US2453451A - Voltage regulator system - Google Patents

Description

Nov..'9, 1948. F. l.. MosELEY VOLTAGE REGULATOR SYSTEM 2 Sheets-Sheet l Filed lay 21, 1947 NY- 9, 1948- F. L. MosELEY 2,453,451

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Patented Nov. 9, 1948 VOLTAGE` REGULATOR SYSTEM Francis L. Moseley, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Application May 21, 1947, Serial No. 749,577

Claims.

This invention relates to voltage regulation and more particularly to an arrangement for maintaining a supply voltage at a predetermined xed level.

A principal object of the invention relates to a voltage-regulating system employing an autotransformer which is controlled by a novel automatic follow-up system which responds to any undesired change in input supply voltage to maintain the output voltage at a predetermined fixed level.

Another object is to provide a novel control arrangement ior follow-up systems of the servomotor type.

A feature of the invention relates to an improved voltage regulator arrangement employing an automatically adjustable autotransformer, in conjunction with a follow-up circuit for the adjusting element of the autotransformer which circuits employ a novel anti-hunting control.

Another feature relates to an anti-hunting control for follow-up systems of the servo-motor type, employing atwo phase induction motor, which is controlled by a pair of grid-controlled gaseous discharge tubes such as Thyratrons A further feature relates to the novel organization, arrangement and relative interconnection of parts which cooperate to provide an improved voltage regulator system.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

In the drawing,

Fig. 1 is a schematic wiring diagram of the voltage regulator and follow-up arrangements according to the invention.

Fig. 2 is a vector diagram explanatory of the operation of part of Fig. 1.

Fig. 3 is a graph diagram also explanatory of the operation of part of Fig. 1.

Referring to Fig. 1, the terminals I0, II, may be considered as input supply terminals and are connectable to a source of alternating current supply voltage which is subject to voltage level fluctuations; and the terminals I2, I3, may be considered as output terminals which are to be connected to a device (not shown) which requires an A. C. supply voltage which is free from such level fluctuations. The two sets of terminals are coupled for voltage transfer by an autotransformer I4 in series with the secondary winding II of a voltage correcting transformer I6. The autotransformer I4 has an adjustable contact arm II, which connects the primary winding Il of the correcting transformer in adjustable relation with the autotransformer, the opposite end of winding I8 being returned to the electrical midpoint of the autotransformer. With this arrangement, the phase of the output in winding I5 can be in either aiding or opposing relation with the voltage at the terminals of the autotransformer. It is thus possible by suitable adjustment of contact I1 to raise or lower the voltage at the output terminals I2, I3, so as to compensate for changes at the input terminals I0, II. In accordance with the invention, this adjustment is effected automatically so that if the voltage at terminals I0, II, changes in either direction from the desired level, the contact arm II is automatically moved in the proper direction and to the proper extent to compensate for this undesired change and thus maintain the voltage level at terminals I2, I3, constant.

For the purpose of automatically controlling the arm I`I, there are provided a voltage-sensitive unit I9, an amplifier unit 20, a phase-sensitive power control unit 2|, a follow-up motor 22, an anti-hunting induction generator 23, and a mechanical connection between the shaft of motor 22 and the arm I'I. If desired, this latter mechanical connection may include a suitable reduction gearing.

Bridged across the output terminals I2 and I3, is a Wheatstone bridge 24, two arms of which comprise adjustable resistors 25, 26, and the other two arms comprising temperature-sensitive or voltage-sensitive resistors 21, 28. I have found that the resistors 21, 28, may, for practical purposes, be ordinary tungsten filament incandescent lamps which are operated at about red heat. Resistors 25 and 26 are adjusted so that when the desired voltage level exists at the terminals I2, I3, the bridge 24 is balanced. Preferably, the bridge is coupled to the said terminals through an adjustable potentiometer 29. Potentiometer 29 serves to adjust the output voltage of the regulator to the desired value. A movement of the potentiometer arm to the left (Fig. 1) increases the percentage 0f the output voltage applied to the bridge 24, and since this bridge can only be balanced at one voltage, the voltage regulating action to be described acts to reduce the regulated output to anew value determined by the setting of potentiometer 29. Preferably the two conjugate points of the bridge are bridged by an indicating meter 29a. Any change in the voltage level at the output terminals I2, I3, will cause an unbalance of the bridge, and the unbalanced bridge current will have a magnitude and phase dependent respectively upon the polarity and extent of change in the voltage at terminals I2 and I3 from the desired fixed level.

The-gnba'lanced bridge current is coupled by transformer 30, to a balanced two-tube amplifier 20, comprising two grid-controlled ampliiier vacuum tubes 3 32. While the drawing shows tubes of the triode type, it will be understood that any other well-known grid-controlled vacuum-tube amplifiers may be employed. Since the input of the amplifier 20 is a two-terminal input, it is necessary to employ any well-known phase inversion network, comprising for example resistors 33, 34, 35, 36, and condenser 31 for that purpose, so that the outputs of the tubes 3|, 32, can be combined in divided balanced relation or pushpull relation, by means of the equal load resistors 38, 39. It will be observed that the A. C. power supply for amplifier 20 is derived through a transformer 40, connected to the A. C. supply conductors through the intermediary of the usual fullwave rectifier tube 4|, and with the usual filter comprising for example resistor 42 and condenser 43. In the manner well-known in pushpull amplifiers, this D, C. plate voltage is connected to the junction of resistors 38 and 39, and thence in parallel to the plates 43 and 44. The output of amplifier 2U will for convenience, be referred to as the follow-up control signal. This control signal is applied in opposite phase to the respective control grids 45, 46, of two grid-controlled gaseous discharge tubes 41, 48, which preferably are of the Thyratron type. While the tubes 41 and 48 are shown as triodes, it will be understood that they may take the form of multigrid gaseous discharge tubes of any well-known type. Thus, the tubes 41 and 48 are rendered selectively conductive between their respective plates and cathodes under control of the phase of the input follow-up signal. In other words, if the bridge 24 is unbalanced in one direction, tube 41 will be conductive; and if the bridge is unbalanced in the opposite direction, tube 48 will be conductive.

The power supply transformer 40 has an additional secondary winding 49 which supplies the plate voltage for tubes 41 and 48, as well as supplying the power current for the field windings 50, 5|, of the follow-up motor 22, which may for example be of the squirrel-cage induction type, whose armature 52 is mechanically connected to the armature 53 of the induction generator 23. Generator 23 has an input field excitation winding 54, which is also fed from the transformer secondary 49; and an output winding 55 which is connected in series with the primary of transformer 30. Thus, when generator 23 is driven by motor 22, it feeds back to the input circuit of the amplifier a voltage of such a phase that it tends always to oppose rotation of the motor 22. The action of generator 23 is therefore such as to control the speed of motor 22, so that it is proportional to the extent of unbalance of the bridge. As the bridge approaches balance, the speed of motor 22 is proportionately reduced, and when balance is finally reached the motor speed becomes zero. The net result is that hunting of the motor shaft and of the Contact arm |1 are positively eliminated.

Since the tubes 41, 48, are of the gas-filled type, when they fire" or become plate-to-cathode conductive, they act in the nature of a short-circuit across the respective primary windings 56 fand l1, of their load transformers. When, for example, tube 41 is rendered conducting through application of a suitable follow-up control voltage to its grid 45, the potential between its plate and cathode is reduced to the arc value representing approximately 8 volts. This large reduction in secondary voltage is reflected as an equivalent short-circuit across the transformer winding 58, so that effectively the phase winding 50 can beconsidered as connected directly across the A. C. supply secondary 49. At the same time, phase winding 5| of the motor is connected to its A. C. supply through the transformer winding 59. Since tube 48 is under this condition substantially open-circuited, the winding 51 is effectively in circuit with condenser 60, and by transfromer action between windings 51 and 59 this condenser is equivalently reflected through said windings and it effectively appears in series between the A. C. supply from transformer winding 49 and the phase winding 5| of the motor. In other words, for all practical purposes, the motor 22 under this condition has its phase 50 connected directly across the A. C. supply and the other phase 5| is connected across this A. C. supply through an equivalent series condenser. The motor 22 therefore runs as a two-phase motor and its direction of rotation can be conveniently reversed by causing the tube 41 to be extinguished or rendered non-conductive, and the tube 48 to be fired or rendered conductive.

It is well-known that grid-controlled gaseous tubes such as Thyratrons, may be progressively controlled by shifting the phase of the grid voltage with respect to the plate voltage. The system as shown in Fig. l is arranged for phase shift control by a voltage addition means. Thus, a voltage from winding 49 is coupled through condenser 6D and thence through grid bias resistor 6|, to the cathodes of both the gaseous tubes. The value of condenser 60 and resistance 6| are chosen so that the voltage across resistor 6| lags the voltage at the plates of the tubes 41, 48, by approximately The input follow-up contro1 voltage from the amplifier 20 applied to the grids 45 and 46, is arranged to be in either zero or phase relationship with the voltage at the plates of the tubes 41, 48. However, these input follow-up control voltages from amplifier 20 have the abovedescribed bias voltage developed in resistor 6| effectively added to them; as a result an increase of follow-up control voltage from the amplifier causes the voltage at one of the grids 45 or 46 to advance progressively to a position substantially in phase with the plate voltage, while at the same time the voltage reaching the grid of the other gas tube is progressively retarded in phase. Thus, the plate current of one of the gas tubes is caused to increase progressively while the other tube is effectively cut off. This action is illustrated in vector form in Fig. 2, and by corresponding wave forms in Fig. 3. Referring to these figures, each of the gaseous tubes is supplied with a like plate Voltage Ep. Likewise, these gas tubes are supplied from resistor 6| with a bias voltage represented in Figs. 2 and 3 as Eties. This bias voltage causes each tube to operate for a few degrees late in the active cycle. As the signal voltage Em from the amplifier 20 is applied to the gas tube grid circuit, it adds to its bias voltage so as to increase the operating angle of one gas tube while simultaneously decreasing the operating angle of the other.

While one particular embodiment has been described herein, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A voltage regulator system comprising input termi'als supplied with alternating voltage, output terminals, transformer means coupling said input and output terminals, said transformer means including an autotransformer having an adjustable Contact arm, means responsive to the position of said arm to apply a compensating voltage to the supply voltage to maintain the output voltage at a desired xed level, and means to automatically adjust said arm, the last-mentioned means including a follow-up motor, means to produce a follow-up control voltage proportional to the extent to which said supply voltage departs from said desired level, and means to apply said control voltage to cause rotation of said motor to an extent suilicient to move said arm to a point to restore said output voltage to said desired level, said means to produce said follow-up control voltage comprising a Wheatstone bridge which is normally balanced when said output voltage is at the desired level; and said means to apply said control voltage comprises a pair of grid-controlled gaseous discharge tubes which are connected to said bridge so as to be selectively fired in accordance with the direction of unbalance of said bridge, said follow-up motor having a pair of excitation windings for producing a rotating field, means coupling each of said windings respectively to the output circuit of one of said gas tubes, a condenser connected in common to the plate circuits of said gaseous tubes, and means responsive to the firing of one tube to connect said condenser eflectively in series with one of the motor windings and the A. C. Power supply therefor while effectively bridging the said A. C. power supply substantially directly across the other winding.

2. A voltage regulator system comprising input terminals supplied with alternating voltage, output terminals, transformer means coupling said input and out put terminals, said transformer means including an autotransformer having an adjustable contact arm, means responsive to the position of said arm to apply a compensating voltage to the supply voltage to maintain the output voltage at a desired fixed level, and means to automatically adjust said arm, the last-mentioned means including a follow-up motor, means to produce a follow-up control voltage proportional to the extent to which said supply voltage departs from said desired level, and means to apply said control voltage to cause rotation of said motor to an extent sufficient to move said arm to a point to restore said output voltage to said desired level, the means for producing said follow-up voltage including a device which produces a signal whose phase and magnitude correspond to the polarity and magnitude of change in the voltage applied to said input terminals with respect to said desired level; and the means for applying said control voltage comprises a pair of grid-controlled discharge tubes rendered selectively conducting in accordance with the phase of said follow-up signal, each of said discharge tubes having its output coupledto a corresponding phase winding of said motor, and a phase shift condenser connected in common to the plates of said tubes and arranged to be selectively associated in series with one of said motor windings in accordance with the particular discharge tube that is rendered conductive.

3. A voltage regulator system according to claim 2 in which said grid-controlled tubes are of the gaseous conduction type and have their output circuits respectively coupled to the motor windings through individual output transformers, and the source of alternating power current for the motor is connected between the junction of said motor windings and the `junction of said transformer windings.

4. A voltage regulator system comprising input terminals supplied with alternating voltage, output terminals, transformer means coupling said input and output terminals, said transformer means including an autotransformer having an adjustable contact arm, means responsive to the position of said arm to apply a compensating voltage to the supply voltage to maintain the output voltage at a desired xed level, and means to automatically adjust said arm, the last-mentioned means including a follow-up motor, means to produce a follow-up control voltage proportional to the extent to which said supply voltage departs from said desired level, and means to apply said control voltage to cause rotation of said motor to an extent sufficient to move said arm to a point to restore said output voltage to said desired level, said means to produce said follow-up control voltage including a balanced bridge network which is normally balanced when the voltage at said output terminals is at the desired level, said follow-up motor having a pair of phase windings for producing a rotating field, a condenser which is selectively associated in series with either of said windings, and a pair of gridcontrolled tubes which are rendered selectively plate current conductive under control oi' the phase of said follow-up voltage to selectively assciate said condenser in series with a correspondlng one of said windings and with the source of alternating current power for said motor.

5. A voltage regulator system comprising input terminals supplied with alternating voltage, output terminals, transformer means coupling said input and output terminals, said transformer means including an autotransformer having an adjustable contact arm, means responsive to the position of said arm to apply a compensating voltage to the supply voltage to maintain the output voltage at a desired fixed level, and means to automatically adjust said arm, the last-mentioned means including a follow-up motor, means to produce a follow-up control voltage proportional to the extent to which said supply voltage departs from said desired level, and means to apply said control voltage to cause rotation of said motor to an extent suiiicient to move said arm to a point to restore said output voltage to said desired level, said means to produce said follow-up control voltage including a. balanced bridge network which is normally balanced when said output voltage is at the desired level, said follow-up motor having a pair of phase windings for producing a rotating eld, and the said means to apply said control voltage includes a pair of gridcontrolled gaseous discharge tubes each selectively controlled |by the direction of unbalance of said bridge, an output transformer in the plate circuit of each of said gaseous discharge tubes, a source of alternating current supply voltage having one terminal connected in parallel with said motor windings and the other terminal connected in parallel with said transformer windings, and a condenser connected to the plates of said gaseous discharge tubes and arranged to be selectively associated in series with one of said motor windings in accordance with the particular 8 one of said discharge tubes which is selectively Number Name Date conductive. A Fitz Gerald Jan- 10, -f FRANCIS L. MOSELEY. 2,115,036 Riggs Apr. 26, 1938 2,325,936 Blume Aug. 3, 1943 REFERENCES CITED 5 2,368,582 Sziklai Jan. 30, 1945 2,396,187 Means Mar. 5 1946 f f d i h mfhferens are o reef n t e 2,424,568 Isbister et a1 Ju1y29,1947 2,424,569 Moseley et 2.1l July 29, 1947 UNITED STATES PATENTS Number Name Date 10 687,147 Fleming Nov. 19, 1901 L v gna

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