1、Comparison of Outer-Rotor Stator-Permanent-Magnet Brushless Motor Drives for Electric Vehicles K.T. Chau1, Senior member IEEE, Chunhua Liu1, and J.Z. Jiang2 1 Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, China 2 Department of Automation, Shanghai Unive
2、rsity, Shanghai, 200072, China AbstractIn this paper, two emerging outer-rotor stator-permanent-magnet (PM) brushless motor drives, namely the doubly-salient PM motor drive and the PM hybrid brushless motor drive, are firstly quantitatively compared, which are particularly attractive for serving as
3、in-wheel motor drives for electric vehicles. In order to enable a fair comparison, these two motor drives are designed with the same peripheral dimensions and based on the same outer-rotor 36/24-pole topology. By utilizing the circuit-field-torque time-stepping finite element method for analysis, th
4、eir steady-state and transient performances are critically compared. Moreover, the cost analysis of these two machines is conducted to evaluate their cost effectiveness. Index Terms Electric vehicle, Finite element method, Machinedesign, Permanent-magnet motor drive. I. INTRODUCTION In recent years,
5、 permanent-magnet (PM) brushless motordrives have been widely used in electric vehicles (EVs) 1-2.The doubly-salient PM (DSPM) motor drive and PM hybridbrushless (PMHB) motor drive are two emerging stator-PMbrushless motor drives which offer high mechanical integrityand high power density, hence sui
6、table for EV applications 3.Their outer-rotor motor structures are particularly attractive fordirect driving of EVs, especially for serving as in-wheel motordrives for EVs 4. However, a quantitative comparison of thesewo motor drives is absent in literature. The purpose of this paper is to newly com
7、pare two emergingouter-rotor stator-PM brushless motor drives, namely the DSPMand PMHB types. Based on the same peripheral dimensions,both motor drives are designed with the identical outer-rotor36/24-pole topology. By using the circuit-field-torquetime-stepping finite element method (CFT-TS-FEM) 5,
8、 thesteady-state and transient performances of both motor drives arecompared and analyzed. Moreover, the corresponding costeffectiveness will be revealed and discussed. Section II will introduce the motor drive systems and their configurations. In Section III, the design and cost effectiveness of tw
9、o motor drives will be compared. Section IV will discuss the analysis approach of these two motor drives. The comparison of their performances will be given in Section V. Finally, a conclusion will be drawn in Section VI. II. SYSTEM CONFIGURATION AND OPERATION MODES Fig. 1 shows the schemes of these
10、 two outer-rotor stator-PM motor drives when they serve as the in-wheel motor drives for EVs, especially for motorcycles. It can be seen that these in-wheel motor drives effectively utilize the outer-rotor nature and directly couple with the tire rims. So, these topologies can fully utilize the spac
11、e and materials of the motor drives, hence greatly reducing the size and weight for EV applications. Fig. 1. Topologies of proposed in-wheel motor drives. (a) DSPM. (b) PMHB The two motor drives configurations are shown in Figs. 2 and 3. It can be found that they have the similar three-phase full br
12、idge driver for the armature windings； while the difference is the H-bridge driver for the DC field windings of the PMHB motor drive. Hence, their operation principles are very similar, except that the controllable field current of the PMHB motor drive. For both motor drives, when the air-gap flux l
13、inkage increases with the rotor angle, a positive current is applied to the armature windings, resulting in a positive torque. When the flux linkage decreases, a negative current is applied, also resulting in a positive torque. For the PMHB motor drive, it can accomplish online flux regulation by tu
14、ning the bidirectional DC field current. When these two motor drives act as in-wheel motor drives and are installed in the EVs, they operate at three modes within the speed range of 01000rpm, namely the starting, the cruising, and the charging. When the EV operates at the starting mode, it needs a h
15、igh torque for launching or accelerating within a short time. For the DSPM motor drive, since its PM volume is much more than that of PMHB motor one, it can provide a sufficiently high torque for the EV starting. For the PMHB motor drive, the positive DC field current will be added to produce the ma
16、gnetic field together with the PM excited field, hence it also able to offer the high torque for the EV to overcome the starting resistance and the friction force on the road. When the EV runs downhill or works in braking condition, it works in the charging mode. In this mode, these two machines can
17、 play the role of electromechanical energy conversion, which recover or regenerate the braking energy to recharge the battery module. Furthermore, for the PMHB machine drive, it can fully utilize its flux controllable ability to maintain the constant output voltage for directly charging the battery,
18、 which is more flexible than the DSPM machine drive. When the EV runs in the cruising mode or in the steady speed, these stator-PM motor drives will enter the constant-power region. This speed range usually covers 400rpm1000rpm for the DSPM in-wheel motor drive. But for the PMHB motor drive, it not only can effectively extend its operating speed range up to 4000rpm which is enough to cover the conventional speed range requirement, but also can regulate its magnetic field situation which can make the power module working at the optimal operation point.
