US2465407A

US2465407A - Rectangular wave impulse generator

Info

Publication number: US2465407A
Application number: US481108A
Authority: US
Inventors: Arthur A Varela
Original assignee: Individual
Current assignee: Individual
Priority date: 1943-03-30
Filing date: 1943-03-30
Publication date: 1949-03-29
Anticipated expiration: 1966-03-29

Description

March 29, 1949. VARELA 2,465,407

RECTANGULAR WAVE IMPULSE GENERATOR Filed March so, 1945 2 She'ets-Sheet 1 f "iffl I [A A5! LSINSQJT l 4 sllvzwr 1 i 1* '1 I :ElE-z-4.

a t V l ARTHUR A. VARELA March 29, 1949. \(ARELA 2,465,407

RECTANGULAR wAvE IMPULSE GENERATOR Filed March 30, 1943 2 Sheets-Sheet 2 ARTHUR A.VARELA A W W Patented Mar. 29, 1949 RECTANGULAR WAVE IMPULSE GENERATOR Arthur A. Varela, Washington, D. 0.

Application March 30, 1943,

15 Claims.

(Granted under Serial No 481,108

the act of March 3, 1883, as

amended April 30, 1928; 370 O. G. 757) This invention is directed to the problem of generating rectangular wave electrical impulses, and is particularly related to systems for accomplishing this object wherein stored energy is periodically discharged through a circuit which includes a pulse-shaping filter.

Systems of this type are described in my copending application, S. N. 447,671, filed June 19, 1942, wherein a potential storing capacity is periodically connected to a discharge circuit including anti-resonant components tuned to the fundamentalperiod of the discharge pulse and to its submultiples. I I

According to the invention ofsaid disclosure, a substantially constant current is maintained through the load during a predetermined time period, after which it falls abruptly to zero, thus developing a rectangular voltage wave across the load impedance. The constant current is obtained by the transient response of the anti-resonant filter sections, which are separately tuned to the various alternatin components of the applied voltage as determined by Fourier analysis. Under transient application of a resonating voltage to an anti-resonant circuit the reactive currents in the two branches are not equal and of inverse phase. as they are in steady state conditions, but diifer by an exponentially decreasing term constituting the inductive transient. This transient, being the unbalance'between the inductive and capacitative currents, represents the line current for the particular frequency component considered, and the sum of the transients form the total line current. By suitably designing the inductances of the filter, the rate of decay of the transients can be made small enough to generate a substantially constant current during the period of pulse duration,- which is relatively short.

It is a further characteristic of the system disclosed in the aforementioned application that the voltage across the storing capacitor decreases linearly with the rectangular wave across the load impedance. Since the voltage applied to the filter as a whole is the difference between the constant load impedance drop and the storage capacitor voltage, it is also of saw-tooth form.-

By Fourier analysis it can be shown that the saw-tooth voltages comprise harmonically related alternating components whose amplitudes decrease in proportion to the harmonic number. Consequently, particularly in high voltage systems, the design requirements for the low harmonic sections are very stringent, and the fundamental section is of especially difficult, expensive, and heavy construction.

Accordingly, it is the chief object of the invention to eliminate one of said filter sections, preferably the fundamental section, While preservin the function of such section in a generating system of the type described.

It is another object of this invention to provide a rectangular wave impulse generating circuit of the type described wherein a filter section is eliminated, and in which the energy storing circuit itself constitutes a circuit component antiresonant at the frequency of the eliminated section.

A further object of the invention is to provide a rectangular wave impulse generating circuit of particularly economical design for high voltage operation. I

The invention will be further described with reference to the exemplary embodiments thereof shown in the drawings, in which:

Fig. 1 is a diagrammatic showing of a simplified rectangular wave impulse generator embodying the principles of the present invention;

Fig. 2 is a schematic representation of voltage and current components of a filter section of the system;

Fig. 3 is a schematic representation of the sawtooth voltage wave resulting from the constant current discharge of the storing circuit, and its direct and alternating voltage components of lower frequency;

Fig. 4 is a schematic representation of the rectangular wave voltage impulse produced by a generating system of the present invention;

Fig. 5 is a diagrammatic showing of another. rectangular wave impulse generator of the present invention, and

Fig. 6 is a diagrammatic rectangular wave present invention.

As shown in Fig. 1, the pulse generating system receives energy from a direct current supply illustrated as battery 5 which may be connected to the generating system by switch 2. The energy storing circuit 3 may be connected by switch 41 to the discharge circuit including filter F and load impedance R. The storing circuit comprises capacitors Ca and Cb, and inductance L. For pulse generation, the storage circuit is connected to the supply to charge the capacitors, and after disconnection from the supply, is connected to the discharge circuit by switch 4.

The pulse shaping filter F comprises a group of anti-resonant circuits connected in series. These filter sections are individually tuned to frequencies which are harmonically related to a fundamental frequency whose period is the discharge time of the generator. Consequently the periods of the filter sections are submultiples of the period of pulse duration. In the circuit as shown. C2-Le constitute a section resonant at the second harmonic, C3L3 at the third harmonic, and in general Cn-Ln is resonant at the nth harmonic. In practice only a limited number or sections need showing of a further impulse generator of the be used, as the amplitudes of the higher harmonic voltages present in the circuit decrease in proportion to the harmonic number.

On initiation of the discharge by closing switch 4, the current flows from the storing circuit through filter F and the load impedance R. The discharge current is determined by the internal impedance of the storing circuit, the impedance of the filter circuit, and the load impedance.

In Fig. 1, the storing circuit comprising capacitors Ca and Cb connected by inductance L is characterized by having an internal impedance anti-resonant at the fundamental frequency, or at one of the harmonic frequencies thereof, the corresponding filter section being absent. For the reasons outlined above, the storing circuit of Fig. 1 is anti-resonant at the fundamental frequency, and the filter sections accordingly are tuned to the second and higher harmonics thereof.

Considering the energizing voltage of the storing capacitors as er, the voltage developed across the filter and the internal impedance of the storing circuit together as es, we have, where E is the original potential of the capacitors:

0 id: cJot Where i is the discharge current at any time t.

The voltage set up across the load impedance 62=Ri The voltage as developed by 2' across the filter and the internal impedance of the storing circuit If we take 63 as above determined as fit), the function may be resolved into a constant voltage and alternating voltage components of a series of harmonically related frequencies, by Fourier analysis. The period of the fundamental component is determined by the discharge time of the circuit, and the other components are of periods equal to the sub-multiples of the discharge time.

The current flow may now be determined for each alternating voltage component. The filter sections and the storing circuit are adjusted for parallel resonance to the several voltages. The impedance ofiered each component by the circuit element resonant thereto is far greater than the impedance of the other elements, and consequently the current flow for the component in the circuit as a whole is substantially determined by the impedance of its respective element.

The reactive current passed by a parallel resonant circuit under application of an alternating voltage of the resonant frequency is, in the steady state condition, zero. This is due to the phase opposition and consequent cancellation of the leading current drawn by the capacitor and the lagging current drawn by the inductor. The line current is negligible due to the high resistance at resonance.

If, however, the alternating voltage is suddenly applied, cancellation does not take place, because the current drawn by the inductor differs from that drawn in the steady state condition by a transient term exponentially decreasing with time at a rate determined by the ratio R/L of the coil, whereas the current drawn by the condenser is the same as that drawn in the steady state condition. The currents in the inductive and capacitative branches with the applied voltage e and the line current i, are shown in Fig. 2.

Under these transient conditions, the line current, being the difference between the currents in the two branches, is manifestly equal to the transient term of the inductive current, as also shown in Fig. 2.

This is the case for each alternating component of the applied voltage, and therefore the discharge current attributable to the alternating voltage components is the sum of the transient terms for each alternating component as applied to its resonant filter section. In a properly constructed coil the ratio R/L will be suificiently low to permit consideration of the transient terms as constant currents during the period of pulse duration. In addition, the constant or D. C. component of the applied voltage will also cause a substantially constant current in the discharge circuit. The deviations of the D. C. current component and the transients from the desired values are in opposite directions and therefore to a considerable extent cancel. Consequently, during the period of the pulse a substantially constant line current is drawn from the storing capacity.

Determination of this fact shows, further, that the voltage e1 across the storing capacity decreases linearly with time, and that the voltage e2 developed across the load impedance is constant during the pulse duration.

The voltage wave form of e1 is resolvable by Fourier analysis into a constant term and alternating components as follows:

f (z) =A+A sin we? sin 2am? sin mat Consequently the alternating voltage components supplied to the filter have an amplitude inversely proportional to their harmonic numbers. The voltage supplied by the storing capacity, together with the direct and lower harmonic alternating voltage components thereof, are illustrated in Fig. 3. In Fig. 4 is shown the square voltage wave developed over the load impedance by the constant current i.

In the circuit of Fig. 1 the impedance of the filter may be represented by Z. If a pi section as shown is discharged with a constant current i through an impedance Z and a load resistor R, the voltage relations on the circuit are as follows, using operational notation and infinite series:

Since it is desired that the filter impedance Z be a harmonic series of parallel L-C circuits, with the omission of the fundamental, IZ.1 may be expressed as follows:

If this value is substituted in the above equation and like frequency terms are equated, the following relationships are obtained For complete dissipation of stored energy in the time interval t=21r/w Where a nonlinear load is employed, however, the matching is not critical.

It is often desirable to employ a plurality of storin sections to supply the energy for pulse generation. The storage sections may be charged in parallel and discharged in series as a Marx generator to produce a high voltage output. The embodiment of the invention shown in Fig. employs a Marx type voltage multiplier including as storing components pi sections of special design.

In Fig. 5 the power supply comprises a halfwave rectifying system including transformer 20 and rectifier 2|. The Marx generator includes similar pi sections 5, t, l and 8, each comprising an inductance 9, and two capacitors l6 and H.

The successive pi sections are connected by chokes I2. The storing components are charged in parallel on the positive half-cycles fed through rectifier 2|. and are discharged in series during negative half cycles by synchronously driven gaps l3. For operating the gaps iii a synchronous motor l4 may advantageously be employed, and energized by the same A. C. supply as transformer 20.

By operation of gaps 13 the potentials across the successive pi sections are connected in series through the filter it to load 22, which, as shown, is a high frequency triode oscillator. During discharge of the storage circuits a blocking effect is obtained by chokes l2 having a time constant suitable to prevent the discharge of the sections except in the desired series relationship.

The filter l5 comprisin parallel tuned components operates in conjunction with the storage circuit to provide a rectangular wave impulse for operation of the load exactly as in the system of Fig. 1. The discharge circuit includes in series circuit element groups which are anti-resonant to the fundamental discharge frequency and its harmonics, the groups referred to being the filter sections and the storing sections. In the embodirnent of Fig. 5 the storing sections are all tuned to the same irequency which in this case, for the reasons mentioned, is fundamental frequency, and the corresponding filter section is absent. Suitable values for the capacitors and inductances may be calculated by the formulas given below in connection with Fig. 6.

- The inductance i5 is placed in the discharge circuit to avoid the necessity for a multiplicity of filter sections, and functions to limit variations in the discharge current that would otherwise be caused by high frequency components.

The system disclosed in Fig. '6 includes a halfwave rectifier supply comprising power trans former 2i) and rectifier 2i ieedii energy storing

pi sections

23, 24, and 25 connected for parallel charging by chokes On the positive haliwaves the capacitors lil ll of each pi section are charged through rectifier 3.1 with increasing potentials which are applied across snarl: discharge gaps 25. These gaps are adjusted to breakdown preferably slightly below the peak voltage to insure dependable operation. On discharge of the gaps 26, a high potential rectangular wave impulseis applied to load impedance R. through filter 21, in the manner described above in connection with the system shown in Fig. 1.

As indicated in Fig. 6, the storage circuit may consist of any desired number of storage sections, and the filter 2'! may also be provided with any desired number of parallel resonant sections.

If the number of storing sections is represented by N, and the number of filter sections is it, then if the value of capacitors It is indicated Cb and H by Ca, and inductance 9 by L, then If the value of the filter condenser components 23 are represented by C2, C3 and Cu, and the inductances 32, 33, 34 etc. are represented by L2, L3 and Ln, where n is the harmonic number of the section:

For complete dissipation of in time t the load resistance is following relation:

It will therefore be seen that if it is desired to employ a plurality of storing sections instead of the single section generator system shown in Fig. 1, the storage capacitors are multiplied in proportion to the number of sections used and the inductance, expressed above as inversely proportional to the capacity, is therefore divided by the number of sections employed, so that the resonant frequency of the storage sections will remain the same. The filter sections will be the same in both cases.

The invention described herein may be ll1&l1.lfactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. In a rectangular wave impulse generating system, an energy storin circuit and a discharge circuit including pulse shaping filter means, said energy storing circuit comprising a pi section anti-resonant at a frequency of a period equal to the impulse duration time or a sub-multiple thereof.

2. A flat topped wave generating system comprising a plurality of circuit sections antiresonant at frequencies ofperiods equal to the impulse duration time and its submultiples, one of said anti-resonant sections including storing capacitor means, and switch means in said system operative to discharge said storing capacitor means through the system to generate the impulse.

3. In a rectangular wave impulse generating system, an energy storing circuit comprising a pi section, and a discharge circuit including a plurality of filter sections and a load impedance, said filter section and load impedance being connectable in series across the pi section, said pi section and filter sections being. anti-resonant at frequencies of periods equal to the impulse duration time and its submultiples.

4. In a rectangular wave impulse generating system, an energy storing circuit comprising a pi section anti-resonant at a fundamental frequency the stored energy determined by the of a period equal to the impulse duration time, and a filter circuit including a plurality of sec tions anti-resonant at harmonics of said fundamental frequency, said sections being connectable in series with each other across the pi section.

5. In a rectangular wave impulse generating system, an energy storing circuit comprising a plurality of pi sections, and a discharge circuit including a plurality of filter sections connectable across the pi section in series with each other, said circuit sections being anti-resonant at frequencies of periods equal to the impulse duration time and its submultiples.

6. In a rectangular Wave impulse generating system, an energy storing circuit comprising a plurality of identical sections, and a discharge circuit including a plurality of filter sections connectable across the pi section in series with each other, said circuit sections being anti-resonant at frequencies of periods equal to the impulse duration time and its submultiples.

7. In a rectangular Wave impulse generating system, an energy storing circuit comprising a plurality of identical pi sections, and a discharge circuit including a plurality of filter sections connectable across the pi section in series with each other, said circuit sections being anti-resonant at frequencies of periods equal to the impulse duration time and its submultiples.

8. In a rectangular wave impulse generating system, an energy storing circuit comprising a plurality of pi sections anti-resonant at a fundamental frequency of a period equal to the impulse duration time, and a discharge circuit including filter sections connectable across the pi section in series with each other anti-resonant at frequencies harmonically related to said fundamental frequency connectable across the pi section in series with each other.

9. In a rectangular wave impulse generating system, an energy storing circuit anti-resonant at a fundamental frequency of a period equal to the impulse duration time, and a discharge circuit including pulse-shaping filter sections connectable across the pi section in series with each other anti-resonant at frequencies harmonically related to said fundamental frequency connectable across the pi section in series with each other.

10. A rectangular wave impulse generating sys tem including energy storing circuit means and a discharge circuit therefor comprising filter circuit means having a series of inductance-capacity circuits connectable across the storing circuit in series with each other, the capacitors of the filter circuit means all having the same value, and the energy storing circuit means including a low pass pi section, the capacitor in series with the inductance having a value of 4/3 of one of the filter capacitors, and the other capacitor having a value equal to 2/3 of one of the filter capacitors.

11. A rectangular wave impulse generating system including energy storing circuit means and a discharge circuit therefor comprising filter circuit means having a series of inductance-capacity circuits connectable across the storing circuit in series with each other, the capacitors of the filter circuit means all having the same value, and the energy storing circuit means including a low pass pi section, the capacitor in series with the inductance having a value of 4/3 of one of the filter capacitors, and the other capacitor having a value equal to 2/3 of one of the filter capacitors, the

low pass pi section being anti-resonant at a fundamental frequency of a period equal to the impulse duration time, and the inductance-capacity filter circuits being anti-resonant at frequencies harmonically related to said fundamental frequency.

12. A rectangular wave impulse generating system including energy storing circuit means comprising a plurality N of low pass pi sections and a discharge circuit therefor comprising filter circuit means having a series of inductance-capacity circuits connectable across the storing circuit in series with each other, the capacitors of the filter circuit means all having the same value, the capacitors of the low pass pi section in series with the inductance having a value of 4N/3 of one of the filter capacitors, and the other capacitors of the low pass pi sections having a value of 2N/3 of one of the filter capacitors.

13. A rectangular wave impulse generating system including energy storing circuit means comprising a plurality N of low pass pi sections and a discharge circuit therefor comprising filter circuit means having a series of inductance-capacity circuits connectable across the storing circuit in series with each other, the capacitors of the filter circuit means all having the same value, the capacitors of the low pass pi section in series with the inductance having a value of 4N/3 of one of the filter capacitors, and the other capacitors of the low pass pi sections having a value of 2N/3 of one of the filter capacitors, the low pass pi sections being all anti-resonant at a fundamental frequency of a period equal to the impulse duration time, and the inductance-capacity filter circuits being anti-resonant at frequencies harmonically related to said fundamental frequency.

14. In a wave impulse generator, an energy storing circuit, a discharge circuit including a pulse shaping network and a load impedance, said energy storing circuit comprising inductance and capacity means. means for charging the capacity means to a predetermined voltage, and means for connecting the storage circuit to the discharge circuit to discharge the storage circuit and generate an impulse, the energy storage circuit being anti-resonant at a frequency of a period equal to the impulse duration or a submultiple thereof.

15. In a wave impulse generator, an energy storing circuit, a discharge circuit including a pulse shaping network and a load impedance. said energy storing circuit comprising inductance and capacity means, means for charging the capacity means to a predetermined voltage, and means for connecting the storage circuit to the discharge circuit to discharge the storage circuit and generate an impulse, the energy storage circuit and the pulse shaping network being anti-resonant at frequencies of periods equal to the impulse duration and its sub-multiples.

ARTHUR A. VARELA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS