US2338118A - Inverter - Google Patents

Description

Jan. 4, 1944. H. KLEMPERER v 2,338,118

INVERTER Filed Aug. 6, 1940 v 4 Sheets-Sheet 1 OUTPUT PRIMARY d GuRRcN-r 22 Ad ra cunnem In L-G Cmcum M f f Fl 6. Z. 2$ f L-C'Cmcun' K+t2 .."ll/- v flow-Ac: Acaoss The:

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Jail. 4, 1944 KLEMPERER 2,338,118

INVERTER Filed Aug. 6, 1940 4 Sheets-Sheet 2 INVENTOR HANS KLEMPERER I BY a'fl XT-rm Jan. 4, 1944. H; KLEMPE-RER 2,338,118

INVERTER Filed Aug. 6, 1940 4 Sheets-Sheet 3 l3 32 l8 I v -4 0.05OURCEJ hwzm-o R. HANs KLENPERER Patented Jan. 4, 1944 i INVERTER Hans Klemperer, Belmont, Mass, assignor to Raytheon Manufacturing Company, Newton,

Mass, a corporation of Delaware Application August 6, 1940, Serlal No. 351,630

18 Claims. This invention relates to inverters of the series type utilizing controlled gas filled electrical discharge tubes for converting direct current into alternating current.

Heretofore when it was attempted to increase the frequency or the power handled by such converters, failure has occurred due to the fact that an'insuflicient de-ionization time was available for each tube and therefore control of the tube was destroyed.

An object of this invention is to increase the reliability of operation of inverters of the foregoing type so that de-ionizati'on and consequent protection of the system against short circuiting v the direct current source is reliably secured.

Another object of this invention is to increase both power and the frequency which such inverters are capable of handling.

A further object is to devise an arrangement in which the forward voltage on each tube is suitable direct current source. Likewise,- an inductance iii. in parallel with a condenser H is connected from the anode 5 tea conductor l2 which extends to the positive side of the direct current source. The anode 3 andthecathode 8 are connected to the ends of the primary winding 13 on an output transformer l4 having a secondary winding l9 which is adapted to be connected to some suitable nu'tput device. A pair of condensers l5 and I6 are connected in series between the conductors 9 and I}. The primary winding 13 is provided with a center tap I! from whicha conductor I8 is connected to a point intermediate the condensers l5 and IS.

The tubes l and 2 are provided with-suitable igniting electrode elements and 2| for the. cathodes 4 and B respectively. Although these igniters are of any suitable kind, they preferably increased when conduction is desired but is-decreased when non-conduction is desired.

A still further object is to increase the inductance in series with the direct current source so as to limit the rate of rise of short circuit direct currents without, at the same time, substantially increasing the impedance of the system to alternating currents of the output frequency.

The foregoing and other objects of this invention will be best understoodfrom the following description of exempliflcations thereof, reference being had to the accompanying drawings wherein:

Fig. 1- is a diagrammatic representation of an inverter system embodying my invention;

Fig. 2 is a set of curves illustrating the mode .of operation of the arrangement shown in Fig. 1;

Figs. 3, 4, and 5are diagrams of modifications of the arrangement shown in Fig. 15

Fig. 6 is a diagram of an embodiment of m invention utilizing a larger number of tubes and capable of greater power and higher frequency operation; and p Fig. 'I is a set of curves illustrating. the mode of operationof the arrangement shown in Fig. 6. The inverter illustrated in Fig. 1 consists of a .pair of controlled discharge tubes 1 and 2. These are preferably gas filled tubes of the controlled ignition type. Tube I contains an anode 3 and a cathode 4, preferably of the mercury pool type. The tube 2 likewise contains an anode [and a cathode 6 which preferably'is similar to cathode 4; An inductance I in parallel with a condenser by a thin glass layer.

are of the electrostatic type as described and claimed in the co-pending application of Percy- L. Spencer, Serial No. 303,963, filed November 13, r 1939. Such igniters are generally a conductor separated. and insulated from the cathode. pool In order to supply igniting impulses tothe igniters 20 and 2|, a source of alternating current 22 is connected to the'primary winding 23 of a peaking transformer 24 having a saturable leg 25 which carries a pair of secondary windings 26 and 21 in which peaked igniting voltages are generated. A pair'of conductors 28 and 29 connect the secondary winding 26' between the cathode l and its associated igniter 20. A'pair of conductors 30 and ill connect the secondary winding 2'! between the cathode 8 and its associated igniter 2i.

When the system described above is energized, the condensers l5 and I6 are each charged to a voltage which is approximately half the voltage of the direct current source connected between the conductors 9 and I2. Thereupon the secondary winding 26, for example, supplies an igniting impulse to the igniter 20 which starts an are spot on the cathode 4 and permits the tube l to conduct current. The condenser l5 having been charged to a direct current voltage as described above makes the anode 8 positive with respect to the cathode l and thereforecauses the tube l to conduct a pulse of current which discharges the condenser I5. The discharge circuit of the condenser l5 may not be critically damped-and. therefore its discharge current may tend to be oscillatory. Therefore, when the condenser l5 discharges through the tube I, its voltage is reversed and the magnitude of the reversed voltage is determined by the degree to which energy is absorbed in the output circuit. Since the voltage which is impressed upon the condenser I6 is the sum of the direct current source of voltage and the voltage on the condenser I 5, it will be seen that during the discharge of the condenser I5, the condenser I6 is charged to a somewhat higher potential than that of the direct curren source.

The discharge current for the condenser I and the charging current for the condenser I6 flows primarily through the condenser 8 due to the fact that the inductance 1' offers a relatively high impedance to such currents. Therefore the condenser B likewise is charged to a voltage which makes its upper end positive and its lower end negative. It will be seen likewise that the charge on the condenser I6 is such that its left end is negative and its right end is positive. The voltage on the condenser I6 substantially neutralizes the voltage of the direct current source so as to tend to extinguish the tube I. In addition, the voltage on the condenser 8 is in a direction so as to extinguish the tube I. The result, therefore, is that when the condenser I5 is discharged the condensers 8 and I6 extinguish the flow of current in the tube I. The foregoing operation causes a short pulse of current toflow from the center tap I! through the left half of the primary winding I3. At some later time, the secondary winding 21 supplies an igniting impulse to the igniter 2| which causes the tube 2 to fire. Current now flows in such a direction as to discharge the condenser I6 and charge the condenser I 5 to a higher voltage than it initially had, in a manner similar to that described in connection with the initial discharge of condenser I5. In this case also, the discharge current for condenser I6 and the charging current for the.

condenser I5 flows primarily through the condenser II and the charge on the condensers II and I5 extinguishes the discharge in the tube 2. Thisaction likewise causes a short pulse of current to flow to the center tap I! through the ht half of the primary winding I3.

The flowing of current pulses through each half of the primary winding I3 introduces an additional commutating action into the system. When tube l, for example, is fired so as to produce a pulse of current flowing from the center tap 11 through the left half of the prima y Winding I3, a back voltage is generated opposing such flow of current. This back voltage is likewise generated in the right half of the primary winding I3 and is in the non-conducting direction of tube 2. If at this time, there is any tendecy for tube 2 to conduct current in the forward direction, the voltage impulses thus generated cause such tendency to be extinguished.

In absence of the parallel circuits comprising the inductance I and the condenser 8, and the inductance Ill and condenser II, shortly after the starting of either tube I or 2, a relatively high forward voltage would be impressed on the opposite tube. This would occur within a very short time interval after conduction in said opposite tube ceases. This time interval would be decreased as the frequency would increase. In the present invention, however, the charges on the condensers 8 and II respectively do not immediately disappear inasmuch as they can only be reversed through the inductances I and I0 respectively. Therefore, the voltages on these condensers 8 and II remain as voltages in opposition to the forward voltage applied to the associated tubes following the starting of theop posite tube. The effect, therefore, is to delay the application of the forward voltage to the tubes I and 2 and thus give them alonger time in which to de-ionize. The frequency of the parallel inductance and capacity circuits is not critical, but the maximum effect is produced when the frequency of each of these circuits equals the frequency of firing of the associated tube. Under these conditions, when the time arises for either tube I or 2 to fire, the charge on the associated condensers 8 or II will have reversed and thus be in a direction to assist the tube to fire. Part of the energy which is stored in the charge on the condenser will, under these conditions, be delivered as useful energy to the out put system by the current flowing through the primary winding l3 and due to the fact that the discharge circuit for such condensers contains considerable inductance, part of the energy will be returned-to the condenser to charge it in the opposite direction so as to assist in the de-ionization of its associated tube.

The foregoing operation may be more clearly understood from the curves of Fig. 2. Along axis a are shown a series of current pulses d representing the current pulses delivered to the primary winding I3. The left hand current pulse may, for example, be delivered as a result of the firing of tube I. A substantially similar pulse of current J shown on the b axis is delivered to the condenser 8. Said condenser, prior to this time, has acquired a certain charge a will be pointed out below. When the pulse of current f is delivered to the condenser, it neutralizes the previous charge and causes the condenser to be charged up in the opposite direction to a somewhat higher potential. Along the axis a, the time during which the left pulse of current d flows is represented as k. During this time, the tube is conducting and its voltage, represented by g remains substantially constant at the voltage drop of said tube. At the end of the time k the current 11 which is likewise flowing through the tube, tends to reverse and since the tube cannot conduct such reversed current, it stops conducting. In absence of the inductance I and condenser 8, when tube i stops conducting current, the reversed voltage of the condenser I5 would appear across it. This voltage is represented by the lower horizontal portion of the dotted curve It on the axis 0. In the arrangement as shown in Fig. 1, however, in addition to the reversed voltage of the condenser I5, the voltage on the condenser 8 is likewise impressed on the tube I in the non-conducting direction, so that the voltage which appears across the tube I in the non-conducting direction at the end of the time k is the sum of these two voltages as stated above. Since the back voltage is increased to this extent, the ions are swept out of the discharge space at a more rapid rate and de-ionization is accelerated.

After the time k the condenser 8 starts to discharge through the inductance I at a rate determined by the natural frequency of the parallel inductance-capacity circuit as shown on the axis 2) in Fig. 2. In the arrangement as shown in Fig. 1, the natural frequency of the parallel inductance-capacity circuit is somewhat lower than the output frequency of the system. Due to the discharge current flowing from the condenser 8, its voltage will decrease along the curve e, reverse in direction, and acquire a certain value in the opposite direction. When the associated tube is again fired, the voltage which would appear capacity circut represented by thedotted curve h after the time k, continues at the value of the reversedvoltage on the condenser II for atime h when the tube 2 is fired. Due to theback voltage generated in the primary winding I! as pointed out above, an increased inverse voltage would be impressed on the tube causing the lower peak to occur on the curve 7;. Due to the firing of the tube 2 the next pulseoi' current d is supplied to the primary winding it. During this time, under the conditions of operation, in absence of the parallel. inductance-capacity circuit, the discharge and revers l of voltage of the condenser l6 would cause the voltage across the tube l to decrease, reverse, and increase in the opposite direction as shown by the dotted curve h. Since each tube is not extinguished exactly at the zero value of current but at a value slightly above it, a back voltage generated in the primary winding l3 upon the termination of the current how in the tube 2 causes a slight decrease in the value to which the condenser I5 is charged dur ing the discharge and reversal of voltage on the condenser i6. This produce the drop in the curve h from its upper peak value as shown in Fig. 2. Thereupon the voltage across the tubel would conduct along the upperhorizontal value of the curve h which likewise represents the value of the voltage acquired by the condenser l5.

" Since, as pointed out above, the resultant voltage on the tube l in the arrangement shown in Fig. 1 is the summation of the voltage across the inductance-capacity circuit and the voltage which would appear across the tube in absence of said circuit, this resultant voltage may be represented in Fig. 2 by the summation of the curves e and h. ---In Fig. 2, curve g after the time k represents this summation. It will be seen by the curves on the axis that without the inductancecapacit-y c rcuit, the voltage 'across tube 1 remains in the non-conducting direction following the stoppageof conduction in said tube forthe time is. However, due to the delay in the reversal of this voltage by the inductance-capacity circuit. in the present arrangement, the voltage thus remains in the non-conducting direction for a longer time t3. The time during which the voltage remains in the non-conducting direction is the de-ionization time of the tube, and therefore, it will be seen that by the present arrangement the de-ionization time of each tube can be decreased. Furthermore, it will be noted that when the voltage on the tube I does reverse, it does not increase at as rapid rate as that which would occur in absence of the parallel inductancecapacity circuit. Since the tendency of this type of tube to break down before beingsupplied with an igniting impulse depends to a large degree on the rapidity at which the forward voltage 'is applied thereto, this decrease in the rate at which the forward voltage is applied increases the reliability of operation and decreases the tendency the condenser 8 a well as that of the condenser -stantially independent commutating means present in the arrangement shown in Fig. 1."

These are the two condensers Ill and I8, the'primary winding i3 acting through its back E. M. I". on each of the tubes, and the parallel inductancecapacity circuits associated with the two tubes. This makes for a very reliable type of operation.

In some instances, however, 'one of the foregoingcommutating means may be dispensed with and satisfactory operation obtained. For example, Fig. 3 shows an arrangement in which the commutating effect of the center tapped primary winding l3 of Fig. l is eliminated by placing said primary winding directly in series with the conductor l8 extending to a point intermediate the condensers l and it. In Fig. 3 where the elements are identical with those hown in Fig. 1,

the same reference numerals are applied. Fig. 3

operates in the same way as described in connection with Fig. 1- except that the commutating effect of the center tapped primary winding 03 of Fig. l is eliminated. It will be noted that in Fig. 3, instead of taking the output energy from the upper connection between the two tubes as shown in Fig. 1, the output energy is taken from the central connection. Under these conditions, instead of the pulses of output current being delivered successively in the same direction as in the case of Fig. 1, such pulses are delivered successively in opposite directions in Fig. 3.

Fig. 4 shows an additional modification of Fig. l in which the commutating effects of the condensers l 5 and I6 are eliminated. In Fig. 4 likewise, where the elements are identical with those of Fig. 1 the same reference numerals are applied. In Fig. 4 the series connection of the two condensers l5 and I6 of Fig. 1 is replaced by a voltage dividing resistance IS. The arrangement s own in Fig. 4- operate's in a manner similar to that described in connection with Fig. 1 'except that the commutating effects of condensers l5 and i6 are eliminated and the energy for commutating each tube is stored primarily in the condensers 8 and II, respectively.

If it is desired to take oi the output energy from the central connection as shown in Fig. 3 and at the same time utilize the commutating effects of a center tapped'co-il connected between the two tubes, the arrangement shown in Fig. 5 may be utilized. In this figure a voltage dividing resistance or inductance I5 is used as in Fig. 4 instead of the condensers l5 and it of Fig. 1. The primary winding I3 is arranged in series with the central conductor It as in Fig. 3. In

- addition, an induction coil I3 is connected between the anode 3 and the cathode 6. This coil is wound upon a suitable magnetic core [4. The center tap H in this instance is on the coil l3. In Fig. 5 the system operates in a manner similar to that of Fig. 4 differing therefrom in the output current impulses in the same way as Fig. 3 differs from Fig. 1.

If it is desired to increase either the power or the frequency of the inverter over that which is practical for the foregoing embodiments, a system utilizing a larger number of tubes may be 15 so that the forward voltage on said tube is used. Such an arrangement is shown in Fig.6. Here also where the elements are identical with those in Fig. 1, the same reference numerals are applied. Instead of using two tubes as in Fig. 1,

however, a plurality of pairs of tubes 32, 33, 34,

35, 36, and 31 are provided. Each of these tubes is'preferably' similar to the tubes I and 2 of Fig. 1 and are therefore provided with an anode, pool type cathode, and an igniting electrode element.

The tubes 32, 33, and 34 have their anodes connected to one side of the primary winding I3 while the tubes 35, 36, and 31 have their cathodes connected to the right end of said primary winding in a manner similar to that described in connection with tubes l and 2 of Fig. 1.- In Fig. 6, each of the tubes has connected in series there with a parallel inductance-capacity circuit consisting of an inductance 38 and a capacitor 39. Each of the igniting electrode, elements is supplied with igniting impulses from an igniting transformer 40, having a primary winding 4! preferably connected in delta. Said primary winding is connected through leads 42, 43 and 44 to a suitable source of three phase alternating current 45. The igniting transformer 40 is provided with a six phase secondary winding 46 connected in star. The secondary winding 46 consists of secondary coils 41 to 52 inclusive. The neutral point of the secondary winding 46. is provided with a ground connection 53. In series between the outer ends of the secondary coils ill to 52 inclusive and ground, are connected primary windings 54 to 59 inclusive of peaking transformers 60 to 65 inclusive. These peaking transformers are provided with secondary windings 66 to H inclusive. Connections are made from the peaking transformers to the tubes so that the tubes on opposite sides of the inverters are alternately fired in sequence. For this purpose, the secondary windings of the peaking transformers are connected to the tubes as follows: secondary winding 66 to tube 32, secondary winding 61 to tube 35, secondary winding 68 to tube 33, secondary winding 69 to tube 36,- secondary winding 10 to tube 34, and secondary winding 1| to tube 31. Each igniter of the type described above produces an arc spot on its associated cathode when it is supplied with a voltage impulse which is positive with respect to the cathode. The peaking transformers, however, each supplies pulses which are alternately opposite in polarity. As shown in Fig. 6, by reversing the connections to the secondary windings 69 to H, each compared to the secondary windings 66 to 68, the alternate firing of tubes on opposite sides of the inverter may be produced.

The operation of the arrangement shown in Fig. 6 may be more clearly understood by referring to the curves of Fig. '7. Along axis a are shown a series of current pulses d representing pulses of current delivered to the primary winding I 3. The left hand current pulses may, for example, be delivered as a result of the firing of tube 32. As described in connection with Fig. 2, during this period which is again represented by k a pulse of current f is delivered to the associated condenser 39, causing the voltage e of said condenser to reverse as indicated on the axis b of Fig. '7. Thereafter, the charge on the condenser 39 discharges through its associated inductance 38 in a pulsatory manner so that the voltage e of said condenser reverses, also as shown on the axis b, while the current in the inductance-capacity circuit varies in accordance with the curve f. In absence of the use of the condenser 39 and inductance 38, the voltage across each tube in the arrangement of Fig. 6 would follow the dotted curve h on the axis of Fig. '7. However in the arrangement shown, the voltage e of the inductance-capacity circuit is added to said voltage h and the resultant voltage across each tube is represented by the summation curve a. From Fig. 7, it will be seen that in absence of the inductance 38 and capacity 39,

the de-lonlzation of each tube would be represented by the relatively short time is while in the arrangement of Fig. 6, the de-ionization is considerably increased to the value as represented by 153. In order to produce the maximum effect of the parallel inductance-capacity circuit, the frequency of oscillation is selected as a sub-multiple of the output frequency so that the voltage across each of the condensers 39 completely reverses between each pulse of charging current supplied thereto. As previously stated, the frequency-of this inductance-capacity circuit is not critical and may vary considerably from such a Value.

Of course, it is to be understood that this inventionis not limited to the particular details as described above as many equivalents will suggest themselves to those skilled in the art. For

example, other types of controlled discharge tubes may be utilized as well as various other numbers of such tubes. Other variations and utilizations of principles innumerable will suggest themselves to those skilled in the art. It *is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

-What is claimed is:

1. An inverter comprising a space discharge tube, a commutating means and an output means in series, means for connecting said inverter to a source of voltage, and means for generating a periodic voltage tending to increase current flow throughsaid tube during the conducting period and to oppose such flow of current during the non-conducting period following stoppage of current flow upon commutation.

2. An inverter comprising a space discharge tube, a commutating means and an output means in series, means for connecting said inverter to a source of voltage and means for generating a periodic voltage aiding the first named voltage during flow of current through said tube and opposing said first named voltage upon stoppage of current flow by said commutating means.

3. An inverter comprising a space discharge tube, a commutating means and an output means in series, means for connecting said inverter to a source of voltage, and means responsive to the initiation of current through said tube to increase the magnitude of said current and to decrease the 'tendency of said current to flow during the nonconducting period following stoppage of current by said commutating means.

4. An inverter comprising a space discharge tube, a commutating means, an impedance means, and an output means in series, and means for connecting said inverter to a source of voltage, said impedance means having a relatively high inductance value and a relatively low alternating current impedance value to periodic currents of substantially the output frequency of said inverter.

5. An inverter comprising a. space discharge tube, a commutating means, an impedance means, and an output means in series, and means for connecting said inverter to a source of voltage, said inverter being tuned to substantially the desired output frequency, said impedance means having a relatively high inductance value and such a relatively low alternating current impedance value that said tuned frequency is substantially unimpeded by said impedance means.

6. An inverter comprising a space discharge tube, a condenser, and an output means in series, an inductance and a condenser connected in parallel with each other in series with said tube, and means for connecting said inverter to a source of voltage. I

7. An inverter comprising a space discharge tube, a condenser, and an output means in series,

an inductance and a condenser connected in parallel with each other in series with said tube,

. being tuned to a substantially'lower frequency than said output frequency. v

9. An inverter comprising a space discharge tube, a condenser, and an output means in series, and means for connecting said inverter to a source of voltage, said inverter having a predetermined output frequency, an inductance and a condenser connected in parallel with each other in series with said tube, said parallel circuit being tuned to a substantially lower frequency than said output frequency.

10. An inverter comprising a space discharge tube, a condenser and an output means in series, means for connectingsaid inverter to a source of voltage, said inverter having a predetermined output frequency, an inductance and a condenser connected in parallel with each other in series with said tube, said parallel circuit being tuned to a substantially lower frequency than said output frequency, and means for discharging said first-named condenser.

11. An inverter comprising a plurality of space discharge tube paths, a commutating means and an output means in series and a separate independent inductance and a condenser connected in parallel with each other in series with each of said paths, and means for connecting said inverter to a source of voltage.

12. An inverter comprising a plurality of space discharge tubes connected in paralleland connected in series with a commutating means, and feeding a common output means, means for connecting said inverter to a source of voltage, an independent inductance and a condenser connected in parallel with each other in series with condenser connected in parallelwith each other in series with each of said tubes and means for firing--v each of said tubes at a submultiple of the desired'gutput frequency, said firing means being displaced in phase so that said tubes supply pulses of current successively to said output means..

14. An inverter comprising two condensers connected in series and adapted to be connected across a source of current, a space discharge tube feeding an output means and connected between one end of said series circuit and a point between each of said tubes and means for firing each of said tubes at a submultiple of the desired output frequency, said firing means being displaced in phase so that said tubes supply pulses of current successively to said output means.

13. An inverter comprising a plurality of space discharge tubes each connected in series with a commutating means and feeding a common output means, an independent inductance and a said condensera'another space discharge tube feeding said output' means and connected between the other end of said series circuit and said point, an independent inductance and a condenser connected in parallel with each other in series with each of said tubes, and means for alternately firing said tubes.

15. An inverter comprising two condensers connected in series and adapted to be connected across a source of current, a space discharge tube feeding an inductance and connected between one end of said series circuit and a point between said condensers, another space discharge tube feeding said inductance, and .connected between the other end ofsaid series circuit and said point, an independent inductance and a condenser connected in parallel with each other in series with each of said tubes, and means for alternately firing said tubes.

16. An inverter comprising two condensers connected in series and adapted to be connected across a source of current, a space discharge tube feeding a part of an inductance and connected between one end of said series circuit and a point between said condensers, another space discharge tube feeding another part of said. inductance and connected between the other end of said series circuit and said point, an independent inductance and a condenser connected in parallel with each other in series with each of said tubes, and means for alternatelyv firing said tubes.

17. An inverter comprising a resistance adapted to be connected across a source of current, a space discharge tube feeding an output means and connected between one end of said resistance and an intermediate point in said resistance, another space discharge tube feeding said output means and connected between the other end of said resistance and said point and means for alternately firing said tubes.

18. An inverter comprising a space discharge tube, a commutating means, an impedance means, and an output means in series, and means for connecting said inverter to a source of voltage,

said impedance meanshaving a relatively high

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