Transient torque and short circuit capabilities of variable speed permanent magnet motors

A high performance motor drive must produce peak torque which is much larger than its continuously rated value. This paper analyzes the capability of two types of permanent magnet motors using NdFeB magnets and shows that an essentially linear relationship between torque and stator current can be achieved up to the order of 6 times rated current without magnet demagnetization. Also, the motors can be designed to withstand terminal short circuits without magnet damage. These properties have been experimentally verified on two laboratory motors.