Electro-thermal Modeling of Modern Power Devices for Studying Abnormal Operating Conditions

In modern power electronic systems, there are increasing demands to improve the whole system endurance and safety level while reducing manufacturing and maintenance costs. Insulated Gate Bipolar Transistor (IGBT) power modules are the most widely used as well as most critical power devices in industrial power electronic systems in the range above 10 kW. The failure of IGBTs can be generally classified as catastrophic failures and wear out failures. A wear out failure is mainly induced by accumulated degradation with time, while a catastrophic failure is triggered by a single-event abnormal condition, for example overvoltage, overcurrent, overheating, and cosmic rays. The degradation and wear out failure of IGBTs can be monitored by Prognostics and Health Management methods; however, it is more difficult to predict the catastrophic failure, for instance the short circuit conditions. The objective of this project has been to model and predict the electro-thermal behavior of IGBT power modules under abnormal conditions, especially short circuits.

A thorough investigation on catastrophic failure modes and mechanisms of modern power semiconductor devices, including IGBTs and power diodes, has been given in Chapter 2. The failure mechanisms investigation suggests that the abnormal junction temperature or hot spots normally happen with the occurrence of failure. Practical challenges of predicting junction temperature during short circuit operations are also identified: a) electro-thermal interacting effects become significant in high current and high temperature variation conditions; b) uneven current distribution and thermal loading inside the IGBT chip as well as among the different chips in an IGBT module during high dynamics of short-circuit; c) there is still a lack of methods to measure the IGBT junction temperature precisely in a time duration of several or tens of µs in order to protect the devices.

According to the aforementioned investigations, a PSpice-Icepak co-simulation method is proposed to be used for studies in this thesis, which is introduced and discussed in Chapter 3. It combines a physics-based, device-level, distributed PSpice model with a thermal Finite-Element Method (FEM) simulation, gaining the possibility to take into account the electro-thermal interacting effects and uneven electro-thermal stresses among the chips. Case studies on the new and degraded modules, as well as geometrical parameters variations, further prove the effectiveness of the proposed approach in Chapter 4. Then, a 1.1 kV/ 6 kA non-destructive testing facility is built up at Center of Reliable Power Electronics (CORPE), Aalborg University, to experimentally verify the simulated results of IGBT power modules as described in Chapter 5, as well as to study the wide-band-gap devices short circuit behavior in the future.

It is found that modern power device catastrophic failure is the shortfall of the reliability, and the behavior is difficult to be predicted. The proposed PSpice-Icepak electro-thermal co-simulation method shows the capability of predicting IGBT power modules electrical and thermal stresses during short circuits, which can be used for further optimizing module’s performance.