A Calorimetric Loss Measurement for Switching Power Devices

This thesis introduces a new calorimetric measurement method for losses of switching power devices, allowing to avoid most disadvantages of traditional electrical and calorimetric methods. The electrical method (namely, DPT) is currently the de facto standard for this type of measurement, because of its ease of implementation and established usage. However, it requires very accurate timing to synchronize current and voltage measurements, in particular when dealing with fast-switching devices ─ such as WBG transistors ─ and when operating with minimal current-voltage overlap losses. In its simplest form, the calorimetric method takes a long time to reach a steady temperature of the devices, but it can be applied whatever the speed and type of the devices. Yet, only the case temperature can be measured, while reliably estimating the junction temperature ─ hence the on-state resistance and conduction losses ─ is not trivial. Refined calorimetric methods are presented in the literature, making use of the exponential rise of temperature to estimate the power loss, by having characterized the dynamic thermal model of the system. This way, the measurement is quicker and the temperature of the devices is limited to a narrower range. The novel calorimetric measurement method herein proposed is faster than the traditional one, operates at a constant case temperature, and accurately estimates the on-resistance of devices, to isolate switching losses from conduction ones. A measurement setup has been developed to be immune to switching noise and tested up to 500 V DC-link voltage and 53.3 A switched current in ZVS mode. Measurements were then compared with measurements of losses using a traditional calorimetric method.