METHOD FOR OPERATING AN ELECTRICAL CIRCUIT COMPRISING AT LEAST ONE SWITCHING ELEMENT OF A MOTOR VEHICLE, AND A MOTOR VEHICLE

Abstract

A method for operating an electrical circuit comprising at least one switching element of a motor vehicle is disclosed, wherein the switching element has a control voltage applied to it by a control device and the switching element is switched by the control voltage, wherein during at least one switching process there is determined at least one voltage measurement value describing a voltage of a Miller plateau of the control voltage and/or at least one time measurement value describing a duration of the Miller plateau, wherein the voltage measurement value and/or the time measurement value is compared respectively to at least one associated limit value and upon exceeding at least one limit value the control device initiates at least one action associated with the exceeded limit value.

Claims

1. A method for operating an electrical circuit comprising at least one switching element of a motor vehicle, the method comprising: applying a control voltage, by a control device, to the switching element, wherein the switching element is switched by the control voltage; during at least one switching process, determining at least one voltage measurement value describing a voltage of a Miller plateau of the control voltage and/or at least one time measurement value describing a duration of the Miller plateau; comparing the voltage measurement value and/or the time measurement value to at least one associated respective limit value; and upon the voltage measurement value and/or the time measurement value exceeding the at least one limit value, initiating, by the control device, at least one action associated with the exceeded limit value.

2. The method according to claim 1, wherein the voltage measurement value and/or the time measurement value are respectively compared to multiple limit values, and different actions are associated respectively with the limit values.

3. The method according to claim 1, wherein the action involves decreasing a time interval between the determination of the voltage measurement values and/or the time measurement values for different switching processes, decreasing a frequency of the switching processes of the switching element, decreasing an output voltage and/or an output current of the switching element, disconnecting of the switching element and/or the electrical circuit and/or an indication of aging information regarding aging of the switching element in the motor vehicle and/or the relaying of this information to a communication device external to the vehicle.

4. The method according to claim 1, wherein the action undertaken is a change in operating state of the motor vehicle.

5. The method according to claim 4, wherein a traction motor of the motor vehicle is operated by the switching element, and the action undertaken is a reduction of power and/or a limitation of power of the traction motor.

6. The method according to claim 4, wherein the motor vehicle is adapted to carry out an autonomous driving operation, wherein the action initiated is an autonomous driving maneuver of the motor vehicle and/or a scheduling of performance of an autonomous driving maneuver for a later time.

7. The method according to claim 6, wherein the autonomous driving maneuver performed is a stopping maneuver or driving to a predetermined target position.

8. The method according to claim 7 wherein the predetermined target position is a repair shop or a service facility.

9. The method according to claim 1, wherein a traction inverter of the motor vehicle is used as the electrical circuit.

10. The method according to claim 1, wherein the determination of the voltage measurement value and/or the time measurement value begins when an output voltage falling across a switchable switching portion of the switching element and/or an output current flowing in the switching portion corresponds respectively to a first limit value, and the determination of the voltage measurement value and/or the time measurement value ends when the output voltage and/or the output current corresponds respectively to a second limit value.

11. The method according to claim 1, wherein a control device is used, comprising a driver circuit to generate the control voltage and a measurement device to detect the voltage measurement value and/or the time measurement value, wherein the driver circuit and the measurement device are realized on a common circuit board arrangement.

12. The method according to claim 10, wherein the measurement device comprises a measurement value detection circuit and the driver circuit comprises a control circuit, wherein a measurement value detection circuit and a control circuit are used which are designed as a common integrated circuit.

13. A motor vehicle, comprising: an electrical circuit including at least one switching element; and a control device; wherein the switching element has a control voltage applied to it by the control device and the switching element can be switched by the control voltage, wherein the control device is adapted to carry out a method including: applying the control voltage, by the control device, to the switching element, wherein the switching element is switched by the control voltage; during at least one switching process, determining at least one voltage measurement value describing a voltage of a Miller plateau of the control voltage and/or at least one time measurement value describing a duration of the Miller plateau; comparing the voltage measurement value and/or the time measurement value to at least one associated respective limit value; and upon the voltage measurement value and/or the time measurement value exceeding the at least one limit value, initiating, by the control device, at least one action associated with the exceeded limit value.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0037] Further benefits and details will emerge from the embodiments described in the following, and with the aid of the drawings.

[0038] FIG. 1 illustrates a motor vehicle.

[0039] FIG. 2 is a detail view of an electrical circuit comprising multiple switching elements, as well as a control device of the motor vehicle.

[0040] FIG. 3 is a first diagram, showing the variation of the control voltage of a switching element in various states of aging.

[0041] FIG. 4 is a second diagram, showing the variation of the control voltage over time to explain an embodiment of a method.

[0042] FIG. 5 is a block diagram of a method.

DETAILED DESCRIPTION

[0043] FIG. 1 represents an embodiment of a motor vehicle 1. The motor vehicle 1 comprises an electrical circuit 3 having multiple switching elements 2 as well as a control device 4. The control device 4 can apply a control voltage on the switching elements 2 of the electrical circuit 3, whereupon the switching elements 2 are respectively switched by the control voltage, i.e., alternately turned on and off, in particular.

[0044] The electrical circuit 3 in the present instance is designed as a traction inverter, which converts a direct current from a traction energy accumulator 5 of the motor vehicle 1 into an alternating current to operate an electrical traction motor 6 of the motor vehicle 1. The traction energy accumulator 5 may be designed, for example, as a high-voltage battery, wherein the electrical circuit 3 converts the direct current taken from the traction energy accumulator 5 into a three-phase alternating current, for example, to operate the traction motor 6. Conversely, the converting of an alternating current generated by the traction motor 6 in a generator operation into a direct current for charging the traction energy accumulator 5 by the electrical circuit 3 is also possible. The layout of the electrical circuit 3 and the control device 4 will be explained in detail in the following.

[0045] FIG. 2 shows the electrical circuit 3 and the control device 4 of the motor vehicle 1. The electrical circuit 3 is designed as a three-phase bridge rectifier and it comprises six switching elements 2, which are wired as three half-bridges 7. The switching elements 2 are respectively designed as MOSFETs on a silicon carbide base (SiC-MOSFETs) and have for example a voltage strength of at least 1200 V. The electrical circuit 3 furthermore comprises an intermediate circuit capacitor 8 as well as two terminals on the direct current side, HV+ and HV−, which are connected to the traction energy accumulator 5 of the motor vehicle 1. Moreover, the electrical circuit 3 comprises three phase terminals on the alternating current side, U, V and W, which are connected to the traction motor 6 of the motor vehicle 1.

[0046] The control device 4 comprises a measurement device 9 as well as a driver circuit 10. The driver circuit 10 serves for generating a control voltage for the switching of the switching elements 2 of the electrical circuit 3. The driver circuit 10 and the measurement device 4 are realized on a common circuit board arrangement. The measurement device 9 comprises a measurement value detection circuit 11, which is implemented with a control circuit 21 of the driver circuit 10 as a common integrated circuit 22. The measurement device 9 furthermore comprises two voltage dividers 12, 13, which are formed by separate resistances arranged on the common circuit board arrangement of the driver circuit 10 and the measurement device 9.

[0047] The measurement device 9 serves for determining, during at least one switching process of one of the switching elements 2 of the electrical circuit device 3, at least one voltage measurement value describing a voltage of a Miller plateau of the control voltage U.sub.GS and/or at least one time measurement value describing a duration of the Miller plateau. In the present instance, there is represented the determination of a voltage measurement value and a time measurement value by the measurement device 9 for one of the switching elements 2. The measuring of voltage measurement values and time measurement values can be carried out in particular for all switching elements 2 of the electrical circuit 3, while the components of the measurement device 9 needed for the detecting of the measurement values at the other switching elements 2 are not represented for reasons of clarity.

[0048] Also only a portion 14 of the driver circuit 10 is represented, which serves for triggering one of the switching elements 2 by means of a control voltage. A control voltage is also applied to the other switching elements 2 by corresponding parts 14 of the driver circuit, these parts and the connections between the part 14 and the other parts to the control circuit 21 of the driver circuit 10 not being shown for sake of clarity.

[0049] In the present instance, the control voltage of the switching element 2 designed as a SiC-MOSFET is a gate-source voltage U.sub.GS. The switching element 2 furthermore has a drain-source voltage U.sub.DS as its output voltage as well as a drain current I.sub.D as its output current. A voltage U.sub.DS,mess proportional to the output voltage U.sub.DS of the switching element 2 is picked off by the voltage divider 12 of the measurement device 9. The control voltage U.sub.GS of the switching element 2 is accordingly picked off by the voltage divider 13 as the proportional voltage U.sub.GS,mess. The picking off of the control voltage U.sub.GS occurs between the gate terminal of the switching element 2 and a serially connected gate resistance R.sub.G.

[0050] For the detecting of the measurement values, the measurement device 9 furthermore comprises a unity-gain amplifier 15 for impedance conversion and a comparator 16, with which the detected output voltage U.sub.DS,mess can be compared to at least one limit value U.sub.ref. The output of the comparator 16 and the voltage measurement value U.sub.GS,mess of the gate voltage, picked off by the voltage divider 13, are detected by a tripping and holding device 17 of the measurement device 9. The detection of U.sub.GS,mess is tripped by the output of the comparator 16, especially if the falling or rising measured output voltage U.sub.DS,mess corresponds to the limit value U.sub.ref and the output of the comparator 16 switches over.

[0051] The measurement values U.sub.GS,mess now detected in the tripping and holding device 17 can then be digitalized by an analog-digital converter, such as a Delta-Sigma converter, and relayed via a communication interface 19, designed in particular as a galvanically separating, bidirectional communication interface, across terminals 20 to a communication link of the motor vehicle 1, such as a data bus or the like. A determination at the control circuit 21 of the driver circuit 10, designed for example as a controller, is also possible. Moreover, aging information regarding the aging of the switching element 2 can also be relayed by the communication interface 19 to a display device within the vehicle and/or to a communication device outside the vehicle.

[0052] The voltage divider 12 is designed such that it reduces the output voltage U.sub.DS corresponding to the voltage level of the traction energy accumulator 5 down to a lower level for the detection in the integrated circuit, for example to a voltage level of 5 Volt. Accordingly, the voltage divider 13 is also designed to reduce the gate voltage of the switching element 2, which can be between 15 Volt and 18 Volt in the switched-on state, for example, down to a comparable voltage level.

[0053] Thanks to the detecting of the voltage measurement value U.sub.GS, mess, at least one voltage value is detected during a switching process of the switching element 2 that describes the voltage level of a Miller plateau in the variation of the control voltage U.sub.GS of the switching element 2. In addition or alternatively, a time measurement value can also be detected, describing the duration of the Miller plateau in the variation of the control voltage U.sub.GS of the switching element 2. For this, the time measurement value so determined can be the duration between a decrease in magnitude of the output voltage U.sub.DS,mess between a first limit value U.sub.ref,1 and a second limit value U.sub.ref,2. This shall be further explained in relation to FIG. 4.

[0054] The time measurement values and/or voltage measurement values determined in this way are compared each time by the measurement device 9 and/or another device of the control device 4 to at least one limit value. If at least one limit value is exceeded, the control device 4 initiates at least one action associated with the limit value so exceeded, as will be described more fully in relation to FIG. 5.

[0055] The voltage measurement value describing a voltage of the Miller plateau in the variation of the control voltage of the switching element 2 and the time measurement value describing the duration of the Miller plateau each represent a measure of the aging of the switching element 2. The switching element 2 ages during the operation of the electrical circuit 3, especially due to the temperature fluctuations which it experiences. Especially in the switched-on state, the switching element 2 can become greatly heated, since the output current I.sub.D is flowing through it.

[0056] FIG. 3 shows schematically the variation of the control voltage U.sub.GS for three different aging states. The variation of the control voltage U.sub.GS here represents each time a switching-on process of the switching element 2. The curve U.sub.GS,0(t) shows the least aging phenomena, the curve U.sub.GS,1(t) corresponds to the variation of the gate voltage with slight age-related effects, and the curve U.sub.GS,2(t) corresponds to the variation of the gate voltage with stronger aging effects. Each of the curves of the control voltage U.sub.GS(t) has a Miller plateau, associated each time with a voltage U.sub.GP,0, U.sub.GP,1 or U.sub.GP,2. Moreover, the plateaus each have a duration t.sub.GP,0, t.sub.GP,1 or t.sub.GP,2. With increasing aging of the switching element 2, both the voltage of the Miller plateau U.sub.GP and the duration t.sub.GP of the Miller plateau increase. For example, the values given in the following table may occur:

TABLE-US-00001 U.sub.GS, 0(t) U.sub.GS, 1(t) U.sub.GS, 2(t) gate-plateau voltage U.sub.GP, i [V] 5.2 6.5 7.2 gate-plateau time t.sub.GP, i [ns] 50 64 86

[0057] The times t.sub.GP,i can be detected directly by the measurement device 9 as time measurement values. Based on the voltage dividers 12, 13 used, voltage measurement values U.sub.GS,mess proportional to U.sub.GP,i are detected.

[0058] FIG. 4 shows schematically the variation of one switching voltage U.sub.GS. The switching-on process starts at the time t.sub.0 with a rising control voltage U.sub.GS. At the time t.sub.1, when the control voltage corresponds to the threshold voltage U.sub.th, the output current I.sub.D also begins to rise. At the time t.sub.2, when the Miller plateau begins, the output voltage U.sub.DS of the switching element 2 drops and the output current I.sub.D has reached its maximum value. At this time, the detecting of one or more voltage measurement values describing the voltage U.sub.GP of the Miller plateau can be commenced.

[0059] The detecting of the measurement values by the measurement device 9 can be triggered in particular when the output voltage U.sub.DS of the switching element 2, dropping across the switchable portion of the transistor, i.e., the drain-source section, is detected as U.sub.DS,mess and compared to at least one limit value U.sub.ref. This is represented schematically in FIG. 2 as the limit value U.sub.ref,1 at the input of the comparator 16. The limit value U.sub.ref,1 may correspond, for example, by 95% to a maximum possible drain-source voltage U.sub.DS,mess. In addition, it is possible for the output current I.sub.D to be measured by the measurement device 9 or relayed to the measurement device 9, for example, from a control system of the traction motor 6, in which the corresponding current occurs as a measurement value. In addition to the comparison of U.sub.DS,mess, a comparison of I.sub.D to a limit value can also be done to trigger the measurement, in which case the limit value may correspond in particular to the maximum attainable drain current I.sub.D,max.

[0060] The Miller plateau ends at the time t.sub.3 when the voltage U.sub.DS has reached the value of the forward voltage U.sub.DS,on. At this time, the measurement value detection can be halted, or the time measurement value can be detected as the time between the times t.sub.2 and t.sub.3. For this, U.sub.DS,mess can be compared to a second limit value U.sub.th,2, corresponding to the forward voltage U.sub.DS,on of the switching element 2.

[0061] It is possible to detect several voltage measurement values U.sub.GS,mess within the duration of the Miller plateau between t.sub.2 and t.sub.3, especially when the variation of the control voltage U.sub.GS also has a rise in the region of the Miller plateau. A voltage measurement value described as the voltage of the Miller plateau can also be formed as the average of the detected voltage measurement values U.sub.GS,mess or the measurement value detected at time t.sub.2 and the measurement value detected at time t.sub.3 can be compared to each their own limit value, for example.

[0062] FIG. 5 shows a block diagram of one embodiment of a method. The method starts with a step S1, for example, when the electrical circuit 3 of the motor vehicle 1 is placed in operation. Thus, the method can start for example when the motor vehicle 1 begins to travel, and the electrical circuit 3 designed as a traction inverter will also commence its operation.

[0063] After this, in step S2, one or more voltage measurement values, each describing a voltage of the Miller plateau, are determined from the control voltage of each of the switching elements 2 of the electrical circuit 3. In addition or alternatively, as was described above, a time measurement value is also determined for each of the switching elements 2, each time representing the duration of the Miller plateau in the variation of the control voltage of the particular switching element 2.

[0064] Next, in step S3, the measurement values are compared to a respective associated limit value. If at least one of the limit values is exceeded, an action associated with the limit value will then be taken in step 4 in order to allow for the aging of the switching element. It is possible to compare the detected voltage measurement values and/or time measurement values to multiple limit values. This is represented schematically by step S5, in which a further limit value comparison is done. If this limit value is exceeded, an action associated with the further limit value so exceeded will be initiated in a step S6. Different associated actions are possible for different degrees of aging of the switching element 2 thanks to the use of different limit values. If multiple limit values are exceeded, multiple actions can be carried out, or only one action may be initiated, especially the action associated with the highest limit value.

[0065] As a first action, for example, a time interval between the determination of the voltage measurement values and/or the time measurement values for different switching processes can be decreased. For example, instead of a detection of the voltage measurement values and/or the time measurement values each time at the start of a driving operation of the motor vehicle 1, the time interval can be diminished, so that at least one voltage measurement value and/or at least one time measurement value is also detected at one or more times during the driving operation and/or at the end of the driving operation and compared to the respectively associated limit values. In this way, the frequency of detection can be increased for increasing aging of the switching element 2, so that a more precise tracking of the further aging process of the switching element 2 can occur.

[0066] Another action which can be initiated is a decreasing of the frequency of the switching processes of the switching element 2. A lowering of the output voltage U.sub.DS and/or the output current I.sub.D of the switching element 2 is also possible. As a last action, a disconnecting of the switching element 2 and/or the electrical circuit 3 can also be done if the aging of the switching element 2 may result in immediate impairment of the operation of the electrical circuit 3 and/or the motor vehicle 1.

[0067] It is also possible to undertake a change in operating state and/or a limitation of operating state of the motor vehicle 1 as the action. For example, the action performed can be a reduction and/or a limitation of the power capacity of the traction motor 6.

[0068] It is possible for the motor vehicle 1 to be designed to carry out an autonomous driving operation, in which case the action initiated will be an autonomous driving maneuver of the motor vehicle 1 and/or the performance of an autonomous driving maneuver at a later time. The autonomous driving maneuver performed may be in particular a stopping maneuver. It is also possible for the driving maneuver to be the driving to a predetermined target position, such as a work shop or a service facility. This makes it possible for the motor vehicle 1 in autonomous driving operation to itself seek out a servicing location when an age-related replacement of the switching elements 2 becomes necessary. In this way, a predictive maintenance of the motor vehicle 1 becomes possible. Defective switching elements 2 can thus be replaced before age-related impairments occur during their operation or the operation of the motor vehicle 1.

[0069] Furthermore, an action may be the displaying of information about the aging of the switching element 2 in the motor vehicle 1. In this way, the driver or a passenger of the motor vehicle can be made aware of the aging so discovered. The aging information may also describe a further action taken on account of the limit value exceeded, so that this action can also be made known to them. The aging information can be indicated for example on a display device of the motor vehicle. In addition or alternatively, the aging information can also be relayed to a communication device outside the vehicle.

[0070] It is also possible to employ the method as described herein for switching elements other than the switching elements of a traction inverter. Moreover, it is possible for the switching elements 2 to be designed not as silicon carbide MOSFETs, but rather as other MOSFETs or as IGBTs. In the case of IGBTs, the control voltage accordingly represents the gate-emitter voltage, the output voltage corresponds to the collector-emitter voltage, and the output current corresponds to the collector current. The detection of the voltage measurement values and/or the time measurement values can also be done in the case of the IGBT as previously described in regard to the SiC-MOSFET.

[0071] German patent application no. 10 2021 116772.8, filed Jun. 30, 2021, to which this application claims priority, is hereby incorporated herein by reference in its entirety. Aspects of the various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.