Dissertation submitted: April 6th 2016 PhD supervisor: Prof. Stig Munk-Nielsen Aalborg University, Denmark PhD
committee: Professor Josep Guerrero (chairman) Aalborg University Dr. Gernot J. Riedel ABB Cooperate Research Professor Philip Andrew Mawby University of Warwick PhD Series: Faculty of Engineering and Science, Aalborg University
Power semiconductor switches are critical components in power electronic converters and operate in thermally stressful environments. The junction temperature of a power semiconductor directly influences its power loss and is intrinsically linked to numerous failure mechanisms. Knowledge of this temperature is therefore important for optimal operation and for reliability reasons. If the junction temperature is known during the operation of a converter, real-time condition monitoring and active thermal control systems could be developed to improve system reliability. Performing direct measurements of junction temperature is difficult since the power semiconductor is generally encapsulated inside an array of packaging materials. Alternatively, the electrical behaviour of a semiconductor largely depends on temperature. If this relationship is known, the electrical parameters of the device can be monitored and used to estimate the junction temperature. These are known as Temperature Sensitive Electrical Parameters (TSEPs) and are one way to carry out non-invasive, real-time junction temperature measurements on fully packaged devices. Nevertheless, successful implementation of these techniques during the normal operation of a power semiconductor is thus far limited. Often holding back their use is the need to compensate for inherent fluctuations caused by a constantly changing electrical environment (or alternatively requiring interruption to normal operation to force fixed electrical conditions), and significant uncertainty over accuracy. As a result, this PhD aims to develop new methods, or improvements to existing methods, for junction temperature measurement via TSEPs during the operation of power semiconductor switches. In Chapter 1, the state-of-the-art in the topic of junction temperature measurement is introduced. A literature review of TSEPs investigated for use in operating power semiconductor switches is then provided. From this, several implementation issues are identified and used to formulate technical objectives for the PhD thesis. Chapter 2 introduces the first original contribution of the thesis. Two TSEP-based methods for junction temperature measurement, unpublished in scientific literature before the commencement of the PhD, are presented. The measurement principles are explained, and experimental validation is provided on Insulated-Gate-Bipolar-Transistors (IGBTs). The foremost advantages in the presented TSEPs are that they are measured without interruption to normal IGBT operation, and do not require compensation for varying load current conditions. The primary method presented is referred to as the Peak Gate Current (IGPeak) method, which is selected for further examination in Chapter 3. In Chapter 3, the second scientific contribution of the thesis is provided. Here, the accuracy of the IGPeak method on IGBTs is extensively examined using direct measurements of junction temperature from an Infra-Red camera. The validation is performed on IGBT dies with differing geometry, as well as IGBTs in both healthy and degraded conditions. Finally, IGBTs in a paralleled configuration are investigated. These results in terms of accuracy are compared with a traditional TSEP method commonly found in prior art.