Motor control apparatus

A motor control system designed to monitor a failure in a multi-phase dc motor is provided. The motor control system includes an inverter which controls an operation of the motor, a failure detecting circuit which monitors the voltage appearing at one of terminals of armature windings of the motor every active time when a PWM signal is at an active level to turn on switching elements of the inverter and determines occurrence of the failure based on the monitored voltage, and a switching operation prohibiting circuit which prohibits one of the switching elements connected to the one of the terminals of the windings of the motor from being turned on, thereby avoiding additional damages of the motor control system.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detailed description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.

In the drawings:

FIG. 1 is a block diagram which shows a motor control apparatus according to the first embodiment of the invention;

FIG. 2 is a time chart which shows an operation of a motor to be controlled by the motor control apparatus in FIG. 1;

FIG. 3 is a block diagram which shows a motor control apparatus according to the second embodiment of the invention;

FIG. 4 is a block diagram which shows a motor current detecting apparatus according to the third embodiment of the invention;

FIG. 5 is a time chart which shows a relation between voltage Vo indicating the current flowing through a motor and an operation of the motor;

FIG. 6 is a block diagram which shows a conventional motor control apparatus; and

FIG. 7 is a time chart which shows an operation of a motor to be controlled by the motor control apparatus in FIG.

6.

1. An apparatus for detecting a motor current flowing through delta-connected armature windings of a three-phase brushless dc motor when the motor is operated through a motor driver, comprising:

V

2=

A·N  (1)

where A is a constant of proportion which is given by a relation of A =k·/2 where k is a constant of electromotive force and is magnetic flux over one of the armature windings

Vo=VB−V

1−

V

2  (2)

where VB is a voltage supplied to the motor driver to operate the motor.

2. An apparatus as set forth in claim 1, further comprising an operation suspending circuit which suspends the operation of the motor for a preselected period of time when the voltage Vo exceeds a given threshold value.

3. An apparatus as set forth in claim 2, wherein said operation suspending circuit stops the operation of the motor completely when the number of times the operation of the motor is suspended reaches a preselected number.