US2451834A - Phase shifting circuit - Google Patents

Description

Oct. 19, 1948.

E. F. KUBLER 2,451,834

PHASE SHIFTING CIRCUIT Filed Sept. 26, 1947 2 Sheets-Sheet 1 Inventor Ernest F. Kubler,

by m His Attohney.

0d. 19, 1948. 5 KUBLEVR PHASE SHIFTING CIRCUIT 2 Sheets-She'et 2 Fig.3.

Filed Sept. 26,1 1947 I as Inventor I Ernest. F. Kub'ler,

His Attorney Patented Oct. 19, 1948 PHASE SHIF'I'ING CIRCUIT Ernest F. Kubler, Schenectady,

General Electric Company,

New York N. Y., assignor to a corporation of Application September 26, 1947, Serial No. 776,375

This invention relates to control systems; more particularly to systems for controlling the operation of electric valves, and it has for one object the provision of a simple, reliable and improved control system of this character.

More specifically the invention relates to systems for controlling the operation of gas filled electric valves, and a more specific object of the invention is the provision of improved means forshifting the phase of the grid voltage with respect to the anode voltage to vary the conductivity of the valve.

In carrying the invention into effect in one form thereof, a gas-filled electric valve having an anode. a cathode and a control grid is connected to have an alternating voltage supplied to its anode-cathode circuit. For supplying an alternating voltage to the grid catrode or input circuit a phase shifting network is provided. It comprises two bridge circuits. Each of these bridge circuits has an individual reactance arm and they have a variable resistance arm which is common to both. In this common arm there is connected 9. control electric valve and a source of direct voltage from which it is supplied. The direct voltage supplied to this control valve is modulatedby alternating voltages which are supplied to both bridge circuits from the secondary winding of a transformer. Two portions of this winding are connected to constitute arms of one of the bridges and two other portions constitute arms of the other bridge. Across the output terminals of the two bridges are connected two primary windings of a grid transformer of which the secondary winding is connected between the cathode and gr d of the gas filled valve. The control valve in the common arm acts as a variable resistor. 0011- sequently. variation of the grid voltage of the control valve varies the phase of the modulated voltage supplied to the grid of the gas fllled valve relative to its anode voltage and thus varies its conductivity. In a modification, one gas filled valve is supplied from one phase of a quarter phase source and a second gas filled valve is supplied from the other phase. The phase shifting network for the grid voltage comprises four bridge circuits, i. e. a double bridge circuit for each valve. A resistance arm common to all four bridge circuits includes a source of directvoltage and a control valve supplied therefrom. Variation of this grid voltage of the control valve in the common arm produces simultaneous phase shift of the modulated voltages supplied to the grids of both gas filled valves.

For a better and more complete understanding 4 Claims. (Cl. 323-119) the valves i and 2, means are provided for supof the invention. reference should now be had to the following specification and to the accompanying drawing of which Fig. 1 is a simple, schematic diagram of an embodiment of the invention; Fig. 2 is a simple, schematic diagram 01 a modification; Fig. 3 is a chart of characteristic curves which serve to illustrate the invention; and Fig. 4 is detail.

Referring now to the drawing, and particularly to Fig. l, a pair of gas filled electric valves i and 2, such as thyratrons, are connected as a biphase, half wave rectifier. The valves have anodes la and 2a. cathodes lb and 2b and control grids lo and 20 respectively. Within their envelopes is contained a small quantity of mercury vapor or inert gas such as argon. They are supplied from a suitable source of alternating voltage which is illustrated as a secondary winding (la of a power supply transformer 3. As shown. the anodes Ia and 2a are connected to opposite terminals of the secondary winding is. A load i which may be any electrical translating device is connected between the cathodes and the center tap of secondary winding is.

For the purpose of varying the conductivity of plying periodically varying voltages to the grids la and 2c and for varying the phase relationships of these grid voltages relative to the anode voltages. This means comprises two alternating voltage bridge circuits having their output terminals connected through a grid transformer to the input circuit of the valves. These bridge circuits comprise a secondary winding 8b of the transformer 3. It has five taps 5, 6, l. and $3 equally spaced apart. The two portions 5-8 and 8'1 of the secondary winding constitute two arms of one of the bridge circuits. A reactance device such as the capacitor l0 constitutes the third arm of this bridge. Similarly the portions 7-8 and 3-9 of the secondary winding constitute two arms of the second bridge circuit and the capacitor ii constitutes the third arm. An electric valve I2 is included in a connection which is common to both bridges and constitutes the fourth arm of each bridge. This connection is traced from the tap 1 through a rectifier i3 and a secondary winding 30 and through vacuum valve 92 and rectiflers i4 and IS in parallel to the lower terminals of capacitors i0 and H.

Between the output terminals 8 and its of the first bridge is connected the primary winding Na of a transformer I 6 of which the secondary winding I 6b is connected between the grid and cathode of thyratron valve i. Similarly, between the circuit of the valve which are connected phase with each other.

output terminals 8 and ll of the second bridge is connected another primary winding lBc of the transformer i8d ofthe transformer is connected between the cathode 2b and grid 2c of thyratron valve 2. The arrangement of the primary windings I80. and I Sc and secondary windings l6?) and-ltd on the core of the grid transformer is indicated in Fig. 4.

The electric valve I2 is provided with an anode 82a, a cathode llb and a control grid I20. A direct voltage is supplied to the anode-cathode is by means of the transformer secondary winding 8c and the rectifier is in the arm which is common to both bridges. The current fiowis traced from the lefthand terminal of secondary winding 30 through rectifier l3, conductor it, to the midtap i. At this point the circuit divides and current flows in the arm l-d, primary winding 16a of the grid transformer l8, and rectifier M. In the parallel branch current flows through bridge arm 'I-B, primary winding Iiic of the grid transformer l6 and the rectifier l5. At this point the parallel branches unite and current fiows through the anode-cathode circuit of valve i2 and conductor it to the right-hand terminal oi secondary winding 30.

A suitable direct voltage is supplied between the grid and cathode of valve l2 by means of a potentiometer 20 connected across a source of direct voltage such as the battery 2d.

The operation is as follows: The direct voltage which is supplied to the anode-cathode circuit of valve i2 is modulated by the alternating voltage between the center tap and output terminal 950. and also by the alternating voltage between the center tap l and the output terminal 5?. These two alternating voltages are, 180 out of Alternating voltages displaced 186 from each other appear across the primary winding Ida and isc of the grid transformer.

Varying the conductivity of the valve 62 by varying its gird voltage produces the same efiect that would be produced by varying the ohmic resistance of the common arm. In other words, the valve i2 behaves like a resistance. Consequently, the phase of the modulated voltage across the valve l2 and the phase of the modulated voltages across the primary windings ltd and idc are varied when the grid voltage of valve 52 is varied. Since the anode voltage of the valve varies with the amount of modulation and since the resistance of the valve varies with its anode voltage. the alternating voltages across the primary windings led and iiie are distorted considerably from the desired pure sine wave form. This distortion is illustrated in the curve chart of Fig. 3 in which curve 2i represents the voltage across primary winding loo during a positive half cycle of the voltage. The positive half cycles of this voltage embrace more than 180 electrical degrees and the negative half cycles embrace less than 180 degrees. Furthermore, the amplitude of the negative half cycle is greater than the amplitude of the positive half cycle.

The alternating voltage which appears across the primary lGc is represented by the curve 29'. Since the direct current flows in opposite directions through the arms 6'l and 7-8 with respect to the alternating voltage, the distortion in the alternating voltage across primary winding I60 is opposite to the distortion of the voltage across primary winding lGa. This opposite distortion is indicated by the curve 2!.

l6,and another secondary winding During its positive half cycles it embraces less than 180 electrical degrees and conversely during its negative half cycles it embraces more than 180 degrees. Its amplitude during positive half cycles is greater than its amplitude during negative half cycles.

Since both windings Ida and itb are wound cumulatively on the same core, the resultant flux has the shape of the curve 22 which is a symmetrical wave, 1. e. its positive and negative amplitudes are symmetrical with respect to theaxes and positive and negative half cycles each embrace 180 electrical degrees. In other words, the distortion of one of the voltages is counteracted by the opposite distortion of the other so that the positive and negative half cycle are. symmetrical.

Alternating voltages having substantially pure sine wave form are induced in the secondary windings 56b and ltd and are supplied to the grid-cathode or input circuits of the valves i and 2. Since the anode voltages of valves l and 2 are 180 out of phase, the connections of the grid transformer secondary windings are poled so that the voltages supplied to the grids lo and 2c are 180 out of phase with each other.

To vary the phase relationship of the grid voltage of valves i and 2 relative to their anode voltages, the grid voltage of valve it in the common arm of the two bridges is varied. Since the valve i2 behaves as a variable resistor when its grid voltage is varied, and since the reactance of the capacitors iii and ii in the capacitance arms remain unchanged, the phase of the bridge output voltages supplied to the primary windings 56a and its are varied. Consequently, the voltages supplied to the grids to and 2c and current conducted by the thyratrons i and 2 are correspondingly varied.

The rectlfiers i l and iii serve as blocking rectifiers to isolate the two resistance reactance bridges, i. e. to prevent their interference with each other.

A capacitor 23 is connected in parallel with the rectifier "it" and secondary winding do. This capacitor extends the range of phase shift of the thyratron grid voltages and makes it possible to phase the thyratrons to cut-oil.

In the modification disclosed in Fig. 2, the invention is embodied in a phase control system for a quarter phase rectifier.

It comprises two rectifiers 2 3 and 25 each of which is substantially identical with the rectifier of the modification of Fig. 1. For example, the thyratron valves 28 and 2? correspond to the valves l and 2 of Fig. 1, and the supply transformer secondary winding 28 corresponds to the secondary winding 3b. The remaining elements oi rectifier 2d are readily identifiable with their corresponding elements in the rectifier of Fig. 1 Similarly, the elements of rectifier '25 are readily identifiable with the corresponding elements of the rectifier of Fig. 1.

The windingsit and 29 are secondary windings of a quarter phase transformer and consequently the alternating voltages induced in these windings are degrees out of phase with each other. An interphase transformer winding 30 is connected between the center taps 28a and 28a.

An arm which is common to all four bridge circuits is connected from the center tap 30a. of the interphase transformer to the common output terminal 3| of the bridges and includes the conduetor 32, the rectifier 33, transformer secondary winding 34 and electric valve 36.

By varying the grid voltage of the valve 35, the phase of the voltages on the grids of all four thyratrons are simultaneously varied with respect to their anode voltages, and the currents conducted by both rectifiers are correspondingly varied.

Although in accordance with the provisions of the patent statutes this invention is described as embodied in concrete form and the principle thereof has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the ele ments shown and described are merely illustra=- tive and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit or this invention or from the scope of the annexed claims.

What I claim as new desire to secure by otters Patent of the States is:

l. control system for an electric valve provided with an anode, a cathode and a control grid comprising means for supplying to the anode cathode circuit a periodically varying voltage, means for supplying to the grid and cathode a periodically varying yoltage of adjustable phase with respect to the anode voltage comprising a of bridge circuits having a common arm, a source of direct voltage connected in said common means for supplying the input terminals of said bridges a periodically varying voltage oi? the same periodicity as said anode voltage to modulate the direct voltages at the output terminals, a transformer having a primary Winding connected acres the output terminals or" one of d bridges, a second primary winding connected across the output terminals of the other oil said bridges and a secondary Winding connected between said grid and cathode, and a control electric valve connected said common a control system for electric valve pro-= ed with an anode, cathode and control d, means for supplying the anode cathode circuit of said valve a periodically varying vclt= means for supplying to the grid and cathode periodically varying voltage comprising a pair at bridge circuits having individual reactance arms and a common resistance arm including a source of direct voltage and a control electric valve, means for supplying to the input terminals said bridges periodically varying voltages of the some periodicity as said anode voltage to modulate the direct voltages at the output terminals, transformer means comprising a core structure provided "with a first primary winding connected across the output terminals of one of said bridges, or second primary Winding connected across the output terminals of the other of said bridges and a secondary winding connected between said grid and cathode, and means for varying the con ductivity of said control valve thereby to shift the phase of the voltages of said grid relative to the voltages of said anodes.

3. A control system for an electric valve pro-. video with an anode, a cathode and a control grid, connections from the anode cathode circuit to a source of periodically varying voltage, a pair of bridge circuits having individual reactance arms and a common resistance arm, a CIZXLS- former having a rectifier included in its secondary circuit for supplying a direct voltage in said common arm, a transformer having primary con nections to said source and a secondary winding having a portion constituting two arms of one of said bridges and a second portion constituting two arm oi the other of said bridges for modulatlng said direct voltage at the output terminals of said bridge circuit with a periodically varying voltage of. the same periodicity as the voltage of said source, a pair of blocking rectifiers connected between corresponding output terminals of said bridge circuits and a terminal 01 said common arm, transformer means comprising a core structure provided with a first primary winding connected across the output terminals of one of said bridges and a second primary winding connected across the output terminals of the other of bridges and having a secondary winding connected between said grid and cathode, for supplying thereto a periodically varying voltage, and a control electric valve in said common arm, and means for varying the conductivity of said control valve to vary the phase relationship or the grid and anode voltages of said first mentioned valve.

4. A control system comprising first and second electric valves each provided with an one e, a cathode and a control grid, at source of quarter phase alternating voltages for supplying quart phase voltages to the anode cathode circuits said valves, means for supplying quarter voltages to the grid cathode circuits of vs ves comprising a pair of phase sh ing nettv for each valve and each comprising two circuits, each bridge circuit having individual reactance arm and all said bridge circuits havi a common resistance arm, a source oi voltage included in said common arm, a W phase transformer supp-lied from said source, one secondary phase winding constituting bridge a ms tor the both bridge circuits of one of said :netrloi s and the other phase winding constituting arms for the bridge circuits of the other of said netvvorlrs for supplying quarter phase alternating voltages to modulate the direct voltages at the output terminals of said bridges, a f rst grid transformer having two primary windings connected across the output terminals of the two bridges respectively of one of said networks and having a secondary winding connected to the grid and cathode of one of said valves, a second grid tran former having two primary windings connected across the output terminals of the tvvo bridges respectively of the other of said networks and having a secondary winding connected to the grid and cathode of the other of said valves, and a variable control valve connected in said common arm.

.ZQNEST KUBIER.

No references cited.

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