Evaluation of Torque Characteristics in Saturated Magnetic Field for Permanent-Magnet Synchronous Motors

The evaluation of torque characteristics in saturated magnetic field for permanent-magnet (PM) synchronous motors is presented. Using the modified two-axis machine model that considers the cross-coupling effect, two important phenomena resulting from magnetic saturation are indicated: the decrease in magnet torque because of an anomalous flux of PMs and the existence of cross-magnetizing torque. These two kinds of torque characteristics cannot be considered by the conventional two-axis machine model, which assumes a constant value of induced electromotive force due to PMs. Measurement results indicate the validity of the modified method while they demonstrate the conventional method has difficulty in deducing torque components.