High Torque Density Low Voltage Traction Drives with Preformed Coils: Evaluation of Operating Limitations

The geometry of preformed coils with a varying conductor width allows a high copper fill factor in parallel teeth stator electrical machines with concentrated windings. The increase in efficiency, torque and power density is however limited: Skin and proximity effect lead to increased losses at high frequencies. Additionally, the production process of the coil leads to a non-ideal geometry and therefore to an elevated resistance of the coil. Furthermore, there is no available state-of-the-art insulation system for the preformed coils which are studied in the present work. Newly developed insulation systems might not meet the same thermal requirements as conventional enameled wire. In this paper, the operating limitations of two electrical machines, one with a classical round wire winding and one with preformed coils, are compared. The results are validated using test bench data.