Speed control of a motor

Abstract

A three-phase motor having three Hall-effect devices for production of as many rotor position signals for use in excitation control of its windings, the signals being indicative of the angular position of the motor rotor with respect to the stator and having phase differences of 120 degrees. A motor speed control system is disclosed which utilizes the rotor position signals for detection of the actual running speed of the motor. Included are differentiating circuits connected one to each Hall-effect device for producing outputs in prescribed phase relationship with the rotor position signals. Connected to the differentiating circuits, switching transistors are controlled by binary switch control signals derived from the rotor position signals, passing the positive half-waves, or approximately positive half-waves, of the differentiating circuit outputs. The thus-obtained half-waves are then added together into a motor speed signal representative of the actual running speed of the motor. This signal is subsequently compared with a target speed signal indicative of a desired running speed of the motor, and the difference, if any, therebetween is fed as a speed control signal into a motor excitation circuit, which responds to both the rotor position signals and the speed control signal for exciting the motor windings for rotation at the desired speed.