Low-Speed High Torque Direct Drive Permanent-Magnet Brushless Motor

Compared with the traditional motor system with gear transmission, low speed high torque direct drive motor has special advantages. Permanent magnetic brushless motor has obvious potential in the application of low speed high torque direct-drive field due to its characteristics of high efficiency and high torque density, which is studied in this thesis as follows.Firstly, the magnetic circuit of permanent magnet brushless motor (PMBM) is analyzed. The equivalent magnetic circuit and its simplified configuration of the surface PMBM are deduced, on the base of which, no-load magnetic flux leakage coefficient expression is given theoretically and is verified successfully by FEM. The relationship between no-load magnetic flux leakage coefficient and the motor's structure parameters is also depicted.Secondly, the PMBMs with the same pole numbers, same rated parameters, and with the slot number per phase per pole q equal and less than 1, which enjoys an important potential in direct drive applications are studied comparatively. The comparisons concern the differences of their inductance parameters, maximum power, cogging torque, phase EMF, MMF and their components, unbalanced magnetic forces and so on. Then winding design rules of this kind of PMBM when used in the direct drive field are given finally.Thirdly, the approach for achieving optimal flux-wakening for the permanent magnet brushless motor is introduced. Based on the magnetic circuit method, d-axis inductance differences between concentrated fractional-slot winding PMBM and distributed integral-slot winding one is analyzed, as a result, the conclusion that the concentrated fractional-slot winding PMBM features a good flux-weakening potential compared to its counter part is drawn theoretically.Finally, a permanent magnet brushless motor with concentrated fractional-slot windings for a flywheel drive application is designed. The dissertation gives some analytical and experimental results which are proved to be in coincidence with each other.