In many industrial and domestic applications an electric motor is required to operate in the so-called constant power region. Constant power, when referred to an electrical motor, is characterised by a constant mechanical output power of the motor at any rated torque and speed.
The mechanical output power of a motor is the product of its torque and speed. For constant power operation, this means that at low speed, a high torque is generated and at high speed a low torque is produced. Electrical Vehicles (EV), washing machines and most domestic appliances, milling machines and many of industrial applications operate in constant power operation region. In selecting a low cost and low maintenance variable speed direct drive system for constant power applications, three drive systems can be considered. These drive systems are Induction Motor (IM) drive, Switched Reluctance Motor (SRM) drive and Permanent Magnet Brushless Motor (PMBM) drive.