Bigger and faster machines with higher requirements on power demand, control accuracy, system uptime, and lower life cycle costs have placed increasing demands on machine drives and has highlighted the need to simplify those drives. Development of practical permanent magnet synchronous AC electric motor technology permits lower speed and higher torque output as compared to a conventional AC induction motor. This technology permits reduction in the number of mechanical drive components required in many machine applications. In most cases, this technology permits elimination of a gearbox and reduces the mechanical drive to the coupling between the AC drive motor and machine section. The savings in the required machine-side footprint can be significant. Conventional induction motor speeds are normally about 900 to 1,800 RPM, requiring a gear reducer to match motor speed rating and section speed requirement. The corresponding gearless speeds are typically from 300 to 600 RPM. AC permanent magnet motors have proven high performance and flexibility at very wide speed ranges, making the direct drive concept feasible for most applications. In the direct drive motor, permanent magnets in "V"-shaped rotor slots replace the squirrel cage conductors of a conventional induction motor. In this new design rotor losses are extremely low, enabling higher stator current loading and a reduced size motor frame. The elimination of slip, due to the synchronous design, improves both motor efficiency and dynamic control performance of the entire drive.
