US2215313A - Electric valve converting system and control circuit therefor - Google Patents

Description

p 1940- E. F. w. ALEXANDERSON 2,215,313

ELECTRIC VALVE CONVERTING SYSTEM AND CONTROL CIRCUIT THEREFOR Filed Sept.- 29, 1959 Ernst F. W Al exanderson,

is Attorneg.

Patented Sept. 17, 1940 UNITED STATES PATENT OFFICE Ernst F. W. Alexanderson, Schenectady, N. Y.,

assignor to General Electric Company, a corporation of New York Application September 29, 1939, Serial No. 297,123

7 Claims.

My invention relates to electric valve converting systems adapted to transmit energy between alternating current circuits of the same or different frequencies, and more particularly to a control circuit for such systems.

Heretofore there have been devised various types of converting apparatus for transmitting energy between alternating current circuits of the same or different frequencies. Coincidently, there have been developed numerous arrangements for controlling the systems to effect the desired operation of the electric valve systems. Many of the control or excitation circuits for the main or power electric valves have involved apparatus complicated in arrangement and intricate in operation. In such arrangements it has been found preferable to use electric valve means of the gaseous type for the power valves because of the relatively large amounts of energy that may be handled at ordinary operating voltages. In the electric valve converting systems of the prior art it has been found desirable to control the electric discharge valves in response to a number of different electrical conditions to obtain the desired periodic energy transfer. Generally the prior art arrangements involve the use of auxiliary equipment of inordinate proportions to obtain the periodic energization of the associated main electric valve means, especially where a single control electrode is used for each electric discharge valve. In order to eliminate the complicated excitation circuits and the large amount of auxiliary equipment necessary to operate the electric valve apparatus, electric discharge valves have been used having two separate control electrodes each of which is energized in accordance with a different electrical condition. Such a system has been described and broadly claimed in my United States Letters Patent No. 2,122,271, granted June 28-, 1938. However, it would often be desirable to use electric discharge valves having a single electrode without requiring the complicated excitation circuits of the prior art but rather using control circuits which would be simple in arrangement and operation and which would assure certain and reliable performance.

It it an object of my invention, therefore, to provide an improved control circuit for electric valve converting systems adapted to transmit energy from an alternating current supply circuit to a load circuit which obviates the above mentioned undesirable features of the prior art arrangements and which is simple and reliable in operation.

It is another object of my invention to provide by means of improved and simplified control apparatus.

In accordance with the illustrated embodiment of my invention I provide an electric valve converting apparatus and excitation circuit therefor for transmitting energy between alternating current circuits of the same or different frequencies. The single control electrodes of the plurality of electric discharge valves utilized in the electric valve converting apparatus are arranged to be energized in accordance with a plurality of control potentials each responsive to a different electrical condition. A positive biasing means is connected in the grid to cathode circuit of the electric discharge valves tending to render the valves conductive, but a counteracting voltage appearing across a resistor in series with the positive biasing means nullifies the effect of said positive biasing means except at predetermined periodic intervals when it is desired that certain valves are to become conductive. This counteracting voltage is responsive to a plurality of different electrical conditions of said supply and load circuits, and until these electrical conditions are in a certain definite relationship the positive potential biasing means cannot render the electric discharge valves conductive.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, will best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure thereof diagrammatically represents an embodiment of my invention.

Referring now to the single figure of the drawing, I have illustrated therein an electric valve converting apparatus for transmitting energy between alternating current circuits l0 and II which may be of the same or different frequencies, and one of the frequencies may even be variable. Since my invention is equally applicable to the many different types of electric valve converting apparatus known to those skilled in the art, for simplicity of disclosure and explanation I have illustrated my invention as applied to a frequency changing apparatusutilizing a minimum number of electric discharge valves for transmitting energy between alternat ing current circuits I and II. rent circuit I0 is illustrated as a three-phase circuit although only a single phase electric valve converting system is connected thereto while alternating current circuit II is illustrated as a single phase circuit, but it will be understood that the number of phases of alternating current circuits In and II is not critical as far as this invention is concerned. The electric valve converting apparatus interconnecting circuits I0 and II which will be hereinafter termed load and supply circuits, respectively, comprises a transformer I2 and a plurality of electric discharge valves I3, I4, I5, I8. Transformer I2 is provided with a primary winding I! connected across one phase of alternating current supply circuit I0 and a secondary winding I8 the terminals of which are connected to one of the electrodes of the plurality of electric discharge valves I3--I6, respectively. Each of the electric discharge valves I3IB is provided with an anode I9, a cathode 20 and a control electrode or grid 2| and may be any of the types of electric valves known to those skilled in the art, although I prefer to use valves of the vapor electric type containing an ionizable medium. The electric discharge valves are illustrated as being of the type comprising a single set of electrodes mounted in an envelope but it is to be understood that multi-anode, single cathode valves could be utilized in certain cases. Electric discharge valves I3 and I4 have their anodes I 9 connected to the terminals of secondary winding I8 of transformer I2 and are arranged in the form of a biphase rectifier for periodically transmitting a potential of one polarity to alternating current circuit II. Electric discharge valves I and IS, on the other hand, have their cathodes 20 connected to the terminals of secondary winding I8 of transformer I2 and are also arranged as a biphase rectifier so as to periodically transmit a potential of the opposite polarity to alternating current load circuit II. A reactor 22 having terminals 23 and 24 respectively, and a midtap 25, has its terminal 23 connected to the cathodes 20 of electric discharge valves I3 and I4, while its terminal 24 is connected to the anodes I9 of electric discharge valves I5 and I6, respectively. It will be obvious that regardless of whether energy is being transmitted by electric discharge valves I3 and I4 or I5 and I6, current will fiow through a portion of reactor 22 wound on a single core 26 so as to produce flux in only a single direction in the core 26 thereof. Since it is not necessary to build up flux first in one direction and then in the other with reversal of energy flow, reactor 22, therefore, presents little or no impedance to the normal energy flow between alternating current circuits I9 and II although a very high impedance is afforded to any short circuit or cross currents between electric discharge valves I3, I4 and I5, I6.

In order to control the conductivity of electric discharge valves I3l6 in accordance with a plurality of different electrical conditions, each of the control electrodes or grids 2| is provided with an excitation circuit 21, 28, 29 and 30, respectively. These excitation circuits 2I--3ll include a positive biasing means illustrated as Alternating curbattery 3| connected in series with a resistor 32 in each of the gridto cathode circuits of electric discharge valves I3-I6, respectively. The positive biasing means 3| continuously tends to render electric discharge valves |3--IG conductive. However, excitation circuits 2'|--30 also include a plurality of transformers 33 and 34 having their secondary windings 35 and 35 each connected in series with a unilaterally conductive device 31 and 38, respectively. Each of the secondary windings 35 and 36 and the serially connected unilaterally conductive devices are connected in parallel with one another but in series with the resistor 32. Transformer 33 is provided with a primary winding 39 while transformer 34 is provided with a primary winding 40. The primary winding 39 of transformer 33 is arranged to be energized from a source of primary frequency and is illustrated as being energized by an alternating potential of the frequency of alternating current circuit I0 through rotary phase shifting transformer 4| and control transformer 42. The primary winding 40 of transformer 34, on the other hand, is arranged to be energized from a source of secondary frequency and is illustrated as being energized by an alternating potential obtained from alternating current circuit I I through transformer 43. If the control potentials of primary frequency impressed on secondary windings 35 of transformers 33 are such as to cause current to flow in a direction opposite to the direction of the arrow on the drawing, which will be referred to as negative potentials hereinafter, unilaterally conductive devices 31 will allow current to flow through battery 3| and resistor 32 in such a direction as to produce a potential drop across resistor 32 and cause a negative potential to appear on control electrode 2| which overcomes the positive bias of biasing means 3| thereby maintaining the associated electric discharge valve nonconductive. The same will also be true if a negative potential appearsacross the secondary winding 35 of transformer 34. Therefore, as long as either one or both of the potentials of the secondary windings 35 and 33 of transformers 33 and 34 are negative the associated electric discharge valve will be maintained in a nonconductive condition by virtue of the negative bias appearing across resistor 32. However, if both of the potentials of the secondary windings 35 and 36 of transformers 33 and 34, respectively, are positive (e. g. such as to tend to cause currents to flow in the direction of the arrows shown in the drawing) unilaterally conductive devices 31 and 38 will prevent any current from flowing through resistor 32 and therefore the positive bias of biasing means I is impressed upon the control electrode 2| of the associated electric discharge valve rendering such electric discharge valve conductive. It will be observed that the control alternating potential obtained from the source of primary frequency I 0 and impressed on excitation circuits 21 and 28 are displaced in phase by 180 electrical degrees with respect to the potential of alternating current circuit I II. However, the control potentials obtained from the source of secondary frequency II and impressed on excitation circuits 2! and 28 are in phase with one another and 180 degrees displaced in phase with respect to the control potentials from alternating current circuit ll impressed on excitation circuits 29 and 30, respectively,

The operation of the electric valve converting apparatus described above will be well understood by those skilled in the art and only a brief description will follow. Assuming, for example, that alternating current circuit I is the higher frequency circuit which alternating current circuit I I is the lower frequency circuit, then electric discharge valves I3 and I4 will be rendered alternately conductive at the frequency of the alternating current circuit I0 so as to produce a half cycle of the alternating potential of load circuit II, after which these valves will be rendered nonconductive and electric discharge valves l5 and I6 will be alternately rendered conductive at the frequency of alternating current circuit I0 so as to produce a half cycle of opposite polarity at alternating current circuit II. Groups of valves I3-I4 andIS-Iii are rendered alternately conductive and nonconductive at the frequency of alternating current circuit II. At one particular instant the control potentials from the source of secondary frequency II impressed on secondary windings 36 of transformer 34in excitation circuits 2'! and 28 are positive so that unilaterally conductive devices 38 allow substantially no current to flow through resistors 32 associated with electric discharge valves I3 and I4. At this same instant the control potentials from the source of secondary frequency II impressed on excitation circuits 29 and 30 are negative so that currents flow through resistors 32 of excitation circuits 29 and 30 and electric discharge valves I5 and I6 are rendered nonconductive. If now a positive potential is also impressed on secondary Winding of transformer 33 associated with excitation circuit 21 current will flow through resistor 32 of excitation circuit 2! and electric discharge valve I3 is rendered conductive. It is assumed that the anode cathode voltage of electric discharge valve I3 at this instant is in such a direction as to cause current to flow through electric discharge valve I3 through upper portion of reactor 22 to one side. of alternating current circuit II. At this same instant the potential across secondary winding 35 of transformer 33 of excitation circuit 28 is negative so that current flows through resistor 32 associated with electric discharge valve I4, overcoming the positive bias of battery 3I thereby maintaining electric discharge valve I4 nonconductive. One hundred eighty electrical degrees later with respect to alternating current circuit Ill electric discharge valve I4 is rendered conductive and current is commutated from electric discharge valve I3 to electric discharge valve I4. Thus electric discharge valves I3 and I4 are rendered alternately conductive and nonconductive until the potential of alternating current circuit II reverses, thereby causing a negative potential to be impressed on secondary windings 36 of transformers 34 associated with excitation circuits 21 and 28, respectively, and a positive potential to be impressed on secondary windings 36 of transformers 34 associated with excitation circuits 29 and 30, respectively. Thereafter electric discharge valves I5 and I6 are alternately rendered conductive and nonconductive at the frequency of the source of primary frequency III in the same manner as described in connection with electric discharge valves I3 and I4, and the next half cycle of the alternating potential of alternating current circuit II is produced. Therefore, electric discharge valves I3 and I4 are controlled as a biphase rectifier to produce a half cycle of one polarity on alternating current circuit II and the electric discharge valves I5 and I6 are controlled as a biphase rectifier to produce the next half cycle of opposite polarity on alternating current circuit II.

While I have described what I at present consider the preferred embodiment of my invention, 5 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. In combination, an alternating current circuit of primary frequency, an alternating current circuit of secondary frequency, a plurality of electric discharge valves interconnecting said circuits, a control electrode and excitation circuit for each of said electric discharge valves comprising a biasing means continuously tending to render said electric discharge valves conductive, and means for deriving a control potential at each of said frequencies of such magnitude that either of said control potentials periodically overcomes said biasing means to render said electric discharge valves nonconductive in a predetermined sequence.

2. In combination, a supply circuit, a load circuit, an electric translating apparatus interconnecting said circuits comprising a plurality of electric valve means, each provided with a control electrode and an excitation circuit comprising means for impressing a positive bias potential on each of said control electrodes continuously tending to render said electric discharge valves conductive, and means responsive toelectrical conditions of said supply and load circuits for overcoming said biasing means to render said electric valve means nonconductive in a predetermined sequence.

3. In combination, an electric valve means having a control member and employing an ionizable medium, a control system for energizing said control member comprising a plurality of sources of control potentials connected in parallel and each derived in response to a different electrical condition, means continuously tending to render said electric valve means conductive, and means for periodically impressing unidirectional impulses of said control potentials on said control member, each of said control potentials being of sufficient magnitude to overcome said first mentioned means to render said electric valve means nonconductive for predetermined intervals.

4. In combination, an alternating current eircuit of one frequency, a second alternating current circuit, an electric translating apparatus interconnecting said circuits and comprising a plurality of electric valve means, each provided with a control electrode and associated excitation circuit, said excitation circuit comprising a resistance serially connected with said control electrode, means responsive to an electrical condition of said first mentioned alternating current circuit for producing a potential across said resistor, means responsive to an electrical condition of said second alternating current circuit for producing a potential across said resistor, unilaterally conductive devices for determining the polarity of the potential produced across said resistor by both said responsive means and a positive biasing means for rendering said associated electric discharge valve conductive when there is substantially no potential across said resistor.

5, In combination, an electric valve means hav- 75 ing a control member, a control circuit for energizing said control member comprising a plurality of sources of control potential, a resistance serially connected with said control member, means responsive to one of said sources of control potential for producing a potential across said resistor, means responsive to another of said sources of control potential for producing a potential across said resistor, unilaterally conductive devices for determining the polarity of the potential produced across said resistor by said sources of control potential, and a positive biasing means for rendering said electric valve means conductive when there is substantially no potential across said resistor.

6. In'combination, an alternating current circuit of one frequency, an alternating current circuit of another frequency, an electric valve frequency changer interconnecting said circuits and including a plurality of electric discharge valves, an excitation circuit for each of said valves comprising a source of potential tending to maintain said valves continuously in one state of conductivity, means for deriving a control potential from each of said alternating current circuits and impressing half waves of one polarity of each of said control potentials on said excitation circuit, the magnitude of each of said control potentials being suflicient to overcome said biasing means to change said valves to the opposite state of conductivity periodically.

7. In combination, an alternating current circuit of one frequency, an alternating current circuit of a second frequency, an electric valve frequency changer interconnecting said circuits and comprising a plurality of groups of valves, an excitation circuit for rendering the valves of one of said groups alternately conductive and nonconductive at the frequency of one of said circuits and for rendering said groups alternately conductive and nonconductive at the frequency of the other of said circuits comprising means for biasing all of said valves to one state of conductivity, means for deriving a control potential from each of said circuits, and means for impressing on said excitation circuit half waves of each of said control potentials of a polarity opposite to said biasing potential to reverse the state of conductivity of said valves, said control potentials each having a magnitude suificient to overcome the effect of said biasing potential.

ERNST F. W. ALEXANDERSON.

Images