DRIVE CIRCUIT FOR THREE-PHASE INDUCTION MOTOR AND DRIVE CIRCUIT FOR BRUSHLESS MOTOR

摘要

PROBLEM TO BE SOLVED: To obtain a drive circuit with which sine waves having a small torque ripple are driven without using a current sensor, through which an electrification phase matched to the magnetic flux of a motor can be achieved and whose drive efficiency is enhanced. SOLUTION: A pulse-width modulation is performed with one arm of a three- phase bridge circuit 5. The remaining arms are controlled to be turned off. A phase whose voltage which becomes the lowest from among three phases turns on only a lower arm. Other phases perform a pulse-width modulation by one arm, in such a way that a potential difference from the turned-on phase becomes a prescribed value. The direction of a current is detected by a current- polarity detection circuit, on the basis of the terminal voltage of a motor 1 and on the basis of a modulation signal. When the inversion of the direction of the current is detected, the arm which performs the pulse-width modulation is turned off, and a pulse-width modulation is performed by an opposite arm. The amplitude of a voltage is adjusted, in such a way that the zero-crossing timing of the phase of the voltage and the detecting timing of the inversion of the direction of the current becomes a fixed phase relationship.