3,262,036
`C. D. CLARKE ETAL:
`July 19, 1966
`MBANS FOR SMOOTALY VARYING THE SPEED OF A STAR-CONNECTED
`POLYPHASE INDUCTION MOTOR
`
`Filed Sept. 19, 1962
`
`7 Sheets-Sheet 1
`
`cs3.cs5
`
`Wtélll + 2] 3+2 \3+4j5+4 \S+6]ll + 6lll+2/j3+2 |3+4][5+.4] 546]! 7 él +2{]3-2]
`FIGSC
`
`
`
`LIBERTY EXHIBIT 1029, Page 1
`
`LIBERTY EXHIBIT 1029, Page 1
`
`

`

`3,262,036
`C. D. CLARKE ETAL:
`July 19, 1966
`MEANS FOR SMOOTHLY VARYING THE SPEED: OF A STAR-CONNECTED
`FOLYPHASE INDUCTION MOTOR
`
`Filed Sept. 19, 1962
`
`7 Sheets-Sheet 2
`
`
`
`cs3 cs5
`
`LIBERTY EXHIBIT 1029, Page 2
`
`LIBERTY EXHIBIT 1029, Page 2
`
`

`

`July 19, 1966
`
`6. D. CLARKE ETAL
`
`3,262,036
`MBANS FOR SMOOTHLY. VARYING THE SPEED.OF A STAR-CONNECTED
`POLYPHASE INDUCTION MOTOR
`
`Filed Sept. 19, 1962
`
`7 Sheets-sheet 3
`
`
`
`A
`
`B4
`
`{0 +13 10413 H+12 +12 1043 lO+I3 H+ 12 ti +l2
`14417 15416 IS+1614H7 14417 15 + 1615416 14417
`ee te
`
`FIG8E.
`
`'
`
`Al A2
`-FIG8C.
`
`LIBERTY EXHIBIT 1 029, Page 3
`
`LIBERTY EXHIBIT 1029, Page 3
`
`

`

`3,262,036
`C. D. CLARKE ETAL
`‘July 19, 1966
`MEANS FOR SMOOTHLY VARYING THE SPEED OF A STAR-CONNECTED
`POLYPHASE INDUCTION MOTOR
`/
`
`Filed Sept. 19, 1962
`
`7 Sheets-Sheet 4
`
`LIBERTY EXHIBIT 1029, Page 4
`
`LIBERTY EXHIBIT 1029, Page 4
`
`

`

`3,262,036
`C. D. CLARKE ETAL
`July 19, 1966
`MEANS FOR SMOOTHLY VARYING THE SPEED OF A STAR-CONNECTED
`POLYPHASE INDUCTION MOTOR
`
`Filed Sept. 19, 1962
`
`7 Sheets-Sheet 5
`
`
`.eu
`‘aiLite
`
`
`
`L_+*
`eT
`
`P38 of
`
`FIG.
`
`LIBERTY EXHIBIT 1029, Page 5
`
`LIBERTY EXHIBIT 1029, Page 5
`
`

`

`3,262,036
`C. D. CLARKE ETAL
`July 19, 1966
`MBANS FOR SMOOTHLY VARYING THE SPEED OF A STAR-CONNECTED
`POLYPHASH INDUCTION MOTOR
`
`Filed Sept. 19, 1962
`
`7 Sheets-Sheet 6
`
`LIBERTY EXHIBIT 1029, Page 6
`
`LIBERTY EXHIBIT 1029, Page 6
`
`

`

`Filed Sept. 19, 1962
`
`~ 3,262,036
`C. D. CLARKE ETAL
`July 19, 1966
`1966 FOR SMOOTHLY VARYING THE SPEED OF A STAR-CONNECTED
`POLYPHASE INDUCTION MOTOR
`
`7 Sheets—Sheet 7
`
`LIBERTY EXHIBIT 1929, Page 7
`
`LIBERTY EXHIBIT 1029, Page 7
`
`

`

`United States PatentOffice
`
`3,262,036
`Patented July 19, 1966
`
`1
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`2
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`an adjacent one to cause a smooth change in the current
`3,262,036
`therein and to establish a smooth change in the angular
`MEANS FOR SMOOTHLY VARYING THE SPEED
`position of the magnetic field developed in the electric
`OF A STAR-CONNECTED POLYPHASE INDUC:
`motor.
`TION MOTOR
`It will be seen that as the angular position of the
`Christopher D. Clarke and David A. Jones, Lough-
`magnetic field is made to change gtadually a substantially
`borough, England, assignors to Brush Electrical Engi-
`neering Company Limited, Falcon Works, Lough-
`smoothly rotating field is produced which enables the
`borough, England
`motor to deliver substantially smooth torque at
`low,
`Filed Sept. 19, 1962, Ser. No. 224,768
`and very low speeds.
`Claims priority, application Great Britain, Sept. 21, 1961,
`in the case where a
`According to a further feature,
`33,779/61
`single inverter means has.
`two separate D.C. supplies,
`7 Claims.
`(CI. 318—-230)
`one of the D.C. supplies develops a positive voltage,
`The invention relates to controlling the speed of a
`and the other a negative voltage with respect
`to the
`star-connected polyphase. induction motor of which the
`common terminal; while according to an alternative fea-
`phases are star-connected or independent, and has ref-
`ture both D.C. supplies develop a positive voltage and
`erence to a variable frequency D.C.link inverter means
`have their negative poles connected to a common ter-
`minal.
`,
`for supplying such a motor (e.g., a squirrel-cage-type mo-
`tor). With a known form of variable frequency D.C.
`According to another aspect of the invention each
`inverter means for supplying such a motor the inverter
`motor phase has its own D.C. supply and an individual
`inverter means.
`has been fed from a single D.C. supply, but at very low
`motor speeds the motor rotor moves in discrete ‘steps
`Means for commutating the controlled switching el-
`ements of the inverter means can be connected in circuit
`thus rendering the arrangement unsuitable for use in
`applications where a smooth motor torque is required at
`between the inverter means and the D.C. supplies, or
`such low speeds (e.g.,
`in the case where the motor is
`between the inverter means and the motor phases.
`According to a further feature in the case where a
`for locomotive traction). The main object of the in-
`vention is
`to mitigate that disadvantage by providing
`single inverter means is associated with two D.C. sup-
`a variable frequency drive to a polyphase star-connected,
`plies the outer end of each motor phase is connected
`induction motor such that the speed of the electric motor
`to each D.C. supply throughasilicon controlled rectifier
`may be varied smoothly. at
`low speeds ranging from
`acting as controlled switching element, and the silicon
`zero, and that the electric motor develops substantially
`controlled rectifiers are actuated in pairs by respective
`smooth torque at all motor speeds down to zero, an
`gating circuits which are selected sequentially by a driven
`essential characteristic of
`the drive being that
`if
`the
`selector switch such that each motor phase in turn will be
`electric motor is a squirrel-cage induction motor, there
`connected to one of the D.C. supplies while the voltage
`are no electrical contacts in the power circuit of the
`of the latter is increasing, and the motor phase cyclically
`drive which rub, slide or move during operation of
`in advance will be connected to the other D.C. supply
`the drive, on-off contactors and overload contactors be-
`while the voltage of the latteris falling.
`,
`ing permitted in the powercircuit as no sliding, rubbing
`In such a case, and according to yet another feature,
`or moving of the electrical contacts occur in these units
`use is made of a bistable circuit actuated by an oscillator
`during normal operation.
`—
`for first commutating the silicon controlled rectifiers
`According to one aspect of the invention, two variable
`connected to one of the D.C, supplies, and. then those
`voltage D.C. supplies, which operate at
`identical vari-
`connected to the other D.C. supply, alternately, the oscil-
`able frequencies but are out of phase, are connected
`lator also actuating the rotary switch through .a delay
`through one or more inverter means to the motor wind-
`means whereby, immediately after commutation, to ener-
`ings, such that for a period in each half cycle an increas-
`gise a gating circuit to fire its associated pair of silicon
`ing current, derived from the one of the variable voltage
`controlled rectifiers for connecting the phases appropri-
`D.C. supplies whose voltage is increasing, is fed through
`ately to the D.C. supplies.
`an inverter means to one phase or section of the motor
`The invention will now be described further with ref-
`windings while in the same period a decreasing current,
`erence to the accompanying drawings, in which:
`derived from the other variable voltage D.C.
`supply
`FIGURE1 is a block diagram of the aforesaid known
`whose voltage is decreasing,
`is fed through the same
`form of variable frequency D.C. inverter means for driv-
`or different inverter means to another phase or section
`ing a 3-phase, squirrel-cage induction motor;
`of the motor windings displaced from the first, the alter-
`FIGURE 2 is a diagram of the output potentials of
`nate increasing and decreasing variation of voltage of
`the inverter means of FIGURE 1;
`the D.C. supplies being so synchronised to the switching
`FIGURE 3 is a diagram illustrating the torque de-
`action of the inverter means that the magnetic field in
`veloped by the motor when driven in the manner of
`the motor rotates continuously in a substantially smooth
`FIGURE 1 at low and very low speeds;
`manner to exert a substantially smooth torque on the
`FIGURE 4 is a block diagram illustrating one em-
`rotor at low and. very low speeds.
`bodiment of the present invention;
`According to a feature of this aspect of the invention,
`FIGURE 4A is. the same as FIGURE 4 but shows a
`the two D.C. supplies have a common terminal con-
`commutating arrangement in a different position;
`nected to the star-point of the motor phases and supply
`FIGURE 5 is a composite diagram concerning the
`a single inverter means, the D.C. supplies being arranged
`embodiment of FIGURE 4 and showing at FIGURES
`such that the voltage of one of them will be at its max-
`Sa and 56 the waveforms associated with the two D.C.
`imum value when that of the other is at a minimum,
`supplies; at FIGURE Sc the sequencing of the switching
`and vice versa, and the inverter means includes controlled
`elements of the inverter; and at FIGURES 5d, 5e and
`switching elements which are controlled in phased re-
`5f the voltages developed across the three phases of the
`lationship to the D.C. supplies and cause the motor
`motor;
`phases to be connected, sequentially, to the inverter volt-
`FIGURE6 is a block diagram illustrating another em-
`age input first from one of the two D.C. supplies, and
`bodiment of the invention;
`then the other, alternately, whereby an A.C. voltage is
`FIGURE7 is a block diagram illustrating yet another
`developed across each selected motor phase such that
`embodiment of the invention in which a 2-phase motor
`as the voltage increases in one motor phase it wanes in
`
`60
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`LIBERTY EXHIBIT 1929, Page 8
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`LIBERTY EXHIBIT 1029, Page 8
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`

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`3,262,086
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`2c
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`e)
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`60
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`70
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`LIBERTY EXHIBIT 1029, Page 9
`
`has each phase supplied from a separate D.C. supply and
`inverter combination;
`FIGURE 8 is a composite diagram showing at FIG-
`URES 8a and 8) the waveforms associated with the two
`D.C, supplies of FIGURE 7; at FIGURE 8cthe arrange-
`ment of the two windings of the motor; at FIGURE 8d
`the firing sequence for the controlled switching elements
`of the two inverters of FIGURE 7, and at FIGURE 8¢
`the manner in which the direction of the magnetic field
`of the motor varies due to the fluctuation of the D.C.
`supplies and the switching action of the inverters;
`FIGURE 9 is a circuit diagram corresponding with
`FIGURE4 illustrating the power circuit;
`FIGURE 10 shows how the commutation and the fre-
`quency. of the D.C. supplies shown in FIGURE 9 are
`controlled;
`FIGURE 11 shows how the inverter of FIGURE 9 is
`controlled;
`FIGURE 12 is a circuit diagram of one of the paired
`gating circuits of FIGURE 11;
`FIGURE13 is a circuit diagram of an electronic pulse
`generator shown in FIGURE11; and
`FIGURE 14 is a circuit diagram combining the circuits
`of FIGURES 10, 11 and 13.
`Referring firstly to FIGURE 1, the said known form
`of D.C. link inverter has, as shown, a single, steady D.C.
`supply, and the inverter, shown generally at 20, has a
`3-phase output. The inverter has controlled switching
`elements CSi to CS6 which are extinguished by a com-
`mutating arrangement 21, in either of the positions shown,
`so as to become conducting in the sequence 11-6, 14-2,
`34-2, 3+4, 5+4, 5+6, repeated,
`the frequency of op-
`eration of
`the commutating arrangements and the in-
`verter being controllable by means
`(not shown)
`for
`varying the speed of the motor. The outputs of the in-
`verter to motor phases A, B and C will follow the po-
`tentials shown in FIGURE 2, and the torque from the
`electric motor will be as shown in FIGURE3 for low in-
`verter frequencies, and thus, for the consequent low motor
`speeds.
`Reference to FIGURE 3 shows that at slow, or very
`slow speeds the output torque alternates between a maxi-
`mum and zero, thus causing the motor rotor to rotate in
`a series of jerky steps; but it will be realised that as the
`motor speed increases the time interval between the jerks
`becomes progressively reduced until such time as the
`motorwill, to all intents and purposes, run smoothly.
`This jerky operation at low speeds is a great disad-
`vantage in many motor applications, particularly in the
`cases where the motor is for propelling a locomotive.
`The invention overcomes this disadvantage of discon-
`tinuous torque at low speed, as will be appreciated by
`referring to FIGURE 4. The latter shows a positive D.C.
`supply DCi and a negative D.C. supply DC2 having. a
`common terminal T. These supplies are such as to de-
`velop rising and falling voltage waveforms at a common,
`controlled variable frequency as hereinafter more fully
`described. The voltage waveform of the positive supply
`DC1 is shown in FIGURE Sa and that of the negative
`supply BC2 in FIGURE 56, and these waveforms con-
`stitute the input to the inverter 20. The latter, as in the
`known case, includes controlled switching elements CSi
`to CS6 with a commutating arrangement 21 in one of the
`positions shown in FIGURE 4 or FIGURE 4A and con-
`stituting a 3-phase output bridge for feeding a 3-phase,
`star-connected, squirrel-cage induction motor of which
`the phases are indicated at A, B and C. The star-point
`of these phases is connected to the common terminal T
`of the two D.C. supplies.
`The controlled switching elements of the inverter CS1
`to CSG are made conducting in the sequence 14-6, 14-2,
`342, 34+4, 544, 5+6, repeated, being correlated in
`respect of frequency and time to the variation of the
`D.C. supplies such that CS1 and CS6 are made conduct-
`ing when the positive D.C. inverter supply DCI is zero
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`and the negative D.C. inverter supply DC2 is a maximum
`as shown in FIGURE 5c. Thereafter the controlled
`switching elements of the inverter are made conducting
`in the sequence detailed above, the action of switching
`to the next inverter pair of controlled switching elements
`coinciding with the next maximum occurring in the out-
`put of either the positive or negative D.C. supply to the
`inverter.
`In this way,
`the potentials at the outputs of
`the inverter and the voltage developed across the phases
`of the electric motor are as shown in FIGURES 5d, e
`and f.
`A comparison between the output voltages of the known
`arrangement as shown in FIGURE 2, with the output
`voltages shown in FIGURES 5d, ¢ and f discloses that
`the latter output voltages change far more smoothly.
`Thus,
`the application to the motor phases of the. wave-
`forms shown in FIGURES 54d, e and f will cause the
`magneticfield of the motor to rotate substantially smooth-
`ly and provide a substantially smooth output torque from
`the motor. The above description is for illustration only,
`and the application of the invention is described later.
`By using this system, and arranging a suitable number
`of controlled switching inverter elements each arranged
`to be made conducting at a suitable time, any number
`of A.C. outputs may be provided by the inverter in cor-
`rect phase relationship to provide a smoothly rotating
`magnetic field in an electric motor with a corresponding
`number of phases and will result in the development of
`a smooth torque by the motor.
`Further,
`it
`is not essential that the rise and fall of
`voltage of the positive and negative D.C. supplies should
`be linear or absolutely smooth. The rise in voltage may
`follow any law which is suitable for use with the system
`to provide at least a substantially smooth torque from
`the electric motor, and the actual rise and fall of the volt-
`age of the D.C. supplies may be in the form of a stair-
`case or any other form suitable for providing at least
`. a substantially smooth torque from the electric motor.
`In addition to the foregiing, it must be understood that
`40
`some methods of commutation may produce short dura-
`tion transient voltages on the waveforms developed at the
`output terminals of the inverter, and that any such transi-
`ents shall be acceptable, provided that the torque output
`from the electric motor is substantially smooth.
`The modification shown in FIGURE 6 differs from
`that in FIGURE4 in that the two D.C. supplies are posi-
`tive and have their common terminal T1 connected both
`to the star-point of the motor and to a commutating cir-
`cuit 21. The waveforms of the two D.C. sources are in-
`dicated respectively beneath them in the figure. The
`switching elements 1 to 6 are silicon controlled rectifiers,
`and the odd numbcred elements are commutated bya sili-
`con controlled rectifier 7, and the even numbered ones by
`a silicon controlled rectifier 8, and the said elements 1
`to 6 afte made conducting in the same sequence as in
`FIGURE4, and the arrangement operates in a manner
`similar to that described with reference to the latter
`figure.
`FIGURE7 shows an application of the invention in
`which each phase of a motor is supplied from a separate
`D.C. source and inverter combination. The figure shows
`the arrangement for a 2-phase motor, but this embodi-
`ment of the invention is of equal application when the
`motor has more than two phases, the provisions made
`for each phase being precisely the same.
`In the figure the two motor phases are shown at A
`and B, and their respective, variable D.C. supplies at
`DC1 and DC2, The inverter 20a for phase A includes
`controlled switching elements CR1@ to CR1i3, and the
`inverter 205 for phase B includes. controlled switching
`elements CRI4 to CRI7. Between each D.C. supply
`and its associated inverter is a commutating arrangement
`21 for the controlled switching elements.
`It will be seen from FIGURE8c that the ends marked
`
`55
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`LIBERTY EXHIBIT 1029, Page 9
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`3,262,036
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`39 to point 38 whereby point 38 is made more positive
`A2 and B4 of phases A and-B respectively. may be con-
`than point 37 by an amount equal to twice the voltage
`nected together.
`of source 39,.This commutatesrectifier 6.
`Referring now to FIGURES 8a, 8b, 8d and 8¢,
`it
`will be seen from FIGURES 8a and 8b that while the
`Capacitor 40 recharges negative while current flows
`through choke 41, source 39 andsilicon controlled recti-
`voliage of D.C. supply DC1 rises from zero to maximum
`fier C1, until the capacitor 40 reaches a potential equal
`positive, the voltage of D.C. supply DC2 falls from maxi-
`to the negative voltage of DC2 plus the negative voltage
`mum positive to zero, and vice versa. By firing the con-
`of source 39. At this point the silicon controlled recti-
`trolled switching elements in the order shown in FIG-
`fier C1 extinguishes itself and the current that_is flow-
`URE8d the direction of the magnetic field of the motor
`ing through choke 41 is now carried by diode 42.
`is changed as indicated in FIGURE 8¢. Thus, and taking
`In a somewhat similar manner, when one of the odd
`the first firing combinations at
`the left of FIGURE 8d,
`rectifiers is to be commutated, silicon controlled recti-
`an increasing voltage will be applied at end Al of phase
`A relative to end A2 at the same time as the voltage ap-
`fier C2 in series with a D.C, source 43 acts to convey the
`negative charge on capacitor 40 to line 44, common to
`plied at end B3 of phase B is decreasing relative to end
`the odd rectifiers, so as to make it more negative than
`B4, during the next firing combination the voltage ap-
`their respective motor phases.
`:
`plied at end Al of phase A will decrease relative to end
`Capacitor 40 recharges positive while current flows
`A2 while the voltage applied to end B4 of phase B in-
`through choke 45, source 43 and silicon controlled recti-
`creases relative to end B3, and during the third firing
`combination the voltage applied to end B4 of phase B
`fier C2 until the capacitor 40 reaches a potential equal to
`decreases relative to end B3 while. the voltage applied to
`the positive voltage of DCI plus the positive voltage
`end AZ of phase A increases relative to.end Al.
`of source. 43. At this point the silicon controlled recti-
`The benefits of performance due to the action above
`fier C2 extinguishes itself and the current flowing through
`choke 45 is now carried by diode 46.
`described, as opposed to the performance of the said
`known D.C.
`link inverter, reduce as the speed of the
`When any of silicon controlled rectifiers 1 to @ are
`drive is increased. There is a point, when increasing the
`commutated it is important to dispose of reactive cur-
`tent of the motor phase concerned, and this is done
`drive speed from zero, where the torque from the known
`D.C. link inverter is sufficiently smooth, due to the fly-
`through respective diodes 47.
`wheel effect of the motor and load, and to the inductive
`FIGURE 10 repeats the showing of FIGURE 9 and
`effects of the motor windings, to be as suitable as the
`shows, in addition, how the commutation of the silicon
`torque at the same speed. from the D.C. link inverter of
`controlled rectifiers 1 to 6, and the frequency of the varia-
`the invention. At drive speeds above this point -more
`ble-voltage D.C. supplies DC1 and DC2 are controlled.
`power can be developed from the electric motor if it is
`In this figure is shown an oscillator 50, of which the
`fed from the known D.C. link inverter than if it is fed
`frequency can be controlled, which is connected to the
`from the D.C.
`link inverter of the invention.
`It. may
`devices 30 and 31 so as to operate them at its own fre-
`therefore be desirable in some instances to switch from
`quency, and, at the said frequency, to a bistable circuit
`the new system to the old at this point.
`51 for firing the commutatingsilicon controlled rectifiers
`C1 and C2 in turn.
`FIGURE 9 shows the power circuit involved in FIG-
`URE 4 in greater detail. The controlled switching ele-
`FIGURE11 also repeats the showing of FIGURE 9,
`ments CS1 to CS6 are, however, in this case shown as
`but additionally shows the oscillator 50 of FIGURE 10
`silicon controlled rectifiers 1 to 6. The positive and
`performing another function of synchronising the action
`of the inverter.
`negative D.C. supplies DC4 and DC2 are respectively
`derived from the outputs of devices 30 and 31 which are
`The said oscillator drives a rotary switch 60, through a
`respectively fed from steady D.C. sources indicated at
`delay device 61 of any suitable known kind, in synchro-
`32 and 33. The devices 30 and 31, which can be of any
`nism with its own frequency. The rotary switch feeds a
`signal pulse, having a square waveform, from a device 62,
`known kind, are for providing the fluctuating voltages re-
`quired for DCI and DC2, and the fluctuation is controlled
`more.fully described with reference to FIGURE13, selec-
`as presently described with reference to FIGURE 10.
`tively to gating circuits for cach associated pair of odd
`and even silicon controlled rectifiers 1 to 6. The gating
`The DC1 and DC2 supplies are connected to the common
`circuits for the rectifiers are shown in block form and are
`terminal T through capacitors 34 and 35 to provide a
`reference point of zero potential connected to the star-
`identified in the figure by the reference numerals of the
`point of the motor phases through line 36.
`rectifiers they respectively fire (ie., 1+6, 142, 3+2,
`The silicon controlled rectifiers are fired in the appro-
`3-44, 544, 5+6).
`The outputs from these gating circuits, which latter are
`priate order by gating circuits, as wiil presently be de-
`scribed with reference to FIGURE 11, and before each
`more fully described with reference to FIGURE 12, are
`new pair of them are fired a commutating pulse is fed
`applied across their associated pairs of rectifiers,
`in the
`either to the even, or odd numbered ones whereby to
`order dictated by rotary switch 60, to fire them for feed-
`extinguish the silicon controlled rectifier, of the pre-
`ing the associated motor phases with the outputs from
`viously fired pair, which is not required.
`DC1 and DC2,as appropriate.
`For convenience of the subsequent description rectifiers
`It will be observed that each adjacent pair of gating cir-
`cuits controls one of the silicon controlled rectifiers in
`1, 3 and 5 will be referred to collectively as the odd recti-
`fiers, and 2, 4 and 6 as the evenrectifiers.
`common. Thus, rectifier 1 is common to gating circuits
`Having regard to the order in which the rectifiers are
`1+6 and 1+2, and rectifier 2 is commonto gating circuits
`fired (i.e., 1+6, 142, 3+-2, 3-+4, 5-++4, 54-6) it will be
`1+2 and 3-+2, and so on. For this purpose gating circuit
`assumed that the pair 14-6 has already been fired and that
`1-+2 is shown as having a connection to the outputcircuit
`it is now desired to fire 1+2. Before this can be done
`from gating circuit 146 for supplying rectifier 1, but in
`it is necessary to extinguish 6. The latter is among the
`order to avoid-a feed back into gating circuit 1+6 when
`even rectifiers, of which 2 and 4 were previously extin-
`gating circuit 1+2 isoperating, the path to rectifier 1 from
`guished, For extinguishing rectifier 6 it is necessary to
`gating circuit 1-16 is through a diode 63. Another diode
`make phase-connection point 37 negative with respect to
`64 performs the same function when gating circuit 146
`point 38, and this is done by firing a silicon controlled
`is operating and gating circuit 14+2 is not. The corre-
`rectifier C1 which is in series with a D.C. source 39
`sponding diodes for gating circuits 1+6 and 5-++6 are
`whereby to convey the charge of capacitor 40 which is
`shown at 65 and 66.
`It will be seen that a similar pro-
`at a voltage equal to the positive voltage DC2 plus the
`vision is made as between gating circuit 1+2 and 3+-2,
`positive voltage of source 39. The.capacitor 40 applies
`and between gating circuits 1+6 and 5+6, but for the
`this. positive voltage plus the positive voltage of source
`
`50
`
`55
`
`60
`
`65
`
`70
`
`LIBERTY EXHIBIT 1029, Page 10
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`LIBERTY EXHIBIT 1029, Page 10
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`

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`3,262,036
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`oO
`a
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`7
`purpose of simplified reading the equivalent provisions
`for the other gating circuits are not shown.
`/
`Each of these gating circuits includes a transformer
`of which the primary winding is fed with the square
`wave form output from device 62, and which has two
`secondary windings whose outputs are applied to the
`respective rectifiers for firing them. Such a gating cir-
`cuit for firing the pair of rectifiers 1 and 6 is shown in
`FIGURE12.
`In FIGURE 12 the square waveform output from de-
`vice 62 is indicated at 70 and is applied. to the primary
`winding 71 of a transformer of which the magnetic core
`is shown at 72.
`‘The core has secondary windings 73 and
`74 aboutit, and these are respectively connected for firing
`rectifiers 1 and 6.
`The secondary winding 73 has a central connection to
`point 75 and its ends are connected to the grid 76 of
`rectifier 1 through diodes 77 and 78 which make the grid
`positive with reference to point 75 whereby to fire the
`rectifier. The secondary winding 74 and its diodes 79
`and 80 fire rectifier 6 in precisely the same manner.
`The device 62 is shown in FIGURE 13 as a typical,
`known circuit employing transistors 81 and 82, and di-
`odes 83 and 84 whereby to induce a square waveform
`pulse in a secondary winding 85 to be fed to the rotary
`switch 6@,
`the associated components shown being a
`steady D.C. source 86 connected to a central tapping of
`a primary winding 87, a capacitor 88, a feed-back wind-
`ing 89 and a resistor 90. The square waveform pulse is
`fed to the movable contact of the rotary switch 60 for
`selective feeding to the gating circuits.
`For ease of comprehension the various circuits have
`been described separately with reference to FIGURES
`9 to 13, but are shown co-ordinated in FIGURE 14, in
`which latter the power circuit has been drawn in heavy
`lines, and the various control circuits have been drawn
`in lighter lines. Thus, FIGURE 14 showsthe oscillator
`50 controlling the frequency of the voltage fluctuations
`of the supplies DC1 and DC2, the firing of the rectifiers
`and their commutation. Delay 61 ensures that com-
`mutation takes place before the rotary switch 69 selects
`a new pair of rectifiers to be fired.
`It will therefore be
`seen that by increasing the frequency of the oscillator
`from zero the motor can be accelerated smoothly from
`rest.
`What we claim as our invention and desire to secure
`by Letters Patent of the United States is:
`1. A variable frequency D.C. link inverter means for
`supplying a star-connected polyphase induction motor
`such that its speed can be varied smoothly from zero to
`very high speeds and such that it develops substantially
`smooth torque at all speeds within its range, comprising
`an inverter having a number of output phases equal to
`the number of phases of the motor, said inverter includ-
`ing controlled switching elements for sequentially con-
`necting its said output phases to said motor phases re-
`spectively, a commutating circuit for artificially commutat-
`ing said switching elements, a firing circuit for firing said
`switching elements for sequentially connecting said out-
`put phases of said inverter to said motor phases respec-
`tively, a D.C. voltage supply for said inverter, a connec-
`tion from said D.C. voltage supply to the star point of
`said motor, a circuit for repeatedly varying the voltage
`of said D.C. supply in synchronism with the operation
`of the switching elements of the inverter, and a circuit
`for varying the frequency at which the voltage variations
`occur.
`2. A variable frequency D.C. link inverter means for
`supplying a star-connected polyphase induction motor
`such that its speed can be varied smoothly from zero to
`very high speeds and such that it develops substantially
`smooth torque at all speeds within its range, comprising
`an inverter having a number of output phases equal to
`the number of phases of the motor, said inverter includ-
`ing controlled switching elements for sequentially con-
`
`necting its output phases to said motor phases respec-
`tively, a commutating circuit for artificially commutat-
`ing said switching elements, a firing circuit for firing said
`switching elements for sequentially connecting said out-
`put phases of said inverter to said motor phases respec-
`tively, two D.C. voltage supplies for said inverter, a com-
`mon terminal to which said D.C. voltage supplies are
`connected together, one of said D.C. voltage supplies hav-
`ing a positive voltage with respect to said common termi-
`nal and the other of said D.C, voltage supplies having a
`negative voltage with respect to said common terminal,
`a connection between said common terminal and the star
`point of said motor, a circuit for smoothly and repeatedly
`varying the voltages of said supplies from zero to maxi-
`mum inversely and in synchronism, a circuit for varying
`the frequency at which the voltage variations occur, and
`means for operating said commutating means and said
`firing means in timed relation to the voltage variations
`of said sources, and at the same frequency.
`3. A variable frequency D.C. link inverter means for
`supplying a star-connected polyphase induction motor
`such that its speed can be varied smoothly from zero to
`very high speeds and such that it develops substantially
`smooth torque at all speeds within its range, comprising
`‘an inverter having a number of output phases equal to
`the number of phases of the motor, said inverter includ-
`ing switching elements for sequentially connecting its said
`output phases to said motor phases respectively,
`two
`D.C. voltage supplies for said inverter, a common termi-
`nal
`to which said D.C. voltage supplies are connected
`together, one of said D.C. voltage supplies having a posi-
`tive voltage with respect to said common terminal and
`the other of said D.C. voltage supplies having a negative
`voltage with respect to said common terminal, a con-
`nection between said common terminal and the star point
`of said motor, a circuit for smoothly and repeatedly vary-
`ing the voltages of said supplies from zero to maximum
`inversely and in synchronism, a circuit for varying the
`frequency at which the voltage variations occur, said
`switching elements adapted sequentially to connect one
`motor phase during a period in each half cycle to be sup-
`plied from said inverter with an increasing current de-
`rived from the one of said variable voltage D.C. supplies
`whose voltage is increasing, and in the same period to
`connect another motor phase to be supplied from said
`inverter with a decreasing current derived from the other
`of said variable voltage D.C. supplies whose voltage is
`decreasing, and means for synchronizing the variation in
`voltage of said D.C. supplies with the switching action
`of said inverter.
`4, A variable frequency D.C. link inverter means for
`supplying a star-connected polyphase induction motor
`such that its speed can be varied smoothly from zero to
`very high speeds and such that it develops. substantially
`smooth torque at all speeds within its range, comprising
`an inverter having a number of output phases equal to
`the number of phases of the motor,
`two D.C. voltage
`supplies for said inverter, a common terminal
`to which
`said D.C. voltage supplies are connected together, one
`of said D.C. voltage supplies having a positive voltage
`with respect to said common terminal and the other of
`said D.C. voltage supplies having a negative voltage with
`respect to said common terminal, a connection between
`said common terminal and the star point of said motor,
`a circuit for smoothly and repeatedly varying the voltages
`of said D.C. supplies from zero to maxi