| 摘要 |
1,261,821. Control of A.C. motors. DANFOSS A.S. 23 Jan., 1969 [23 Jan., 1968], No. 1558/69. Heading H2J. [Also in Division G3] A direct-current source is connected to a semi-conductor switch 4 associated with a filter 5 to produce a regulated voltage Ur which is applied to an inverter 9 for feeding a threephase motor 10. Control equipment for the switch 4 comprises a monostable multivibrator 13 which is connected to a pulse-width controller 14 and to a frequency controller 15. A switch 16 enables the pulse-width to be reduced to a predetermined value, whereupon the frequency is reduced. The switch 16 is operated by a discriminator 17 which compares the voltage Ur with a reference voltage applied to terminal 18. The current through resistor Rl is detected by switch 19 which is connected to the switch 16 either directly or through the discriminator 17 to limit the load current. The discriminator 17 also receives a signal representing the slip of the motor 10, and a process control signal. The switch 4 is constituted by a controlled rectifier which is associated with a capacitor adapted to be charged through diodes until a further rectifier receives a quenching impulse. The capacitor then discharges through a choke and gains a reverse charge to quench both rectifiers, Fig. 3 (not shown). The frequency controller 15 comprises a unijunction relaxation oscillator having a capacitor in series with a transistor whose base is connected through a Zener diode to the switch 16. The multivibrator 13 comprises two transistors coupled through a capacity for determining the pulse-width. The multivibrator controls a further transistor in series with the primary winding of a transformer having two secondary windings for supplying the respective firing and quenching pulses to the switch 4. The switch 16 comprises a transistor for controlling the rate of charge of the capacitor which determines the pulse-width. When this transistor becomes more conductive, the pulse-width is reduced as well as the frequency of the controller 15. The discriminator 17 is connected through intercoupled transistors to the switch 16. A further pair of transistors receives the currentsignal which exerts an over-riding control to block the output of the discriminator and reduce the pulse-width and frequency when a limiting value is exceeded, Figs. 4, 5 (not shown). |
