Shafigh Nategh

Thermal Analysis of a PMaSRM Using Partial FEA and Lumped Parameter Modeling

This paper presents an advanced lumped parameter (LP) thermal model for a permanent-magnet assisted synchronous reluctance machine (PMaSRM) developed for propulsion in a hybrid electric vehicle. Particular focus is put on the stator winding and a thermal model is proposed that divides the stator slot into a number of elliptical copper and impregnation layers. The model is enabled by the derivation of an approximate analytical expression for the thermal resistance of an elliptical cylinder with constant thickness. The approach is attractive due to its simplicity and the fact that it closely models the actual temperature distribution for common slot geometries. Additionally, an analysis, using results from a proposed simplified thermal finite element model representing only one slot of the stator and its corresponding end winding, is presented in which the number of layers and the proper connection between the parts of the LP thermal model representing the end winding and the active part of winding is determined. The presented thermal model is evaluated experimentally on a PMaSRM equipped with a water cooling jacket, and a good correspondence between the predicted and measured temperatures is obtained.

Thermal Modeling of Directly Cooled Electric Machines Using Lumped Parameter and Limited CFD Analysis

This paper presents a practical approach to model thermal effects in directly cooled electric machines. The main focus is put on modeling the heat transfer in the stator winding and to the cooling system, which are the two critical parts of the studied machines from a thermal point of view. A multisegment structure is proposed that divides the stator, winding, and cooling system into a number of angular segments. Thereby, the circumferential temperature variation due to the nonuniform distribution of the coolant in the cooling channels can be predicted. Additionally, partial computational fluid dynamics (CFD) simulations are carried out to model the coolant flow in the cooling channels and also on the outer surface of the end winding bodies. The CFD simulation results are used as input to the analytical models describing the convective heat transfer to the coolant. The modeling approach is attractive due to its simplicity since CFD simulations of the complete machine are avoided. The proposed thermal model is evaluated experimentally on two directly cooled induction machines where the stator winding is impregnated using varnish and epoxy, respectively. A good correspondence between the predicted and measured temperatures under different cooling conditions and loss levels is obtained.

Direct oil cooling of traction motors in hybrid drives

This paper presents comparisons of utilizing direct oil cooling approaches and conventional indirect cooling approaches for electrical motors which are mounted in HEVs or ZEVs. Both finite volume Computational Fluid Dynamic (CFD) model by FLUENT and finite element electromagnetic model by JMAG are applied to make the simulation accurate and comprehensive. Average temperature over the stator back, pressure drop between inlet and outlet and average heat transfer coefficient over the cooling duct are evaluated under identical flow rate, velocity and pressure drop for different cooling approaches. In addition, the influences on torque and power performances by the cooling ducts made in the housing or stator back are evaluated by JMAG model. The directly cooled motors show lower temperature rises at the stator back since the direct contact between coolant and stator back can avoid the unnecessary thermal contact resistances between the stator back and housing, meanwhile make the coolant more close to the heat sources, and thus improve the cooling efficiency.

Influence of the Welding Process on the Performance of Slotless PM Motors With SiFe and NiFe Stator Laminations

The influence of the welding process during the manufacturing of small slotless permanent-magnet synchronous machines (PMSMs) is studied in this paper. The focus lies on the change of the magnetic properties in high-quality silicon-iron (SiFe) and nickel-iron (NiFe) electrical steel sheets with thicknesses of 0.1 and 0.2 mm. It is shown that the welding process changes the magnetic material properties significantly and increases the specific iron losses. Experimental results are provided for magnetic flux densities up to 1.5 T and frequencies from quasi-static to 200 Hz. The obtained measurement data is afterward used in finite-element method (FEM) simulations to investigate the influence of the magnetic property changes on the motor performance, particularly with regard to stator core losses.