Performances Comparison of Permanent Magnet Brushless DC and Doubly Salient Reluctance Motors for an Urban Electric Vehicle
Résumé
In this paper, we carried out a dimensional parametric analysis of average torque and copper losses in the case of two synchronous brushless motors. These motors were, on the one hand, a Permanent-Magnet Brushless DC (PMBLDC) motor supplied by quasi-square currents, with surface magnet mounted rotor and trapezoidal e.m.f. waveform, and, on the other hand, a Doubly Salient Variable Reluctance (DSVR) motor fed by quasi-square currents at low speed, and by full wave square voltage at high speed. Comparison of these machines is interesting because of their potentially easy building and assembling and because of their rudimentary supply waveforms that accept a low resolution and low cost position sensor. The proposed study is analytical so as to establish an elementary comparison. Magnetic material properties, however, are taken into account and basic sizes are external stator diameter D and stack length L. To make comparison easier, we tried to make as many analogies as possible between both motors, whose basic parameters are defined in chapters 2 for DSVRM and 3 for PMBLDCM. As an example, we chose dimensions D = 250 mm, L = 150 mm, and copper losses were computed for a torque value of 100 N.m. These values correspond to an electric city vehicle with a power of about 26 kW from 2,500 to 10,000 rpm. Both compared motors have three phases ; the reluctance machine has a 6/4 structure and PMBLDC machines (Sm-Co and ferrite magnets) have two pairs of poles and only one slot per pole and per phase. In the case of the permanent magnet motor, ceramic and samarium-cobalt magnets were considered. In chapter 4, we presented a synthesis of the comparison of the motors based on our example. This comparison showed that the performances of a switched reluctance motor are close to those of a high energy permanent-magnet motor thanks to the former's short winding ends and good slot filling factor, insofar as the airgap is sufficiently small, in accordance with the requirements of electric vehicles. In the last chapter, the main experimentation results of a 27 kW designed and built 6/4 DSVRM are given.
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