Maximum torque-per-ampere control of a saturated surface-mounted permanent magnet motor

The surface-mounted permanent magnet (SMPM) synchronous motor has high torque density and good dynamic response. Consequently, these machines have found applications in electric/hybrid vehicles, where size and volume are at a premium and dynamic response is important for vehicle performance. In these applications, high torque output from the motor is required for short time duration. The high stator current associated with this mode of operation can induce saturation in portions of the motor magnetic circuit and thus introduce saliency into a normally symmetric machine. This phenomenon can be exploited in order to maximize the torque output of the motor for the same stator current. The case of a 75 kW SMPM machine for automotive application is presented. By taking advantage of the saturation induced reluctance torque, up to 4% extra torque output is produced for the same maximum stator current. The improved performance is predicted using FEM calculations and is verified through experimental results.