Method and apparatus for minimizing torque ripple in a dc brushless

Abstract

A method for minimizing torque ripple in a permanent magnet brushless DC motor includes the steps of energizing a first winding of the motor to generate a first current, energizing a second winding of the motor to generate a second current, and overlapping the first and second currents in time by a preselected time to reduce torque ripple. The structure for performing the method includes conventional brushless DC motor drive circuitry responsive to a motor rotor position signal, and a speed control signal, to sequentially generate a gate drive signal for driving a respective semiconductor switch to energize each winding of the motor. The structure further includes a phase overlapping circuit interposed between the conventional brushless DC motor control circuitry output and the semiconductor switches used to energize each winding of the motor. The phase current overlap circuit includes a monostable multi-vibrator for generating a 'one-shot.' The pulse width or duration of the 'one-shot' determines the extent of the phase current overlap. The overlapping circuit detects transitions on the gate drive signal lines, and in response generates a trigger signal. The trigger signal triggers generation of the 'one-shot.' The overlapping circuit maintains two of its gate drive signals for the duration of the 'one-shot.'