DE2150117A1 - Speed control device for an electric asynchronous motor with a wound rotor, in particular for the operation of a lifting device - Google Patents

Description

DR. MÜLLER-BORE DlPL-PHYS. DR. MANITZ DIPL.-CHEM, DR. DEUFEL DIPL.-ING. FINSTERWALD DIPL.-INQ. GRÄMKOW

PATENT LAWYERS 9 1 RD 1 1

"October 7, 1971

We / th - T 1155

LA lELEMECANIQUE ELEOTRIQUE 33bis Avenue du Marechal Joffre, 92 Nanterre / France

Speed control device for an electric Asynchronous motor with wound rotor, especially for the operation of a lifting device

The invention relates to a mixed electronic and electromechanical system, which is intended to use the speed of a polyphase asynchronous motor wound rotor and with several normal running types change, which is followed by a fine control with very low speed. This system is suitable in particular for a lifting device such as a crane, for which the fine control must be achieved when the lifting hook is near the desired height or when the load is being set down.

In conventional technology, one changes the torque and the speed of an asynchronous motor with a wound Rotor by using the rotor circuit via resistors

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Yi eleven axis taps are closed, with gradual short-circuit devices via mechanical contacts or through Reostats with sliding contacts or by means of fluids. There is a discontinuous change in the resistances but not compatible with fine control, and on the other hand the continuously variable ones are suitable Resistors not for quick regulation.

Arrangements have already been proposed in which an electronic breaker with a springy rotor resistance is connected in series, this electronic breaker being formed from an anti-parallel circuit, either by two Thyxatms or thyristors or from a thyraton <and "? a diode, from which it follows that the resistance formed depends on the ignition delay of the thyratron or thyratron. The main difficulty lies however, in the fact that the rotor voltage and the rotor frequency are both variable during the ignition delay for a given error, d. i.e., a difference between the real value and the target value must be independent of the frequency. It is still a system has been proposed in which the voltage is represented by a "tachometric dynamo machine, where the constancy of the delay for a given Value is achieved through a complex arrangement.

The invention provides one for such arrangements significant technical progress by using the traditional method of short-circuiting through stages a resistor is combined with a fine control device which is controlled by an electronic method

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that does not use a tachometric dynamo machine. It allows you to work within a range of given displacements by approximating the displacement 1, d. that is, the zero velocity that can be achieved, either as the charge rises or as it falls with a cargo carried. It also allows the additional arrangement of a safety device, which the operation of the electronic device is suppressed in the event that it is not below the required Conditions can affect the speed.

It should first be briefly reminded that in an induction motor with a wound rotor the activation of Resistance in each of the phases of the rotor has the effect of the speed-torque characteristic of the motor to change, and that with a greater slope, the more the value of the switched on resistors the Increased displacement or the slip of the rotor with respect to the rotating multiphase field. The activation of step resistors makes it possible to change the speed with the same load, with a loss of energy in the resistors. It is not always pleasant to see the number of steps and sections of the resistors to multiply excessively, and in addition it is necessary to the zone of instability of the speed-moment en-Eurye Invoice. A complementary procedure which consists in running in a slow mode of the engine, d. i.e., periodically opening and closing the rotor circuit in the event of significant slip is one Regulation, which is useful to bring the speed of the motor very gradually to zero. Such a

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Method is applicable to a set of controlled Semiconductors, which are connected downstream of the usual circuit of resistors, which are connected to mechanical Poles per rotor phase can be short-circuited with at least one controlled semiconductor rectifier, which can close the circle on a neutral point.

The basic idea of the invention consists in the delay of the ignition of each rectifier as a puncture of an analog Voltage control resulting from a comparison between a The voltage representing the setpoint and the speed of the motor results, with the delay being a constant Is fraction of any rotor current period.

The invention comprises for actuating each of the above-mentioned rectifiers, each with an ignition signal receiving control electrode are equipped, the associated facilities described below. ' Each signal is supplied by an ignition generator which essentially has three inputs to which the following signals are applied: a first square wave signal, whose periodic width is a selected fraction of the rotor current period, a second voltage signal, which is generated by a comparison between the voltage measured by a rotor frequency measuring device is sent out and a target voltage of the speed, a third signal, which is from the rotor voltage period »» Is dependent and determines a triggering threshold of the ignition generator, whereby the ignition generator contains a first element, · which receives the first and the second signal in such a way that a sawtooth voltage is formed whose tooth width is determined by the first signal while the slope

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the amplitude of the second signal is proportional and where the sawtooth voltage is only an effective signal delivers when the second organ that controls it establishes a coincidence with the third signal, which the ignition threshold is determined on the basis of which the voltage deviation between the target speed and the Speed of the motor has the effect that the slope of the sawtooth voltage is varied, with the Ignition takes place constantly for a predetermined fraction of the rotor current period and the regulation for one the fraction corresponding to the electrical step is effected.

The first above-mentioned organ for forming a sawtooth voltage can have a capacitor, which by a generator is charged with an intensity that depends on the second signal and discharged through an organ which is equipped with a semiconductor controlled by the first signal, such that the Charging operation of the capacitor is blocked during a fraction of the rotor current period. The first signal can can be achieved in that the voltage is brought into a rectangular shape, which is at the terminals of a resistor occurs, which is in series with a diode of a three-phase Graetz bridge, which in turn is short-circuited with itself is connected, namely via the branches, which each contain such a resistor in series, wherein the bridge by transforming the tensions on the Clamping the rotor is fed in such a way that after inversion of the · output signal, which extends over the two thirds of the Rotor current period extends, the aforementioned blocking element operates during the last third of the period.

209 816 / 1-012.

To get the second signal which is the speed deviation voltage and the third signal, which is the threshold voltage of the detonators for a fraction of the period, becomes an auxiliary device used, which for example consists of a group of rectifier transformers, which in the star are connected and have a resistor in series with each diode so that this rectifier with itself is short-circuited via the series resistors mentioned.

The voltages previously taken from the terminals of these resistors are measured with the help of corresponding pormer steps transformed into rectangular voltages are then differentiated, whereupon the arrangement of the six received pulses is then rectified, and one thus receives six pulses per rotor period Are spaced from each other.

Six pulses per rotor period, which are at 60 °

Using an analog device, six times the frequency of the rotor frequency is converted into one that is proportional to the rotor frequency Stress transformed with two applications in mind.

On the one hand there is that of the rotor frequency for an approximate constant proportional voltage the speed, which in a conventional manner with the target speed is compared to provide the second signal; on the other hand, the voltage proportional to the rotor frequency delivers Inversion in a non-linear system is a voltage that is proportional to the specified period, which supplies the third signal or a threshold voltage of the detonators.

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■ 21 & 0117

The invention is described below, for example, with reference to FIG Drawing; "; it shows:

ig. 1 shows a general block diagram of the device according to the invention,

2 shows a simplified diagram of the ignition generator,

Fig. J is a graph showing the mode of operation of the ignition generator illustrates

Fig. 4- shows a preferred embodiment of the apparatus showing the synchronization signals and pulses with six times the frequency of the rotor frequency and

Figure 5 is a graphical representation of the waveforms which lead to six times the repetition rate.

Referring to Fig. 1, an annular three-phase asynchronous motor comprises a stator 1 and a wound rotor 2, the stator being fed via the mains through terminals 3, 4 and 5 takes place. The clamps of the rotor are marked with 6, 7 and and they are connected on the one hand to an electronic block 28, which is described below and on the other hand with a pulp phase resistor, the branches of which are generally designated 9 »10 and 11. In conventional The resistor branches, which are not described in detail, have intermediate taps, which can be short-circuited to a neutral point by mechanical poles 12, 13 and 14 via

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three control levels I, II and III. The resistance output terminals 6 ', 7' "and 8 'are marked with a generally marked 41 designated short-circuit member connected and each with three electronic breakers- 16, 17 and 18. These the latter in this embodiment each comprise a controlled rectifier 20, · 22 and 24, each with a current return diode 19 »21 and 23. Obviously other forms of electronic circuit breaker could be used, for example two thyristors, which are used in each phase could be connected in antiparallel or triax elements or the like. In the present case each thyristor 20, 21, 24- has an ignition electrode, which is actuated by the signal from an ignition generator 25, 26 or 27. Each ignition generator is powered by a Feed block 43 supplied with energy, which does not form part of the invention, of which the Lines 110, 111 and 112 exit to the generators. The latter receive the actuation signals whose Means of production are considered below.

The block 28, which is branched off from the terminals 6, 7 and 8 and according to E ¹ Ig. 4 is arranged, contains in the above-mentioned branches a transformer P, which has two secondary windings S. and So. The secondary winding S- feeds the Grätz bridge, which is formed by the diodes 63> 64, 65, 66, 67, 68, the three anodes of the diodes 63, 64 and 65 being combined on a common conductor 69, which is three Resistors 70, 71 and leads, each of which has its second end branched off from the cathodes of the three diodes 66, 67 and 68. In this embodiment, the voltage U tapped at the terminals of a resistor such as 70 is represented by curve 73,

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which represents the intersection of two sine waves which extend over two thirds of the rotor period, namely over 240 °, since the signals tapped at terminals 70, 71 and 72 form a three-phase system. The conventional wave formers 74 ¹ J 75 and 76 derive first signals, namely three signals in rectangular form 77, each of which sweeps two thirds of the rotor period and is applied through connections 29, 30 and 31 as a first signal , in each case to one of the inputs of the ignition generators. In each of these generators, a signal inverter (not described) forms the complement of signals 77, specifically in such a way that a voltage xri-rd which occurs only during the last third of the period is supplied.

For structural reasons, block 28 also contains an additional device, the function of which is completed by that of block 32, which is connected downstream of block 28. The secondary winding S ^ _5, which is connected in a star, feeds three rectifiers 83, 84 and 85 via three resistors 87, 88 and 89, the resistors themselves being connected in a star with a return to the neutral point 86 via their second end in such a way that a voltage ν at its end provides a wave 90 which extends over 180 °. As above, three waveformers 91, 92 and 93 extract square wave signals therefrom which are differentiated at 96, 95 and 97 to provide a signal 98 with alternating positive and negative peaks in each wave.

The signal passing through conductors 99 indicating the three Combined differentiating stages is the sum of the impulses of the jps 98, which correspond to the three phases, this The signal alternates between positive and negative impulses, "

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which are offset from each other by 60 electrical degrees are.

After rectification by the organ 101, one obtains a Pulse train, for example negative pulses, which a Have regular spacing and have six times the frequency of the Rotprfrequency.

^ The table in FIG. 5 shows, on the one hand, the synchronization waves which are sent out by the elements 74, 75 and 76 and appear on the conductors 29 ₅ 30 and 31, these waves being shown at 77A, 77B and 770 . On the other hand, it illustrates the successive wave transformations as derived from the star-connected auxiliary rectifier.

At 94A, 94B and 94C the waves are shown which are formed by the elements 91, 92 and 93. At 99A the pulse sequence is shown which is obtained by differentiating the waves 94A ₁ 94B and 94C and at 100A the pulse sequence which appears after rectification by the element P 101, the repetition pulse 6f "

That converted into an analog voltage by 32 and with Signal 6f designated Z is fed to block 35, which the speed measurement is effected by changing the rotor frequency is derived from a constant and by supplying a voltage proportional to this result. The latter is fed to the speed controller 40, which supplies an error signal 42 by calculating the difference between the voltage through the block 35 and that through a Potentiometer 140 displayed control voltage is formed,

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\ irwhich is controlled by a handle. The exit 42 "forms the second signal which is sent to the ignition generators is fed.

With further reference to FIG. 1, it can be stated that the signal Z supplied by block 32 is also fed to a block 53 which effects the measurement of the motor period, namely by inversion by means of a non-linear system and thus one of the period duration supplies proportional voltage. This so-called threshold voltage is fed to the ignition generator at 34 and forms the third signal which is essential for its operation \ tf is recorded by block 36 and compared with two limit values 37 and 3S, which represent the sliding limits which are changed during the very slow speed control. Whenever the margin between two positive and negative slides or slip ranges is exceeded, the comparator triggers a generator 39 This latter acts on a controlled rectifier, which closes a contact breaker 41, and this short- ^{circuits the terminals 6 1} , 7 ¹ and 8 ^{1 through its poles.} 17 and 18 anulates so that the motor does the speed homen ten characteristic, which is determined by the arrangement of the resistors, it being assumed that the arrangement of the short circuit device I, II and III is already open by commutation devices, not shown.

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The ignition voltage generators 25, 26 and 27 each include a constant current generator 46 according to FIG is passed through the conductor 42 (see Pig. 1). The generator 46 is connected to the plate 47a of a capacitor 47, which is connected to ground via the plate 47b. The capacitor is geshüntet by a transistor 48, in which the collector and emitter balls are inverted w that the loss voltage Vq ^ is reduced. The base 48b of this transistor is controlled by the terminal 49 which receives the voltage transformed from the first signal or from the synchronization signal coming from block 28, as already explained above. The charge on the capacitor, which is limited to fractions of the periods permitted by the synchronization signal, is a linearly increasing voltage, which is referred to as the ramp voltage. It is fed via the conductor 51 to an element 50, which can be a differential operational amplifier. The latter receives the threshold voltage, which arrives at terminal 53, via a second input at 52. This voltage is the one referred to above as the third signal coming from block 33 (see FIG. 1). The output of the amplifier 50 is connected to an oscillator with an increased frequency 54, the signals of which, appropriately amplified at 55, are fed to the ignition electrode of an electronic breaker 16, 17 or 18, via a transformer 56. A diode system, not shown only allows positive waves to access a thyristor control electrode, and a series resistor diode located on the secondary winding of transformer 56 prevents saturation.

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Fig. 3 shows the mode of operation of the ignition generators in graphical format. At U ^ q, U ^ ₀ and U ,. the applied synchronization voltages which are fed to the blocking elements 48 are shown. In the generators the linearly increasing voltages which appear on the capacitors are represented by the three straight lines 59, 60 and 61, each of which overlaps one third of the rotor period with the preceding one and also with the following. The slope of the straight line 59 »60 and is a puncture of the voltage deviation, which corresponds to the. Generator 46 is supplied. The threshold voltage is represented by the ordinate OV and determines an operating point N,., N ^ and N, on the voltage rises 59 »60 and 61, which corresponds to an ignition delay oCi» οίο undoC * of the three electronic breakers for a fixed period. The amplitude of the variation of <x can reach 2 ^ 0 electrical degrees such that when the rise in voltages 59 »60 and 61 decreases from a maximum regulation, the blocking of the breakers can be progressively achieved.

Thus, the generator forms with a variable slope and a ramp duration which is proportional to the rotor period is, according to the description above, the central part of the system according to the invention. This can be different adopt electronic embodiments due to the numerous nature of the electronic components given possibilities.

-Patent approach-

2 Ü 9 3 1 6/1 Q Ί 2

Claims (8)

Claims I.JSpeed control system for an asynchronous polyphase motor with a wound rotor with a gradual inclusion of resistors in the Rotor phases, followed by a periodic interruption of the current in these phases, whichever triggered by a device of controlled semiconductors placed in each of them is, whereby these devices close the phases to a neutral point in the conductive state, thereby gekennzei chnet that the facilities for periodic interruption each have at least one rectifier with a control electrode, which is actuated by an ignition signal, that the ignition signal is supplied by an ignition generator, which essentially has three inputs, to which the following signals are applied: * a first signal (29, 30, 3Ό with a square wave form, the period width of which is a selected fraction of the period of the rotor current, a second voltage signal (4-2), which is generated by a comparison between the voltage generated by a device which measures the rotor frequency and a speed setpoint voltage, a third signal (3 ² O ₅ which depends on the rotor current period and determines an ignition level of the controlled rectifier, that the ignition generator has a first element, which the first and the second Signal picks up, in such a way that a sawtooth voltage with 209816/1012 a tooth width is formed, which by the first Signal is fixed, while the slope of the sawtooth is proportional to the amplitude of the second signal is that the sawtooth voltage only delivers an effective signal when a second organ that feeds it, builds up a coincidence with the third signal, which determines the ignition threshold "on the basis of which the voltage deviation between the target speed and the Speed of the motor a change in the voltage slope causes the ignition of the rectifier constant for a given fraction of the rotor current period is effected and that the speed control takes place for a corresponding fraction of the electrical step. 2. Speed control system according to claim 1, characterized in that the first organ of the Ignition generator has a capacitor, which is regulated by a generator for the second signal Current is charged and discharged through an organ which is controlled by the first signal Semiconductor, such that the charging function of the capacitor during a fraction of the rotor current period Is blocked. 3. Speed control system according to claim 1 and 2, characterized in that the locking member is a transistor whose emitter-collector circuit is arranged inversely with respect to the saturation current. 209816/1012 4. speed control system according to claim 1 and 2, characterized in that the first signal is achieved by shaping the voltage which occurs at the terminals of a resistor which is connected to a diode of a Grätz bridge with three phases in Row, which is short-circuited with itself via its branches, each having such a resistance contain that bridge through triangle transformation of the voltages at the rotor terminals is fed in such a way that after inversion of the output signal, which is about which extends two thirds of the rotor current period, the blocking element works during the last third of the period. 5 speed control system according to claim 1, 2 and 4, characterized in that a second device is provided which is provided by a secondary winding is fed in the star of the transformer, which is branched off from the Grätz bridge that the The star-connected secondary winding is led to a neutral point via three diodes and three resistors while the voltage appearing across each resistor is transformed into a square wave, then three differentiating stages is fed, the outputs of which are connected in star, so that the on the return conductor resulting signal obtained after rectification from a sequence of pulses of the same Composed of polarity, the repetition frequency of which is six times the rotor frequency. 6. Speed control system according to claim 1, 2, 4, and 5> characterized ei chnet that the rotor frequency proportional pulse signal into an analog voltage 209816/101 2 is integrated, which is converted depending on the speed, and in a target speed controller is compared to produce the second signal (the deviation signal), which is fed to the ignition generator. 7 · Speed control system according to claim 1, 2, 4 and 5 » characterized by the fact that the frequency signal integrated in an analog voltage is not a linear measuring device is supplied in such a way that an analog signal is generated which corresponds to the period of the Corresponds to the rotor current and that this signal is sent to the ignition generator as a third signal or as a threshold voltage is fed. 8. Control system according to claim 1, 2, 4 · and 5, characterized marked ei chnet that integrated into an analog voltage and dependent on the speed The transformed frequency signal is fed to a comparator, which also has two input voltages receives which correspond to the sliding or slippage permitted for the control speed and that "when exceeded, the comparator emits a control signal to an electronic device that has a Switching device puts into operation, which eliminates the controlled rectifier by moving upstream the rotor phases and all resistances are closed to a neutral point. 209816/1012