| With the continuous improvement of life quality and ever increasing concerns on environmental crisis, direct-drive systems which aims to achieve low speed and high torque in new energy areas such as wind generators and electric vehicles, have been attracting considerable interests in electric-drive industry. In recent years, a novel magnetic-geared permanent magnet(PM) motor which can realize a high torque density “pseudo†direct-drive has been proposed. By integrating a field-modulating PM magnetic gear into a PM motor with external rotor, the proposed motor has good potential applications in transmission system due to the reducation of volume and weight. Both field-modulating PM magnetic gear and magnetic-geared motor rely on the use of the modulating ring to modulate the magnetic fields excited by the two rotors. However, because of the modulation effect, the magnetic fields have many sub-harmonics. These unwanted harmonics lead to undesirable effects, such as high PM eddy current(EC) loss and iron core loss, low efficiency, noise and vibration. In addition, complex structures increase the difficulty in heat dissipation. Due to significant amount of heat caused by the losses, partial irreversible demagnetization of the magnets may occur, which is particularly important for Nd-Fe-B magnet. Hence,the topic of loss analysis and optimization design for magnetic-geared motor has theoretical significance and practical value.In this thesis, the operation principle of the field-modulating PM magnetic gear will firstly be introduced, and the following chapter investigates the loss characteristic of magnetic gear and magnetic-geared motor, as well as components of space sub-harmonics which cause rotor losses. By using magnetic flux barriers in the outer rotor, a novel rotor structure for CMGs is proposed to reduce the rotor losse, which will give useful guidelines for design optimization of a magnetic-geared motor.The fruits of this work are as follows:1. Based on the analytical method, the basic topology and operation principle of the field-modulating PM magnetic gear is generally introduced and the components of space sub-harmonics which produce a constant torque are investigated.Finite-element analysis(FEA) results are given to identify the distribution of magnetic fields in inner and outer air-gap.2. According to the generating mechanism of iron core loss and PM EC loss, the losses calculation model of magnetic-geared motor is introduced, and the loss of each part are calculated and analyzed. From the analysis of harmonic components causing rotor losses, it can be concluded that non-sinusoidal distribution of magnetic field excited by the one rotor is the main reason for losses of the other rotor. Futhermore, this paper investigates the effect of magnetic field coupling on the motor losses.3. Some topologys of magnetic gear are introduced to decrease rotor losses,including segmented PM, single polarity PM and Halbach PM Array, and two models with different shapes of modulating ring are quantitatively compared with existing magnetic gear.4. By using magnetic flux barriers in the outer rotor, a novel rotor structure for magnetic gear is proposed to reduce the rotor losses, in which sub-harmonics are considered. A 1-D magnetic permeability model is also introduced in order to understand the principle of reducing the main sub-harmonics. Then, the validity of the optimization design has been confirmed by the FEA results. |
