Application of 3-D Computation of Magnetic Fields to the Design of Claw-Pole Motors

Doktorsavhandling, 2005

The main advantage of claw-pole machines lies in their ability to yield higher torque density values than is obtainable from a conventional machine. However, the high torque density has its price; leakage flux is often high resulting in low power factor and efficiency. This thesis is mainly concerned with the design of a claw-pole motor that meets application requirements of reasonably high torque density and a power factor comparable to conventional topologies. After critically reviewing previously proposed designs of Transverse-flux and Claw-pole machines, the thesis focuses on a special type of claw pole motor having claws in both the stator and the rotor. The claws are made of Soft Magnetic Composites (SMC); consisting of iron powder particles that are individually insulated and can be readily pressed into complex geometries. Detailed explanation of the operation of such a design is then provided. Internal design of the claw-pole motor is investigated with the aid of three-dimensional finite-element field computation. In particular, the effect of the following parameters on the motor's performance has been investigated: number of poles, main dimensions, magnet material and dimensions, pole-face profile and claw angle. This theoretical work was verified, to some extent, against measurements obtained from an experimental machine especially constructed for this purpose. Details of this experimental motor are also presented. The investigation of the internal design of the claw-pole motors presented in this thesis provides a physical insight into their operation and, therefore, can be utilised for their general design. Indeed, this work enabled realisation of a claw-pole servomotor that is capable of achieving a torque density of about 1.5 Nm/Kg at a power factor of 0.9. The decisions made in arriving at the servomotor design are presented and clearly related to the conclusions of the internal design investigation.