General Motors (GM) teaches us about, while promoting, their new permanent magnet (PM) electric motor. Forcing out 114 hp (85 kE) of torque, the new motor is set to be central to the Chevrolet Spark electric vehicle coming out in 2013. Of course, the full 114 hp will not be completely sustained during all operations, only about 75 hp can be maintained. However, peak power is available when the motor starts up, delivering instant torque.
A permanent magnet motor does not have a field winding on the stator. The permanent magnets provide the magnetic field for the rotor field to interact. In this case, there are windings on the permanent magnet ring, which are used to improve commutation under load. Large PM motors are not very common due to cost and difficulty with assembly. It has been difficult to find a material able to retain the high-strength field needed. Only with recent developments with neodymium magnets has GM, or any company, been able to use PM motors for large applications.
GM never mentioned the issues that might rise from the use of PM motors. Over saturation of the PM core can lead to over voltages or other control reliability issues. Occasionally, air gaps in the material left over after manufacturing may have to be repaired. Assembling of PM motors are also fraught with problems, electrocution being the biggest. High performance permanent magnets have inherent structural and thermal issues. As more work is done with PM materials, I am sure the issues can be subdued.
This may usher in a the wave of electric vehicles the world needs.
Eavesdropper
