The thermal management of electric machines is investigated with the application of techniques to a Switched Reluctance Machine and a high-speed Switched Reluctance Machine. Two novel concepts for said management of a Switched Reluctance Machine are proposed and developed: Inter-Laminate Cooling and a Continuous Toroidal Winding. The Inter-Laminate Cooling concept is developed with application to an iron core inductor which serves as a proxy for the electric machine. The experimental results confirmed the capability of the method, expressed by the effectiveness, which defines the performance measure of the applied cooling method; a concept which itself is equally applicable to other cooling methods that may be applied to any electric machine. The effectiveness also describes the gain in allowable input power to the machine which is realized to reach the same thermal limit versus the case without Inter-Laminate Cooling. The Inter-Laminate Cooling was not applied in experimental test to a Switched Reluctance Machine due to the present economic and fabrication limitations. The Continuous Toroidal Winding concept, originally conceived to permit the consideration of a fluid capillary core type of winding to enhance machine cooling, is developed to allow for peripheral cooling of the machine windings and end windings. The Continuous Toroidal Winding version of the Switched Reluctance Machine is investigated for both its thermal and electrical performance in the context of a machine that is equivalent electromagnetically to its conventional counterpart. The Continuous Toroidal Winding Switched Reluctance Machine was found to perform thermally as tested, in a manner superior to that of the conventional machine where the Toroidal machine was simulated and researched at an equivalent level of operation to the conventional machine. The electrical performance of the Toroidal Switched Reluctance Machine although supportive of the simulation analysis used to develop the machine, was not fully conclusive. This may have been due to problematic iron cores used in the construction of the experimental machines. The application of the Inter-Laminate Cooling method to a Switched Reluctance Machine is considered on an analytical basis for the special case of a High Speed Switched Reluctance Machine and found to be of net positive benefit as the machine’s iron losses are dominant over its copper losses. Application of the Inter-Laminate Cooling method to a lower speed machine, whilst beneficial, is not sufficient to significantly impact the temperature of the machine’s windings such that it would offset the loss of specific torque and power. As such, Inter-Laminate Cooling is only applicable where the net benefit is positive overall; in that the gain in input power realized is sufficient to overcome the loss of specific power and torque which will occur due to the increased machine volume. The “effectiveness” and “gain” approach for the evaluation of cooling methods applied to electric machines is a concept which should be adopted to aid in the comparative understanding of the performance of myriad different cooling methods being applied to electric machines both in research and practice, of which there is only minimal understanding. / Thesis / Doctor of Philosophy (PhD)

The electronic market is continually moving towards higher power densities. As a result, the demand on the cooling is increasing. Focus has to be put on the whole thermal management chain, from the component to be cooled to the ambient. Thermal interface materials are used to efficiently transfer heat between two mating surfaces or in some cases across larger gaps. There are several different thermal interface materials with various application areas, advantages and disadvantages. This study aimed to evaluate thermal and mechanical properties of graphite sheets and graphite gap pads. The work was done in cooperation with Ericsson AB. A test rig based on the ASTM D5470 standard was used to measure the thermal resistance and thermal conductivity of the materials at different pressures. It was found that several graphite sheets and gap pads performed better than the materials used in Ericsson’s products today. According to the tests, the thermal resistance could be reduced by about 50 % for the graphite sheets and 90 % for the graphite gap pads. That was also verified by placing the materials in a radio unit and comparing the results with a reference test. Both thermal values and mechanical values were better than for the reference materials. However, the long term reliability of graphite gap pads could be an issue and needs to be examined further. / Elektronikbranschen rör sig mot högre elektriska effektertätheter, det vill säga högre effekt per volymenhet. Som en följd av detta ökar också efterfrågan på god kylning. Kylningen måste hanteras på alla nivåer, från komponenten som ska kylas, ända ut till omgivningen. Termiska interface material (TIM) används för att förbättra värmeöverföringen mellan två ytor i kontakt med varandra eller för att leda värmen över större gap. Det finns flera olika TIM med olika tillämpningsområden, fördelar och nackdelar. Denna studie gick ut på att utvärdera termiska och mekaniska egenskaper hos grafitfilmer och så kallade ”graphite gap pads” då de används som TIM. Projektet gjordes i sammarbete med Ericsson AB. En testuppställning baserat på ASTM D5470-standarden användes för att utvärdera värmeledningsförmågan och den termiska resistansen hos de olika materialen vid olika trycknivåer. Resultaten visade att flera grafitfilmer och ”gap pads” presterade bättre än materialen som används Ericssons produkter idag. Enligt testerna skulle den termiska resistansen kunna minskas med 50 % för grafitfilmerna och 90 % för ”gap padsen”. Materialens fördelaktiga egenskaper verifierades i en radioenhet där temperaturerna kunde sänkas i jämförelse med ett referenstest med standard-TIM. De nya materialen var mjukare än referensmaterialen och skulle därför inte orsaka några mekaniska problem vid användning.  Den långsiktiga tillförlitligheten för grafitbaserade ”gap pads” måste dock undersökas vidare eftersom de elektriskt ledande materialen skulle kunna skapa kortslutningar på kretskorten.