Method for fault diagnosis of a switching element and control unit

Abstract

The invention relates to a method for fault diagnosis of a switching element (100) which has an electromagnet (101) and a switching piece (104) and which is configured to close or open an electrical connection (109) by moving the switching piece (104) by means of a magnetic field of the electromagnet (101).The method comprises the following steps: (i) opening or closing the switching element (100) by means of a control circuit (111), wherein the control circuit (111) includes a resistor (126) and a coil (102) of the electromagnet (101), the resistor (126) and the coil (102) being connected in parallel in the control circuit (111); (ii) performing a fault diagnosis of the switching element (100) by means of an evaluation criterion which takes into account the current (Ic) through the resistor (126) and / or the voltage (Uc) applied across the resistor (126) in response to the actuation of the switching element (100). The invention further relates to a corresponding control unit (130) and a computer program.

Description

TECHNICAL AREA

[0001] The present disclosure relates to methods and control devices for fault diagnosis of a switching element, for example a relay or a contactor, such as those used in battery management systems of electric vehicles. Specifically, methods and control devices are described for detecting whether the switching element has opened correctly or incorrectly. BACKGROUND OF THE INVENTION

[0002] Modern electric vehicles and plug-in hybrids are equipped with high-voltage batteries. To connect or disconnect the battery from the system depending on the operating mode, contactors are installed at the positive and negative terminals of the battery. These contactors can be located, for example, in a battery management system or in a high-voltage unit with charging and / or conversion electronics.

[0003] Due to safety requirements, it is important that the contactors open cleanly to reliably disconnect the high-voltage battery from the system. Disconnecting the battery is necessary, for example, when the vehicle is switched off, in the event of an accident, or in certain fault conditions. This ensures that no dangerous voltage is present in such situations.

[0004] However, various faults can occur during the control and operation of contactors. In particular, the contactors can stick or weld together while closed, for example due to high currents, and consequently no longer open. Such a fault must be reliably detected and diagnosed.

[0005] A conventional method for contact state detection in contactors is the use of positively guided auxiliary contacts, which are electrically connected when the contactor closes. Determining the contact state of the load switching contact is relatively easy for the user because the auxiliary contacts are typically electrically isolated from both the coil circuit and the load circuit. However, such auxiliary contacts increase the cost of the contactor, require additional installation space, additional drive power, and necessitate consideration of reliability and service life.

[0006] Another conventional method is the direct measurement and evaluation of the electrical voltages in the contactor's load circuit. With the contact open, a large voltage difference across the load terminals is to be expected. Conversely, with the contact closed, the voltage difference should be very small. However, especially in applications with higher operating voltages on the load side, the measurement effort becomes considerable, particularly if galvanic isolation from the control and evaluation electronics is to be maintained. Furthermore, there are cases where a clear determination of the contact state by voltage measurement is difficult, for example, when decoupling capacitors are used on the load side. SUMMARY AND FORMS OF EXECUTION

[0007] It is therefore an objective of the present disclosure to provide a convenient and reliable method for diagnosing faults in a switching element, in particular for detecting proper and / or faulty opening or closing of the switching element, and especially for detecting a welded switching element.

[0008] This task is solved by a method for fault diagnosis of a switching element, by a control unit, and by a computer program according to the independent patent claims. Advantageous embodiments and further developments are described in the respective dependent claims, the following description, and the drawings.

[0009] Thus, according to a first aspect, a method for fault diagnosis of a switching element, in particular a contactor or power contactor, is provided. The switching element comprises an electromagnet and a switching element, in particular an armature, and is configured to close or open an electrical connection by means of a magnetic field of the electromagnet moving the switching element.The method comprises the following steps: (a) opening or closing the switching element using a control circuit, wherein the control circuit includes a coil of the electromagnet and a resistor, the resistor and the coil being connected in parallel in the control circuit; (b) performing a fault diagnosis of the switching element using an evaluation criterion that considers the current waveform through the resistor and / or the voltage waveform across the resistor in response to the actuation of the switching element. The current waveform and / or voltage waveform can correlate with an arrangement of the switching element relative to the electromagnet. The arrangement can be a time-varying arrangement, i.e., a movement, or a static arrangement. The waveform can be a time-dependent waveform. The waveform can be discrete or continuous.

[0010] According to another aspect, a control unit is provided which is configured to carry out the previously described procedure. The control unit can be a battery management system, or a battery management system can incorporate the control unit.

[0011] According to another aspect, a computer program is provided that includes instructions which, when executed by a computer, cause it to perform the procedure described above. In the context of this disclosure, a computer is defined, for example, as a device that processes data using programmable computational instructions. Computers can be embedded in everyday devices, such as the control units of motor vehicles.

[0012] According to another aspect, a storage medium is provided with a computer program, wherein the computer program includes instructions which, when the computer program is executed by a computer, cause it to carry out the procedure described above.

[0013] In the context of this disclosure, the switching element is defined, for example, as an electrically or electromagnetically actuated switch. The switching may be mechanical. The switch may be designed, in particular, for switching high electrical powers, such as those encountered, for example, when charging the high-voltage batteries of electric vehicles and / or when driving electric motors using such high-voltage batteries. The switching element may have two or more switching positions, in particular a switching position in which the connection is open and another switching position in which the connection is closed. The switching element may, for example, be a contactor, in particular a power contactor, or a relay. The switching element may be a solenoid actuator. The power contactor may be configured for switching the aforementioned high powers.The switching element can be arranged at an electrical connection to the positive terminal of a battery, particularly between the battery and a load. Alternatively, the switching element can be arranged at an electrical connection to the negative terminal of the battery, particularly between the battery and the load. Switching elements can be arranged at either connection.

[0014] In the context of this disclosure, an electromagnet is defined, for example, as a component capable of generating a magnetic field due to a current flowing through it. The electromagnet may be or comprise a coil. The electromagnet may have a core or magnetic core capable of guiding, amplifying, and / or increasing the inductance of the electromagnet. The core may comprise or consist of a soft magnetic material, such as a ferromagnetic material, for example, iron.

[0015] In the context of the present disclosure, the switching element is defined, for example, as a movable element by whose movement the electrical connection can be opened or closed. The switching element may have an armature which is moved by the magnetic field of the electromagnet. The armature, like the magnetic core, may also be made of or consist of a soft magnetic material. The switching element may further have an electrically conductive closing element by means of which the electrical connection is opened or closed. The closing element may be mechanically connected to the armature, in particular rigidly connected. The closing element may have an overtravel spring or contact spring which is configured to assist in closing the electrical connection by means of spring force.

[0016] In the context of this disclosure, a control circuit is defined, for example, as a circuit by means of which the switching element, in particular the electromagnet of the switching element, is controlled. The control circuit may be configured to provide and / or control a voltage applied to the coil of the electromagnet and / or a current flowing through the coil of the electromagnet. The control circuit may be galvanically isolated from a load circuit that has the electrical connection to be closed or opened. The control circuit may be a low-voltage circuit, in particular with a voltage < 60 V DC. The load circuit may be a high-voltage circuit, in particular with a voltage > 60 V DC.

[0017] The described method and the corresponding control unit can be advantageous for reliably diagnosing the opening or closing of the switching element, or the disconnection or connection of the electrical link. Because the current flow through the resistor and / or the voltage across the resistor after activation depends on the arrangement of the switching element relative to the electromagnet, an analysis of this behavior using an appropriate evaluation criterion can detect expected or unusual movement of the switching element. For example, a lack of movement or insufficient movement can be detected if the switching element is stuck in a position, such as stuck open or stuck closed.Furthermore, an unusual position of the switching element can be diagnosed, for example, if the switching element jams in the closed state even without being actuated, perhaps because the switching element is welded shut. The relationship between current through the resistor and / or voltage across the resistor with the switching element's arrangement or movement is caused by the fact that the arrangement or movement of the switching element, especially its armature, affects the magnetic circuit and / or the inductance of the electromagnet, and thus also the aforementioned quantities.

[0018] Connecting a resistor in parallel with the electromagnet coil in the control circuit can be advantageous for limiting the voltage applied to the coil, for example, during and / or after the switching element is activated. This can contribute to the protection and longevity of the switching element and the components of the control circuit. The resistor can be used, in particular, to limit an inductive voltage, especially a negative overvoltage, that arises when the coil is switched off.

[0019] A diagnostic check during the opening actuation of the switching element can be advantageous because a non-opening switching element is particularly problematic from a safety perspective. For example, uncontrolled current flows can occur if the contact surfaces of the switching element are welded together, which in extreme cases can endanger human lives and cause fires. Diagnostic checks during the opening actuation allow a properly functioning switching element to be identified at the end of a driving cycle. Conversely, diagnostic checks during the closing actuation can also be advantageous, for example, for ensuring the proper operation of a vehicle in the subsequent driving cycle.

[0020] Furthermore, this method can be advantageous because the diagnostics are performed on the coil side within the control circuit, which is typically operated at a low voltage. The contact state can therefore be detected by evaluating electrical parameters on the coil side, which is usually galvanically isolated from the high-voltage and high-current sides. In contrast, load-side diagnostics, as practiced in the prior art, are more demanding and complex in many applications due to the generally higher voltages and currents involved.

[0021] Finally, electrical measurements from the coil circuit, which are often already routed to the control unit for monitoring and diagnosing the coil driver and the coil itself, can be used to detect the contact state. This eliminates or minimizes the need for additional hardware if a coil driver controlled by a control unit is already in place. The additional processing of the measurements for contact state detection can be performed entirely or largely in separate software.

[0022] According to one embodiment, the switching element is a contactor, in particular a power contactor. A contactor can be designed to protect electrical components connected to the electrical connection that the contactor closes or opens, for example, to protect high-voltage components of a motor vehicle, such as an electric motor, an inverter, an air conditioner, or a high-voltage battery. A contactor can be double-break, particularly unlike a relay. Finally, the contactor can have an arc-quenching chamber to counteract the formation of arcs at the switching contacts.

[0023] According to one embodiment, the switching element is used in a battery management system, in particular for disconnecting an electrical connection to an associated battery, especially a vehicle battery. In the context of the present disclosure, a battery management system or BMS is defined, for example, as a component connected to the battery that performs at least one of the following functions: monitoring, regulating, and protecting the battery and / or components connected to the battery. The battery management system may include the control unit.

[0024] In the context of the present disclosure, a battery is defined, for example, as a storage device for electrical energy, particularly on an electrochemical basis. In one embodiment, the battery is an accumulator, i.e., a rechargeable battery. The battery can be a motor vehicle battery, in particular a high-voltage battery of a motor vehicle.

[0025] According to one embodiment, the evaluation criterion is based on a time integral of a quantity that depends on a current through the resistor and / or a voltage applied across the resistor. Such an embodiment can be particularly advantageous for opening actuation because, compared to closing actuation of the switching element, the differences in the behavior of electrical parameters between a functioning and a faulty switching element may be smaller. Therefore, by integrating values ​​over an extended period, a more precise fault analysis can be achieved compared, for example, to a point-in-time evaluation of the behavior or a point-in-time evaluation of a time derivative of the behavior.

[0026] According to one embodiment, the value depends on the current through the coil and / or the voltage across a resistance of the coil. Such an embodiment can be advantageous because inductive effects generated by the arrangement or movement of the switching element particularly affect the coil voltage and / or coil current. Accordingly, a particularly accurate fault analysis can be possible if the voltage drop across the coil resistance is taken into account.

[0027] According to one embodiment, the starting point of the time integral is correlated with a change in the sign of the electromagnet's coil voltage in response to activation. Such an embodiment can be advantageous for defining the start of the integration with particular precision. According to another embodiment, the endpoint of the time integral is defined by a fixed integration time or by the coil voltage falling below a threshold value.

[0028] According to one embodiment, the integration of the time integral is performed using an integration circuit. Such hardware-implemented integration can have the advantage over software-implemented integration of typically being faster and more reliable. Furthermore, less expensive analog-to-digital converters with lower temporal resolution can be used. Alternatively, the integration can, of course, be implemented using software.

[0029] According to one embodiment, the integration circuit integrates a voltage signal, which may be provided, for example, by a voltmeter connected in parallel to the coil and / or the resistor in the control circuit.

[0030] According to one embodiment, integration start is implemented using a diode. For example, the diode can be configured and arranged such that only values ​​after a sign change of the quantity to be integrated, for example the coil voltage, contribute to the time integral.

[0031] According to one embodiment, the time integral is representative of at least one of the following quantities: work done on the resistor; work done on the resistor and a coil resistance; energy stored in a restoring element and / or an overtravel element of the switching element; an integral over a voltage induced in response to actuation; a magnetic flux that has flowed through a magnetic circuit of the switching element before actuation, in particular opening actuation.

[0032] According to one embodiment, the time integral is compared with a reference value for the evaluation criterion. In particular, it can be checked whether the integral is greater or less than the reference value. For example, proper switch opening can be assumed if the integral is greater than the reference value. A fault, such as welding of the switching element, can be assumed if the integral is less than the reference value. The reference value can be determined, for example, using a plurality of instances of the switching element in which the switching piece is either free or blocked.

[0033] According to one embodiment, the reference value depends on the current flowing through the coil before actuation, particularly before the opening actuation. Accordingly, it may be necessary for the coil current to assume a predetermined value before the opening actuation. Alternatively, coil current-dependent reference values ​​can be stored in a lookup table, a characteristic map, or a formula. The method then comprises determining the coil current before the opening actuation and selecting the reference value based on this determination.

[0034] According to one embodiment, no ammeter is arranged in the parallel branches of the control circuit in which the resistor and the coil are located, and in particular, no ammeter suitable for determining the current of the coil. Accordingly, the waveform of the corresponding currents after activation can be dispensed with for determining the time integral. For example, the waveform of the coil voltage and / or the waveform of the voltage across the resistor can be sufficient for determining the time integral. Such an embodiment can be advantageous because the aforementioned ammeter can be omitted.

[0035] According to one embodiment, at least one of the following quantities is considered for the evaluation criterion: the coil resistance of the electromagnet; the voltage across the coil resistance; or the current through the coil resistance. Considering these quantities allows for a particularly accurate and reliable fault analysis.

[0036] According to one embodiment, the resistance value of the coil is determined based on the current of a driver current of the control circuit, which is supplied to the control circuit before activation, particularly immediately before activation. The activation is preferably an opening activation. The driver current can be supplied by means of a coil driver. Such an embodiment can be advantageous because the coil resistance can be determined without measuring the current in the branch containing the coil.

[0037] According to one embodiment, the temperature dependence of the coil resistance is taken into account. This temperature dependence can be considered, for example, by measuring a coil voltage and a coil current or coil driver current before the switching element is activated and then calculating the coil resistance based on these measurements. Such an embodiment can be advantageous if the switching element is to be operated over a wide temperature range, such as in automotive applications.

[0038] According to one embodiment, performing the fault diagnosis includes detecting a faulty switching element and / or detecting a proper switching element, in particular based on the evaluation criterion.

[0039] According to one embodiment, during fault diagnosis, a faulty switching element and / or a functioning switching element is detected based on a current and / or a voltage induced by the arrangement, particularly the movement, of the switching element. Such diagnoses can be advantageous because they are particularly robust and reliable.

[0040] According to one embodiment, the evaluation criterion used during fault diagnosis detects whether the switching element, for example a contactor, is stuck closed, particularly if it is welded shut. Such an embodiment can be advantageous because a welded switching element cannot be reopened, and therefore the electrical connection cannot be disconnected. This can be problematic if disconnecting the connection is necessary for safety reasons, for example in the event of a short circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Further advantages and beneficial designs and further developments of the method, the control unit and the computer program result from the following exemplary embodiments shown in connection with the figures.

[0042] They show: Fig. 1 a switching element and a control unit for controlling the switching element according to an embodiment of the present disclosure; Fig. 2 a control circuit for controlling a switching element in order to carry out a fault diagnosis method according to an embodiment of the present disclosure; Fig. 3 an integration circuit for use in a method for fault diagnosis according to an embodiment of the present disclosure; Fig. 4 and Fig. 5 exemplary waveforms of a coil current and a coil voltage during the opening actuation of a switching element for evaluation in a method according to an embodiment of the present disclosure; the waveform of Fig. Figure 4 illustrates a proper switching element, the course of Fig. 5 a closed clamping switching element.

[0043] Identical, similar, or similarly effective elements are marked with the same reference symbols in the figures. In some figures, individual reference symbols have been omitted for clarity. The figures and the relative sizes of the elements depicted within them are not to be considered to scale. Rather, individual elements may be exaggerated for better representation and / or comprehensibility. DETAILED DESCRIPTION OF EXAMPLES OF EXECUTION

[0044] Fig. Figure 1 shows a switching element 100, here a contactor, which has an electromagnet 101 and a switching piece 104 and which is designed to close or open an electrical connection by moving the switching piece 104 by means of a magnetic field of the electromagnet 101.

[0045] The electromagnet 101 has a coil 102 and a magnetic core 103 located at least partially inside the coil 102. A voltage can be applied to the coil 102 and a current can be passed through the coil 102 via control lines 110. The voltage signal at the control lines 110 and the current signal through the control lines 110 are implemented by a control unit 130.

[0046] Adjacent to the electromagnet 101 is the switching element 104, which is movable along a predetermined direction with respect to the electromagnet 101, in particular the coil 102 of the electromagnet 101. The switching element 104 has an armature 105 and a closing element 106 attached to the armature 105 by means of a connecting piece. The closing element 106 is an electrical conductor or has one, which closes the electrical connection 109 by means of contacts 107 when the switching element 104 is in the corresponding position.

[0047] The electrical connection 109 is closed when the coil 102 is sufficiently energized by the control lines 110 to generate a magnetic field that moves the switching element towards the magnetic core 103. When no more current flows through the coil 102, the magnetic field disappears and the return element 108, in this case a return spring, causes the switching element 100 to open and the electrical connection 109 to be disconnected.

[0048] The control unit 130 is configured to perform a fault diagnosis procedure for the switching element 100. The procedure comprises the following steps: (a) opening or closing the switching element 100 by means of a control circuit (see reference numeral 111 in Fig. 2) wherein the control circuit 111 comprises a resistor 126 and a coil 102 of the electromagnet 101, wherein the resistor 126 and the coil 102 are connected in parallel in the control circuit 111; (b) Performing a fault diagnosis of the switching element 100 by means of an evaluation criterion which takes into account a current Ic through the resistor 126 and / or a voltage Uc applied across the resistor 126 in response to the activation of the switching element 100.

[0049] Fig. Figure 2 shows a control circuit 111 for controlling, for example, the switching element 100. Fig. 1. The control circuit 111 includes a coil driver 113 and a measuring device 115 for determining the coil driver current Ic_d. The following elements are connected in parallel in the control circuit 111: a measuring device 114 for determining the coil voltage Uc; a resistor 126; and finally an electromechanical drive with winding 116 or a coil 102 of an electromagnet 101, which is configured to move a switching element 104 that can open and close an electrical connection 109 by means of a closing element 106 (see figure). Fig. 1) In the branch of the parallel circuit with the electromechanical drive 116, the coil current Ic can be measured using a measuring device. The coil has an inductance Lc and a temperature-dependent resistance Rc. The working connection 109 is part of a high-voltage load circuit 112, while the control circuit 111 is a low-voltage circuit that is galvanically isolated from the load circuit 112.

[0050] The Fig. 4 and Fig. Figure 5 shows the curves of various electrical quantities characterizing the control circuit 111, in particular the coil current Ic and the coil voltage Uc (see Figure 5). Fig. 2), plotted against time t. The course of Fig. Figure 4 illustrates the proper opening of the switching element, the course of Fig. 5 a closing clamping switching element. In comparison of the Fig. 4 and Fig. 5 is in Fig. 4 a bump-shaped deviation from the exponential curve is recognizable in both the current signal Ic and the voltage signal Uc, which indicates a proper opening movement 143 of the switching element 100.

[0051] The proposed diagnosis of the contact state after switching off a DC relay or contactor coil 116 refers to the typical control of such a coil 116 by a coil driver 113, which provides either a predetermined voltage or a predetermined current and switches this voltage or current on and off to switch the relay / contactor on and off. A circuit resistor R (reference numeral 126) is provided to limit the inductive negative overvoltage that occurs when the coil 116 is switched off. The following explanations apply to this type of limiting element, in contrast to limiting elements such as suppressor diode circuits, Zener diode circuits, or freewheeling diode circuits.

[0052] The aforementioned basic control concept is in Fig. Figure 2 shows the coil circuit 111, which is often located at a low-voltage level, e.g., 12 V DC. In contrast, the load circuit 112 is galvanically isolated and located at a high-voltage level, e.g., 400 V DC or AC. Very often, the coil circuit 111 includes a coil current measurement Ic_d (see reference numeral 115) and a coil voltage measurement Uc (see reference numeral 114) for the function of the coil driver 113 and for functional diagnostics. During operation, the relay coil 116 carries the coil current Ic and is electrically characterized by the ohmic coil resistance Rc and the coil inductance Lc, where Rc and Lc vary depending on the operating state of the relay / contactor due to heating and magnetic saturation.

[0053] Especially in safety-relevant applications, a challenge lies in diagnosing the safe open state of the switching contact 107 on the load side after the switching element 100, here a relay or a contactor, has been switched off, i.e. to be able to reliably detect, for example, a stuck or welded contact 107 or a blocked armature 105.

[0054] The approach described here is based on a special dynamic effect when relays and contactors are switched off. This effect is commonly called armature reaction. Fig. 4 and Fig. Figure 5 illustrates the effect of the coil voltage Uc and coil current Ic over time when a relay or contactor coil is switched off, using the example of a DC contactor for high-voltage vehicle battery applications with a resistor circuit. When an inductor with a resistor R (reference numeral 126) is switched off, the coil current Ic and the coil voltage Uc do not drop abruptly to zero, but rather exhibit a characteristic curve typical for this type of circuit. The coil voltage Uc first jumps to a high negative value before approaching zero with an approximate exponential function. Starting from its holding current value before switching off, the coil current Ic also follows an exponential curve towards zero.

[0055] If, as in the case of a relay or contactor, a movable armature 105 is present that is spring-loaded in the opening direction, then the exponential function of the decay curves is significantly deformed at the opening moment of the armature 105. This is due to the dramatic increase in the magnetic resistance of the iron core due to the opening of the working air gap. The mechanical energy stored by the pre-loaded return spring 108 is released and is partially visible as additional electrical voltage and current, or electrical work, at the circuit resistance. Fig. 4) In the case of a mechanically blocked armature 105, e.g. if the switching contact 107 connected to the armature 105 is welded shut, the course of Uc is actually almost a smooth exponential function ( Fig. 5).

[0056] In the approach described here, according to the first and second embodiments, the switching energy is measured immediately after the switching moment by integrating it over the switching power and then compared with a previously stored value of the switching energy, the reference energy. If the measured switching energy is greater than the reference energy, then the armature 105 has opened, and thus also the connected switching contact 107. The reference energy is determined in advance by measurements of the free armature and the blocked armature on a sufficient number of units of the respective type series. If there is too much variation among the units, the switching energy for the normally free armature can also be determined for each individual unit before use, and the reference energy can then be set by subtracting a suitable amount.

[0057] An important aspect for the correct functioning of this approach is that the switch-off energy, and thus also the reference energy, is quadratically dependent on the coil current Ic flowing before switch-off, in addition to magnetic saturation effects. Therefore, it must either be ensured that the coil current Ic always has a fixed value within small error limits before switch-off, to which the reference energy is then referenced. Or, as is also taken into account in the following embodiments, the coil current Ic, Ic_d must have been measured directly before the switch-off process. Then, a stored function, characteristic curve, or table of values ​​is used that defines the reference energy as a function of the coil current.

[0058] Furthermore, it must be taken into account that the switching power occurs not only across the circuit resistance 126, but also across the ohmic resistance of the coil 102. While the significantly larger proportion of the switching power occurs across the circuit resistance (R is typically 4-5 times greater than Rc for a 12V coil), neglecting the ohmic coil resistance would introduce a considerable error. This is because the ohmic coil resistance is dependent on the coil temperature by approximately 0.4% / K, which can vary considerably depending on the ambient temperature and operating conditions, e.g., between -40°C and 180°C.

[0059] Several examples of implementation are presented below.

[0060] A first embodiment relates to the case where coil voltage Uc and coil current Ic are taken from the coil circuit according to Fig. 2 are available and the electrical work is calculated as a comparison value. In this first embodiment, the switch-off energy is determined as the electrical work W that is converted at the circuit resistance R and the ohmic coil resistance Rc directly after the coil is switched off, with the coil voltage Uc(t) and the coil current Ic(t) available as input measurements. The contact state determination process can, for example, be programmed on microcontroller hardware, but can also be implemented as an analog computer using operational amplifiers (op-amps).

[0061] The electrical work W is obtained as the time integral of the electrical power PR(t) across the circuit resistor R126 and the electrical power PR_c(t) across the ohmic resistance of the coil 102. The starting point of the integration is defined by the jump in the coil voltage Uc(t) into the negative range. The endpoint of the integration is defined either by a fixed integration time for this type of relay or contactor, or by the point at which one of the input measured variables has sufficiently approached zero. W=∫(PR(t)+PR_c(t))dt

[0062] The power dissipated at the circuit resistor is calculated as the product of the two input measurements: coil voltage Uc(t) and coil current Ic(t). PR(t)=Uc(t)⋅Ic(t)

[0063] The power dissipated at the ohmic coil resistance is calculated as the product of the ohmic coil resistance Rc and the squared input measurement Ic(t): PRc(t)=Rc⋅Ic2(t)

[0064] The ohmic coil resistance Rc cannot be assumed to be constant and stored as a fixed value due to its strong dependence on the operating temperature, but is calculated from the coil voltage Uc_h and the coil current Ic_h in the holding state of the relay or contactor, immediately before the coil 102 is switched off: Rc=Uc_hIc_h

[0065] To compare the measured electrical work W with the reference energy, the latter is first determined by applying the coil current Ic_h, which flowed through the coil immediately before switching off, to a stored characteristic curve or table of values. Finally, the comparison between the measured electrical work W and the reference energy results in the output "Contact is open" if W is greater than the reference value, and otherwise in the statement "Contact is still closed".

[0066] A second embodiment concerns the case where coil voltage Uc and coil driver current Ic_d are taken from the coil circuit according to Fig. 2 are available and the electrical work is calculated as a comparison value.

[0067] In this second embodiment, the switch-off energy is determined as the electrical work W dissipated at the circuit resistor R126 and the ohmic coil resistance Rc immediately after the coil 102 is switched off. Only the coil voltage Uc(t) is used as the input measurement with high temporal resolution. The coil drive current Ic_d is measured as a steady-state value, and therefore also with permissible low temporal resolution, immediately before switch-off. From this, the coil holding current Ic_h and the ohmic resistance Rc immediately before switch-off are calculated. Thus, compared to the first embodiment, the additional current sensor in the inductive discharge circuit is eliminated, and only one fast A / D channel is used. The contact state determination process can be programmed, for example, on microcontroller hardware, but can also be implemented as an analog computer using operational amplifiers (op-amps).

[0068] The electrical work W is also fundamentally derived as a time integral of the electrical power dissipated at the circuit resistor 126 and the ohmic resistance of the coil 102. However, as a special feature of this embodiment, the integration operation is performed using only the coil voltage Uc(t) and subsequently converted into work W. The starting point of the integration is again defined by the jump of the coil voltage Uc(t) into the negative range. The endpoint of the integration is defined either by a fixed integration time for this type of relay or contactor, or by the point at which the input measured value Uc(t) has sufficiently approached zero. The following describes how the integration over the power dissipated at R and Rc can be transformed into an integration over the squared coil voltage: W=∫(PR(t)+PRcoil(t))dt W=∫(Ucoil2(t)R+Icoil2(t)⋅Rcoil)dt W=∫(Ucoil2(t)R+Ucoil2(t)R2⋅Rcoil)dt W=R+RcoilR2∫Ucoil2(t)dt

[0069] The switching energy is calculated by first squaring the input measurement, coil voltage Uc(t), and then integrating over the integration time. Subsequent multiplication by a constant factor for this switching process, derived from the resistance values ​​of the circuit resistance R and the coil resistance Rc, finally yields the switching work W.

[0070] The circuit resistance R is stored in memory for the respective coil circuit configuration. The coil resistance Rc is determined from the total resistance Rtot of the parallel connection of R and Rc and the known circuit resistance R: Rc=R⋅RtotR−Rtot

[0071] The total resistance Rtot is determined by the quotient of coil voltage Uc_h and coil current Ic_h, each measured in the holding state immediately before the coil is switched off: Rtot=Uc_hIc_h

[0072] The coil current in the holding state, immediately before the coil is switched off, Ic_h, is calculated from the measured coil driver current Ic_d by subtracting from the measured coil driver current Ic_d the portion of the current flowing through the circuit resistance in the holding state. This portion is calculated from the measured coil voltage in the holding state, Uc_h, and the known circuit resistance R. Ic_h=Ic_d−Uc_hR

[0073] To compare the measured electrical work W with the reference energy, the latter is first determined by applying the coil current Ic_h, which flowed through the coil immediately before switching off, to a stored characteristic curve or table of values. Finally, the comparison between the measured electrical work W and the reference energy results in the output "Contact is open" if W is greater than the reference value, and otherwise in the statement "Contact is still closed".

[0074] A third embodiment concerns the case where coil voltage Uc and coil driver current Ic_d are taken from the coil circuit according to Fig. 2 are available and the induced voltage integral is calculated as a comparison value.

[0075] In this third embodiment, instead of the electrical work, the time integral of the induced voltage generated when the coil is switched off is determined. Similar to the electrical switching work, the induced voltage integral is also sensitive to the armature's movement when the coil is switched off and can therefore be used for contact state detection by comparison with a reference value, as described below. Physically, the induced voltage integral is a measure of the magnetic flux Φ that flowed through the relay or contactor's magnetic circuit before switching off and depends essentially only on the coil holding current and, of course, the armature position.

[0076] The same suggestions apply analogously to determining the reference value for the induced voltage integral as previously explained for the reference value for the electrical switching work. As with the switching work, it must also be noted here that the entire induced voltage, both that which drops across the circuit resistor 126 and that which drops across the ohmic resistance of the coil 102, is used to eliminate the strong temperature dependence of the ohmic resistance of the coil Rc as an error influence.

[0077] The only input measurement with high temporal resolution is the coil voltage Uc(t). The coil drive current Ic_d is measured as a steady-state value, and therefore also with permissible low temporal resolution, immediately before switch-off, in order to calculate the coil holding current Ic_h and the ohmic resistance Rc immediately before switch-off. Compared to the first embodiment, this eliminates the need for an additional current sensor for the coil current Ic in the inductive discharge circuit and requires only one fast A / D channel. The contact state determination process can be programmed on microcontroller hardware, for example, or implemented as an analog computer using an op-amp.

[0078] The induced voltage integral Ψ is defined as the integral over the time course of the measured coil voltage Uc(t), which is equal to the voltage drop across the circuit resistor R, and the time course of the voltage drop UR_c(t) across the coil's ohmic resistance Rc. The starting point of the integration is defined by the jump of the coil voltage Uc(t) into the negative range. The endpoint of the integration is defined either by a fixed integration time for this type of relay or contactor, or by the point at which the input measurement has sufficiently approached zero. The following describes how the integration over the voltage waveforms Uc(t) and UR_c(t) can be transformed into an integration solely over the time course of the coil voltage Uc(t): Ψ=∫(Uc(t)+UR_c(t))dt Ψ=∫(Uc(t)+Ic(t)⋅Rc)dt Ψ=∫(Uc(t)+Uc(t)R⋅Rc)dt Ψ=R+RcR∫Uc(t)dt

[0079] The induced voltage integral is calculated by first integrating only the input measurement, the coil voltage Uc(t), over the integration time. This yields the voltage integral ΨR, which initially only includes the voltage drop across the circuit resistance R. Subsequent multiplication by a constant factor for this switching process, derived from the resistance values ​​of the circuit resistance R and the coil resistance Rc, finally yields the total induced voltage integral Ψ.

[0080] The circuit resistance R is stored in memory for the respective coil circuit configuration. The coil resistance Rc is determined from the total resistance Rtot of the parallel connection of R and Rc and the known circuit resistance R: Rc=R⋅RtotR−Rtot

[0081] The total resistance Rtot is determined by the quotient of coil voltage Uc_h and coil current Ic_h, each measured in the holding state immediately before switching off the coil: Rtot=Uc_hIc_h

[0082] The coil current in the holding state, immediately before the coil is switched off, Ic_h, is calculated from the measured coil driver current Ic_d by subtracting from the measured coil driver current Ic_d the portion of the current flowing through the circuit resistance R in the holding state. This portion is calculated from the measured coil voltage in the holding state, Uc_h, and the known circuit resistance R: Ic_h=Ic_d−Uc_hR

[0083] To compare the determined induced voltage integral Ψ with the reference value for the induced voltage integral, the latter is determined beforehand by applying the coil current Ic_h, which flowed through the coil immediately before switching off, to a stored characteristic curve or table of values.

[0084] Finally, the comparison between the determined induced voltage integral Ψ and the reference value leads to the output "Contact is open" if |Ψ| is larger than the reference value, otherwise to the statement "Contact is still closed".

[0085] An advantageous variant of the third embodiment relates to the case where the coil voltage Uc and coil driver current Ic_d are taken from the coil circuit according to Fig. Two values ​​are available, and the induced voltage integral is calculated as a comparison value. According to this variant, the integrator is implemented in hardware.

[0086] Such an integrator is in Fig.Figure 3 shows the input variable Uc of the integration circuit 150 on the left and the input variables to a corresponding control unit on the right. The control unit can also reset the integration circuit 150. The integration circuit 150 has the output variable ΨR. In this advantageous embodiment of the third model, the integration over the negative time course of the coil voltage Uc(t) is performed in real time by means of an electronic circuit. The further processing of the integration result ΨR to obtain the comparison value Ψ and the comparison with the reference value to determine the contact state then takes place on a microcontroller control unit, which is advantageously also responsible for controlling the coil driver 113.The advantage of this variant is that, for the integration task, which must start precisely at the negative voltage step of Uc, no high-precision and high-resolution analog-to-digital conversion of Uc(t) is required. Instead, the integration result ΨR is read in as a DC voltage value by the control unit at the end of the integration time. The other values ​​to be read in, Uc and Ic_d, as operating parameters of the coil circuit 111 immediately before the coil 102 is switched off, are also DC voltage values.

[0087] The coil voltage Uc(t) coming from coil circuit 111 is first fed to a circuit consisting of diode D 151 and resistor R1. This circuit ensures that only the negative portion of Uc(t) after coil 102 is switched off is present at R1, and thus at the input of the integrator Int. Advantageously, a type with a short forward recovery time and low forward voltage is used for diode 151. The negative portion of Uc(t) is then fed to an inverting integrator amplifier, which essentially consists of an operational amplifier in combination with resistor R2 and capacitor C, as shown. The product of R2 and C represents the integration time constant and ensures scaling of the output voltage of the integrator Int. ΨR=−1R2⋅C⋅∫Uc(t)dt

[0088] If the output voltage of the integrator Int, which is read by the control unit, is to be exactly the mathematical integral of Uc(t), then the value 1 must be chosen for the product R2*C. However, it can sometimes be advantageous to use a scaling factor other than 1 to optimally utilize a given voltage range of the A / D converter for reading ΨR. This scaling factor is then taken into account when processing ΨR or in the reference value on the control unit. The integrating amplifier also has a reset switch for shorting C to reset the accumulated output voltage to zero after reading and to prevent the output from drifting due to offset voltages and small voltage errors over time. The control unit will advantageously open the reset switch only at the same time as sending the command to the coil driver to switch off "Coil driver OFF". Examples of suitable reset switches include...A junction field-effect transistor (JFET) or analog switch is a possibility.

[0089] The further processing of ΨR to Ψ using the read values ​​of coil holding voltage and coil driver current in the holding state before switching off, as well as the comparison of Ψ with the reference value, is carried out analogously to the described procedure in the third embodiment.

[0090] The invention is not limited to the exemplary embodiments described therein. Rather, the invention encompasses every new feature as well as every combination of features, which in particular includes every combination of features in the exemplary embodiments and claims. REFERENCE MARK 100 switching elements 101 Electromagnet 102 coil 103 Magnetic core 104 Switch piece 105 anchors 106 Locking piece 107 Contact (work contact) 108 Reset element 109 electrical connection (working connection) 110 Control line / coil connection 111 Control circuit / Low-voltage coil circuit 112 High-voltage load circuit 113 Coil drivers 114 Voltage meters 115 current meters 116 electromechanical drive with winding 126 Resistance 130 control unit 143 Opening movement 150 Integration circuit 151 Diode Uc coil voltage URc voltage across the coil's ohmic resistance IC coil current RC coil resistance Lc coil inductance Ic_d coil driver current Int Integrator res Reset element U voltage I current t time

Claims

Method for fault diagnosis of a switching element (100) comprising an electromagnet (101) and a switching piece (104) and configured to close or open an electrical connection (109) by moving the switching piece (104) by means of a magnetic field of the electromagnet (101), the method comprising the following steps: - opening or closing the switching element (100) by means of a control circuit (111), wherein the control circuit (111) comprises a coil (102) of the electromagnet (101) and a resistor (126), wherein the resistor (126) and the coil (102) are connected in parallel in the control circuit (111); - performing a fault diagnosis of the switching element (100) by means of an evaluation criterion which measures the current (Ic) through the resistor (126) and / or the voltage (Uc) applied across the resistor (126). The response to the activation of the switching element (100) is taken into account. Method according to the preceding claim, wherein the evaluation criterion is based on a time integral of a quantity that depends on the current (Ic) through the resistor (126) and / or on the voltage (Uc) applied to the resistor (126). Method according to the preceding claim, wherein the size depends on a current (Ic) through the coil (102) and / or a voltage (UR_c) across a resistance (Rc) of the coil (102). Method according to claim 2 or 3, wherein a starting point of the time integral correlates with a change in sign of a coil voltage (Uc) of the electromagnet (101) in response to being driven. Method according to one of claims 2 to 4, wherein an integration of the time integral is performed by means of an integration circuit (150). Method according to the preceding claim, wherein an integration start is implemented by means of a diode (151). Method according to any one of claims 2 to 6, wherein the time integral is representative of at least one of the following quantities: work done on the resistor (126); work done on the resistor (126) and a coil resistance; energy stored in a restoring element (108) and / or an overtravel element of the switching element (100); an integral over a voltage induced in response to the actuation; a magnetic flux that has flowed through a magnetic circuit of the switching element (100) before the opening actuation. Method according to one of claims 2 to 7, wherein the time integral is compared with a reference value for the evaluation criterion. Method according to the preceding claim, wherein the reference value depends on a current (Ic) flowing through the coil (102) before activation. Method according to one of the preceding claims, wherein no current measuring device is arranged in the parallel connected branches of the control circuit (111) in which the resistor (126) and the coil (102) are arranged. Method according to one of the preceding claims, wherein at least one of the following quantities is taken into account for the evaluation criterion: a coil resistance (Rc) of the electromagnet (101); a voltage (URc) across the coil resistance (Rc); a current (Ic) through the coil resistance (Rc). Method according to the preceding claim, wherein a resistance value of the coil resistance (Rc) is determined based on a current (Ic_d) of a driver current of the control circuit (111) which is provided to the control circuit (111) prior to activation. Method according to claim 11 or 12, wherein a temperature dependence of the coil resistance (Rc) is taken into account. Control unit (130) which is configured to perform a method according to one of the preceding claims. Computer program comprising instructions which, when executed by a computer, cause the computer to perform a method according to any one of claims 1 to 13.

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