Evaluate I2t Capability of SiC MOSFETs in Solid State Circuit Breaker Applications

Solid State Circuit Breakers (SSCBs) protect equipment in power systems during short circuit and overload. Evaluating the i²t capability of devices can be critical to the overload protection design of the SSCB. Previous methods used the junction-to-case dynamic thermal impedance to estimate the i²t capability. However, the overall dynamic thermal impedance can be influenced by the thermal management. In this paper, we investigated the influence of the heatsink on the dynamic thermal performance of the power switch. More importantly, we presented an experimental method to characterize the i²t capability of devices under the worst operating condition for the SSCB. The on-resistance of the switch is measured to predict the junction temperature with an improved voltage sensing circuit. Then, by applying over-current pulses with various current levels and pulse lengths, the relationship between the i²t value of over-current pulses and the junction temperature rise of the device can be investigated. The presented method has been verified to characterize the i²t capability of a SiC power module.