Gearless Permanent Magnet Motor for Vehicle Traction Applications

SatCon proposes to develop a gearless high torque density permanent magnet machine for traction motor applications. The combination of a large diameter air gap, high coercivity rare earth magnets, and a high ratio of magnet length to pole pitch permits torque densities in excess of 1600 ft-lbs./ft(3) without the added complexity and inefficiency of a gear reducer. SatCon has developed and analyzed a conceptual design of a permanent magnet which is roughly 10 inches long by 23 inches i diameter. Initial analyses indicate that it can achieve 300 kW over an operating speed of 400-3600 rpm, while maintaining an efficiency of better than 93% down to 400 rpm. At 400 rpm and 300 kW the machine is producing 5280 ft-lbs. and, therefore, is achieving a torque density of 2200 ft-lbs./ft(3). the high efficiency of the motor and the absence of a gearbox allows overall efficiency of the motor and electronics to exceed 90% over the entire speed range. At speeds above 400 rpm the same power is achieved at even better efficiency, since the required torque falls off. Since the maximum power capability remains constant at 300 kW over the speed range, the terminal voltage required for maximum power need not change with speed. THis approach, known a field weakening, is commonly used with DC and induction motors. The phase I will proceed through requirements definition, design tradeoffs, and detail design to arrive at a optimum design which would be built and tested in a phase II. Emphasis will be given to efficiency, torque production and control, thermal management, control/commutation of phase currents, and drive inverter design and performance.