Constant speed control for a motor

A motor control circuit for use with a power source, a rotating assembly, and a stationary assembly in magnetic coupling relation to the rotating assembly and including a winding, said control comprising:

• a power switching circuit including power switches adapted to selectively connect the power source to the winding during a commutation period, said power switches for receiving gate drive signals for selectively energizing the winding to generate a magnetic field which causes the rotating assembly to rotate relative to the stationary assembly;
• a circuit generating a speed signal representative of a rotational speed of the rotatable assembly relative to the stationary assembly;
• and
• a commutating circuit responsive to the speed signal and including a generating circuit for generating commutation signals corresponding to the speed signal, the commutation signals for controlling the power switches, said commutating circuit providing the gate drive signals for commutating the power switches at a commutating angle for a commutation period, said commutating circuit determining a difference between a reference representing a desired rotational speed of the rotating assembly and a repetition rate of the commutation signals, which repetition rate corresponds to an actual rotational speed of the rotating assembly, said commutating circuit retarding the commutating angle of the commutation period and/or decreasing a length of the commutation period by delaying a start of ON time of the gate drive signals when the determined difference indicates that the actual speed of the rotating assembly is greater than the desired rotating speed to maintain a substantially constant rotating speed of the rotating assembly whereby the efficiency of the motor is reduced to maintain the substantially constant rotating speed.

A motor for use with a substantially constant power source comprising:

• a rotating assembly;
• a stationary assembly in magnetic coupling relation to the rotating assembly and including a winding;
• a power switching circuit including power switches adapted to selectively connect the power source to the winding during a commutation period, said power switches for receiving gate drive signals for selectively energizing the winding to generate a magnetic field which causes the rotating assembly to rotate relative to the stationary assembly;
• a circuit generating a speed signal representative of a rotational speed of the rotatable assembly relative to the stationary assembly;
• and
• a commutating circuit including:
• a generating circuit responsive to the speed signal for generating commutation signals corresponding to the speed signal, said commutation signals for controlling the power switches;
• a comparing circuit for determining a difference between a reference representing a desired rotational speed of the rotating assembly and a repetition rate of the commutation signals, which repetition rate corresponds to an actual rotational speed of the rotating assembly;
• and
• a delay circuit providing the gate drive signals to the power switches, said delay circuit delaying the switching of the power devices by the gate drive signals relative to the commutation signals when the determined difference indicates that the actual rotational speed of the rotating assembly is greater than the desired rotational speed to maintain a substantially constant rotating speed of the rotating assembly whereby the efficiency of the motor is reduced to maintain the substantially constant rotating speed.