Transient modeling and performance of variable-speed permanent-magnet motors

The d-q equivalent circuit models for surface-mounted permanent magnet motors are presented and are validated through tests on a motor with neodymium-iron-boron magnets built in a 5 hp induction motor frame. The magnetic conductivity is shown to have a negligible effect on dynamic response. The response is limited mainly by the link voltage of the inverter. An expression is developed for the maximum stator current, which can be used without magnetic damage. Experimental results from the test motor show that an essentially linear relationship exists between torque and stator current, up to six times rated current, where the torque is about nine times its rated value as an induction motor.<>