US2184309A - Arrangement for controlling rectifiers - Google Patents

Description

Dec. 26, 1939. w, LEUKERT 2,184,309

ARRANGEMENT FOR CONTROLLING REGTIFIERS Filed April 12, 1937 2 Sheets-Sheet 1 72 IN 7; 73 a; r

EKJLJl/fi 101mm wm MM Dec. 26, 1939. w. LEUKERT 2,184,309

ARRANGEMENT FOR CONTROLLING RECTIFIERS Filed April 12, 1937 2 Sheets-Sheet 2 WM. W

Patented Dec. 26, 1939 UNITED STATES T QFFICE ARRANGEMENT FOR CONTROLLING RECTHFEERS Application April 12,

1937, Serial No. 136,342

In Germany February 5, 1936 9 Claims.

My invention relates to an arrangement for controlling rectifiers.

The essence of the invention consists in controlling the amount of energy of a half wave of the alternating-current supply circuit connected to a rectifier. To this end, the invention utilizes the valve efiect of electric devices, particularly the valve effect of electric discharge devices. The control arrangements operating with such electric discharge devices differ, however, considerably from the control arrangements hitherto employed for controlling the rectification of alternating currents.

An essential feature of the invention consists in the fact that the moment at which the conducting period of an electric discharge device of a converter begins during the flow phase of the alternating voltage, is not controlled by directly influencing the conductivity of the electric dis- 20 charge device, but by arranging a circuit breaker in series with the electric discharge device, which circuit breaker establishes at a given moment within the half wave of the alternating voltage the conductive connection between the electric discharge device and the alternating-current supply circuit. Consequently, the electric discharge device according to the invention remains, in contradistinction to the control arrangements hitherto known, isolated from the alternatingcurrent supply circuit until-the conductive peroad is initiated, i. e., until, for instance, the arc in the case of a gasor vapor-filled electric discharge device is started.

The usual rectifying arrangements which opcrate with electric discharge devices with valve action effect the control of the rectification in the manner that the electric circuit externally of the electric discharge device is kept permanently closed and that the switching in at any moment within the half wave of the alternating voltage is effected by establishing the conductivity of the electric discharge device at the moment in question. To this end, either a mercury cathode is caused to emit electrons when ignited by starting electrodes, immersion electrodes or the like or a control grid which. is impressed at the moment of ignition with a control potential which initiates the conducting period is arranged in the electric discharge device between the anode and a continuously electron emitting cathode. Characteristic of these prior art devices, and by which they are distingui hed from the present invention, is that the electric discharge device in question is already conductively connected to the alternating-current supply circuit before the ignition takes place or at least from the moment at which a. starting of the arc is possible. The anode of a mercury vapor rectifier which is, for instance, ignited when the alternating supply voltage attains the maximum value, is already impressed a relatively long time with the full anode voltage orin the case of polyphase rectifiers-with the difierence between the voltages of two successive anodes.

The invention differs fundamentally from this method by the fact that the electric discharge device is only switched in the circuit at the moment of ignition or immediately prior thereto by a circuitbreaker of any type arranged externally of the electric discharge device. In this manner the advantage is obtained that during the stop phase of an electric discharge device no trouble may arise owing to undesired voltage stresses of the anodes. Furthermore, the invention has the advantage that the type of the rectifier device may be far more liberally chosen than has hitherto been the case. The controllable rectification has hitherto been possible only by the use of tubes which operate with controllable electric discharge devices, i. e., for instance, with vacuum tubes, such as mercury vapor discharge devices. The invention renders for the first time possible the use of known dry rectifiers and the utilization of their advantages in operation for the controllable rectification.

While in the conversion of polyphase currents for each phase a separate valve may be provided, an arrangement is also possible in which only two valves are used or, generally speaking, in which the number of valves is equal to the maximum number of phases which carry simultaneously current of the same direction. Circuits involving this feature are known in the art. As soon as the current has ceased to flow in one phase, the valve is disconnected from this phase and may now be switched over to another phase which commences to carry current at a later time. In the customary rectifier arrangement inwhich at most, namely during the overlapping period, two phases partake simultaneously in the current supply, the valve which first ceases to supply current is then connected to the phase which is second next in the sequence of currentcarrying phases. In case transformers are used which, due to their particular circuit arrangement, permit an increase in the current flow periods of the individual phases the number of valves must be correspondingly increased, so that the individual phase currents may always fiow over one valve. By the reduction in the number of valves and the incidentally required switching over of the valves, however, no fundamental change is brought about in the rectifying process or in current or voltage curves of the converter system. Above all it is possible, the same as in the arrangements which provide an individual valve for each phase, to control the voltage, delivered by the converter, by shifting the closing time of the valves within the range of the voltage half wave within which a given phase may carry any current at all.

By reducing the number of valves, the total amount of apparatus is reduced, so far as the provision for valves is concerned. It is true, in such cases each valve is inserted in circuit more often and therefore it must be dimensioned somewhat larger so far as its current-carrying capacity is concerned, but this necessary increase in size of the individual valves has not nearly the economic eiifect on one side as the reduction in the number of valves on the other side. The reason for this may be found in the fact that in case of a smaller number the valves are now subject to more uniform loads, so that the mean value of the valve current in relation to the best effect, so far as heating and losses are concerned, increases.

Since the total time, during which a phase of a polyphase rectifier carries current is practically independent of the degree of control of a half wave, the time interval between the switching in and switching out of an alternating-current phase remains always constant. Only under particular circumstances, for instance when converting direct current into alternating current, it may be preferable to control this time interval by making it conditional, for instance, upon one or more of certain operating conditions, for instance, upon the load current of the converter. In general, a simple switching gear between the rectifier units and the alternating-current source is sufficient; for instance, a revolving switching gear which is designed in the form of a commutator provided with stationary brushes and which is driven by a synchronous motor connected to the alternating-current supply circuit.

Here it may be mentioned that it is quite immaterial by what type of circuit breaker the connection between the alternating-current phases and the electric discharge devices is established and broken. Mechanical switching gears with direct contact between stationary contacts or also switching gears be employed in which either contact is replaced by a liquid electrode. Switching gears of this type. for instance, in the form of electrolytic circuit breakers or mercury iet circuit breakers have hitherto been employed for other converting purposes. At all events, a switching gear must be inserted between the alternating-current source and the rectifier units. which gear establishes and breaks at the proper time the conductive connection between the rectifier unit and the alternating-current source. To facilitate the switching operation, condensers are preferably connected in parallel relation to the contacts or other protective means, such as series reactors or series resistors are employed.

For a further understanding of my invention reference may be had to the following description taken in connection with the accompanying drawings, in which Fig. 1 shows diagrammatically a six-phase rectifier arrangement employing dry rectifier units,

Fig. 2 shows the cylindrical rotary switch gear 4 of Fig. 1 developed in a plane, and indicates the interconnection between the several contact elements,

Fig. 3 shows a modified form of Fig. 1 in which the secondary of the transformer is divided,

Fig. 4 shows a controllable dry rectifier system for exchanging energy between an alternating current supply circuit and a direct current consuming device,

Fig. 5 shows a rectifier system employing a double anode mercury vapor rectifier, and

Fig. 6 shows the invention applied to an inverter.

Referring now to Fig. 1, this figure shows a six-phase rectifier with dry rectifiers. The pri mary winding of the transformer 2 is connected to the three-phase supply circuit l, the secondary, six-phase winding 3 of the transformer being connected to the switching gear 4. The latter is driven by a synchronous motor 5 which is connected to the three-phase supply circuit I through an induction-voltage regulator l in order that the synchronous position of the contact movement may be varied. The switching gear 4 consists of a contact drum cooperating with a number of brushes. Six of the brushes are connected in cyclic sequence to the siX phases of the transformer winding 3, whereas each of the other two brushes is connected to the positive conductor of the direct-current circuit 8 through one of the rectifier units 6. In this case the brushes connected to the rectifier units, contact with the complete slip rings 9 and i0, whereas the segmented contact rings which cover only a portion of the periphery of the contact drum are allotted to the other brushes. The contact drum is shown developed in Fig. 2. As will be seen from this figure at most two phases of the transformer winding 3 are connected to one rectifier unit at a given time moment by the switching gear cooperating with the rectifier units 6. During the greater portion of the rectifier flow phases only one transformer phase is switched in. The individual contacts overlap one another in the direction of rotation so that also the flow periods of the individual phases overlap one another. The overlapping of the switching-in periods is necessary on account of the commutation.

The moment, at which the switching in takes place within the half cycle of the alternating voltage of the alternating-current supply circuit 1, is adjusted by varying the relative position between the revolving system and the vector of the alternating-current supply circuit i. To this end, various known means are available: Either an induction-voltage regulator 1 shown in Fig. 1, or a displacement of the stator of the synchronous motor 5, or a variation of the excitation of the part-windings in the direct-current exciting circuit of this motor, by means of which the vector position of the excitation. is displaced with respect to the supply circuit vector.

It may be further added that the invention is also applicable to converters operating with dry rectifiers if one rectifier unit is allotted to each alternating-current phase.

In Fig. 3 is shown an embodiment for a controllable dry rectifier employing a transformer connection in which the duration of fiow phase of the rectifier is increased by making use of the known, interphase choke coil. In this case two secondary three-phase windings l2 and I3, which are each star-connected, are provided. These windings are phase difierentiated 180 and supplement one another to a six-phase system and are associated with the primary winding ll of the transformer. Between the neutral points of both secondary windings is arranged the choking coil l t whose center represents the neutral point of the entire secondary transformer winding. This arrangement of the divided secondary winding has the effect that the two secondary threephase systems operate independent from one another, though they supplement one another to a secondary three-phase system. The switching gear I45 is shown schematically and may be designed in any suitable manner. Since in this case three phases of the entire transformer secondary winding carry current at the same time, also three rectifier units it must be provided. These units are so connected to the break contacts of the switching gear it that the units are successively connected to three successive phases of the secondary winding of the transformer. In general, also in this case the entire switching gear between the trans former and the rectifier units must be designed so that it connects the individual transformerphases cyclically in succession.

Instead. of the choking coil 14 shown in Fig. 3 also other known devices serving the same purpose. for instance, magnetically interconnected reactors may be employed in the individual phase conductors.

Fig. 4 shows the regulable dry unit rectifier for exchanging energy between an alternatingcurrent supply circuit E and a direct-current consuming device ll. The connection of the entire arrangement corresponds to the cross-connection employed in other regulable rectifiers, whereas each rectifier unit is connected in a manner corresponding to the connection shown in Fig. 1. Accordingly, the primary winding is of the transformer is coupled with two secondary windings i9 and ill each of which in the embodiment shown in Fig. 4 is star-connected in six phases. To each transformer winding is'allotted a particular switching gear 23 and 24 respectively which is driven through an induction voltage regulator 25 and 26 respectively, and each switching gear is arranged in series with a pair of dry rectifier units 2| and 22 respectively. The connection according to Fig. 4 may also be employed to connect a direct-current supply circuit to an alternating-current supply circuit and to exchange energy in any direction between the two supply circuits.

In Fig. is shown an embodiment of the invention in which a double anode mercury vapor discharge device 2'l is employed to take the place of two separate rectifier units such as in Fig. l.

The connection between the two individual anodes of the electric discharge device and the switching gear is the same as that shown in the connectionaccording to Fig. l. The two electric discharge devices embodied in tube 21 are providcd with control grids 35 which in order to be protected against disturbances may be connected to a negative inverse voltage source 29 through a relay arrangement 29 The same control grids may also be employed to ignite the electric discharge devices at the beginning of the flow phase. In this arrangement the electric discharge is switched in by the revolving contact device 41 and then immediately ignited by correspondingly influencing the control grids. In the connection according to Fig. 5 it is assumed that the control grids 35 are controlled through a revolving contact device 28 which as well as the switching gear in the anode circuits of the electric discharge devices is driven by a synchronous motor 5. Instead of the control grids also other means, for instance, starting electrodes immersed in the mercury may be employed. The twoanode discharge device 2'! shown in Fig. 5 may be replaced by two sing1eanode units. If divided transformer secondaries with choking coils or the like, such as in Fig. 3, are employed the number of the electric discharge units must be correspondingly increased the same as in the connection shown in Fig. 3.

Fig. 6 shows the invention as applied to an inverter. Also in this case electric discharge units 3i and 32 are connected to the secondary winding 3 of a polyphase transformer through a switching gear 36 in the same manner as in the connection according to Figs. 1 or 5. Condensers 33 are arranged between the anodes of the two electric discharge devices. Such condensers are, however, only necessary if the inverter is con-- nected to a separate alternating-current supply circuit, that is if there is no alternating voltage independent of the inverter available in the alternating-current supply circuit l in order to control the quenching of the electric discharge devices. As will be apparent from the connection shown in Fig. 6 the means employed according to the invention in the polyphase inverter are very simple. The two electric discharge units SI and 32 of the inverter are equipped with control grids 34 which in turn are connected to a control voltage source hi and which have the same controlling functions as the grids 35 of the electric discharge devices in Fig. 5. Instead of the electric discharge devices shown in Fig. 6 also dry rectifiers or other non-controllable electric valves may be employed in this connection.

The converter according to the invention may easily be dimensioned also for high voltage; in this case care should be taken to provide suflicient insulation of the contact device through which the rectifier units are connected to the secondary windings of the transformer. Both the stationary and the revolving contacts may be secured to high voltage insulators. Since the rectifier units are not impressed with any voltage during the stop phase, the voltage stress is considerably smaller; accordingly the rectifier units may be designed with correspondingly smaller dimensions, which is particularly advantageous in the case of high voltages. In such rectifiers backfires are also eliminated. In this case it is of particular advantage to employ besides the contact devices also control grids as above described in connection with Fig. 5.

I claim as my invention:

i. In a converter for exchanging energy between a polyphase alternating current supply circuit and a direct current consuming circuit, a transformer having its primary winding connected to said alternating current circuit and having two secondary windings, two groups of rectifiers and a switching gear for each secondary winding having contacts associated circuits for connecting the phases of each of said secondary windings insuccession with timely overlapping through its switching gear to one group of said rectifiers for connecting said rectifier said alternating current within a portion of said cycle which represents the actual current flow phases of the rectifiers of the appertaining group.

2. In a converter for exchanging energy between a polyphase alternating and a direct current circuit, a plurality of gas discharge rectifiers connected at similar poles to one pole of said direct current circuit, a switching gear having contacts connectable in series with the other poles of said rectifiers, and associated circuit connections for connecting the several phases of said alternating current circuit through said switching gear to the other poles of said rectifiers, means for actuating the contacts of said gear in synchronism with the frequency of said alternating current circuit, means for varying the closing time of said contacts with respect to the voltage cycle of said alternating current within a portion of said cycle which represents the actual current fiow phases of said rectifiers, a circuit connection between said rectifiers for connecting them in series with opposing polarity, and a condenser in said connection suitably dimensioned to alternately quench said rectifiers at the ends of their flow phases.

3. In a converter for exchanging energy between a polyphase alternating and a direct current circuit, a transformer having its secondary winding divided into a sufiicient number of phases to permit the simultaneous switching in of a desired number of similar current-carrying phases, a plurality of rectifiers equal in number to the number of said simultaneous current-carrying phases, a switching gear having contacts connectable in series with said rectifiers, said switching gear being designed to cyclically close its contacts during overlapping closure periods the length of which is smaller than half the period of the voltage cycle of said alternating current, circuit connections for connecting the several phases of said secondary transformer winding through said switching gear to said direct current circuit so as to form within the simultaneously switched-in phases short circuit paths including said rectifiers, each path including two rectifiers having opposite conducting directions, means for actuating the contacts of said gear in synchronism with the frequency of said alternat ing current circuit, and means for shifting the closure periods of said contacts with respect to the voltage cycle of said alternating current within a portion of said cycle which represents the actual current fiow phases of the rectifiers so as to control the energy exchanged between said alternating and said direct current circuit.

4. In a converter for exchanging energy between an alternating and a direct current circuit, a plurality of gas discharge rectifiers connected at similar poles to one pole of said direct current circuit, a switching gear having contacts connectable in series with the other poles of said rectifiers, and associated circuit connections for connecting the several phases of said alternating current circuit through said switching gear to the other poles of said rectifiers, means for actuating the contacts of said gear in synchronism with the frequency of said alternating current circuit, means for varying the closing time of said contacts with respect to the voltage cycle of said alternating current within a portion of said cycle which represents the actual current flow phases of said rectifiers so as to control the energy exchanged between said alternating and said direct current circuit, auxiliary electrodes and a voltage source for said electrodes for controlling the operation of said rectifiers, and means connected with said auxiliary electrodes for rendering said rectifiers inoperative in case of excess current.

5. In a converter for exchanging energy between an alternating and a direct current circuit, a plurality of gas discharge rectifiers connected at similar poles to one pole of said direct current circuit, a switching gear having main contacts connectable in series with the other poles of said rectifiers, auxiliary contacts, and associated circuit connections for connecting the several phases of said alternating current supply circuit through main contacts of said switching gear to the other poles of said rectifiers, in combination with means for actuating main and auxiliary contacts of said gear in synchronism with the frequency of said alternating current circuit, means for varying the closing time of said contacts with respect to the voltage cycle of said alternating current within a portion of said cycle which represents the actual current flow phases of said rectifiers, auxiliary electrodes and a voltage source for said electrodes for controlling the operation of said rectifiers, said auxiliary electrodes being controlled by said auxiliary contacts of said gear to effect the ignition of said rectifiers before the closing time of said main contacts.

6. In a converting arrangement for exchanging energy between an alternating current circuit and a direct current circuit, in combination, a set of electrical valves of uncontrollable type, said valves being arranged between said alternating and said direct current circuits so as to establish a rectifying connection, a commutating contact device series-connected with said valves the alternating current side of said valves, said device being designed for connecting in timely succession several phases of said alternating current circuit with said valves in synchronism with the alterhating current, and means for controlling the energy exchanged between said circuits, said means comprising a device for shifting the phase position of the contact closing periods of said device within the periods in which the voltage in said phases corresponds with the conductive direction.

'7. In a converting arrangement for exchanging energy between an alternating current circuit and a direct current circuit, in combination, a plurality of dry rectifiers equal in number to the number of simultaneous current-carrying phases of said alternating circuit, a commutating contact device series-connected with said rectifiers in said alternating current circuit, associated circuit connections for connecting several phases of said alternating current circuit through said device and said rectifiers with said direct current circuit, a synchronous drive for operating said device with the frequency of said alternating current, and means for controlling the energy exchanged between said circuits, said means comprising a device for varying the phase position of said drive so as to shift the contact closing periods of said device within the periods in which the voltage in said phases corresponds with the conductive direction of said rectifiers.

8. In an arrangement for exchanging energy between an alternating current circuit and a direct current circuit, a group of electric valves connected between said two circuits, control means for periodically establishing the conductive condition of said valves, a commutating contact device having contacts series connected with said valves and associated circuit connections for connecting the phases of said alternating current circuit through said contact device to said valves in timely overlapping succession, drive means for actuating said contact device in the frequency of said alternating current circuit, said control means and said drive means being inter-coupled so as to effect the closing of said contacts at a moment within a period in which the valves connected to said contacts are in conductive condition and the conductive direction corresponds to the direction of the voltage at said contacts, and means for shifting the closing moments of said contacts within said period.

9. In an arrangement for exchanging energy between an alternating and a direct current circult, a plurality of electric rectifiers connected between said two circuits, a commutating switching gear having contacts connectable in series with said electric rectifiers and associated circuit connections for connecting several phases of said alternating current circuit through said switching gear to said rectifiers in timely overlapping succession, means for actuating the contacts of the switching gear in synchronism with the frequency of said alternating current circuit, said means being designed to close each contact within a period in which the rectifier in the phase connected to said contact is conductive in the direction of the voltage in said phase, and means for controlling the power output of the arrangement, said control means comprising a device for dis placing the closing time of said contacts within said period.

WILHELM LEUKERT.

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