Electric Machine Comparison for Mild Hybrid Light Vehicles with Respect to Performance and Thermal Capability

Examensarbete för masterexamen
Master Thesis
Electric power engineering (MPEPO), MSc
Larqvist, Sebastian
Östergren, Hannes
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 quantified when they are implemented in a 48 V mild hybrid system. Moreover, power losses for whole operating regions in various machine components have been specified, which are used as input data for the thermal models. From the thermal model, the temperature distribution within the machines have been determined during continuous 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 operating 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 kWcontinuously without exceeding the critical temperature limits. The SynRM has the most environmental 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 utilized 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.
Elkraftteknik , Electric power engineering
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