EP0252808B1 - Command and control device for a contactor, and corresponding control process - Google Patents

Abstract

A contactor provided for AC is DC fed, the coil 1 being in series with a transistor 5 operating as a chopper, and a resistor 7. At the measuring point 8, the current in the coil is compared with reference values. Each cycle of operation of the contactor comprises a feed period and a pause. At the end of the pause, a measurement of the current in the coil enables the position of the armature to be determined. <IMAGE>

Description

The invention relates to a device for controlling and verifying a contactor, and more particularly to a device for controlling an electromechanical contactor designed to be supplied with alternating current, and for controlling (in the sense of a verification) the position of the movable armature of this contactor, as well as the corresponding control method.

AC contactors are generally smaller, at equal power, than DC contactors. They are therefore more practical, they consume less and they heat less. But they have a drawback: they tend to open during the zero crossing of the current value, and they make noise.

Document US-A-3 678 344 describes an apparatus for command and control of the position of the armature of an electromechanical contactor. But this document relates to the dynamic control of the armature and not to the control of the maintenance of the armature.

Document DE-A-2 513 043 describes a device for controlling a contactor operating in direct current, having the characteristics of the preamble of claim 1.

This document also describes a method for controlling the position of the armature of a contactor operating in direct current, consisting in making an indirect measurement of the inductance of the contactor coil.

One of the aims of the invention is to propose a control circuit enabling a contactor constructed to be supplied with alternating current to be used under a direct current supply, the control circuit-contactor assembly having the advantages of the contactor in alternative without having the disadvantages.

Another object of the invention is to propose a circuit and a method for controlling (in the sense of a verification) a contactor proceeding by measuring the intensity in the coil to verify whether the armature is glued or not .

The subject of the invention is a device for controlling an electromechanical contactor with armature, as defined in claim 1.

Other embodiments of the invention are defined by dependent claims 2 to 5.

• ladite mesure indirecte de l'inductance de la bobine du contacteur est faite à intervalles de temps réguliers,
• ladite mesure indirecte intervient à l' issue d'une période de pause pendant laquelle le hacheur est coupé,
• ladite mesure indirecte consiste en une mesure de l' intensité du courant dans la bobine par comparaison avec une intensité de référence.

The invention also relates to a method for verifying the position of the armature of an electromechanical contactor, constructed to be supplied with alternating current, of the type supplied by means of a direct current chopper, the verification of the glued or distant position of the armature being effected by means of an indirect measurement of the inductance of the contactor coil, characterized in that:

• said indirect measurement of the inductance of the contactor coil is made at regular time intervals,
• said indirect measurement occurs after a period of pause during which the chopper is cut,
• said indirect measurement consists of a measurement of the intensity of the current in the coil by comparison with a reference intensity.

• à l'issue de la pause, la comparaison de la valeur du courant de la bobine à l' intensité de courant de référence est effectuée avec un petit retard pour masquer le régime transitoire d'établissement du comparateur ;
• l'intensité de référence du courant est de l'ordre de la moitié de l'intensité moyenne traversant la bobine et qui assure le maintien de l'armature.

According to other embodiments of the invention:

• at the end of the pause, the comparison of the value of the coil current with the reference current intensity is carried out with a small delay to mask the transient state of establishment of the comparator;
• the reference current intensity is of the order of half the average intensity passing through the coil and which maintains the armature.

• Figure 1 : un schéma symbolique d'un premier mode de réalisation d'un dispositif de commande et de contrôle d'un contacteur , selon l'invention.
• Figure 2 : un schéma d'un deuxième mode de réalisation du dispositif selon l'invention ;
• Figure 3 : un schéma de quelques signaux en différents points du dispositif de la figure 1.

By way of example, the drawing shows:

• Figure 1: a symbolic diagram of a first embodiment of a command and control device of a contactor, according to the invention.
• Figure 2: a diagram of a second embodiment of the device according to the invention;
• Figure 3: a diagram of some signals at different points of the device of Figure 1.

Referring to the drawing, we see a contactor symbolized by its coil 1, carrying in parallel a freewheeling diode 2. This contactor is constructed to be supplied with alternating current, but it is supplied with direct current by a power source 3,4. This feeds in series the coil 1 of the contactor, a transistor 5 with its control circuit 6 and a resistor 7 which is disposed between the transistor 5 and the negative supply terminal 4. The point common to the transistor 5 and to the resistance 7 is the measurement point 8 of the intensity of the current in the coil 1 during the conduction periods of the transistor 5. This measurement point is connected to an input of a comparator 9 whose other input, corresponding to l reference intensity Ir1, Ir2 or Ir3 is supplied by a logic circuit 10̸ via a digital-analog converter 12. A clock 11 supplies the logic circuit 10̸ with pulses of determined frequency.

The logic circuit 10̸ is connected to the control circuit 6 of the transistor 5 by two wires: one 13, transmits the opening orders of the transistor 5, the other 14, the closing orders. Here as in all of the description, the notion of wires is not imperative, it is simply an electrical connection, the circuits being able to be integrated. The logic circuit 10̸ is capable of transmitting at its output 15 a signal corresponding to the state of the movable armature of the contactor: stuck or distant.

Finally, by its input terminal 16, the logic circuit 10̸ is capable of receiving remote-controlled commands to operate the contactor. The power supply of the control circuit 6 is not shown in the drawing. It can be permanent, and then the device works by remote control; or it can be taken in parallel on the contactor, and in this case, when the contactor is energized, there is a general reset.

The transistor 5 operates as a chopper with a fixed frequency and a variable duty cycle. Resistor 7, of low value which transforms current information into voltage information, is crossed by the current in the coil only during the conduction periods of transistor 5; when transistor 5 is blocked, diode 2 fulfills its role of freewheeling diode. In this way, a substantially constant mean current is maintained in the coil 1, which always flows in the same direction. The thief of this average current is high during the duration of call of the movable armature of the contactor, and low during the duration of maintenance of the bonded armature. The call duration is defined a priori depending on the contactor, with a certain safety margin. It is the value of the reference intensity Ir1 which defines the value of the average current in the coil 1 during the call duration.

In Figure 3, we see on the first line the current Ib in the coil 1, and on the second line the reference value Ir1, Ir2 or Ir3. During operation, this reference value (setpoint), imposed by the logic circuit 10̸, varies. At start-up, the logic circuit 10̸ imposes a high reference value Ir1 for the current for a duration t1 corresponding to the duration of the call of the movable armature. Then, the reference value becomes lower, Ir2, for a period t2 corresponding to the maintenance of the bonded reinforcement. Then, during the pause period t3, and the measurement period t4, the reference value Ir3 becomes even lower and on the order of half of Ir2.

After the general reset pulse (fourth line) delivered by logic circuit 10̸ or when the contactor is energized, the reference changes to its high value Ir1 (call).

The chopper begins to operate at a fixed frequency imposed by the logic circuit 10̸, and which, for the duration t1 of the call, is for example 1.875 kHz. The current Ib in the coil therefore tends to rise and settle just below the value Ir1 imposed during the duration t1 of call. At the end of this duration t1, and throughout the holding time t2, the logic circuit 10̸ imposes the low reference value Ir2, and the current in the coil is established just below this new reference value. During this time t2, the frequency of the chopper is fixed, by the logic circuit 10, at a higher value, for example 15 kHz. The control circuit 6 is for example a flip-flop which receives from the logic circuit 10̸ the switching orders by the wire 13 and the re-switching orders by the wire 14.

At the end of duration t2 there is a pause period of duration t3. During this pause, transistor 5 is blocked. At the same time, the reference value for the intensity is brought to the value necessary for the time period t4; this Ir3 value is approximately half of the Ir2 reference value.

During the pause period t3, the current in the coil depends only on the position of the movable armature, and on the reference value Ir2 imposed before the pause.

If the armature is not glued, the inductance of the contactor is low and the current decreases rapidly and cancels. This is the case corresponding to the upper part of FIG. 3. At the end of the duration t3 the current Ib in the coil is practically zero. At the end of the duration t3, the logic circuit 10̸ triggers the opening of the transistor 5. After a short time, in order to mask the transient establishment of comparator 9, the logic circuit 1O examines the output state of comparator 9. The third line of FIG. 3 presents a pulse, in duration t4 , corresponding to the instant of this examination of the output state of the comparator 9. The reference value being always Ir3, if the current in the coil has become practically zero, it has not yet had time to take a value greater than Ir3. The logic circuit 10̸ then finds that the current in the coil is below the reference value Ir3, it deduces therefrom that the movable armature is not stuck, and it triggers a reset pulse (line 4, Figure 3) to general zero which re-triggers the initial process with reference value Ir1. Simultaneously, it sends by its output 15 a signal indicating that the reinforcement is not glued.

If, on the contrary, the movable armature is glued, the inductance of the system is very high and the current in the coil is maintained, decreasing slightly. This is the case corresponding to the lower part of FIG. 3. At the end of the duration t3, the logic circuit triggers the opening of the transistor 5 and, after a short time, examines the output state of the comparator 9. At the time of the pulse shown in the third line of Figure 3, below, the current in the coil is greater than the reference value Ir3. The logic circuit 10̸ then controls the transition to a maintenance phase of a duration (t1 + t2), with the reference value Ir2, and there is no general reset pulse on line 4, but the logic circuit 10̸ sends on its output 15 a signal indicating that the armature is stuck.

In FIG. 3, the durations are not shown on the same scale for clarity of the drawing. By way of illustration, the durations t1 and t2 are each a few tens of milliseconds (68 for example), the duration t3 is a few milliseconds (8.53 for example) and the duration t4 is a few microseconds (16.8 for example). In other words, on the scale of FIG. 3, the duration t4 is practically not visible.

FIG. 2 shows a second embodiment of the device for controlling and controlling a contactor. The same references designate the same elements as in FIG. 1. The main difference comes from the fact that instead of varying the reference according to the stage of operation, three comparators 9, 21, 22 are used, each receiving permanently , a reference, respectively Ir1, Ir2 and Ir3. The output of the first two comparators 9, 21 is applied to an AND gate, 20̸, 18, respectively, which receives from the logic circuit 10̸ a validation pulse during the corresponding duration, respectively t1 and t2. At the output of the AND gates, 20̸ and 18, wires 19 and 17, respectively, transmit to the control circuit 6 the blocking orders of the transistor 5 as a function of the switching of the comparators 9, 21.

The wire 13 always transmits the opening orders of the transistor 5, and the wire 14 transmits the general closing order during the pause time t3.

The third comparator 22 transmits its output state to a buffer memory 23. This memory is read by the logic circuit 10̸ during the pulse, transmitted by the wire 24, which intervenes during the duration t4 and which is shown diagrammatically on the third line of figure 3.

The advantages of the monitoring and control device according to the invention are, in particular, the following. Of the fact that a contactor built to be supplied with alternating current is used, this saves space, weight and consumption. Due to the fact that this contactor is supplied continuously via a chopper, the current in the coil is always in the same direction and the problems associated with the zero current crossing, that is to say the detachment of the armature.

In the usual contactors, the coils are calculated for a given supply voltage, and the coil must be changed if the supply voltage varies by around 10̸%. According to the invention, it is possible to accept, for the same coil, voltage ranges varying in the ratio from 1 to 10̸.

Because the measurement resistor 7 is placed in the immediate vicinity of the negative supply terminal 4, it is traversed by the current only during the opening periods of the chopper, which prevents it from heating.

In order to maintain a practically constant current in the contactor coil during each of the operating stages (calling the armature and maintaining the armature), a chopper with fixed frequency and variable duty cycle is used, which makes it possible to control the impression of noise associated with the operation of the chopper.

During the call period (duration t1), a lower chopper frequency (approximately 1.8 kHz) is used to transmit more power to the coil to ensure bonding of the armature. During the holding period (duration t2), a higher chopper frequency (approximately 15 kHz) is used, beyond the audible range to eliminate the impression of noise linked to the operation of the chopper. Switching between call and hold frequencies for the chopper has at the same time as the switching between call and hold reference values, for the intensity.

Thus, the contactor is supplied with a high power and low frequency supply for calling and bonding the movable armature, and a low power and high frequency supply for maintaining it.

According to the invention, each contactor operating cycle (duration: t1 + t2) is followed by a pause (duration t3) at the end of which the position of the movable armature is checked by comparison of the current in the coil with a reference value. The result of this operation is used by the control system and / or transmitted remotely, and it allows the restarting process to be restarted if the movable armature is not glued. The pause allows the current in the coil to evolve according to the position of the movable armature. Therefore, after the pause, the comparative measurement of the current with respect to the reference value corresponds to an indirect measurement of the inductance of the contactor coil, which is defined by the position of the movable armature. In the context of the invention, the duration t1 has not been defined. This duration can be fixed and determined by the construction characteristics of the contactor. It then corresponds to the duration necessary to attract the movable frame, increased by a safety duration. It can also be variable and end when the movable frame is glued. This supposes that one can determine the moment of bonding of the reinforcement.

Claims (8)

1. A device for controlling an electromechanical contactor having an armature and being constructed to be supplied by alternative current, and for checking of the tight-fitting or remote position of its armature, of the type comprising : an alternative current power supply (3, 4) for serial supply of the contactor coil (1), a transistor (5) functioning, with its control circuit (6), as a chopper, and a resistance (7) coupled to the negative terminal (4); a comparator (9) comparing the value of the current (1b) in the coil (1) with one of the reference values (Ir1, Ir2, Ir3), and a logic circuit (10) defining, for the contactor, a function cycle, characterized in that:

   - the transistor (5) controlling the current in the coil (1) functions, during the coil supply periods, as a chopper having a fixed frequency and a variable cyclic ratio,

   - the common point of the resistance (7) and of the transistor (5) is chosen as measure point (8) for the current (Ib) in the coil (1) during the conduction periods of the transistor (5), and

   - said function cycle comprises a supply period (t1 + t2) during which said logic circuit (10) controls the chopper, and a pause (t3) during which the chopper is blocked and at the end of which the current (1b) in the coil is compared with the smallest one of the reference values (Ir3) for checking the tight-fitting or remote position of the contactor armature.
2. A device as claimed in claim 1, characterized in that, for controlling the contactor, the logic circuit (10) defines, during the contactor supply period (t1 + t2), a first period of pick-up (t1) of the armature, and a second period of catching (t2) of the armature.
3. A device as claimed in claim 1, characterized in that the logic circuit (10) defines besides said smallest reference value (Ir3) utilized for checking of the armature position, two other current reference values (Ir1), Ir2) of which the first one (Ir1) is the reference for the pick-up of the armature and the second one (Ir2) is the reference for the catching of the armature.
4. A device as claimed in claim 1, characterized in that the logic circuit (10) defines a plurality of fixed function frequencies of the chopper, a first one for the pick-up period of the armature and a second one for the catching period.
5. A device as claimed in claim 1, characterized in that two supplementary comparators (21, 22) are provided, every one of said three comparators (9, 21, 22) utilizing one of the reference values (Ir1, Ir2, Ir3) worked out by the logic circuit (22) which transfers its output signal to a buffer memory (23) read by the logic circuit (10).
6. A method for checking the position of the armature of an electromechanical contactor constructed for being supplied by alternative current, of the type being supplied through a direct current chopper, the checking of the tight-fitting or remote position of the contactor armature being carried out by means of an indirect measuring of the inductance in the contactor coil (1), characterized in that:

   - said indirect measurement of the inductance in the contactor coil (1) is carried out at regular time intervals,

   - said indirect measurement takes place at the end of a pause period (t3) during which the chopper is disconnected,

   - said indirect measurement consists in measuring the current in the coil in comparison with a reference current (Ir3).
7. A method as claimed in claim 6, characterized in that, at the end of the pause, the comparison of the current value in the coil (1) and the reference current (Ir3) is carried out with a slight lag in order to mask transient state establishment of the comparator.
8. A method as claimed in claim 6, characterized in that the reference current (Ir3) is about half the mean current (Ir2) passing through the coil (1) and which ensures the catching of the armature.

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