Over-current Protection for Series-connected IGBTs based on Desaturation Detection

One major challenge regarding series-connected IGBTs is the protection against over-current faults, besides voltage balancing among the devices. In this paper, an over-current protection method based on desaturation detection is proposed for series-connected IGBTs which are controlled by a digital signal processor (DSP) to realize voltage sharing. A hardware test platform was built, which is capable of generating current spikes of various magnitudes and durations. Different aspects of system behavior under fault are characterized to provide design guidance to ensure safety. Finally, experimental results show that the proposed series IGBT control can achieve voltage balance without slowing down the switching transients. Additionally, the desaturation circuit can detect an over-current in less than 1 µs. Furthermore, with the proposed protection method, the fault can be fully cleared depending solely on voltage balancing circuits, while maintaining voltage balance during the entire process.