Temperature Analysis of Parallel-Connected IGBTs under PWM Operating Conditions Using a Physics Model

This paper presents a physics-based IGBT model and a junction temperature analysis of parallel-connected IGBTs under PWM operating conditions using a physics-based IGBT model. The authors developed a physics-based IGBT model in which the excess carrier distribution within a drift region is represented using a one-dimentional ambipolar diffusion equation. The physics-based IGBT model makes it possible to predict losses and switching waveforms for converter applications. IGBTs are connected in parallel for medium- or large-capacity converters. In these applications, a transient current imbalance might occur owing to a difference in the wiring inductance or device characteristics between the IGBTs. An experiment shows that a difference in the wiring inductance between the two IGBTs causes a transient current imbalance, and the result is in excellent agreement with the result of a simulation using the physics-based IGBT model. The two parallel-connected IGBTs in this study correspond to a power module for 3.7kW motor drives, and the junction temperatures of both IGBTs are simulated by electro-thermal simulation under the following two conditions: a difference in the wiring inductance and a difference in the device characteristics. The temperature difference between the two IGBTs is approximately 4-7℃ under the applied conditions: a wiring inductance mismatch (20nH) and a threshold voltage mismatch (0.5V). The validity of the physics-based IGBT model is verified, and the model is found to be very useful when designing power converters.