Optical switches make motor a variable-speed drive

Oct. 26, 2006
The DynaMotor from DynaMotors Inc., Warrensville Heights, Ohio, uses optically controlled solid-state switches embedded in the rotor windings to control current and, thus, torque, making the motor a self-contained variable-speed drive.

Edited by Stephen Mraz

The DynaMotor from DynaMotors Inc., Warrensville Heights, Ohio (dynamotors.com), uses optically controlled solid-state switches embedded in the rotor windings to control current and, thus, torque, making the motor a self-contained variable-speed drive. The result is high torque on start-up and at low speeds.

The motor has a pair of opposed salient poles whose copper windings connect to two legs of a single or threephase line. The rotor resembles those in universal and dc motors, with slotted steel laminations stacked on a shaft. Copper wire is wound in opposite slots and the two ends of each coil are connected by a solid-state switch, such as a transistor. When the stator poles connect to an ac line, the resultant magnetic field varies with line current and flux passes directly through the rotor, inducing a voltage in each rotor coil. Closing the solid-state switch sends current through the coil, generating flux, torque, and rotation.

When the switch opens, current cannot flow and the coils stop generating torque and rotation. Closing the switch for longer periods produces more torque and increases the speed. Thus, how long, and over what rotational angle, the switches are open determines torque and speed.

A photodetector actuates each switch as it rotates past a stationary illuminated infrared LED. An array of LEDs mounted on the motor end-bell can be turned on for varying amounts of time to adjust motor speed. Rotation direction can be reversed easily without contactors or additional power electronics by merely turning on LEDs on the opposite side of each stator pole.

Optically controlled noncontact, solid-state switches eliminate traditional motor-drive pulse-width modulation that generates significant RFI and ground currents that prevent use on GFCI protected circuits.

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