Switched Reluctance Motor Drives
The name switched reluctance has now become the popular term for this class of electric machine. The first reference to the term switched-reluctance was made by Nasar in a paper in the IEE Proceedings in 1969. The term became popular from the 1980s onwards, through the efforts of the first commercial exploiters of the technology, Switched Reluctance Drives Ltd. The machines are alternatively known as variable reluctance motors, reflecting the origins of the technology being derived from VR stepper motors. Even so the first recognisable reluctance machines were built over 150 years ago, most famously by Davidson as a traction drive for an electric locomotive in 1838.
Key Features Of SR TechnologyPrinciple of Operation
The motor is doubly salient with phase coils mounted around diametrically opposite stator poles. Energisation of a phase will lead to the rotor moving into alignment with the stator poles, so minimising the reluctance of the magnetic path. This is the same principle of operation as the VR stepper motor. As a high performance variable speed drive, the motor's magnetics are optimised for closed-loop operation. Rotor position information is used to control phase energisation in an optimal way to achieve smooth, continuous torque and high efficency. The theoretical equations governing the torque production mechanism have been published countless times in the literature, so below is a simple graphical explanation. The current waveforms are superimposed on the angular unsaturated phase inductance. The maximum inductance corresponds to the minimum reluctance pole-aligned position. Positive torque is only produced at angles when the inductance gradient is positive.