| 摘要 |
<p>1,255,040. Control of A.C. motors. DANFOSS A.S. 10 March, 1969 [16 March, 1968], No. 12374/69. Heading H2J. An asynchronous motor 26 is supplied from rectifier 12 through a voltage regulator 15 associated with a battery-fed resistor 16, for adjusting the output voltage of the regulator, and a voltage divider 18, 19, connected across leads 13, 14. An intermediate circuit comprises choke 21 and capacitor 22 for smoothing voltage U1 which is applied to an inverter comprising controlled rectifiers 24 and diodes 25, and incorporating a common quenching circuit 27. The voltage U1 is also applied to frequency regulator 29 which transmits pulses to a control device 30 feeding the quenching circuit 27, at a frequency much greater than the mains frequency, and which provides the rectifiers 24 with triggering pulses. When the regulator voltage is reduced for lowering the motor speed, the frequency is also reduced but the motor operates only slightly above synchronous speed and the regenerated current is easily absorbed by the capacitor 22. The voltage regulator 15 may comprise a controlled rectifier shunted by a diode, a quenching rectifier, and a series arrangement comprising a choke and a commutating capacitor. The controlled rectifier is triggered to pass pulses at a predetermined frequency, the width of these pulses being determined by the firing of the quenching rectifier in dependence upon the required voltage, Fig. 5 (not shown). The frequency regulator 29 comprises a transistor which receives the control voltage U1 and charges a capacitor in proportion. When the capacitor voltage reaches a threshold value, the capacitor discharges through a unijunction transistor the base of which is connected to output terminals through a transformer, Fig. 7 (not shown).</p> |
