A novel technique for minimizing torque ripple in axial flux segmented rotor SRM

Abstract

Axial flux machine is an attractive option for inwheel electric vehicle (EV) application, which requires high ratio of outer diameter to axial length. Further, utilization of lamination material in axial flux machines is better than that of radial flux machines. In order to reduce cost, magnet-less machines are desirable. In view of all these factors a singlestator, dual-rotor, three-phase axial flux segmented rotor switched reluctance motor (AFSSRM) with toroidal windings was recently proposed [1]. It was observed that torque ripple is high in this machine. In this paper, a simple and effective technique to reduce torque ripple in AFSSRM is proposed. Two rotors of AFSSRM are circumferentially displaced with respect to each other. It is analytically proved that torque ripple can be reduced using this technique. This is also verified by finite element method (FEM) analysis based simulation studies. It is observed that the torque ripple is reduced by 54.6%. Effect of rotor displacement on axial attraction forces is also discussed.

Evaluation of A Novel Axial Flux Variable Reluctance Machine

“…Since this is a reluctance machine, the other major concern is the selection of a highpermeability material for the rotor disk to maximize the inductance variation for large torque according to (5). Non-grain-orientated (NGO) silicon steel is chosen for its high permeability, relatively low cost, and saturation flux density near that of iron.…”

“…Next is the significant task of determining unaligned (minimum) and aligned (maximum) position inductances. In reluctance machine design it is desirable for the inductance ratio α to be high to produce a high torque according to (5). Equation (7) Determining the minimum inductance however is not so straightforward.…”

“…Numerous solutions have been proposed in order to minimize torque ripple, either through modification of the machine geometry or through electronic control [4]. Examples include circumferentially displacing the rotors [5] or control of the square of the phase currents using current sensors [6]. The other drawback to VRMs is the inherent complexity of their control.…”

“…In contrast to permanent magnet machines, VRMs can operate at higher speeds, are simpler in structure, and are less costly [5]. The achievable magnetic field of VRMs is stronger and may be controlled unlike permanent magnet machines.…”

“…The accelerating development and commercialization of electric vehicles, for instance, is stimulating research into reluctance machines for this purpose [2], [3], [9], [8], [5]. Still other uses for VRMs include aerospace and appliance industries [10].…”