US3436631A

US3436631A - System for forming pilot voltages for controlling electronic commutation channels for induction motors

Info

Publication number: US3436631A
Application number: US518440A
Authority: US
Inventors: Robert Favre
Original assignee: GOLAY BUCHLE AND CIE SA
Current assignee: GOLAY BUCHLE AND CIE SA
Priority date: 1965-01-06
Filing date: 1966-01-03
Publication date: 1969-04-01
Anticipated expiration: 1986-04-01
Also published as: NL6600163A; DE1513174B2; DE1513174A1; GB1127263A; FR1469044A

Description

Filed Jan. 5, 1966 April 1', 1969 R. FAVRE 3,436,631

SYSTEM FOR FORMING PILOT VOLTAGES FOR CONTROLLING ELECTRONIC COMMUTATION CHANNELS FOR INDUCTION MOTORS Sheet L of a April 1, 1969 FAVRE 3,436,631

SYSTEM FOR FORMI PILOT v TAGES FOR CONTROLLING ELECTRONIC COMMU CHA LS FOR IND ION UGTION MOTO Filed Jan. 5. 1966 Sb 2 of 8 FIG.2 FlG.2b

FlG.2c

FlG.2d

April 1, 1969 R. FAVRE 3,436,631

SYSTEM FOR FORMING PILOT VOLTAGES FOR CONTROLLING ELECTRONIC Y COMMU'IATION CHANNELS FOR INDUCTION MOTORS Filed Jan. 5. 1966 Sheet 3 of 8 V3 I v2 Vp j H P1 &]

April 1, 1969 R. FAVRE 3, 3

SYSTEM FOR FORMING PILOT VOLTAGES FOR CONTROLLING ELECTRONIC COMMUTATION CHANNELS FOR INDUCTION MOTORS Filed Jan. 5. 1966 Sheet of 8 April 1, 1969 V E 3,436,631

SYSTEM FOR FORMING PILOT VOLTAGES FOR CONTROLLING ELECTRONIC COMMUTATION CHANNELS FOR INDUCTION MOTORS Filed Jan. :5. 1966 Sheet 5 of a Aprll 1, 1969 R. FAVRE 3,436,631

SYSTEM FOR FORMING PILOT VOLTAGES FOR CONTROLLING ELECTRONIC COMMUTATION CHANNELS FOR INDUCTION MOTORS Filed Jan. 5. 1966 Sheet 6 of 8 a3 84 as 86 a7 89 L 3,436,631 ECTRONIC R. FAVRE April 1, 1969 SYSTEM FOR FORMING PILOT VOLTAGES FOR CONTROLLING EL COMMUTATION CHANNELS FOR INDUCTION MOTORS Sheet Filed Jan. 5. 1966 Aprll l, 1969 R. FAVRE 3,436,631

SYSTEM FOR FORMING PILOT VOLTAGES FOR CONTROLLING ELECTRONIC COMMUTATION CHANNELS FOR INDUCTION MOTORS Filed Jan. 3, 1966 Sheet 6 of s United States Patent US. Cl. 318138 12 Claims ABSTRACT OF THE DISCLOSURE This disclsoure relates to an apparatus for supplying polyphase current to the windings of a polyphase electric induction motor, including means for generating a plurality of step-wise pilot voltage pulses, these means including electronic switching means having a plurality of output states, each output state corresponding to a particular step of the step-wise pilot voltage pulses, the switching means being operable cyclically among its plurality of output states to generate periodically the step-wise voltage pulses, at least one channel of electronic commutation for each phase adapted to be connected to its corresponding phase of the windings and means for distributing the step-wise voltage pulses among the channels of commutation, each channel being uni-directional, and being controlled by the pilot voltage pulses to generate a driving current for its corresponding phase of the windings, the driving current corresponding in shape to the shape of the pilot voltage pulses, whereby the parameters of frequency and amplitude of the pilot voltage pulses can regulate the speed of the motor, at least one of these two parameters being variable.

Already known are various systems for feeding an induction motor with an alternating current or voltage of variable frequency, in particular by electronic means.

One of the most advantageous systems is described in British Patent No. 1,058,284 consists in an electronic commutation which periodically cuts off the voltage supplied to the motor winding, this periodical cut off being independent of the phase angle of the motor. Such a system permits the motor current to be applied in its most adapted form, in particular, in a form almost sinusoidal. For this purpose two commutation channels are provided per phase, that is to say, one channel per type of reversal, the electronic commutation being very generally uni-directional.

In accordance with the principle of this technique, each electronic commutation channel is provided with a cutoff circuit adapted to block commutation as soon as the intensity of the motor current exceeds the limit given thereto at the moment considered. The self induction voltage of the motor winding is then limited in such a way that the self induction current prolongs the motor current while decreasing exponentially. When the value of this self induction current falls below a certain level, commutation is once again established until the current reaches the new limit assigned thereto, which brings about blocking of commutation and so on.

The instantaneous limit of the motor current being dictated by the instantaneous amplitude of a pilot voltage, the motor current actually assumes the approximate form of the pilot voltage.

With two electronic commutation channels per phase, this type of motor is very well adapted to a two phase system which gives it practically all the advantages of polyphase induction motors while limiting the number of commutation channels to four.

ICC

While the starting torque of a polyphase induction motor fed by a network is relatively high despite an appreciable slip frequency thanks to a considerable excess current, it is not possible to ensure such a power reserve in the supply circuit by electronic commutation. The process for forming pilot voltages must preferably be such that the slip frequency never exceeds the value corresponding to the maximum torque for a given current, that is from 3 to -6 c.p.s. Other obvious conditions permit to summarise briefly the essential characteristics of an ideal process for forming pilot voltages:

(a) Allow a dependency of the pilot frequency on the speed of rotation of the motor in such a way that the slip frequency does not exceed the value corresponding to a maximum torque for a given current.

(b) Permit a system of polyphase voltages to be produced, especially bi-phase, and preferably almost sinusoidal.

(c) Allow a rapid change of frequency while avoiding that the transient state substantially affects the shape, the amplitude or the phase of the pilot voltages.

(d) Permit the control of the speed preferably by manual and automatic means.

The present invention provides apparatus for supplying polyphase current to the windings of a polyphase electric induction motor, the apparatus comprising generating means for generating a plurality of step-wise pilot voltage pulses, said generating means including eletcronic switching means having a plurality of output states, each output state corresponding to a particular step of the stepwise pilot voltage pulses, the switching means being operable cyclically among its plurality of output states to generate periodically the step-wise voltage pulses, at least one channel of electronic commutation for each phase and adapted to be connecetd to its corresponding phase of the winding, and means for distributing said step-wise voltage pulses among the channels of commutation, each channel being uni-directional, and being controlled by said pilot voltage pulses to generate a driving current for its corresponding phase of the winding, the driving current corresponding in shape to the shape of the pilot voltage pulses, whereby the parameters of frequency and amplitude of the pilot voltage pulses regulate the speed of the motor, at least one of these two parameters being variable.

Preferably the pilot voltages are applied to the unblocking of the driving current of an induction motor fed by a source of continuous voltage, the winding of each phase of said motor being subjected to the alternate commutation of two uni-directional electronic channels of commutation in such a way as to produce in said phase coils, an alternating driving current preferably almost sinusoidal, the command voltages of each commutation channel of a motor differing only by their respective phase, the pilot voltages corresponding to the two channels of commutation of a given phase being out of phase by In one embodiment of the invention, the pilot voltages are formed by the digitial juxtaposition of periodic constituent voltages in the form of successive steps, the length of each step being only influenced by the frequency in such a way as to eliminate the transient state during a rapid change of frequency, the process being characterised, additionally, by means permitting this digital juxtaposition of the constituent voltages, by means for making the frequency of these power voltages dependent upon the speed of rotation of said motor, by means permitting limiting the slip frequency to a value not exceeding that corresponding to the maximum torque, and by means stabilising the speed assigned to said motor.

This installation permits essentially the generation of a system of two-phase functions obtained by the juxtaposition of half reversals two by two.

The invention can also generate a system of functions not only bi-phase but also polyphase in any manner.

In a preferred embodiment of the invention the electronic switching means forming part of the means for generating the stepwise pilot voltage pulses comprises a plurality of electronic switching elements, each element having a conductive and a non-conductive state and being adapted to switch back and forth between these two states, the switching means having a plurality of output states, each output state corresponding to a particular combination of the states of the switching elements.

Two embodiments of an installation according to the invention are described below by way of non-limiting example with respect to the annexed drawings in which:

FIGURE 1 shows a circuit adapted to generate pilot voltages on the digital basis of the juxtaposition of constituent voltages, in order to apply the process to the control of a two-phase motor;

FIGURES 2a to 2d are two forms of pilot voltage at two stages of development;

FIGURE 3 shows a distribution circuit for bi-phase pilot voltages generated by the circuit of FIGURE 1 between the four channels of commutations;

FIGURE 4 shows schematically a circuit for providing impulses and controlling the speed;

FIGURE 5 shows an overall blocking diagram;

FIGURE 6 shows one type of digital constituent circuit and of a multi-stable circuit associated therewith, a set up as an impulse counter in such a way as to generate the tri-phase pilot functions R, S and T;

FIGURE 7 gives, by way of non-limiting example, a circuit for regulating the parameters of frequency and amplitude of the pilot functions so as to stabilise the speed of an induction motor;

FIGURE 8 is an example of pilot functions formed of a series of positive semi-sinusoidal reversals obtained with the circuit of FIGURE 6;

FIGURE 9 relates to a multi-vibrator circuit generating a slip frequency.

As shown on FIGURE 1 the basic circuit for the invention comprises a multi-stable circuit set up as an impulse counter. This multi-stable circuit comprises three conventional bi-stable stages B3, B4 and B5 coupled in series. Each stage consists of two transistors, one conductive while the other is non-conductive or vice versa, a change of state resulting from the application of a positive implse on

paths

7, 8 and 9. The results of this is that stage B4 changes once for two of stage B3 and stage B5 once for two changes by stage B4, which makes a total of 8 distinct stable positions for the multi-stable circuit composed of three stages.

The initial state of these multi-stable circuits is characterised by the fact that each stage will change over only at the second impulse received by the stage which precedes it (in a particular case when the even transistors are conductive).

It is understood that V1 is a positive voltage while V2 is negative. Let us consider then the contribution of resistances of

uni-directional conductivity

11, 13 and on the voltage at the terminals of the charge resistance 17, it being known that resistance 13 has ohmic value twice that of resistance 15 and resistance 11 has a value twice that of resistance 13.

At the start, all the odd transistors are non-conductive, there is then no voltage across the terminals of 17.

At the first entrance impulse, stage B3 alone switches and current flows through resistances 11 and 117.

At the second entrance impulse, B3 returns to its initial position and it is B4 which switches thence the current flow through 13 with a resistance half as large as after the first impulse.

At the third impulse, current flows through 11 and 13 in parallel (resistance three times smaller).

At the fourth impulse, current flows through 15 alone (resistance four times smaller).

At the fifth impulse, current flows through 15 in parallel with 11 (resistance five times smaller); etc.

At the sixth impulse, the resistance is six times smaller. It is seven times smaller at the seventh impulse and once again infinite at 8 (return to initial state).

FIGURE 2 gives the voltage across terminals 17. The compression toward the top depends evidently upon the relationship between resistance 17 and resistance 11 which is easily adjustable, for example, with a -view to making the voltage of FIGURE 2a resemble as 'much as possible a sinusoidal half reversal. The approximation will be all the better as the half reversal has more steps but generally 8 steps are more than enough.

It is evident that

resistances

12, 14 and 16 having a value respectively equal to their homologues generated on resistance 18 a reciprocal voltage give nby FIGURE 2b, the process taking place in reverse.

In order to obtain a series of complete reversals, it is a question of alternately juxtaposing a stepwise half reversal of the voltage across the resistance 17 with the stepwise half reversal of the voltage across the resistance 18.

Two transistor couples 19 and 20 on one side and 21 and 22 on the other side, have a common collector resistance 23 on one side and 24 on the other while the bases of the transistors of one couple are respectively connected with

resistances

17 and 18. A supplementary binary stage B7, coupled in series, after stage B5, changes over upon each return of the multi-stable circuit to its initial state and alternately blocks one and the other transistor of each couple by strongly biasing its emitter resistance in such a way that the resistance 23 alternately reproduces the voltage across the terminals 17 and 18 (FIGURE 20) while resistance 24 reproduces the voltages according to FIGURE 2d, out of phase by a half reversal with respect to the first. Circuit B6 thus permits the reconstitution of complete reversals of negative polarity.

FIGURE 3 gives, in B10 and B11, a simplified circuit diagram of two channels of electronic commutation for a same phase, the winding of the phase of the motor being here divided into two parts M1 and M2, working in push pull.

At rest, transistor T1 is blocked and with it all the chain of channel B10 with transistors T2, T3 and T4.

If the base voltage of transistor T1 becomes negative, the entire chain unblocks and a commutation current is applied to winding M1. The unblocking of T1 takes place by means of transistor P1 the base of which is subjected to pilot voltage Vpl.

Commutation of transistor T4 initiates a voltage in winding M1. Because of the self induction of this latter, this current increases progressively more or less rapidly and with it the voltage in a very small resistance R5. When, as a result, the emitter of transistor T1 reaches the potential of its base (instantaneous value of the pilot voltage) the commutation will be interrupted for a very short instant here determined by the reaction condenser C6. A limiting device for the self induction voltage generated on winding M1 (not shown) allows the self induction current, which prolongs the motor current, to decrease progressively. The commutation is soon reestablished and the current increases anew until the voltage on R5 equals the new instantaneous value of the pilot voltage. Commutation is then interrupted anew and so on.

The motor current comprises also the self induction current during interruptions and oscillates about the instantaneous value assigned by the pilot voltage of which it reproduces the general shape.

Voltage Vpl, taken from the circuit of FIGURE 3 for example, naturally must be distributed alternately on channel B10 and B11, at the rate of one reversal per channel. This reverse commutation is ensured by a new supplementary binary stage coupled in series after stage B7 of FIGURE 1 and, by means of diodes 29 and 30, paralyses alternately at the rhythm of the reversals, one and the other channel by a strongly positive bias applied on transistor T1 or its homologue of channel B11.

Binary stage B9 operates alternately with B8 for the control of another phase. While B8 is driven by the collector of one of the transistors of stage B7 (FIGURE 1), B9 will be driven by the collector circuit of the other transistor of this stage B7. The choice of driving transistor must be made while bearing in mind that the reversal distributed by stages B8 and B9 must not be cut in two which implies a suitable phase relation between reversals considered and their alternate commutation.

An auxiliary circuit formed of resistances 25 and 27, diode 26 and condenser 28 imposes a phase rotation in a predetermined direction to the exclusion of the reverse direction which would bring about a reversal in the direction of rotation of the motor.

Returning to FIGURE 1 we must find which are the impulse sources applied at 7.

A half reversal or a quarter of a period implies 8 entrance impulses. A complete period thus requires 32 entrance impulses.

A first impulse generator, driven synchronously with the motor produces 32 impulses for each turn of the motor. For this effect may be provided a pair of emitterreceiver members the coupling of which is periodically intercepted by the teeth of a peripherally channelled disc. For example, a source of light and a photosensitive pickup, or better still, an emitter coil traversed by a high frequency current and a pickup coil attuned to the frequency of the first and energising the base of a transistor when coupling is possible between the coils, this coupling being periodically intercepted by the teeth of a conductive disc unitary with the rotor of the motor. Other couplings of an inductive, capacitive, magnetic, radioactive, etc. nature can be used to finally produce 32 impulses per motor turn.

synchronisation between the speed of the motor and the frequency of the supply current is thus ensured but does not allow the production of any slip frequency. However, since this is desirable for motors of this general type, the following means are provided.

A second impulse generator or slip generator is provided to this effect. This generator, for example of the multivibrator type delivers a maximum impulse frequency corresponding to the optimum slip frequency (3 to 6 c.p.s.) that is to say, bearing in mind the factor 32 for forming pilot voltages, a frequency of 100 to 200 c.p.s. These slip impulses are added to the synchronisation impulses at the entrance 7 of the multistable circuit of FIGURE 1.

The frequency of the motor current is then greater than the synchronisation frequency by a fixed optimum value representing the slip frequency whereby the motor assumes a vmaximum acceleration to reach its assigned speed.

The stabilisation of the assigned speed can then be considered by means of three associated or independent operations:

(a) By lowering the slip frequency.

(b) By eliminating at least a part of the synchronisation impulses.

(0) By reducing the amplitude of the pilot voltages and hence motor current.

In every case the speed of rotation can be measured by the frequency of the synchronisation impulses of the first impulse generator driven by the motor.

FIGURE 4 gives an example of a circuit for treating these impulses so as to control speed.

51 represents a pickup placed on the motor so as to deliever 32 impulses per turn or possibly 16 signals large enough so that the beginning and the end can be formed in impulses. 52 and 53 are two transistors of a conventional Sch-mitt trigger circuit for putting into operation signals delivered by 51. The collector of transistor 53 forms the first exit delivering 16 impulses per motor turn.

Transistors

56 and 57 constitute a second Schmitt trigger operating as a re-energisable monostable multivibrator during its metastable period. For this purpose, transistor 54 discharges complete a delaying capacitance 58 each time it is rendered conductive by a negative impulse on its base, that is to say at each unblocking of the first Schmitt trigger. The capacitance 58 recharges then more or less rapidly through variable resistance 59 until, by the intermediary of the amplifying current transistor 55, the monostable multivibrator switches. The impulse following the discharge of condenser 58 brings the monostable multivibrator back to its initial state by giving a positive exit impulse on the collector of transistor 57 which also will produce 16 impulses per turn, forming an equidistant sequence with the 16 impulses per turn coming from transistor 53 for as long as the required speed has not been reached. When the assigned speed has been reached, resistance 59 no longer allows time for condenser 58 to recharge so as to cause the monostable trigger to change over. Transistor 57 then no longer delivers impulses and the frequency falls by substantially one half.

If the speed is reduced then the interval between the impulses increases, resistance 59 once again has time to charge condenser 58 so as to cause the change-over of the monostable multivibrator and impulses reappear on transistor 57.

In reality, the control is not so abrupt, the mechanical flaws of the channels on the periphery of the disc driven by the motor having for example as a result a certain cyclic dispersion of the intervals between impulses; these are actually eliminated one after the other from the outlet of transistor 57, which smooths the control.

It should be noted that in particular cases it may be desired that the slip frequency increases slightly with speed. In this case, the first impulse generator instead of delivering impulses in a number suitable for synchronising the supply current with the speed, will deliver only one or two per turn and which will no way interfere with the efiiciency of the speed control by the above process, while producing a component of the sliding frequency as a function of the speed.

The lower part of FIGURE 4, with

transistors

60, 61 and 62, refers to another way of controlling speed by acting on the intensity of the motor current by means of the amplitude of the pilot voltages. In the present embodiment, this amplitude control is used in addition to the frequency control provided by the circuit shown in the upper part of FIGURE 4.

The circuit shown by way of non-limiting example functions in the following manner: Transistor 60, saturated at rest, ensures the balance of the monostable multivibrator consisting of transistors 61 and 62, the latter being conductive at rest. A branch issues from its collector resistance 67 in order to arrive through a diode and resistances 6 8 and 69 on the slider of

resistances

17 and 18 in FIGURE 1. In the conductive state of transistor 62, the relative voltages are such that resistance 67 does not participate in the definition of the pilot voltages produced in

resistances

17 and 18 of FIGURE 1. On the contrary, if transistor 62 is blocked, the active side of resistance 67 is brought back to voltage V3, which is more negative than V2.

Resistances

67, 68 and 69 cooperate to reduce the amplitude of the pilot voltages. Transistor 62 must only become blocked when the required speed of the motor is reached. For this reason, transistor 60 which is normally conductive is driven by blocking impulses coming from the collector of transistor 57 through an auxiliary circuit consisting of resistance 65 and diode 63. If transistor 57 is previously blocked, resistance 65 strongly biases diode 63 in the blocking direction. A positive impulse from condenser 64 is not transmitted to transistor 60 which remains conductive. However, if transistor 57 is conductive, the bias on diode 6 3 disappears and a positive impulse of condenser 64 will be transmitted to the base of transistor 60- which will become blocked for the time necessary to trip the monostable multivibrator and thus block momentarily transistor 62.

An analysis of the circuit shows that a blocking bias is applied to diode 63 at the moment of impulse on condenser 64 for as long as the interval between two successive impulses transmitted by the first Schmitt trigger (transistors 52 and 53) is not very near to or lower than the delay period of condenser 58, that is, for as long as the required motor speed is not reached. On the contrary, as soon as this speed is reached, transistor 57 remains conductive until the application of the positive impulse on condenser 64 which consequently results, each time, in the momentary blocking of transistor 62.

It is evident that this monostable multivibrator for controlling the amplitude of the pilot voltages can also be of the re-energizing type during its metastable period.

FIGURE 5 is a block schematic drawing of the circuits permitting the carrying out of the invention:

B1 represents the motor with a feed path coming from source B16, four commutation paths coming from channels B to B13 while B1 delivers synchronisation signals to the operating discriminator B2. synchronisation impulses are transmitted to the multistable circuit formed of blocks B3 to B5. In B6 are located the digital composition circuits for forming half reversals, while B7 constitutes the forming circuit for complete reversals along two biphased paths. B8 alternately distributes pilot reversals to one and the other of two commutation channels of the same phase, B10 and B11, while B9 does the same for the two channels of commutation of the other phase, B12 and B13. Square B15 represents the slip impulse generator, the impulses of which add to those of B2 at the entrance of B3. Square B14 is the speed selection circuit which beginning with the frequency of the synchronisation impulses, controls either the outlet impulses from B2, the frequency of the slip generator B15, the amplitude of the pilot voltages generated in B6 or still some combination of these three possibilities as shown in FIGURE 4 in which both frequency and amplitude are controlled.

FIGURE 6 shows one type of digital component circuit and a multistable circuit associated therewith, set up as an impulse counter in such a way as to generate the three-phase pilot functions R, S and T. These pilot functions are then fed to a circuit analogous to that shown in FIGURE 3 but modified to handle three phase, to control the motor current.

The functioning of the circuit of FIGURE 6 can be understood as follows:

A first bistable stage consisting of

transistors

73 and 73 plays the auxiliary role of pre-divider and dispatcher of the entrance impulses. The synchronisation impulses in a particular case delivered at the rate of 24 per motor turn, are introduced in 71, while the slip impulses are inserted in 72 with -a frequency which depends on the conditions of functioning.

The three bistable stages 74-74, 75-75, 76-76, are associated as a counting ring with the circuits associated to resistances 77 which give them their property of triggering in turn cyclically from one state to the other and inversely. This counting ring forms the multistable control circuit for the digital composition circuit comprising the three paths R, S and T of a tri-phase system, each of the paths being fed by three transistors, for example 80, 84 and 87, for the first.

Let us define the initial state of the counting ring as being that for which all the left-hand side transistors (74, 75, 76) are blocked and those on the right (74, 75, 76) are consequently conductive. The three supply transistors of phase R (80, 84, 87) are then blocked, thence a zero voltage on R. At the first active impulse transmitted by condenser 78, stage 74-74 triggers of switches, transistor 74 then being blocked whence the unblocking of transistor 80 and the appearance of one step of positive voltage in R (see FIGURE 8). At the second impulse it is stage 75-75 which switches with unblocking of 84 and the appearance of a second step of positive voltage in R. The third impulse switches 76-76 with unblocking of 87 and the appearance of a third step of positive voltage in R. The fourth impulse occasions the return of 74-74' to its initial state with blocking of 80 which occasions the reduction of one step in R. With the return of 75-75, the fifth impulse causes another step to retrogress, while the sixth impulse returns the entire system to its initial state (the end of a reversal on R).

The periodic repetition of this cycle generates the function drawn in FIGURE 8. The compression of the steps toward to the top is simply obtained by judicious relationship of resistances 88 and of the load resistances with a view to approach, for example, reversals of a sinusoid the definition of which will be all the better as each reversal comprises more steps. The amplitude of a reversal is defined by the voltage 89 which is subjected to the operating conditions of the motor and in particular its speed. Resistances to 97 only play a role of adaptation while commutator 90 permits the reversal of two phases with a view to reversing the direction of rotation of the induction motor.

The way the transistors are coupled on lines S and T shows that functions R, S and T are identical but out of phase by 120 so as to form a system of tri-phased pilot voltages which can be generalised in any given manner by an adaptation of the capacity of the counting ring.

The outlets 98, 99 and 100 are used in the coordinating circuit associated with the electronic commutation system of the induction motor. It is in this coordinating system that can be placed a condenser 91 in order to vary slightly the setting up of the first step of positive voltage of each reversal.

The electronic commutation process has two reversals of pilot function for each complete period of the driving current. These two reversals require 12 active impulses at entrance 78, that is 24 at entrance 71, from which obtains the synchronisation at the rate of 24 impulses per turn for a two pole motor. The additional impulses injected by 72 generates then the slip frequency in the ordinary meaning of the word in the field of electronics. The slip impulses must have a frequency of 24 c.p.s. to generate the slip frequency of 1 c.p.s.

FIGURE 7 relates to a control circuit the functioning of which can be understood from the following:

by a first Schmitt trigger circuit consisting of transistors 32 and 33.

The formed impulses are divided along two paths. One by way of transistor 49 feeds the digital circuit of FIG- URE 6 at 71 at the rate of 24 impulses per turn of a two pole motor. The other, by way of transistor 34, generates at each impulse an abrupt discharge of condenser 35 which is linearly recharged through transistor 36 by an adjustable current at 37. A second Schmitt trigger circuit 38-39 reacts as soon as the charge of 35 reaches a discriminating threshold, the relatively high impedance of this second trigger circuit being transmitted to a third Schmitt trigger circuit 40-41 having a low response impedance. The integrating transistor 42 is followed by two transistors 44 and 45 which lower the impedance.

When the speed of the motor is lower than that corresponding to the setting of potentiometer 37, the interval between two synchronisation impulses is high enough to permit the periodic switching of discriminators 38-39 and 40, 41. There results a periodic unblocking of 42 and the charging of filter condenser 43, whence a signal 46 which becomes all the higher as the speed of the motor is lower with respect to the control 37.

Signal 46 spreads along two paths. One controls the frequency of the slip multivibrator at 46 in FIGURE 9 in such a way that the slip frequency be all the higher as the signal 46 is greater but with a maximum corresponding to the maximum motor torque. The other, after a decrease in impedance, gives at 89 a signal which determines the amplitude of the pilot voltages of FIGURE 6, said amplitude being proportional to that of signal 89.

If the speed of the motor reaches or exceeds that set at 37, switches 38-39 and 40-41 are no longer energized, transistor 42 remains blocked, signals 46 and 89 disappear, the slip frequency falls to its minimum value and the amplitude of the pilot functions cancel, whence weakening then disappearance of the motor torque.

The entire control process occurs between these extreme conditions. To act on the slip frequency has been found fundamental from stability of the control, while it is essential to act on the amplitude for the sake of the efficiency of the control.

The negative feed back circuit 48 contributes to the stabilising of the speed as a function of the charge in the following manner: As the charge increases, the decrease in speed causes the signal 46 to increase, which through the negative feed back circuit 48, tends to increase the speed controlled at 37. It is possible, by this means, to obtain any practical relationship desired between speed and loadeven to the extent of obtaining an increase of speed with charge.

At 50 is located an interrupter for stopping the pilot functions by eliminating voltage 89. In 70 is provided a system for braking the motor, the pilot voltages being replaced by a fixed voltage, and by means of diodes and resistances on paths S and T.

The slip multivibrator shown on FIGURE 9 does not need comment. The frequency, adjustable by means of the current of transistor 92 is variable over a wide range, for example, between 8 and 120 c.p.s. which corresponds respectively to a slip frequency of /3 to 5 c.p.s., the motor torque being negligible for the weakest and maximum for the strongest. The adaptation of the slip frequency to the running of the motor is ensured by path 46 which corresponds to signal 46 in FIGURE 7.

The advantages of the generator of pilot functions according to the invention are based in part on its general application to any number of phases whatever, on the other part to its reliability, the tolerance of the characteristic of the elements of the circuit being high. Finally, it lends itself to a good control of speed and to its variation, manual or automatic, along a large wide range (in excess of -1).

The advantages of such a process for forming pilot voltages are considerable even if they be limited to perfecting basic conditions required for the good functioning of an induction motor driven by electronic commutation. No starting overcharge is possible, the intensity of the motor current being generally limited by the predetermined amplitude of the pilot voltages. Acceleration nevertheless takes place under the best possible conditions with optimum slip frequency and a maximum starting torque. The manual or automatic variation of the speed is very simple and it is not possible to exceed the break down torque.

It goes without saying that the invention is not limited to the type of electronic commutation given in the description. It extends on the contrary to all types of control by alternating voltage or voltage modulated at varia-ble frequency with the considerable advantage of permitting an instantaneous variation of the frequency without affecting the shape, the amplitude or the relative phase of the pilot voltages.

The invention is not limited to what is specifically described but encompasses also a multitude of embodiments of diflerent circuits. Thus the multistable circuit can assume a great number of forms including all the electronic impulse counting devices. The same is true of the synchronisation impulse generator, the slip impulse generator and the circuit for selecting the speed which can also include a tachometer generator.

What is claimed is:

1. Apparatus for supplying polyphase current to a winding of a polyphase electric induction motor, said apparatus comprising:

(i) generating means for generating a plurality of step-wise pilot voltage pulses; and controlled by a series of main input signals;

(ii) said generating means including electronic switching means having a plurality of output states;

(a) each output state corresponding to a particular step of the step-wise pilot voltage pulses,

(b) the switching means being operable cyclically among its plurality of output states to generate periodically the step-wise voltage pulses;

(iii) at least one channel of electronic commutation for each phase and adapted to be connected to its corresponding phase of the Winding;

(iv) and means for distributing said step-wise voltage pulses among the chanels of commutation;

(v) each channel being uni-directional; and being controlled by said pilot voltage pulses to generate a driving current for its corresponding phase of the winding;

(vi) auxiliary means for generating a plurality of auxiliary input signals for the generating means; said auxiliary input signals being added on or suppressing the main input signals to change or modify the frequency of the step-wise pilot voltage pulses; the frequency of the auxiliary input signals being limited to a value which does not exceed the value corresponding to the maximum motor torque; and which disappears when the motor operates normally; the driving current corresponding in shape to the shape of the pilot voltage pulses, whereby the parameters of frequency and amplitude of the pilot voltage pulses regulate the speed of the motor.

2. Apparatus according to claim 1 in which:

(i) the motor is a two-phase motor;

(ii) there being two uni-directional channels of electronic commutation provided for each phase, the two channels being adapted to be connected to their corresponding phase of the winding, and to supply the driving current to their corresponding phase of the winding alternately, the shape of the driving current being quasi-sinusoidal;

(iii) and in which the pilot voltage pulses which are distributed to each of the two channels of commutation for each phase are the same but out of phase one from the other by (iv) and in which the generating means is responsive to an input signal to generate one step of the stepwise pilot voltage pulse each time an input signal is received;

(v) the width of each step being determined solely by the frequency of the input signals, and being independent of transient effects during a rapid change of frequency;

(vi) and in which means are provided to generate a plurality of main input signals for the generating means;

(vii) the frequency of the main input signals being proportional to the speed of the motor;

(viii) there being regulating and stabilising means to regulate and stabilise the pilot voltage and thereby to regulate and stabilise the speed of the motor.

3. Apparatus according to claim 2, in which each channel of commutation is alternately blocked and unblocked by the pilot voltage pulses, the pilot voltage pulses being adapted to unblock their respective channels of commutation only above a given amplitude threshold, the portions of the pilot voltage pulses above said threshold forming a series of uni-polar periodic reversals of substantially sinusoidal shape.

4. Apparatus according to claim 3, in which the driving current in each commutation channel is substantially proportional to the voltage of the corresponding pilot voltage pulses.

5. Apparatus according to claim 2, in which said electronic switching means forming part of said generating means includes at least one multistable circuit in the form of an impulse counter adapted to switch cyclically among its various stable states, the impulse counter being of the binary type and comprising a plurality of bi-stable switches connected in series, and in which the generating means includes a digital composition circuit connected to said multi-sta'ble circuit, and being adapted to generate one step of the step-wise pilot voltage pulses for each stable state of the multi-stable circuit, and being further adapted to juxtapose the steps to form one pulse during each cycle of the multi-stable circuit.

6. Apparatus according to claim 5, in which each bistable switch comprises two active elements, one being conductive while the other is nonconductive, and vice versa, and in which there are two digital composition circuits each comprising a plurality of resistances, the resistances of one digital composition circuit each being connected to one of the active elements of said bi-stable switches which is non-conductive in the initial state of said binary rnulti-stable circuit, the resistances of the other digital composition circuit each being connected to one of the active elements of said bi-sta-ble switches which is conductive in the initial state of said binary multi-stable circuit, each resistance conducting a current only when the active element to which it is connected is in the conductive state, and in which the value of the resistances diminishes by half from one bi-stable switch to the following switch in such a way as to generate a succession of component voltages during the operating cycle of said multi-stable circuit, and in which the voltage obtained during an operating cycle of said multistable circuit on the circuit of digital composition corresponding therewith, forms a series of half reversals of pilot voltage, the voltage simultaneously obtained on the other circuit of digital composition forming a series of half reversals complementing those on the first circuit of digital composition, in such a way that a complete reversal of pilot voltage is obtained by chronological juxtaposition of two complementary half reversals.

7. Apparatus according to claim '6, in which the said chronological juxtaposition is controlled by a juxtaposition circuit comprising a supplementary bi-stable stage connected in series at the end of said multi-sta-ble circuit in such a way that it switches upon each cycle of the multi-stage circuit, said juxtaposition circuit being adapted to connect alternately a first outlet circuit to one and then the other of said digital composition circuits, at the frequency of the operating cycles of said multi-stable circuit, said juxtaposition circuit being further adapted to connect alternately a second outlet circuit to one and then the other of said digital composition circuits, at

the frequency of the operating cycles of said multi-stable circuit, the pilot voltages thus obtained on each of the outlets consisting of a continuous series of complete reversals, the pilot voltage of one of these outlets being out of phase by a half reversal with respect to the pilot voltage of the other outlet, in such a way that they comprise a system of two-phase pilot voltages adapted for use with a two-phase induction motor, and in which each of said pilot voltages consisting of a continuous series of complete reversals controls two commutation channels for the same phase, splitting means being provided to split each of said pilot voltages between the two channels, so that one channel receives the even reversals and the other channel receives the odd reversals of said pilot voltage, said splitting means comprising a second supplemental bi-stable stage placed in series after the first supplemental bi-stable stage.

8. Apparatus according to claim 2, in which the regulating and stablising means is adapted to decrease the frequency of said auxiliary means for generating a plurality of auxiliary input signals when the motor reaches a predetermined speed.

9. Apparatus according to claim 2, in which the regulating and stabilising means comprises a circuit adapted to eliminate at least some of said main input signals when the motor reaches a predetermined speed so as to stop acceleration of the motor.

10. Apparatus according to claim 2, in which said circuit of the regulating and stabilising means comprises a monostable multi-vi'brator to which are fed at least some of said main input signals, said mono-stable multi-Vibrator having a predetermined meta-stable period, and being adapted to eliminate the said some main input signals when the interval between successive input signals becomes smaller than said meta-stable period so as to stabilise the motor at a speed at which the intervals between successive input signals substantially equals said metastable period.

11. Apparatus according to claim 2, in which said regulating and stabilising means reduces the amplitude of said pilot voltage pulses when the motor reaches a predetermined speed.

12. Apparatus according to claim 10, in which said regulating and stabilising means includes amplitude-reducing means for reducing the amplitude of said pilot voltage pulses when the motor reaches said predetermined speed, said amplitude-reducing means being adapted to be pre-sensitized by the triggering of said mono-stable multi-vibrator, and being adapted to reduce the amplitude of the pilot voltage pulses when the interval between successive input signals fed to the mono-stable multi-vibrator falls below said meta-stable period.

References Cited UNITED STATES PATENTS 3,262,036 7/1966 Clarke et al. 318-227 XR 3,280,395 10/1966 Madsen 318-138 3,320,506 5/1967 Humphrey 318227 3,348,109 10/ 1967 Wright 318227 XR 3,353,081 11/1967 Sternmler 318-227 XR ORIS L. RADER, Primary Examiner.

G. SIMMONS, Assistant Examiner.

US. Cl. X.R.