US2814773A - Voltage regulator - Google Patents

Description

Nov. 26, 1957 J. s. comms ETIAL 2,814,773

- VOLTAGE REGULATOR Filed Feb. 4, 1957 9 Sensing Circuit OUT SUPPLY Suturcble Reactor Magnetic Amplifier JAMES S. COMINS PAUL J. GALLAGHER INVENTORS ATTORNEY VOLTAGE REGULATOR James S. Ccmius, Stamford, Conn, and Paul J. Gallagher,

Mamaroneck, N. Y., assignors to Sorensen & Company, Inc, Stamford, Conn, a corporation Application February 4, 1957, Serial No. 638,131

9 Claims. (Cl. 32366) This invention relates to a voltage regulator which receives power from an alternating current supply and delivers regulated voltage to an alternating current load. It has particular reference to the combination of a saturable reactor and a magnetic amplifier for producing a regulated voltage which remains substantially constant while the supply voltage varies through a wide range of voltage values.

Many types of voltage regulators have been proposed and used. Many of these have employed vacuum tubes as passing impedances or in conjunction with an amplifier means for strengthening the error voltage determined by a sensing circuit. The present invention employs a saturable reactor in series with an autotransformer for controlling the input voltage. A double core magnetic amplifier is employed to amplify the error voltage sensed by an output sensing circuit and apply it to a control circuit on the saturable reactor. The sensing circuit includes two Zener rectifier units. Details of the novel circuit will be described hereinafter.

One of the objects of this invention is to provide an improved alternating current voltage regulator which avoids one or more of the disadvantages and limitations of prior art arrangements.

Another object of the invention is to control and regulate an alternating current supply line which is devoid of vacuum tubes, space discharge elements, and all components containing glass.

Another object of the invention is to use a bridge type sensing circuit containing Zener diodes, these diodes having the property of a constant voltage characteristic in the potential region which is normally in the reversed current direction.

Another object of the invention is to simplify and improve the construction of alternating current voltage regulators.

The invention includes input terminals which are to be connected to an alternating current supply line in series with a portion of an alternating current transformer and two reactor coils on a saturable reactor. A bias flux is produced by a transformer connected to a pair of load terminals and a magnetizing coil on the saturable reactor in series with two rectifier components. This circuit produces a direct current which partially saturates the core and makes the device more sensitive. The sensing circuit inculdes a step-down transformer and a rectifier system which applies a direct current to a sensing bridge so that an error signal may be obtained. The bridge includes two Zener diodes and the output of the opposite junction points of the bridge is applied to a magnetic amplifier, the output of which is connected to a control circuit on the saturable reactor.

One feature of the invention includes a positive feedback connection between a winding on the magnetic amplifier and the control winding on the saturable reactor. Another feature of the invention includes a nega tive feed-back circuit from the magnetic amplifier to a portion of the control circuit on the saturable reactor in atent O ice order to prevent hunting and low frequency oscillations.

For a better understanding of the present invention, together with other and further objects thereof, referonce is made to the following description taken in con nection with the accompanying drawing. The figure is a schematic diagram of connections of the voltage regulater.

in the figure a pair of input terminals 10, 11, are provided for connection with an alternating current supply which may vary over a wide range of voltage values. One terminal 10 is connected to a tap on an autotransformer 12 which includes windings 13 and 14. A saturable reactor 15 has two of its windings 16 and 17 connected in series with each other and connected between input terminal 11 and one end of winding 14. Saturable reactor 15 includes a three-legged core 18 with two control windings 2t and 21 positioned on the central leg.

The voltage regulator also includes output terminals 22 and 23 which are to be connected to a load 24. Terminal 22 is connected to one end of autotransformer winding 13 while terminal 23 is connected directly to input terminal 11.

In order to obtain a direct current which may be used for a magnetic bias, a step-down transformer 25 has its primary winding 26 connected to terminals 22 and 23 while the secondary winding 27 of this transformer has its end points connected to rectifiers 28 and 30, the cathode portion of these rectifiers being connected to one side of bias winding 29 while the other side is connected to the mid-point of secondary winding 27.

in order to sense the output voltage across the load 24 a sensing transformer 31 is provided. This transformer includes a primary winding 32 which is connected across output terminals 22, 23, and a secondary winding 33 which is coupled to a sensing bridge 34. Rectifiers 35 and as are connected in series with the ends of winding 33 with their cathodes connected together to supply positive pulses for the bridge. The mid-point of winding 33 is connected to the negative terminal of sensing bridge 34. In order to eliminate a major portion of the alternating current components a reactor 37 is connected in series between the sensing bridge and the rectifiers.

The sensing bridge 34 comprises four arms, resistors 38 and 40 and Zener diodes 41 and 42, connected as indicated. The Zener diodes, it should be pointed out, are connected in the circuit in a manner which is opposite to the usual conductive connection. That is, the rectifier component which is usually the cathode is connected to the positive source while the component which is usually the anode is connected to the negative side. Rectifiers connected in this manner pass very little current for all values between zero potential and the Zener voltage, but when the Zener voltage is reached a large current is passed. Since these Zener diodes are selected so that their Zener voltage corresponds to the applied potential across them, they represent constant voltage circuit elements and for this reason are particularly adapted for use in a sensing bridge, practically all the voltage variation being applied across resistors 38 and 40.

The current from sensing bridge 34 is transferred by conductors 43 and 44 to control windings 45, 46, on magnetic amplifier cores 47 and 48. These cores are supplied with magnetic flux by means of power windings 50 and 51 which receive rectified current pulses from the conductors connected to terminals 22 and 23. The paths of these currents may be traced as follows: When terminal 22 is positive, current flows over conductor 49, through rectifier 52, through winding 51, over conductors 53 and 54 to coil 21, then through resistor 55, rectifier 56, to the other side of the line by way of conductor 57. When terminal 23 is positive, current flows over conductor 57,

through rectifier 58, over conductors 53 and 54, through coil 21 (in the same direction as before), through resistor 55, through coil 50 on core 48, through rectifier 60, over conductor 49 to terminal 22. This circuit provides magnetic biasing action to fully saturate cores 47 and 48 and also provides magnetic biasing for core 18 by means of the current in coil 21.

In addition to the above components and control cir cuits there are two feed-back circuits, one positive and the other negative. The positive feed-back circuit increases the direct current amplification of the magnetic amplifier. This feed-back circuit can be traced from the upper end of resistor 55, through inductor 61, through resistor 62, then through coils 63 and 64 on cores 48 and 47, and back to the lower end of resistor 55. The current through coils 63 and 64 is obviously proportional to the voltage across resistor 55, which in turn varies with the current in coil 21 and coils 50 and 51. An increase in current through coils 50 and 51, causing increased magnetic saturation in cores 47 and 48, increases the voltage drop across resistor 55 and current through coils 63 and 64, thereby producing an additional increase in magnetic core saturation. The degree of feed-back can be conveniently adjusted by varying the resistance of resistor 62.

The negative feed-back circuit operates between the input and output of the magnetic amplifier. This circuit has only a small effect on the direct current amplification of the magnetic amplifier and is used to modify the alternating current response of the magnetic amplifier in such a manner as to prevent low-frequency oscillation or hunting. The negative feed-back circuit may be traced from the positive conductor 66 of the sensing bridge supply, over conductor 54 to the upper portion 67 of coil 21, then through resistor 68 to the negative conductor 70 of the sensing bridge supply. It will be apparent that this negative feed-back circuit eilectively couples the magnetic amplifier input (the sensing bridge) and the magnetic amplifier output (coil 21). Coil 21 is shunted by a resistor '71 which helps to reduce abrupt voltage pulses across this winding.

The operation of the circuit as a voltage regulator is as follows: If the load impedance is increased or if the A. C. supply voltage is increased, the voltage across the output terminals 22, 23, is increased and this increment in voltage is applied to the sensing bridge 34 on conductors 66 and 70. Because the Zener diodes are operating on a constant voltage part of their characteristic, the entire voltage increment is impressed on conductors 43 and 44 and produces a current increase in coils 4-5 and 46 on saturable cores 47 and 48. This increase acts to increase the negative bias ampere-turns which are in opposition to the ampere-turns caused by windings 50 and 51. The result is a decrease of magnetic saturation in cores 47 and 48 and a corresponding increase in inductance of coils 50 and 51 thereby reducing the current flow into coil 21 on core 18. The reduced current in coil 21 reduces the magnetic saturation of core 18 and increases the inductance of coils 16 and 17 to lower the voltage across the output terminals 22, 23, to the original desired value.

Having thus fully described the invention, what is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A voltage regulator for an alternating current supply system comprising; a coupling circuit which transfers alternating current power from a pair of input terminals to a pair of output terminals connected to a load; said coupling circuit including a variable impedance which may be controlled to vary the voltage at the output terminals, a voltage sensing circuit connected across the output terminals for determining an error voltage; and a coupling means between the sensing circuit and a control means in said variable impedance which changes the impedance in response to the error voltage; said coupling means including a magnetic amplifier having an input circuit connected across a portion of said voltage sensing circuit, an output circuit connected tosaid control means,

Al and a positive feed-back circuit which includes windings on each of a pair of saturable cores in the magnetic amplifier connected in parallel with an impedance in series with said output circuit.

2. A voltage regulator for an alternating current supply system comprising; a coupling circuit which transfers alternating current power from a pair of input terminals to a pair of output terminals connected to a load; said coupling circuit including a variable impedance which may be controlled to vary the voltage at the output terminals, a voltage sensing circuit connected across the output terminals for determining an error voltage; and a coupling means between the sensing circuit and a control means in said variable impedance which changes the impedance in response to the error voltage; and coupling means including a magnetic amplifier having an input circuit connected across a portion of said voltage sensing circuit, an output circuit connected to said control means, and a negative feed-back circuit which includes a portion of said control means which is connected in parallel arrangement with a direct current supply which energizes a portion of said voltage sensing circuit.

3. A voltage regulator for an alternating current supply system comprising; a coupling circuit which transfers alternating current pOWer from a pair of input terminals to a pair of output terminals connected to a load; said coupling circuit including a saturable core reactor whose reactance is controlled by the direct current in a control winding to vary the voltage at the output terminals; a voltage sensing circuit connected across the output terminals for determining an error voltage; and a coupling means between the sensing circuit and said control winding in said saturable reactor which changes the reactance in response to the error voltage; said coupling mean including a magnetic amplifier having an input circuit connected across a portion of said voltage sensing circuit, and output circuit connected to said control winding, and a positive feed-back circuit which includes windings on each of a pair of saturable cores in the magnetic amplifier connected in parallel with an impedance in series with said control winding.

4. A voltage regulator for an alternating current supply system comprising; a coupling circuit which transfers alternating current power from a pair of input terminals to a pair of output terminals connected to a load; said coupling circuit including a saturable core reactor whose reactance is controlled by the direct current in a control winding to vary the voltage at the output terminals; a voltage sensing circuit connected across the output terminals for determining an error voltage; and a coupling means between the sensing circuit and said control winding in said saturable reactor which changes the reactance in response to the error voltage; said coupling means including a magnetic amplifier having an input circuit connected across a portion of aid voltage sensing circuit, an output circuit connected to said control winding, and a negative feed-back circuit which includes a portion of said control winding which is connected in parallel arrangement with a direct current supply which energizes a portion of said voltage sensing circuit.

5. A voltage regulator for an alternating current supply system comprising; a coupling circuit which transfers alternating current power from a pair of input terminals to a pair of output terminals connected to a load; said coupling circuit including a saturable core reactor whose reactance is controlled by the direct current in a control winding to vary the voltage at the output terminals; a voltage sensing circuit connected across the output terminals for determining an error voltage; and a coupling means between the sensing circuit and said control winding in said saturable reactor which changes the reactance in response to the error voltage; said coupling means including a magnetic amplifier having an input circuit connected across a portion of said voltage sensing circuit, an output circuit connected to said control winding, a positive feed-back circuit which includes windings on each of a pair of saturable cores in the magnetic amplifier connected in parallel with an impedance in series with said control winding, and a negative feed-back circuit which includes a portion of said control winding which is connected in parallel arrangement with a direct current supply which energizes a portion of said voltage sensing circuit.

6. A voltage regulator for an alternating current supply system comprising; a coupling circuit which transfers alternating current power from a pair of input terminals to a pair of output terminals connected to a load; said coupling circuit including a saturable core reactor having two reactance windings and a control winding, the reactance of said reactance windings controlled by the direct current in the control winding; a voltage sensing circuit connected across the output terminals for determining an error voltage; and a coupling means between the sensing circuit and the control winding in the saturable reactor which changes the reactance in response to the amplitude of the error voltage; said coupling means including a magnetic amplifier having two saturable paramagnetic cores, an input circuit, an output circuit, and electrical means for saturating the cores; said output circuit connected to the control winding on the saturable reactor; a positive feed-back circuit which includes windings on each of said cores in the magnetic amplifier, said windings connected in series and arranged to receive a current from the output circuit of the magnetic amplifier; and a negative feedback circuit which includes a portion of said control Winding connected to a direct current supply which is derived from the voltage sensing circuit.

'7. A voltage regulator as set forth in claim 6 wherein said positive feed-back circuit includes in series connection, an inductor for suppressing alternating current components, and a variable resistor for adjusting the magnitude of the feed-back.

8. A voltage regulator as set forth in claim 6 wherein said magnetic amplifier input circuit includes two coils connected through rectifier components to the load, said rectifier components arranged to apply only positive pulses to one of said coils and only negative pulses to the other of said coils.

9. A voltage regulator as set forth in claim 8 wherein said two coils are both connected to the control coil in the saturable reactor and arranged to send current through said coil in one direction only.

No references cited.

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