Abstract
The thermal analysis of a high performance brushless synchronous electric motor with permanent magnets and water jacket cooling is presented. The analysis is carried out following a lumped parameter thermal network approach which allows to identify the most important thermal paths in the motor and the main parameters influencing them. Thanks to its simplicity, the solution of such a thermal network model is very fast, allowing a large number of what-if scenarios to be computed over a short amount of time. For this reason, the model is coupled with external tools for performing systematic sensitivity analyses and optimizations. Goal of the investigation is the reduction of the windings temperature being this temperature inversely proportional to the efficiency and the power delivered by the motor. The sensitivity analysis, performed over a series of material, geometric, and operational factors, leads to the identification of the most relevant parameters influencing the thermal behaviour of the motor. A series of optimizations, focusing on these parameters and including suitable constraints granting the well-posedness of the problem and the feasibility of the solution, bring to the definition of an optimum layout of the water jacket and of the stator geometries. The optimized geometry allows a significant reduction of the windings temperature to be achieved.
Highlights
In recent years electric motors have attracted the attention of researchers and automotive companies due to the pressing environmental issues
From a preliminary multi-level Full-Factorial Design of Experiments (FF-DOE) it was seen that the response surface in terms of average windings temperature has a rather flat optimum region so that there are a number of equivalent (Hw∗j, Ww∗j) choices for the two variables that as long as they both span in the range [0.8, 1.1] and allow to meet the pressure constraint, they are substantially optimal
As the convective water jacket thermal resistance does not affect any other resistance of the Lumped Parameter Thermal Network (LPTN), and is independent from the other free parameters, there is no need to include the water jacket variables in further optimizations
Summary
In recent years electric motors have attracted the attention of researchers and automotive companies due to the pressing environmental issues. They have taken hold in the field of competitions with the inauguration of the ABB FIA Formula E championship in 2014. Formula E is the maximum competition using only electric-powered cars, and represents a privileged environment where advanced solutions that could possibly be adopted in road vehicles are tested. Continuous research is leading to improved car performances and durability. The thermal management of the motor, and of the vehicle in general, becomes important, considering the electric power densities at stake. Overheating reduces battery life, degrades the rare earths of the motor magnets, and promotes the dissipation by Joule heating of the copper windings
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