Torque-speed control system for asynchronous D.C. brushless motor

摘要

A closed loop, asynchronous control circuit for a brushless D. C. motor is disclosed. The motor includes a stator having two-phase windings and a permanent magnet rotor. A binary code corresponding to the stator poles is carried by the rotor, and is detected by a sensor upon rotation of the rotor. The sensor provides a feedback signal comprising a train of pulses having a repetition rate, or pulse width, proportional to the rotor speed. The feedback signal is supplied to a delay circuit, and a delayed control pulse train is supplied to a logic circuit which produces a two-phase output. The logic circuit output charges the polarities of the motor stator windings in accordance with the transitions of the control pulse train between high and low values, to thereby control the motor speed. The delay circuit is variable to control the speed of the motor. A variable supply provides a controlled voltage level to switching circuits which drive the motor under the control of the two-phase logic circuit output. The voltage level is varied inversely with the delay time of the delay circuit to control the motor torque-speed characteristic.