Control circuit for the electromagnetic drive of a switching device, in particular a contactor

Abstract

Drive circuit (10) for a switching device with - a switching element (S) for controlling the current supply to a coil (12) connected in series with the switching element (S) of an electromagnetic drive of the switching device, - a freewheeling circuit (D1, D2) for energy stored in the coil (12); - an energy storage device (C) connected in parallel to the switching element (S) and in series with a component (D2) serving as a switching element for storing energy stored in the coil (12) when the current supply to the coil (12) is switched off, and - a circuit (14) that is coupled to the energy storage device and is supplied with energy by it after the current supply to the coil (12) is switched off and is designed to perform a switching device-specific function after the current supply to the coil (12) is switched off.

Description

[0001] The invention relates to a control circuit for the electromagnetic drive of a switching device, in particular a contactor, and to a switching device with such a control circuit.

[0002] Publications DE 195 39 071 A1 and DE 38 26 087 A1 describe a drive circuit for a switching device or an auxiliary voltage generation using a capacitor according to the state of the art.

[0003] In switching devices such as high-power contactors, the electromagnetic switching actuator comprises one or more coils, a circuit for controlling the coils, and a mechanical arrangement for opening and closing the switching device contacts. In most mechanisms, the contacts are held open by contact and release springs. Only when the coil is energized by the control circuit is a force generated from the coil's magnetic field. This force is dimensioned to overcome the spring forces and set the switching actuator mechanism in motion, thereby closing the switching device contacts. In most mechanisms, the force of the coil's magnetic field must be maintained while the contacts are closed to overcome the spring forces constantly acting on the contacts.When the current through the coil is switched off or interrupted, the spring forces set the switching drive in motion again to open the contacts.

[0004] The forces generated by the springs are usually very large in order to keep the contacts securely in the open state. Therefore, closing the contacts requires a correspondingly strong magnetic field from the coil to generate a sufficiently large force to move the switching mechanism. Since the energy E stored in the coil to generate such a magnetic field Spule , which are determined by the coil inductance L and the coil current I according to formula E Spule = ½ * L * I 2 Since the stored energy cannot be dissipated abruptly when the coil current is switched off, the control circuits of electromagnetic drives in switching devices incorporate freewheeling circuits, which allow the stored coil energy to be converted into heat. Such a freewheeling circuit is found in theFig. The control circuit for an electromagnetic contactor drive is shown in Figure 1.

[0005] In the Fig. In the circuit shown in Figure 1, a coil 12 of the electromagnetic contactor drive, labelled "drive", is connected to a supply voltage U. BThe other terminal of the coil can be connected to a reference potential via a switch S of the control circuit. When switch S is closed, a current flows through coil 12, generating a magnetic field to move the switching actuator to close the contactor contacts. Energy is stored in coil 12 to build up this magnetic field. To open the contactor contacts, switch S is opened again, interrupting the current flow through coil 12. Coil 12 attempts to maintain the current. This causes the voltage drop across coil 12 to reverse polarity, making freewheeling diode D1 conductive and allowing current to flow through it. As a result, the voltage drop across coil 12 becomes so high that suppressor diode D2 also conducts, and the energy stored in coil 12 is converted into heat in the two freewheeling diodes D1 and D2.

[0006] The object of the present invention is now to propose an improved control circuit for the electromagnetic drive of a switching device, in particular a contactor, as well as an improved switching device with such a control circuit.

[0007] This problem is solved by the subject matter of the independent claims. Further embodiments of the invention are the subject matter of the dependent claims.

[0008] One of the underlying concepts of the present invention is to transfer the energy stored in the coil of an electromagnetic drive of a switching device into an energy storage device after the current supply to the coil is switched off by a drive circuit. This energy storage device then makes the transferred energy available for performing a switching device-specific function. The switching device-specific function is designed to be executed for a specific period of time after the coil's current supply is switched off, in particular to continue operating a processor of a switching device, for data communication, for parameter measurement, or for extinguishing arcs.

[0009] One embodiment of the invention relates to a drive circuit for a switching device comprising a switching element for controlling the current supply to a coil of an electromagnetic drive of the switching device connected in series with the switching element, a freewheeling circuit for energy stored in the coil, an energy storage device connected in parallel to the switching element and in series with a component serving as a switching element for storing energy stored in the coil when the current supply to the coil is switched off, and a circuit that is coupled to the energy storage device and is supplied with energy by it after the current supply to the coil is switched off and is configured to perform a switching device-specific function after the current supply to the coil is switched off.

[0010] The switching element connected in series with the energy storage device can be a semiconductor element that becomes conductive after the current supply to the coil is switched off and enables the energy storage device to be charged with the energy stored in the coil, wherein the semiconductor element and the switching element are connected to a reference potential of the drive circuit in such a way that the storage of energy stored in the coil in the energy storage device only takes place when the freewheeling circuits of the freewheeling circuit are active.

[0011] The semiconductor element can, for example, be a suppressor diode dimensioned such that its breakdown voltage is greater than a supply voltage of the drive circuit.

[0012] The circuit coupled to the energy storage device may include a processor that is kept in operation for a certain period of time by the energy stored in the energy storage device, in particular to send and / or receive and / or store data and / or to perform security tasks.

[0013] The circuit coupled to the energy storage device can further be designed to generate at least one magnetic field to assist in extinguishing arcs occurring in the switching device.

[0014] The circuit coupled to the energy storage device can be configured to generate at least one magnetic field to assist in extinguishing arcs occurring in the switching device, and can further include a processor that is kept in operation for a certain period of time by the energy stored in the energy storage device in order to generate the magnetic field with a characteristic adapted to the switching device.

[0015] The circuit coupled to the energy storage device can include a quenching coil to generate at least one magnetic field to assist in extinguishing arcs occurring in the switching device and a diode connected in series with the quenching coil.

[0016] Another embodiment of the invention relates to a switching device, in particular a contactor, with a switching drive having a coil, and a drive circuit according to one of the preceding claims for controlling the switching drive, which is connected to the coil of the switching drive in order to control the current supply to the coil.

[0017] Further advantages and application possibilities of the present invention will become apparent from the following description in conjunction with the exemplary embodiments shown in the drawings.

[0018] The terms and associated reference numerals used in the list of reference numerals at the end are used in the description, claims, summary and drawings.

[0019] The drawings show in Fig. 1 a conventional control circuit for an electromagnetic contactor drive; Fig. 2 an embodiment of a control circuit for an electromagnetic contactor drive according to the invention; and Fig. 3 a partial circuit diagram of a further embodiment of a control circuit for an electromagnetic contactor drive according to the invention.

[0020] In the following description, identical, functionally equivalent, and functionally related elements may be designated with the same reference numerals. Absolute values ​​are given below only as examples and are not to be understood as limiting the invention.

[0021] The in Fig. The drive circuit 10 shown in the invention for an electromagnetic contactor drive differs from the one shown in Figure 2. Fig. The difference in the conventional drive circuit shown in Figure 1 is that in the circuit path parallel to the switch S, a capacitor C is connected as an energy storage device between a suppressor diode D2 serving as a switching element and the reference potential.

[0022] Generally speaking, when switching between Fig. 2. Energy from coil 12 is transferred to another energy storage device after the power supply to the coil is switched off, in the circuit of Fig. 2. The capacitor C is recharged, which is then available for performing contactor-specific functions.

[0023] The capacitance of capacitor C determines the voltage to which it can be charged. The energy balance is calculated according to the following formula: ESpool=ED2+Ecapacitor

[0024] From this relationship, the energy available for executing contactor-specific functions can be calculated. Furthermore, the voltage across capacitor C can be determined.

[0025] In the circuit of Fig. 2 The suppressor diode D2 serves as a switching element, which controls the transfer of the energy stored in the coil 12 into the capacitor C, as will be explained in detail below.

[0026] When switch S is closed, a current flows through coil 12, storing energy in the coil. Coil 12 generates a magnetic field that moves the electromagnetic drive of the contactor, thereby bringing the (not shown) contactor main contacts into a specific state (e.g., closed).

[0027] When switch S is opened, for example to open the contactor main contacts, the freewheeling diode D1 becomes conductive due to the reversing voltage across coil 12, as explained at the beginning, and the suppressor diode D2 also becomes conductive due to the increasing voltage across coil 12, causing the same current i to flow through capacitor C. Antrieb how the flow passes through coil 12.

[0028] The voltage U c The capacitor C can be used depending on the coil current i. Antrieb and the time from opening the switch S t aus up to the time t iL=0 , at which the current through the coil 12 0 is, can be determined according to the following formula: UC=1C∫taustiL=0iDrive⋅dt

[0029] The energy stored in coil 12 is transferred to capacitor C until the energy stored in coil 12 is less than the energy stored in capacitor C, at which point the suppressor diode D2 blocks.

[0030] The energy stored in capacitor C is released during the circuit of Fig. 2 is used to supply a circuit 14, which is connected on one side to the circuit node formed by the series connection of the suppressor diode D2 and the capacitor C, and on the other side to the reference potential. A current therefore flows from the capacitor C into the circuit 14, causing the capacitor C to discharge and the voltage across the capacitor C to drop until the diode D2 becomes conductive again and the remaining energy stored in the coil 12 is transferred into the capacitor C until the diode D2 is again reverse-biased.

[0031] This charging process continues until the coil 12 is completely discharged. The time required for the complete discharge of the coil 12, which is determined in particular by the energy stored in the coil 12 and the power consumption of the circuit 14, dictates how long the circuit 14 can operate and how long its function is available in the contactor.

[0032] For certain applications of a contactor, it is advantageous if the breakdown voltage of the suppressor diode D2 is greater than the operating voltage U. B The contactor is designed to ensure that diode D2 only conducts when coil 12 is switched off. If coil 12 has been discharged via diode D2, the latter blocks again, even if the operating voltage U is applied. B still pending. This can occur, for example, if the contactor is operated in a PLC (Programmable Logic Controller) operating mode.

[0033] Circuit 14 is designed and configured to perform a switching device-specific function after the current supply to the coil is switched off. Examples of such functions are explained below: Tasks such as data communication can be performed for a certain period of time, for example, sending or receiving data. For instance, operating settings can be sent, the contactor can disconnect from a monitoring device when switched off, or data can be received and stored that sets specific operating states of the contactor, which the contactor should be in after being restarted. - Tasks such as measurements can be performed for a certain period of time, for example parameter measurement, in which various parameters of the contactor can be measured and, for example, stored or sent to other units such as a central data processing unit or a control unit, safety functions or the suppression of a re-energizing of the main contacts of the contactor in certain periods of time. - With the help of the energy stored in the capacitor, magnetic fields can be generated in DC contactors, which can help to extinguish an arc between the main contacts of a contactor (this function will be explained in detail later using an exemplary embodiment). Processors can be kept running for a certain period of time, for example to process, store, send, receive and / or perform security tasks. By combining the two aforementioned examples, a magnetic field can be generated to extinguish an electric arc, possessing a specific characteristic tailored to the conditions within the contactor. For instance, a processor can execute a special program that controls a coil for generating such a magnetic field, adjusting the magnetic field to the mechanical design of the contactor using parameters.

[0034] Other examples are conceivable. The function supplied by the energy storage device or capacitor C can be operated depending on the required energy. Functions with low energy requirements remain operational for longer.

[0035] In principle, functions could also be powered by the supply voltage of a contactor. However, in some operating modes of contactors, the supply voltage is used as a "switching signal," meaning that, for example, when the contactor's main contacts are to be opened, the contactor's supply voltage is switched off. In such operating modes, no supply voltage is then available for executing further contactor-specific functions. Furthermore, any existing energy storage devices would be discharged directly. The advantage of the present invention, in contrast, is that the supply for executing contactor-specific functions is only established when the supply to the coil 12 of the contactor's electromagnetic drive is switched off.

[0036] The following section describes a circuit for generating a magnetic field to extinguish a DC arc in a DC contactor as a functional example of circuit 14. An embodiment of such a circuit is shown in Fig. Figure 3 shows the circuit 14, which includes a quenching coil 16 for generating a magnetic field to extinguish an arc. A diode D3 prevents the capacitor C and the quenching coil 16 from forming a resonant circuit.

[0037] As soon as energy is transferred from coil 12 to capacitor C and the voltage across capacitor C rises, a current is simultaneously driven through the quenching coil 16, which generates a magnetic field. The quenching coil 16, which may have a core arrangement, is installed in the contactor such that the magnetic field generated by the quenching coil 16 is approximately perpendicular between the open main contacts of the contactor. The contactor can be designed or operated such that the magnetic field between the main contacts is only generated by the quenching coil 16 when the main contacts of the contactor open. Therefore, the magnetic field is only generated when needed. The diode D4 of circuit 14 is a freewheeling diode that, after an arc has been extinguished and no current flows from capacitor C through the quenching coil 16, converts the energy stored in the quenching coil 16 into heat.

[0038] The magnetic field generated by the quenching coil 16 between the open main contacts, i.e., between the main current path of the contactor, causes the arc to be expelled from the contact area, preferably into an arc quenching chamber. An arc is a plasma flow, i.e., moving charge carriers. If these move perpendicularly through the magnetic field of the quenching coil 16, the Lorentz force F acts on the charge carriers. Lösch (Q: charge of the moving charge carriers, v Ladungsträger : Velocity vector of the charge carriers, B Lösch : Magnetic field vector of the magnetic field generated by the extinguishing coil 16): F→Lo¨sch=Q⋅(v→Charge carrier×B→Lo¨sch)

[0039] A force F therefore acts on the charged particles of the electric arc. Lösch , which is perpendicular to the direction of flow or movement and simultaneously to the magnetic field and is typically directed into an extinguishing chamber of the contactor.

[0040] The circuit 14 can also be extended, for example, by a control such as a processor, which adjusts the generation of the magnetic field by the quenching coil 16, in particular generating the magnetic field with a characteristic matched to the contactor.

[0041] The present invention allows the energy stored in the coil of an electromagnetic drive of a switching device to be used, after the current supply to the coil is switched off, to perform switching device-specific functions, such as data communication or the generation of a magnetic field for deflecting arcs in arc-quenching chambers. The invention is particularly suitable for use in high-power DC switching devices, and more generally in DC switching devices, as well as in switching devices with additional functions such as deactivating communication-enabled switching devices upon shutdown, implementing safety functions, or suppressing restarts within specific time periods. Reference sign 10 Drive circuit for a switching device 12 Coil of an electromagnetic drive of the switching device 14 Circuit for executing a switching device-specific function 16 Extinguishing coil S Schalter C Kondensator D1 Diode D2 Suppressordiode D3 Diode D4 Diode

Claims

[1] Drive circuit (10) for a switching device with - a switching element (S) for controlling the current supply to a coil (12) connected in series with the switching element (S) of an electromagnetic drive of the switching device, - a freewheeling circuit (D1, D2) for energy stored in the coil (12); - an energy storage device (C) connected in parallel to the switching element (S) and in series with a component (D2) serving as a switching element for storing energy stored in the coil (12) when the current supply to the coil (12) is switched off, and - a circuit (14) that is coupled to the energy storage device and is supplied with energy by it after the current supply to the coil (12) is switched off and is designed to perform a switching device-specific function after the current supply to the coil (12) is switched off. [2] Drive circuit (10) according to claim 1, characterized by, that the component connected in series with the energy storage device (C) and serving as a switching element is a semiconductor element (D2) which becomes conductive after the current supply to the coil (12) is switched off and enables the charging of the energy storage device (C) with the energy stored in the coil (12), wherein the semiconductor element (D2) and the switching element (S) are connected to a reference potential of the drive circuit in such a way that the storage of energy stored in the coil (12) in the energy storage device (C) only takes place when the freewheeling circuits of the freewheeling circuit (D1, D2) are active. [3] Drive circuit (10) according to claim 2, characterized by , that the semiconductor element (D2) is a suppressor diode dimensioned such that its breakdown voltage is greater than a supply voltage of the drive circuit (10). [4] Drive circuit (10) according to claim 1, 2 or 3, characterized bythat the circuit coupled to the energy storage device includes a processor which is kept in operation for a certain period of time by the energy stored in the energy storage device, in particular to send and / or receive and / or store data and / or to perform security tasks. [5] Drive circuit (10) according to claim 1, 2, 3 or 4, characterized by , that the circuit (14) coupled to the energy storage device is designed to generate at least one magnetic field to assist in extinguishing arcs occurring in the switching device. [6] Drive circuit (10) according to claim 1, 2 or 3, characterized by, that the circuit (14) coupled to the energy storage device is configured to generate at least one magnetic field to assist in extinguishing arcs occurring in the switching device, and furthermore includes a processor which is kept in operation for a certain time by the energy stored in the energy storage device in order to generate the magnetic field with a characteristic adapted to the switching device. [7] Drive circuit (10) according to claim 5 or 6, characterized by , that the circuit (14) coupled to the energy storage device has a quenching coil (16) for generating the at least one magnetic field to assist in the quenching of arcs occurring in the switching device and a diode (D3) connected in series with the quenching coil (16). [8] Switching device, in particular contactor, with - a switching drive comprising a coil (12), and - a drive circuit (10) according to one of the preceding claims for controlling the switching drive, which is connected to the coil (12) of the switching drive in order to control the current supply to the coil (12).

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