Accuracy Study of Calorimetric Switching Loss Energy Measurements for Wide Bandgap Power Transistors

Abstract

Despite soft-switching topologies and modern wide bandgap power semiconductors, switching loss energy is still significant in power electronic application but too small for characterization with electrical measurements. In contrast calorimetric measurements of the soft-switching energy of a commutation cell have been successfully demonstrated for different power classes and semiconductor technologies. In particular, the transient calorimetric measurement method calibrated by thermal impedance (Z<inf>th</inf>-calibrated) promises an extremely fast and non-invasive loss characterization in a wide power range without modification of the half-bridge. This enables automated determination of the switching behavior and losses over the entire operating point range of different switching voltages and switching currents in a reasonable time frame compared to other thermal measurement methods. Furthermore, it promises to greatly reduce the requirements on the measurement setup in terms of thermal insulation and the integration of temperature sensors.Purpose of this work is to investigate the accuracy of Z<inf>th</inf>-calibrated calorimetric measurements and to estimate the influence of measurement duration, temperature sensing and thermal insulation, which so far prevent simple application-oriented characterization. Therefore, a gallium nitride (GaN) high-electronmobility transistor (HEMT) half-bridge is used to derive the loss measurement accuracy of different temperature sensors and the modeling of junction temperature dependend on resistance by comparing it to conduction losses that are electrically easy to determine. In addition, the worst-case accuracy of the switching energy calculation based on multiple power dissipation measurements with different switching frequencies is presented.