Method of closing of a contactor and contactor with temperature compensation

Description

[0001] The present invention relates to a method for closing the contacts of an electrical switching device during a switch-on process according to the preamble of independent claim 1. The electrical switching device comprises an electromechanical actuator with a coil and an armature movable between an open position and a closed position, wherein the coil is energized via a microcontroller to close the contacts of the electrical switching device. The armature of the electromechanical actuator 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] Electrical switching devices, especially high-performance contactors, are exposed to significant temperature fluctuations in many applications. This applies, for example, to high-performance contactors used in railway vehicles, motor vehicles, or in outdoor installations. Furthermore, the coil of the electromagnetic drive can be subject to very large temperature fluctuations simply due to self-heating during operation.

[0003] 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. Without compensation, the pull-in current—the current flowing in the coil when the contacts close—and the switching behavior of the switching device also change accordingly. In cold conditions, the lower resistance results in faster pull-in, which can lead to increased contact bounce during closing and, more generally, to increased mechanical stress on the components. At very high temperatures, the contacts may not close quickly enough, potentially leading to contact flutter and increased wear due to arcing.

[0004] If no temperature compensation is performed, the drive must be more robust and therefore larger. This results in comparatively heavy and expensive switching devices.

[0005] If 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, i.e., a uniform on / off time or pull-in time, across the entire temperature range. For this purpose, the temperature within the coil, or the coil resistance dependent on it, must be measured. This can be done, for example, using a temperature sensor. However, an additional temperature sensor leads to a more complex design and increases the manufacturing cost of the electrical switching device.

[0006] However, methods for measuring coil inductance and resistance without directly determining the coil temperature already exist. One such method is known, for example, from US 20180174786 A1. These methods, however, require comparatively high computing power and therefore necessitate the use of expensive microprocessors.

[0007] A method for temperature compensation when closing electrical contacts is also known from EP 3 018 678 A1. The document shows an electrical switching device comprising an electromagnetic actuator with a coil and an armature movable between an open and a closed position. The coil is energized to open and close the contacts.

[0008] Further related prior art is known from documents EP 1 811 539 A1, EP 3 432 335 A1 and JP 4 862062 B2.

[0009] 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 adversely prolong the dressing process.

[0010] The problem is solved by the features of independent claim 1.

[0011] Accordingly, in a method according to the preamble of independent claim 1, a solution to the problem according to the invention is present if, first, a constant first voltage U 1 is applied to the coil for a first period of time T 1 and a measured value is determined, wherein either the first time period T1 is fixed, and the measured value is a current value Imeasured, which is determined at the end of the first time period T1 by measuring the current flowing in the coil, wherein the first time period T1 and the first voltage U1 are chosen 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 Itarget of the current flowing in the coil is reached, wherein the first time period T1 is the time until this certain current value Itarget is reached, wherein the first time period T1 represents the measured value, and wherein the first voltage U1 is chosen such that the armature is not set in motion during the first time period T1. where the The first time period T1 is selected such that the current increases during the entire first time period T1 and no steady-state final current is established in the coil during the first time period T1.

[0012] The idea of ​​the present invention is based on the following known equation for the current through a coil after applying a voltage (valid as long as the armature does not move): I t = U R 1 − e − t τ mit τ = L R U the voltage applied to the coil, R the (temperature-dependent) coil resistance, L the inductance of the coil with the armature in the starting position.

[0013] 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, according to the invention, the actual calculation of the coil resistance is not necessary. Only a measured value that depends on the coil resistance and thus on the temperature is determined.

[0014] If the initial time period T1 is fixed, this measured value is the current Imeas, which is established at the end of the initial time period T1. Depending on this current Imeas, the voltage U2 is then determined, with which the coil is ultimately applied to attract the armature, that is, to move the armature from the open position to the closed position and thereby close the contacts. The optimal attracting voltage U2 for a specific current Imeas can, for example, be determined experimentally beforehand through corresponding measurement series and stored in the memory of the switching device's control unit.

[0015] The first time period T1 must be chosen such that the armature does not move during this period. Otherwise, the armature reaction occurring when the armature moves within the magnetic field would distort the current measurement at the end of the first time period, and the equation above would no longer be valid. The first time period must be long enough that the final values ​​of the current measurement—due to the change in coil resistance caused by temperature—are sufficiently far apart at the upper and lower temperature limits to achieve a sufficiently large measuring range. The measurement accuracy and resolution of the measuring device for the coil current must be taken into account.The initial voltage U1, which is applied to the coil during the initial time period T1, should be chosen to be as large as possible so that the current flowing in the coil becomes as large as possible during the initial time period, in such a way that no movement of the armature occurs during the initial time period at the lowest operating temperature and taking tolerances into account.

[0016] On the other hand, the initial duration should be as short as possible so that the switching-on process is not unnecessarily delayed.

[0017] As an alternative to the measurement method described above, which uses a fixed initial time interval T1, a fixed current limit Itarget can also be defined. In this case, the measured value, which depends on the temperature and thus on the coil resistance, is the initial time interval T1, the elapsed time until the current limit Itarget is reached. Compared to the first alternative, however, this second alternative is somewhat more complex to implement, as the coil current must be measured throughout the entire initial time interval T1. It goes without saying that, with this second alternative as well, firstly, the initial voltage U1 must be kept constant until the specified current value Itarget is reached, and secondly, the initial voltage U1, or the target current value Itarget, must be set in such a way that the armature is not set in motion until the current limit Itarget is reached.

[0018] In both of the above-mentioned cases, the current increases throughout the entire initial time period T1. This means that the initial time period T1 is not long enough for a steady-state final current to establish itself in the coil. While the resistance could easily be determined using R = U / I in this case, the required measurement time would be significantly longer than the entire typical pull-in process of the switching device and would therefore be unacceptable. A major advantage of the method according to the invention is thus that the pull-in process is not significantly extended.

[0019] During the initial time period T1, a constant initial voltage U1 is applied to the coil according to the invention. This means that the current flowing in the coil is not regulated. The constant voltage is applied to the coil for the entire initial time period T1.

[0020] The present invention enables simple temperature compensation without complex and expensive hardware. In particular, no temperature sensor is required to carry out the method according to the invention. Only a suitable current measuring device is necessary to measure the current flowing in the coil. Such a current measuring device is already present in electrical switching devices with control of the holding current after the switch-on process. A small and inexpensive microcontroller can be used to implement the method.

[0021] The present invention is particularly suitable for use with electrical contactors.

[0022] Advantageous embodiments of the method according to the invention are the subject of the dependent claims.

[0023] According to a preferred embodiment of the present invention, the first time period T1 is fixed, wherein the measured value is a current measurement Imeasured, which 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 simpler to implement than the alternative with a fixed current limit Iset.

[0024] According to a further preferred embodiment of the present invention, the second time period immediately follows the first. This ensures a short switch-on time. When determining or setting the second voltage U2, which is applied to the coil after the first time period T1 has elapsed 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.

[0025] 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 profile 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 means of pulse width modulation during the second time period.

[0026] 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 the contacts close, regardless of the coil temperature. The required pull-in voltage U₂ for a specific temperature-dependent measured value can be determined experimentally by corresponding series of measurements. For this purpose, the switching device can, for example, be heated or cooled accordingly, and then both the measured current Imeasure at the end of the first time period T₁ and the switching behavior at different pull-in voltages during the second time period T₂ are measured.

[0027] In an alternative embodiment, the second voltage is set as a function of the measured value such that the armature is always moved to the closed position within 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 as well, the necessary pull-in voltage U₂ can be determined experimentally for a specific temperature-dependent measured value.

[0028] 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 preset value from a table stored in memory. This eliminates the need for complex calculations during the switch-on process. A cost-effective and simple microcontroller can be used for control. The aforementioned table is preferably stored in the memory of the microcontroller used for control. The table can contain, for example, the specific values ​​for the switch-on voltage (second voltage U₂) or other preset values ​​suitable for control. For instance, pulse-width modulation preset 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. Only the relationship between the measured value and the setpoint value or voltage value U₂, derived from the resistance or temperature, is decisive.

[0029] Alternatively, an approximation function for calculating the target value based on the measured value can be derived from the specifically determined target values ​​or from the values ​​for the second voltage U2. This means 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 slightly more processing power, it uses less memory. In this embodiment as well, any fluctuations in the supply voltage are preferably compensated for by corresponding adjustments to the pulse width modulation.

[0030] The values ​​for the pull-in voltage U₂ corresponding to a specific measured value, or the aforementioned target values, are preferably determined for a wider 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 most 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 formula derived from it is transferred to the microcontroller's memory. 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 specific 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 temperature delta.

[0031] 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 tighten it, the power consumption 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, it is preferable that the second time period T2 ends when a suitable sensor or evaluation detects that the armature is in the closed position. In this embodiment of the method according to the invention as well, the control system can then switch to holding mode.

[0032] The invention further provides an electrical switching device according to the preamble of independent claim 10, the control of which, comprising a microcontroller, is designed and configured to carry out the method according to the invention.

[0033] According to a preferred embodiment of the electrical switching device, the microcontroller contains a table with possible measured values ​​and associated target values ​​or, according to an alternative embodiment, a calculation rule for calculating a target value based on the measured value.

[0034] The invention will be explained in more detail below with reference to the drawings.

[0035] They show: Figure 1 shows a schematic representation of a contactor according to the invention in an exemplary embodiment, Figure 2 shows a circuit diagram of the contactor according to the invention. Figure 1 , and Figure 3 shows the current flow in the coil of the contactor according to the invention.

[0036] In the following explanations, identical parts are designated by the same reference numerals. If a drawing contains reference numerals that are not further explained in the corresponding figure description, reference is made to preceding or subsequent figure descriptions.

[0037] Figure 1Figure 1 shows a schematic representation of a contactor 1 according to an embodiment of the present invention. The contactor 1 has a housing 10, shown only in part, and a double-break contact point. The contact point consists of the two fixed contacts 5 and the movable contact bridge 6. The contact bridge 6 is mounted on a contact carrier 9 via contact compression springs 7. The contact carrier 9 is connected to the movable armature 3 of the electromagnetic drive of the contactor 1 via the switching rod 4. 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.

[0038] Figure 2The circuit diagram of the contactor according to the invention is shown. Figure 1 A current measuring device 12 is used to measure the current flowing in the coil 2 during operation. Component 15 is a voltage measuring device for measuring the supply voltage UVers, which may be subject to certain fluctuations. The measured values ​​from 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, which controls the coil 2. A power supply 16 for the microcontroller 11, the two measuring devices 12 and 15, and optionally for a driver to control the power switch 17, is connected to the supply voltage UVers. A freewheeling diode 18 is also located at the coil 2.

[0039] The supply voltage is switched on via the supply voltage switch 14.

[0040] Figure 3 Figure 1 shows the current I flowing in coil 2 over time t. The switch-on process is divided into two phases. In the first phase, during the first time period T1, a constant initial voltage U1 is applied to coil 2. In the embodiment presented here, the initial time period T1 is fixed, and at the end of this period, the resulting current IMeasure in coil 2 is measured. The initial voltage U1 and the initial time period T1 are chosen such that the armature is not set in motion during the initial time period T1.

[0041] Depending on the measured current value Imeas, which is dependent on the coil temperature, a suitable second voltage U2 is then determined. This voltage is greater than the first voltage U1 and is applied to coil 2 during a second time period T2, which immediately follows the first time period T1. This second voltage moves the armature 3 from the open position to the closed position, thereby closing the contacts. The second time period T2 thus represents the second phase of the switch-on process. The second voltage U2 corresponding to a specific current measurement Imeas is read, for example, from a table stored in the microcontroller.

[0042] After the switch-on process is complete, the contactor control enters a holding mode. This holding mode is maintained for the duration of the third time period, T3. Reference symbol list

[0043] 1 Electrical switching device 2 Coil 3 Armature 4 Switching rod 5 Fixed contact 6 Contact bridge 7 Contact compression spring 8 Yoke 9 Contact carrier 10 Housing 11 Microcontroller 12 Current measuring device 13 Return spring 14 Supply voltage switch 15 Voltage measuring device 16 Power supply 17 Circuit breaker 18 Freewheeling diode t Time T1 First time duration T2 Second time duration T3 Third time duration U Supply voltage U1 First voltage U2 Second voltage I Current I Measured current value I Setpoint current value R Coil resistance

Claims

1. Method for closing the contacts (5, 6) of an electrical switching device (1) during a switch-on process, wherein the electrical switching device (1) has an electromechanical drive with a coil (2) and an armature (3) which can be moved between an open and a closed position, and wherein the coil (2) is energized via a microcontroller (11) in order to close the contacts (5, 6) of the electrical switching device (1), wherein first a first voltage U1 is applied to the coil (2) during a first time period T1, and a measurement value is determined, wherein a suitable second voltage U2 is defined in accordance with the measurement value 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 into the closed position, characterized in that the first voltage U1 is constant, and wherein - either the first time period T1 is fixed, and the measurement value is a current measurement value IMess determined at the end of the first time period T1 by measuring the current flowing in the coil (2), the first time period T1 and the first voltage U1 being selected in such a way that the armature (3) is not set into motion during the first time period T1, - or the first voltage U1 is applied to the coil (2) until a certain current value ISoll of the current flowing in the coil (2) is reached, the first time period T1 being the time period until said certain current value ISoll is reached, the first time period T1 being the measurement value, and the first voltage U1 being selected in such a way that the armature (3) is not set into motion during the first time period T1, wherein the first time period T1 is selected in such a way that the current increases during the total first time period T1 and no stationary final current appears in the coil during the first time period T1.

2. Method according to claim 1, characterized in that the first time period T1 is fixed, and the measurement value is a current measurement value IMess 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 in such a way that the armature (3) is not set into motion during the first time period T1.

3. Method according to claim 1 or 2, characterized in that the second time period T2 directly follows the first time period T1.

4. Method according to one of claims 1 to 3, characterized in that the second voltage U2 is constant during the second time period T2.

5. Method according to one of claims 1 to 4, characterized in that the second voltage U2 is determined in accordance with the measurement value such that the armature (3) always reaches the same speed during the closing of the contacts (5, 6) independent of the temperature of the coil (2).

6. Method according to one of claims 1 to 5, characterized in that the second voltage U2 is determined in accordance with the measurement value such that the armature (3) is moved into the closed position always within the same time period during the closing of the contacts (5, 6) independent of the temperature of the coil (2).

7. Method according to one of claims 1 to 6, characterized in that the definition of the second voltage U2 by means of the measurement value is effected by reading out a default value from a table stored in a memory, or by applying a calculation specification for calculating the default value by means of the measurement value.

8. Method according to one of claims 1 to 7, characterized in that the second time period T2 is fixed.

9. Method according to one of claims 1 to 7, characterized in that the second time period T2 ends when a suited sensory mechanism or evaluation recognizes 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 comprises a coil (2) and an armature (3) movable between an open position and a closed position, wherein the electrical switching device furthermore comprises a current measuring means (12) for measuring the current flowing in the coil (2), and wherein the electrical switching device (1) comprises a control unit comprising a microcontroller (11), characterized in that the control unit is designed and configured to carry out the method according to one of claims 1 to 9.

11. Electrical switching device (1) according to claim 10, characterized in that the control unit comprises the microcontroller (11), wherein in the microcontroller (11) a table with possible measurement values and corresponding default values, or a calculation specification for calculating the default values by means of the measurement values, is stored.

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