Investigation of winding topologies for permanent magnet in-wheel motors

Permanent magnet synchronous motors (PMSMs) are usually favored as traction machines for large-size hybrid vehicles, e.g. hybrid trucks, because of their high torque density and extended speed capability. They can also be intentionally placed attached to the wheels in a series hybrid drive system to exclude the mechanical drive path and thus enlarge the cargo space for a redesign of the trucks. To design such an in-wheel PMSM for this application, one of the most important steps is to find the optimal armature winding topology. In this paper, different winding topologies, e.g. distributed, concentrated, and toroidal are discussed based on a 7 pole-pair in-wheel PMSM. A general method to calculate the winding factors with different combinations of pole and slot numbers is proposed so that optimal slot numbers (12, 15, and 18) for concentrated windings with relative high winding factors are found. Those winding layouts prove to be advantageous to exhibit lower Joule losses compared to the full-pitch distributed windings. Nevertheless, a further study shows that a better thermal performance can be achieved by the toroidal winding topology in spite of its even higher Joule loss, due to its large area of exposed coils where an effective cooling mechanism can be implemented.