Driving control apparatus for brushless motor with optimum controlled

Abstract

A position detector detects the position of a rotor of a brushless motor. A driving signal generator generates a driving signal at a timing corresponding to the detected position. While the driving signal is received, a driving circuit sequentially ON/OFF-operates switching elements of an inverter circuit. At this time, a rotational speed detector detects a rotational speed of the brushless motor. A rotational speed controller controls the duty of ON/OFF operations of the switching elements, performed by the driving circuit, through a chopper signal generator in accordance with the difference between a detected rotational speed and a designated rotational speed. If the detected rotational speed does not reach the designated rotational speed even when the duty becomes a preset value or more, the rotational speed controller generates a phase shift signal for advancing the phase of the driving signal from that of a driving signal in a normal operation, and supplies it to the driving signal generator. Upon this phase shift operation, in the brushless motor, a magnetic flux effectively acting from the rotor to armature windings is reduced as compared with a magnetic flux in a normal operation. Thus, the rotational speed of the brushless motor can be reliably set to a desired value without decreasing the operation efficiency.