The system consists of a brushless switched reluctance motor combined with high-power semiconductor switches and digital controls. The SR motor includes a rotor with no magnets or windings and a stator whose poles contain a winding, similar to a field of a DC motor. The SR system employs the principle of magnetic attraction to move the motor's rotor from pole to pole, creating rotation.
SR motor achieves rotation by the sequential energizing of stator poles. When the stator pole winding is energized, the nearest rotor pole is attracted into alignment with that stator pole (see Figure 1). The rotor will follow this sequence, attempting to align rotor poles with energized stator poles. However, as the rotor and stator poles align, the stator poles switch off and the next group of stator poles switch on, continuing the rotation of the rotor.
The switched reluctance motor generates continuous movement by consecutively switching the currents on and off, thus ensuring the poles on the rotor are continually chasing the stator current. The movement achieved is a function of the current flowing through the winding and the characteristics of the iron in the rotor. For added reliability, all LeTourneau SR Systems feature sensorless technology that allows the position of the rotor to be determined without external sensors (see Figure 2).
Insulated Gate Bi-Polar Transistor (IGBT) Switching
The success of Switched Reluctance technology has been made possible by utilizing the principle of magnetic attraction in conjunction with today's high-power semiconductor switches and digital control techniques. IGBT switching provides the required precise control of high horsepower SR motors. In addition, SR drives feature a motor coil in line with each IGBT, providing system impedance and a higher level of control over any type of system fault, resulting in a durable and reliable system.
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