Patent GB-1289546-A (GB)
IPC: G05F1/13
Filed: 1969-09-30
Abstract: 1289546 Automatic voltage regulation and control WESTERN ELECTRIC CO Inc 30 Sept 1969 [30 Sept 1968 (2)] 48068/69 Headings G3R and G3X A voltage regulator which has a ferroresonant operation but which does not use a saturating action to produce such operation, comprises a transformer core 11 carrying a primary winding 12 for connection to an A. C. supply and closelycoupled secondary windings 13, 14 which are separated from the winding 12 by a magnetic shunt 16 and which are respectively connected to a ferrocapacitor 18, rectifier 19 and load terminals 21, 22 and to an inductor 26 and a Triac 27 controlled by the voltage across an integrating network 28, 29. In operation the core 11 does not saturate to discharge the capacitor 18, but this action is produced by members 26--29 of which the capacitor 29 develops a voltage proportional to the volt-time integral of the voltage across the capacitor 18. When the voltage across capacitor 29 exceeds the breakdown voltage of that one of Zener diodes 25, 30 which is currently backbiased, the Triac 27 fires to connect the inductor 26 across the winding 14 and so cause the capacitor 18 to discharge indirectly through members 26, 27 and then recharge to the opposite polarity, completion of the latter action causing the Triac 27 to turn off. Variation of the A. C. supply to the winding 12 varies the charging time of capacitor 29, and hence the firing instant of Triac 27, to maintain constant the A. C. voltage across winding 13 or the D. C. voltage across terminals 21, 22. Additional stabilization of the latter voltage is provided by a retroactive control loop comprising a transistor 32 whose base receives the actual value of the D.C. voltage (sensed by divider 33), whose emitter receives a reference voltage set by a Zener diode 34 and whose collector-emitter path receives the A. C. voltage across resistor 28 as rectified by a bridge 31. Variations of the voltage across terminals 21, 22 thus vary the conductivity of transistor 32, whose collector-emitter path effectively shunts the resistor 28 to vary the resistance of the integrating network 28, 29 and hence the firing instant of the Triac 27. If closed loop regulation of the D. C. voltage is not required, winding 14 may be omitted and all of the components connected to windings 13, 14 may be connected to a single secondary winding, with or without taps. Resistor 28 may be made variable to vary the A. C. or D. C. output voltage. Typical operating waveforms are discussed for the basic regulating operation and closed loop control, Fig. 2 (not shown), together with the choice of such design parameters as the inductance of member 26 and the number of turns in windings 13, 14. Capacitor 18 may be connected across either of the windings 13, 14 or across a third winding closely coupled thereto. Zener diodes 25, 30 may be replaced by a bilateral diode switch (Disc) and the Zener diode 34 may be connected in series with the base of transistor 32. For operation at higher frequencies, the portion 40 of the regulator may be replaced by an arrangement comprising two oppositely-poled controlled rectifiers each in series with a respective inductor and each controlled by a respective capacitor and Zener diode, the two capacitors being in series with a common adjustable resistor, Fig. 3 (not shown). In another modification, Fig.4 (not shown), the portion 42 of the regulator is replaced by a linear inductor in series with the A.C. supply, which combination is connected to the capacitor 18 and to the primary winding of a transformer whose secondary winding is shunted by the members 26, 27. As before, this secondary winding may be omitted to reduce the transformer to a cored inductor with members 26, 27 and the integrating circuit connected in parallel therewith. The embodiment of Fig. 5 employs a transformer 311 having a centre leg 312 carrying a winding 316 connected to an A. C. supply, a winding 318 supplying load terminals 323, 324 and a winding 317 shunted by a ferrocapacitor 326 and tapped to provide connections to series-aiding windings 327, 328 carried by the outer legs 313, 314 and to the circuit including the integrating network 331. 332 and Triac 329. Magnetic shunts 319, 320 and air gaps 321 decouple windings 317, 318 from winding 316. In operation, firing of Triac 329 causes the windings 327, 328 to produce fluxes which respectively oppose and aid the flux produced in the centre leg 312, the effect being to prevent saturation of the outer leg 313 and speed up saturation of the outer leg 314. When saturation occurs, the impedance of winding 328 drops so that its flux no longer balances that produced by the winding 327 and further increase of flux in the centre leg 312 is prevented. This allows the capacitor 326 to discharge through the winding 317 and recharge to opposite polarity in ferroresonant manner. As before, the firing instant of the Triac 329 in automatically varied by the integrating network 331, 332 to maintain constant the voltage at terminals 323, 324, typical cycles of operation being described for different values of the resistor 331, Figs. 6 and 7 (not shown), together with a discussion of the advantages of producing ferroresonant operation by saturation of only the outer leg 314 of the transformer. In a modification, Fig. 8 (not shown), the portion 361 of the regulator is replaced by an arrangement in which the winding on the outer leg 314 is omitted and the winding on the outer leg 313 is short  circuited by the Triac 329 when it fires. The leg 314 still saturates and the method of operation remains the same. The connections of the capacitor 326 and Zener diode 339 may be modified as previously described for the embodiment of Fig.1. A further regulator is described, Fig. 9 (not shown) wherein the above-described modification of Fig.5 is constructed in two core form, the winding 316 being replaced by a linear inductor in series with the A.C. supply and the windings 317, 318 being carried on the centre leg of a conventional three-legged transformer.