Field-weakening operation of cylindrical permanent-magnet motors

For cylindrical permanent-magnet motors in the operation of field-weakening mode, this paper presents the way to develop maximum torque-outputs under the constraints of terminal voltages and armature currents. As compared with the conventional method of constant power operation, this design promotes the available torque-output and fully utilizes the potential of a motor drive, thus reducing the weight and size of a motor drive required to fulfill certain performance specifications. The minimum travelling time to reach a speed command by this design is also formulated so that it can be checked if the hardware capacity of a motor drive is intrinsically enough for specific performance requirement. Besides the promotion of available torque-outputs, another benefit of using this design is to extend the range of reachable speeds, which is important in the applications utilizing mechanical transmissions with high gear ratios.