72, 74, 76, 78) for each of the switching devices, a voltage calculation module (80) and a failure detection algorithm (82). The logic module generates a blocking state logic signal (Vc1, Vc2, Vc3, Vc4) by comparing a switching device voltage (Vsw1, Vsw2, Vsw3, Vsw4) and a threshold reference voltage (Vth) and the voltage calculation module determines an expected voltage blocking state (Vs1, Vs2, Vs3, Vs4) for each of the switching devices based on the gate drive signals (G1, G2, G3, G4) of the switching devices and an output current direction (Io). The failure detection algorithm detects a failure condition in any of the switching devices based on the blocking state logic signals and the expected voltage blocking states of the switching devices.