Electromagnetic and Calorimetric Validation of a Direct Oil Cooled Tooth Coil Winding PM Machine for Traction Application

Abstract

Tooth coil winding machines offer a low cost manufacturing process, high efficiency and high power density, making these attractive for traction applications. Using direct oil cooling in combination with tooth coil windings is an effective way of reaching higher power densities compared to an external cooling jacket. In this paper, the validation of the electromagnetic design for an automotive 600 V, 50 kW tooth coil winding traction machine is presented. The design process is a combination of an analytical sizing process and FEA optimization. It is shown that removing iron in the stator yoke for cooling channels does not affect electromagnetic performance significantly. In a previous publication, the machine is shown to be thermally capable of 25 A/mm 2 (105 Nm) continuously, and 35 A/mm 2 (140 Nm) during a 10 s peak with 6 l/min oil cooling. In this paper, inductance, torque and back EMF are measured and compared with FEA results showing very good agreement with the numerical design. Furthermore, the efficiency of the machine is validated by direct loss measurements, using a custom built calorimetric set-up in six operating points with an agreement within 0.9 units of percent between FEA and measured results.

Recent Developments in Electrical Machine Design for the Electrification of Industrial and Transportation Systems

“…In addition to the design optimization of electric motors, new cooling techniques were incorporated to expand further the current limits of electrical machines in aircraft and automobile applications [14][15][16]. Using advanced cooling techniques increases the current loading and, thus, specific power and torque.…”

A Complex Study of Stator Tooth-Coil Winding Thermal Models for PM Synchronous Motors Used in Electric Vehicle Applications

“…This detailed model can be used again for the estimation of the temperatures of conductors after the whole model is solved and the boundary conditions are known. However, this procedure is not possible for random-wound windings where the positions of the conductors are not clearly defined [5].…”

“…These temperature differences are then considered in the calculation of the thermal resistances R th according to Equation (5), where ∆T is the temperature difference and ∆P Cu are Joule losses for rated current, in our case 625 W. The tested machine had a star-connected winding without an achievable zero node and the winding was connected in series-parallel during the tests.…”

“…One of the commonly used construction typologies of PMSM in the automotive industry is a machine with tooth-coil winding or a machine with concentrated winding. This brings the advantage of low-cost production, high torque density and high efficiency [5][6][7]. On the other hand, the manufacturing process brings new challenges to the thermal design of a PMSM [8].…”

“…The first problem is that the area of the winding in the slot contains several materials with orders of magnitude different thermal conductivity values. The second problem is that for randomwound windings, it is impossible to determine the exact positions of the conductors in the slot [5]. These facts do not allow simple homogenization of the region.…”