A semi-empirical closed-form healthy-state baseline model for online junction temperature monitoring of high-power IGBTs across a wide current operating range

IGBTs are core devices in high-power electronic equipment, and online monitoring of their junction temperature is of great significance for ensuring safe device operation and condition assessment. Junction-temperature monitoring based on static current–voltage characteristics measured at different temperatures is one of the key technical approaches. Existing data-based or polynomial-fitting models for describing IGBT current–voltage characteristics rely heavily on experimental data and exhibit limited applicability or insufficient accuracy over a wide current operating range. Moreover, a unified closed-form healthy-state baseline model capable of characterizing device behavior under multiple operating conditions is still lacking. Based on the fundamental semiconductor physics of IGBTs, this paper proposes a three-dimensional semi-empirical closed-form healthy-state baseline model that correlates the on-state voltage drop, collector–emitter current, and junction temperature, and validates the proposed model experimentally using three different IGBTs. The results show that the proposed three-dimensional mapping model can characterize the on-state current–voltage characteristics under different operating conditions using a unified set of characteristic parameters. Good predictive capability is achieved over a temperature range of 25–105 °C, a current range extending to approximately 4.5 times the rated current, and a gate-drive voltage range of 15–24 V. The maximum absolute junction-temperature estimation errors at gate-drive voltages of 15, 20, and 24 V are 1.50, 2.91, and 1.05 °C, respectively. While maintaining applicability over a wide current operating range, the proposed model reduces its dependence on experimental data and demonstrates good practical applicability, providing an effective healthy-state baseline for subsequent aging-condition assessment of IGBTs.