Method for estimating the characteristics of electrical switching devices and related devices

Abstract

To provide a method for estimating characteristics of an electric switching device, and a related device.SOLUTION: A method includes a step comprising a step 102 for measuring current flowing through a coil, a step 104 for measuring a supply voltage of a control circuit for an actuator, a step 106 for injecting a current pulse to the coil, a step 108 for identifying a first time corresponding to a time when the current flowing through the coil reaches a prescribed threshold when the current increases after injecting the pulse, a step 110 for identifying a second time corresponding to a time when the current flowing through the coil reaches the prescribed threshold again when the current decreases after a spike, and a step 112 for estimating the resistance of the coil on the basis of the ratio of the total of values of the voltage measured between the second time and the first time to the total of values of the current measured between the second time and the first time.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to methods for estimating the characteristics of electrical switching devices, and related devices for implementing these methods.

[0002] More particularly, the present invention relates to an electrical contactor that includes an electromagnetic actuator with a coil. [Background technology]

[0003] Such electrical switching devices are configured to switch between open and closed states, for example to control the supply of power to an electrical load. A movable electrical contact is typically connected to a movable part of an actuator, which is moved by the action of a magnetic field created by a coil when a suitable current is passed through the coil.

[0004] For example, it is desirable to be able to automatically estimate one or more characteristics of a device during operation in order to discover its condition and / or detect the onset of a malfunction, thereby performing appropriate preventative maintenance.

[0005] Some devices have dedicated sensors to measure device characteristics such as temperature or the wear state of electrical contacts. However, these sensors increase the manufacturing cost of the device. Furthermore, it is not always possible to integrate new sensors into existing devices. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention is intended to overcome these drawbacks, more particularly by proposing a method for estimating one or more characteristics of an electrical switching device. [Means for solving the problem]

[0007] To this end, one aspect of the invention relates to a method for estimating a characteristic of an electrical switching device, said device including an electromagnetic actuator comprising a coil, the method comprising: measuring the current through the coil; measuring the supply voltage of a control circuit for the actuator; injecting a current pulse into a coil of the actuator; identifying a first time corresponding to the time when the current through the coil reaches a predetermined threshold as the current increases after injection of the pulse; identifying a second time corresponding to a time when the current through the coil again reaches a predetermined threshold when the current decreases after the spike; estimating a resistance of the coil based on a ratio of a sum of the voltage values measured between the second time and the first time to a sum of the current values measured between the second time and the first time; The method includes the steps of:

[0008] The present invention allows the value of the resistance of an actuator coil to be determined automatically and reliably during operation of the device, without the need for a dedicated sensor.

[0009] According to some advantageous but non-essential aspects, such methods may incorporate one or more of the following features, either alone or in any technically acceptable combination:

[0010] The method further comprises the step of estimating the inductance of the coil of the actuator based on the estimated resistance value.

[0011] - said inductance is calculated by the following formula:

number

[0012] where Rbob is the estimated resistance and IcoilTon and Icoil Toff are the current values measured at the peak of the pulse and at the end of the current pulse, respectively; Toff is the remaining duration of the current pulse after the peak of the pulse has been reached; and Drl, Rsh, and RT1 are design constants of the device stored in memory.

[0013] The method further comprises the step of estimating the temperature of the coil of the actuator based on the estimated resistance value.

[0014] - The coil temperature is calculated iteratively by the following formula:

number

[0015] where Temp2 is the current value of the coil's temperature, Temp1 is the previous estimate of the temperature, Rbob2 is the current value of the coil's resistance, Rbob1 is the previous value of the coil's resistance, and K is the thermal coefficient of the material forming the coil.

[0016] - The resistance of the coil is estimated by the following formula:

number

[0017] Here, the total

number

[0018] is the sum of the current values measured between the first and second times, "trs" is the measured coil voltage, "t" is the first time defined above, Ton is the duration of the current pulse from the first time t1 until the peak value of the current pulse is reached, Toff is the remaining duration of the current pulse until the second time after the peak current is reached, and Drl, Rsh, R1, R2, RT4, and RT1 are design constants of the device stored in memory.

[0019] The method is performed when the switching device is in an open state.

[0020] The method is carried out when the switching device is in the closed state, preferably during a holding phase in which the current pulses are repeated periodically.

[0021] A second time is identified as the time when the measured current value is closest to the predetermined threshold value as the current is decreasing after the spike of the pulse.

[0022] According to another aspect, the present invention relates to an electrical switching device including an electromagnetic actuator with a coil and a control circuit, the control circuit comprising: - measuring the current through the coil; - measuring the supply voltage of a control circuit for the actuator; - injecting a current pulse into a coil of the actuator; - identifying a first time corresponding to the time when the current through the coil reaches a predetermined threshold when said current increases after injection of a pulse; - identifying a second time corresponding to a time when the current through the coil again reaches a predetermined threshold when the current decreases after the spike; - estimating a resistance of the coil based on a ratio of a sum of the voltage values measured between the second time and the first time to a sum of the current values measured between the second time and the first time; The method is configured to perform the steps of:

[0023] The invention will be more readily understood and other advantages of the invention will become more clearly apparent in the light of the following description of one embodiment of the method, given by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a schematic diagram of an electrical switching device including an electromagnetic actuator according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram of an example of a control circuit for the electromagnetic actuator of the switching device of FIG. [Figure 3] 3 is a graph showing the variation of the electrical control current of the electromagnetic actuator of FIG. 2 during several stages of operation. [Figure 4] 3 is a diagram of an example of a current pulse used to estimate one or more characteristics of the electromagnetic actuator of FIG. 2. [Figure 5] 2A-2C are diagrams illustrating steps of a method for characterizing the switching device of FIG. 1 according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] FIG. 1 shows an electrical switching device 2, such as a contactor.

[0026] The device 2 is configured to be switched between a closed state that allows current to flow and an open state that prevents current flow.

[0027] For example, the device 2 can be installed in an electrical installation to control the power supply provided to an electrical load, such as a motor, by an electrical energy source, for example a power supply network or a generator.

[0028] In the example shown, the device 2 is connected to an upstream electrical line 4 on the one hand and to a downstream electrical line 6 on the other hand.

[0029] Electrical lines 4 and 6 may include multiple electrical phases, for example, to carry three-phase alternating current. Regardless of the number of phases, device 2 is configured to interrupt or alternatively allow current flow in each of the phases. However, for simplicity in FIG. 1 , only one electrical phase conductor is shown for each of electrical lines 4 and 6.

[0030] The device 2 includes, for example, a casing 8 .

[0031] For each electrical phase, the device 2 comprises a separable contact 10 arranged on the movable part 12 and a fixed contact 14 connected to the upstream electrical line 4 and the downstream electrical line 6. Each of the contacts 10 and 14 comprises a conductor pad 16, which in this case is made of metal, preferably a silver alloy or any equivalent material.

[0032] The movable part 12 of the device 2 is movable between a closed position in which the movable contact 10 is in contact with the fixed contact 14 and an open position shown in FIG. 1 in which the movable contact 10 is separated from the fixed contact 14.

[0033] In fact, during each cycle comprising a closing phase and an opening phase, the contact pad 16 wears, for example due to the action of an electric arc during opening or due to separation of material caused by microwelding. Due to this loss of material, the thickness of the contact pad 16 decreases throughout the life of the device 2, thereby increasing the amplitude of movement of the moving part during the opening or closing phase.

[0034] To remedy this, the device 2 may include a mechanism, shown diagrammatically by the spring in Figure 1, connected to the bar of the moving part, which can maintain the fixed and moving contacts in electrical contact with sufficient contact pressure.

[0035] The mechanism can be adjusted to compress the contacts in the closed position to create sufficient contact pressure. For this purpose, the mechanism can be provided with overtravel, i.e., in the closed position, the contacts are pushed beyond the position strictly necessary to make electrical contact between the fixed and movable contacts.

[0036] If the contact pads 16 are insufficiently thick or if the surface condition of the pads 16 is poor, there is an increased risk of malfunction of the device 2. The device 2 then has to be replaced. For this reason, diagnosing the state of contact depression makes it possible to assess the progression of deterioration of the device 2.

[0037] The device 2 further includes an electromagnetic actuator 20 configured to move the movable part 12 between the closed and open positions.

[0038] The electromagnetic actuator 20 includes a coil 22 configured to generate a magnetic field when supplied with an electrical control current to move the movable part 12 .

[0039] For example, the coil 22 comprises a winding of a conductive wire. The movable part 12 can be integrally mounted on a magnetic core, which is arranged coaxially with the coil 22 and is moved by the action of the magnetic field generated by the coil 22 when the coil 22 is energized by injection of a suitable current.

[0040] The device 2 further includes a power supply circuit 24 configured to supply power to the coil 22 and an electronic control device 26 configured to control the power supply circuit 24 .

[0041] In many embodiments, device 2 includes an input interface configured to receive an open or close command from a user, for example, a control voltage can be applied across terminals of the input interface.

[0042] In numerous embodiments, device 2 further comprises a current sensor 28 configured to measure the current flowing in each of the phases of upstream line 4. In other embodiments, the current sensor and electronic control device are integrated into a casing separate from device 2.

[0043] FIG. 2 shows one embodiment of the power supply circuit 24.

[0044] In the illustrated example, the power supply circuit 24 includes a power supply bus Vc configured to be powered by an external power source or by control signals received by the device 2 .

[0045] Preferably, the power supply circuit 24 comprises a measuring device configured to measure the value of the voltage between the power supply bus Vc of the circuit 24 and the electrical ground GND.

[0046] For example, the measurement device may include two resistors R1 and R2 connected in series with a diode Dt between the power supply bus Vc and electrical ground GND, where a first measurement point located between the resistors R1 and R2 may be used to collect a first measured voltage V1 representative of the voltage present between the power supply bus Vc and electrical ground GND.

[0047] The power supply circuit 24 further includes one or more power switches connected to the coil 22 for selectively connecting or disconnecting the coil 22 from the power supply bus Vc and ground GND.

[0048] For example, a first switch T1 is connected between the coil 22 and the ground GND, and a second switch T2 is connected between the coil 22 and the power supply bus Vc.

[0049] For example, when the two switches T1 and T2 are closed, a voltage corresponding to the voltage Vc is applied to the terminals of the coil 22, causing a current to flow through the coil 22. When only the second switch T2 is opened, the coil 22 can be discharged, and a residual current can continue to flow through the coil 22 temporarily.

[0050] Switches T1 and T2 are controlled, for example, by electronic control device 26. According to an example embodiment, switches T1 and T2 are semiconductor type power switches such as MOSFET transistors, thyristors, insulated gate bipolar transistors (IGBTs), or other equivalent devices.

[0051] In the illustrated example, a diode Drl, called a freewheeling diode, is connected between the second switch T2 and ground GND. A Zener diode Dz can be connected in parallel with the first switch T1. A diode D1 can be placed in the power supply bus Vc between the second switch T2 and the measuring device to prevent current return towards the measuring device.

[0052] In many embodiments, a resistor Rsh is connected in series with the first switch T1 to collect a second measured voltage V2 representative of the current flowing through the coil 22.

[0053] The configuration of the power supply circuit 24 is not limiting and there are other possible implementations.

[0054] Typically, the electronic control device 26 is configured to cause the device 2 to make the switch upon receiving an appropriate control command.

[0055] Advantageously, the electronic control device 26 is also configured to estimate at least one characteristic of the device 2 during operation of the device 2, in particular one or more characteristics of the coil 22, such as the resistance of the coil 22, the inductance of the coil 22, and the temperature of the coil 22, as will become more readily apparent from reading the text below.

[0056] In many embodiments, the electronic control device 26 is implemented by one or more electronic circuits.

[0057] For example, electronic control device 26 includes a processor, such as a programmable microcontroller or microprocessor, and computer memory or any medium for recording computer-readable data.

[0058] By way of example, the memory may be ROM, RAM, EPROM, Flash, or a similar type of non-volatile memory, and may include executable instructions and / or computer code that, when executed by a processor, cause the control device 26 to operate according to one or more of the embodiments described below.

[0059] According to variants, the electronic control device 26 may comprise a signal processor (DSP), a reprogrammable logic component (FPGA), or an application specific integrated circuit (ASIC), or any equivalent element.

[0060] 3 shows a graph 40 illustrating the variation of the current (I) flowing through the coil 22 over time (t) at different successive operational stages of the device 2, represented by P1, P2, P3, and P4, when the device 2 is switched to a closed state and then switched back to an open state. This current will be referred to in the following text as the "coil current."

[0061] The first stage P1 is the initial stage in which the device 2 is stable and open. In fact, the second switch T2 remains open and the coil current remains zero.

[0062] Optionally, as can be seen in the figure, a current pulse may be injected into the coil 22 to estimate said characteristic.

[0063] The second phase, P2, is the closing phase after a close command is received by device 2. For example, switches T1 and T2 are closed. The coil current increases until it reaches a threshold at which the movable part 12 begins to move from the open position to the closed position. For the remainder of the closing phase, the coil current increases to a plateau value when the movable contact 10 begins to compress against the fixed contact 14. At that time, device 2 is in the closed state.

[0064] In the third phase P3, called the hold phase, the coil current continues to be held above the threshold value. In fact, during this hold phase, the coil current can remain below the plateau value reached in the close phase.

[0065] Optionally, as can be seen in the figure, the coil voltage may be varied periodically to reduce the coil current as much as possible while keeping it above the threshold to avoid unnecessary energy loss.

[0066] In the illustrated example, the periodic variation of the coil voltage is achieved by alternately opening and closing the second switch T2 at a predefined chopping frequency, thereby creating an oscillation of the coil voltage according to a predefined profile. As a result, the coil current also oscillates 42 between two intensity values. During this time, the first switch T1 may remain closed.

[0067] To prevent the mechanical vibrations caused by these vibrations from generating noise audible to the human ear, the chopping frequency is advantageously chosen to be less than 100 Hz or greater than 25 kHz. In the example shown, the chopping frequency is less than 100 Hz.

[0068] The opening phase P4 begins when the electronic control device 26 receives an open command: switches T1 and T2 are both opened.

[0069] An example of the operation of a method for estimating a characteristic of a device 2 will now be described with reference to FIGS.

[0070] As illustrated by the diagram of FIG. 5, the method is first initialized by step 100 .

[0071] The control circuit 26 then begins measuring the current flowing through the coil (step 102) and measuring the supply voltage Vc set by the power supply circuit 24 (step 104).

[0072] For example, these measurements are repeated with sequential sampling over a period of time. In the example shown in Figure 2, these measurements consist of measuring the values of the first voltage V1 and the second voltage V2. The measurements can be recorded in the memory of the control device 26.

[0073] Then, in step 106, a current pulse is injected by the power supply circuit 24 into the coil 22 of the actuator 20, for example by varying the voltage applied to the terminals of the coil 22. For this purpose, the switches T1 and T2 may be temporarily closed.

[0074] As shown in the example of FIG. 4, which represents the change in coil current (I) as a function of time (t), the current pulse 50 may have an increasing rising front that increases, for example, according to an exponential law of change, up to a maximum value I2.

[0075] The reaching of this maximum value corresponds here to a spike 52 in the pulse 50 .

[0076] This rising front is followed by a falling front that drops from a maximum value I2 to a final value, such as the original value or zero, where it decreases according to an exponential law. Thus, the current pulse has what is known herein as a shark fin shape.

[0077] A predetermined threshold, here denoted I1, is defined and is between the minimum and maximum coil current values I2. When a current pulse 50 is injected, the coil current passes this predetermined threshold I1 at a first time during the rising front, and then passes the predetermined threshold I1 at a second time during the falling front.

[0078] Thus, in step 108 after step 106, the control device 26 identifies a first time (t1) corresponding to the time at which the current through the coil reaches a predetermined threshold I1 when said current increases after the injection of the pulse.

[0079] The predetermined threshold I1 may be fixed in advance and, for example, stored in a memory. For example, the threshold is chosen to be low enough to retain a sufficient signal and to perform a measurement. By way of example, the threshold may be equal to 10% of the maximum value I2.

[0080] Then, in step 110, the control device 26 identifies a second time (t2) corresponding to the time when the current through the coil again reaches the predetermined threshold I1 as said current decreases after the spike of the pulse.

[0081] For example, the identification of the first and second times is based on subsequent coil current measurements beginning at step 102 .

[0082] In step 112, the resistance of the coil is estimated based on the ratio of the sum of the voltage values measured between the second time t2 and the first time t1 to the sum of the current values measured between the second time t2 and the first time t1.

[0083] According to an example embodiment, as soon as the passage of threshold I1 is detected at time t1, control device 26 begins summing voltage values until the passage of coil current threshold I1 is detected at time t2, and records the corresponding sum ΣU in memory. Control device 26 continues in a similar manner for measurements of coil current, and records the corresponding sum ΣI in memory.

[0084] The resistance, denoted R, is then estimated as the ratio of these two sums, as shown by the following formula:

number

[0085] In other words, the summation of coil current and voltage samples can start from the current threshold I1, and the summation is stopped when the coil current reaches this threshold again.

[0086] The method for estimating the resistance is carried out when the device 2 is in the open state, preferably during the above-mentioned phase P1. In this case, optionally but advantageously, the estimation method can be carried out as soon as the device 2 is switched on, to ensure that the operating state of the device complies with safety requirements before the closing phase can be initiated.

[0087] The method for estimating the resistance may also be implemented when the device 2 is in the closed state, in particular during the above-mentioned holding phase P3. In this case, the current pulse may be one of the periodic oscillations 42 of the current due to the chopping of the coil voltage implemented by the power supply circuit 24.

[0088] In this way, a reliable and relatively simple method of estimating resistance is provided, regardless of the state of the device 2.

[0089] In a variant, this calculation can be simplified by estimating the resistance R using the following formula:

number

[0090] Here, the total

number

[0091] is the sum of the coil currents measured between times t1 and t2, "trs" is the measured coil voltage (first measured voltage V1), "t" is time t1 as defined above, Ton is the duration of the current pulse between the first time t1 and the current spike 52 (maximum value), the constants R1, R2, Rsh are the values of the previously defined resistors of the same name in the power supply circuit 24, Drl is the voltage across the diode Drl in the conducting state, RT1 is the impedance of the first switch T1, RT4 is the impedance of the second switch, and Toff is the remaining duration of the pulse until the second time t2 after the current spike 52.

[0092] The values of R1 and R2 are considered to be design constants specific to device 2 and can be recorded in memory, for example, during construction of device 2. The constants Drl, RT4, Rsh, RT1 are also constants specific to device 2 and can also be recorded in memory, although their values may be temperature dependent.

[0093] In practice, known values of these constants can be recorded in memory in advance and then loaded when device 2 is started, and then updated during operation of the device, for example during a correction operation, based on the temperature values estimated in step 114 described below and laws governing the variation of each constant as a function of temperature.

[0094] Optionally, the identification of times t1 and t2 includes a correction substep to improve the accuracy of the detection.

[0095] This is because, depending on the method used to detect when the threshold I1 is crossed, the crossing may be detected with a delay, thereby introducing an error into the resistance estimate.

[0096] In particular, in step 110, in order to minimize measurement errors during the drop phase, instead of stopping at the first current measurement having a value less than threshold I1, time t2 is considered to be the time at which the current value closest to threshold I1 is measured, even if this measurement is greater than threshold I1.

[0097] In other words, once this modification is implemented, the second time t2 is identified as the time at which the measured current value is closest to the threshold I1 as the current is decreasing after the spike of the pulse.

[0098] In particular, it will be clear that this method primarily makes it possible to estimate the resistance of the coil 22. Advantageously, other properties of the coil 22, such as temperature and inductance, can be estimated in subsequent steps based on the estimated resistance value.

[0099] For example, in step 114, the control device 26 estimates the temperature of the coil 22 based on the estimated coil resistance R.

[0100] According to one example embodiment, the estimation of the coil temperature can be performed iteratively over a period of time, starting from a previous temperature value.

[0101] This estimation can be performed by the following formula:

number

[0102] where Temp2 is the new temperature estimate, Temp1 is the previous temperature estimate, Rbob2 is the current value of the resistance of the coil 22, Rbob1 is the previous value of the resistance of the coil 22, and K is the thermal coefficient of the material (e.g., copper) forming the coil. The coil resistance is estimated, for example, by the method described above.

[0103] Step 114 may be repeated a number of times over a period of time, for example periodically. In the first iteration of step 114, it is possible to use as initial values Rbob1 and Temp1 from initial values measured or estimated during the first switch-on of device 2 and then recorded in the memory of control device 26.

[0104] In another embodiment, in step 116, the control device 26 estimates the inductance of the coil 22 based on the estimated resistance value.

[0105] For example, the inductance of a coil, denoted L, can be estimated based on the following formula:

number

[0106] where the values presented are those previously defined. Ton and Icoil Toff and correspond to the current values measured at the current spike 52 and at the end t2 of the current pulse, respectively.

[0107] Therefore, the inductance can be easily estimated, taking into account all voltage drops. The result is more accurate because it takes into account all parameters that may cause inaccuracies to a greater or lesser extent, such as residual voltages and parasitic resistances. Furthermore, the calculation is easy to perform, i.e., only small computing resources are required.

[0108] These examples are not limiting and steps 114 or 116 may be implemented in different ways.

[0109] In variants, the steps of the method may be performed in a different order, some steps may be omitted, and the described examples do not preclude other steps from being performed in other embodiments jointly or sequentially with the described steps.

[0110] The present invention enables the value of the resistance of an actuator coil to be determined automatically and reliably during device operation, without the need for a dedicated sensor. Other characteristics, such as temperature and inductance, can then be estimated based on the estimated resistance. In this way, an easily implemented method is provided for obtaining reliable values regarding the state of the coil 22, without the need for additional sensors (such as a temperature sensor near the coil 22).

[0111] Optionally, the state of the device 2 (open or closed) can be determined from one or more of the characteristics estimated by the methods described above.

[0112] For example, a method for determining the state of device 2 may include a step, not shown, of comparing one or more of these estimated characteristics to one or more reference values, and the state of device 2 is determined based on the results of this comparison.

[0113] Features of one of the above-described embodiments or variations can be implemented in other described embodiments and variations. [Explanation of symbols]

[0114] 2 Electrical Switching Devices 4 Electric lines 6 Electric lines 8 Casing 10 Separable contacts, movable contacts 12 Moving parts 14 Fixed contacts 16 Conductor pad, contact pad 20 Electromagnetic Actuator 22 coils 24 Power supply circuit 26 Electronic Control Devices 28 Current Sensor 40 graphs 42 Periodic vibration 50 current pulses 52 Current Spike D1 Diode Dt diode R1 resistor R2 resistor T1 First Switch T2 Second switch V1 First voltage V2 Second voltage Drl Diode Dz Zener diode Rsh resistor GND Electrical ground P1 First stage P2 Second Stage P3 Third stage, retention stage P4 Opening stage I1 Predetermined threshold I2 maximum value t1 first time t2 second time

Claims

1. A method for estimating the characteristics of an electrical switching device (2), said device comprising an electromagnetic actuator (20) comprising a coil (22), said method comprising: - a step (102) of measuring the current flowing through said coil; - a step (104) of measuring the supply voltage of a control circuit for said actuator; - a step (106) of injecting a current pulse into said coil (22) of said actuator (20); - a step (108) of identifying a first time (t1) corresponding to the time at which the current flowing through said coil reaches a predetermined threshold (I1) when the current flowing through said coil increases after said injection of said current pulse; - a step (110) of identifying a second time (t2) corresponding to the time at which the current flowing through said coil reaches said predetermined threshold (I1) again when the current flowing through said coil decreases after the spike of said current pulse; - a step (112) of estimating the resistance of said coil based on the ratio of the sum of the values of the voltage measured between said second time and said first time to the sum of the values of the current flowing through said coil measured between said second time and said first time.

2. The method according to claim 1, further comprising a step (116) of estimating the inductance of said coil (22) of said actuator based on said estimated resistance value.

3. Said inductance (L) is calculated by the following formula: 【Number 1】 Here, Rbob is the estimated resistance value, and Icoil Ｔｏｎ and Icoil Ｔｏｆｆ are the current values measured at the peak (52) of the pulse and at the end (t2) of the current pulse, respectively. Toff is the remaining period of the current pulse after the peak (52) of the pulse is reached. Drl, Rsh, and RT1 are design constants specific to the device (2) recorded in the memory. The method according to claim 2

4. The method according to any one of claims 1 to 3, further comprising a step (114) of estimating the temperature of said coil of said actuator based on said estimated resistance value.

5. The temperature of said coil is repeatedly calculated by the following formula: 【Number 2】 wherein Rbob2 is the latest value of the resistance of said coil estimated at said second time (t2), Rbob1 is the previous value of the resistance of said coil, Temp2 is the value of the temperature of said coil corresponding to said second time (t2) at which Rbob2 is estimated, Temp1 is the previous value of the temperature of said coil, and K is the thermal coefficient of the material forming said coil.

6. The resistance of said coil is estimated by the following formula: 【Mathematics 3】 where the total 【Number 4】 is the sum of the current values measured between the first time (t1) and the second time (t2), "trs" is the measured coil voltage, "t" is the first time (t1) defined above, Ton is the period of the current pulse from the first time (t1) until the peak value (52) of the current pulse is reached, Toff is the remaining period of the current pulse from the time when the peak value (52) of the current pulse is reached until the second time (t2), and Drl, Rsh, R1, R2, RT4, and RT1 are design constants of the device (2) recorded in the memory. The method according to any one of claims 1 to 5.

7. The method according to any one of claims 1 to 6, wherein the method is carried out when the switching device (2) is in the open state.

8. The method according to any one of claims 1 to 7, wherein the method is carried out when the switching device (2) is in the closed state, preferably during a holding phase in which the current pulse is periodically repeated.

9. The second time (t2) is identified as the time at which the measured current value is closest to the predetermined threshold value (I1) at the end (t2) of the current pulse when the current is decreasing after the spike of the pulse. The method according to claim 3.

10. An electrical switching device including an electromagnetic actuator comprising a coil and a control circuit, wherein the control circuit - measures the current flowing through the coil (step 102); - measures the supply voltage of the control circuit for the actuator (step 104); - injects a current pulse into the coil (22) of the actuator (20) (step 106); - identifies a first time (t1) corresponding to the time when the current flowing through the coil reaches a predetermined threshold value (I1) when the current flowing through the coil increases after the injection of the current pulse (step 108); - identifies a second time (t2) corresponding to the time when the current flowing through the coil reaches the predetermined threshold value (I1) again when the current flowing through the coil decreases after the spike of the current pulse (step 110); - a step (112) of estimating the resistance of the coil based on a ratio of a sum of the values of the voltage measured between the second time and the first time to a sum of the values of the current flowing through the coil measured between the second time and the first time An electrical switching device configured to perform the steps consisting of.

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