| 摘要 |
A control system for a three-phase motor has two triac switches connected in respective supply lines to the motor. Both switches are initially closed so that power is supplied to the motor on all three lines. After a predetermined time, when the motor has reached its operating speed, one switch is opened by a logic unit so that single phase power is supplied to the motor on two lines. One of the switches is subsequently periodically closed for short intervals, and the other switch is periodically opened for short intervals under control of a monostable unit, so as to produce hunting of the motor. Hunting of the motor is detected by a speed monitor responsive to the counter EMF of the motor. The system has a phase detector responsive to the phase relationship between signals on the supply lines which prevents the switches being closed if there is not the desired phase relationship between the signals. |
