The present invention relates to a motor drive apparatus, and particularly to a motor drive apparatus which drives a 3-phase brushless motor without using a Hall sensor.
There has heretofore been known a motor drive apparatus which drives a 3-phase brushless motor without using a Hall sensor. In the motor drive apparatus, the position of rotation of a rotor is detected using back electromotive forces (B-EMF) generated in coils of a stator by the rotation of the rotor instead of the detection of the rotational position of the rotor by the Hall sensor. Based on the result of detection, 3-phase PWM voltages 120° out of phase with one another are applied to 3-phase coils.
As one example of such a motor drive apparatus, there is cited a configuration disclosed in a patent document 1 (Japanese Unexamined Patent Publication No. 2006-217681 (FIGS. 1 and 2)). Although such a configuration that the position of rotation of a rotor is detected by detecting a zero cross point of each drive voltage has been disclosed in the patent document 1, there is a need to temporarily interrupt a drive current of a position detection phase at a predetermined timing for the purpose of the above. A problem, however, arises in that the interruption of the drive current results in the occurrence of motor's torque ripples and noise at motor driving.
An interruption time of each drive current is determined depending on to which extent it is caused to adapt or correspond to variations between motor’ phases and sudden acceleration of the motor. As the range in which it is caused to adapt thereto, becomes wider, the interruption time increases and noise becomes large. Therefore, a stable position detection and noise at motor's driving were placed in a trade-off relationship.
In recent markets, however, there has been a demand for provision of a motor drive apparatus which performs driving that reduces noise in Hall sensorless form. There has been a demand to improve the trade-off relationship between the stable position detection and the noise at the motor driving.