Permanent magnet motor temperature compensated constant torque control

Abstract

Temperature variation changes the flux remanence in the permanent magnets, the residual flux density of ferrite and neodymium magnet will decrease 19% and 12% with a temperature change of 100 degree. For electric motors with permanent magnet establishing the flux, the torque output of the motor will decrease with temperature rise if only the current is held constant. The permanent magnet synchronous motor are the most popular ones used in the electric vehicles for their efficiency, the usual way these motors are controlled is that the current is controlled according to the reference command, since torque is directly proportional to the current. The drawback is that if the temperature variation is nonnegligible, the torque output of the motor will vary noticeably with different temperatures. This article first analyzes the effect of temperature change on the motor; a control method is then introduced to compensate this effect.