Design Study for Controllable Electric Motor for Three Wheel Drive, In Wheel Mounting on Professional, Electric, Lawn Mower

Design of a new generation of electric drive motor for professional lawnmowers forms the basic objective of this thesis.

Modern drive concepts produces a growing demand for electrical machines featuring high torque density, and suitable for direct drive applications. Much attention is presently focused upon the transverse flux permanent magnet machine, which attracts great interests in electric and hybrid propulsion systems.

This thesis deals with modelling, performance analysis, design, test and measurement of permanent magnet transverse flux machines (PMTFM). It is important to understand the main aspects that influence the behaviour of a PMTFM, as this may lead to improved designs of PMTFM or may reveal the limitations of the transverse flux technology.

Generally, in PMTFM, the flux has a complex 3D pattern. Finite Element Method (FEM) needs to be used to analyse the magnetic field properties accurately in a PMTFM. Both 2D and 3D FEM may be used. A proper modelling and analysis method for using FEM is needed, to facilitate the analysis of different kinds of PMTFM. Analysis of PMTFM using FEM is covered in this thesis.

A good model of the PMTFM in circuit steady state operation, and a dynamic model would be very useful for performance prediction. This may also be used for controller design. Methods for instantaneous torque calculation, and estimation of the cogging torque, are also very important and need to be developed. Saturation may easily occur in PMTFM and may cause problems, e.g. reduction of the output torque and changes of inductance, which will cause non-linearity in the machine. Saturation effects may not be neglected if accurate results are required. A substantial part of this thesis is devoted to modelling and performance analysis of PMTFM.

Design improvement of PMTFM is another important issue discussed in this thesis. Based on the magnetic and electrical performance analysis, and by studying the influence of the number of poles, width of C-core tooth, and size of magnets on the torque production capability, an improved design of PMTFM was achieved. The improved design and proposed methods for performance analysis were verified using two prototypes.