Research On Interior-modulating-ring Brushless Double-rotor Machine For Hybrid Electric Vehicles

In current hybrid system, the electronic continuously variable transmission system based on the planetary gear is the most mature one. However, the planetary gear, which is the key part of the system, is a pure mechanical structure. So there a re inevitable problems of vibration, noise and abrasion. To solve these problems, Many researchers have proposed various pure electrical schemes based on the compound-structure electrical machine. However, most of the schemes have brushes. The problems, such as the poor reliability of brushes and the severe heating problem of the inner rotor, limit their possibilities. To solve the above problems, an interior-modulating-ring brushless double-rotor machine(IMR-BDRM) is proposed in this paper. Cooprating with a traditional machine, the IMR-BDRM can replace the planetary gear system. It also solves the problems in those pure electrical schemes with brushes such as the poor reliability of brushes and the severe heating problem of the inner rotor. In this paper, the research work mainly focuses on the IMR-BDRM as follows.Firstly, the principle of the IMR-BDRM is analyzed. The relation of the pole pairs, the speed and the torque of the PM rotor, the modulating ring rotor and the stator magnetic field is deduced by the analysis of magnetic fields. Then a 2D finite element model is built for verification. The performance of the IMR-BDRM is compared with that of the planetary gear system to prove their consistency in the function.Secondly, the air-gap magnetic field distribution is analyzed. The magnetic field distributions of the IMR-BDRM and the traditional magnetic-field-modulated brushless double-rotor machine are compared and the discrepancy of electromagnetic performance is explained from the perspective of magnetic fields. The influence of the machine structure parameters on air-gap magnetic fields is investigated, to provide the reference for the electromagnetic scheme selection of the IMR-BDRM.Next, to improve the electromagnetic performance of the IMR-BDRM, the torque and the power factor of the IMR-BDRM is analyzed. The electromagnetic torque is deduced by virtual displacement method and the power factor is deduced by phasor diagram method. On the basis of the analysis result, the influence of the structure parameters on the electromagnetic performance is researched by finite element simulation, to provide the reference for the final scheme.Lastly, considering the large iron loss of the IMR-BDRM, the loss distribution is analyzed. The change law of the iron loss in different regions is researched under different operating conditions. A sinusoidal-permeance model is proposed to reduce the iron loss. The main idea of that is to minimize the harmonic permeance of air gap, thereby the harmonic magnetic fields can be restrained.