Investigation Study of the Influence of Pole Numbers on Torque Density and Flux-Weakening Ability of Fractional Slot Concentrated Winding Wheel-Hub Machines

Abstract

Fractional slot concentrated winding machines (FSCWMs) with the low operation speed and large diameter usually have a large number of poles and slots; thus, numerous pole/slot combinations are feasible. The common practice to choose pole/slot combinations by multiplying the basic combinations may neglect some competitive candidates. Taking 36-slot FSCWMs as examples, this paper investigates the influence of pole numbers on torque density and flux-weakening ability, the two most vital performances of wheel-hub machine. It is shown that the machines with pole number slightly less than the slot number have the highest torque densities. Each component of synchronous inductance is separately analyzed, and its variation against pole numbers shows obvious regularity. Machines with pole numbers larger than the slot numbers have an excellent flux-weakening ability due to the large inductance and small permanent magnet flux linkage. The measurements together with the finite element analysis results confirm that the stator leakage inductance contributes the most to the superior flux-weakening ability. The identical analysis is also performed on 54-slot and 81-slot FSCWMs, with similar regularities observed.

Investigation of a Low-Speed High-Torque-Density Direct-Drive External-Rotor PMSM for Belt Conveyor Application

“…Rmo and Rmi denotes the outer radius and inner radius of the PM block, respectively. The expressions of Rmo and Rmi can be expressed as ( 6)- (7).…”

“…In [6], a new pole-slot combination with higher winding factor, lower total harmonics distortion (THD) of the no-load BEMF and lower cogging torque is presented based on three-slot pitch coils. In [7], the influence of slot-pole combination on torque density and flux weaking ability of the wheel-hub machine is analyzed, and the result indicates that it is best to choose a slightly smaller pole number than the slot number. In [8], for in-wheel permanent magnet vernier motors (PMVM), the influence of slot-pole combination on BEMF harmonic is researched and the PMVM with two slot pitches corporate with openslot stator is determined as the better combination.…”

Seven-phase Axial And Radial Flux In-wheel Machine With Three Active Air Gaps

“…2 (b)), thus also making active part of the end windings. Unfortunately, when the number of poles is the same for this third rotor, the necessary thickness of the rotor yoke, in order to verify magnetic constraint of saturation, can be important [8] in comparison with a simple linking mechanical piece. As consequence, the second idea is to use a higher polarity for the radial-flux rotor while maintaining a high quality of torque as it is possible with multiphase machines [9] thanks to decoupling between harmonics.…”

Design Consideration of Fractional Slot Concentrated Winding Interior Permanent Magnet Synchronous Motor for EV and HEV Applications

“…The comparative study of the flux weakening capability for a large number of slots per pole per phase (Spp) family is presented in [15]. In [16] and [17], the torque density of the motors is presented. Fornasiero et al introduced a thorough method to select the fractional slot nonoverlapping windings considering torque density, torque ripple, induced rotor losses, and fault-tolerance features [18].…”