A discussion on IGBT short-circuit behavior and fault protection schemes

IGBTs are available with short-circuit withstand times approaching those of bipolar transistors. These IGBTs can therefore be protected by the same relatively slow-acting circuitry. The more efficient IGBTs, however, have lower short-circuit withstand times. While protection of these types of IGBTs is not difficult, it does require a reassessment of the traditional protection methods used for bipolar transistors. An in-depth discussion on the behavior of IGBTs under different short-circuit conditions is carried out and the effects of various parameters on permissible short-circuit time are analyzed. The paper also rethinks the problem of providing short-circuit protection in relation to the special characteristics of the most efficient IGBTs. The pros and cons of some of the existing protection circuits are discussed and, based on the recommendations, a protection scheme is implemented to demonstrate that reliable short-circuit protection of these types of IGBTs can be achieved without difficulty in a PWM power convertor motor drive application