Electric Machine Comparison for Mild Hybrid Light Vehicles with Respect to Performance and Thermal Capability Master’s Thesis in Electrical Power Engineering SEBASTIAN LARQVIST HANNES ÖSTERGREN Department of Energy and Environment CHALMERS UNIVERSITY OF TECHNOLOGY Gothenburg, Sweden 2017 Master’s thesis 2017 Electric Machine Comparison for Mild Hybrid Light Vehicles with Respect to Performance and Thermal Capability SEBASTIAN LARQVIST AND HANNES ÖSTERGREN Department of Energy and Environment Division of Electric Power Engineering Chalmers University of Technology Gothenburg, Sweden 2017 Electric Machine Comparison for Mild Hybrid Light Vehicles with Respect to Performance and Thermal Capability Sebastian Larqvist & Hannes Östergren © SEBASTIAN LARQVIST & HANNES ÖSTERGREN, 2017. Supervisors: Stefan Skoog, Chalmers University of Technology Patrik Stridh, Volvo Car Corporation Alexander Robertsson, Volvo Car Corporation Examiner: Torbjörn Thiringer, Chalmers University of Technology Master’s Thesis 2017 Department of Energy and Environment Division of Electric Power Engineering Chalmers University of Technology SE-412 96 Gothenburg Telephone +46 (0)31 772 1622 Cover: Field plots over magnetic flux density in four studied machine topologies: PMSM, SynRM, PMSynRM and IM. Gothenburg, Sweden 2017 iv Electric Machine Comparison for Mild Hybrid Light Vehicles with Respect to Performance and Thermal Capability SEBASTIAN LARQVIST HANNES ÖSTERGREN Department of Energy and Environment Chalmers University of Technology Abstract In this thesis, various electric machine topologies have been modeled and optimized according to constraints related to mild hybrid applications. With the assistance of electromagnetic field calculation software using FEM simulations, the performance characteristics as well as thermal capability have been analyzed. By utilizing full vehicle simulations, the machines have been evaluated and the performance quan- tified when they are implemented in a 48 V mild hybrid system. Moreover, power losses for whole operating regions in various machine components have been speci- fied, which are used as input data for the thermal models. From the thermal model, the temperature distribution within the machines have been determined during con- tinuous operation. In this work, four machine topologies were chosen to be studied: PMSM, SynRM, PMSynRM and IM. A number of operating points relevant to mild hybrid systems were selected to be used as basis for the performance comparison. From the simulations, it was found that the 8-pole PMSM has the highest op- erating efficiency of 96.9 %. The implemented ferrite magnets of the PMSynRM improve the highest operating efficiency by 1 % and increase the maximum torque by 7 Nm compared to the SynRM. The PMSM and the IM fulfill the cold crank torque requirement, and all machines can be operated at 10 kW continuously without exceeding the critical temperature limits. The SynRM has the most environmen- tal friendly design in terms of material combination, emissions are 53 % less in comparison the 4-pole PMSM. To conclude, due to beneficial properties such as high power and torque density, along with great performance in the specified operating points and solid thermal characteristics, the PMSM topology is found to be an interesting option to be uti- lized in mild hybrid traction applications. Furthermore, the ferrite magnets in the PMSynRM makes likewise this machine topology an interesting alternative to be applied in mild hybrids, due to the overall high operating performance in relation to its low material cost and CO2 equivalent per produced machine. Keywords: Mild Hybrid, Electric Vehicle, Electric Machine, PMSM, SynRM, IM, FEM, Operating Efficiency, Thermal Capability. v Acknowledgements First of all, we would like thank our main supervisor Stefan Skoog for his vital support, feedback, and for sharing his inspiring research in the field of mild hybrid applications with us. We would also like to express our sincere gratitude towards our examiner Professor Torbjörn Thiringer, for always dedicating his time and his great encouragement during the thesis work. Furthermore, we would like to thank our supervisors at Volvo Cars, Patrik Stridh and Alexander Robertsson, for their commitment and for deepen our knowledge within the field of electrified vehicles. In addition, we would like to address our appreciation to Andreas Andersson for his helpful advice regarding FEM simulations, and to Emma Arfa Grunditz for her guidance concerning thermal modeling of electric machines. I, Sebastian, would like to thank my family and friends for the continuous love and encouragement throughout the years, your support means everything. I, Hannes, give my warmest thanks to my family, especially my dear fiancée Emma for the endless love and support through all the years. Sebastian Larqvist & Hannes Östergren, Gothenburg, June 2017 vii List of Abbreviations BEV Battery Electric Vehicle BSG Belt Driven Starter-Generator emf Electromotive Force FEM Finite Element Method HEV Hybrid Electric Vehicle ICE Internal Combustion Engine IM Induction Machine IPMSM Interior Permanent Magnet Synchronous Machine ISG Integrated Starter-Generator MTPA Maximum Torque Per Ampere PM Permanent Magnet PMSynRM Permanent Magnet Assisted Synchronous Reluctance Machine PMSM Permanent Magnet Synchronous Machine SRM Switched Reluctance Machine SynRM Synchronous Reluctance Machine ix