Method for estimating characteristics of an electrical switching device and related device

Abstract

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

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for estimating a characteristic of an electrical switching device, and to a related device for implementing these methods.

[0002] More specifically, the present invention relates to an electrical contactor comprising an electromagnetic actuator comprising a coil. BACKGROUND

[0003] Such electrical switching devices are configured for switching between an open state and a closed state, for example in order to control the supply of an electrical load. The mobile electrical contact is usually connected to a mobile part of the actuator which moves under the effect of the magnetic field generated by the coil when a suitable current is passed through the coil.

[0004] It is desirable to be able to estimate one or more characteristics of the device automatically while the device is in operation, for example in order to discover its state and / or to detect the occurrence of a fault and thus to provide suitable preventive maintenance.

[0005] Some devices have dedicated sensors for measuring a characteristic of the device, for example for measuring the temperature or the state of wear of the electrical contact. However, these sensors increase the production cost of the device. Moreover, it is not always possible to integrate a new sensor into an existing device.

[0006] More specifically, the present invention aims to overcome these drawbacks by proposing a method for estimating one or more characteristics of an electrical switching device. SUMMARY

[0007] To this end, one aspect of the invention relates to a method for estimating a characteristic of an electrical switching device, said device comprising an electromagnetic actuator comprising a coil, the method comprising the steps of:

[0008] measuring the current flowing through the coil;

[0009] measuring the supply voltage of the control circuit for the actuator;

[0010] injecting a current pulse into the coil of the actuator;

[0011] when said current increases after the injection of the pulse, identifying a first time corresponding to the time at which the current flowing through the coil reaches a predetermined threshold value;

[0012] when said current decreases after the peak, identifying a second time corresponding to the time at which the current flowing through the coil reaches the predetermined threshold value again;

[0013] estimating the resistance of the coil on the basis of the ratio of the sum of the values of said voltage measured between the second time and the first time to the sum of the values of said current measured between the second time and the first time.

[0014] The application can automatically and reliably determine the resistance value of the actuator coil during the operation of the device, without the need for a dedicated sensor.

[0015] According to some advantageous but non-mandatory aspects, this method can incorporate one or more of the following features, which can be used alone or in any technically admissible combination:

[0016] - the method also comprises a step of estimating the inductance of the actuator coil based on the estimated resistance value.

[0017] - the inductance is calculated by the following formula:

[0018]

[0019] where Rbob is the estimated resistance value, Icoil Ton and Icoil Toff are the current values measured at the peak of the pulse and at the end of the pulse, respectively, Toff is the remaining duration of the current pulse after reaching the peak of the pulse, Drl, Rsh and RT1 are design constants of the device, recorded in the memory.

[0020] - the method also comprises a step of estimating the temperature of the actuator coil based on the estimated resistance value.

[0021] - the temperature of the coil is iteratively calculated by the following formula:

[0022]

[0023] where Temp2 is the current value of the temperature of the coil, Temp1 is the previous estimated value of the temperature, Rbob2 is the current value of the resistance of the coil, Rbob1 is the previous value of the resistance of the coil, K is the thermal coefficient of the material forming the coil.

[0024] - the resistance of the coil is estimated by the following formula:

[0025]

[0026] where is the sum of the current values measured between the first time and the second time, "trs" is the measured voltage of the coil, "t" is the first time defined above, Ton is the duration of the current pulse between the first time t1 and the peak of the current pulse, Toff is the remaining duration of the current pulse after reaching the peak current until the second time, Drl, Rsh, R1, R2, RT4 and RT1 are design constants of the device, recorded in the memory.

[0027] - the method is performed when the switching device is in the open state.

[0028] - the method is performed when the switching device is in a closed state, preferably during a hold phase in which the current pulse is periodically repeated.

[0029] - the second time is identified as the time at which the measured current value is closest to the measured current value of the predetermined threshold when the current decreases after the pulse peak.

[0030] According to another aspect, the application relates to an electrical switching device comprising an electromagnetic actuator comprising a coil and a control circuit configured to implement the steps of:

[0031] - measuring the current flowing through the coil;

[0032] - measuring the supply voltage of the control circuit of the actuator;

[0033] - injecting a current pulse into the coil of the actuator;

[0034] - when the current increases after the pulse injection, identifying a first time corresponding to the time at which the current flowing through the coil reaches a predetermined threshold;

[0035] - when the current decreases after the peak, identifying a second time corresponding to the time at which the current flowing through the coil reaches the predetermined threshold again;

[0036] - estimating the resistance of the coil based on the ratio of the sum of the values of the voltage measured between the second time and the first time to the sum of the values of the current measured between the second time and the first time. BRIEF DESCRIPTION OF DRAWINGS

[0037] The application will be more readily understood and other advantages thereof will become more apparent upon reference to the following description, given by way of example only, of embodiments of the method, with reference to the accompanying drawings in which:

[0038] Figure 1 is a schematic view of an electrical switching device comprising an electromagnetic actuator according to an embodiment of the application;

[0039] Figure 2 is a schematic view of an example of the control circuit of the electromagnetic actuator of the switching device of Figure 1

[0040] Figure 3 is a graph representing the variation of the electrical control current of the electromagnetic actuator of Figure 2

[0041] Figure 4 is an example of a current pulse for estimating one or more characteristics of the electromagnetic actuator of Figure 2

[0042] Figure 5 ​​​This indicates that the evaluation is based on an embodiment of the present invention. Figure 1 A diagram showing the steps of a method for determining the characteristics of a switching device. Detailed Implementation

[0043] Figure 1 An electrical switching device 2, such as a contactor, is shown.

[0044] Device 2 is configured to switch between a closed state that allows current flow and an open state that prevents current flow.

[0045] For example, device 2 can be installed in an electrical facility to control the power supply to an electrical load, such as a motor, by an electrical energy source. The energy source is, for example, a power grid or a generator.

[0046] In the example shown, device 2 is connected to the upstream wire 4 on one side and the downstream wire 6 on the other.

[0047] Wires 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 to flow in each phase. However, for simplicity... Figure 1 Only one electrical phase conductor is shown for each of wires 4 and 6.

[0048] Device 2 includes, for example, housing 8.

[0049] For each electrical phase, the device 2 includes a separable contact 10 disposed on the moving part 12 and a fixed contact 14 connected to the upstream wire 4 and the downstream wire 6. Each of the contacts 10 and 14 includes a contact pad 16, which in this case is made of metal, preferably a silver alloy or any equivalent material.

[0050] The moving part 12 of device 2 can move between a closed position and an open position. In the closed position, the moving contact 10 is in contact with the fixed contact 14, and in the open position, as shown in the figure. Figure 1 As shown, the moving contact 10 is separated from the fixed contact 14.

[0051] In practice, during each cycle, including the closing and opening phases, the contact pad 16 becomes worn, for example, due to the action of the electric arc during the opening phase, or due to material separation caused by micro-welding. This material loss causes the thickness of the contact pad 16 to decrease throughout the life of the device 2, thereby increasing the movement amplitude of the moving parts during the opening or closing phase.

[0052] To solve this problem, device 2 may include a mechanism that, in Figure 1 The mechanism is schematically represented by a spring, which is connected to the rod of the moving part and enables the fixed and moving contacts to maintain electrical contact with sufficient contact pressure.

[0053] The mechanism can be adjusted to press the contacts in the closed position to generate sufficient contact pressure. To this end, the mechanism can be provided with an overtravel; that is, in the closed position, the contacts are pushed to a position beyond that strictly necessary to provide electrical contact between the fixed and mobile contacts.

[0054] If the thickness of the contact pad 16 is insufficient, or if the surface condition of the pad 16 is poor, the risk of malfunction of the device 2 increases. The device 2 then needs to be replaced. It is precisely for these reasons that the diagnosis of the pressed condition of the contacts makes it possible to assess the progress of the deterioration of the device 2.

[0055] The device 2 also comprises an electromagnetic actuator 20 configured to move the mobile part 12 between the closed position and the open position.

[0056] The electromagnetic actuator 20 comprises a coil 22 configured to generate a magnetic field when it is supplied with a control current in order to move the mobile part 12.

[0057] For example, the coil 22 comprises a winding of electrically conductive wire. The mobile part 12 can be mounted integrally with a magnetic core arranged coaxially with the coil 22 and which moves by the action of the magnetic field generated by the coil 22 when the coil 22 is excited by the input of an appropriate current.

[0058] The device 2 also comprises a power supply circuit 24 configured to supply the coil 12, and an electronic control device 26 for controlling the power supply circuit 24.

[0059] In many embodiments, the device 2 comprises an input interface configured for receiving an opening or closing instruction from a user. For example, a control voltage can be applied between the terminals of the input interface.

[0060] In many embodiments, the device 2 also comprises a current sensor 28 configured for measuring the current flowing in each phase of the upstream line 4. In other embodiments, the current sensor and the electronic control device are integrated into a housing separate from the device 2.

[0061] Figure 2 An embodiment of the power supply circuit 24 is shown.

[0062] In the example shown, the power supply circuit 24 comprises a power supply bus Vc adapted to be powered by an external power supply or by a control signal received by the device 2.

[0063] Preferably, the power supply circuit 24 comprises a measuring device configured to measure the value of the voltage between the power supply bus Vc and an electrical ground GND of the circuit 24.

[0064] For example, the measuring device comprises two resistors R1 and R2 connected in series between the power supply bus Vc and the electrical ground GND with the diode Dt. In this case, a first measuring point located between the resistors R1 and R2 can be used to collect a first measured voltage V1 representative of the voltage present between the power supply bus Vc and the electrical ground GND.

[0065] The power supply circuit 24 also comprises one or more power switches connected to the coil 22 for selectively connecting the coil 22 to the power supply bus Vc and the ground GND or disconnecting the coil 22 from the power supply bus Vc and the ground GND.

[0066] For example, a first switch T1 is connected between the coil 22 and the ground GND. A second switch T2 is connected between the coil 22 and the power supply bus Vc.

[0067] For example, when the two switches T1 and T2 are closed, a voltage depending on the voltage Vc is applied to the terminals of the coil 22 and an excitation current flows in the coil 22. When only the second switch T2 is open, the coil 22 can be discharged and a residual current can continue to flow in the coil 22 for a while.

[0068] The switches T1 and T2 are controlled, for example, by the electronic control device 26. According to an example of embodiment, the switches T1 and T2 are semiconductor-type power switches, for example Mosfet transistors, thyristors, Insulated Gate Bipolar Transistors (IGBT) or any other equivalent device.

[0069] In the example shown, a diode Dr1, called freewheeling diode, is connected between the second switch T2 and the ground GND. A Zener diode Dz can be connected in parallel with the first switch T1. A diode D1 can be placed on the power supply bus Vc between the second switch T2 and the measuring device to prevent any current from returning to the latter.

[0070] 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 in the coil 22.

[0071] The architecture of the power supply circuit 24 is not limiting and other possible implementations are possible.

[0072] As a general rule, the electronic control device 26 is configured to make the device 2 switch when it receives appropriate control instructions.

[0073] Advantageously, the electronic control device 26 is also configured to estimate at least one characteristic 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, which will be easier to understand by reading the following text.

[0074] In many embodiments, the electronic control device 26 is implemented by one or more electronic circuits.

[0075] For example, the electronic control device 26 comprises a processor, such as a programmable microcontroller or microprocessor, and a computer memory or any medium for recording computer readable data.

[0076] According to an example, the memory is a ROM or a RAM or an EPROM or a flash memory or a non-volatile memory of equivalent type. The memory comprises executable instructions and / or computer code for causing the control device 26 to operate according to one or more embodiments described below, when executed by the processor.

[0077] According to a variant, the electronic control device 26 can comprise a signal processing processor (DSP), or a reprogrammable logic component (FPGA), or an application specific integrated circuit (ASIC), or any equivalent element.

[0078] Figure 3 A graph 40 is shown, which illustrates the variation of the current (I) flowing in the coil 22 during the time (t) in different successive operating phases (denoted PI, P2, P3 and P4) of the device 2, in the case where the device 2 switches to the closed state and then again to the open state. This current is hereinafter referred to as the "coil current".

[0079] The first phase PI is an initial phase in which the device 2 is stable in the open state. Indeed, the second switch T2 remains open and the coil current remains zero.

[0080] Optionally, as seen in the figure, a current pulse can be injected into the coil 22 for estimating said characteristic.

[0081] The second phase P2 is a closing phase, after the device 2 has received a closing command. For example, the switches T1 and T2 are closed. The coil current increases until it reaches a threshold value above which the moving part 12 starts to move from its open position to its closed position. In the rest of the closing phase, when the mobile contact 14 comes into contact with the fixed contact 10, the coil current increases to a plateau value. The device 2 is then in the closed state.

[0082] In a third phase P3, called a holding phase, the coil current continues to be held above the threshold value. Indeed, in this holding phase, the coil current can be held below the plateau value reached in the closing phase.

[0083] Optionally, as seen in the figure, the coil voltage can be varied periodically in order to reduce the coil current as much as possible while keeping it above said threshold value, in order to avoid unnecessary energy losses.

[0084] In the example shown, periodic variations in the coil voltage are obtained by alternately opening and closing the second switch T2 at a predefined chopping frequency, thereby generating oscillations in the coil voltage according to a predefined profile. Consequently, the coil current also oscillates between two intensity values. During this period, the first switch T1 can remain closed.

[0085] To prevent the mechanical vibrations caused by these oscillations from generating noise perceptible to the human ear, it is advantageous to choose a chopping frequency below 100 Hz or above 25 kHz. In the example shown, the chopping frequency is below 100 Hz.

[0086] When the electronic control unit 26 receives the opening command, the opening phase P4 begins. Switches T1 and T2 are both opened.

[0087] Now refer to Figure 4 and 5 An example of the operation of a method for estimating the characteristics of device 2.

[0088] like Figure 5 As shown, the method is first initialized in step 100.

[0089] The control circuit 26 then begins to measure the current flowing in the coil (step 102) and the supply voltage Vc set by the power supply circuit 24 (step 104).

[0090] For example, these measurements are repeated in consecutive sampling over time. Figure 2 In the example shown, these measurements include measuring the values ​​of the first and second voltages V1 and V2. The measured values ​​can be recorded in the memory of the control device 26.

[0091] Then, in step 106, a current pulse is injected into the coil 22 of the actuator 20 via the power supply circuit 24, for example by changing the voltage applied to the terminals of the coil 22. For this purpose, switches T1 and T2 can be briefly closed.

[0092] like Figure 4 As shown in the example, it represents the change of coil current (I) with time (t), and the current pulse 40 may have a rising edge that increases to a maximum value I2, following, for example, a law of exponential change.

[0093] This maximum value corresponds to the peak value 52 of pulse 50.

[0094] This rising edge is followed by a falling edge, which descends from the maximum value I2 to a final value, such as the original value or zero, decreasing exponentially. Therefore, the current pulse here exhibits what is known as a shark fin shape.

[0095] A predetermined threshold, denoted here as Ii, is defined between the minimum value and the maximum value I2 of the coil current. When the current pulse 50 is injected, the coil current passes the predetermined threshold Ii for the first time during the rising front, and then passes the predetermined threshold Ii for the second time during the falling front.

[0096] Therefore, in a step 108 following the step 106, the control device 26 identifies, when the current increases after the pulse injection, a first time (ti) corresponding to the time at which the current flowing through the coil reaches the predetermined threshold Ii.

[0097] The predetermined threshold Ii can be fixed in advance, for example recorded in a memory. For example, the threshold is chosen low enough to preserve enough signal and to make the measurement. For example, the threshold can be equal to 10% of the maximum value I2.

[0098] Then, in a step 110, the control device 26 identifies, when the current decreases after the pulse peak, a second time (t2) corresponding to the time at which the current flowing through the coil reaches the predetermined threshold Ii again.

[0099] For example, the identification of the first and second times is based on the measurement of the coil current which is started in the step 102 and continues to occur.

[0100] In a step 112, the resistance of the coil is estimated based on the ratio of the sum of the values of the voltage measured between the second time t2 and the first time ti, and the sum of the values of the current measured between the second time t2 and the first time ti.

[0101] According to an example of embodiment, as soon as the passage through the threshold Ii is detected at the time ti, the control device 26 starts the summation of the voltage values until the passage through the threshold Ii of the coil current is detected at the time t2, and records the corresponding sum ΣU in a memory. The control device 26 processes the measurement values of the coil current in the same way and records the corresponding sum ΣI in a memory.

[0102] The resistance value, denoted R, is then estimated as the ratio of these two sums, as shown in the following formula:

[0103]

[0104] That is, the summation of the samples of the coil current and voltage can be started from the current threshold Ii and stopped when the coil current reaches this threshold again.

[0105] The method for estimating the resistance is preferably performed when the device 2 is in the open state, preferably during the above-mentioned phase PI. In this case, optionally but advantageously, the estimation method can be performed as soon as the device 2 is switched on, to ensure that the operating conditions of the device comply with the safety requirements before the closing phase can be initiated.

[0106] The method for estimating the resistance can also be implemented when the device 2 is in the closed condition, in particular during the above-mentioned holding phase P3. In this case, the current pulse can 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.

[0107] Therefore, a reliable and relatively simple method for estimating the resistance is provided, regardless of the state of the device 2.

[0108] In a variant, this calculation can be simplified by estimating the resistance R by using the following formula:

[0109]

[0110] wherein is the sum of the values of the coil current measured between ti and t2, "trs" is the coil voltage measured (first measured voltage Vi), "t" is ti defined above, Ton is the duration of the current pulse between the first time ti and the current peak 52 (maximum), the constants R1, R2, Rsh are the values of the resistors of the same name previously defined for the power supply circuit 24, Dr1 is the voltage of the diode Dr1 in the conducting state, RT1 is the impedance of the first switch T1, RT4 is the impedance of the second switch, Toff is the remaining duration of the pulse from the current peak 52 until the second time t2.

[0111] The values of R1 and R2 can be considered as design constants specific to the device 2 and recorded in the memory, for example during the construction of the device 2. The constants Dr1, RT4, Rsh, RT1 are constants specific to the device 2, which can also be recorded in the memory, but whose values can depend on the temperature.

[0112] In practice, the known values of these constants can be recorded in the memory in advance, then loaded at the start of the device 2, and can be updated during the operation of the device, for example during the correction operation, on the basis of the temperature value estimated in step 114 described below and of the law specifying the variation of each constant as a function of the temperature.

[0113] Optionally, the identification of the times ti and t2 includes a correction sub-step to improve the accuracy of the detection.

[0114] This is because, according to the method for detecting when the threshold I1 is crossed, it is possible to delay the detection of this crossing, thereby introducing an error into the resistance estimate.

[0115] It is worth noting that, in step 110, in order to minimize the measurement error in the falling phase, instead of stopping at the first current measurement having a value lower than the threshold Ii, the time t2 is considered as the time at which the current value closest to the threshold Ii is measured, even if this measurement value is greater than the threshold Ii.

[0116] In other words, when this correction is implemented, the second time t2 is identified as the time at which the current value measured when the current decreases after the peak of the pulse is the measured current value closest to the threshold Ii.

[0117] Obviously, this method mainly allows the resistance of the coil 22 to be estimated. Advantageously, other characteristics of the coil 22, such as the temperature and the inductance, can be estimated in subsequent steps on the basis of the estimated resistance value.

[0118] For example, in step 114, the control device 26 estimates the temperature of the coil 22 on the basis of the estimated value of the resistance of the coil R.

[0119] According to an example of embodiment, the estimation of the temperature of the coil can be performed iteratively over time starting from a previous temperature value.

[0120] This estimation can be made through the following formula:

[0121]

[0122] 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, K is the thermal coefficient of the material forming the coil, for example copper. The value of the resistance of the coil is estimated, for example, through the method described above.

[0123] Step 114 can be repeated several times over time, for example periodically. In the first iteration of step 114, the initial values Rbob1 and Temp1 from the initial values measured or estimated during the first turn-on of the device 2 can be used, then recorded in the memory of the control device 26.

[0124] In other embodiments, in step 116, the control device 26 estimates the inductance of the coil 22 on the basis of the estimated resistance value.

[0125] For example, the inductance of the coil, indicated with L, can be estimated according to the following formula:

[0126]

[0127] where the values shown are the previously defined values. The value Icoil Ton and Icoil Toff correspond to the current values measured for the current peak 52 and the end of the current pulse t2, respectively.

[0128] Therefore, considering all the voltage drops, the inductance can be simply estimated. This result is more accurate because it takes into account all the parameters that can lead to more or less inaccurate results, such as the residual voltage and the parasitic resistance. Moreover, this calculation is easy to implement; that is, it requires little computational resources.

[0129] These examples are not limiting and the steps 114 or 116 can be implemented differently.

[0130] In variants, the steps of the present method can be performed in a different order. Some steps can be omitted. In other embodiments, the described examples do not prevent other steps from being implemented jointly or sequentially with the described steps.

[0131] The present invention can automatically and reliably determine the resistance value of the actuator coil during the operation of the device, without the need for a dedicated sensor. Other properties, such as temperature and inductance, can then be estimated based on the estimate of the resistance. Thus, an easy-to-implement method is provided for obtaining reliable values about the state of the coil 22 without the need to add auxiliary sensors (such as a temperature sensor near the coil 22).

[0132] Optionally, the state (open or closed state) of the device 2 can be determined from one or more properties estimated by the above method.

[0133] For example, the method of determining the state of the device 2 can comprise a step (not shown) of comparing one or more of these estimated properties with one or more reference values. The state of the device 2 is determined based on the result of this comparison.

[0134] Any feature of one of the above embodiments or variants can be implemented in other described embodiments and variants.

Claims

1. A method for estimating characteristics of an electrical switching device (2), said device comprising an electromagnetic actuator (20) having a coil (22), said method comprising the steps of: - measuring (102) the current flowing through said coil; - measuring (104) the supply voltage of the control circuit for the actuator; - injecting (106) a current pulse into the coil (22) of the actuator (20); - identifying (108) a first time (ti) corresponding to the time at which the current flowing through the coil reaches a predetermined threshold (II) when said current increases after the pulse injection; - identifying (110) a second time (t2) corresponding to the time at which the current flowing through the coil reaches again the predetermined threshold (II) when said current decreases after the pulse peak; - estimating (112) the resistance of the coil based on the ratio between the sum of the values of said voltage measured between said second and first times and the sum of the values of said current measured between said second and first times; and - estimating (116) the inductance of the coil (22) of the actuator based on the estimated resistance value, wherein the inductance L is calculated by the following formula: where Rbob is the estimated resistance value, Icoil Ton and Icoil Toff are the current values measured at the pulse peak (52) and at the end of the current pulse (t2) respectively, Toff is the remaining duration of the current pulse after the pulse peak (52) has been reached, DrI, Rsh and RT1 are design constants specific to the device (2) and recorded in memory.

2. The method of claim 1, wherein, The method further comprises the step of estimating (114) the temperature of the coil of the actuator based on the estimated resistance value.

3. The method of claim 2, wherein, The temperature of the coil is iteratively calculated by the following formula: wherein Temp2 is the current value of the coil temperature, Temp1 is the previous estimated value of the temperature, Rbob2 is the current value of the coil resistance, Rbob1 is the previous value of the coil resistance, K is the thermal coefficient of the material forming the coil.

4. The method of claim 1, wherein, The resistance of the coil is estimated by the following formula: wherein 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 duration of the current pulse between the first time (t1) and the reaching of the peak of the current pulse (52), Toff is the remaining duration of the current pulse after the reaching of the peak current (52) until the second time (t2), Dr1, Rsh, R1, R2, RT4 and RT1 are design constants of the device (2), recorded in the memory.

5. The method of claim 1, wherein, The method is performed when the switching device (2) is in open state.

6. The method of claim 1, wherein, The method is performed when the switching device (2) is in closed state.

7. The method of claim 6, wherein, The method is performed during a hold phase in which the current pulse is periodically repeated.

8. The method of claim 1, wherein, The second time (t2) is identified as the time at which the measured current value is the closest to the predetermined threshold (II) when said current decreases after the pulse peak.

9. An electrical switching device comprising an electromagnetic actuator comprising a coil and a control circuit, said control circuit being configured to perform the steps of: - measuring (102) the current flowing through said coil; - measuring (104) the supply voltage of the control circuit for the actuator; - injecting (106) a current pulse into the coil (22) of the actuator (20); - identifying (108) a first time (ti) corresponding to the time at which the current flowing through the coil reaches a predetermined threshold (II) when said current increases after the pulse injection; - identifying (110) a second time (t2) corresponding to the time at which the current flowing through the coil reaches again the predetermined threshold (II) when said current decreases after the pulse peak; - estimating (112) the resistance of the coil based on the ratio between the sum of the values of said voltage measured between said second and first times and the sum of the values of said current measured between said second and first times; and - estimating (116) the inductance of the coil (22) of the actuator based on the estimated resistance value, - estimating (116) an inductance of the coil (22) of the actuator based on the estimated resistance value, wherein, The inductance (L) is calculated by the following formula: where Rbob is the estimated resistance value, Icoil Ton and Icoil Toff are the current values measured at the pulse peak (52) and at the end of the current pulse (t2) respectively, Toff is the remaining duration of the current pulse after the pulse peak (52) has been reached, DrI, Rsh and RT1 are design constants specific to the device (2) and recorded in memory.

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