Research area of the flux-modulated motors with permanent magnets began developing in the
1990s. Before that, the machine was known as Vernier reluctance motor, which used only
reluctance for operation. With the usage of permanent magnets, the torque density of this motor
type has been increased, but the power factor remained low. Current researches do not discuss
the connection between the geometric parameters on one hand and the torque and power factor
on the other.
In the first section, the thesis describes the procedure for analytical calculation of the air-gap
magnetic field and shows the imperfections in the basic torque equation, which has been used
in the scientific literature. The torque equation has been improved in a way that it takes also the
leakage magnetic field in a slot into account, which can be calculated also analytically with the
procedure, described in the first section. The power-factor equation is derived. It shows that the
power factor is influenced by the magnetic field shape, share of the leakage magnetic field and
inductance of the stator winding. The latter can be calculated analytically using the derived
equation and can be used generally for any rotating electric machine with open slots and nonsalient
rotor. At the end of the first section, the calculations of the cogging torque and torque
ripple are made as well as the operational properties.
An electric motor has been built in order to confirm the theory (“realistic verification model”).
It was used to conduct the measurements that are described in the second section. At first glance
it seems that the measurements’ results are completely different from the theoretical
assumptions. After further analysis of the increased losses had been made, it turned out that the
assumptions were correct. However, more attention has to be dedicated to the production
technologies.
In the third section the motor design procedure for the use in the road electric vehicle is
described. Design of experiments via Taguchi method is used to find the most influential
parameters, whereas the multiparameter optimisation using genetic algorithm is used to find
their optimal values. The optimal design, which was confirmed with the final numerical
calculation, has higher maximum torque, lower weight, but also slightly lower efficiency.
VI
In the fourth section, a comparison between different rotor types is made, where the magnets
are positioned differently in the rotor. When comparing the rotor types, the theoretical basis
from the first section is used. It turns out that only the rotors with surface-mounted and spoke
permanent magnets can be used. The properties of other types are too poor.
Fifth section deals with the flux-modulated motor that uses more harmonic components of
magnetic field than permanent-magnet Vernier motor. This can be achieved in two ways, either
with permanent-magnet MMF reshaping or permeance reshaping. It turns out that the properties
are not as good as in Verner motor, thus it is not attractive for the vehicle propulsion, unless a
method for achieving the desired values of certain harmonic components of magnetic field is
found. The usage of multiple harmonic components can be transferred to the general
synchronous motor. Its properties are comparable with the Vernier motor.
The patents are also the source of the technical knowledge, thus some of the most interesting
ones have been read. They are gathered in the sixth section. One of them stands out, thus more
attention has been drawn to it. Using different combinations of the number of magnets and
number of stator teeth, the operational properties can be improved.
In the conclusion, the next steps in research of flux-modulated motor are given.
In the scope of this thesis, all of the expected contribution to science have been fulfilled. They
are presented and explained in the eight section. During the research, some novelties on this
research area that are gathered and presented in the ninth section have been found.
Within the research process, a scientific paper Design of a permanent-magnet flux-modulated
machine with a high torque density and high power factor has been published in the journal
IET Electric Power Applications in January 2016.
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