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Title: 3-D thermal modelling of power device packaging
Author: Swan, Ian R.
ISNI:       0000 0004 2705 0366
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2010
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Power converters enable e±cient conversion of electric power, thereby reducing power consumption and cost. The key enabling technologies inside power converters, typically used in hybrid electric vehicles, are the semiconductor devices. Device reliability is of high priority because they generate heat from the dissipation of electric power which can lead to failure if the device maximum junction temperature is exceeded. Furthermore, device temperatures can vary largely in switching applications, leading to thermal-mechanical fatigue failure. As electronic designers are pushed to deliver smaller and more powerful packages, they are finding thermal issues increasingly di±cult to solve. The primary goal of this thesis is to develop a fast and accurate thermal simulation design tool which is capable of simulating realistic power converter operation. Most commercial thermal simulators use finite-element software. Despite their perceived accuracy, they suffer from severe computational requirements and offer limited ability to explore power converter packaging converter designs during realistic converter operation. Traditional approaches using R-C networks as thermal equivalent circuits are of little use as a design tool since for every geometrical layout of the packaging structure which is tested, the designer must return to the starting point which is either a time-consuming FE simulation or a practical experiment. The Fourier thermal model presented in this thesis is a purely conductive model requiring no parameter extraction or use of a FE simulator. The starting point for the Fourier model is the heat equation. The Fourier thermal model yields solutions to the heat equation by carrying out spatial discretisation using a truncated Fourier series and using MATLAB/Simulink to perform temporal discretisation using a dynamic ODE solver. Validation using the finite volume thermal simulator FLOTHERM showed that the transient Fourier model could accurately simulate 3-D heat conduction through a wide range of power converter packaging structures. The Fourier thermal model is an excellent early stage design tool because its simulation speed is far superior to FLOTHERM, even though both models operate with a similar accuracy. The use of MATLAB/Simulink as the simulation environment enabled the Fourier thermal model to operate within the framework of an electro-thermal simulator and therefore simulate realistic load conditions. This is major advantage over existing approaches which fail to simulate electro-thermal interaction. Experimental validation of the fast electro-thermal converter simulator was achieved by utilising an inverter back-to-back rig and recording transient device temperatures using an infrared camera. The similarity between the experimental and simulated results indicated that the Fourier thermal model was sufficiently accurate. The electro-thermal simulator operated at a simulation speed which was ten times real time, which is extremely fast compared to existing approaches which can take up to two days to simulate a 60 second drive cycle. 'Ten times real time' represents a significant step forward for power converter packaging design. In the future device reliability can be accurately predicted if the electro-thermal simulator model is combined with a reliability model. The potential of the Fourier thermal model to aid numerical optimisation of the whole power converter is exciting.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering