Design And Analysis Of A Less-rare-earth Brushless Motor With Hybrid Permanent Magnet Material For Electric Vehicles

With the development of economy, vehicle industry is thriving. Though vehicles bring convenience to our lives, they also have caused the deterioration of energy crisis and environmental pollution. Therefore, electric vehicles which possess characteristics of energy conservation and environmental protection have become the new trend of the future auto industry. As the core component of electric vehicle drive system, permanent magnet brushless motors are widely used in auto industry due to their high torque density and high power density, etc. The rapid depletion of rare-earth resources have emerged with the wide use of rare earth resources in the permanent magnet motors. Due to the lack of reasonable and sensible planning of the use of rare earth resources, the price of rare earth permanent magnet is still on the continuous rise,which make the non-rare-earth or less-rare-earth permanent magnet motors raise considerable attention.The paper proposes a hybrid permanent magnet material brushless(HPMM-BL)motor which solves the problems of rare earth resources crisis and satisfies the requirements of the electric vehicles traction motors. The motor not only reduces the manufacturing cost, but also offers relatively wide constant power operating range and high efficiency during the whole speed regulation range.Thereafter, based on the design theory of traditional permanent magnet brushless motors, a new design method, which takes hybrid permanent magnets and various driving conditions of electric vehicles into consideration, is given to the HPMM-BL motor for electric vehicles. Besides, design process of the motor structure and calculation process of key parameters are described in details.Moreover, the comprehensive optimization method which based on the motor rated operating point and multi operation modes is proposed. The optimization method can not only realize the low cogging torque, high electromagnetic torque andlow cost at the rated operating point, but also widen the constant power speed regulation range, improve the efficiency during the whole speed regulation range, and the operating performance at UDDS working cycle.As the ferrite permanent magnet is easy to be demagnetized, the paper analyzes the demagnetization performances of the HPMM-BL motor under the rated load and the overload condition. In addition, by comparing the electromagnetic performance of the HPMM-BL motor and the pure earth permanent magnet brushless motor of the same power rating, the proposed HPMM-BL motor is proved to possess well electromagnetic performance and speed regulation characteristics.Finally, a prototype machine of the HPMM-BL motor is manufactured and the experiment platform is built. On this basis, no-load and load characteristics of the HPMM-BL motor are tested, hence verifying the reliability and validity of the motor structure and the proposed optimization method.