Fundamental Theory And Design Research Of A Flux-Decoupling Magnetic-Geared Permanent-Magnet Brushless Machine

The development of the magnetic-geared permanent-magnet brushless machine(MG-PMBM), which artfully integrates a coaxial magnetic gear(MG) into a permanent-magnet brushless machine(PMBM), is a key breakthrough specific to the researches on the direct-drive machine with low speed operation and high torque output. The traditional high power rating direct-drive machines are facing a development bottleneck, which is their bulky construction and relatively low torque density. The MG-PMBM has some magically capacities such as velocity reduction and torque amplification, which can offer an impact mechanical structure and obtain a higher torque density. Nevertheless, there are some issues about losses and efficiencies caused by the harmonic components of the air-gap magnetic fields in the integrated machine. In order to suppress these negative infections and get a better operation performance, this dissertation devotes to the fundamental researches on the MG-PMBM. The idiographic works are as follows:First of all, the inner PMBM field and the outer MG field effectively decoupled in the proposed machine, which makes it possible to choose different pole-pairs on both sides of the high-speed rotor. At the same time, the inner PMBM and the outer MG can be designed independently. For taking both advantages of the analytical method and the finite-element method(FEM), an optimal design procedure of the proposed machine is presented in this dissertation, which is using the analytical method for the pre-design and using FEM for solving the problems of nonlinear and complicated boundaries.Secondly, some important parameters have been confirmed in the pre-design of the outer MG by using the exact analytical method. Then the FEM is adopted to optimize the thickness of MG rotor yoke, adjust the configuration of ferromagnetic pieces, and predict the demagnetization of permanent-magnets(PMs). It should be noted that, a ferromagnetic bridge is added between two adjacent ferromagnetic pieces, two slots are made on both sides of the ferromagnetic piece, and the ferromagnetic pieces cylinder is casted by the epoxy resin fillers. Consequently, the mechanical strength of the MG is significantly improved.Thirdly, the flux-decoupling MG-PMBM has a dual-stator/dual-rotor structure, which means the concentricity issue will extensively affect the operation performance of the proposed machine. For solving the potential troubles, an exact analytical model of the slotted surface-mounted PM machine with rotor eccentricity is established. It is well known that, the analytical method has the advantages of rapid magnetic field computation and flexible parameter adjustment. Depending on that, the even-slots schemes are selected because of their lower unbalanced magnetic pull forces with rotor eccentricity. What’s more, the accuracy of the analytical model is verified by the contrast to the FEM results.Fourthly, an exact analytical method of Halbach-arrays PM machine with semi-closed slots is employed to confirm the parameters in the PMBM pre-design, viz. poles and slots, segments of each pole in Halbach PM arrays, and radius of the air-gap circle. Some other parameters such as rotor yoke thickness, PM thickness, stator tooth width, stator yoke thickness, stator boots dimension, cogging torque, are optimized by the FEM. It should be noticed that, the electromagnetic output torque of the inner PMBM must be designed for matching the torque capacity of the high-speed rotor of the outer MG. So the schemes with sinusoidal back electromotive force(back-EMF), lower cogging torque, and larger output torque are preferred in the optimal design.Fifthly, the magnetic field distributions in the flux decoupling MG-PMBM are near-sinusoidal, so the BLAC driving is a better choice for a qualified output performance. In this dissertation, the Simulink-analytical field-circuit simulation system is built by the combination of the MG field analytical model and the SVPWM algorithm control system. The simulation results indicate that, the output torque and output speed of the flux-decoupling MG-PMBM are coincide with the given values. And the excellent over-load protection ability greatly increases the operation security of the proposed machine.Finally, after the pre-design based on the analytical method and the optimal design based on the FEM, a prototype with 150 Nm/50 rpm is designed and fabricated. The corresponding dual-loop control system of the proposed machine has been constructed. The experimental results demonstrate that, the operation efficiency, power factor and torque density are 88.7%, 0.9 and 43 k Nm/m3 respectively, which meets the requirements of the applications with low speed operation and high torque output.With the popularization of the electrical machine driving and control, it makes the concept of “all-electronics” become reality in the applications of the large-scale driving system. The researches in this dissertation will provide a good foundation on the practicality of the MG-PMBM, which would like to realize a self-independent innovation and reach the advanced level in the world.