Shahjalal, Mohammad (2018) Electric-thermal modelling of power electronics components. PhD thesis, University of Greenwich.

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Abstract

Electro-thermal modelling of power electronics system is considered to be one of the most important design techniques for the development of compact and high-power density power electronics systems for the future. For handling inevitable heat generation due to non-ideal nature of components both active and passive, electro-thermal modelling should be seriously emphasized in earlier design stages to prevent premature failure of the components and to avoid over-design or under-design issues so that all the components can operate within permissible thermal limits. Earlier consideration of electro-thermal issues in achieving high power dense and compact power electronics system design will ensure the reliability of the component and help to optimise the design in terms of design constraints and performances such as the thermal limits, reliability, power density, weight and costs etc.

Traditional electro-thermal modelling methods model the power electronic components using the parameters based on steady state temperature and seldom take into account the thermal effect in power loss modelling of the component and thermal coupling between the components. However, these electric-thermal dependencies are important, particularly for applications where components stay proximity to each other in a converter and share the same substrate and cooling system. Integrated electro-thermal modelling is a method which combines the thermal model and temperature-dependent power loss model can be employed at the early design stage to predict the temperature.

The aim of this work is to develop an integrated electro-thermal framework and demonstrate its benefits in carrying out electro-thermal analysis of power dense power electronics systems where component interactions must be taken into account.

The integrated electro-thermal analysis framework that has been developed in this work combines the Finite Element Analysis (FEA) method and circuit-based thermal network method. In this framework, the circuit simulator PLECS is used to predict the power losses in the components and the results are used in FEA thermal analyses to predict the transient thermal responses of power electronics systems. These results are then used to extract compact thermal model parameters using a curve fit approach. The resulting combined electro-thermal compact model is analysed using PLECS again to obtain temperature profile for various loading conditions.

By using the proposed modelling framework, the component thermal interaction has been studied for the three applications which include a boost converter, a three-phase voltage source inverter and an IPT based dual interleaved bidirectional boost converter. The variation of temperature due to thermal coupling has been found significant in all these applications. The result in the first application suggests that if thermal interactions are not taken into account, the estimated junction temperature would result in errors of 17% and 26.7% for IGBT & diode in the first application, i.e. the boost converter, respectively. For the second application, the predicted errors in the temperatures at the junction, at the solder, at the baseplate solder and at the baseplate in the IGBT would be 2.42°C, 2.59°C, 2.56°C and 2.63°C respectively, if the component interactions are not included in the analysis. Furthermore, it has been found that thermal grease layer has great impact on the temperature in power electronics components. If the thermal grease layer is not included in the simulation, temperatures would be underestimated by about 9.8°C, 12.16°C, 12.14°C and 11.8°C respectively at the junction, at the chip solder interface, at the baseplate solder and at the baseplate respectively. In the FET switch application, by taking into account component interaction, the junction temperature is increased by 6°C. It can be concluded that by taking into account the thermal coupling and by extracting RC parameters from FEA thermal analysis results, temperature can be predicted more accurately than using lumped parameter thermal network model alone.

The benefits of proposed electro-thermal model can be exploited by power electronics design engineers. It will help accurately predict temperature at the critical locations of the components under varying electric loading conditions and eliminate the errors in temperature prediction. It will significantly speed up the design process and help analyse real long mission profiles. The integrated framework will also help save time and cost in power electronics system design eliminating the need of test rig for temperature measurement and help to assess the electrical and thermal performance of the converter applications.

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Power electronics systems; electronics systems design; electro-thermal modelling; electro-thermal analysis; thermal network; mathematical modelling;
Subjects:	Q Science > QA Mathematics T Technology > TK Electrical engineering. Electronics Nuclear engineering
Faculty / School / Research Centre / Research Group:	Faculty of Engineering & Science > School of Computing & Mathematical Sciences (CMS) Faculty of Engineering & Science
Last Modified:	04 Mar 2022 13:06
URI:	http://gala.gre.ac.uk/id/eprint/23658

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