Method for closing a contactor and contactor with temperature compensation

Abstract

The invention relates to a method for closing the contacts of an electrical switching device during the make process, wherein the electrical switching device has an electromechanical drive device which has a coil and an armature movable between an open position and a closed position, and wherein the coil is energized to close the contacts of the electrical switching device. According to the invention, a constant first voltage is first applied to the coil for a first duration and a measured value is determined, wherein either the first duration is fixedly pre-given and the measured value is a current value which is determined by measuring the current flowing in the coil at the end of the first duration, wherein the first duration and the first voltage are selected such that the armature is not set in motion during the first duration, or the first voltage is applied to the coil until a specific current value of the current flowing in the coil is reached, wherein the first duration is the duration until this specific current value is reached, wherein the first duration represents the measured value, and wherein the first voltage is selected such that the armature is not set in motion during the first duration, wherein a suitable second voltage is specified according to the measured value, the second voltage being greater than the first voltage and being applied to the coil during a second duration in order to move the armature from the open position to the closed position.

Description

Field of the Invention

[0001] The present invention relates to a method for closing the contacts of an electrical switching device during the make process. Here, the electrical switching device has an electromechanical drive device having a coil and an armature movable between an open position and a closed position, wherein the coil is energized to close the contacts of the electrical switching device. Here, the armature of the electromechanical drive device is connected to the movable contact of the electrical switching device. The present invention furthermore relates to an electrical switching device. Background Art

[0002] Electrical switching devices, in particular high-power contactors, sometimes suffer high temperature fluctuations in many application areas. For example, this applies to high-power contactors used in rail vehicles, motor vehicles or outdoor installations. In addition, the coils of electromagnetic drive devices may suffer very large temperature fluctuations during operation solely due to self-heating.

[0003] In rail applications, the temperature bandwidth ranges from about -40 °C in Siberia to 110 °C in certain desert regions. Here, the resistance of the coil changes by a factor of 1.8 ( sich um den Faktor 1,8). If no compensation is made, the pull-in current, i.e., the current flowing in the coil when closing the contacts, and the switching behavior of the switching device change accordingly. In the cold state, due to the lower resistance, a faster pull-in occurs, which may lead to increased bouncing of the contacts of the electrical switching device during closing and, in principle, to increased mechanical loading of the components. At very high temperatures, the contacts may not be closed quickly enough, so that chatter phenomena may occur and increased wear due to the arcs occurring may occur.

[0004] If no temperature compensation is made, the drive device must thus be designed more robustly and thus larger. This results in a relatively heavy and expensive switching device.

[0005] And if temperature compensation should be made, a lower voltage must be applied to the coil at low temperatures and a higher voltage at higher temperatures in order to be able to ensure a uniform switching behavior or a uniform make time or pull-in time over the entire temperature range. For this purpose, the temperature prevailing in the coil or the coil resistance related thereto must be detected. This can be done, for example, by means of a temperature sensor. However, additional temperature sensors result in a more costly construction and make the manufacture of the electrical switching device expensive.

[0006] However, there are already methods for measuring the coil inductance and the coil resistance without directly determining the coil temperature. Such a method is known, for example, from US20180174786 A1. However, this method requires a relatively high computational efficiency and thus presupposes the use of an expensive microprocessor. SUMMARY OF THE INVENTION

[0007] Accordingly, it is an object of the present invention to provide a method of the type mentioned at the beginning which allows simple temperature compensation with low hardware requirements and in particular without the need for a temperature sensor and which does not prolong the actuation process in an adverse manner.

[0008] This object is achieved by a method for closing the contacts of an electrical switching device during the closing process.

[0009] Thus, in a method for closing the contacts of an electrical switching device during the closing process, if first a constant first voltage U1 is applied to the coil for a first duration T1 and a measured value is determined, where - either the first duration T1 is fixedly pre-given and the measured value is a current value I Mess , the current value is determined by measuring the current flowing in the coil at the end of the first duration T1, where the first duration T1 and the first voltage U1 are selected such that the armature is not set in motion during the first duration T1,

[0010] - or the first voltage U1 is applied to the coil until a specific current value I Soll is reached in the current flowing in the coil, where the first duration T1 is the duration until this specific current value I Soll is reached, where the first duration T1 represents the measured value, and where the first voltage U1 is selected such that the armature is not set in motion during the first duration T1,

[0011] where a suitable second voltage U2 is specified according to the measured value so determined, the second voltage being greater than the first voltage U1 and being applied to the coil for a second duration T2 in order to move the armature from the open position to the closed position,

[0012] then there is a solution to the object according to the invention.

[0013] The idea of the present invention is based on the following known equation for the current through a coil after the application of a voltage (which is valid as long as the armature does not move):

[0014] where The voltage U applied to the coil,

[0015] R (temperature-dependent) coil resistance,

[0016] L Inductance of the coil when the armature is in the starting position.

[0017] If the parameters L, I, U, and t are known, the coil resistance R can be calculated therefrom, which in turn depends on the temperature. However, according to the invention, the actual calculation of the coil resistance is not required. Only the measured value related to the coil resistance and thus to the temperature is determined.

[0018] If a first duration T1 is fixedly pre-given, then the measured value is the current value I Mess , which occurs at the end of the first duration T1. Then, according to this current measurement value I Mess a voltage U2 is specified, and finally the coil is loaded with this voltage in order to attract the armature, that is, in order to move the armature from the open position to the closed position and thereby close the contact. The optimal pick-up voltage U2 at a specific current measurement value I Mess can, for example, be determined in advance by corresponding measurement series according to experiments and stored in the memory of the control device of the switching device.

[0019] The first duration T1 must be chosen such that the armature does not move yet during the first duration. Otherwise, the armature reaction occurring in the magnetic field during the movement of the armature will distort the current measurement at the end of the first duration and the above equation will no longer apply. The first duration must be long enough so that the final values of the current measurement - caused by the change in the resistance of the coil due to temperature influence (bedingt) - are so far apart at the temperature upper limit and the temperature lower limit that a sufficiently large measurement range is achieved. Here, the measurement accuracy and resolution of the measuring device for the coil current should be considered. The first voltage U1 applied to the coil during the first duration T1 should be chosen as large as possible so that the current flowing through the coil during the first duration becomes as large as possible, and so that no armature movement occurs during the first duration at the lowest operating temperature and taking into account the tolerances.

[0020] On the other hand, the first duration should be as short as possible so that the switching-on process is not unnecessarily delayed.

[0021] Instead of the above determination of the measured value at a fixedly pre-given first duration T1, a fixed current limit I to be reached can also be specified Soll . In this case, the measured value related to the temperature and thus to the coil resistance is the first duration T1 that elapses until the current limit I is reachedSoll up to. However, since the coil current must be measured throughout the first duration T1, this second alternative should be implemented slightly more expensively compared to the first alternative. It goes without saying that even in this second alternative, the first voltage U1 must first be kept constant until a pre-given current value I is reached. Soll up to, and secondly the first voltage U1 or the current value I to be reached must be specified. Soll such that the armature is not yet set in motion until the current limit I is reached. Soll up to.

[0022] In both of the above cases, the current rises throughout the first duration T1. This means that the first duration T1 is not long enough for a stable final current to possibly occur in the coil. In this case, although the resistance can be determined quite easily using R = U / I. However, the measurement time required for this would be significantly longer than the entire common pull-in process of the switching device and would therefore be unacceptable. Thus, a great advantage of the method according to the invention is that the pull-in process is negligibly extended.

[0023] According to the invention, a constant first voltage U1 is applied to the coil during the first duration T1. This means that the current flowing in the coil is not regulated. The constant voltage is applied to the coil throughout the first duration T1.

[0024] The invention allows for simple temperature compensation without costly and expensive hardware. In particular, no temperature sensor is required to carry out the method according to the invention. Only a corresponding current measuring device is needed in order to be able to measure the current flowing in the coil. Such a current measuring device already exists in an electrical switching device having a holding current regulation after the switching-on process. A small and low-cost microcontroller can be used to carry out the method.

[0025] The invention is particularly suitable for electrical contactors.

[0026] Advantageous embodiments of the method according to the invention are the subject of other embodiments.

[0027] According to a preferred embodiment of the invention, the first duration T1 is fixedly pre-given, where the measured value is a current measurement value I Mess which is determined by measuring the current flowing in the coil at the end of the first duration T1, and where the first duration T1 and the first voltage U1 are selected such that the armature is not set in motion during the first duration T1. As already described above, this embodiment can be implemented more simply than an alternative with a fixedly pre-given current limit I Soll is.

[0028] According to another preferred embodiment of the present invention, the second duration immediately follows the first duration. This ensures a short closing time. When determining or prescribing the second voltage U2 applied to the coil after the expiration of the first duration T1 in order to move the armature from the open position to the closed position and thereby close the contact, the current value of the coil current that has been reached at the end of the first duration and thus forms the starting value of the pull-in phase during the second duration T2 must be taken into account here.

[0029] According to another preferred embodiment of the present invention, the second voltage U2 is constant during the second duration T2. This significantly simplifies the method according to the present invention. However, theoretically it is conceivable that a specific voltage characteristic curve is applied during the second duration, and the parameters of the voltage characteristic curve are prescribed according to the determined measured values. In the sense of this embodiment, a constant voltage is also understood as the average voltage adjusted by pulse width modulation during the second duration. In another embodiment of the present invention, the second voltage is prescribed according to the measured values such that the armature always reaches the same speed regardless of the temperature of the coil when closing the contact. The pull-in voltage U2 required in the case of specific temperature-related measured values can be determined experimentally through corresponding measurement series. For this purpose, for example, the switching device can be heated or cooled accordingly, where not only the current measured value I at the end of the first duration T1

[0030] but also the switching behavior during the second duration T2 at different pull-in voltages is subsequently determined. Mess Moreover, the switching behavior during the second duration T2 at different pull-in voltages is subsequently determined.

[0031] In an alternative embodiment, the second voltage is prescribed according to the measured values such that the armature is always moved to the closed position in the same duration regardless of the temperature of the coil when closing the contact. This means that the duration until the contact is closed should always be the same length. Even in this embodiment, the required pull-in voltage U2 can be determined experimentally in the case of specific temperature-related measured values.

[0032] According to another preferred embodiment of the method according to the invention, the second voltage U2 is specified based on the measured value by reading a preset value from a table stored in a memory. Thereby, complex calculations are not required during the switching-on process. A beneficial and simple microcontroller can be used for control. The mentioned table is furthermore preferably stored in the memory for controlling the used microcontroller. For example, specific values of the pull-in voltage (second voltage U2) can be stored in the table or else other preset values suitable for control can also be stored. For example, instead of specific voltage values, pulse width modulation preset values can be stored. Since the voltage values U1 and U2 are preferably adjusted by means of pulse width modulation. The possible fluctuations of the supply voltage are preferably compensated by corresponding changes in the pulse width modulation here. For the method according to the invention, it is not necessary to determine specific values of the resistance and / or temperature of the coil during operation. Only the relationship between the measured value and the preset value or the voltage value U2 derived from the resistance or temperature is decisive.

[0033] Alternatively, an approximation function for calculating the preset value can also be derived from specifically determined preset values or from the value of the second voltage U2 based on the measured value, such that instead of the complete table, only the parameters of the calculation criterion have to be transmitted to the memory for controlling the used microcontroller. Although this requires slightly higher computational efficiency, less memory is needed. Even in this embodiment case, the possible fluctuations of the supply voltage are preferably compensated by corresponding changes in the pulse width modulation.

[0034] The value for the pull-in voltage U2 or the above-mentioned preset value belonging to a specific measured value is preferably determined for a larger temperature range, for example for a temperature range from a maximum of 0 °C to at least 50 °C, further preferably for a temperature range from a maximum of -20 °C to at least 80 °C, further 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 criterion derived therefrom is transmitted to the memory of the microcontroller. For satisfactory temperature compensation, it is sufficient if the values are determined for discrete temperatures with an increment (Delta) of, for example, 1 °C or also with a larger difference of, for example, 5 °C. However, since the specific temperature is ultimately irrelevant for the method, the input parameter into the table is the measured value. Therefore, for the table, measured values with a constant increment are preferably used, which is not reflected in a constant increment of the temperature.

[0035] After the expiration of the second duration, the control device can switch to the holding mode. Since less force is required to hold the armature in the closed position than to pull in the armature, the power can be reduced. According to another embodiment of the method according to the invention, the second duration T2 is fixedly pre-given, thereby further simplifying the method. However, preferably alternatively it can be provided that the second duration T2 ends if it is recognized by a suitable sensor system or evaluation that the armature is in the closed position. Even in this embodiment of the method according to the invention, the control device can subsequently switch to the holding mode.

[0036] The invention further provides an electrical switching device, the control device of which is designed and set up to carry out the method according to the invention.

[0037] According to a preferred embodiment of the electrical switching device, the control device has a microcontroller in which a table with possible measured values and the associated preset values is stored, or according to an alternative embodiment, calculation criteria for calculating the preset values from the measured values are stored. Description of the Drawings

[0038] The invention will be explained in more detail below with reference to the drawings.

[0039] Figure 1 Schematic illustration of a contactor according to the invention according to an embodiment,

[0040] Figure 2 shows Figure 1 the circuit diagram of the contactor according to the invention, and

[0041] Figure 3 shows the current characteristic curve in the coil of the contactor according to the invention.

[0042] For the following discussion, the same parts are marked with the same reference numerals. If reference numerals are included in the drawings that are not discussed in more detail in the associated drawing description, reference is made to the previous or subsequent drawing description. Detailed Description of the Invention

[0043] Figure 1Schematic diagram of contactor 1 according to an embodiment of the present invention. The contactor 1 has a housing 10 shown only in part and a contact part with double breaks. The contact part consists of two fixed contacts 5 and a movable contact bridge 6. The contact bridge 6 is placed at the contact carrier 9 via a contact pressure spring 7, and the contact carrier 9 is connected to the movable armature 3 of the electromagnetic drive device of the contactor 1 via an insulating rod 4. The armature 3 of the electromagnetic drive device and the yoke 8 are at least partially surrounded by the coil 2 of the electromagnetic drive device. 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.

[0044] Figure 2 Shows Figure 1 Circuit diagram of the contactor according to the present invention. The current measuring device 12 is used to measure the current flowing in the coil 2 during operation. The component 15 is a voltage measuring device for measuring the supply voltage U Vers which may be subject to certain fluctuations. The measured parameters of the current measuring device 12 and the voltage measuring device 15 are fed to the microcontroller 11, which processes these two measured parameters and generates a control signal for the circuit breaker 17 from them, and controls the coil 2 through the control signal. The voltage supply device 16 for the microcontroller 11, the two measuring devices 12 and 15 and, if necessary, the driver for controlling the circuit breaker 17 is connected to the supply voltage U Vers . In addition, a freewheeling diode 18 is located at the coil 2.

[0045] The supply voltage is switched on by the supply voltage switch 14.

[0046] Figure 3 Shows the characteristic curve of the current I flowing in the coil 2 over time t. The closing process is divided into two stages. In the first stage, during the first duration T1, a constant first voltage U1 is applied to the coil 2. In the embodiment described here, the first duration T1 is fixedly preset, and the resulting current value I in the coil 2 is measured at the end of the first duration T1 Mess . Here, the first voltage U1 and the first duration T1 are selected such that the armature is not set in motion during the first duration T1.

[0047] Then, according to the measured current value I related to the coil temperature Mess, a suitable second voltage U2 is specified, which is greater than the first voltage U1 and is applied to the coil 2 during a second duration T2 immediately following the first duration T1 in order to move the armature 3 from the open position to the closed position and thereby close the contact. Thus, the second duration T2 represents the second stage of the closing process. For example, the second voltage U2 belonging to a specific current measurement value I is read from a table stored in the microcontroller. Mess of the second voltage U2.

[0048] After the closing process has ended, the control of the contactor switches to the holding mode. The holding mode is maintained during a third duration T3.

[0049] List of reference numerals

[0050] 1 Electrical switching device

[0051] 2 Coil

[0052] 3 Armature

[0053] 4 Insulating rod

[0054] 5 Fixed contact

[0055] 6 Contact bridge

[0056] 7 Contact pressure spring

[0057] 8 Yoke

[0058] 9 Contact carrier

[0059] 10 Housing

[0060] 11 Microcontroller

[0061] 12 Current measuring device

[0062] 13 Return spring

[0063] 14 Supply voltage switch

[0064] 15 Voltage measuring device

[0065] 16 Voltage supply device

[0066] 17 Circuit breaker

[0067] 18 Idle diode

[0068] t Time

[0069] T1 First duration

[0070] T2 Second duration

[0071] T3 Third duration

[0072] U Vers Power supply voltage

[0073] U1 First voltage

[0074] U2 Second voltage

[0075] I Current

[0076] I Mess Measured value of current

[0077] I Soll Predetermined current value

[0078] R Coil resistance.

Claims

1. A method for closing the contacts (5, 6) of an electrical switching device (1) during the make process, wherein the electrical switching device (1) has an electromechanical drive device having 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 first a first voltage U1 is applied to the coil (2) for a first duration T1, wherein the first voltage U1 is constant, and a measured value is determined, and wherein a second voltage U2 is specified based on the measured value, the second voltage being greater than the first voltage U1 and being applied to the coil (2) for a second duration T2 in order to move the armature (3) from the open position to the closed position, wherein - Either the first duration T1 is fixedly pre-given, and the measured value is a current measurement value I Mess , the current measurement value is determined by measuring the current flowing in the coil (2) at the end of the first duration T1, and the first duration T1 and the first voltage U1 are selected such that the armature (3) is not set in motion during the first duration T1 - Either the first voltage U1 is continuously applied to the coil (2) until the rated current value I of the current flowing in the coil (2) is reached Soll wherein the first duration T1 is the duration until the rated current value I is reached Soll wherein the first duration T1 is a measured value, and the first voltage U1 is selected such that the armature (3) is not set in motion during the first duration T1 the first duration T1 is selected such that the current rises throughout the first duration T1 and no stable final current occurs in the coil during the first duration T1.

2. The method according to claim 1, wherein The first duration T1 is fixedly pre-given, and the measured value is a current measurement value I Mess , the current measurement value is determined by measuring the current flowing in the coil (2) at the end of the first duration T1, wherein the first duration T1 and the first voltage U1 are selected such that the armature (3) is not set in motion during the first duration T1.

3. The method according to claim 1 or 2, characterized in that, The second duration T2 immediately follows the first duration T1.

4. The method according to claim 1 or 2, characterized in that, The second voltage U2 is constant during the second duration T2.

5. The method according to claim 1 or 2, characterized in that, The second voltage U2 is specified based on the measured value such that the armature (3) always reaches the same speed regardless of the temperature of the coil (2) during closing of the contacts (5, 6).

6. The method according to claim 1 or 2, characterized in that, The second voltage U2 is specified based on the measured value such that the armature (3) is always moved to the closed position in the same duration regardless of the temperature of the coil (2) during closing of the contacts (5, 6).

7. The method according to claim 1 or 2, characterized in that, The second voltage U2 is specified based on the measured value by reading a preset value from a table stored in a memory or by applying a calculation criterion to calculate the preset value from the measured value.

8. The method according to claim 1 or 2, characterized in that, The second duration T2 is fixedly pre-given.

9. The method according to claim 1 or 2, characterized in that, If a suitable sensor system or evaluation recognizes that the armature is in the closed position, the second duration T2 ends.

10. An electrical switching device (1), which has contacts (5, 6) and an electromagnetic drive device for closing the contacts (5, 6), wherein the electromechanical drive device has a coil (2) and an armature (3) movable between an open position and a closed position, wherein the electrical switching device furthermore 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 device, characterized in that, The control device is designed and set up to carry out the method according to any one of claims 1 to 9.

11. The electrical switchgear (1) according to claim 10, characterized in that, The control device has a microcontroller (11), and a table with possible measured values and corresponding preset values or a calculation criterion for calculating the preset value from the measured value is stored in the microcontroller.

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