The aim of this paper is to explain the intrinsic fail-safe capability of a high-voltage
IGBT inverter source. The inverter is an imbricated cells structure which provides redundancy.
The major failures can be either a wrong gate voltage (malfunctioning of the driver board,
auxiliary power supply failure, dv/dt disturbance) or an intrinsic IGBT failure (over-voltage/avalanche stress, temperature overshoot). The IGBT failures are studied and show that no
opening of the bondings can appear and consequently no risk of explosion. Owing to the
imbricated cells structure, an IGBT failure can be withstand a few switching periods, with
nevertheless non-optimized output waveforms. The design and the lab-test of a sensor able to
perform monitoring and failure diagnosis are also presented. This real-time diagnosis allows
either a safety stop or a remedial control strategy based on the reconfiguration of the control
signals. The real-time reconfiguration allows to decrease internal stresses and to optimize the
shape of the output voltage. In this case, a fail-safe operating may be gained for high power
applications.