Study On Magnetic Field Modulated Permanent Magnet Gear And Low Speed Motor

In modern practical industry applications, nearly90%of electrical drives involve with bulky and fragile mechanical transmission trains and gearboxes in order to achieve low speed and high torque. There are various inherent demerits for such kind of drive systems, such as large volume and weight, high acoustic noise, low efficiency, poor transmission precision and slow dynamic response. Moreover, the reliability and life span of the systems would deteriorate significantly due to the inevitable abrasion of the gears. Hence, the low-speed high-torque direct-drive systems that involve no mechanical gearboxes are becoming commodities in more and more applications. On the other hand, the contactless permanent magnet magnetic gears based on flux modulation, which have unique characteristics such as low acoustic noise, maintenance free, high reliability, great toque density, excellent efficiency and inherent overload protection, have been attracting considerable interests in recent years. The system torque density and reliability can be significantly improved by combining a conventional PM motor with such a magnetic gear.In this thesis, the development of the permanent magnet gear to reveal the emergence procedure of the combination of conventional permanent magnet machine with such a magnetic gear will firstly be introduced, and then the related literatures are reviewed systematically. The permanent magnet gears and low-speed high-torque electric machines, which use the basic principle of field modulation, are studied, particularly on the following aspects.First, the basic topology and operation principle of the field-modulating permanent magnet magnetic gear is generally introduced and the influences of the key parameters on the performance of the magnetic gear are comprehensively investigated. A new manufacture technique for the field-modulating ring, which would significantly reduce the difficulty and cost of production but slightly deteriorate the performance, is proposed and analyzed. A prototype with optimal parameters and the field-modulating ring from the new manufacture technique has been designed and fabricated. The validity of the finite element analysis results and new field-modulating ring manufacture technique has been confirmed by the experimental results from the prototype.Second, Topology of low-speed field-modulating motor is proposed based on the operation principle of the field-modulating permanent magnet magnetic gear and the corresponding two operational modes are studied. The prototype machine with optimal design has verified low-speed field-modulating concept. Furthermore, the experimental comparison between the two operational modes has revealed that the equivalence of the two modes under certain condition. The field-modulating concept introduces a new design way of low-speed high-torque machine.Third, a new type of mechanical set, which couples the field-modulating permanent magnet magnetic gear and permanent magnet brushless machine both mechanically and magnetically, together with its operation principle, is introduced and studied. Finite element analysis is employed to comprehensively investigate the impacts of the key parameters on the machine performance. The prototype machine with optimal design has confirmed the validity of the hybrid field-modulating machine concept. Furthermore, the predicted performance of the machine from finite element analysis has been validated by the experiment test on the prototype.