US2114856A - Electric valve converting system - Google Patents

Description

April 19, 1938. H. NE/IDHARDT 2,114,856

ELECTRIC VALVE CONVERTING SYSTEM Filed Sept. 20, 1937 4 SheetE-Sheet l Figl.

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- April 19,- 1938. H. 'NE IDHARDT 2,114,856

ELECTRIC VALVE CONVERTING SYSTEM Filed Sept. 20, 1937 4 Sheets-Sheet 2 Inventor:

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April 19, 1938. H. NEIDHARDT I 2,114,856

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April 19,1938. H. NE IDHARDT 1 7 ELECTRIC VALVE CONVERTING SYSTEM Filed Sept. 20, 1937 4 Sheets-Sheet 4.

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Inventor:

Hans Neidhardt Z w M His Attorhey Patented Apr. 19, 1938 PATENT OFFICE ELECTRIC VALVE CONVERTING SYSTEM Hans Neidhardt, Berlin, Germany, assignor to General Electric Company, a corporation of New York Application September 20, 1937, Serial No. 164,811 In Germany October 9, 1936 5 Claims.

My invention relates to electric valve converting systems for transmitting energy between alternating current circuits of different frequencies and more particularly to improved excitation ap- 5 paratus for such converting systems.

Heretofore in frequency changers it has been proposed to control the control electrode or grid of the electric valve of such a system by impressing thereon voltage components obtained from each of the alternating current circuits. In some instances this has been accomplished by distributors coupled to synchronous motors and in other arrangements one or more control transformers were supplied for each of the valves or discharge l5 paths. Such arrangements often havethe dis-- advantage that the control equipment is neither simple nor economical to produce. It furthermore has been suggested that these voltage components from the different circuits which are sup- 20 plied to the control electrodes b of substantially rectangular wave shape. Where? such rectangular impulses have been utilized 1 has often been found difficult to prevent undesired gaps between the various impulses, and the abnormal operation 25 of the system resulting from such gaps in the control potentials. In some instances where the output voltage was decreasing in magnitude it is found that the rectangular voltage component increased in time duration so that it was not at all 30 certain that proper commutation would occur at all times. In some arrangements it has been found that the output characteristics and the frequency thereof were varied due to the fact that when the output voltage began to drop, the

35 rectangular voltage component obtained from the output circuit would increase thereby causing such undesired changes in the characteristics and frequency of the system. In still other arrangements it has been found that a change in the 40 phase of the voltage components supplied to the' control electrode produced an undesired change in the phase of the voltage output of the system without changing appreciably the output voltage.

It is an object of my invention, therefore, to provide a new and improved electric valve convertlngsystem and an improved grid excitation apparatus therefor which will simplify the systems of the prior art and which will solve the above mentioned difficulties.

It is another object of my invention to provide a new 'and improved electric valve converting system and an excitation apparatus therefor wherein the apparatus is greatly simplified and 55 a single apparatus supplies automatically the proper voltage component for both rectifier and I inverter operation.

In accordance with the preferred embodiment of my invention the disadvantages of the prior art have been obviated by the use of a grid excitation 5 circuit which uses a minimum of apparatus. In a system utilizing two polyphase networks with zero anodes or electric valves for the neutral points thereof two transformers are common to all of the control circuits and one transformer 10 supplies control energy to two discharge paths corresponding to phase opposed windings in the two networks. The one transformer supplies voltage components which insure proper commutation between the zero anode and the anode connected to the various terminals of the phase network and the second common transformer supplies negative voltage components which insure that an anode will not become conductive during its normal nonconductive periods. By means of a plurality of windings and unilaterally conductive devices such as contact rectifiers the remaining transformers supply control components to the anodes of one of the phase networks so that this network will operate as an inverter and simultaneously the transformer operates at the proper time intervals to supply voltage components having the proper relation to the other anodes on the other network so that this network will operate as a rectifier. Since this latter transformer is effectively in series with the transformers deriving voltage components from the output source, it operates to reverse the operation of the various networks whenever the direction of the flow of the energy between the two circuits is reversed. This occurs automatically without the use of auxiliary windings or auxiliary apparatus.

My invention itself, however, both as to its organization and method of operation, together 40 with further objects and advantages thereof, will be better understood by reference to the following description taken 'in connection with the accompanying drawings in which Fig. 1 shows one embodiment of my invention; Fig. 2 is an explanatory figure; Fig. 3 shows the detail of one of the transformers utilized therein; Fig. 4 shows a modification which may be utilized in the embodiment shown in Fig. 1; Fig. 5 shows a preferred embodiment of my invention, and Fig. 6 shows curves explanatory of the operation of the em.- bodiment shown in Fig. 5.

Referring now to Fig. 1 of the drawings, I have illustrated an electric valve converting systern for 'ransferring energy between two altergized from the circuits f1 and f2.

nating current circuits of different frequencies such as the circuit indicated as h and the circuit indicated as f2. This electric valve converting system includes a transformer having its primary winding connected to the circuit f1 and having two groups of secondary windings I, 3, 5 and I, 3", 5", the neutral points of which are connected through the primary winding of the transformer connected to the circuit f2 and the reactor D to the cathode K of a multi-anode single-cathode controlled electric valve. The various extremities of the groups of secondary windings A and A are each connected to anodes of the rectifier which are controlled by starting electrodes or grids. The neutral points of each of these secondary windings are each connected to a grid controlled anode. The various grids of the anodes which are connected to the extremities of the secondary windings A and A" are controlled by means of a control circuit indicated by the rectangle St which comprises a plurality of transformers arranged to be ener- For the purposes of explanation it will be assumed that the transformer T2 is connected to the circuit f2 which is of a lower frequency than the circuit f1. The grid control circuit utilizes only one such transformer, but three transformers similar to T1 which are each connected to the high frequency circuit ii are utilized. For the purpose of simplifying the disclosure the grid circuit for only one of the grids of the secondary network A and A" is shown. The transformers T1 and T2 are so designed as to supply rectangular voltage impulses such as illustrated in Fig. 2. In Fig. 2 the line Uz indicates the critical voltage which must be exceeded in order to initiate the flow of current between one of the anodes and the cathode. The curve UT represents a voltage impulse applied by the transformer T1 and the curve UT represents the voltage impulses supplied by the transformer T2. As is apparent from Fig. 2, the duration of the positive impulse of the transformer T2 as shown by curve UTZ is somewhat shorter than the time interval of the positive impulse supplied by the transformer T1 as shown by curve UT The critical voltage U2 is only exceeded when thevoltage impulse of UT, and U12 are cumulative.

The transformer T1 is provided with a primary winding which is connected to the circuit f1 and a plurality of secondary windings 8, 9, I0 and II and an auxiliary winding I2 which is connected to a variable source of direct current Ug. One of the secondary windings 8 of the transformer T1 is connected through the conductor IT, a unilateral conducting device or contact rectifier 6, a current limiting resistor I, to.the grid of the anode which is connected to the phase winding I. The secondary winding 9 is connected through the conductor I8 through a contact rectifler 6 and a current limiting resistor I to the grid of the anode which is connected to the phase winding I". The remaining connections of the secondary windings 8 and 9 are connected winding I; and the secondary winding II is.

connected through conductor I6, the contactrectifier 6, the current limiting resistor I to the grid of the anode of the phasewinding I. The remaining extremities of the secondary windings 8i] and II are connected together through one of the secondary windings of the transformer T2 and the biasing battery Uv to the cathode K of the electric valve. A pair 'of resistors I5 are each connected between the current limiting resistors I and an intermediate point on the bias battery Uv so as to prevent retardation of deionization of the discharge paths between the various anodes and the cathode of the electric valve. If very high potentials are utilized in the grid circuit it mayv occur that the control voltages would deviate from the rectangular shape, and in order to avoid such deviation a voltage and limiting device may be connected across each of the secondary windings of the transformer T2.v A transformer T0 is connected to the circuit 12 through a pair of contact rectifiers to energize the grids of the anode connected to the neutral points of the networks A and A. The midpoint of the secondary winding of the transformer To is connected through a portion of the bias battery Uv to the cathode of the electric valve.

In operation the various anodes become conductive only when there is applied to the grids thereof the accumulative effect of the two rectangular voltages Ur and Ur shown in Fig. 2 so that they exceed the negative bias Ut thereby intersecting the critical voltage line Uz. contact rectifiers 6 operate to prevent the secondary windings of the transformer T1 from. becoming short circuited and furthermore permit only the positive voltage impulses to be applied to the control grid. If it is assumed at a given instant that the left side of the transformer T2 is positive the transformer produces the' positive voltage impulse UT of Fig. 2. At the same instant the transformer T1 will supply the positive voltage impulse Ur so that the anode connected to the winding I becomes conductive. The curves shown in Fig. 2 show that the voltage waves Ur and UT coincide substantially because there has been no direct current magnetization of the transformer T1 by the winding I2 which is energized from a suitable source of current Ug. If now the winding I2 is supplying direct current magnetization to the transformer T2 the impulses supplied to the anode connected to the phase winding I will be shifted in a lagging sense, and the impulses transmitted to the grid of the anode connected to the phase winding I" will be shifted in a leading sense. This phase relation will be maintained in the same direction as long as the flow of power between the two circuits remains the same, but ifthe power fiow reverses, this direction of phase difference will also be reversed. The connections 3 and 5 shown adjacent to the secondary winding T2 indicate the points at which the other two transformers similar to T1 are to be connected in order to provide the necessary control circuits for the grids of the anodes 3', 5', 3", 5"

Fig. 3- illustrates the magnetic core structure of one of the grid transformers T1, the primary winding of which is energized from the circuit ii. The terminals indicated bythe reference character I are connected to opposite terminals of the secondary winding of the transformer T2 whereas the remaining terminals of the windings 8, 9, I0 and II are connected respectively to the conductors Il, I8, l9 and Hi. The magnetization of the core is controlled by energization of the winding l2 from a suitable source of direct current such as U2. This change in the magnetization of the core shifts the phase of the control impulses.

In accordance with further modifications of my invention, the arrangement shown in Fig. 4 illustrates how the transformer T1 may be constructed with only two secondary windings instead of four secondary windings. For the sake of clarity the primary and magnetizing windings of the transformers T1 and T2 have been omitted. The transformer T1 is therefore provided with two secondary windings l3 and M which are each connected between two groups of contact rectifiers, 6 and 6'. The series operation is the same as that shown in connection with Fig. 1.

Of course, it will be understood by those skilled in the art that while the operation has been described as occurring between two alternating current circuits having a frequency f1 and f2 that the ratio between these two frequencies need not be constant, but may vary during the operation of the system. It furthermore will be apparent that for optimum operation the zero anodes or the anodes connected to the neutral points of the networks A and A should not be rendered conductive until such time, in the instants of rectifier operation, that the rectangular voltage impulse supplied by the transformer T2 has reached a zero value. It furthermore will be apparent that between the positive impulses supplied to the various grids there always is a time interval between each sufficient to permit the zero anodes to become conductive.

In Fig. 5 there is shown a preferred embodiment of my invention in which the power circuit and certain portions of the grid circuit are identical to the arrangement shown in Fig. l and hence these parts have been given similar reference characters. The control circuits for the grids of the anodes of the windings I and I" include a transformer T1 which is identical to the transformer T1 of Fig. 1. The arrangement of the transformer T2 has been modified by the addition of the contact rectifier 6' across each of the secondary windings thereof 26, 21, so that the transformer T2 now supplies to the grid control circuit only the negative half wave component appearing across the secondary winding. A transformer T1 is connected between the source of biasing voltage Uv and the transformer T2 so as to supply negative half wave components to the grid circuits at the same time that positive half wave components arebeing supplied to the grid circuits of the anodes connected to the neutral points ofthe networks A .and A. The transformer T3 therefore comprises a primary winding connected to the circuit f2 and two secondary windings comprising respectively the inductive portions 20, 2| and 22, 23. A pair of contact rectifiers 25 are connected across the.

inductive portions 20, 2| of one of the secondary windings, which inductive portions are connected in series between the biasing source Uv and the transformers T2 and T1 of the grid circuits of the networks A and A". The transformers T1 and T3 are common to all of the grid controlled circuits of the anodes of the networks A and A, but three transformers similar to T1 -are utilized, one for each of the groups of the anodes I, I": 3, 3"; and 5', 5".

The inductive windings 22 and 23 each bypassed by one of the rectifiers 24 are connected between the source of biasing voltage Uv and the current limiting resistor I of the control circuits of the grids of the anodes of the neutral points of the networks A and A". Thus the control grids or electrodes of the zero anodes receive only the positive half wave impulses appearing across the secondary winding of the transformer T3. 1

The operation of the grid control circuits may be best understood by referring to Fig. 6 in connection with Fig. 5 from which it will be observed that the transformer T1 supplies a voltage impulse UT., and shown in the first curve of Fig. 6 ma manner similar to the arrangement shown in connection with Fig. l. The voltage UT must have a phase shift in a direction dependent on whether the network is operating as an inverter or a rectifier and this phase shift is indicated by the angle 25. Thus in certain instances the component supplied by this transformer will appear as shown in the second curve of Fig. 6. The degree of'this phase shift is controlled by the magnitude of the current flowing through the winding l2 and which is suppliedfrom a suitable source of current Ug. Due to the use of a contact rectifier 6 across the secondary winding portions of the transformer T2, this transformer supplies to the grid control circuit negative half wave components illustrated in the third curve of Fig. 6. The transformer T2 supplies negative voltage components which appear in the fourth curve of Fig. 6. This voltage obtained from the transformer T3 is about degrees out of phase with respect to the voltage obtained from transformer T2 since the primary winding of the transformer T2 is so arranged that a voltage supplied thereby is approximately 90 degrees out of phase with respect to the voltage suppliedby the primary winding of the transformer T2. These three components combine so as to produce the control represented by the sixth curve of Fig. 6.

In the sixth curve of Fig. 6 the dotted line which is separated from the center line by an interval of Uv represents the critical voltage which must be exceeded and which critical voltage has been obtained by proper adjustment of the source of biasing voltage Uv. Thus, during the first time interval 1, the high frequency impulses obtained from the transformer T1 operate to render conductive the anode controlled by this transformer. During the time interval II'the voltage impulses supplied by the transformer T2 prevent these anodes from becoming conductive and during the time interval III the negative voltage impulse supplied by the transformerT2 continues to prevent these anodes from becoming conductive and still further during the interval II these anodes still remain non-conductive due to the voltage supplied by transformer T3. During the time intervals II and II a voltage wave corresponding to the fifth curve and indicated as Ur operates to exceed the biasing voltage Uv thereby rendering conductive the zero anode or the anode connected to the neutral point of the networks A and A. From the last curve of Fig. 6 it is quite apparent that the voltage component supplied by the transformer T2 operates as .a rough control of the times at which certain anodes are not to be conductive and that the voltage component supplied by the transformer T3 operates as a finer control to determine with accuracy the time during which the anodes are not to be conductive. The curve shown in Fig. 6 at the bottom of the page of course is a representation of the control supplied when the particular network is operating as an inverter. 7

While the control voltages U'r3 and Ur have been obtained by the use of a saturable transformer together with contact rectifiers 2 4 and 25 across the secondary windings of the transformer T3 it will of course become apparent to those skilled in the art that any other means may be utilized in order to produce a similar wave shape. Furthermore it will be apparent to those skilled in the art that the voltage component obtained from the transformer T2 by means of the contact rectifier 6' may also be obtained by means of the well known full wave rectifier connection.

If during the time for commutation a change of direction of energy occurs there has been the possibility in prior arrangements that short circuit currents would arise. This would happen, for instance, when there is a short circuit current flowing between the different windings of the network A or between the two windings A and A". The initial magnetization of the transformer T1 by the winding I2 causes this current to be suppressed. The transformer Tl furthermore may be provided with such a winding which receives its energy from that portion of the circuit which includes the inductive choke D.

It of course. will be understood that if desired the arrangement in Fig. 5 can be made to supply any predetermined load characteristic by providing the transformer T1 with a magnetizing winding similar to winding l2 which is energized from the direct current flowing to-the cathodes of the multi-anode single cathode valve. If the transformer T1 is thus energized the voltage wave supplied thereby for both rectifier and inverter operation will be shifted in phase so that the system will have a predetermined operating characteristic. If with such an arrangement the rectifier should supply an excess current, the phase shift may be so great as to render all the valve aths nonconductive thereby protecting the operation of the system. It of course will be apparent to those skilled in the art that regulation of the power output of the system can also be obtained by variation of the voltage components UT, and U'r' supplied by the transformer T2 and Ta. A variation in the duration of these voltage impulses may be obtained by supplying each of the transformers T2 and T3 with auxiliary windings energized from a suitable source of direct current which source may be proportional to the current flowing to the cathode K.

While I have described what I at present consider the preferred embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An electric valve convertingsystem for transmitting energy in either directionbetween a high frequency alternating current circuit and a low frequency alternating current circuit comprising two groups of inductive windings, an electric valve for each of said windings, each of said valves having a control electrode, a control circuit for said valves comprising means for deriving an alternating potential of rectangular wave form from said low frequency circuit, means for deriving rectangular positive potential components from'said high frequency circuits, means for controlling the phase of said latter components with respect to said high frequency potential, and means for supplying said control electrodes with said alternating potential of rectangular wave form together with said rectangular positive potential component.

2. An electric valve converting system for transferring energy between high frequency and low frequency alternating current circuits comprising two groups of inductive windings each provided with an electrical neutral, an electric valve for each of said inductive windings and said neutrals, each of said valves being provided with a control electrode, a control circuit for said valves comprising means for deriving from said low frequency circuit alternating potentials of rectangular wave form, means for deriving from said high frequency circuit rectangularpositive potential components, means for controlling the phase of said latter components with respect to said high frequency potential, means for supplying the control electrodes of the valves associated with said inductive windings with said alternating potentials of rectangular wave form together with said rectangular positive potential components, and means for supplying to the control electrodes of said valves associated with said neutral point rectangular positive potential components derived from said low frequency circuit.

3. An electric valve converting system for transferring energy between high frequency and low frequency alternating current circuits comprising two groups of inductive windings each provided with an electrical neutral, an electric valve for each of said inductive windings and said neutrals, each of said valves being provided with a control electrode, a control circuit for said valve comprising means for deriving from said low frequency circuit rectangular negative potential components, means for deriving from said high frequency circuit rectangular positive potential components, means for controlling the phase of said latter components with respect to the potential of said high frequency circuit, means for deriving from said low frequency circuit simultaneously positive and negative rectangular potential components displaced in phase with respect to the potential of said low frequency circuit, a common source of negative biasing potentialfor all of said valves, means for supplying to the control electrodes of said inductive windings said high frequency positive potential components, said low frequency negative potential components and said phase displaced low frequency negative potential components, and means for supplying said phase displaced positive potential components to the control electrodes of the valves associated with said neutral points.

4. An electric valve converting system for transferring energy between two alternating current circuits of different frequency comprising two groups of inductive windings each provided with an electrical neutral, an electric valve for each of said windings and said neutrals, each of said valves being provided with a control electrode, a control circuit for said control electrodes comprising means for supplying to the control electrodes of the valves of said inductive windings voltage components derived from one of said alternating current circuits, means for supplying voltage components derived from the other of said alternating current circuits to the control electrodes of the valves of one of said inductive windings for rectifier operation and to the control electrodes of the valves of the other of said inductive windings for inverter operation, and means for supplying simultaneously to the control electrodes of said valves of said inductive windings negative voltage components and to the control electrodes of the valves of said neutral points positive voltage components.

5. An electric valve converting system for transferring energy between a high frequency alternating current circuit and a low frequency alternating current circuit comprising two groups of inductive windings each provided with an electrical neutral, an electric valve for each of said inductive windings and said neutrals, each of said valves being provided with a control electrode, a control circuit for said valves comprising means for supplying to the control electrodes of the valves of both-of said inductive windings voltage components derived from said low frequency circuit, means for simultaneously supplying to the control electrodes of the valves of one of said inductive windings voltage components derived from said high frequency circuit and retarded in phase relative thereto and to the control electrodes of the valves of the other of said inductive windings voltage components advanced in'phase relative to said high frequency circuit, and means for supplying simultaneously to the control electrodes of the valves of said inductive windings negative voltage components derived from said low frequency circuit and to the control electrodes of the valves of said neutral point positive voltage components.

HANS NEIDHARDT.

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