Method for closing a contactor and contactor with temperature compensation

Abstract

The present invention relates to a method for closing the contacts of an electrical switching device (1) during a switching-on process, wherein the electrical switching device (1) has an electromechanical drive with a coil (2) and an armature (3) movable between an open position and a closed position, and wherein the coil (2) is energized to close the contacts of the electrical switching device (1), wherein initially, during a first time period T1, a first voltage U1 is applied to the coil (2) and a measured value is determined, wherein, depending on the measured value, a suitable second voltage U2 is determined, which is greater than the first voltage U1 and is applied to the coil (2) during a second time period T2 in order to move the armature (3) from the open position to the closed position. According to the invention, it is provided that the first voltage U1 is constant, and wherein - either the first time period is fixed and the measured value is a current value which is determined at the end of the first time period by measuring the current flowing in the coil (2), wherein the first time period and the first voltage are selected such that the armature (3) is not set in motion during the first time period, - or the first voltage is applied to the coil (2) until a specific current value of the current flowing in the coil is reached, wherein the first time period is the time period until this specific current value is reached, wherein the first time period represents the measured value, and wherein the first voltage is selected such that the armature (3) is not set in motion during the first time period, wherein the first time period T1 is selected such that the current increases during the entire first time period T1 and no stationary final current is established in the coil during the first time period T1.

Description

[0001] The present invention relates to a method for closing the contacts of an electrical switching device during a switching-on process according to the preamble of independent claim 1. The electrical switching device has an electromechanical drive with a coil and an armature which can be moved between an open position and a closed position, wherein the coil is energized to close the contacts of the electrical switching device, wherein initially a first voltage U1 is applied to the coil (2) during a first time period T1 and a measured value is determined, wherein a suitable second voltage U2 is determined as a function of the measured value, which is greater than the first voltage U1 and which is applied to the coil (2) during a second time period T2 in order to move the armature (3) from the open position to the closed position.The armature of the electromechanical drive is connected to a movable contact of the electrical switching device. The present invention further relates to an electrical switching device according to the preamble of independent claim 10.

[0002] A switching device according to the preamble of claim 1 is known from the document US 10,101,393 B2.

[0003] Electrical switching devices, especially high-performance contactors, are sometimes exposed to significant temperature fluctuations in many applications. This applies, for example, to high-performance contactors used in railway vehicles, motor vehicles, or outdoor installations. Furthermore, the coil of the electromagnetic drive can be exposed to very large temperature fluctuations simply due to its own heating during operation.

[0004] In railway applications, the temperature range extends from approximately -40°C in Siberia to 110°C in certain desert regions. The electrical resistance of the coil changes by a factor of 1.8. If no compensation is made, the pickup current - the current that flows in the coil when the contacts close - and the switching behavior of the switching device also change accordingly. In cold conditions, the pickup occurs more quickly due to the lower resistance, which can lead to increased bounce of the contacts of the electrical switching device when closing and, more generally, to increased mechanical stress on the components. At very high temperatures, the contacts may not close quickly enough, which can lead to fluttering and increased wear due to arcing.

[0005] If temperature compensation is not implemented, the drive must be designed more robustly and therefore larger. This results in comparatively heavy and expensive switching devices.

[0006] If, however, temperature compensation is required, a lower voltage must be applied to the coil at low temperatures and a higher voltage at higher temperatures to ensure consistent switching behavior and a consistent turn-on time or pull-in time across the entire temperature range. For this purpose, the temperature prevailing in the coil or the dependent coil resistance must be measured. This can be achieved, for example, using a temperature sensor. However, an additional temperature sensor results in a more complex design and increases the cost of manufacturing the electrical switching device.

[0007] However, there are already methods for measuring coil inductance and coil resistance without directly determining the coil temperature. One such method is known, for example, from US 20180174786 A1. However, such methods require comparatively high computing power and therefore require the use of expensive microprocessors.

[0008] The object of the present invention is therefore to provide a method of the type mentioned at the outset which allows simple temperature compensation with low hardware requirements and in particular without the need for a temperature sensor and which does not disadvantageously prolong the tightening process.

[0009] The problem is solved by the features of independent claim 1.

[0010] Accordingly, in a method according to the preamble of independent claim 1, the object is achieved according to the invention if the first voltage U1 is constant, and wherein - either the first time period T1 is fixed and the measured value is a current value I Mess which is determined at the end of the first time period T1 by measuring the current flowing in the coil, the first time period T1 and the first voltage U1 being selected such that the armature is not set in motion during the first time period T1, - or the first voltage U1 is applied to the coil until a certain current value I Soll of the current flowing in the coil is reached, the first time period T1 being the time until this specific current value I is reached Sollwherein the first time period T1 represents the measured value, and wherein the first voltage U1 is selected such that the armature is not set in motion during the first time period T1, wherein the first time period T1 is selected such that the current increases during the entire first time period T1 and no stationary final current is established in the coil during the first time period T1.

[0011] The idea of the present invention is based on the following well-known equation for the current through a coil after applying a voltage (valid as long as the armature is not moving): I(t)=UR(1−e−tτ)with τ=LR U is the voltage applied to the coil, R is the (temperature-dependent) coil resistance, L is the inductance of the coil with the armature in the initial position.

[0012] If the quantities L, I, U, and t are known, the coil resistance R can be calculated, which in turn depends on the temperature. However, the actual calculation of the coil resistance is not necessary according to the invention. Only a measured value dependent on the coil resistance and thus on the temperature is determined.

[0013] If the first time period T1 is fixed, this measured value is the current value I Mess , which occurs at the end of the first time period T1. Depending on this current measurement value I Mess The voltage U2 is then determined, which is ultimately applied to the coil to attract the armature, i.e., to move the armature from the open position to the closed position and thereby close the contacts. The optimal pull-in voltage U2 for a specific current measurement value I Messcan, for example, be determined experimentally beforehand by means of appropriate series of measurements and stored in a memory of a control system of the switching device.

[0014] The first time period T1 must be selected so that the armature is not moving during the initial time period. Otherwise, the armature reaction occurring when the armature moves in the magnetic field would falsify the current measurement at the end of the initial time period, and the above equation would no longer apply. The initial time period must be long enough so that the final values of the current measurement—due to the change in coil resistance due to temperature influences—are sufficiently far apart at the upper and lower temperature limits to achieve a sufficiently wide measuring range. The measurement accuracy and resolution of the coil current measuring device must be taken into account.The first voltage U1, which is applied to the coil during the first time period T1, should be selected to be as large as possible so that the current flowing in the coil becomes as large as possible during the first time period, in such a way that during the first time period at the lowest operating temperature and taking tolerances into account, no movement of the armature occurs.

[0015] On the other hand, the initial time period should be as short as possible so that the switching-on process is not unnecessarily delayed.

[0016] As an alternative to the above-described measurement determination with a fixed first time period T1, a fixed current limit I Soll to be reached. In this case, the measured value, which depends on the temperature and thus on the coil resistance, is the first time period T1 that elapses until the current limit I Sollis reached. However, compared to the first alternative, this second alternative is somewhat more complex to implement, since the coil current must be measured during the entire first time period T1. It goes without saying that with this second alternative, the first voltage U1 must be measured until the specified current value I is reached. Soll must be kept constant, and secondly the first voltage U1 or the current value I to be achieved Soll must be set in such a way that the armature is kept at the current limit I Soll has not yet been set in motion.

[0017] In both of the above cases, the current increases throughout the entire first period T1. This means that the first period T1 does not last long enough for a steady-state final current to develop in the coil. Using R = U / l, the resistance could be easily determined in this case. However, the measurement time required for this would be significantly longer than the entire usual pickup process of the switching device and would therefore be unacceptable. A major advantage of the method according to the invention is that the pickup process is not significantly prolonged.

[0018] The present invention allows for simple temperature compensation without complex and expensive hardware. In particular, no temperature sensor is required to implement the inventive method. Only a suitable current measuring device is needed to measure the current flowing in the coil. In electrical switching devices with control of the holding current after the switch-on process, such a current measuring device is already present. A small and cost-effective microcontroller can be used to implement the method.

[0019] The present invention is particularly suitable for electrical contactors.

[0020] Advantageous embodiments of the method according to the invention are the subject of the subclaims.

[0021] According to a preferred embodiment of the present invention, the first time period T1 is fixed, wherein the measured value is a current measured value I Messwhich is determined at the end of the first time period T1 by measuring a current flowing in the coil, wherein the first time period T1 and the first voltage U1 are selected such that the armature is not set in motion during the first time period T1. As already described above, this embodiment is easier to implement than the alternative with a fixed current limit I Soll .

[0022] According to a further preferred embodiment of the present invention, the second time period immediately follows the first time period. This ensures a short on-time. When determining or setting the second voltage U2, which is applied to the coil after the expiration of the first time period T1 in order to move the armature from the open position to the closed position and thereby close the contacts, the current value for the coil current must be taken into account. This current value is already reached at the end of the first time period and thus forms the starting value for the pull-in phase during the second time period T2.

[0023] According to a further preferred embodiment of the present invention, the second voltage U2 is constant during the second time period T2. This significantly simplifies the method according to the invention. However, purely theoretically, it is conceivable to impose a specific voltage curve during the second time period, the parameters of which are determined based on the measured value. A constant voltage in the sense of this embodiment also includes an average voltage set by pulse width modulation during the second time period.

[0024] According to a further embodiment of the present invention, the second voltage is set as a function of the measured value such that the armature always reaches the same speed when closing the contacts, regardless of the coil temperature. The required pull-in voltage U2 for a specific temperature-dependent measured value can be determined experimentally through appropriate series of measurements. For this purpose, the switching device can, for example, be heated or cooled accordingly, with both the measured current value I Mess at the end of the first time period T1, as well as the switching behavior at different pull-in voltages during the second time period T2.

[0025] In an alternative embodiment, the second voltage is set depending on the measured value such that the armature is always moved into the closed position in the same time period when the contacts close, regardless of the coil temperature. This means that the time until the contacts close should always be the same. In this embodiment, too, the required pull-in voltage U2 can be determined experimentally for a specific temperature-dependent measured value.

[0026] According to a further preferred embodiment of the method according to the invention, the second voltage U2 is determined based on the measured value by reading a default value from a table stored in a memory. This eliminates the need for complicated calculations during the switch-on process. An inexpensive and simple microcontroller can be used for control. The table in question is further preferably stored in the memory of the microcontroller used for control. The table can contain, for example, the specific values for the pull-in voltage (second voltage U2) or other default values suitable for control. For example, pulse width modulation default values can be stored instead of the specific voltage values. This is because the voltage values U1 and U2 are preferably set using pulse width modulation.Possible fluctuations in the supply voltage are preferably compensated for by corresponding changes in the pulse width modulation. For the method according to the invention, it is not necessary to determine specific values for the resistance and / or temperature of the coil during operation. The only decisive factor is the relationship between the measured value and the specified value or voltage value U2, derived from the resistance or temperature.

[0027] Alternatively, an approximate function for calculating the specified value based on the measured value can be derived from the specifically determined specified values or from the values for the second voltage U2, so that instead of a complete table, only the parameters of a calculation rule need to be transferred to the memory of the microcontroller used for control. While this requires somewhat higher computing power, it requires less memory. In this embodiment, too, possible fluctuations in the supply voltage are preferably compensated for by corresponding changes in the pulse width modulation.

[0028] The values for the pull-in voltage U2 corresponding to a specific measured value or the above-mentioned preset values are preferably determined for a larger temperature range, for example for a temperature range from a maximum of 0°C to at least 50°C, more preferably for a temperature range from a maximum of -20°C to at least 80°C, more preferably for a temperature range from a maximum of -40°C to at least 110°C, and particularly preferably for a temperature range from a maximum of -60°C to at least 130°C. The values are stored in a table, and either the table itself or the calculation rule derived from it is transferred to the memory of the microcontroller. For satisfactory temperature compensation, it is sufficient if the values are determined for discrete temperatures with a delta of, for example, 1°C or even with larger differences of, for example, 5°C.Since the actual temperatures ultimately play no role in the process, the input variable for the table is the measured value. Therefore, measured values with a constant delta are preferably used for the table, which is not reflected in a constant delta of the temperature.

[0029] After the second time period has elapsed, the control system can switch to a holding mode. Since less force is required to hold the armature in the closed position than to attract the armature, the power can be reduced. According to a further embodiment of the method according to the invention, the second time period T2 is fixed, which further simplifies the method. Alternatively, however, it can preferably be provided that the second time period T2 ends when a suitable sensor or evaluation system detects that the armature is in the closed position. In this embodiment of the method according to the invention, the control system can then also switch to the holding mode.

[0030] The invention further provides an electrical switching device according to the preamble of independent claim 10, the control of which is designed and configured to carry out the method according to the invention.

[0031] According to a preferred embodiment of the electrical switching device, the control unit comprises a microcontroller in which a table with possible measured values and associated default values or, according to an alternative embodiment, a calculation rule for calculating a default value based on the measured value is stored.

[0032] The invention is explained in more detail below with reference to drawings.

[0033] They show: Fig. 1 a schematic representation of a contactor according to the invention according to an embodiment, Fig. 2 a circuit diagram of the contactor according to the invention from Fig. 1, and Fig. 3 the current flow in the coil of the contactor according to the invention.

[0034] In the following explanations, identical parts are designated by identical reference symbols. If a drawing contains reference symbols that are not further explained in the corresponding figure description, reference is made to the preceding or subsequent figure descriptions.

[0035] Fig. 1 shows a schematic representation of a contactor 1 according to the invention in accordance with an exemplary embodiment of the present invention. The contactor 1 has a housing 10, only partially shown, and a contact point with double interruption. The contact point consists of the two fixed contacts 5 and the movable contact bridge 6. The contact bridge 6 is mounted via contact pressure springs 7 on a contact carrier 9, which is connected via the switching rod 4 to the movable armature 3 of the electromagnetic drive of the contactor 1. The armature 3 and the yoke 8 of the electromagnetic drive are at least partially enclosed by the coil 2 of the electromagnetic drive. When the coil 2 is energized by applying a sufficient voltage, the armature 3 is attracted against the force of the return spring 13 acting between the yoke 8 and the armature 3, so that the contacts are closed.

[0036] Fig. 2 shows the circuit diagram of the contactor according to the invention from Fig. 1. A current measuring device 12 is used to measure the current flowing in coil 2 during operation. Component 15 is a voltage measuring device for measuring the supply voltage U Vers , which may be subject to certain fluctuations. The measured values of the current measuring device 12 and the voltage measuring device 15 are fed to a microcontroller 11, which processes the two measured values and generates a control signal for the power switch 17, via which the coil 2 is controlled. The supply voltage U Vers A power supply 16 is connected for the microcontroller 11, the two measuring devices 12 and 15, and, if necessary, for a driver for controlling the power switch 17. A freewheeling diode 18 is also located on the coil 2.

[0037] The supply voltage is switched on via the supply voltage switch 14.

[0038] Fig. Figure 3 shows the course of the current I flowing in coil 2 over time t. The switching-on process is divided into two phases. In the first phase, during the first time period T1, a constant first voltage U1 is applied to coil 2. In the exemplary embodiment presented here, the first time period T1 is fixed, with the resulting current value I at the end of the first time period T1. Mess is measured in coil 2. The first voltage U1 and the first time period T1 are selected such that the armature is not set in motion during the first time period T1.

[0039] Depending on the measured current value I, which depends on the temperature of the coil MessA suitable second voltage U2 is then determined, which is greater than the first voltage U1 and which is applied to the coil 2 for a second time period T2 immediately following the first time period T1, in order to move the armature 3 from the open position to the closed position and thereby close the contacts. The second time period T2 thus represents the second phase of the switching-on process. The voltage at a specific current measurement value I Mess The corresponding second voltage U2 is read out, for example, from a table stored in the microcontroller.

[0040] After the switch-on process is complete, the contactor control system enters a hold mode. This hold mode is maintained for the third time period T3. List of reference symbols 1 electrical switching device 2 coils 3 anchors 4 shift rod 5 fixed contact 6 contact bridge 7 Contact pressure spring 8 yoke 9 contact carriers 10 housings 11 microcontrollers 12 Current measuring device 13 Return spring 14 supply voltage switch 15 Voltage measuring device 16 Power supply 17 circuit breakers 18 Freewheeling diode t time T1 first time period T2 second time period T3 third period U Vers Supply voltage U1 first voltage U2 second voltage I Current I Mess Current measurement value I Soll specified current value R coil resistance

Claims

[1] Method for closing the contacts (5, 6) of an electrical switching device (1) during a switching-on process, wherein the electrical switching device (1) has an electromechanical drive with a coil (2) and an armature (3) movable between an open position and a closed position, and wherein the coil (2) is energized to close the contacts (5, 6) of the electrical switching device (1), wherein initially a first voltage U1 is applied to the coil (2) during a first time period T1 and a measured value is determined, wherein, depending on the measured value, a suitable second voltage U2 is determined, which is greater than the first voltage U1 and which is applied to the coil (2) during a second time period T2 in order to move the armature (3) from the open position to the closed position, characterized by that the first voltage U1 is constant, and where - either the first time period T1 is fixed and the measured value is a current measured value I Mess which is determined at the end of the first time period T1 by measuring the current flowing in the coil (2), wherein the first time period T1 and the first voltage U1 are selected such that the armature (3) is not set in motion during the first time period T1, - or the first voltage U1 is applied to the coil (2) until a certain current value I Soll of the current flowing in the coil (2), wherein the first time period T1 is the time until this specific current value I Sollwherein the first time period T1 represents the measured value, and wherein the first voltage U1 is selected such that the armature (3) is not set in motion during the first time period T1, wherein the first time period T1 is selected such that the current increases during the entire first time period T1 and no stationary final current is established in the coil during the first time period T1. [2] Method according to claim 1, characterized by that the first time period T1 is fixed and the measured value is a current measured value I Mess which is determined at the end of the first time period T1 by measuring the current flowing in the coil (2), wherein the first time period T1 and the first voltage U1 are selected such that the armature (3) is not set in motion during the first time period T1. [3] Method according to claim 1 or 2, characterized by that the second time period T2 immediately follows the first time period T1. [4] Method according to one of claims 1 to 3, characterized by that the second voltage U2 is constant during the second time period T2. [5] Method according to one of claims 1 to 4, characterized by that the second voltage U2 is set as a function of the measured value in such a way that the armature (3) always reaches the same speed when the contacts (5, 6) are closed, regardless of the temperature of the coil (2). [6] Method according to one of claims 1 to 5, characterized by that the second voltage U2 is determined as a function of the measured value in such a way that the armature (3) is always moved into the closed position in the same time period when the contacts (5, 6) are closed, regardless of the temperature of the coil (2). [7] Method according to one of claims 1 to 6, characterized bythat the second voltage U2 is determined on the basis of the measured value by reading out a default value from a table stored in a memory or by applying a calculation rule to calculate the default value on the basis of the measured value. [8] Method according to one of claims 1 to 7, characterized by that the second time period T2 is fixed. [9] Method according to one of claims 1 to 7, characterized by that the second time period T2 ends when a suitable sensor or evaluation detects that the armature is in the closed position. [10] Electrical switching device (1) with contacts (5, 6) and an electromagnetic drive for closing the contacts (5, 6), wherein the electromechanical drive has a coil (2) and an armature (3) movable between an open position and a closed position, wherein the electrical switching device further has a current measuring device (12) for measuring the current flowing in the coil (2), and wherein the electrical switching device (1) has a control, characterized by that the controller is designed and arranged to carry out the method according to one of claims 1 to 9. [11] Electrical switching device (1) according to claim 10, characterized by that the control has a microcontroller (11) in which a table with possible measured values and associated default values or a calculation rule for calculating the default values based on the measured values is stored.

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