Diagnosis strategies and reconfiguration of a 5-level double-boost PFC with fault-tolerant capability

A new 5-level PFC topology with fault-diagnosis and fault-tolerant capability is proposed and compared to known structures. It is derived from a 3-level non differential double-boost PFC including 2-stacked fly-cap cells. The series-connection of the two low-voltage switching-cells is decoupled by a single flying capacitor that provides a failed-safe tolerant capability increasing the availability of converter. Two fault-diagnosis strategies are presented. The first one directly monitors the voltages across the flying capacitors to detect and to localize the faulty switch by means of two sensors. The second one is based on a harmonic detection (magnitude and phase-shift) at the switching frequency through only one voltage sensor at the input of the PFC. All these strategies are analyzed and simulated with the efficient PD-PWM technique that exhibits a lower THD of the leg-leg input voltage for three-phase application. The design and the most important features are highlighted thanks to a digital control frame and a single-phase mock-up rated to AC115V - DC400V - 4kW - 2 × 31kHz.