Method and apparatus for operating a power semiconductor element

Abstract

The invention relates to a method and device for operating a power semiconductor element with an adjustable through-resistance for a power current (I), wherein a control variable (SGmin) for setting the minimum through-resistance is changed, wherein the control variable (SGmin) for setting the minimum through-resistance is set to a target value (ZW) that deviates from a recommended value (SGmin_r) for setting a nominal minimum through-resistance and leads to a reduction of the minimum through-resistance compared to the nominal minimum through-resistance. where the control variable (SGmin) is set to the target value (ZW) if a current or future high current event is detected.

Description

[0001] The invention relates to a method and device for operating a power semiconductor element.

[0002] Power semiconductor elements are used in electric or hybrid vehicles, as well as in other applications. These can, for example, be part of a pulse-controlled inverter (PWR), which is one of the key components of e-mobility. Optimizing this component has a positive effect on the entire drive train and thus leads to real added value for the end user. A commutation cell of a PWR consists of an intermediate circuit and at least one half-bridge. Optimizations can be made both mechanically, e.g. in the layout of the half-bridge, the connection to the intermediate circuit, and electrically, e.g. by optimizing the gate driver circuit or optimizing the semiconductor characteristics. In an electric or hybrid vehicle, the PWR can be part of a traction network and serve to provide an alternating voltage for an electric drive motor.

[0003] For example, power semiconductor devices can be implemented as silicon carbide MOSFETs. Recommended gate voltages for such MOSFETs for setting a nominal maximum or minimum contact resistance are usually specified by the semiconductor manufacturer. For example, recommended values ​​for setting a nominal minimum contact resistance range between 15V and 18V depending on the manufacturer. The recommended value is usually kept constant during operation. The chip area of ​​a power semiconductor device is often designed based on the highest current occurring in the drive. Such a current can occur, for example, during short-term boost operation lasting 5-20 seconds at high coolant and ambient temperatures. The active short circuit of the drive motor can also be selected as a design criterion, because this is where the highest currents occur.

[0004] US 2011 / 007536 A1 relates to a device for controlling an inverter and in particular to the suppression of surge voltages and the reduction of stationary losses.

[0005] US 2019 / 0149145 A1 discloses a gate driver for a solid-state switch of a vehicle power module in which a variable resistor is coupled between a mirror switch emitter and a load switch emitter.

[0006] US 10,505,538 B1 discloses circuit topologies and associated control methods for use in a system when energizing a driven load, e.g., a multiphase electric machine or a resistive load. In particular, a dynamic gate drive system and control method are disclosed that together address limitations of certain circuit topologies tailored to the worst-case sizing of the gate resistance.

[0007] WO 2021 / 047768 A1 discloses power semiconductor switches such as IGBTs and in particular reducing the thermal load of a power semiconductor switch.

[0008] US 2009 / 0001915 A1 relates to the control of electric drives, in particular methods and devices for voltage control of electric motors.

[0009] The technical problem is to create a method and a device for operating a power semiconductor element which increase the application range of the power semiconductor element without changing, in particular enlarging, the installation space of the power semiconductor element.

[0010] The solution to the technical problem is achieved by the subject matter having the features of the independent claims. Further advantageous embodiments of the invention are set forth in the subclaims.

[0011] A method for operating a power semiconductor element with an adjustable contact resistance for a power current is proposed. The power semiconductor element can be a field-effect transistor or a thyristor. For example, a power semiconductor element can be a MOSFET, in particular a SI-MOSFET or a GaN-MOSFET, an IBGT, an IGCT, or another power semiconductor element.

[0012] The power semiconductor element can be a component of a power converter, in particular an inverter or rectifier, in particular a component of a single-phase or multi-phase, in particular three-phase, inverter. The power converter can in turn be a component of an electrical network, in particular a traction network of a vehicle, e.g., an electric or hybrid vehicle. In addition to the power converter or power semiconductor element, the traction network can comprise an energy storage device, in particular a traction battery, a drive motor, in particular an electric drive motor, and / or an intermediate circuit capacitor. Thus, a power converter, a traction network, and a vehicle having one or more power semiconductor elements according to one of the embodiments described in this disclosure are also described.

[0013] In the method, a control variable is changed to set a minimum contact resistance. To switch the power semiconductor element on and off, the control variable can be changed between a recommended minimum value and a recommended maximum value, whereby the power semiconductor element is switched on and thus conducts power current when the control variable is set to the recommended minimum value or the recommended maximum value. If the control variable is set to the remaining of the two recommended values, the power semiconductor element is switched off and thus does not conduct power current. The recommended minimum value and the recommended maximum value can be fixed, power semiconductor element-specific values. These can, for example, be specified by the manufacturer of the power semiconductor element.Thus, one of the recommended values ​​is assigned to the conducting state. The nominal minimum contact resistance refers to the resistance in the conducting, i.e., switched-on, state and can also be referred to as Rds_on, i.e., the resistance in a state in which the control variable is set to the corresponding recommended value. The nominal maximum contact resistance refers to the resistance in the non-conducting, i.e., switched-off, state, i.e., in a state in which the control variable is set to the corresponding recommended value. The control variable can be a voltage or a current, e.g., a gate voltage.

[0014] In the case of a MOSFET, the control variable is a gate voltage. Setting the gate voltage to a recommended maximum value, e.g., +15V, places the MOSFET in a conducting state with the nominal minimum on-resistance. This value is also commonly referred to as Vgs, max, or recommended Vgs. The MOSFET can be set to a non-conducting state with the nominal maximum on-resistance if the gate voltage is set to a recommended minimum value, e.g., -4V.

[0015] Furthermore, the control variable for setting the minimum contact resistance is set to a target value that deviates from a recommended value for setting a nominal minimum contact resistance and leads to a reduction in the minimum contact resistance compared to the nominal minimum contact resistance. The nominal minimum contact resistance refers to the contact resistance that results when the control variable is set to the recommended value for setting the minimum contact resistance. This value is derived from the properties of the power semiconductor element and can, for example, also be specified by the manufacturer of the power semiconductor element.In particular, the target value lies outside the value range between the nominal minimum contact resistance and the nominal maximum contact resistance, in particular such that the actual minimum contact resistance is lower than the nominal minimum contact resistance resulting from setting the control variable to the recommended value associated with the conducting state. For this purpose, for example, in the case of a MOSFET, the gate voltage can be set to a value that is greater than the recommended maximum value by a predetermined difference, e.g. +3V. In other words, the target value in this exemplary embodiment is +18V. The control variable for setting the minimum contact resistance can be set to the target value for a predetermined period of time, wherein the predetermined period of time is fixedly parameterized.Fixed parameterization can mean, in particular, that the time period is not changed during the service life of the power semiconductor element or that the time period is only slightly changed during the service life of the power semiconductor element, for example, by no more than 10%. The predetermined time period can be in the range of seconds, for example, less than 10 seconds. The change can depend on the operating time already achieved. The predetermined time period can, for example, be stored in a memory device before the power semiconductor element is put into operation. The setting to the target value occurs, in particular, independently of any surge voltage of the power semiconductor element.The value of the predetermined time period can be set such that the total duration of the periods in which the target value is set does not exceed a predetermined value during a predetermined lifetime of the power semiconductor element. For this purpose, the number of periods in which the target value is set can be predetermined based on expert and / or empirical knowledge or based on a model.

[0016] However, fixed parameterization is not mandatory. As explained in more detail below, the duration of the control variable can also be set to the specified value for a period not specified in advance.

[0017] The control variable can be provided by at least one control variable provision device, as explained in more detail below. This device, in turn, can be controlled by a control and evaluation device to provide a desired control variable. This control and evaluation device can also evaluate at least one criterion for setting the control variable to the target value. Example criteria are explained below.

[0018] According to the invention, the control variable is set to the target value when a future high-current event is detected. A high-current event can, in particular, represent an operating scenario in which a desired or actual power current through the power semiconductor element is greater than a predetermined threshold value. In addition, a high-current event can be characterized by a switching frequency of the power semiconductor element that is lower than a predetermined switching frequency. The predetermined switching frequency is, in particular, selected such that a rotational frequency of the electric drive machine, which is provided by the power semiconductor element with the aid of the operating voltage or the operating current, is lower than a predetermined rotational frequency. Low rotational frequencies can lead to a high load on the power semiconductor elements, which together provide the operating voltage or the operating current for the drive machine.The rotational frequency can correlate with the frequency of the operating current (i.e. the power current) or the operating voltage.

[0019] The detection of a current or future high-current event can be carried out in particular by an evaluation device, e.g. the control and evaluation device explained above. This can, for example, evaluate a current target or actual value of the power current, which is detected, for example, by an existing current sensor, and detect a current high-current event if the value is greater than a predetermined threshold. In addition, the evaluation device can evaluate a current target or actual value of the switching frequency, which is specified, for example, by an existing control device, and detect a current high-current event if the value is less than a predetermined threshold. The switching frequency can also be determined as a function of a frequency of the power current, which can in particular be detected with the aid of a sensor.

[0020] A future high-current event can, for example, be determined depending on the time profile of a power current. For example, a rate of change of the power current can be determined, with a high-current event being detected if the sum of a current actual value of the power current and the product of the rate of change and a predetermined time period is greater than a predetermined threshold value. In addition, the evaluation device can determine a rate of change of the switching frequency and detect a future high-current event if the sum of a current actual value of the switching frequency and the product of the rate of change and the predetermined time period is less than a predetermined threshold value. A high-current event can occur in particular if a vehicle driven by the drive motor drives up a curb, with the operating voltage orThe operating current of the drive motor is provided at least in part by the power semiconductor element. In this case, a high-current event can be detected if such a curb crossing or curb climbing is detected. This advantageously enables easier crossing of the curb.

[0021] Of course, other high-current events are also conceivable.

[0022] This advantageously results in the power semiconductor element being able to be operated with a reduced minimum contact resistance in operating scenarios requiring a high power current compared to normal operation. This in turn advantageously reduces the generation of thermal energy due to resistance losses when a power current flows through the power semiconductor element, and thus also reduces thermal stress on the power semiconductor element. This in turn enables, for example, the power semiconductor element to be operated briefly at high (semiconductor and / or ambient) temperatures without exceeding a permissible maximum temperature of the power semiconductor element, wherein the temperature of the power semiconductor element is particularly dependent on an ambient temperature, a coolant temperature, and the resistance losses. A reduction in the resistance losses thus allows, for example,an increase in the ambient temperature and / or the coolant temperature without exceeding a permissible maximum temperature. Furthermore, it is advantageously achieved that such operation is also possible without increasing the installation space of the power semiconductor element, in particular the required chip area, since no increase in installation space is required to reduce the minimum contact resistance. In other words, the power density of the semiconductor component can thus be advantageously increased. This, in turn, can be advantageously...

[0023] This can be achieved without increasing manufacturing costs. This expands the application range of the power semiconductor device. If the high-current event is detected using components already present in the vehicle, particularly sensors and evaluation devices, this advantageously results in a simple and cost-effective implementation of the method. Overall, the method can also lead to improved acceptance of e-mobility.

[0024] The described method can also be used in industry, energy technology, consumer electronics, medical technology, and other fields, particularly for operating a power semiconductor element as a component of a power converter. In a vehicle, the described method can advantageously achieve increased efficiency, low losses, and thus an extended range.

[0025] In a further embodiment, the control variable is immediately set to the target value when a future high-current event is detected. In this case, the setting takes place before the high-current event occurs. This in turn can result in a power current through the power semiconductor element increasing before the high-current event occurs due to the reduced contact resistance, whereby at the time of occurrence, the difference between the then required target power current and the actual power current changed by the increase is smaller than without the explained increase. The required target power current can then also advantageously be set more quickly, which leads to an improved driving experience when and during the high-current event, e.g., smoother driving over the curb.

[0026] In a further embodiment, the control variable is set to the target value after a predetermined period of time has elapsed after a detection time if a future high-current event is detected at the detection time. The predetermined period of time can be the period of time until the high-current event occurs. The predetermined period of time can also be a period of time until a time shortly before the high-current event occurs, which, for example, lies before the time of occurrence of the high-current event by a predetermined time threshold. The predetermined period of time can be determined, in particular by evaluating a value detected by at least one sensor or its time profile and / or by evaluating a value predetermined by at least one control device or its time profile, e.g. by the evaluation device explained.Such values ​​can be values ​​of the power current or the switching frequency, but also values ​​other than these. This advantageously reduces the generation of thermal energy due to resistance losses when a power current flows through the power semiconductor element, and thus also reduces thermal stress on the power semiconductor element. However, the time required to adjust the control variable to the target value is also kept as short as possible, which has a beneficial effect on the service life of the power semiconductor element.

[0027] In a further embodiment, a current or future high-current event is detected by evaluating a signal generated by a vehicle sensor. The vehicle sensor can refer to a sensor that is already permanently installed in the vehicle. Example sensors are explained in more detail below. In particular, by evaluating the optical signal, an obstacle, e.g. a curb, that lies in front of the vehicle in a current or predicted direction of travel can be detected, wherein driving over the obstacle represents a high-current event. It is possible for the high-current event to be detected by evaluating a plurality of signals generated by at least two different vehicle sensors. It is also possible for the high-current event to be detected by evaluating a fused signal generated from the output signals of at least two different vehicle sensors.As previously explained, this has the advantage that the high-current event can be detected using components already present in the vehicle, which enables a simple and cost-effective implementation of the method.

[0028] In a further embodiment, the signal is generated by at least one image capture device of the vehicle. This image capture device can comprise a CMOS or CCD sensor and generate a two-dimensional image. The image capture device can be a front or rear view camera of the vehicle. Alternatively, the signal can be generated by at least one radar sensor or by at least one lidar sensor. Further alternatively, the signal can be generated by at least one torque sensor. This can detect or determine the torque required or provided at at least one driven wheel, e.g., by a suitable calculation depending on further variables. For example, a high-current event can be detected if the torque is higher than a predetermined threshold value. If a vehicle comprises several driven wheels, such asIn the case of an all-wheel drive, a difference between the torques required or supplied to various driven wheels can also be evaluated to detect the high-current event. In this way, a first torque for driving a first wheel or a first set of wheels, e.g. the rear wheels, and a further torque for driving a further wheel or a further set of wheels, e.g. the front wheels, can be determined, with the high-current event being detected as a function of the difference between the further torque and the first torque, e.g. if the difference is greater than a predetermined threshold. If, for example, the vehicle is driving forward and it is detected that the further torque is greater than the first torque for both wheels / sets of wheels at the same target speed, it can be detected that the vehicle is driving over an obstacle.In this case, a future high-current event can be detected for the power semiconductor elements that are part of the inverter for driving the first wheel or the first set of wheels. Alternatively, the signal can be generated by at least one tire position sensor. A tire position sensor can refer to a device that can detect or determine a tire position, e.g., by a suitable calculation depending on other variables, e.g., a distance, speed, or acceleration variable. A current or future high-current event can be detected if, based on the current tire position, an obstacle is detected that lies in front of the vehicle in a current or predicted direction of travel, wherein an obstacle position can be determined, for example, from predetermined map data.The use of the output signals of the sensors described advantageously results in a reliable and accurate detection of a high current event.

[0029] In a further embodiment, a current or future high-current event is detected depending on an actual value of a power current and / or a temporal profile of the actual value of a power current, wherein the power current is a current flowing through the power semiconductor element. An exemplary embodiment of such a detection has already been explained above. However, the essential feature of this embodiment is that the power current of the power semiconductor element is evaluated, whose contact resistance is then changed. Since power semiconductor element-specific current variables are thus evaluated, reliable detection is advantageously achieved.

[0030] In a further embodiment, a current or future high-current event is detected depending on an actual value of a power current and / or a temporal profile of the actual value of a power current, wherein the power current is a current flowing through another power semiconductor element. An exemplary embodiment of such a detection has already been explained above. What is essential in this embodiment, however, is that it is not the power current of the power semiconductor element whose contact resistance is then changed that is evaluated, but rather the power current of a different, further power semiconductor element. This advantageously results in an alternative detection of the high-current event.If the power semiconductor element whose contact resistance is then changed is part of a first inverter, the further power semiconductor element can, for example, also be part of this first inverter. Preferably, however, the further power semiconductor element is part of a further inverter which is different from the first inverter. For example, the vehicle can comprise various drive inverters, e.g. for driving different wheels, as in the case of an all-wheel drive vehicle. In this case, the first inverter can, for example, serve to drive a first wheel or a first set of wheels, e.g. the rear wheels, and the further inverter can, for example, serve to drive a further wheel or a further set of wheels, e.g. the front wheels.

[0031] In a further embodiment, a cooling power and / or a power current is additionally increased if a current or future high-current event is detected. The cooling power can refer to a power of a cooling device for cooling the power semiconductor element. The power current can refer to a current through the power semiconductor element whose contact resistance is reduced. The increase can occur here—as explained above with regard to the control variable—immediately after the detection time or a predetermined period of time after the detection time. The increase in the power current can occur in particular if the power semiconductor element is part of an inverter that serves to provide an operating voltage for a separately excited synchronous machine, which in this case forms the drive machine explained.The cooling capacity can be increased, in particular, by increasing the coolant volume flow of a coolant pump. By increasing the coolant capacity, the temperature increase of the power semiconductor element, particularly during the high-current event, can be slowed or the temperature can even be reduced, which has a positive effect on service life and, in particular, extends it. By increasing the power current, the difference between the target power current required when the high-current event occurs and the actual power current changed by the increase is reduced, as already explained above. This also advantageously allows the required target power current to be adjusted more quickly, leading to an improved driving experience when and during the high-current event.

[0032] In a further embodiment, the adjustment of the control variable to the target value is canceled if a predetermined period of time has elapsed or if a power semiconductor temperature-dependent criterion is met. In particular, the adjustment can be terminated if the semiconductor temperature is greater than a predetermined temperature threshold or if the semiconductor temperature changes by more than a predetermined amount. This can advantageously increase operational reliability and extend the service life of the power semiconductor element.

[0033] Furthermore, the control variable can be set to the target value if, in addition, a setpoint value of the power current is greater than a predetermined threshold value. The setting to the target value can also be made if, alternatively but preferably cumulatively, a semiconductor temperature, i.e. a temperature of the power semiconductor element, is greater than a predetermined threshold value. Furthermore, the setpoint value of the power current can be provided via a bus system, in particular via an SPI bus system. Alternatively or cumulatively, the semiconductor temperature and / or the ambient temperature can be detected by a temperature sensor and / or provided via a bus system. Furthermore, the fixed parameterized time period can be less than or equal to 20 seconds, preferably less than or equal to 10 seconds.Furthermore, a sum of the time periods in which the control variable for setting the minimum contact resistance to the target value was set can be determined, wherein the adjustment of the control variable for setting the minimum contact resistance to the target value is only carried out if the sum is less than or equal to a predetermined threshold value. It is possible, for example, for the sum valid at a current point in time as well as the predetermined threshold value to be stored in a memory device and retrieved, e.g. by the control device. If the test shows that the setting to the target value can be carried out, the currently stored sum can be incremented by the predetermined time period and the resulting value can be saved as an updated sum. The predetermined threshold value can be selected depending on the application and can be, for example, 100 hours or more.In particular, it can be selected such that the power semiconductor element is not operated with control variables outside the recommended value range for longer than a permissible period during its service life. This advantageously results in improved operational reliability while simultaneously expanding the application range.

[0034] Furthermore, the adjustment to the target value can be achieved by transmitting the target value as a setpoint to a device for providing the control variable. In this case, the device that also provides the control variable with the recommended value for setting the nominal minimum contact resistance can be controlled to provide the control variable with the target value. This can be achieved using a suitable control or regulation strategy. This advantageously results in an easy-to-implement adjustment to the target value, particularly without the need for additional components.

[0035] Alternatively, the recommended value for setting the nominal minimum contact resistance can be transmitted to the device for providing the control variable as a target value, with a device for providing an additional control variable providing an additional variable corresponding to the difference between the target value and the output value provided by the device for generating the control variable or the recommended value. This advantageously results in the corresponding functionality being easy to retrofit, particularly if the device for providing the control variable is not designed to provide the target value.

[0036] The device for providing an additional variable can, in particular, be a device that is designed separately in terms of hardware from the device for providing the control variable. It is also possible, particularly if a fault such as a short circuit or active short circuit, or a failure or unavailability of the device for providing the control variable is detected, for the device for providing an additional control variable to be operated in such a way that it provides the target value or the recommended value (and thus not just an additional variable). This advantageously results in an expansion of the application area.

[0037] Further proposed is a device for operating a power semiconductor element with an adjustable contact resistance for a power current, wherein the device comprises at least one device for providing a control variable for adjusting the contact resistance. This device can be, for example, a driver circuit, in particular a gate driver circuit. The device can also comprise the previously explained device for providing an additional control variable and can be designed such that the control variable and the additional control variable are additively superimposed to provide a resulting control variable.

[0038] Furthermore, the control variable for setting the minimum contact resistance is changed, whereby the control variable for setting the minimum contact resistance is set to a target value which deviates from a recommended value for setting a nominal minimum contact resistance and leads to a reduction of the minimum contact resistance compared to the nominal contact resistance.

[0039] According to the invention, the device comprises at least one device for detecting a high-current event, wherein the control variable is set to the target value if a current or future high-current event is detected. The device can comprise the previously explained control device or control and evaluation device or evaluation device, which controls operation of the device for providing the control variable and optionally also operation of the device for providing an additional control variable and detects a high-current event. Furthermore, the device can comprise a memory device, e.g. for the value of the fixedly parameterized time period. The memory device can also be used to store the previously explained sum. Furthermore, the device can comprise at least one interface, e.g. for receiving a setpoint, a temperature value, an activation signal orfor data connection to a higher-level system, which may in particular be an internal vehicle system, but also an external vehicle system. The device may also comprise the power semiconductor element. Furthermore, the device may comprise at least one vehicle sensor, in particular one of the vehicle sensors explained above. The device may also comprise at least one current sensor for detecting a power current and / or a device for determining / detecting a switching frequency of a power semiconductor element and / or a temperature sensor or interfaces for connecting such sensors.

[0040] The device can be configured such that a method having the explained advantages according to one of the embodiments described in this disclosure can be carried out with the device. Thus, the method can be carried out with a device configured according to one of the embodiments described in this disclosure.

[0041] The invention is explained in more detail using exemplary embodiments. The figures show: Fig. 1 a schematic flow diagram of a method according to the invention, Fig. 2 a schematic flow diagram of a method according to the invention in a further embodiment, Fig. 3 a schematic temporal progression of a control variable, Fig. 4 a schematic block diagram of a device according to the invention, Fig. 5 a schematic block diagram of a device according to the invention in a vehicle and Fig. 6 exemplary time courses of a power current.

[0042] In the following, the same reference symbols designate elements with the same or similar technical properties.

[0043] Fig. 1 shows a schematic flow diagram of a method according to the invention. In a first step S1, it is checked whether a control variable SGmin for setting the minimum contact resistance, for example a gate voltage VG (see Fig. 3), a power semiconductor element, for example a MOSFET 1, 2 (see Fig. 4) is to be set to a target value ZW that deviates from a recommended value SGmin_r for setting a nominal minimum contact resistance and leads to a reduction of the minimum contact resistance compared to the nominal minimum contact resistance that is achieved when the control variable SGmin is set to the recommended value SGmin_r. If a current or future high-current event is detected, the control variable SGmin is set to the target value in a second step S2. Cumulatively, a cooling power for the power semiconductor element and / or a power current I (see Fig. 6) can be increased by the power semiconductor element. The adjustment or increase can occur immediately after the detection time. Alternatively, the adjustment or increase can occur after a predetermined period of time has elapsed after a detection time, particularly if a future high-current event is detected. Thus, the adjustment can occur upon the occurrence of the high-current event or shortly before, e.g., a predetermined period of time before its occurrence.

[0044] The control variable SGmin can be set to the target value ZW for a predetermined period of time. This predetermined period of time can be permanently parameterized. In this case, a third step S3 can be repeatedly checked, in particular periodically, whether the period of time with the set target value ZW is less than a predetermined and permanently parameterized threshold value Tf or equal to this threshold value Tf. The threshold value Tf thus corresponds to the predetermined period of time. If this is not the case, the time counter value ct is incremented by a time increment Δt and the third step S3 is performed again. As soon as the time counter value ct is greater than the predetermined threshold value Tf, the control variable SGmin is reset to the recommended value SGmin_r in a fourth step S4. Of course, the control variable can then also be reset to values ​​that deviate from the control variable SGmin for setting the nominal minimum contact resistance.The predetermined threshold value Tf can be stored in a memory device 9 (see . Fig. 4) and retrieved from it for evaluation. However, it is also possible for the control variable SGmin to be set to a value different from the target value when the high-current event is over, especially before the target value is reached.

[0045] If no current or future high current event is detected in the first step S1, the control variable SGmin is set to the recommended value SGmin_r or is not changed.

[0046] A high-current event can be detected by evaluating a signal generated by a vehicle sensor. A current value of the signal and / or a temporal profile of the signal can be evaluated. Such a vehicle sensor can be, for example, an image capture device 11 of the vehicle, in particular an image capture device 11 configured as a front camera. A vehicle sensor can also be a torque sensor or a device for determining a torque applied to a driven wheel.

[0047] A high current event can also be triggered depending on an actual value of a power current I (see Fig. 6) and / or a time profile of the actual value of a power current I flowing through the power semiconductor element whose contact resistance is being reduced. Alternatively or cumulatively, a high-current event can be detected depending on an actual value of a power current I and / or a time profile of the actual value of a power current I flowing through a power semiconductor element that is different from the power semiconductor element whose contact resistance is being reduced.

[0048] Fig. Figure 2 shows a schematic flow diagram of a method according to the invention in a further embodiment. In contrast to the Fig. 1, the control variable SGmin is not set to the target value ZW for a predetermined period of time. Rather, the setting is canceled if the temperature T of the power semiconductor element is greater than a predetermined threshold value Ts. For this purpose, it can be checked, in particular periodically, in a third step S3 whether the temperature T is less than or equal to this threshold value Ts. If this is the case, the third step S3 is carried out again. As soon as the temperature T is greater than the predetermined threshold value Ts, the control variable SGmin is set back to the recommended value SGmin_r in a fourth step S4. The predetermined threshold value Ts can be stored in a memory device 9 (see Fig. 4) and retrieved from it for evaluation. Of course, it is also possible in this embodiment for the setting to be canceled when the high-current event is over, especially before the temperature threshold Ts is reached.

[0049] Fig. 3 shows a schematic time course of a control variable, namely a gate voltage VG of a MOSFET 1, 2 (see Fig. 4). The MOSFET 1, 2 can, for example, be part of a power converter, which in turn can provide an alternating voltage for operating an electrical machine, such as a traction motor in an electric or hybrid vehicle. For this purpose, the MOSFET 1, 2 can be operated in a pulsed manner, with the gate voltage VG being operated with a duty cycle, which can be determined by a higher-level system, between a value for setting a minimum contact resistance and a value for setting a maximum contact resistance. Fig. Figure 3 shows that a recommended value of the control variable SGmin_r for setting a nominal minimum contact resistance, i.e., the recommended minimum contact resistance, is +15 V. A recommended value for setting a nominal maximum contact resistance is -4 V.

[0050] At a first time t1, a high-current event is detected, and the minimum contact resistance is further reduced compared to the contact resistance at the set recommended control variable SGmin_r. The target value ZW is, for example, +18 V. It is further shown that this control variable SGmin remains set to the target value ZW until a second time t2, with the time difference between the second and the first time t2, t1 corresponding to the predetermined threshold value Tf, which can be, for example, 10 or 20 seconds.

[0051] Fig. 4 shows a schematic block diagram of a device 3 according to the invention. The device 3 serves to operate a power semiconductor element with an adjustable contact resistance for a power current I (see Fig. 6), e.g., for operating a MOSFET 1, 2. The power semiconductor element can be part of a power grid, which can be, e.g., a traction network of an electric or hybrid vehicle. The power grid can comprise an intermediate circuit capacitor CZ. A first MOSFET 1 can be a so-called high-side MOSFET and a second MOSFET 2 can be a so-called low-side MOSFET of a half-bridge of a power converter, wherein the MOSFETs 1, 2 are operated such that a DC voltage in an intermediate circuit 4 is converted into an AC voltage of a phase line 5. The device 3 comprises a first device 6 for providing a control variable for adjusting the contact resistance of the first MOSFET 1 and a second device 7 for adjusting the contact resistance of the second MOSFET 2. Such devices 6, 7 are known to those skilled in the art and can be electrical or electronic components for providing, e.g.,The device 3 further comprises a control and evaluation device 8, which is designed, for example, as a microcontroller or integrated circuit or can comprise one of these. This control and evaluation device 8 controls the devices 6, 7 in such a way that they provide a desired temporal profile of the control variable.

[0052] Not in Fig. 4 shows a power supply device for supplying the devices 6, 7, wherein said device provides the desired control variable from the power supply device, for example a capacitor or an energy storage device different therefrom. In particular, the control and evaluation device 8 can detect a high-current event. For this purpose, the control and evaluation device 8 can evaluate the variables used for detection, e.g. an output signal of at least one sensor. Then, the control and evaluation device 8 can control the first device 6, the second device 7 or both devices 6, 7 in such a way that a target value ZW (see e.g. Fig. 1), which—as already explained—deviates from a recommended value SGmin_r for setting a nominal minimum contact resistance. For this purpose, the control and evaluation device 8 can, in particular, change a setpoint for the control variable provided by the device 6, 7, which is an output variable of this device 6, 7, e.g., from a value of +15V to +18V.

[0053] Fig. Figure 5 shows a schematic block diagram of a device 3 according to the invention in a vehicle 14, in particular an electric or hybrid vehicle. The vehicle 14 comprises the device 3 and an image capture device 11, which can form, for example, a front camera of the vehicle 14. A curb 12 is shown, which is arranged in front of the vehicle 14 in the direction of travel 13. If the vehicle 14 continues to travel in the direction of travel 13, it drives over the curb 12, in particular it drives up the curb 12. By evaluating the output signal provided by the image capture device 11, for example by the control and evaluation device 8 (see Fig. 4) The curb 12, which lies in front of the vehicle 14 in the current direction of travel 13, can be detected. The crossing can then be detected as a future high-current event. Furthermore, by evaluating the output signal provided by the image capture device 11, a distance of the vehicle 14 to the curb 12 can be determined, and then, depending on the vehicle speed, a time until the curb 12 is reached and thus until the high-current event occurs. A tire position can also be determined to predict or detect the occurrence of the high-current event.

[0054] Fig.Figure 6 shows exemplary time courses of a power current I over time t. The first line shows an ideal time course of the power current I during normal operation without the occurrence of a high-current event. It can be seen that neither the amplitude nor the frequency of the power current changes. The second line shows a time course of the power current I with the occurrence of a high-current event. Starting at a first time t1, both the amplitude of the power current I increases and the frequency of the power current I decreases. Thus, after the first time t1, a high-current event can be detected by evaluating these two variables. List of reference symbols 1, 2 MOSFET 3 Device 4 intermediate circuit 5 phase line 6 first facility for providing a control variable 7 second device for providing a control variable 8 Control and evaluation device 9 Storage device 11 Image capture device 12 curb 13 Direction of travel 14 vehicles ct time counter value CZ DC link capacitor I Power current S1 first step S2 second step S3 third step S4 fourth step SGmin control variable for setting a minimum contact resistance SGmin_r recommended value for setting a nominal minimum contact resistance T Temperature Tf parameterized threshold Ts threshold temperature t time t1 first time point t2 second time point VG Gate voltage ZW target value Δt time increment QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 2011 / 007536 A1

[0004] US 2019 / 0149145 A1

[0005] US 10,505,538 B1

[0006] WO 2021 / 047768 A1

[0007] US 2009 / 0001915 A1

[0008]

Claims

[1] Method for operating a power semiconductor element with an adjustable contact resistance for a power current (I), wherein a control variable (SGmin) for setting the minimum contact resistance is changed, wherein the control variable (SGmin) for setting the minimum contact resistance is set to a target value (ZW) which deviates from a recommended value (SGmin_r) for setting a nominal minimum contact resistance and leads to a reduction of the minimum contact resistance compared to the nominal minimum contact resistance, characterized by that the control variable (SGmin) is set to the target value (ZW) if a current or future high current event is detected. [2] Method according to claim 1, characterized by that the control variable (SGmin) is immediately set to the target value (ZW) when a future high current event is detected. [3] Method according to claim 1, characterized by that the control variable (SGmin) is set to the target value (ZW) after a predetermined period of time has elapsed after a detection time if a future high-current event is detected at the detection time. [4] Method according to one of the preceding claims, characterized by that a current or future high current event is detected by evaluating a signal generated by a vehicle sensor. [5] Method according to claim 4, characterized by that the signal is generated by at least one image capture device (11), at least one radar sensor, at least one lidar sensor, at least one torque sensor and / or at least one tire position sensor. [6] Method according to one of claims 1 to 3, characterized bythat a current or future high-current event is detected depending on an actual value of a power current (I) and / or a time profile of the actual value of a power current (I), wherein the power current (I) is a current flowing through the power semiconductor element. [7] Method according to one of claims 1 to 3, characterized by that a current or future high-current event is detected depending on an actual value of a power current (I) and / or a time profile of the actual value of a power current (I), wherein the power current (I) is a current flowing through another power semiconductor element. [8] Method according to one of the preceding claims, characterized by that additionally a cooling power and / or a power current (I) is increased if a current or future high current event is detected. [9] Method according to one of the preceding claims, characterized bythat the setting of the control variable (SGmin) to the target value (ZW) is canceled if a predetermined period of time has elapsed or if a power semiconductor temperature-dependent criterion is met. [10] Device for operating a power semiconductor element with an adjustable contact resistance for a power current (I), wherein the device (3) comprises at least one device (6, 7) for providing a control variable (SGmin) for adjusting the contact resistance, wherein the control variable (SGmin) is changed for adjusting the minimum contact resistance, wherein the control variable (SGmin) for adjusting the minimum contact resistance is set to a target value (ZW) which deviates from a recommended value (SGmin_r) for adjusting a nominal minimum contact resistance and leads to a reduction in the minimum contact resistance compared to the nominal minimum contact resistance, characterized bythat the device (3) comprises at least one device for detecting a high-current event, wherein the control variable (SGmin) is set to the target value (ZW) if a current or future high-current event is detected.

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