This paper presents the design, construction, analysis and test results of an axial-field, permanent-magnet (PM) brushless d.c. motor drive system for use on an electric bicycle. High-energy neodyminium-iron-boron (NdFeB) magnets and a multi-pole motor design are used to reduce the overall weight of the motor, The axial-field motor has an outer-rotor arrangement, with the shaft acting as the wheel hub. Radial spokes connect the motor frame with the road wheel, yielding a direct-drive system. To minimize maintenance and to eliminate the commutator and the associated problems, a permanentmagnet brushless d.c. motor configuration is adopted. The electronic controller is fed by two 12 V batteries and supply the motor armature winding. For speed control, a push-button device enables the duty cycle of the pulse-width modulated (PWM) inverter to be varied, thereby changing the average voltage applied to the motor terminals. For computation of the motor performance, two-dimensional finite element method (2-D FEM) is used and magnetic vector potential A is chosen as the variable. The FEM solver uses an iterative procedure in order to satisfy both the magnetic field and circuit equations. To study the feasibility of the design, a prototype motor drive system was constructed. Load tests on the motor were carried out using a special test jig. The good correlation between the theoretical and experimental results confirmed the accuracy of finite element modelling of the motor and the solution method. At an input current of 6.85 A (80% of rated value), the motor could deliver an output power of 74 W and a torque of 4.5 Nm at a speed of 160 r/min (which corresponds to a linear speed of 20 km/h). The test results indicate that both the power output and torque of the motor drive are sufficient for driving an electric bicycle of the power-assisted type, Le. one in which the pedals provide extra torque during acceleration and uphill journeys.
A novel brushless D.C. motor drive system for an electric bicycle
Ein neuartiges Antriebssystem für ein Fahrrad mit Hilfe eines bürstenlosen Gleichstrommotors
1999
10 Seiten, 6 Bilder, 1 Tabelle, 6 Quellen
Conference paper
English
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