US3569792A

US3569792A - Method and circuit for rapid field excitation control of electromagnetic devices

Info

Publication number: US3569792A
Application number: US17345A
Authority: US
Inventors: Heinz Schaffersmann; Ernst Tuchen; Friedel Twellsiek
Original assignee: Binder Magnete GmbH
Current assignee: Binder Magnete GmbH
Priority date: 1965-06-10
Filing date: 1970-03-06
Publication date: 1971-03-09
Anticipated expiration: 1988-03-09
Also published as: DE1514725A1; AT268462B; GB1182106A

Abstract

The method for rapid field excitation control of an electromagnetic device, which includes converting an alternating multiphase voltage into several mutually superimposed unidirectional voltages of respectively different maximal amplitudes to obtain a resultant unidirectional fluctuating excitation voltage, temporarily impressing the fluctuating excitation voltage upon the electromagnetic device during at least one of the magnetic field buildup and decay periods of the device, applying the resultant fluctuating excitation voltage during the buildup period and maintaining the resultant voltage until the current through the device attains a value above that of the continuous energization, terminating the energization by disconnecting the normal operating voltage from the device, impressing upon the device a deenergizing equally poled voltage in response to a first change occurring in the load circuit of the device as a result of the disconnection, said deenergizing voltage being opposed to that of the device and being higher than the operating voltage, and removing the deenergizing voltage in response to a second change occurring in the circuit.

Description

United States Patent Heinz Sehaflersmann [72] lnventors Brake; Ernst Tuchen, Jerxen-Orbke; Friede Twellsiek, Milse, Germany [21] Appl. No. 17,345 [22] Filed Mar. 6, 1970 [45] Patented Mar. 9, 1971 [73] Assignee Binder Magnete KG Villingen/Schvvarzw., Germany [32] Priority June 18, 1966 [33] Germany [31] P15 14 725.8

Continuation of application Ser. No. 647,171, June 19, 1967, now abandoned.

[54] METHOD AND CIRCUIT FOR RAPID FIELD EXCITATION CONTROL OF ELECTROMAGNETIC DEVICES 13 Claims, 11 Drawing Figs.

[52] U.S. 317/123, 3l7/l48.5,317/l56,321/5 [51] Int. Cl. "01h 47/32 [50] Field ot'Search 317/123,

148.5, 123 (CD), 156; 321/5, (lnquired) [56] References Cited UNITED STATES PATENTS 3,330,998 7/1967 Winograd 317/ 148.5X

3,401,310 9/1968 Schaffersmannetal 317/123 Primary Examiner- Lee T. Hix Attorneys-Arthur E. Wilfond, Herbert L. Lerner and Daniel J. Tick ABSTRACT: The method for rapid field excitation control of an electromagnetic device, which includes converting an alternating multiphase voltage into several mutually superimage during the buildup period and maintaining the resultant voltage until the current through the device attains a value above that of the continuous energization, terminating the energization by disconnecting the normal operating voltage from the device, impressing upon the device a deenergizing equally poled voltage in response to a first change occurring in the load circuit of the device as-a result of the disconnection,

said deenergizing voltage being opposed to that of the device and being higher than the operating voltage, and removing the deenergizing voltage in response to a second change occurring in the circuit.

PATENTEDMAR 9mm 31569792 sum 2 or 7 Fig.4

CURRENT SUPPLY v I; 100 7 110 fit 85 GEN A L ON-OFF 21-24 4 120 I 90 CONTROL AMP METHOD AND CIRCUIT FOR RAPID FIELD EXCITATION CONTROL OF ELECTROMAGNETIC DEVICES This application is a continuation of application Ser. No. 647,171, filed 6- 1 9-67, now abandoned.

My invention relates to methods and circuits for rapid deenergization and/or rapid deenergization of the magnetic system in electrical devices such as magnetic clutches, brakes, and valves, lifting magnets, holding magnets, as well as any other device comprising a magnetic field winding for performing a switching function, transmitting, driving or stopping forces or serving other control functions in various machine tools and processing machines or the like.

For a precise operation of such devices it is necessary to attain very short time periods for the desired switching operation or other response. Minimizing such time periods, however, is subject to limitation by delays inherent in the buildingup and decaying of the magnetic field.

For shortening the buildup time of a magnetic field it is known to provide a rapid excitation circuit wherein an ohmic resistor is connected in series with the magnetic field winding. This has the disadvantage of an additional consumption of power which in the series resistance is converted into waste heat.

Another rapid excitation system employs an additional voltage which is substantially higher than the operating voltage and which is switched off by time-delayed switching means after the switching-on process has been completed. This requires providing a switching means rated for the greatly increased voltage and also capable of switching off the full value of increased current subsequent to the switching-on process. Systems of this type are affected by all of the difficulties encountered with the interruption of high DC voltages at inductances. If mechanical contacts are used, a high degree of contact burning is encountered unless additional arc arresters are employed. If electronic switches in the form of semiconductor components are employed, the induction voltages must be taken into account and the components must be rated for the resulting high direct currents. Overcoming these difficulties causes a substantial expense and in some circuits also an undesireable delay of the switching off operation.

According to the generally prevailing view in this art, the time necessary for the deenergization of a magnetic field (also called sticking time) cannot be reduced below the time that elapses upon interrupting the energizing circuit by directly opening contacts without any spark-arresting means; which means that the shortest attainable decaying period would be expected if there is no shunt connected in parallel to the magnetic field winding and a portion of the energy stored in the field winding is dissipated through the are occurring between the switch contacts. This possibility of deenergization, how ever, has its limitation because the resulting induction voltages are several times higher than the normal operating voltage and, when exceeding a given value, may destroy the magnetic field winding. The protective expedients necessary to prevent such destruction result in prolonging the deenergization time.

It is an object of my invention to remove the above drawbacks.

Another object of my invention is to provide a method and electrical circuit arrangements for the rapid energization and deenergization of the magnetic system in electrical devices, wherein the control of the switching operation is accomplished by electronic circuit components in such a manner as to secure a reliable and maintenance-free performance with minimized switching periods as well as minimized energy losses.

Another object of my invention is to accomplish the rapid energization as well as the rapid deenergization with substantially the same circuit arrangement.

To achieve these objects, and in accordance with the invention, I secure a rapid energization ofa magnetic field by deriving from an alternating-current multiphase power supply, a unidirectional voltage comprising a plurality of voltage components superimposed upon each other and having respective- Iy different maximal values; and I apply the resultant fluctuating direct voltage to the magnetic field winding to be energized until the current through the winding exceeds the normal operating or rated current of such winding.

According to another feature of the invention, 1 provide for rapid deenergization by applying a voltage opposing any induction voltage, the auxiliary voltage being switched on in response to changes which occur in the load current circuit of the magnetic device as a result of initiating the interruption of that circuit. The opposing voltage has a higher absolute value than the normal operatingvoltage of the magnetic device and is switched off in response to the occurrence of another change in said load current circuit.

According to another feature of the invention, it is preferable for the rapid deenergization to preset the switching-on point of the opposing or deenergizing voltage on the trailing edge of its positive half-wave at a constant value. Thus only the positive deenergizing voltage will have the necessary magnitude and any additional magnetization dependent upon the instantaneous value of the energizing voltage is prevented from occurring just prior to the beginning of the deenergization period. a

A circuit according to the invention for rapid energizatio and rapid deenergization of a magnetic field device comprises thyristors for deriving from several phases of a multiphase transformer an increased voltage for the rapid energization and deenergization, and monostable transistor flip-flop stages for controlling the firing of the thyristors. A first arc of the monostable flip-flops determines the duration of the rapid energization. A second one of the flip-flops is timed for the duration of the rapid deenergization, the components of the second flip-flop being complementary to those of the first flipflop (PNP and NPN germanium or silicon transistors). The second flip-flop is connected to a further transistor stage for determining a switching-on point of the deenergizing voltage on the positive trailing portion of its wave. The transistor stage thus provides for synchronization, deriving the required current from the transformer through an RC-member. Preferably the one monostable flip-flop stage has its control input lead and its current supply lead controlled by the switch or other actuating member for controlling the energization and deenergization, whereby disturbances are suppressed.

In order that the invention will be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein FIGS. 1 to 5 (corresponding to FIGS. 1 to 5 in the copending application Ser. No. 5 15,3 72, filed Dec. 21, 1965, now US. Pat. No. 3,401,310, and assigned to the assignee of the present invention) are explanatory, whereas FIGS. 6 to 11 relate to the invention proper.

FIG. I shows graphs of voltages used according to the invention; i

FIG. 2 is a phase diagram of the voltages across transformer windings in the circuit arrangement of FIG. 3;

FIG. 3 is the diagram of a circuit for rapidly energizing an electrical apparatus including a magnetic field coil;

FIG. 4 is a more detailed circuit diagram of part of the circuit of FIG. 3;

FIG. 5 is a block diagram of a complete system incorporating the details of FIGS. 3 and 4;

FIGS. 6 and 7 are the circuit diagrams of different systems embodying the present invention and suitable for rapid energization as well as rapid deenergization or magnetic apparatus;

FIGS. 8, 9 and 10 are explanatory graphs of deenergization voltages employed according to the invention for assuring that the deenergizing voltage is switched on at a given cyclical point of time; and

FIG. 11 is a circuit diagram of another system according to the invention for rapid energization and deenergization of magnetic apparatus.

Exemplified in FIG. 1 are time curves of excitation voltages typical of a system according to the invention, the abscissa denoting time and the ordinate values being indicative of voltage amplitudes. The increased voltage superimposed upon the field coil of the device to be rapidly excited is represented by the curve a. The permanent or steady-state operating voltage of the device is shown at b. The particular conditions demonstrated by FIG. 1 involve the advantage that the maximum values of the rapid excitation voltage a cover the gaps in the steady-state field excitation voltage b. Consequently, when the field winding is being switched on at an unfavorable moment, such as at the moment t,, the voltage impressed upon the winding has at least the maximum value of the normal operating voltage. The high auxiliary voltage a is shown discontinued at the moment 1,, assuming that up to this moment the magnetic field has become fully excited so that thereafter only the normal excitation voltage b is effective.

It should be understood that the voltage diagram of FIG. 1 relates to one phase of an excitation voltage derived from all of the secondary phases of a three-phase transformer. The vector diagram for all three phases of rectified voltage is shown in FIG. 2. Ia+lb denote the respective vectors of the positive and negative voltages respectively in the first phase. The vectors Ila and llb are the positive and negative voltages respectively of the second phase which is connected in series with the third phase whose positive and negative voltages are shown as vectors Illa and "lb. The resultant of these voltages is composed of four component vectors each being phase displaced 90 from the adjacent voltage, the two vectors resulting from Ila, lIIa and Ilb, lllb being represented by broken lines.

Referring now to the system jointly represented by FIGS. 3, 4 and 5, in which an excitation performance according to FIGS. 1 and 2 is realized, the magnetic device whose field is to be rapidly excited is exemplified by the coil 51 of a contactor. This coil is connected to a three-phase power supply line 9 (FIG. 4) through a transformer 10 and a group of controlled rectifiers, preferably thyristors. As shown in FIG. 3, the transformer 10 has six secondary windings denoted by la, lb, Ila, llb, Illa, Illb in accordance with the respective voltage vectors of FIG. 2. The secondary windings Ia, lb, Ila, lIb have a common midpoint connected to one end of the coil 51 to be rapidly excited. The other end of the coil 51 is connected to four parallel arranged

thyristors

21, 22, 23 and 24. The respective other poles of

thyristors

23 and 24 are connected to the free ends of windings Ia and lb respectively. The corresponding poles of

thyristors

21 and 22 are connected in series with the respective windings lIIb and "la to the free ends of respective windings IIb and Ila. The

thyristors

21 and 22 serve to supply the contactor coil 51 with steady-state excitation in accordance with the voltage b in FIG. 1. The

thyristors

23 and 24 conduct only during the building-up interval of the magnetic field of coil 51 and hence are connected in a circuit of increased voltage, this being indicated by greater length of transformer windings Ia, lb. The

thyristors

23, 24 are to be turned off upon completion of the rapid excitation stage, whereafter only the

thyristors

21 and 22 are to remain in operation.

This particular control of the thyristors is effected by the circuit means separately illustrated in FIG. 4 and described presently. The excitation current I flowing through the magnet coil 51 causes a voltage drop in an IR-drop resistor 62 connected in series with the coil 51. This voltage is applied through a resistor 63 to a capacitor 64, both constituting an RC-member. A transformer 80 has its primary winding 81 connected through a diode 84 across the same capacitor 64. The potentiometer 85 permits adjusting the current intensity for rapid excitation in the circuits, 81-84-64-63-62. This current intensity is a measure of the counter voltage to be formed at the capacitor 64 and consequently also determines the moment when the rapid excitation is discontinued. In other words, by adjusting the potentiometer 85, the duration of the rapid excitation stage can be preadjusted or varied as may be desired.

The initially uncharged capacitor 64 represents a short circuit for the transformer primary winding 81 relative to the high frequency of the firing voltage supplied by the output circuit 120 (FIG. 4) of an amplifier 120 (FIG. 5) as more fully explained below. The secondary'winding 82 of the auxiliary transformer is series connected in the primary circuit of a transformer 71 which supplies firing pulses to the

thyristors

23 and 24. The secondary winding 82, therefore, has the low inductive impedance required by the firing circuit in which the transformer 71 is connected. As soon as the capacitor 64 is fully charged, its voltage is higher than the voltage at the transformer primary winding 81. Now a current attempts to flow through the diode 84 in the opposite direction, thus blocking this diode. Since now the current can no longer flow in the primary winding 81, the inductive impedance of the secondary winding 82 increases considerably and thereby prevents a sufficient firing current from passing through the transformer 71. As a result, the firing of the

thyristors

23 and 24 ceases. With the next zero passage, that is, when the cycle period of the voltage is terminated, the rapid excitation stage is concluded since the increased voltage is no longer present.

The circuit of the secondary winding 82 shown in FIG. 4 has a diode 76 connected across the series connection of winding 82 and the primary winding of the firing-circuit transformer 71. The diode 76 serves to always secure the same polarity of the voltage in the circuit 120 to make certain that the

thyristors

21, 22, 23 and 24 can be fired.

The primary winding of another firing transformer 72 for the

thyristors

21 and 22 is connected to the firing circuit 120 in series with a resistor 75 which compensates the ohmic share of the winding 82.

It will be recognized that the switching from rapid excitation to normal excitation is effected without mechanical contacts and in dependence upon the operating current of the magnetic field winding being excited. If voltage fluctuations occur in the alternating-current supply line, they automatically result in shortening or prolonging the rapid excitation stage. Analogously, an increased induction of the magnet coil is overcome by an automatic prolongation of the rapid excitation stage.

The overall diagram of the system shown in FIG. 5 represents the control network of FIG. 4 by the block marked 60. The diagram of FIG. 5 analogously illustrates by blocks all of the above-described other components and also indicates further features relating to the production of the firing voltage.

The firing voltage is derived from the multiphase power supply line 9 through the above-mentioned transformer 10. Produced from the output of transformer 10 is a direct voltage exhibiting only a slight ripple and hence having a low contents of harmonics. A conventional astable flip-flop, such as an astable multivibrator 110, is connected to the direct voltage and furnishes a square-wave output voltage at a frequency which is a multiple of the 50 or 60 c.p.s. line frequency. The squarewave frequency, for example about 2 k.c.p.s. is applied through an actuator or control unit to the above-mentioned amplifier 120 and thence to the firing-

circuit transformers

71 and 72 as described with reference to FIG. 4. The unit 90 contains any desired on-off control means for starting and stopping the current supply to the field winding 51.

lnterposing an amplifier 120 between the frequency generator and the

transformers

71, 72 permits operating the control unit 90 at lower power so that it may be equipped with transistors or to be controlled by light (photoelectric) barriers, punch tapes, sound tracks or the like information carriers. However, if the output of unit 90 is sufficient for directly energizing the

transformers

71, 72, the amplifier can be dispensed with. Since the greater part of the apparatus forms part of the network connected to the power supply line, this applying for example to the transformers, rectifiers and astable flip-flop, the major portion of the apparatus may be used for any desired number of magnetic devices simultaneously the remaining portion required for any particular device 51 being very small so that the device affords a highly economical use.

The control system may also be modified in various respects, for example by providing a smaller or larger number of phases or providing a different number of controllable rectifiers or thyristors. The discontinuance of the increased voltage (rapid excitation) may be readily effected in some other way, for example by providing a switch on the magnet being excited, in dependence upon a rotary movement of a magnetic coupling being excited by the control system, and in some analogous position-responsive or condition-responsive manner. While we prefer providing the system with semiconductor rectifiers, the system may instead be equipped with tubes or transductors (controlled saturable reactors or magnetic amplifiers).

In a system of the type described, the deenergization of the magnetic field winding, that is the time required for the field to decay from its full value down to substantially zero, can be further shortened to a considerable extent by applying the method and means according to the present invention, now to be explained with reference to FIGS. 6 to 11.

The continuous operating DC voltage produced by rectifying the line voltage, causes a current flow in a given direction, which determines the direction of the induction current which continues to flow after the thyristors are turned off. According to the invention such induction current is counterbalanced without interruption by an opposing current caused by the auxiliary opposing voltage which is higher than the continuous operating voltage and of the opposite polarity. For this purpose, advantage is taken of the normally undesirable characteristic of semiconductors to block the flow of current, independently of the polarity of the applied voltage, only then when the current begins to flow in the reverse direction. This means that the instantaneous value of the applied voltage must be higher than the induction voltage.

Accordingly, the energy storedin the magnetic field winding is opposed by a several times higher energy which, in accordance with its potential difference, will instantaneously tend to drive a current through the magnetic field winding in a direction opposed to that of the induction current. Any remanent field will be compensated by the further increase of the negative (counter) current. By properly dimensioning the circuit components, the deenergization is completed within one-quarter cycle, which corresponds to 5 msec. if the line frequency is 50 c.p.s. Still shorter deenergization periods are attainable with higher frequencies.

According to the method of the invention, the application of the auxiliary opposing voltage is controlled in response to changes occurring in the load circuit of the field winding due to the initiation of the circuit interruption. Among these changes are:

l The decrease of the operating current;

2. the prolongation of the conducting state of the thyristor last operated in forward conduction; and

3. the change of one or several of the thyristors from onto off-statedue to cessation of the firing pulse.

Any other interruption-dependent change in the load circuit may-also be used for controlling the application of the opposing voltage, provided it is followed by a further change at the end of the deenergizing operation, for example:

I. by decrease of the operating current to zero, or

2. by termination of the prolonged conduction of the thyristor last operated,

3. or by the event that, after one or several of the thyristors have changed to the off-state, the remaining thyristors ultimately also change to the off-state.

The method just described is performed by the system illustrated in FIG. 6. This system is adapted for rapid energization as well as for rapid deenergization. As far as rapid energization is concerned, the circuit of FIG. 6 corresponds substantially to that of FIG. 4, the same components being designated by the same reference numerals. Contrary to FIG. 4, however, the system of FIG. 6 comprises a diode 65 connected between the capacitor 64 and the resistor 63. The rapid energization occurs as described with reference to FIG. 4.

For rapid deenergization, the system of FIG. 6 is further provided with an additional transformer 73 whose primary winding is connected through a diode 85 to the capacitor 64. The secondary windings of transformer 73 are connected through

diodes

86 and 87 to the

thyristors

23 and 24. The secondary windings of the transformer 71 are connected to the

same thyristors

23 and 24 through

respective diodes

88 and 89.

The rapid deenergization, according to the invention, takes place as follows:

The deenergization of the magnetic field winding 51 is initiated by interrupting the control voltage in circuit 120. This stops the firing of

thyristors

21 and 22. The current flowing through winding 51 decreases and, accordingly the voltage drop of resistor 62 becomes smaller. The capacitor 64 discharges through the diode 85 and the transformer 73. The change in current through the primary winding of transformer 73 induces a voltage in the secondary winding of transformer 73. Such voltage fires either thyristor 23 or thyristor 24, depending upon which of the thyristors in that instant has applied thereto a positive potential. A current will continue to flow through the fired thyristor even after the voltage has passed through its zero value. Such current, however, will be maintained only as long as the instantaneous value of the induction voltage is higher than the instantaneous value of the increased energizing voltage. Since the increased voltage is several times as high as the operating voltage, such current will become zero before the negative peak value is reached. As soon as the current changes its direction, the fired thyristor, either 23 or 24, will change to its off-state. Since the firing voltage has decayed prior to such change in current direction, no new firing ofa thyristor will take place.

As a result, the induction voltage decays and the induction current decreases to zero within a'quarter of a cycle. The small negative current has a beneficial influence on the remanent field of the magnetic winding. In this manner the invention achieves a most rapid deenergization, which prevents the occurrence of excessively increased induction voltages.

The deenergization periods thus attainable are substantially shorter than those resulting from a direct opening of the circuit by means of mechanical contacts.

A further advantage of the electronic systems according to the invention resides in the fact that the time previously neces sary for the electromechanical actuation of contacts, is at viated. Since further, no arcing periods need be taken into account, the total reduction of time delays is substantial. Another advantage of the above-described embodiment of the invention (FIG. 6) is the fact that the improved rapid deenergization is achieved by simply adding a small transformer :70 and six diodes to the previously proposed system (FIG. 4).

The same result is accomplished, according to the invention, by effecting the control of the rapid deenergization in response to the current which, subsequent to the interruption of the control voltage, continues to flow through the

thyristors

21 and 22. The required synchronization is secured by having the last operating thyristor coordinated to a predetermined other thyristor. Such a circuit may, for example, include an RC-member tuned'in such a manner that the firing voltage is not reached within the duration of a half-cycle but becomes effective after elapse of such duration.

A system embodying the type of performance just described is exemplified in FIG. 7. In this system the

thyristors

21 and 22, normally used to supply the operating current, are also employed as switches for controlling the rapid energization as well as the rapid deenergization. This is especially advantageous because the firing of the thyristors is always effected by pulses having steep leading and trailing flanksaiid because for deenergization only that one thyristor is fired which, in the phase sequence, most closely follows the negative voltage. Due to the fact that the induction current now flows through one of the

thyristors

23 or 24, the thyristor last traversed by the normal operating current will go to the offstate and the firing voltage will be switched off before the deenergization is terminated. I

The control operation of the system according to FIG. 7 is as follows:

The firing voltage is supplied continuously to the terminals 120" and has preferably steep leading and trailing flanks and a frequency of about 2 kc. The

thyristors

21 and 22 in the load circuit of the magnet winding 51 receive firing voltage through a small transformer 70 when a control switch 90 is closed. Closing of switch 90 also completes the rapid-excitation circuit, since the

thyristors

23 and 24 are immediately fired through the following circuits: terminals 120" transformer 72 thyristor 21 transformer 71 transformer 80 thyristor 23; and transformer 72 thyristor 22 transformer 73 transformer 80 thyristor 24. Diodes 83 and 89 serve to block current flow in undesired directions.

Subsequent to the switching on, the rapid excitation operation is terminated as follows. The voltage at the terminals of the magnetic field winding 51, which is dependent upon the operating voltage, charges the capacitor 64 through the resistor 63. During charging a current also flows through the winding 81 of the transformer 80. When the capacitor 64 is charged its voltage exceeds the voltage of the winding 81 and, as a result, no more current can flow through the secondary winding of transformer 80. Hence the reactance of the

primary windings

82a and 82b increases substantially so that the firing current flowing from transformer s 71 and 73 is no longer sufficient to fire the

thyristors

23 and 24. This terminates the rapid excitation operation. I

The deenergization according to the invention works as follows. After opening the primary circuit of transformer 70 at the switching member 90, the firing voltage of

thyristors

21 and 22 is switched off. However, since semiconductor thyristors (four-layer diodes) continue to conduct until the current passes through zero, the firing circuit remains closed for one

thyristor

23 or 24 in the circuit supplying the increased voltage. Due to

thyristors

21 and 22 being switched off, the voltage of the load circuit decreases whereby the capacitor 64 is discharged. As a result the blocking action of transformer 80 is removed and either

thyristor

23 or 24 is fired. When now the voltage passes through zero, the

last conducting thyristor

21 and 22 changes to its off-state and the remaining firing voltage from transformer 72 is thus switched off. At this time a thyristor in the circuit supplying the increased voltage continues to conduct the induction current after the positive voltage has become zero. Thus again, the induction voltage is opposed by the substantially higher increased negative voltage, and as soon as the negative voltage exceeds the induction voltage the current passes through zero and then flows in the opposite direction, thus turning the last conducting thyristor off. This completes the switching off operation. For all practical purposes the switching off is accomplished when the current and thus the induction voltage becomes zero because a slight negative current is sufficient to change the thyristor to its nonconducting state. The deenergization of the field winding 51 is assured within the one-half cycle period during which the above-described operations take place.

The method according to the invention will be further explained with reference to FIGS. 8to 10, showing how the switching-on instant of the deenergizing voltage, having a higher absolute value than the operating voltage, is predetermined to occur on the trailing portion of the positive halfwave at a constant amplitude value. In each of FIGS. 8, 9 and the abscissa denotes time and the ordinate denotes voltage.

FIG. 8 shows the waveform of the increased deenergizing voltage a which is also employed as the rapid excitation voltage. The continuous operating voltage is represented by curve b. The switching-on instant is shown at point 6. Point 11' designates the end of the deenergizing operation. The deenergizing voltage becomes zero at point e. Denoted by t and t are the beginning and end of a time duration. The heavy-line curve shown results from the following sequence of operational steps.

When the operating voltage b is switched off at any arbitrary point of time between t, and t the firing of the thyristors will cease, and the deenergizing voltage will always occur at point c which occurs not later than at the moment The point c was intentionally placed somewhat above the maximum amplitude of the curve b, so that the switched-on voltage according to curve a will block the thyristors in the circuit which normally is energized by the voltage according to curve b.

A synchronizing circuit assures that the deenergizing voltage b is switched on at point c. The synchronizing circuit is made effective in response to the control member in FIG. 7) that initiates the deenergization of the magnetic field. Such synchronizing circuit, may, in a manner known as such, comprise a zener diode and an RC-member or it may comprise a pulse-forming circuit, for instance, a Schmitt-trigger circuit.

It is an advantage of the above-described rapid deenergization system that only that portion of the positive increased voltage is switched on that is indispensable for deenergization. The fixing of the switching-on instant at point c prevents the deenergizing voltage from starting with the peak value of curve a, for example when the firing voltage happens to be switched off at the moment t,. If this occurred, the deenergization would require correspondingly more time, and point d would be located closer to the negative peak of curve f as is shown in FIG. 9 where f designates the negative half of curve a. It follows that starting the application of the deenergizing voltage at point c does not introduce any additional delay into the deenergization. On the contrary, the avoidance of a higher positive voltage has the effect of shortening the deenergizing period, a fact apparent from a comparison of FIG. 8 with FIG. 9.

FIG. 10 shows the voltage curves for the case wherein the switching-off process is started during the period between t and The sequence of operational steps then is as follows:

Since the synchronization moment 0, cannot be reached, the positive operating voltage b goes through zero at moment t and follows its negative half-wave whereby a deenergization already begins. At a moment corresponding to point of the preceding half-wave, the

thyristors

23, 24 in the circuit supplying the increased voltage start conducting (point The deenergization is completed at a point of time designated by d (e Where an increased deenergizing voltage is employed with but one phase, the time spacing between points 0, and c will correspond to one-half of a cycle period. This duration may occur as the maximum switching delay. If desired, the deenergization time can be further reduced by employing phaseshifted voltages.

It will be recognized that a substantial shortening of the deenergization is achieved by giving the deenergizing voltage a predetermined waveform. Undesirable heating of the magnetic field winding by high current peaks or shocks is avoided, this being of advantage particularly where high switching frequencies are involved.

Another advantage of the invention is the fact that the full energization may be restarted at any instant of a progressing deenergization by simply restoring the firing voltage and thus preventing the deenergization from being completed. Furthermore, the rapid deenergization may be started at any instant while a rapid energization is in progress.

FIG. 11 illustrates a preferred system which affords rapid energization as well as rapid deenergization with a minimum of circuit components.

A multiphase transformer 210 has its primary windings 211 connected to a multiphase power supply line RST and serves as the voltagesource for a control device and as a current supply for a magnetic apparatus 270. A set of secondary windings 212 furnishes the control voltage which in a rectifier 220 is rectified by

diodes

221, 222, 223 and smoothed by a capacitor 224. A two-phase secondary winding 213 is used to produce a rapid energizing voltage which is preferably rated to correspond to a multiple of the normal operating voltage. For example, the voltage of winding 213 may correspond to four times the normal operating voltage supplied by further secon' dary windings 214.

A set 230 of controlled rectifiers is preferably equipped with thyristors. Two

thyristors

231 and 232 supply the increased rapid energizing voltage to the magnetic apparatus 270. Two

other thyristors

233 and 234 conduct the normal operating current. The control voltage furnished by rectifier 220 is connected to a control circuit which comprises transistor flip-

flop stages

240, 250 and a synchronizing state 260 for producing a firing pulse for the thyristor group 230. The system is controlled by a switch 290 and operates as follows:

Upon closing of the switch 290, the first transistor flip-flop stage 240, depending on its setting (set or reset), supplies a firing pulse to the thyristors 230. Upon opening of switch 290, the second transistor flip-flop state 250 in conjunction with the synchronizing stage 260 furnishes a short firing pulse to the same thyristor group 230. The firing voltage required for the thyristors 230 to be turned on, is supplied directly through the switch 290. The synchronizing stage 260 is connected to a phase-shifting stage 280 by whose phase shift the desired synchronizing point is secured. This group of circuits 260, 280 is arranged in such a manner that a differing connection of the transformer 210 does not affect the phase relation. The magnetic apparatus 270 may be supplied with a voltage for rapid energization as well as for rapid deenergization.

A capacitor 414 is normally charged through series resistors 412 and 415. Upon closure of the switch 290 the polarity of the capacitor charge is changed through a diode 417.

The emitter of a transistor 24] of flip-flop 240 is connected to a point 418 which is initially at zero potential. Upon closure of the switch 290 however, the point 418 receives a positive voltage. As a result, the transistor 241 is turned off and a transistor 242 of flip-flop 240 is turned on. Transistor 242 connects the

thyristors

231 and 232 to the firing voltage furnished by the control circuit common to all thyristors. Thus, the circuit for rapid energization of the magnetic apparatus 270 is closed. The supply of voltage is sustained by the transformer windings 213.

The above-described switching on of the rapid energization in practice requires about 10 microseconds. For comparison, the conventional switching by means of electromagnetically actuated contacts requires about 10 msec.

When the capacitor 414 has discharged through an adjustable resistor 413 and the resistor 415, the transistor 241 changes from off to on. This also causes the transistor 242 to be turned on, and the firing voltage for the

thyristors

231 and 232 is switched off. Thus the duration of rapid energization is determined by the discharge time of the capacitor 414. The

thyristors

233 and 234 which upon closing of the switch 290 are connected to the control voltage, carry the normal operating current after termination of the rapid energization.

Thus, the switching-on operation characterized by the rapid v energization of the magnetic apparatus 270, is completed. The

operational switching on of the magnetic apparatus 270 takes place through the already fired

thyristors

233 and 234 whose firing current continues to flow through the closed switch 290.

For inactivating the magnetic apparatus 270, the switch 290 is to be opened. This operates the second transistor flip-flop stage 250 as follows.

The semiconductor junction components of the second stage 250 are complementary to those of the first stage 240. For example, the second stage may comprise

NPN silicon transistors

251 and 252 whereas the first stage comprises

PNP germanium transistors

241, 242.

A voltage divider of the second

stage comprising resistors

515 and 516 defines initially the charge polarity of a capacitor 514. Upon opening of the switch 290 a negative abrupt change of potential takes place across the capacitor 514 so that now the capacitor discharges through the adjustable resistor 513 and the resistor 516. During such discharge, which is limited to the duration of one-half of a cycle, the silicon transistor 251 is nonconducting so that the base of the silicon transistor 252 is connected to positive potential whereby transistor 252 is turned on.

A positive voltage is applied through

resistors

511 and 611 to the collector ofa transistor 261 in the synchronizing stage 260, whereby the transistor 261 is in a state of readiness for 10 msec. subsequent to the opening moment of the switch 290. The base of the transistor 261 in the synchronizing stage 260 is connected to a circuit 280 for producing a pulsating direct voltage which, on the average, is shifted in phase by 45 rela tive to the normal operating voltage. For producing the pulsating and phase-shifted direct voltage from an alternating voltage, the circuit 280 comprises a series connection of an inductance, formed by a winding 215 of the transformer 210, a resistor 28] and a rectifier 283. This direct voltage is applied to the base of the transistor 261 which thus periodically switches on and off at intervals of 10 msec.

The timing of synchronizing stage 260 is such, that the transistor 261 is on for 9 msec. and off for l msec. That is, the transistor is turned off for 0.5 msec. at the beginning and at the end of each cycle.

When the silicon transistor 261 is turned off, a positive voltage is applied to the firing electrodes of the

thyristors

231 and 232. Hence the thyristors will be switched on each time at a predetermined point on the trailing portion of the half-wave of the rapid deenergization voltage. Since this switching takes just 1 msec., only the one thyristor will be fired that will conduct the operating currentin the forward direction. The firing point appears approximately at of each half-wave. The increased rapid energizing voltage at such point is higher than the normal energizing voltage. Therefore, either

thyristor

231 or 232 begins to conduct and the current, upon passing through zero, continues flowing during its negative half-wave. Since now the firing voltage has ceased, the induction voltage of the magnetic apparatus 270 is opposed by the negative increased voltage and the switching off takes place at the instant when the current passes through zero. The performance exemplified can also be carried out if the transistors of the two flip-flop stages which differ from each other (NPN; PNP) are used in another suitable combination.

The above-described system requires a minimum of circuit components and is applicable wherever a rapid current rise is desired in electromagnetic devices, including electric motors and generators. The system may be modified for special cohtrol purposes, for example by omitting the

thyristors

233, 234 for carrying the operating current if merely a pulse excitation rather than continuous excitation is desired. There are also uses that permit omitting the first transistor flip-flop stage, for example where a rapid deenergization but no rapid energization is desired. 1

In a control system accordingto the invention, the voltage for rapid energization and for rapid deenergization is derived from a multiphase transformer. This has the advantage that the impulse load resulting from the rapid energization is distributed over several phases. Furthermore, a transformer of a given size affords drawing a pulse or shock power higher than rated continuous power, and the pulse load derived from the transformer has no disturbing effect upon the control voltage derived from the same transformer. Taking the rapid energization voltage and the normal operating voltage from a singlephase transformer, would require providing considerably more smoothing means for the control voltage and a much higher sensitivity to disturbances would be encountered.

Due to the fact that monostable complementary flip-flops are employed for producing the firing voltage for the thyristors, the number of circuit components is substantially reduced since the need for the interposition of inverter stages is obviated. A fact that also contributes to minimizing the time delays involved in the performance of the system and permits reducing the necessary biasing current for the transistor circuits.

Deriving of the current for the synchronization from the transformer through an RC-member assures by the resulting phase shift a faultless operation irrespective of the particular phase connections of the multiphase transformer to the power line. A rotating primary field differing in phase or phase rotation from another rotating field does not have any influence, so that a wrong phase connection of the transformer to the power supply line is impossible.

The leads of the control electrodes and of the currentsupply electrode of the first or input transistor flip-flop stage extend through the control member 290 in order to suppress disturbing influences. Due to such connection a spurious voltages or potential shifts on the supply leads of the control member 290 do not affect the control performance. By virtue of these features, the invention lends itself readily to being realized in existing systems by merely adding the needed additional component and without substantially changing the wiring of the existing system. In addition, the wiring required for the purposes of the invention does not necessarily require screening or shielding.

The variable resistor 413 has been provided in the flip-flop stage for adjusting the duration of the increased rapid energization voltage. This affords an economical production due to the resulting adaptability of the system to different magnetic devices.

It is to be understood that the invention is not limited to the particular embodiments described and shown, but that it comprises any modifications and equivalents within the scope of the appended claims.

We claim:

1. Method of rapid deenergization of an electromagnetic device, which comprises disconnecting the normal operating voltage from the device, impressing upon the device a deenergizing equally poled voltage in response to a first change occurring in the load circuit of the device as a result of the disconnection, said deenergizing voltage being opposed to that of said device and being higher than the operating voltage, and removing said deenergizing voltage in response to a second change occurring in said circuit.

2. The method of claim 1, for rapid energization as well as rapid deenergization of an electromagnetic device, which comprises converting and alternating multiphase voltage into several mutually superimposed unidirectional voltages of respectively different maximal amplitudes to obtain a resultant unidirectional fluctuating excitation voltage, temporarily impressing said fluctuating excitation voltage during a magnetic field buildup period of the device and maintaining said resultant voltage until the current through said device attains a value above that of the continuous energization, the energization being terminated by the disconnection of the normal operating voltage from the device.

3. The method of claim 1, which comprises setting for said equally poled voltage a switching-on point having a predetermined constant amplitude value on the trailing portion of the positive half-wave of said equally poled voltage.

4. The method of claim 1, wherein said first change is the occurrence of a given difference between the mean value of the normal operating current and the induction current of said load circuit, and wherein said second change is the zero passage of the current in said load circuit.

5. A system for rapid field excitation control of an electromagnetic device, comprising direct-current supply means having a load circuit including said device for providing normal operating voltage therefor and having control switch means for switching said operating voltage on and off; multiphase alternating-voltage supply means having a plurality of mutually phase-displaced output voltages of respectively different amplitudes, controllable rectifiers connecting said respective output voltages to said load circuit for applying rectified auxiliary voltages upon said load circuit when said rectifiers are conductive, condition-responsive control means connected to said rectifiers for controlling them to conduct only during a given interval of time, circuit means for effecting removal of said auxiliary voltages, said control means being in connection with said load circuit and responsive to respective first and second changes occurring in said load circuit due to opening of said control switch means so as to apply said auxiliary voltages during decay of the field of said device, said auxiliary voltages forming a resultant fluctuating voltage opposed to the induction voltage of said device for shortening said decay 6. A system according to claim 5, comprising a multiphase power supply transformer, said direct-current supply means comprising controlled rectifier means connected to said transformer for providing said normal operating voltage, said trans former forming part of said alternating-voltage supply means, and said resultant fluctuating voltage having a higher absolute value than said operating voltage.

7. In a system according to claim 6, said condition-responsive control means being responsive to the forward current which in said load circuit continues to flow through said controlled rectifier means upon opening of said control switch means, whereby said forward current constitutes said first change which causes said resultant auxiliary voltage to be applied.

8. A system for rapid field excitation control of an electromagnetic device, comprising direct-current supply means having a load circuit including said device for providing normal operating voltage therefor and having control switch means for switching said operating voltage on and off; multiphase alternating-voltage supply means having a plurality of mutually phase-displaced output voltages of respectively different amplitudes, controllable rectifiers connecting said respective output voltages to said load circuit for applying rectified auxiliary voltages upon said load circuit when said rectifiers are conductive, condition-responsive control means connected to said rectifiers for controlling them to conduct only during a given interval of time, said control means being in connection with said load circuit and responsive to respective first and second changes occurring in said load circuit due to opening of said control switch means so as to apply said auxiliary voltages during decay of the field of said device, said auxiliary voltages forming a resultant fluctuating voltage opposed to the induction voltage of said device for shortening said decay, a multiphase power supply transformer, said direct-current supply means comprising controlled rectifier means connected to said transformer for providing said normal operating voltage, said transformer forming part of said alternating-voltage supply means, and said resultant fluctuating voltage having a higher absolute value than said operating voltage, said conditionresponsive control means being responsive to the forward current which in said load circuit continues to flow through said controlled rectifier means upon opening of said control switch means, whereby said forward current constitutes said first change which causes said resultant auxiliary voltage to be applied, said conditionresponsive control means being responsive to at least one of said rectifier means in said load circuit changing to the offstate, whereby said change of state constitutes said first change which causes said resultant auxiliary voltage to be applied; and said condition-responsive control means being further responsive to another one of said rectifier means changing to the off-state, whereby said latter change causes said resultant auxiliary voltage to be switched off.

9. A system according to claim 5, comprising a synchronizing stage connected with said control switch means and with said condition-responsive control means for securing a given switching-on point of said fluctuating auxiliary voltage relative to its cycle period.

10. A system according to claim 5, comprising a multiphase transformer having a plurality of secondary windings, first and second controllable rectifier means having respective control electrodes, said first controllable rectifier means being connected to respective ones of said secondary windings and to said device for supplying an operating field voltage to said device, said second controllable rectifier means being connected to other ones of said secondary windings and to said device for supplying an increased auxiliary field voltage to said device, firing control circuit means comprising three firing circuits, a first one of said firing circuits being connected to said control electrodes of said first rectifier means, a second and the third one of said firing circuits being coupled to said first firing control circuit and connected to said control electrodes of said second rectifier means, sensing circuit means coupled to said second and third firing circuits and thereby to said first firing circuit for discontinuing the firing of any one of said first and second rectifier means in response to sensing of a change in the excitation of said device; control switch means arranged in said first firing circuit for closing said first firing circuit to cause initial energization of all of said rectifier means, said sensing circuit means being adapted, when responding, to cause blocking of said second rectifier means after a predetermined period following the closing of said switch means. said switch means being also operative to cause blocking of said first rectifier means when said switch means is opened.

11. A system according to claim 10, comprising a further rectifier circuit for energizing said firing control circuit means, said firing control circuit means comprising flip-flop means connected between said further rectifier circuit and the control electrodes of said second rectifier means, and synchronizing means in said firing control circuit means for setting the firing of said second rectifier means at a predetermined point relative to the wave of the increased voltage.

12. in a system according to claim all, said flip-flop means comprising two monostable flip-flop stages of which each has components complementary to those of the other flip-flop stage, said flip-flop stages having control electrodes and supply electrodes and output electrodes, the control and supply electrodes of at least one of said flip-flop stages being couple through said control switch means to said further rectifier circuit, said synchronizing vmeans comprising an RC member for connecting the synchronizing means to one of said secondary windings of said transformer.

13. In the system according to claim 12, said one monostable flip-flop stage comprising an adjustable member connected to said control electrode for adapting the circuit arrangement to respectively different electromagnetic devices.

Claims

5. A system for rapid field excitation control of an electromagnetic device, comprising direct-current supply means having a load circuit including said device for providing normal operating voltage therefor and having control switch means for switching said operating voltage on and off; multiphase alternating-voltage supply means having a plurality of mutually phase-displaced output voltages of respectively different amplitudes, controllable rectifiers connecting said respective output voltages to said load circuit for applying rectified auxiliary voltages upon said load circuit when said rectifiers are conductive, condition-responsive control means connected to said rectifiers for controlling them to conduct only during a given interval of time, circuit means for effecting removal of said auxiliary voltages, said control means being in connection with said load circuit and responsive to respective first and second changes occurring in said load circuit due to opening of said control switch means so as to apply said auxiliary voltages during decay of the field of said device, said auxiliary voltages forming a resultant fluctuating voltage opposed to the induction voltage of said device for shortening said decay

6. A system according to claim 5, comprising a multiphase power supply transformer, said direct-current supply means comprising controlled rectifier means connected to said transformer for providing said normal operating voltage, said transformer forming part of said alternating-voltage supply means, and said resultant fluctuating voltage having a higher absolute value than said operating voltage.

8. A system for rapid field excitation control of an electromagnetic device, comprising direct-current supply means having a load circuit including said device for providing normal operating voltage therefor and having control switch means for switching said operating voltage on and off; multiphase alternating-voltage supply means having a plurality of mutually phase-displaced output voltages of respectively different amplitudes, controllable rectifiers connecting said respective output voltages to said load circuit for applying rectified auxiliary voltages upon said load circuit when said rectifiers are conductive, condition-responsive control means connected to said rectifiers for controlling them to conduct only during a given interval of time, said control means being in connection with said load circuit and responsive to respective first and second changes occurring in said load circuit due to opening of said control switch means so as to apply said auxiliary voltages during decay of the field of said device, said auxiliary voltages forming a resultant fluctuating voltage opposed to the induction voltage of said device for shortening said decay, a multiphase power supply transformer, said direct-current supply means comprising controlled rectifier means connected to said transformer for providing said normal operating voltage, said transformer forming part of said alternating-voltage supply means, and said resultant fluctuating voltage having a higher absolute value than said operating voltage, said condition-responsive control means being responsive to the forward current which in said load circuit continues to flow through said controlled rectifier means upon opening of said control switch means, whereby said forward current constitutes said first change which causes said resultant auxiliary voltage to be applied, said condition-responsive control means being responsive to at least one of said rectifier means in said load ciRcuit changing to the off-state, whereby said change of state constitutes said first change which causes said resultant auxiliary voltage to be applied; and said condition-responsive control means being further responsive to another one of said rectifier means changing to the off-state, whereby said latter change causes said resultant auxiliary voltage to be switched off.

10. A system according to claim 5, comprising a multiphase transformer having a plurality of secondary windings, first and second controllable rectifier means having respective control electrodes, said first controllable rectifier means being connected to respective ones of said secondary windings and to said device for supplying an operating field voltage to said device, said second controllable rectifier means being connected to other ones of said secondary windings and to said device for supplying an increased auxiliary field voltage to said device, firing control circuit means comprising three firing circuits, a first one of said firing circuits being connected to said control electrodes of said first rectifier means, a second and the third one of said firing circuits being coupled to said first firing control circuit and connected to said control electrodes of said second rectifier means, sensing circuit means coupled to said second and third firing circuits and thereby to said first firing circuit for discontinuing the firing of any one of said first and second rectifier means in response to sensing of a change in the excitation of said device, control switch means arranged in said first firing circuit for closing said first firing circuit to cause initial energization of all of said rectifier means, said sensing circuit means being adapted, when responding, to cause blocking of said second rectifier means after a predetermined period following the closing of said switch means, said switch means being also operative to cause blocking of said first rectifier means when said switch means is opened.

12. In a system according to claim 11, said flip-flop means comprising two monostable flip-flop stages of which each has components complementary to those of the other flip-flop stage, said flip-flop stages having control electrodes and supply electrodes and output electrodes, the control and supply electrodes of at least one of said flip-flop stages being couple through said control switch means to said further rectifier circuit, said synchronizing means comprising an RC member for connecting the synchronizing means to one of said secondary windings of said transformer.