US1931111A - Electrical control system - Google Patents

Description

Oct. 17, 1933.

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LL .1. GOLDBERG ELECTRICAL CONTROL SYS TEM Filed Oc'C. 15, 1931 Invefitorw Leon \LGOIdbEPEE,

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Patented Oct. 17, 1933 UNITED STATES PATENT OFFICE ELECTRICAL CONTROL SYSTEM Leon J. Goldberg, Schenectady, N. Y., assignor to General Electric Company, a corporation oi? New York Application October 15, 1931. Serial No. 569,025

6 Claims. (Cl. 172-239) My invention relates to electrical control syscreased excitation as shown by the curve CD. The tems for dynamoelectric machines, and more curve BOD represents the mean curve between particularly to control systems for electric ma- BAD and BCD. It follows therefore that the chines operating in what is known as the Wardvoltage generated for a given value of field our- Leonard system, in which a separately excited rent and excitation is materially affected by the generator has its armature connectedin a local direction and magnitude of the residual magcircuit with the armature of a separately excited netism. Assuming that a value of excitation as motor, and has for its object the provision of such represented by the abscissa: OE is applied to a control system which in 'a simple and eflicient the generator, the voltage generated will be equal 10 manner provides improved operating characterto the ordinate EF plus the ordinate PG or minus istics. the ordinate FH. Whether the ordinate FG be Although it obviously has other applications, added or the ordinate FH be subtracted will demy invention is particularly'useful in connection pend upon the direction of the residual magwith elevators where a prescribed control of the netism when the excitation was applied to the 15 motor is required as in the leveling operation of generator. Hereafter in the specification and the elevator. I claims the term residual magnetism will be ap- Ordinarily the elevator is brought to a landplied to mean the variation in generated voltage ing at a very low speed requiring a consequent low from the mean value of voltage, as represented by t voltage on the generator. It is important that the curve BOD, due to the residual magnetism.

20 the leveling speed be substantially the same ir- In carrying out my inventionl provide a methrespective of load or previous speed of the elevator 0d and means for obtaining the same generain order to prevent the elevator from overrunning tor voltage for a given value of excitation irreor underrunning a floor. And inasmuch as the spective of the direction or magnitude of the voltage generated by the generator depends not residual magnetism of the generator. More spe- 25 only on the field ampere turns but also on the cifically, I provide for the subtraction of a magdirection and magnitude of the residual magnetomotive force proportional to the magnetonetism, it is necessary to compensate for or to motive force applied to the generator from amagcorrect the effect of the residual magnetism. For netomotive force proportional to the total flux of a clear understanding of the effect of the residual the generator. The resultant magnetomotive 30 magnetism on the .generator voltage and for the force is proportional in magnitude and direction definition'of the terms with which I wish to exto the residual magnetism. plain my invention reference should be had to In one form of my invention provision is made Fig. 2 of the drawing. for the subtraction of the magnetomotive forces I have shown in Fig. 2 a typical hysteresis loop from the magnetic circuit of an auxiliary genera- 35 of a generator plotted with ampere turns as tor driven at constant speed. The resultant magabscissee and the terminal voltage E1: of the gennetomotive force produces a flux on the auxilerator as ordinates. Assuming that there is no iary generator armature causing acorrective volt-- residual magnetism and that the generator is age to be generated which is equal to the voltage being rotated at constant speed, the rise in voltdue to the residual magnetism of the generator.

40 age as the excitation is increased may be repre- Though I have shown several modifications I presented by the broken line curve M. As is well fer at the present time to apply the corrective understood by those skilled in the art, the devoltage to increase or decrease the main genercrease in voltage caused by decreasing the excitaator voltage thereby automatically compensating tion is represented by the curve DA. This curve at all times for the eifect of the residual magne- 45 strikes the axis OY a distance above the origin tism on the voltage of the main generator.

O as indicated by the ordinate 0A. The voltage For a more complete understanding of my in- OA generated when the excitation current has vention reference should now be had to the drawbeen reduced to zero is entirely due to the residing whichillustrates several embodiments of my ual magnetism of the generator. If the excitainvention. Fig. 1 is a circuit diagram showing 50 tion is now reversed the voltage is first reduced a control system for a motor generator set emto zero, thereafter building up in the reverse di p y in electric elevator Service in which the rection as shown by the curve AB. As before the corrective voltage is applied to an auxiliary field voltage decreases with decrease of excitation as winding on the generator; Fig. 2 is a typical hysrepresented by the curve BC. If the excitation is teresis View of the load generator together with again reversed, the voltage will build up with inadditonal curves for aiding the explanation of the invention; Fig. 3 is a modified fragmentary circuit of Fig. 1 showing the corrective voltage applied to the load circuit between the generator and the motor; Fig. 4 is a similar fragmentary circuit showing the corrective voltage applied to drive a small motor arranged to vary the amount of resistance in series with a separately excited field winding of the generator; and Fig. 5 shows the corrective voltage applied to an auxiliary field winding provided on the motor. 1

Referring to the drawing, I have shown my invention in one form as applied to a typical Ward- Leonard control system for an elevator. A load generator is driven by a motor 11 at substantially constant speed. The armature of the generator is connected in local circuit through a series field 12 with the armature of motor 13 which motor is arranged to drive the elevator 14 through the cooperation of a gear 15 secured to the motor shaft and a gear 16 secured to the shaft of a cable drum 17. As is well understood by those skilled in the .art, the speed of the elevator is controlled by varying the voltage applied by the generator to the motor 13 by means of a separately excited field winding 18 connected through electromagnetic direction controlling switches 19 and 20 and a speed controlling resistance 21 to supply lines 22 and 23.

The magnetic fiux of ,the generator 10, fixing the value of the generated voltage at any given time, is equal to the flux produced by the magnetomotive forces of the field windings 12 and 18 increased or decreased by the residual magnetism of the generator. It follows, therefore, that a fiux proportional to the residual fiux of the generator 10 may be produced on an auxiliary generator 24 by vectorially subtracting from a magnetomotive force proportional to a magnetomotive force which will produce the totalfiux of generator 10, magnetomotive forces proportional to the magnetomotive forces of the field windings 12 and 18. This result may of course be accomplished in a variety of ways, the principle of my invention having once been explained. The particular means of which I make use, however, consists in connecting a field winding 25 provided on the auxiliary generator 24 across the armature of the generator 10 and connecting additional field windings 26. and 27 provided on the auxiliary generator 24, respectively in shunt 'with the field 18 and the field 12 of the generator 10, the field windings 26 and 27 being in opposition to the field winding 25. The resultant magnetomotive force on the auxiliary generator produces a flux which is proportional to the residual magnetism thereby causing the auxiliary generator to generate a corrective voltage which may be equal or proportional to a part of the voltage of generator 10 due to the residual magnetism. The value of the voltage will depend on the proportionality factor selected for the field windings of the generator 10 and the field windings of the auxiliary generator 24. As shown, the corrective voltage is applied to a field winding 28 provided for the generator 10 in a direction to cause a current to fiow which produces a magnetomotive force which adds to'or subtracts from the magnetomotive force of the field 18 thereby increasing or reducing the fiux and voltage of the generator 10 an amount which is sufIicient to com-' pensate for the effect of the residual magnetism. The effect of correcting for the residual magnetism in this form of my invention is to reduce the generated voltage a predetermined amount. Inasmuch as the correction is applied to the source of the error, the opposing magnetomotive forces applied on the auxiliary generator 24 tend to become equal in magnitude reducing its flux. It is to be here observed that they would exactly neutralize each other if the reduction of fiux and voltage of the auxiliary generator 24 should not at the same time reduce the magnetomotive force of the field winding 28. The resulting correction for the residual magnetism, however, is a close approximation to an exact compensation.

As I have already stated the effect of the residual magnetism may vary from time to time and the reason for the variation in the control of elevator 14 will clearly appear upon an examination of the operation of the generator 10 for varying the speed of the elevator. It will be assumed, as before, that the motor 11 is driving the generator 10 at a constant speed and the separately excited motor field 29 is energized and it is desired to lower the elevator. The car switch 30 is moved in a clockwise direction to its first position so that a pivotally mounted conducting segment 30a completes an energizing circuit for the operating coil 31 of the direc tion controlling switch 20, which circuit may be traced from the supply line 22, conductor 32, conducting segment 30a now bridging contacts 33 and 34, coil 31, and by conductor 35 to the other supply line 23. The direction controlling switch 20 thereupon closes establishing an energizing circuit for the separately excited field 18 of generator 10 and for the field winding 26 of the auxiliary generator 24, which circuit may be traced from the supply line 23, conductor 35a, the lower contact of switch 20, conductor 36, field winding 26, conductor 37, the upper contact of the switch 20,

\conductor 38 and through the resistance 21 to the other supply line 22. Inasmuch as the winding 26 is "connected in parallel with the winding 18,

excitation current is also supplied to the winding 18. The excitation current supplied to the field windings 18 and 26 is limited by the resistance 21 and, of course, the voltage of the generator may only build up to a fraction of its full voltage and the elevator driving motor consequently rotates at low speed. Further movement of the car switch 30 in a clockwise direction increases the speed of the motor 13 by successively shortcircuiting sections of the resistance 21 designated by the reference numerals 39 and 40 thereby increasing the excitation and voltage of the generator 10, consequently accelerating the elevator driving motor 13 through its intermediate and full speeds. It will be remembered that the residual magnetism of the generator 10 will depend upon the magnitude and direction of the magnetomotive force last applied to the magnetic circuitof generator 10. It will be apparent that the greatest magnetomotive force is applied to the magnetic circuit of generatorlO ,when the elevasumed that the elevator is operated only through its intermediate speed, which speed is then re duced, the effect of the residual magnetism is proportionately less and if the.elevator is operated at low speed, the residual magnetism would have the least effect.

If it be desired to operate the motor 13 in the opposite direction to raise the elevator 14, the car switch 30 is rotated in a counter-clockwise direction, thereby energizing the operating coil of the direction controlling switch 19. The switch 19 immediately closes establishing a circuit for the fiow of current through the field winding 18 in a direction such that the resulting voltage the PR losses in the generator armature.

produced by the generator 10 causes the motor 13 to rotate in the proper direction. Under these conditions the residual magnetism of the generator is opposed to the building up of the field and, as I have explained in connection with Fig. 2, causes the generated voltage for a given value of field current to be much less than if the residual magnetism had been in the same direction as the rising magnetic field. The auxiliary generator 24, however, generates a' voltage causing current to fiow through the corrective field 28 ina direction to increase the voltage of the generator 10. This will be apparent by remembering that the magnetomotive force produced by the winding 25 is now derived from the generated voltage decreased by the effect of the residual magnetism. It follows that the sum of the magnetomotive forces produced by the field windings 26 and 27 is greater in magnitude, conse quently producing a net field on the auxiliary generator 24 in the proper direction.

In the modifications of my invention described hereinafter, for the sake of clarity of description, it will be assumed that the effect of the residual magnetism in each case is cumulative. It is to be understood, however, that if the residual magnetism is reversed, the corrective voltage generated by the auxiliary generator also reverses to properly compensate for the effect of the residual magnetism under all conditions of operation.

Referring now to Fig. 3, I have shown the armature of the auxiliary generator 24 connected in series with the local circuit between the load generator 10 and the motor 13. As before, the field windings 25 and 26 are respectively connected in shunt with the armature of the generator 10 and its field winding 18. The corrective voltage produced by the auxiliary generator 24 boosts or bucks the generator voltage thereby neutralizing the efiects of the residual magnetism.

A compounding effect is also obtained in this modification of my invention to compensate for Assuming that the generator 10 is carrying a heavy load, the effect of the PP. losses in the generator armature is to decrease the terminal voltage which causes a corresponding decrease in the magnetomotive force produced by the winding '25, the result of which is an increase of voltage generated by the auxiliary generator.

The effect of the residual magnetism is rela-.

tively greater when the voltage of the generator is low and inasmuch as the generator for low voltages is operating on the straight portion of its characteristic curve, it will be apparent that the saturation eifect of the magnetic circuit of the generator will not diminish the accuracy of the measurement of the effect of the residual magnetism.

In the modification of my invention shown in Fig. 4 the auxiliary generator is connected to a motor driving a rheostat 46 connected in series creased, is to decrease the excitation current of .the separately excited field winding which causes a reduction in generator voltage. The reductions in voltage of the generator and of the magnetic flux in the generator are reflected in the corresponding windings on the auxiliary generator. The difference between the two, however, remains the same, and it will'therefore be seen that an exact compensation for the effect of the residual magnetism may be obtained inasmuch as the correction is not applied in a manner to eliminate the indication of error.

In Fig. 5 the corrective voltage generated by the auxiliary generator 24 is applied to an auxiliary field winding 50 provided on the motor 13. Inasmuch as the residual magnetism of the generator 10 tends to increase the voltage of the generator consequently increasing the speed of the motor, 47, the corrective voltage from the auxiliary generator 24 is applied to the auxiliary field winding 50 on the motor 13 so as to increase the magnetism of the motor, thereby decreasing its speed and eliminating the effect of the residual magnetism on the speed of the motor 13.

While I have shown a particular embodiment of my invention, it will be understood of course that I do not wish to be limited thereto since many modifications may be made and I, therefore, contemplate by the appended claims to cover any such 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. Means for compensating for the residual magnetism of a dynamo-electric machine having field windings, comprising corrective means for modifying the excitation of said machine, means responsive to the electromotive force of said machine for applying a magnetomotive force to said corrective means, and means responsive to the voltage across said field windings for producing on said corrective means magnetomotive forces opposing said aforementioned magnetomotive force so that the resultant magnetomotive force controls said corrective means.

2. Means for compensating for the residual magnetism of a dynamo-electric machine having field windings, comprising an auxiliary generator, means responsive to the electromotive force of said machine for applying a magnetomotive force to said auxiliary generator, means responsive to the voltage across said field windings for producing on said auxiliary machine magnetomotive forces opposing said aforementioned magnetomotive force and means responsive to the electromotive force of said auxiliary generator for affecting the electromotive force of said dynamoelectric machine, V 3. Means for compensating for the residual ,magnetism of a dynamo-electric machine having field windings, comprising an auxiliary generator, means responsive to the electromotive force of said machine for applying a magnetomotive force to said auxiliary generator, means responsive to the voltage across said field windings for producing on said auxiliary machine magnetomotive forces opposing said aforementioned magnetomotiv'e force, and means for applying the electromotive force generated by said auxiliary generatorto said machine to compensate for said residual magnetism.

4. In a Ward-Leonard control system having a generator provided with field windings and a motor connected in a local circuit with said generator, the combination of means responsive to the electromotive force of said generator for producing a magnetomotive force, means for producing magnetomotive forces proportional to the magnetomotive force produced by said field windings, and means differentially responsive to said first mentioned magnetomotive force and said last mentioned magnetomotive forces for applying a corrective effort to said system proportional to the difference between said magnetomotive forces.

5. In a Ward-Leonard control system comprising a generator having a plurality of field windings and a motor connected in a local circuit with said generator, an auxiliary generator provided with a field winding, connections for connecting said winding across the armature of said generator, and other field windings on said auxiliary generator, connections for respectively connecting each of said other field windings to be excited from the same source of supply as each of said generator field windings to oppose said winding excited by said generator, and means for applying the resulting electromotive force of said auxiliary generator to said local circuit to correct for the effect of the residual magnetism of said generator.

6. In a Ward-Leonard control system having a load generator provided with a field winding and a motor connected in a local circuit with said generator, the combination of an auxiliary generator with its armature connected in said local circuit and provided with a field winding for producing on said auxiliary generator a magnetomoforce of said other winding whereby the resultant magnetomoti-ve force produces a flux on said auxiliary generator suflicient to cause a corrective voltage .to be generated by said auxiliary generator equal to the voltage of said load generator due to residual magnetism.

- LEON J. GOLDBERG.

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