US2685669A - Apparatus for converting electric currents - Google Patents

Description

Aug. 3, 1954 P. GABORIAUD APPARATUS FOR CONVERTING ELECTRIC CURRENTS Fig .1.

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Patented Aug. 3, 1954 APPARATUS FOR CONVERTING ELECTRIC CURRENTS Paul Gaboriaud, Issy-les-Moulineaux, France Application May 28, 1951, Serial No. 228,561

Claims priority, application France October 21, 1947 This invention relates to the conversion of direct current into alternating current.

The present application is a continuation-inpart or" applicants cope-riding application Serial No. 55,292, filed October '19, 1948, now abandoned.

It is the essential object of this invention to provide a novel method of converting D.C. into A.-C. by opposition between an A.-C. voltage and a D.-C. source.

It is another object of this invention to pro vide means for carrying out the method mentioned above.

Both method and means will be described hereafter with reference to the affixed drawings forming part of this specification and illustrating diagrammatically by way of example the manner in which the invention can be carried out practically. In the drawings:

Fig. l is the time-voltage diagram of the pilot wave used in the method according to the invention.

Fig. 2 shows the connection between the D.-C. source the pilot voltage.

Fig. 3 illustrates the resultant according to A B or" 2 of both D.-C. and pilot voltages.

Fig. i is a wiring diagram illustrating a practical application of the method.

Fig. 5 illustrates the diagram of Fig. 3 showin the resultant of both D.-C. and pilot voltages superposed to the diagram of the current produced by this resultant voltage in the circuit of Fig. 4.

6 shows the same diagrams as Fig. 5 in the case where the pilot voltage is periodically interrupted.

Fig. 7 is a complete wiring diagram of an apparatus for converting the direct current supplied from a battery into an alternating current by the method according to this invention.

Considering :firstly an impedance P in series with a D.-C. source S (Fig. 2) supplying a resultant voltage available at both terminals A and B. Assuming then the voltage at the terminals of impedance P to have the waveform indicated in Fig. 1, that is an alternative voltage in which each cycle consists of two asymmetrical alternations, one alternation 6 having a short duration and the other alternation having a duration T-e wherein T is the time of recur rence of the pulses.

The short alternation will be called. impulse phase and the long alternation slow phase. If the impedance P is a prefect coil both positive and negative areas will be equal in the diagram In order to simplify the problem 6 Claims. (Cl. 321--36) it will be assumed that both alternations have a rectangular shape; however, this should not be construed as an imperative requirement.

Assuming the slow phase to be in opposition against source S and the amplitude U0 of this phase to be equal to the D.-C. voltage supplied from this source S, the resultant voltage at the terminals A B will have the shape shown in Fig. 3 where the only pulses left have the same polarity. These unipolar pulses will be called unidirectional pulses.

Now let us assume that the circuit is closed at terminals A B across a pair of series-connected impedances, one non-linear impedance M and another impedance 2'. which is the load or utiliration impedance (see Fig. 4). Fig. 4 represents a non-linear impedance lvi obtained by induction coupling with a secondary M1 shunted through a non-linear conductor D. This element D is so constituted and its direction of connection is such that the modulus of impedance M will attain its maximum during the time fraction 6 of every unidirectional pulse and its minimum duing the interval between successive pulses. Thus, a relatively high timewonstant is obtained during the presence of every pulse and a relatively low time-constant results during the interval between successive pulses. A short pulse having a duration 6 fed to a circuit having a high time-constant can only give a very low current, which will very rapidly drop towards Zero value after the pulse is ended, since this cancelling occurs in circuit the time-constant of which has sddenly fallen to a .very low value. A a result, the current flowing through the circuit S P M Z will have the form indicated in Fig. 8 and consists of small ascending exponential arcs followed by small descending arcs forming small elementary triangles of exponential contours, the bases of which are coincident with the time axis. Ehese triangles have very reduced areas and the smaller the duration e, the smaller these areas. Calculus will demonstate that these areas are fairly smaller than those which would result from the D.C. supplied by the source S in the ohmic resistance of the entire circui P M 2.. Therefore, the average current fed from D.C. source S to circuit ,3 P M Z is much lower than the D.-C. indicated by the application of Ohms law and experience corroborates the result of calculus in this respect.

Such a result might appear to be at variance with the theorem of the superimpression of voltages and currents from which the current resulting from the action of a plurality of voltages superimpressed in a circuit is the vectorial sum of the elementary currents which would be produced by every voltage taken separately. However, this discrepancy is purely apparent be cause this theorem is only applicable to linear systems.

Thus, the addition or injection of a pilot oscillation or pulse of suitable shape in an impedance P connected in series with a D.C. source S makes it possible to reduce the D.C. fed by the source to a value considerably lower than that indicated by Ohms law, this value becoming negligible in the present invention.

Therefore, if by any means this pilot-pulse is periodically interrupted with a breaking frequenoy N, an A.-C'. component of N frequency will be caused to appear in the circuit SPMZ, as illustrated in Fig. 6. It will readily be understood that during the time in which this pilotpulse is interrupted the total M. F. developed in the circuit SPMZ will be equal to the D.C. voltage supplied by the source, the latter feeding freely the current value resulting from Ohms law. Conversely, during the passage of every train of pilot-waves the average current is practically negligible. It is therefore obvious that A.-C. has been produced from the energy supplied by a D.C. source.

An apparatus for converting D.C. from a battery into alternating current through the abovedefined method will be described hereunder with reference to Fig. 7 of the drawing, this being but a mere example amongst the embodiments that can be resorted to without departing from the limits and scope of this invention.

A three-electrode tube 3 acting as a Hartley oscillator produces in its oscillating plate circuit an A.-C. voltage having a frequency of 50 cycles per second. This oscillating circuit consists of a lfl-henry coil 4 and a l-microfarad capacitor 5. The triode grid is connected with the end of the oscillating circuit which is opposite to the plate across a grid capacitor I and with the ground across the grid leak 2; the triode cathode is grounded.

The next triode provided in this arrangement is a low-power thyratron tube H the cathode E3 of which is connected to the junction-point or common terminal of a pair of resistors 9, ill connected in turn between the positive terminal of the D.C. source S and the ground. The values of S and it are so determined that the thyratron. tube will be blocked to its inoperative condition when no signal is fed to its control grid. The 50 c./s. oscillation is transmitted to the thyratron grid through connecting capacitor i}, grid resis ance 8 and grid-protection resistance i. During the positive alternations of this 50 c./s. oscillation the thyratron is released and produces a high-frequency sawtooth oscillation defined by the time-constant RC of charge resistor R and capacitor C. The latter is charged from source S through resistor R and discharged through a protective Elm-ohm resistor [2. In the example illustrated and described the conditions are those adopted in experimental tests conducted with a saw tooth recurrence frequency of 16,000 c./s.

Thus, during every positive alternation of the 5G o./s. oscillation there were a little less than 100 saw-tooth cycles.

During every negative alternation of the so c./s. oscillation the thyratron is blocked. Thus, the 10,000-c./s. wavetrains are interrupted at a 50 c./s. frequency.

The saw-tooth oscillations are transmitted through a capacitor M and a grid resistor ill for the control grid of a pentode [6 having its screen I'd connected to the positive terminal of the D.C. source S and its cathode grounded. These sawtooth voltages produce in the plate circuit of pentode it a saw-tooth current in phase with the grid voltage. This saw-tooth current passes through choking-coil impedance P and produces at the terminals thereof a voltage having the Wave-form shown in Fig. l; the positive pulse peaks correspond to the sudden breaks in the plate current which are caused by the steep wavefront oi the saw-tooth grid voltage.

The SPMZ circuit is similar to that described with reference to Fig. l. In this case, the nonlinear impedance M consists of the primary winding of a transformer the secondary M1 of which has a central tap connected to the cathodes 20, ii of a pair of triode tubes i8, 23. Each outer terminal of M1 is connected to a respective plate of these triodes, as illustrates Both grids i9, 22 thereof are connected together and. to the negative terminal of the D.C. source S, and both cathodes 25 are connected to junction point The voltage at terminals A B has the unidirectional shape shown in Fig. 2 and therefore both triodes l8 and 2 2 will be blocked when pulses ar present and become conductive during the intervals between successive pulses. Thus, the requirem nt set forth in the preamble is met and the apparatus provides a high time-constant during the passag of every pulse and a low timeconstant in the interval between successive pulses.

The purpose of capacitor 25 is to iilter the 10,000-c/s. component and that of capacitor 25 is to obtain a series resonance of choke Z on the 50-c./s. conversion frequency in view of obtaining the maximum eficiency. A 50-c./s. A."'C. is produced in the secondary 2 3 connected'to the primary Z.

While I have herein shown and described one form in which my invention may be embodied, it will be understood that the construction thereof and the arrangement of the various parts rnav be altered without departing from the spirit and scope thereof.

What I claim is:

1. Apparatus for producing in a circuit an alternating current having a predetermined frequency from a source of direct current, comprising a choking coil connected in series with said direct-current source in said circuit, means ior producing in said choking-coil a high frequency periodic voltage, means for periodically varying the time-constant of said circuit at frequency of said choking-coil voltage, and means for periodically varying said choking-coil voltage ac cording to the aforesaid predetermined frequency.

2. Apparatus for producing in a circuit an alternating current having predetermined frequency from a source of direct current, coinpris" ing a choking-coil connected series with said direct current-source in said circuit, means for producing in said choking-coil freer ncy periodic pilot voltage having a long alterr in opposition with the voltagof di current source and a short alterna same direction as said direct-current voltage, and of higher voltage than the long alternation, means for giving to the circuit a low time-constant value during the long alternations of said pilot voltage and a high time constant value during the short alternations of said pilot voltage, and means for periodically interrupting said choking-coil voltage according to the aforesaid predetermined frequency.

3. Apparatus for producing alternating cur rent having a predetermined frequency from a source of direct current, comprising a circuit, a choking-coil connected in series with said directcurrent source in said circuit, means for producing in said choking-coil a high-frequency periodic voltage, means for periodically varying the time-constant of said circuit according to the frequency of said choking-coil voltage, means for periodically interrupting said choking-coil voltage according to said predetermined frequency and a transformer having a primary winding connected in said circuit and a secondary winding delivering the alternating current produced by the apparatus.

4. Apparatus for producing alternating current having a predetermined frequency from a source of direct current, comprising a circuit, a choking-coil connected in series with said directcurrent source in said circuit, a high-frequency periodic-voltage generator adapted to produce in said choking-coil a high-frequency periodic voltage, two triode tubes, a transformer comprising a secondary winding shunted across said triode tubes and a primary winding connected in said circuit and adapted to produce periodic variations in the time-constant thereof according to the frequency of said high-frequency periodic-voltage generator, an oscillator operating at said predetermined frequency in order periodically to interrupt the operation of said high-frequency periodic-voltage generator and a transformer having a primary winding connected in said circuit and a secondary winding delivering the alternating current produced by the apparatus.

5. Apparatus for producing alternating current having a predetermined frequency from a source of direct current, comprising a circuit, a choking-coil connected in series with said direct-current source in said circuit, a high-frequency thyratron tube adapted to produce a high-frequency periodic voltage in said chokingcoil, a first triode tube and a second triode tube, a transformer having a secondary winding shunted across said first and second triode tubes and a primary winding connected in said circuit in order periodically to vary the time-constant thereof according to the frequency of said thyratron tube, a third triode tube connected as an oscillator so as periodically to interrupt the operation of said thyratron according to said predetermined frequency, and another transformer comprising a primary winding connected in said circuit and a secondary winding delivering the alternating current produced by the apparatus.

6. Apparatus for producing alternating current having a predetermined frequency from a source of direct current, comprising a circuit, a choking-coil connected in series with said directcurrent source in said circuit, a thyratron tube the control grid of which is so connected as to block said tube when no signal is applied to said control grid and to emit a high-frequency periodic voltage towards said choking-coil whenever a signal is applied to said control grid, a pair of triode tubes, a transformer having a secondary winding shunted across said triode tubes and a primary winding connected in said circuit so as periodically to vary the time-constant of said circuit according to the frequency of said thyratron tube during the emission thereof, another triode tube connected as a periodic oscillator according to said predetermined frequency in order to act upon said thyratron control grid during one-half of each cycle and produce an emission of said thyratron tube, and a transformer comprising a primary winding connected in said circuit and a secondary winding delivering the alternating current produced by the apparatus.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 979,060 Cedergren Dec. 20, 1910 1,929,720 Willis Oct. 10, 1933 1,947,242 Bedford Feb. 13, 1934 2,148,718 Agins Feb. 28, 1939 2,493,669 Gray Jan. 3, 1950

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