US2328037A - Voltage regulator - Google Patents

Description

Aug. 31, 1943. c. M. SUMMERS 2,323,037

VOLTAGE REGULATOR Filed Aug. 14, 1940 IMPEDANCE \J'AGE To souncz T0 SOURCE TO SOURCE T0 LOAD &

Fig. 5.

ofl i O I nventor":

Claude Ml Summers,

His Attorney.

Patented Au 31, 1943 VOLTAGE REGULATOR Claude M. Summers, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Application. August 14, 1940, Serial No. 352,569

11 Claims. (Cl. 171242) This invention relates to automatic Voltage regulators and more particularly to improvements in static circuits for producing a constant output voltage over a wide range of variation of input voltage or of output current or both, the variation in output current being in magnitude or power factor or both.

An important feature of the invention comprises a very sensitive and accurate Wide range impedance means which exhibits a constant volt.- age drop over a wide range of current variation. This impedance means is connected in parallel or shunt circuit relationship with a load whose voltage is to be maintained constant. In this manner variations in suppy voltage, or load magnitude, or load power factor or a combination thereof are automatically corrected for. Thus, if the supply voltage varies, my novel variable impedance means automatically adjusts itself so as is made adjustable by means of a variable voltage auto-transformer; Fig. 4 is a further modification in which the series impedance means has constant current characteristics, and Fig. 5 is a set of volt-ampere characteristics for illustrating the principle of operation for, the constant current portion of Fig. 4..

Referring nowto the drawing and more particularly to Fig. 1, my circuit comprises a pair of input terminals l in series with which is an impedance 2, and a pair of output terminals 3 in parallel withwhich is an impedance means 4 comprising a serially-connected capacitor 5 and a reactor 6. The impedance 2 may be of any kind such as a resistor, a reactor, a capacitor or any combination thereof. Occasionally the inherent internal impedance of a source of current supply will be sufficient as in supply circuits or current sources which have unusually larly, if'the load current varies, the change in voltage drop in the supply circuit causes my novel sufficiently to compensate for the change in impedance of the load. This compensation is characterized by maintaining the vector sum of the supply voltage and the series impedance voltage a constant in magnitude, but not necessarily a constant in phase angle. As'the vector sum of these two voltages equals the load voltage and as the vector sum of all three voltages mustequal zero, it will be seen that the magnitude of the load voltage is independent of the load current.

An object of the invention is toprovide a new and improved regulator'circuit.

Another object of the invention is to provide a new and improved automatic voltage regulator circuit having no moving parts.

The invention willbe better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

' In the drawing Fig. 1 illustrates diagrammat-' poor inherent regulation,

The reactor 6 has a special volt-ampere characteristic indicatedby the curve I in Fig. 2. This curve has a sharp knee or bend near the origin and is practically a straight line over a relatively wide range of current. This characteristic may be obtained by providing the, reactor with a core having an air gap 8 which is bridged by one or more restricted core sections 9.. These restricted core sections saturate quickly and at relatively low values of current and thereafter the reactor acts like an air core reactor by reason of the air gap and thus has a substantially straight line volt-ampere characteristic. The

initial saturated effect produced by the restricted sections serves to oifset the straight line portion of the characteristic from the origin of coordi nate's. This is important as will now be explained.

The capacitor 5 has a volt-ampere characteristic l0 whichin common with all, capacitors is a straight line passing through the originof coordinates. However, the capacitor 5 is so proportioned that the slope of its volt-ampere characteristic'is made numerically equal but of course of opposite sign to the slope of the straight line portion of the reactor characteristic. By reason of the offset produced by saturation of the straight line portion'of the reactor characteristic the numerical -values of the voltage across the reactor and across the capacitor at any given current within the straight line range indicated by the currents I1 and I2 will be different. Furthermore, by reason of their signs being opposite, this difference which actually is the vector sum of the individual voltage is constant throughout the line and consequently the numerical difference between their voltages being the vertical distance between two parallel lines will be equal over the current range.

In practice the capacitor and reactor are so proportioned that their resultant voltage corresponds to the desired constant load voltage. The circuit will then maintain constant load voltage regardless of relatively wide variations in source voltage and load current by automatically varying its resultant impedance in response to any change in resultant voltage or resultant current in such a manner as to change the current drawn through the impedance 2 by an amount sufilcient to cause an impedance voltage drop which will automatically neutralize any variation in supply voltage or any variation in voltage drop caused by a variation in load current.

This regulation is independent of variations in load power factor so long as the current in the impedance means 4 stays within the range I1-I:

in Fig. 2. The worst condition for regulation so far as power factor is concerned is a lagging power factor. This is because the resultant impedance of the capacitor 5 and reactor 6 is inductive. This is clearly shown in Fig. 2 in which the voltage across the reactor always exceeds in magnitude the voltage across the capacitor. Consequently, the quadrature lagging component of load current adds or subtracts numer ically from the'current in the automatically variable impedance means 4 whereas with a resistance or unity power factor load the load current is in quadrature with the current through the impedance means -4 and with a leading power factor load the leading quadrature component is in phase opposition with the current through the impedance means 4.

For these reasons it is best to have the current through the impedance means 4 at some intermediate value In when the supply voltage is normal and the load value is normal and at unity power factor. Assuming that the supply voltage stays constant and that the power factor of the load is zero lagging, any change in load current will cause an equal and opposite change in current in the impedance means 4,

whereas if the power factor is zero leading, the same changes in load current will cause equal changes in the same direction of the current in the impedance means 4. For all intermediate power factors the current change in the impedance means 4 will not be equal in magnitude to the load current change but it will be in the opposite direction or in the same direction depending upon the power factor.

In Fig. 8 the impedance 2 is replaced by a con venflonal supply transformer H whose inherent leakage impedance is all that is necessary to gain control of the voltage. For adjusting the magnitude of the load voltage to our predetermined value a simple variable ratio auto-transformer I 2 is interposed between the output terminals of the circuit of Fig. 1 of the load.

In one modification shown in Fig. 4 the series impedance is made a constant current impedance means "consisting of a capacitor I4 and a reactor l5 connected in parallel with each other. The reactor Ii is provided with a core similar to the core of the reactor 6 of Fig. 1 and the volt-ampere characteristics of elements l4 and i5 are so proportioned that they have the same numerical slope over a predetermined range of Voltage thereacross which is usually greater than the range of suppy voltage variations.

This relationship is shown in Fig. 5 in which the reactor characteristic is shown at i6 and the capacitor characteristic is shown by the straight line H. When the characteristic I1 is rotated into the same quadrant with the reactor characteristic It for purposes of comparison it will be seen that they are parallel, thus showing that their slopes are numerically equal and it will also be seen that over the voltage range V1--Vz the numerical difference or vector sum of the currents of the individual elements is constant. Consequently, over this voltage range means 13 automatically regulates the current to a constant value in the supply circuit.

By reason of this, Fig. 4 has a substantially greater range of regulation than Fig. 1 because means l3 automatically compensates for variations in supply voltage so that means 4 is relieved of this duty and need only compensate for variations in load magnitude and power factor.

For simplicity and ease of manufacture the capacitors 5 and I4 may be made identical and the reactors 6 and I5 may be made identical.

Usually, however, this does not make the most suitable circuit.

On a circuit having such identical elements which I have tested over a variation of supply lation are at low power factor lagging so that if the lagging power factor range is limited to a value .8 the circuit maintains the voltage within i2% or normal.

Under certain conditions, which at the present time are not fully understood, an unstable circuit condition occurs wherein the load voltage apparently oscillates from a low to a high amplitude as well as between two different phase angles. I have found, however, that this can be corrected by inserting a relatively small value of resistance in the impedance means 4 and I have found that it can also be controlled by constructing the reactor 6 so that it has appreciable losses. This unstable condition is not always encountered but when it does occur either of the above remedies is effective.

While there have been shown and described particular embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the inven# tion.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An,automatlc voltage regulator for a load over a current range which is of the order of with each other and in parallel with said load circuit across the load end thereof, said elements having such volt-ampere characteristics that the vector sum of their respective voltages is a constant over a current range which is of the order of magnitude of full load current.

3. In combination,'a circuit having a variable voltage source end and a constant voltage load end, a series impedance connected in said circuit, and a voltage regulating circuit connected across said circuit on the load side of said impedance, said regulating circuit comprising a capacitor in series with a reactor, said reactor having 'a magnetic core provided with an air gap which is bridged by a restricted portion of said core, the volt-ampere characteristic of said reactor over a portion of its range being parallel to but displaced from the volt-ampere characteristic of said capacitor.

4. In combination, an electric circuit for in terconnecting a source of alternating current and a a load, and means for automatically maintaining substantially constant load voltage during substantial variations in source voltage and load magnitude including a capacitor and saturated core reactor connected in series with each other and in shunt with said load, the volt-ampere characteristics of said capacitor and reactor having numerically equal slopes over a predetermined current range.

5. In combination, means including a transformer for supplying alternating current at constant' frequency and at a voltage which is subject to variation above and below a rated value, a variable load connected to be energized by said means, and voltage regulating means for said load connected in shunt therewith'comprising a saturated core reactor and a capacitor connected in series, said reactorhaving a volt-ampere characteristic which issubstantially a straight line above the knee thereof, said capacitor having a volt-ampere characteristic which has the same slope as said straight line portion of said reactor.

characteristic.

6. In combination, a source of variable vol tage, a constant voltage vanableload, constant current impedance means interconnecting said source and load, and constant voltage regulating means connected in shunt with said load, said regulating means comprising a pair of serially of the currents in said parallel connected capacitor and reactor being constant throughout the range of voltage variation of said input terminals, the remaining capacitor and the remaining reactor being connected in series across said' output terminals, the vector sum of the voltages of said remaining capacitor and remaining reactor being constant over a current range which is equal to the vector difierence between the constant currentvalue maintained by the parallel connectedficapacitor and reactor and the variable load current drawn from said output terminals over a wide range of power factor.

9. A voltage regulating system comprising, in combination, a pair of input terminals connected respectively to a pair of output terminals, a capacitor and reactor connected in parallel with each other between one of said input terminals and its associated output terminal, said capacin seriesacross saidroutput terminals, said second capacitor and said-,se cond reactor having offset volt-ampere characteristics whose slopes are numerically equal over apredetermined range of current therethrough, and means for preconnected impedances the vector sum of whose voltages'isconstantover a predetermined range of current therethrough. U

"I. A voltage regulating system comprising in combination, variable voltage input terminals and constant voltage variable load current out-- put terminals, a capacitor and a saturated core reactor connected in parallel with each other.;

and in series with said input terminals, the vector sum of the currents in said capacitor and reactor being constant'over a-predetermined voltage rangethereacross, a second capacitor and a'second reactor connected in-series across said load terminals, the vector. sumo! the voltages across said second capacitor and said second 'reactor being constant over a current range which is equal to the vector diflerence between the venting unstable electrical oscillations in said system.

10. A voltage regulating system comprising, in

combination, a pair of input terminals connected 7 respectively to a pair of output terminals, a. ca-

pacitor and reactor connected in parallel with eachother between oneof said input terminals and its associated output terminal, said capacitor and reactor having offset volt-ampere characteristicswhich have slopes of equal numerical value over a givenvoltage range thereacross, a f

second'capacitor and a second reactor connected in series across said output terminals, said se'cond capacitor and said second reactor having oflset volt-ampere characteristics whose slopes' are nmnerically equal over a predetermined range of current therethrough, and means for preventingunstabie electrical oscillations in said system comprising a power consuming element in circuit with said second capacitor.

11. A voltage regulating system comprising, in combination, a pair. of input terminals connected respectively to a pair oi output terminals, a capecitor and a saturated reactor connected in parallel with each other between one ,or said input terminals. and its associated output terzninalfa second capacitor and asecond saturated reactor connected in series across said output terminals, said second capacitor and said second reactor having volt-ampere character-is;

tics whose slopesare numerically equal Over-"a predetermined range of current therethrough.

- CLAUDE M.

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