MIT Department of Electrical Engineering & Computer Science

SPECIAL EECS SEMINAR

Wednesday, May 17, 1995
Grier Room A, 34-401A

Refreshments at 2:00 PM
Talk at 2:15 PM

[Note the change in date, time, and place.
The talk was previously scheduled for May 18]

Surface-Mounted Permanent Magnet Synchronous Motors and Power Electronics for Direct-Drive Electrical Vehicle Propulsion

John Ofori-Tenkorang
Massachusetts Institute of Technology

Recent environmental legislation in the United States aimed at reducing urban atmospheric pollution has rekindled interest in the development of battery-powererd electric vehicles. In the states of California, New York, and Massachusetts for example, 2% of all vehicles sold by 1998 are expected to have zero emissions and this quota will rise to 10% by 2003. Many technological innovations still remain to be achieved in order to improve the performance of electric vehicles. First on the list is the development of high capacity, low weight traction batteries for extended driving range. The next is the development of a high torque, low weigth direct-drive wheelmotor for a more efficient powertrain. By integrating the drive motor with the wheel, one can eliminate the need for transaxles, differentials, clutches and bulky reduction gears, thus reducing the weight of the vehicle and simplifying the mechanical design of the vehicle. With wheelmotors, losses deriving from the mechanical transmission and the drive line are eliminated, yielding significant improvements in the efficiency of the drive system from battery to wheel.

In this seminar we describe the overall system design of a candidate permanent magnet synchronous wheelmotor and power electronics drive. The motor is capable of producing 65 Nm of peak torque from 0 to 220 rpm, with constant power operation up to a maximum speed of 1100 rpm, corresponding to a road speed of approximately 85 mph for a 16 inch wheel (26 inches with tire). We discuss the stringent requirements for a wheelmotor operating in a harsh automotive environment, space limitations in the hub of the wheel and issues relating to the choice and configuration of the rotor magnets and armature design for high torque production, improved heat transfer, and economical manufacturing. A 5:1 constant power speed range is achieved with novel power electronics, thus circumventing the need for flux weakening and the associated compromise in efficiency. The active mass of the resulting motor is only 9 kg and the total efficiency, from traction battery to wheel, is 86% for the Federal Urban Driving Schedule (FUDS) and 88% for the Federal Highway Driving Schedule (FHDS).