US3419788A - Automatic voltage regulator - Google Patents

Description

8 J. c. MAY 3 AUTOMATIC VOLTAGE REGULATOR Filed Dec. 28, 1964Sheet 2 of s 35b C P A 566 556 I INVENTOR.

C. May

Jose /7 Dec. 31, 1968 J. c. MAY 3,419,788

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INVENTOR.

Joseph 6'. May

' flTTOR/VEYJ United States Patent 3,419,788 AUTOMATIC VOLTAGE REGULATOR Joseph C. May, Cheshire, Conn., assignor to The Superior Electric Company, Bristol, Coun., a corporation of Connecticut Filed Dec. 28, 1964, Ser. No. 421,561 7 Claims. (Cl. 3236) ABSTRACT OF THE DISCLOSURE An automatic voltage regulator for producing a substantially constant A.C. output voltage by initially providing an intermediate voltage and algebraically adding thereto an alternating voltage derived from a DC. source and consisting of a stepped approximation of a sine wave whose value, either in amplitude or phase, is varied as required to maintain the desired value of output voltage.

The present invention relates to an alternating current automatic voltage regulator for maintaining the value of an output voltage substantially constant with changes in the input voltage and the power controlled by the regulator.

While it has heretofore been proposed to provide regulators which maintain a substantially constant output voltage, in many respects these regulators have not been found completely satisfactory. Many regulators have heretofore employed moving parts, such as slip rings, relays, etc. which inherently are objectionable by reason of mechanical wear or action. In addition, other regulators have employed devices such as inductive impedances which are also inherently somewhat slow acting and therefore decrease the time in which the output voltage may be corrected to its desired value with an abrupt change in the input voltage.

An object of the present invention is to provide an alternating current regulator which is quite rapid in correcting the output voltage to its desired value when a change in the input voltage occurs.

Another object of the present invention is to provide an automatic voltage regulator which provides an output of alternating voltage which is relatively low in distortion and which is quite eflicient in operation.

A further object of the present invention is to provide an automatic voltage regulator which achieves the above objects but yet which presents a low internal impedance thereby enabling three phase alternating current to be regulated by a regulator for each phase thereof.

Still another object of the present invention is to provide an automatic voltage regulator which may include semiconductor devices but yet the devices are basically caused to function as on-oif switches rather than as amplifying devices.

In carrying out the present invention the automatic voltage regulator includes a pair of input terminals connectible to a source of alternating current and a pair of output terminals at which the output voltage that is maintained substantially constant appears. The input voltage is initially altered to an intermediate value of alternating current and in the specific embodiment shown is preferably substantially the minimum value which the output voltage rnay have with the maximum input voltage. Added to the intermediate voltage is an alternating current which is derived from a source of direct current and is formed to approximate a sine wave similar to the sine Wave of the input and intermediate voltages in order to have an output voltage that is substantially a sine wave. More specifically, the added voltage is a stepped approximation of a sine wave having a plurality of levels preferably at least three. Thus the output voltage consists of the inter- "ice mediate voltage with which is combined the alternating current stepped voltage to produce the desired value of output voltage.

In order to maintain the value of the output voltage at that desired, the regulator includes an error detector which produces a signal that is indicative of the deviation of the output voltage from a known value with the known value being either the value of the output voltage desired or a different value of voltage bearing a relationship to the desired value of output voltage. The signal controls the value of the voltage of the stepped alternating current that is added to the intermediate voltage and in one embodiment of the invention the signal is employed to control the amplitude of the stepped alternating current and by adding the intermediate voltage and the stepped alternating current in phase with each other, the value of the output voltage may accordingly be changed by the change in the amplitude of the latter voltage. In another embodiment of the present invention the amplitude of the stepped alternating current is maintained constant but its phase is altered with respect to the phase of the intermediate voltage and accordingly the value of the output voltage is changed by changing the relationship of the phases between the two voltages.

Other features and advantages will hereinafter appear.

In the drawing:

FIGURE 1 is a block and schematic diagram of one embodiment of the automatic voltage regulator of the present invention.

FIG. 2 is a view of voltage wave forms which exist in the regulator.

FIG. 3 is a schematic and block diagram of a further embodiment of the present invention.

FIG. 4 is a plurality of voltage wave forms which appear in the regulator of FIG. 3.

FIG. 5 is a further embodiment of the regulator of the present invention.

FIG. 6 is a view of various voltage wave forms which occur in the regulator of FIG. 5.

FIG. 7 is a vector diagram of the phase relationship of the voltages in the regulator of FIG. 5.

Refenring to FIG. 1, the automatic voltage regulator disclose-d therein is generally indicated by thereference numeral 10 and includes a pair ofinput terminals 11 and 12 that are connectible to a source of alternating current, such as the usual volt, 60 cycle having a sine wave form. The input terminals are connected across the winding of anautotransfo rmer 13 having anintermediate tap 14. The output voltage of the regulator appears atoutput terminals 15 and 16 with theterminal 16 being in effect connected to theinput terminal 12 while theterminal 15 is connected to thetap 14 through a lead that includes aprimary Winding 17 of atransformer 18.

It will be appreciated that with the structure set forth above that there is produced in the primary winding 17 an intermediate voltage which is less than the input voltage and as the former has a sine wave form, the latter also has a sine wave form and this wave form of the intermediate voltage is indicated in FIG. 2 by thereference numeral 19. The output voltage wave form excepting minor percentages of harmonics and distortion, in FIG. 2, is indicated by the [reference numeral 20 and consists of theintrerncdiate voltage 19 combined with an alternating current that has the shape shown by the wave form 21.

The wave form 21 is generally referred to as a stepped approximation of a sine wave with each half cycle includingend portions 22 which have a value of .225 of the maximum value of the voltage of the wave form 21; anintermediate portion 23 which may have a value of .770; and a top portion 24 which may have a value of about unity. Preferably, as shown, the maximum amplitude of the stepped wave form 21 is about one-fourth the maxi- K mum value of the output voltage wave form 20 in order to enable the regulator to have a relative wide range of values of output voltage from which one is chosen to be maintained constant with changes in the input voltage values also over a relatively large range.

As shown in FIG. 2, the output voltage wave form 20 results from the addition of thewave forms 19 and 21. The value of the output "voltage may thus be changed by changing the amplitude of the wave form 21. In this embodiment "both thewave forms 19 and 21 are in phase with each other. 'It is also noted that theportions 22 are each substantially 30, theportions 23 each substantially 30 and the portion 24 substantially 60 of the 180 of each half cycle.

Referring to FIG. 1, the wave form 21, as the stepped alternating current, is made to appear in thesecondary winding 25 of thetransformer 18 and is the output of a D.C. to AC. inverter 26. Theinverter 26 preferably may include a plurality of transistors or other semiconductor devices which are switched on and off by asynchronous circuit 27 that not only maintains the stepped alternating current from theinverter 26 in synchronism with theintermediate voltage 19 but also serves to maintain for each half cycle the duration of theportions 22, 23 and 24. For controlling the amplitude of the stepped alternating current, the regulator includes areference source 28 that is connected to anerror detector 29 with the latter being connected across the output terminals and 16. Theerror detector 29 produces a signal in alead 30 to an adjustable output direct current power supply 311. A source of direct current is derived from the input terminals .by means of afull wave bridge 32.

With the above structure, thereference source 28, which may be adjustable to change the value of the output voltage desired to be maintained constant, produces an electrical value which is combined in the error detector with an electrical value related to the actual value of the output voltage to produce in the lead 30 a signal which is indicative of the difference between the output voltage 'value and the reference signal. The signal may be either a change in polarity or may be a greater or lesser value of current or voltage. The adjustable outputD.C. power supply 31 increases its output power when the signal indicates that the output voltage is too low to thereby increase the amplitude of the stepped alternating current wave form 21 or decrease the amplitude thereof when the signal indicates that the value of the output voltage is greater than that desired.

It has been found that the use of a stepped alternating current only introduces a small percentage of distortion in the output voltage and the distortion is generally of the higher harmonics of the frequency of the sine wave. These higher harmonics may be effectively reduced by the use of afilter 33 connected across the output terminals tuned to the frqeuencies of the higher harmonics. It will thus be appreciated that with the present invention the percentage of the output current which consists of unwanted harmonics and is sometimes referred to as distortion is relatively small in comparison with other type regulators and accordingly enables the present regulator to operate quite efliciently.

In the regulator shown in FIG. 3 the same result is achieved as that shown in FIG. 2 in thatthe output voltage consists of an intermediate voltage which is combined with a stepped approximation of a sine wave. The regulator, as in the regulator shown in FIG. 1, includes many identical parts such asinput terminals 11 and 12 connected to the same source of alternating current and to anautotransformer 13 having atap 14 andoutput terminals 15 and 16. In addition there is the fullwave rectifying bridge 32 connected to the adjustable outputD.C. power supply 31, thereference source 28 and theerror detector 29 together with thefilter 33. However, in place of thesingle transformer 18 there is provided in the connection between thetap 14 and theoutput 15 five 4 transformers denoted 34, 35, 36, 37 and 38 each of which has a primary winding that is connected in series with thetap 14 andoutput terminal 15 and a secondary winding that is connected to the output ofsquare wave inverters 34a-38a.

Referring to FIG. 4, the voltage that is added to the intermediate voltage is the same as that shown in FIG. 2, Le. is a stepped approximation of a sine wave, and its wave form is indicated in FIG. 4 by thereference numeral 39. In order to achieve this wave form, however, thesquare wave inverter 34a produces the wave form 34b While the other square wave inverters 3511-3812 produce the wave forms 35b-38b respectively. It will also be understood that with each wave form there is a line 340- 380 which is the zero line for their respective wave form. Referring specifically to the wave form 3411, it is in phase with the intermediate voltage wave form 40 (having aZero line 40a) and has an amplitude which may be considered as being 1.00. The wave form 35b has an amplitude of 1.225 and is 30 advanced from the wave 34b. The wave form 36b has an amplitude of 0.500 and is 60 advanced while the wave form 37b has an amplitude of .500 and is advanced and finally the wave form 381) has an amplitude of 1.225 and is advanced from the zero position of the intermediatevoltage wave form 40.

It will thus be appreciated that at any angle of each half cycle it the five wave forms 3411-3811 are algebraically added together that they will produce the stepped approximation of thesine wave form 39 which is a wave form identical to the wave form 21 in FIG. 2. Moreover, while the relative proportions of amplitude of each of the waves have been given, it will be appreciated that by varying the amplitude of all by the same proportion that the amplitude of thewave form 39 may accordingly be varied.

For providing the switching of the square wave inverters 34a38a into conditions of positive and negative conduction to produce each of the half cycles of the wave forms 34b38b, the regulator in FIG. 3 includes an oscillator andlogic circuit 41. The oscillator circuit produces oscillations at a frequency of 720 cycles per second which is twelve times the 60 cycle alternating current to which theinput terminals 11 and 12 may be connected in order to produce a pulse or other signal for every 30 of the 60 cycle input alternating current and thus enable control of the inverters at specific intervals after each zero crossing of thesine wave 40. Naturally it the frequency of the source is other than 60 cycles, then the oscillator may have a different frequency. It will be understood that theinverters 34a-38a preferably include semiconductor devices which are either switched on or off and thus may be more efliciently operated than if they were merely amplifying devices.

In the embodiment of the automatic voltage regulator of the present invention shown in FIG. 5, rather than having the amplitude of the stepped alternating current changed to provide the change in the value of the output voltage, herein the stepped alternating current may have a constant amplitude; however, its phase relation with the intermediate voltage is changed. Thus when the two voltages are added they are added vectorially thereby pro ducing an output voltage which may have its value maintained at the desired value.

In the regulator in FIG. 5, there are again theinput terminals 11 and 12 connected to a source of 60 cycle alternating current together with theautotransformer 13 having atap 14. Additionally there are providedoutput terminals 15 and 16,filter 33,reference source 28 anderror detector 29. As in the embodiment shown in FIG. 3, the stepped alternating current is added to the intermediate alternating voltage by a plurality oftransformers 34, 35, 36, 37 and 38 having their primaries connected in series and their secondaries connected tosquare wave inverters 34a, 35a, 36a, 37a and 38a. Moreover, connected to each of the square wave inverters 34a38a is a source of direct current, indicated by thereference numeral 42. In order to enable the different waves 34b-38b to be maintained in the same relationship with each other there is provided the oscillator andlogic circuit 41.

The initiation of each cycle of thecircuit 41 to control the zero crossing of the stepped alternating current wave whose wave form is shown in FIG. 6 and indicated by thereference number 43, is elfected by an adjustablephase shifting circuit 44 connected to the error detector together with a synchronousoscillating circuit 45 connected to have the inter-mediate voltage impressed thereacross. Thecircuit 45 introduces into thephase shifting circuit 44, the timing when the intermediate voltage (whose Wave form is shown in FIG. 6 and indicated by the reference number 46) begins each half cycle and the error detector serves to shift, with respect to the signal from theoscillator 45,' the signal to thecircuit 41 to begin each half cycle. Thus thephase shifting circuit 44 merely serves as a delay circuit with the value of the signal from theerror detector 29 changing the amount of the delay which may be from zero up to 180 for each half cycle. The zero delay adds the stepped alternating current in phase with the intermediate voltage while the 180 delay subtracts the stepped alternating current from the inter-mediate voltage. Other phase delays between not only the two extremes mentioned but also for 180 to 360 result in changing the sum of the two voltages to produce the output voltage having the desired value. The wave forms 43 and 46 in FIG. 6 are 60 apart or out of phase and they are combined by the transformers 34-38 in the manner shown vectorially in FIG. 7. Thus the voltage of thewave form 46 is indicated by the vector 46a while the voltage of thewave form 43 is indicated by thevector 43a and the resultant output voltage is indicated by thevector 47. It will be thus understood that by changing the phase relationship between the wave forms 43a and 46a, the value of the output voltage may thus be changed even though there will also be a change between the phase of the output voltage and the phase of the input voltage except for the two conditions when the steppedwave 43 is exactly in phase or exactly out of phase with theintermediate voltage 46. Moreover, by controlling the phase relationship, i.e. between Zero and 180 and 180 and 360, the output voltage may be made leading or lagging with respect to the phase of the input voltage.

It will accordingly be appreciated that there has been disclosed an automatic voltage regulator which regulates an alternating voltage applied to its input terminals to produce at its output terminals an alternating current which is maintained at a substantially constant value. The regulation is achieved by producing an intermediate alternating voltage and then combining with it another voltage which consists of a stepped approximation of a sine wave. By varying the amplitude or the phase of the stepped alternating current by sensing the actual value of the output voltage, the output voltage may thus be maintained at its desired value.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim:

1. An automatic voltage regulator comprising input terminals connectible to a source of alternating current, output terminals at which an output voltage having a substantially constant value appears, means connected to the input terminals for producing an intermediate alternating voltage, a source of direct current, means connected to the direct current source for producing an alternating voltage having for each half cycle a plurality of different voltage levels forming a stepped wave that approximates a sine wave, means for combining the alternating voltage with the intermediate voltage to produce the output voltage, means for sensing the deviation of the output voltage from a known value and producing a signal indicative of the deviation and means receiving the signal and operative to control the value of the alternating voltage added to the intermediate voltage, with the sum of the alternating voltage and intermediate voltage constituting the output voltage having the desired value.

2. The invention as defined in claim 1 in which the means for controlling the value includes means for adjusting the value of the direct current to control the amplitude of the alternating voltage.

3. The invention as defined in claim 1 in which the means for controlling the value includes means for changing the phase relationship between the alternating voltage and the intermediate voltage.

4. An automatic voltage regulator comprising input terminals connectible to a source of alternating current, output terminals at which an output voltage having a substantially constant value appears, means connected to the input terminals for producing an intermediate alter nating voltage having a value related to the input voltage, a source of direct current, means connected to the direct current source for producing an alternating voltage which is a stepped approximation of a sine wave and including a plurality of inverter means with each inverter means producing an alternating square wave with the phases of the square waves being different from each other, means for combining the alternating voltage with the intermediate voltage to produce the output voltage, said means including a plurality of transformers with each having a primary winding and a secondary winding, means connecting the primary windings in series with each other, means connecting each secondary winding to an inverter means, means for sensing the deviation of the output volage from a known value and producing a signal indicative of the deviation and means receiving the signal and operative to control the value of the alternating voltage added to the intermediate voltage, with the sum of the alternating voltage and intermediate voltage constituting the output voltage having the desired value.

5. The invention as defined in claim 4 in which the relative voltage values of each of the square waves and the phase therebetween is such that when algebraically added together they produce the alternating voltage by a step approximation of a sine wave.

6. The invention as defined in claim 5 in which the means for controlling the value of the alternating voltage includes means for changing the amplitude of each square wave while maintaining the same relative voltage values therebetween.

7. The invention as defined in claim 5 in which the means for controlling the value of the alternating voltage includes means for shifting the phase of the alternating voltage with respect to the intermediate voltage while maintaining the same phase relationship between each of the square waves.

References Cited UNITED STATES PATENTS 3,350,631 10/1967 Ingman 323-45 2,644,128 6/ 1953 Henrich 323-45 3,013,202 12/ 1961 Kusko 323--6 3,018,431 1/1962 Goldstein 323-45 3,171,968 3/1965 Sanborn 32345 ORIS L. RADER, Primary Examiner.

HAROLD HUBERFELD, Assistant Examiner.

U.S. Cl. X.R. 323-45

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