Abstract
Modeling of convection heat-transfer at the end-windings for thermal networks using lumped-parameters has been widely discussed in the literature. Unfortunately, the resulting coefficients are highly influenced by the end-winding shape, the area in the vicinity of the end-windings, the cooling method of this region (if any), as well by the size and power of the machine. This makes it extremely difficult for the designer to choose a suitable coefficient for the thermal analysis during the design stage of an electric motor. A methodology to obtain the end-windings convection heat-transfer coefficients for fractional-slot concentrated winding permanent-magnet synchronous motors is proposed in this article. Machine designs with both internal and external rotors will be considered. The experimental tests required for the model characterization are described in detail. In this article, general expressions of the convection heat-transfer coefficients between the end-windings and the housing end-caps are proposed for both internal and external rotor designs. Differences observed with the results reported in the literature are also discussed.
Highlights
P ERMANENT-MAGNET synchronous machines (PMSMs) with fractional-slot concentrated windings (FSCW) have already been employed in electric and hybrid propulsion vehicles due to their high torque density, high efficiency, low torque ripple, good flux-weakening capability and inherent fault-tolerance [1]–[3]
External rotor designs can be beneficial for in-wheel motor topologies for electric vehicles [4], [5] and modern lightweight vehicles, such as electric bicycles [6], [7]
The last group can be divided into finiteelement methods (FEM) and computational fluid dynamics (CFD)
Summary
P ERMANENT-MAGNET synchronous machines (PMSMs) with fractional-slot concentrated windings (FSCW) have already been employed in electric and hybrid propulsion vehicles due to their high torque density, high efficiency, low torque ripple, good flux-weakening capability and inherent fault-tolerance [1]–[3]. Due to numerical methods being high time-consuming, even with advancement in computers, they are not the preferred solution during initial design stages of electric motors In this context, this paper is focused on the accuracy improvement of LPTN methods. For the case of industrial induction machines, fins attached to the rotor short-circuit rings (usually known as wafters) have been traditionally employed in totally enclosed designs to boost the airflow within the end-space region [13], [14]. The main objective of this paper is to obtain the generalized coefficients which are required for the use of (1) with PMSMs with smooth rotors, when no specific end-winding cooling methods are employed, which comprise the majority of the electric motors employed in actual electric/hybrid vehicles [26].
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