Nov. 19, 1946. 2,411,377 A. W. KIMBALL CONTROL SYSTEM Filed June 14, 1944 4s M2 4144 F1 ffy. z. MQ X /Ímperés ffy 4 BY fmëä ATTORNEY Patented Nov. 19, 1946 2,411,377 UNITED STATES PATENT OFFICE 2,411,377 CONTROL SYSTEM Albert W. Kimball, Forest Hills, Pa., assignor to Westinghouse Electric Corporation, East Pitts burgh, Pa., a corporation of Pennsylvania Application June 14, 1944, Serial No. 540,175 7 Claims. (C1. 172-239) 2 My invention relates to control systems of the voltage and the saturation dependent voltage generated by the regulating generator. variable voltage type and particularly to systems containing an auxiliary regulating generator for These and other objects and features, as well as a speciñc example of a control system embody limiting the load current of a motor to be con trolled, systems and generators of this kind being disclosed in the copending applications by J. G. Ivy, Serial No. 496,596, filed July 29, 1943, and Serial No. 532,975, filed April 27, 1944, both as signed to the assignee of the present application. An object of my invention is to provide a con trol system of the type just referred to that pro duces not only a load limiting regulating effect, but is also distinguished by increased accuracy and speed as regards its response of the motor to changes in control adjustment while being sub stantially free of hunting even at a high rate of change of the control adjustments. Another object of my invention, with reference to hoists, particularly mine hoists, is to provide a hoist control system in which the torque of the hoist motor and hence the stress on the ropes and other mechanical hoisting equipment are automatically limited due to control characteris tics inherent in the electrical control system and in which the hoisting speed is a function of the selected controller position regardless of the amount of load, thus reducing the degree of at tention and skill for operating the hoist. In order to achieve these objects and in accord ance with my invention, I provide the motor generator combination of a variable voltage drive with two auxiliary generators for controlling the ñeld excitation of the main generator. One of these auxiliary generators, hereinafter called the “control generator,” has a self-excited field wind ing rated for just sustaining the armature voltage and further field means whose voltage is ad justed under control by the operator. (When referring in this specification to “self-excited” windings, I use this term for designating a i'leld winding which, in contrast to a “separately ex cited” Winding, derives its excitation from the energy generated in the armature of the same machine.) The other auxiliary generator, here inafter called the “regulating generator,” has saturation characteristic so that it generates an armature voltage substantially only when its ñeld excitation exceeds a given finite magnitude. The regulating generator has ñeld means excited in dependence upon the load current of the motor to be controlled. The armatures of both auxiliary generators are connected to a ñeld winding of the above-mentioned main generator so that its ex CH ing them, will be apparent from the following de scription of the mine hoist control system shown diagrammatically in Fig. 1 of the drawing, and elucidated by the explanatory diagram of Figs. 2, 3 and 4, and the detail showing in Fig. 5 of the pole structure of an appertaining regulating gen erator. Referring to the hoist control system shown in Fig. 1, the hoisting equipment proper is schemati cally indicated at | and includes a hoisting drum ._ whose shaft 2 is mechanically connected to the armature I0 of a driving motor HM. The motor has a separately excited winding || and a com pensating series field winding l2. The ñeld wind ing || is energized from a current source of sub stantially constant voltage, and to this end is con nected through an adjusting rheostat RI to an exciter EX with an armature 50, two ñeld wind ings 5| and 52, and a field rheostat R1. The ad justment of rheostats RI and Rl need not be , changed during the operation of the system. The armature |0 of the hoist motor HM is connected, in load circuit Al, with the armature 20 of a main generator MG which forms the cur rent source of circuit AI. The main generator “I MG has a main ñeld winding 2| connected in a control circuit A2 which includes in series two voltage sources represented by the armatures 30 and 40 of a control generator CG and a regulat ing generator RG, respectively. A resistor R2 is OD Si series-arranged in circuit A2. Numeral 22 de notes a compensating or interpole winding of the main generator MG. The control generator CG has four ñeld wind ings 3|, 32, 34, and 35 which cooperate in con trolling the voltage impressed on the main gen erator ñeld winding 2|. The resultant energiza tion of winding 2| determines the voltage and current supplied by the main generator arma ture 2U through circuit A| to the hoist motor HM, cri thereby controlling the torque and speed of the hoisting equipment driven by the motor HM. The current in circuit A2 is principally deter mined by the excitation of ñeld winding 3|, here inafter called the “pattern ñeld winding” of the 50 control generator CG. Field Winding 32 is self energized and serves to amplify the control effect. While the connection of winding 32 in circuit A2 is shown as a series arrangement, a shunt wind citation depends on both the operator-adjusted 55 ing may be used instead. Considering the eX citation of pattern ñeld winding 3| as a stand 2,411,377 ard and assuming that main generator MG sup trol generator CG and is connected in series with plies energy to the hoist motor rather than func tioning in a regenerative sense, both windings voltage adjusted at the controller CO. this winding so as to be energized by the pattern hereinafter called the “voltage winding,” is en ergized in dependence upon the voltage in load circuit AI, and to this end connected by leads 23 and 2d across the armature 2@ of the main gen erator MG. Field winding 35 of control genera tor CG serves to compensate for the IR drop in the main circuit Al and is connected across winding 22 through leads 23 and> 26 and in series with a Calibrating resistor R3. A resistor in cil' cuit Al may be used in place of coil 22, if desired, to obtain excitation for windings 35 and 45, Field winding fifi of regulating generator RG is simi 32 and 35 act cumulatively while winding 3i acts diiierentially with respect to the pattern field winding 3|. Field winding Sil of control generator CG, lar in function to the voltage winding 34 of con trol generator CG and is connected in series therewith across armature 2li of main generator MG, a Calibrating resistor R4 being inserted in series with winding £54. Field winding d5, here io inafter called the “regulating winding,” is excit ed in accordance with the current in the feed cir cuit Ai and to this end connected, through a cal ibrating rheostat R5 and leads 23 and 25, across the interpole or compensating winding 22 of gen erator MG in parallel to the IR-drop compen sating ñeld winding S5 of generator CG. When in operation», both windings 35 and d5 are trav ersed by a current whose magnitude varies in accordance with the Voltage drop across the iield 'I‘he pattern ñeld winding 3|, serving to deter winding 22 or other Voltage measuring resistor mine the basic speed of the hoist motor as to in circuit Ai fromwhom the windings 35 and 45 direction and magnitude, is energized from a cur derive their energization. rent source of constant voltage under control by In order to achieve the control functions in operator-actuated regulating and reversing accordance with the above stated objects oi my means. More in detail, pattern winding. 3l is connectedV to mainsv X and Y of the exciter EX, 25 invention, a particular design of the two auxili ary generators CG and RG and their appertain a reversing switch RS being interposed in order ing field exciting means is necessary, as will be toselect the polarity of the pattern voltage im set forth presently. pressedV on iieldwinding 3l. The connectionin The control generator CG is a small electric cludes. a control device CO. which has a resistor RS. connected between main Y and. reversing 30 generator, similar in design to conventional ex citers. Like exciters, it possesses the ability to switch RS. accurately amplify small amounts of energy sup The reversing switch RS, as illustrated, has plied to its iieids into larger output amounts for two movable contacts tiûand i6), each cooperat the control of large electrical machines. How ing with .two stationary contacts ti, 62 and il, ever, the control generator possesses this ability 12, respectively. In one position of switch RS, to a much higher degree and thus represents a Contact 6G is in engagement with contact 6l, and sensitive amplifier, capable of working on very contact l@ with contact ll, in order to energize small inputs to its fields to produce a very large the hoist motor HM for operation~ in the hoist output in the armature circuit. This sensitivity ing direction. In its other position, the revers ing switch RS connects movable contacts 6B, and 40 and amplification is due to the’ action of the self energized ñeld winding 32 which feeds a small 1li with stationary contacts 62 and 1.2, respective portion of the control generator output power ly, for controlling the hoist motor to operate in back into the control generator as excitation t0 the lowering direction, The control device CO is produce still more output. IThe self-excited iield preferably designed like acustomary master con is just sufiicient to sustain the generated Voltage troller, while the reversingA switch RSi and its con tacts are preferably vformed by electromagnetic but, by itself, is incapable of building up the out contactors whichv are controlled in accordance put. of the machine. Hence, the action of gener erator CG is always under the control of one or more of the separately excited iield windings 3l, with the selected. hoisting or lowering position of the master4 controller. Since the particular de sign of the operator-actuated control elements, here represented by CO and RS, isV not essential, - 33, 34', and 35. Stating this another way, the re sistance of the external control circuit A2 is ad justed relative to the self-excited iield excita for the invention proper and, as such, need not involve novelty over the well'known andv custom, tion so that the machine CG operates on its air ary masterV controllers, the simplified illustration gap line. Y With this adjustment of the self-energizedfield, in Fig. 1 has beenchosen for the sake of. con The armature 26 of the main generator lVIG the ampere turns from the other field exciting means (windings 3l, 33, 35,35) can be balanced , and the armature 3Q of the control generator CG are mounted on a common shaft 3 which, when to the null point. This nullr condition exists when venience and- clarity. ' _ a field excitation which measures the motor speed is balanced by the rleld- excitation of the pat tern field winding caused by the standard or pat tern voltage as adjusted by the operator by se lecting the position of the master controller. rI‘he motor speed corresponds to the` fundamen in operation, is driven by a constant speed mo tor Mi. Satisfactory operation can also be ob tained if armature 3d is driven at constant speed while armature 2D is actuated by a separate drive whose speed does not vary excessively. Armature ¿ââä of regulating generator RG is G) tal equation:V mounted on a common shaft Ewith armature 59 Speed=constant >< (armature voltage-armature of exciter EX. Shaft 5 is connected to a constant IR drop) speed motor M2. It will be understood, however, x that the illustrated arrangement can be modified by using a single constant speed motor for the operation of both shafts 3 and 5, or by connect ing the two shafts 3 and '5 with each other so as As stated previously, the Voltage responsive iield winding se of generator CG measures the arma turevoltage of hoist motor HM, and the IR-drop field winding 35 measure the interpole IR drop which is proportional to the armature IR drop to obtain a single motor generator unit. The regulating generator RG has three iield ofthe motor I0. ' The relative polarities of. the windings fil, dll, and 45. Field winding fil corre sponds to the pattern iield winding 3l of the con 75 two windings 35 and 35 are such that their am 5 2,411,377 pere turns are subtractive and thus satisfy the above equation. The resultant speed measuring ampere turns of windings 35 and 34, as a whole, are balanced against those of the pattern field winding 3l . 6 after the shunt has been saturated, is similar to that of a conventional machine. Due to the fact that ampere turns from the regulating ñeld winding 45 are used for saturat ing the magnetic shunt, the output voltage of gen When the motor is running at the speed called for by any selected setting of the master con troller, the speed measuring ampere turns cancel ampere turns of the pattern ñeld. The entire erator RG is controlled in response to the ar when the load current of the motor HM tends to exceed a given safe limit, the armature di) of gen erator RG generates a bucking voltage which re duces the resultant field excitation of main field speed, and the voltage of the main generator MG also approaches maximum, the corrective effect required by the RG armature 4t to limit the current in winding 2i oi‘ generator MG will mature current (and hence torque) of the hoist motor HM. As a result, the above-mentioned bucking voltage of armature 4i) is not effective excitation on the control generator comes now 10 before the magnetic shunt on the regulating gen from the self-energized ñeld, and there is no tend erator RG is saturated, and this saturation effect ency to change the generator excitation. Should occurs only when the load current of the hoist the motor speed vary from the proper value, the motor has exceeded a given safe limit value. balance between the pattern and speed measuring The control fields of the regulating generator excitations is disturbed. The resulting excess do not saturate the shunt when performing their ampere turns then act to correct the error in mo normal function since they are balanced against tor speed. In this manner, the control genera each other so that their net ampere turns are tor CG provides a sensitive and accurate speed normally zero. In other words, the small tran regulation. sient departures from zero, necessary to obtain The regulating generator RG is so designed 20 the desired regulating function of iield windings that the component voltage imposed on circuit »I and $4, is insufficient to cause appreciable sat A2 remains substantially zero under normal op uration in the shunt, although these windings are erating and load conditions of the system, so that effective to produce the regulating anti-hunting usually the entire neld excitation of the main action mentioned presently. generator MG is produced by the control gen~ 25 When during a control operation initiated by erator in the above-described manner. However, the operator, the hoist motor approaches full winding 2l suiìiciently to prevent a further load increase in the motor circuit Al. To accomplish this limiting eiïect, the regulating generator RG has a special characteristic, similar to that shown in Fig. 2. This characteristic (curve V) differs from that of conventional machines by having an be less because the resultant speed-measuring ñeld of the control generator Will then cancel a greater portion of pattern field ampere turns (winding 3l) which are tending to cause exces` sive load voltage and current. The voltage field (winding 44) on the regulating generator will also cancel pattern ñeld ampere turns (winding extended low voltage or zero voltage interval be tween points E and F which are both displaced fil), and this occurs in the same proportion as from the zero point O by ñxed amounts oi eX~ in the control generator so that the corrective citation. Line R represents the resistance line 40 eñect of the component voltage generated by the of the generator. armature 48 is reduced in the right amount to A characteristic of this type can be obtained maintain the same motor armature current in by providing the ñeld poles of the generator with circuit Al. It is this simultaneous occurrence, a saturable magnetic shunt as exemplified by and its corrective eifect, of the regulating action Fig. 4. of the speed-dependent and operator-adjusted In Fig. 5, numerals 5, to, and Sil denote the shaft, armature, and stator frame, respectively, voltages that decreases the tendency of hunting and thus increases the accuracy, reliability, and of the regulating generator RG. The pole struc permissible speed of control. It is essential in ture comprises a base portion 8l in good magthis connection that the component voltage of netic contact with the stator frame and a pole 50 the regulating generator dil is directly introduced shoe portion S2 adjacent to the armature. rI’he into the ñeld circuit of the main generator MG main pole portion E3 is shunted by a eaturable so that the inherent time delays of the current flux path 35 and contains an air gap or a mag regulating means are reduced to a minimum. netically reluctant shim iid, for instance of brass. In order to further elucidate the above-de The windings 4i, 44 and 135 of the generator are scribed operation of the system, reference is had arranged on the main pole portion 83. The air to the schematic diagram of Fig. 3. gap or shim at the top of the main pole portion In this diagram the values along the ordinate carries the entire pole flux and hence does not represent the output voltage of the control gen iniiuence the division of flux. It primarily de erator CG, while the values along the abscissa termines the spacing F-E of the zero voltage represent the resultant ampere turns of the field interval as well as the sha-pe of the characteristic winding means of this same generator necessary beyond points F and E according to the diagram for obtaining the correlated output voltage. The of Fig. 2. Because of this gap or shim, substann straight line denoted by RL indicates the resist tially all flux íiows through the shunt since the ance line of the circuit A2 while the saturation reluctance of this path is low, and almost none curve SC indicates the relation of ampere turns of it is forced across the air gap into the arma to generated volts under operating conditions ture to generate voltage, as long as the resultant where the output voltage of the regulating gen field excitation is insuiiicient to saturate the erator RG is zero. Curve DC in Fig. 3 represents shunt. The shunt 85 is so proportioned that it the displaced characteristic which occurs when saturates at an excitation corresponding to points 70 the regulating generator RG generates output F and E of Fig. 2 and then becomes unable to voltage due to the occurrence of an overload in carry more flux. Consequently, upon saturation the load circuit of the hoisting motor, as ex of the shunt 85, an increasing field excitation plained in the foregoing. This displacement re forces liux across the air gap into the armature so that now a voltage is generated. The action, 75 duces the field excitation of the main generator ñeld winding 2l in accordance with the voltage value denoted by RV in Fig. 3. The resulting action is a corresponding reduction in the ar mature voltage of the main generator MG, and this action continues until the current in the? voltage coil 3Q on the control generator CG has caused a difference between the pattern and other control fields equal to the ampere turns indicated by DV in Fig. 3. From then on, the control generator CG continues operating inl ac cordance with the displaced saturation curve DC. for controlling. said component voltages respec tively, operator-controlled circuit means for pro viding an> adjustable pattern voltage and circuit means for providing a control voltage variable in accordance with the voltage of said circuit, said diiierent circuit means being connected with said' control means of said control voltage sourcev for varying said appertaining component voltage in accordance with the differential value of said pattern and control voltages, and means for caus ing said regulating voltage source to vary the The shape and slope of the current limiting rate of change of its appertaining voltage com portion of the voltage-ampere turns character ponent when the current in said output circuit istic of the control generator can be modified passes through a given ñnite value, whereby saidby varying the combination of fields on the regu lating generator RG. For instance, with the 15 current is substantially limited to a given maxi mum value. ñeld windings arranged as shown in Fig. 1, the 3. A motor control system comprising a vari characteristic is of the type represented by curve able speed direct current motor, a main voltage CIr in Fig. 4. By providing a current responsive supply means having a load circuit connected to coil 44 on the regulatinggenerator RG but omit ting the current coil Sli on the control generator 20 said motor for energizing the latter and main control means for varying the voltage of said CG, the characteristic can be changed to the type circuit, a controlling voltage source and a reg represented by curve C2 in Fig. 4. ulating voltage source both connected to said If desired, the regulating eiîect of the gen main control means for controlling it in accord erator RG can be amplified by providing it with a self-excited shunt field winding. It is further 25 ance with a. resultant eiiect oi the component voltages of said latter two sources, each of said possible to omit a control generator of the type latter two sources having means for controlling represented by generator CG in Fig. 1 and to said component voltages respectively, operator arrange the appertaining control windings di controlled circuit means for providing an adjust rectly on the main generator, although it will be able pattern voltage and circuit means for pro understood that such a system is not as suitable viding va, control voltage variable substantially in for high power outputs as the one according to accordance with the speed of said motor, both the aboveV describedv embodiment of Fig. 1. said circuit means being connected with said These and other modifications and alterations will be obvious to those skilled in the art and are intended to be within the scope of the essential features of my invention as set forth in the claims control means of said control voltage source for varying said appertaining component voltage in accordance with the differential value of said pattern and control voltages, and means for caus ing said regulating voltage source to vary the I claim as my invention: rate of change of its appertaining voltage corn 1'. A variable voltage control system compris ponent when the load current of said. motor eX ing a main generator having an output circuit 40 ceeds a given maximum value. and a main iield winding for controlling the 4. A variable voltage control system compris voltage oi said circuit, a control generator and ing a main generator having an output circuit a regulating generator connected with said main and a main field winding for controlling the appended thereto. iield winding for exciting it in accordance with a resultant voltage depending upon the corn ponent voltages generated by said latter two gen erators respectively, each of said latter gener ators having field means for controlling said respective component voltages, operator-con ' trolled circuit means for providing an adjustable pattern voltage and circuit means for providing a control voltage variable in accordance with the voltage of said circuit, said different circuit means being connected with said field means of said control generator for exciting said control generator in accordance with the differential value of said pattern and control voltages, said regulating generator having a saturation char voltage of said circuit, a control generator and a regulating generator connected with said main field winding for exciting it in accordance with a resultant voltage depending. upon the com ponent voltages generated by said latter twov gen ' erators respectively, each of said latter gener ators having ñeld means for'controlling said re spective component voltages, operator-con trolled circuit means for providing an adjustable pattern voltage and circuit means for providing a control voltage variable in accordance with the voltage of said circuit, said different circuit means being connected with said field means of said control generator and regulatingv generator acteristic so as to vary the rate of change of said for exciting both in accordance with the difier iinite value, and means for exciting said ñeld means of said regulating generator in dependence upon the load. current in saidl circuit, whereby saidl load current is substantially limited to a 65 characteristic so as to vary the rate of change appertaining component voltage when the excita 60 ential value of said pattern and control volta-ges, said regulating generator having a saturationV tion oi its íield means passes through a given of said appertaining component when the current in said output circuit passes through a given finite value, whereby said current is substantially limited to a given maximum value. 5. A motor control system comprising a vari able speed direct current motor, a main generator having an armature circuit connected with said circuit and a main control means ior varying the voltage oi said circuit, a controlling voltage 70 motor for energizing the latter and a main field winding for contro-lling the Voltage of said cir sourcerand a regulating voltage source both con cuit, a control generator and a regulating gener nected to said main control means for control ator connected with said main ñeld winding forv ling it in accordance with a resultant effect of exciting it in accordance with a resultant voltage the component voltages of said latter two'sources, each of saidV latter two sources having means 75 depending upon the component voltages gener safe maximum value. 2. A variable voltage control system compris ing a main voltage generator having an output 2,411,377 ated by said latter two generators respectively, each of said latter generators having field means for controlling said respective component volt ages, operator-controlled circuit means for pro viding an adjustable pattern voltage and circuit means for providing a control voltage variable in accordance with the voltage of said circuit, said different circuit means being connected with said field means of said control generator and regulat ing generator for exciting both in accordance with the differential value of said pattern and control voltages, said regulating generator having a sat uration characteristic so as to vary the rate of change of said appertaining component voltage when the excitation of its ñeld means passes through a given finite value, and means for ex citing said ñeld means of said regulating gener ator in dependence upon the load current in said 10 value of said pattern and control voltages, said regulating generator having saturation charac teristic so that its component voltage is normally substantially zero, and means for exciting said field means of said regulating generator so as to cause said appertaining component voltage to as sume an effective value when the load current in said circuit exceeds a given limit magnitude. 7. A motor control system comprising a vari able speed direct current motor, a main gener ator having an armature circuit connected with said motor for energizing the latter and a main ñeld winding for controlling the voltage of said circuit, a control generator and a regulating gen erator having respective armatures series-con nected with said main field winding in opposition to each other for exciting said main iield winding in accordance with the resultant differential of circuit, whereby said load current is substantially the component voltages generated by said latter limited to a safe maximum value. 20 two generators respectively, each of said latter 6. A variable voltage control system compris generators having ñeld means for controlling said ing a main generator having an output circuit and respective component voltages, operator-con a main ñeld winding for controlling the voltage of trolled circuit means for providing an adjustable said circuit, a control generator and a regulating pattern voltage and circuit means for providing generator connected with said main field winding . a control voltage variable in accordance with the in opposition to each other for exciting it in ac voltage of said circuit, said different circuit means cordance with the resultant differential of the being connected with said ñeld means or” said con component voltages generated by said latter two trol generator and regulating generator for excit generators respectively, each of said latter gen ing both in accordance with the differential value erators having field means for controlling said respective component voltages, operator-con 30 of said pattern and control voltages, said regu lating generator having saturation character trolled circuit means for providing an adjustable istic so that its component voltage is normally pattern voltage and circuit«means for providing substantially zero, and means for exciting said a control Voltage variable in accordance with the Voltage of said circuit, said different circuit means 35 iield means of said regulating generator so as to cause said appertaining component voltage to being connected with said ñeld means of said assume an effective value when the load current control generator and regulating generator for in said circuit exceeds a given limit magnitude. exciting both in accordance with the differential ALBERT W. KIMBALL.