Advanced lumped parameter model for switched reluctance motors with high performance cooling

In this paper an advanced thermal lumped parameter model for a switched reluctance electric motor (SRM) is constructed, based on a 2D thermal finite element simulation of a radial cross section of the motor. When applying and combining advanced cooling methods such as direct coil cooling, end winding cooling (radial stretched) and spray cooling on an SRM, the conventional lumped parameter models can no longer be used due to the 3D and complex temperature gradients in the motor. In standard LP models, mostly one simple cooling method is implemented by which the thermal gradients are also quite simple (1D or 2D). When combining different cooling methods, the gradients become highly 3D and these LPM are no longer valid. To improve the accuracy of this problem, a fully 3D thermal finite element simulation could be performed, but this would unnecessarily increase effort, complexity and computational time. To avoid this an advanced lumped parameter model is constructed in this paper, such that the high thermal gradients are modeled in more detail. The results from one 2D finite element simulation of a radial cross section of half of a stator tooth are reduced to a simpler lumped parameter model with more nodes in the most crucial parts, i.e., where the highest thermal gradients are expected. The 2D thermal model is then expanded to a 3D lumped parameter model, including the gradients in axial direction. Using this model, various cooling configurations and geometry parameters can be varied easily such that the design of an SRM with advanced cooling can be optimized efficiently

Model-based comparison of thermo-hydraulic performance of various cooling methods for power electronics of electric vehicles

This paper presents a thermo-hydraulic comparison of common and less commonly used cooling methods for power electronics used in electric vehicles, based on models available from literature. The current increase in power density of electric motors requires a higher power delivered by the electronics resulting in a higher heat dissipation. To achieve this, an appropriate method should be selected to cool the junction below the maximum operating temperature. A lot of information about commonly used and more advanced cooling methods is available in literature, but it is difficult to compare these methods for a specific application since the performance is determined starting from different boundary conditions and geometries. However, a comparison of the thermal performance based on the total thermal resistance from coolant to junction, is the starting point when selecting the possible cooling methods. In this paper a comparison is made between the different methods starting from the same conditions, to determine whether the maximum junction temperature can be respected by these methods. For each of the possible cooling methods, a suitable model is selected based on a literature study, which is used to predict the thermal performance. These models are combined with the thermal model of an inverter used in the automotive industry, to predict the junction temperature for a certain flow rate and corresponding pressure drop and pumping power. The obtained results about the thermal performance of the different methods can be used to select the most adequate cooling method by taking into account other criteria (cost, complexity,...). These other criteria such as feasibility and total cost of ownership, are however not studied in this paper. The proposed approach and model-based comparison of this work result in an optimized choice of cooling method and a more performant cooling design