| 摘要 |
PURPOSE:To detect a motor current accurately and stably by a method wherein commutating action is performed by igniting an auxiliary thyristor, and a current flowing in a commutating capacitor through a diode and a commutating reactor is detected. CONSTITUTION:When a chopper CH performs commutation, a negative commutating current being equal to the motor current IM flows in a commutating circuit. Therefore a current transformer CT is provided between the auxiliary thyristor ATh and the secondary winding N2 of a saturable reactor type current transformer SCT to obtain a voltage VCT corresponding to the commutating current, and by detecting thereof with a negative voltage detector VND, the voltage VN corresponding to the motor current IM can be obtained. Accordingly the motor current to flow in the commutating circuit merely for a short time can be detected synchronizing with the action of the chopper, and this device is most suitable for digital control, and is particularly so when a microcomputer is applied. |
