DE102021111773A1 - Method for actively discharging an electrical energy store, control device, electrical circuit device and motor vehicle - Google Patents

Abstract

Method for actively discharging an electrical energy store (6) of an electrical circuit arrangement (5), the electrical circuit arrangement (5) comprising at least one half-bridge (11, 12, 13) made from two switching elements (S1 - S6), the half-bridge (11, 12, 13) is connected in parallel to the energy store (6) and the switching elements (S1 - S6) each have a switchable section whose electrical resistance can be adjusted via a control voltage of the switching element (S1 - S6), wherein at the beginning of the discharge of the energy store (6) the control voltage of the switching elements (S1 - S6) of the half-bridge (11, 12, 13) can each be set to a level between a threshold voltage and a maximum permissible turn-on voltage of the switching element (S1 - S6).

Description

The invention relates to a method for actively discharging an electrical energy store in an electrical circuit arrangement, the electrical circuit arrangement comprising at least one half-bridge made up of two switching elements, the half-bridge being connected in parallel with the energy store and the switching elements each having a switchable section whose electrical resistance has a Control voltage of the switching element is adjustable. Furthermore, the invention relates to a control device, an electrical circuit device and a motor vehicle.

Hybrid motor vehicles and motor vehicles with a purely electric drive generally have a high-voltage vehicle electrical system, via which power electronics components are connected. These power electronics components can be, for example, a drive converter, a DC converter for converting the voltage of the high-voltage vehicle electrical system to a lower voltage, an onboard charger in the motor vehicle, an electric air conditioning compressor and/or an electric heater. These components are fed via the high-voltage vehicle electrical system from a high-voltage energy store in the motor vehicle, for example a traction battery. In electric vehicles, the voltage in the high-voltage electrical system is between 350 V and 860 V, for example.

For reasons of operational safety and functional safety, a circuit for active discharge must be provided in every component of the high-voltage vehicle electrical system that has a high-voltage intermediate circuit capacitor or an X-capacitor for filtering electromagnetic interference. The capacitor can be discharged by this discharge circuit, for example when the high-voltage electrical system of the motor vehicle is taken out of operation or when a fault occurs. The discharge circuit usually consists of a switch and an ohmic resistor, via which the energy stored in the capacitor is converted into heat during discharge. This reduces the voltage at the intermediate circuit capacitor so that it can be lowered within a short period of time to a level that is harmless, for example for touching.

Various methods for discharging an energy store are known from the prior art.

In EP 2 556 981 A2 a discharge circuit is described, by means of which an intermediate circuit capacitor of a high-voltage partial network can be discharged via a series connection of a transistor and a discharge resistor. For this purpose, the transistor of the discharge circuit is subjected to a falling gate voltage ramp via an analog circuit, which is operated via a low-voltage partial network. In addition, when discharging the intermediate circuit capacitor, additional energy taken from the capacitor to be discharged is converted into heat by a DC-DC converter fed between the high-voltage sub-grid and the low-voltage sub-grid and by an inverter connected to the high-voltage grid in order to accelerate the discharging process.

U.S. 2020/0067400 A1 discloses a high-voltage network for an electric motor vehicle, which includes an intermediate circuit capacitor, an inverter and an electric machine. To discharge the intermediate circuit capacitor, energy stored in the capacitor is supplied to the motor windings of the electrical machine as electrical current in a first method step. Then, in a second method step, a circulating current is generated by switching over the switching elements of the inverter in order to consume the energy absorbed in the motor windings as heat. These steps are repeated until a voltage of the intermediate circuit capacitor has fallen below a predetermined limit value.

In DE 10 2018 221 209 A1 a device for discharging an intermediate circuit capacitor is described. In this case, a discharge unit of the device is connected between two connection terminals of the intermediate circuit capacitor. The discharge unit is designed as a transistor, to which a rising gate voltage ramp is fed via an analog circuit. The semiconductor switch provided for discharging can be part of an inverter of the intermediate circuit. By applying the increasing gate voltage ramp, the problem of the parameter-dependent gate voltage is to be counteracted, since the influence of temperature and manufacturing tolerances do not have to be taken into account due to the continuously increasing gate voltages in order to bring about the desired discharge of the intermediate circuit capacitor.

The invention is based on the object of specifying an improved method for discharging an electrical energy store which, in particular, enables the discharging process to be carried out in a controlled manner.

To solve this problem is provided according to the invention in a method of the type mentioned that at the beginning of the discharge of the energy store, the control voltage Switching elements of the half-bridge are each set to a level between a threshold voltage and a maximum allowable turn-on voltage of the switching element.

The switching elements of the half-bridge each have a switchable section whose electrical resistance can be changed by the respective control voltage of the switching element. The switchable section can be z. B. when running the switching elements as metal oxide semiconductor field effect transistors (MOSFETs) act around the drain-source path. The switchable sections of the switching elements of the half-bridge are connected in series, with the series circuit of the switchable sections, ie the half-bridge, being connected in parallel with the energy store of the electrical circuit arrangement.

The electrical resistance of the switchable section can be adjusted by adjusting the control voltage, for example the gate voltage or gate-source voltage of a switching element designed as a MOSFET. For this purpose, the level of the control voltage is set to a value between a threshold voltage of the switching element and a maximum permissible turn-on voltage of the switching element. The threshold voltage is between 0 V and the switch-on voltage of the switching element and is greater than 0 V in terms of magnitude and is therefore also greater than a switch-off voltage of the switching element. The threshold voltage and the maximum permissible control voltage can be assigned to the respective switching element, in particular as component-specific variables. The switching elements of the half-bridge can in particular be structurally identical. It is possible for the control voltages for both switching elements of the half-bridge to be set at the same level or for a different control voltage level to be set for the switching elements.

By applying a voltage between the threshold voltage and the maximum permissible switch-on voltage, a defined resistance of the switchable sections of the switching elements can be set, so that the electrical intermediate circuit capacitor can be discharged via the series connection of the two switchable sections of the switching elements of the half-bridge. The flow of current from the energy store, which is a capacitor, for example, depends on the voltage of the energy store and on the electrical resistance of the switchable sections of the switching elements of the half-bridge.

By setting the control voltage of the switching elements at the beginning of the discharge of the energy store to a level between the threshold voltage and a maximum permissible switch-on voltage, a significant discharge current flow can be generated directly at the beginning of the discharge process. This advantageously enables the capacitor to be discharged quickly and in a controlled manner, so that specified discharge times, ie periods of time in which a voltage of the energy store, such as a capacitor, must be below a limit value, can be reliably reached or fallen below. The electrical resistance of the switchable sections of the switching elements can preferably be set in such a way that a voltage of the energy store can be reduced to a voltage of less than 60 V within one second or less.

The solution according to the invention has the advantage that a separate discharge circuit can be dispensed with. No further discharge resistor is required, in which the energy contained in the energy store is converted into heat during discharge. Discharge resistors of this type usually have the disadvantage that, due to the high discharge power that can occur, for example, when discharging an intermediate circuit capacitor of a high-voltage vehicle electrical system of a motor vehicle, they have to be designed with a high thermal mass and therefore very massively so that they can withstand the thermal load during discharging be able. As a rule, this results in large, space-intensive discharge resistors, which, for example, require a large amount of space within a power electronics circuit. Advantageously, by using the switching elements to discharge the energy store, a separate discharge resistor and thus space-intensive elements such as cement resistors or groups or arrays of surface-mounted thick-film resistors (SMD thick-film resistors) can be dispensed with. By saving the installation space of the discharge resistor, the required area of a circuit board for realizing at least part of the electrical circuit arrangement can also be reduced.

A further advantage of the invention is that a half-bridge can be used for discharging, which is coupled to a cooling device and/or which is connected to a cooling circuit, so that the heat generated when the intermediate circuit capacitor is discharged can advantageously be dissipated to the cooling circuit. As a result, the heat input into the electrical circuit arrangement when discharging the energy store can advantageously be reduced, which can reduce a thermal load on the circuit and increase the service life of the circuit. Advantageously, in particular, multiple discharging processes in a short time sequence without excessive moderate heating of the electrical circuitry are implemented. Discharge resistors that heat up and/or additional cooling of discharge resistors can thus advantageously be dispensed with. Furthermore, better cooling can be achieved than is possible with discharge resistors that are generally cooled by the ambient air in an interior of a housing of the electrical circuit arrangement.

The omission of a discharge resistor also makes it possible to omit further circuits associated with the discharge resistor, such as temperature measurements, filter circuits and/or other circuits for providing interference suppression measures, so that a further saving in installation space and an increase in the robustness of the entire circuit device can be achieved. Furthermore, there are also savings in material costs, in the costs for assembly and connection technology and the connection of the discharge resistor. In particular, the production of the electrical circuit arrangement is also simplified, since no large discharge resistors or groups of a large number of smaller discharge resistors have to be mounted or populated on a printed circuit board. Screwing the discharge resistor inside a housing of the electrical circuit arrangement can also be dispensed with. The electrical circuit arrangement can thus advantageously be designed to be lighter in weight and smaller in size, which increases the flexibility when using the electrical circuit arrangement in other devices.

In a preferred embodiment of the invention, it can be provided that the levels of the control voltages are set at the beginning of the discharge and/or during the discharge as a function of at least one predetermined assignment specification and/or at least one measured or derived measured variable of the electrical circuit arrangement.

The recorded measured variable can be determined directly using a measuring device, for example. A derived measured variable can be determined in particular by measuring another variable and using an assignment rule or a formula that converts the other variable into the derived measured variable. In this way, the control of the discharge process can be further improved. During the discharging process, the level of the control voltage can be changed as a function of a detected or derived measured variable, so that the control voltage and thus the electrical resistance of the switchable sections of the switching elements of the half-bridge can also be adjusted during the discharging process. Undesirable states during discharging can thus be detected and countermeasures can be initiated by changing the control voltages. In particular, it is also possible to prevent the occurrence of an undesired state in advance by changing at least one of the control voltages.

In a preferred embodiment of the invention, it can be provided that a voltage of the energy store, a current flow through at least one of the switching elements and/or a temperature of at least one of the switching elements is used as the measured variable of the electrical circuit arrangement. In this way it is possible to adapt the discharging process and in particular the electrical resistances of the switchable sections of the switching elements to variables which are decisive for a controlled discharging process. It is possible, for example, for a voltage of the energy storage device to be determined using a measuring device assigned to the energy storage device. A current flow through at least one of the switching elements and/or a temperature of at least one of the switching elements can also be determined via a measuring device that is assigned to the switching element or the half-bridge. It is also possible for a current flow through one of the switching elements to be determined, for example, from a temperature of the switching element, the voltage of the energy storage device and a stored assignment specification which, for example, specifies the resistance of the switching element at the set control voltage.

In order to contain further control over the discharging process, it can be provided according to the invention that the levels of the control voltages are regulated during discharging as a function of the measured variable of the electrical circuit arrangement. In doing so, e.g. B. the control voltages can be regulated to a fixed current value, a maximum temperature, a desired discharge time and/or a maximum voltage change at the energy store. In this way, the current state of the switching elements of the half-bridge and/or the energy store can be taken into account in a simple manner, so that the discharge process of the energy store can take place in a controlled and safe manner.

In a preferred embodiment of the invention, it can be provided that an electrical circuit arrangement with a plurality of half-bridges, each connected in parallel with the energy store, is used, in particular an electrical circuit arrangement designed as a multi-phase pulse-controlled inverter. An example as A circuit arrangement designed as a multi-phase pulse-controlled inverter can be used, for example, to convert a DC voltage provided via a high-voltage DC subsystem into an AC voltage, for example for operating an electrical machine. The electrical circuit arrangement can be designed in particular as a three-phase pulse-controlled inverter which correspondingly has three half-bridges connected in parallel with the energy store. The energy store can be designed as an intermediate circuit capacitor or an X-capacitor of the high-voltage direct-current sub-grid.

According to the invention, it can be provided that at the beginning of the discharge of the energy store the control voltage of all switching elements of the half-bridges is set to a level between a threshold voltage and a maximum permissible turn-on voltage of the switching element. This makes it possible for the energy store to be discharged via a number of half-bridges and thus via a number of paths connected in parallel with the energy store. As a result, the current strength of the currents flowing in each case in the paths or the switching elements of the half-bridges is advantageously reduced, so that heating of the switching elements and/or a maximum required discharge time can advantageously be reduced.

In this case, it is possible for the switching elements of a half-bridge and/or the switching elements of the plurality of half-bridges to be acted upon in each case by the same control voltage and/or for the switching elements of the half-bridges to be acted upon by different control voltages. A control voltage can be applied to the switching elements in such a way that their switchable sections have the same or at least essentially the same electrical resistances. In this way, the switching elements are heated as uniformly as possible. At least essentially the same electrical resistance is to be understood here as meaning resistances which differ by at most 20%, in particular by 10% and preferably by 5% or less.

Alternatively, it can be provided according to the invention that the energy store is only discharged via one of the half-bridges, the half-bridge used for discharging being selected depending on the temperature of at least one of the switching elements and/or depending on a period of time that has elapsed since the start of discharging. A different half-bridge can thus be used depending on the temperature of one of the switching elements and/or depending on the elapsed time since the start of discharging. This advantageously enables the half-bridge used for discharging to be switched over.

For example, a first half-bridge used at the beginning of the discharging process can be switched off by setting the control voltage of the switching elements to a blocking voltage, for example, when a predetermined period of time has elapsed since the beginning of discharging and/or when at least one of the switching elements has a temperature above a temperature limit value . At the same time, in a second half-bridge of the plurality of half-bridges, the control voltage can be set to a value between the threshold voltage and the maximum turn-on voltage, so that the discharging process can be continued via the switching elements of the second half-bridge.

Correspondingly, after the period of time has elapsed again or when the second half-bridge heats up, the second half-bridge can be switched off and the discharging process can be continued via a third half-bridge. If the period of time elapses again or the third half-bridge heats up, another half-bridge, in particular the first half-bridge again, can be used to discharge the energy store when the third half-bridge is switched off.

In particular, the multiple half-bridges can be switched through cyclically for discharging the energy store. A half-bridge used for discharging can be changed when the temperature of one of the switching elements of the half-bridge used for discharging exceeds a predetermined limit value, for example 200.degree. In order to avoid further heating of the switching elements, the switching elements previously used for discharging can be brought about to cool down by switching over the half-bridges. It is also possible to switch over or switch through the half-bridges cyclically for discharging as a function of an elapsed time period, so that each of the half-bridges is only used for discharging for a predetermined period of time. As a result, the heating of the individual switching elements can advantageously be reduced, so that the switching elements heat up only slightly overall during discharging.

According to the invention, it can be provided that transistors, in particular metal-oxide-semiconductor field-effect transistors made of silicon carbide, are used as switching elements. The level of the control voltages between the threshold voltage and the maximum switch-on voltage can be varied between 3 V and 18 V, for example the. In particular, it is possible that the threshold voltage is between 3 V and 5 V, for example, and that the maximum switch-on voltage is between 15 V and 18 V, so that depending on the switching element used, control voltage levels between 5 V and 15 V can also be used in order to adjust the electrical resistance of the switchable section.

In a preferred embodiment of the invention, it can be provided that an intermediate circuit capacitor of a high-voltage network, in particular with a voltage between 200 V and 1500 V, is used as the energy store. In this case, the intermediate circuit capacitor can be connected between the poles at which the voltage of the high-voltage network is present, and thus represent an X capacitor. The energy store is a capacitor to which the voltage of the high-voltage network, for example a voltage between 250 V and 1500 V, in particular a voltage between 360 V and 860 V, is applied. Such voltages are not safe to touch, so that when the electrical circuit arrangement is switched off, the intermediate circuit capacitor must be discharged.

Provision can be made for a control device according to the invention to be designed to generate the control voltages for at least two switching elements of a half-bridge of an electrical circuit arrangement which can be connected or is connected to the control device, the control device being set up to carry out a method according to the invention. The controller can, for. B. include a driver circuit designed to generate the control voltages and a control unit, wherein the control unit is connected to the driver circuit and set up to carry out the method. This makes it possible to apply a respective control voltage to the switching elements of the half-bridge of an electrical circuit arrangement, in particular the switching elements of one or more half-bridges of a pulse-controlled inverter, via the control device.

For an electrical circuit device according to the invention, it is provided that it comprises a control device according to the invention and an electrical circuit arrangement with an energy store and at least one half-bridge made up of two switching elements, the half-bridge being connected in parallel with the energy store and the switching elements each having a switchable section whose resistance exceeds a control voltage of the switching element is adjustable.

It is provided for a motor vehicle according to the invention that it comprises an electrical circuit device according to the invention. The electrical circuit device can be connected in particular to a traction energy store of the motor vehicle, the voltage of the traction energy store being present at the energy store to be discharged. In particular, the traction energy store can be designed as a battery and the energy store, which can be discharged via the half-bridge, can be designed as an intermediate circuit capacitor.

All the advantages and configurations described above in relation to the method according to the invention apply correspondingly to the control device according to the invention, the electrical circuit device according to the invention and the electric motor vehicle according to the invention and vice versa.

• 1 ein Ausführungsbeispiel eines erfindungsgemäßem Kraftfahrzeugs, umfassend eine erfindungsgemäße elektrische Schaltungseinrichtung mit einer erfindungsgemäßen Steuereinrichtung,
• 2 eine Detailansicht der erfindungsgemäßen elektrischen Schaltungseinrichtung zur Erläuterung eines Ausführungsbeispiels eines erfindungsgemäßen Verfahrens, und
• 3 ein Widerstands-Ersatzschaltbild einer zum Entladen eines Energiespeichers verwendeten elektrischen Schaltungsanordnung.

Further advantages and details of the invention result from the exemplary embodiments described below and from the drawings. These are schematic representations and show:

• 1 an embodiment of a motor vehicle according to the invention, comprising an electrical circuit device according to the invention with a control device according to the invention,
• 2 a detailed view of the electrical circuit device according to the invention to explain an embodiment of a method according to the invention, and
• 3 a resistance equivalent circuit diagram of an electrical circuit arrangement used for discharging an energy store.

In 1 an exemplary embodiment of a motor vehicle 1 is shown. The motor vehicle 1 comprises an electrical circuit device 2. The electrical circuit device 2 forms a high-voltage vehicle electrical system of the motor vehicle 1 and comprises a traction energy store 3, an electric traction motor 4 and an electrical circuit arrangement 5 designed as a three-phase pulse-controlled inverter. The circuit arrangement 5 allows a traction energy store 3 removed direct current are converted into a three-phase alternating current for the operation of the electric traction motor 4 . It is also possible to convert an alternating current generated by the traction motor 4 in generator operation into a direct current for charging the energy store. The structure of the electrical circuit arrangement 5 is below in relation to 2 shown in more detail.

The electrical circuit device 2 also includes an energy store 6 designed as an intermediate circuit capacitor, which is between tween the voltage levels HV+ and HV- of the electric traction energy store 3 is connected. The energy store 6 thus represents an intermediate circuit capacitor or an X capacitor. The electrical circuit device 2 also includes a control device 7 which includes a driver circuit 8 and a control unit 9 . The driver circuit 8 of the control device 7 can be contained spatially in the circuit arrangement 5, for example by arranging the driver circuit 8 within a housing of the circuit arrangement 5. The control unit 9 can also be arranged in the housing or it can be designed separately and with the driver circuit 8 to be connected. To discharge the energy store 6, the traction energy store 3 can be decoupled, for example via a switching device 10, so that when the energy store 6 is discharged, the traction energy store 3 is not also discharged.

In normal operation of the electrical circuit arrangement 5, for example motor operation or generator operation of the traction motor 4, the control terminals of the switching elements Si are controlled by the control device 7 with a control voltage alternating between the switch-off voltage and the maximum switch-on voltage. In this case, the control can take place in particular by means of pulse width modulation (PWM). Furthermore, the control device 7 can control the electrical circuit arrangement 5 for discharging the energy store 6, as will be described in more detail below. This can take place when discharge information is transmitted to the control device 7 , such a determination being made, for example, at the start of a switch-off process of the electrical circuit device 2 and/or as a result of a detected error in the motor vehicle 1 .

A high-voltage voltage for operating the electrical circuit device 2 can be provided by the traction energy store 3 . This high voltage can be between 250 V and 1500 V, in particular between 360 V and 860 V, for example. When the electrical circuit device 2 or the motor vehicle 1 is in operation, the energy store 6 embodied as an intermediate circuit capacitor has a voltage which corresponds to the voltage of the high-voltage vehicle electrical system or the traction energy store 3 . This means that a high voltage is present at the energy store 5, which must be reduced when the electrical circuit device 2 or the motor vehicle 1 is switched off in order to ensure, for example, that the circuit device 2 or individual components thereof are protected against accidental contact. Functional safety and protection against accidental contact with the components of the motor vehicle 1 are also ensured in this way. This discharging of the energy store 6 can advantageously be carried out by the electrical circuit arrangement 5, as will be described in more detail below.

In 2 a detailed view of the circuit device 2 with the electrical circuit arrangement 5 designed as a three-phase pulse-controlled inverter is shown. Also shown are the control device 7 and the electric traction motor 4 connected to the electric circuit arrangement 5.

The electrical circuit arrangement 5 comprises three half-bridges 11, 12, 13, which are each formed by two of a total of six switching elements S ₁ to S ₆ of the circuit arrangement 5. During normal driving operation of the motor vehicle 1 , the direct current provided by the traction energy store 3 is converted into a three-phase alternating current with the phases U, V and W for operating the electric traction motor 4 by means of the half-bridges 11 , 12 , 13 . Furthermore, the electrical circuit arrangement 5 can be used to discharge the energy store 6 . For this purpose, the control terminals of the switching elements of at least one of the half-bridges 11, 12, 13 are supplied with a control voltage U _G,i , the level of the control voltages U _G,i in each case being between a threshold voltage and a maximum permissible turn-on voltage of the respective switching element S ₁ .

The switching elements S ₁ to S ₆ each include a switchable section, the switchable sections of two switching elements of a half-bridge each being connected in series. The energy store 6 can be discharged by setting the control voltage U _G,i of at least two of the switching elements, for example the control voltages U _G,1 and U _G,4 of the switching elements S ₁ and S ₄ of the first half bridge 11 . The respective electrical resistance of the switchable section of the switching element S ₁ can be adjusted by the control voltage U _G,i of the respective switching elements S ₁ . The control voltages U _G,i of the switching elements S ₁ to S ₆ can be adjusted via the driver circuit 8 of the control device 7 in accordance with the control unit 9 . The connections between the driver circuit 8 and the respective control connections of the switching elements S ₁ to S ₆ are not shown for reasons of clarity.

The switching elements S ₁ to S ₆ are designed as metal oxide semiconductor field effect transistors (MOSFET) and each include a freewheeling diode D _i . In particular, the switching elements S ₁ to S ₆ can be MOSFETs based on silicon carbide (SiC MOSFETs). In this case, the switchable sections of the switching elements S ₁ to S ₆ are the drain-source paths of the MOSFETs, whose electrical resistance R _DS is determined by the level of the gate voltage or gate voltage used as the control voltage U _G,i Source voltage can be adjusted. As the gate voltage increases, the resistance R _DS falls steadily and has its minimum at the maximum permissible gate voltage, ie the maximum permissible turn-on voltage of the switching element. If the gate voltage is set to voltage values in the range between and including the threshold voltage and the maximum turn-on voltage, defined channel resistances R _DS of the switching elements S _i can be set. These resistors R _DS can then be used to discharge the energy store 6. The gate voltages or the control voltages can in each case be set to a level greater than the threshold voltage and less than the maximum turn-on voltage.

In the case of a MOSFET, for example, the threshold voltage indicates that gate voltage at which a conductive path between the terminals of the switchable section is formed. By setting a control voltage U _G,i which is equal to or greater than the respective threshold voltage of the switching element S _i , a resistance of the switchable section or the drain-source path of the switching element S _i can be set in a controlled manner. This can be implemented advantageously with SiC MOSFETs, since these have an ohmic characteristic in the conductive state.

It is possible that, in particular for all switching elements of the three half-bridges 11, 12, 13, a control voltage between the threshold voltage and the maximum permissible turn-on voltage of the respective switching element S _i is set. Depending on the design of the switching elements S _i , the threshold voltage U _G,i can be between 3 V and 5 V, for example, and the maximum switch-on voltage can be between 15 V and 18 V. Thus, for discharging the energy store 6, control voltages U _G,i between 3 V and 18 V, for example between 5 V and 15 V, can be set.

If the three half-bridges 11, 12, 13 are used simultaneously for discharging the energy store 6, the result for the discharge of the energy store 6 is in 3 resistance equivalent circuit diagram of the electrical circuit arrangement 5 shown. The resistance R _DS of the switching elements of one or more of the half-bridges 11, 12, 13 is set in particular in such a way that the intermediate circuit capacitor is discharged to a voltage of less than 60 V within a period of one second or less done.

For this purpose, it is possible for the switching elements S ₁ to S ₆ to be acted upon in each case by a control voltage U _G,i , the level of which is stored in the control units as an assignment specification. A level of the control voltage U _G,i set at the beginning can be adjusted during the discharging of the energy store 6 as a function of the stored assignment specification.

In addition or as an alternative to this, it is possible for the levels of the control voltages U _G,i to be set at the beginning of the discharge and/or during the discharge as a function of at least one measured variable of the electrical circuit arrangement 5 that is measured or derived. The measured variable of the electrical circuit arrangement 5 can be, for example, a voltage of the energy store 6, a current flow through at least one of the switching elements S _i and/or a temperature of at least one of the switching elements S _i .

A voltage U _E of the energy store 6 can be detected, for example, via a measuring device 14 assigned to the energy store 6 . The temperature of the switching elements S _i can be measured, for example, via measuring means (not shown here) integrated in the switching elements S _i and transmitted to the control unit 9, for example, via the connection of the respective control terminals with the driver circuit 8 and the control unit 9. A current flow through one or more of the switching elements S _i can also be determined via an assigned measuring device. In particular, a drain current of the switching element _Si can be considered as a current flow through one of the switching elements, since this flows along the switchable section.

In addition or as an alternative to measuring a current, it is possible for the current flow through one of the switching elements S _i or through one of the half-bridges 11, 12, 13 to be determined as a derived measured variable. For this purpose, for example, the voltage U _E of the energy store 6 and the resistance of the switchable sections of the switching elements S _i set at the start of the discharging process can be taken into account. Since the set resistance R _DS of the drain-source path in a MOSFET is usually temperature-dependent, the temperature of the respective switching elements S _i can also be used when determining the current through the respective switching elements S _i or the respective half-bridges 11, 12, 13 are taken into account.

The discharging of the energy store 6 via at least one of the half-bridges 11, 12, 13 stops the advantage that no additional discharge circuit is required. Furthermore, an electrical circuit arrangement 5 which is assigned to a cooling device 15 of the motor vehicle 1 can advantageously be used. The circuit arrangement 5 connected to the cooling device 15 allows for good cooling of the switching elements Si even when discharging.

This can be achieved in particular by arranging cooling surfaces of the switching elements S _i on a heat sink or a cooling channel of the cooling device 15 .

In this way, in particular, active cooling of the switching elements S _i can take place, so that rapid discharging of the energy storage device 6 is possible even at high voltages in the vehicle electrical system of the motor vehicle 1 or high voltages U _E at the energy storage device 6, since high current flows through the switching elements S _i are possible during discharging without overheating occurring. For example, it is possible for the resistances of the switchable sections of the switching elements S ₁ to S ₆ to be adjusted as a function of the voltage U _E of the energy store 6 as a function of an assignment specification stored in the control unit 9 and a temperature of the switching elements S _i recorded as a measured variable, that a predetermined discharge time, for example until a voltage level of less than 60 V is reached, is reached. The discharge time can in particular be less than one second and for example be between 100 ms and 950 ms, preferably between 500 ms and 750 ms.

In addition to discharging the energy store 6 via each of the three half-bridges 11 , 12 , 13 , it is also possible for the energy store 6 to be discharged via only one of the half-bridges 11 , 12 , 13 . Depending on the temperature of one of the switching elements S ₁ to S ₆ , in particular the temperature of at least one switching element S _i of the half-bridge currently used for discharging the energy store 6, the half-bridge 11, 12, 13 used in each case for discharging the energy store 6 can be switched over . This can prevent the switching elements S _i of the half-bridge 11, 12, 13 currently being used for discharging from heating up too much.

For example, at the beginning of the discharging process of the energy store 6, the first half-bridge 11 can be used for discharging, with the switching elements S ₁ and S ₄ each having a control voltage U _G,1 or U _G,4 between a threshold voltage U _G,1,th or U _G,4,th and a maximum permissible turn-on voltage of the respective switching elements S ₁ and S ₄ are applied. When a predetermined temperature limit value, for example 200° C., is reached, the switching elements S ₁ and S ₄ can be switched off, for which purpose the control voltages U _G,1 and U _G,4 are set to a switch-off voltage, in particular of 0 V or less, for example -4 V, to be set. At the same time, another half-bridge, for example the second half-bridge 12, can be used for discharging, for which purpose the switching elements S ₂ and S ₅ each have a control voltage U _G,2 or UG,5 between a threshold voltage U _G,2,th or U _G,5,th and a maximum switch-on voltage of the switching elements S ₂ and S ₅ are applied.

Correspondingly, the second half-bridge 12 can be switched off in the event of excessive heating, and the discharging process can be continued via the third half-bridge 13 . If the switching elements S ₃ and/or S ₆ of the third half-bridge 13 heat up too much, discharge can then take place again via the first half-bridge 11 . The thermal load on the switching elements S ₁ to S ₆ can advantageously be reduced by such a gradual switching or cyclical changing of the half-bridge 11, 12, 13 respectively used for discharging.

By discharging the energy store 6 via one or more of the half-bridges 11, 12, 13 of the electrical circuit arrangement 5, the use of separate discharge circuits can advantageously be dispensed with. The function of actively discharging the energy store 6 can thus be implemented via the circuit arrangement 5 designed as a pulse-controlled inverter. In particular, no separate discharge resistors are required in this case, as a result of which the electrical circuit arrangement 5 or the electrical circuit device 2 can be designed to be robust and compact and can be produced with reduced assembly effort. This simplifies in particular the use of the electrical circuit arrangement 5 or the electrical circuit device 2 in the motor vehicle 1 and, in addition to the production and development costs, also reduces the weight of the circuit device 2.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 2556981 A2 [0005]
• US 2020/0067400 A1 [0006]
• DE 102018221209 A1 [0007]

Claims (12)

Method for actively discharging an electrical energy store (6) of an electrical circuit arrangement (5), the electrical circuit arrangement (5) comprising at least one half-bridge (11, 12, 13) made from two switching elements (S ₁ - S ₆ ), the half-bridge ( 11, 12, 13) is connected in parallel to the energy store (6) and the switching elements (S ₁ - S ₆ ) each have a switchable section whose electrical resistance can be adjusted via a control voltage of the switching element (S ₁ - S ₆ ), thereby characterized in that at the beginning of the discharge of the energy store (6) the control voltage of the switching elements (S ₁ - S ₆ ) of the half-bridge (11, 12, 13) each to a level between a threshold voltage and a maximum permissible turn-on voltage of the switching element (S ₁ - S ₆ ) can be set. procedure after claim 1 , characterized in that the heights of the control voltages are adjusted at the beginning of the discharge and/or during the discharge as a function of at least one predetermined assignment specification and/or at least one measured variable of the electrical circuit arrangement (5) that is detected or derived. procedure after claim 2 , characterized in that a voltage of the energy store (U _E ), a current flow through at least one of the switching elements (S ₁ - S ₆ ) and/or a temperature of at least one of the switching elements (S ₁ - S ₆ ) is used. procedure after claim 2 or 3 , characterized in that the levels of the control voltages are regulated during the discharge depending on the measured variable of the electrical circuit arrangement (5). Method according to one of the preceding claims, characterized in that an electrical circuit arrangement (5) with a plurality of half-bridges (11, 12, 13) each connected in parallel with the energy store (6), in particular an electrical circuit arrangement (5) designed as a multi-phase pulse-controlled inverter is used. procedure after claim 5 , characterized in that at the beginning of the discharge of the energy store (6) the control voltage of all switching elements (S ₁ - S ₆ ) of the half-bridges (11, 12, 13) is set to a level between a threshold voltage and a maximum permissible switch-on voltage of the switching element (S ₁ - S ₆ ). procedure after claim 5 , characterized in that the energy store (6) is only discharged via one of the half-bridges (11, 12, 13), the half-bridge (11, 12, 13) used for discharging depending on the temperature of at least one of the switching elements (S ₁ - S ₆ ) and/or depending on a period of time that has elapsed since the start of discharging. Method according to one of the preceding claims, characterized in that transistors, in particular metal oxide semiconductor field effect transistors made of silicon carbide, are used as switching elements (S ₁ - S ₆ ). Method according to one of the preceding claims, characterized in that an intermediate circuit capacitor of a high-voltage network, in particular with a voltage between 250 V and 1500 V, is used as the energy store (6). Control device which is designed to generate the control voltages for at least two switching elements (S ₁ - S ₆ ) of a half-bridge (11, 12, 13) of an electrical circuit arrangement (5) which can be or is connected to the control device (7), the control device (7) is set up to carry out a method according to one of the preceding claims. Electrical circuit device comprising a control device (7). claim 10 and an electrical circuit arrangement (5) with an electrical energy store (6) and at least one half-bridge (11, 12, 13) made of two switching elements (S ₁ - S ₆ ), the half-bridge (11, 12, 13) being parallel to the energy store (6) is connected and the switching elements (S ₁ - S ₆ ) each have a switchable section whose resistance can be adjusted via a control voltage of the switching element (S ₁ - S ₆ ). Motor vehicle comprising an electrical circuit device (2). claim 11 .

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