DISCHARGE DEVICE, ELECTRICAL UNIT AND DISCHARGE METHOD

Description

[0001] The invention relates to a discharge device for actively discharging an electrical network, in particular a high-voltage network, or an electrically operated unit of such a network. Furthermore, the invention relates to such an electrical unit and a discharge method.

[0002] In modern motor vehicles, in addition to components typically operated at 12 volts, components are often also used that operate at a significantly higher operating voltage. Particularly in vehicles with fully electric or hybrid drive systems, such high operating voltages can exceed 100 volts. Voltages of more than 60 volts are referred to as "high voltage" in the automotive sector. In particular, electrical units operated at high voltage—usually electric drive systems that include, for example, a traction motor, a coolant or lubricant pump, an air conditioning compressor, or the like—are integrated into a so-called "high-voltage network." Such a high-voltage network usually also includes at least one energy storage device (e.g., a capacitor), which is assigned to one or all of the electrical units of the high-voltage network.This is used, for example, to keep the operating voltage value required for the electrical unit or units constant.

[0003] For safety reasons, however, it is necessary that such high-voltage networks can be switched off and, in particular, discharged. This is particularly the case when people may come into contact with the high-voltage network in question or when short circuits may otherwise occur. This is the case, for example, during vehicle maintenance or repairs or, under certain circumstances, in the event of an accident. To enable automatic discharge, the electrical unit to be discharged, or at least the associated energy storage device, can usually be reversibly connected to a reference potential via a switch and a resistor. The switch, or in particular the control of its control connection, is often designed in such a way that the switch is switched to its conductive state even in the event of an unexpected failure of the control, so that the electrical unit or at least the energy storage device is discharged.The problem is often that the switch and / or resistor heat up during discharge and, in the worst case, are destroyed by the resulting temperature.

[0004] EP 3 182 572 A1 discloses an electronic circuit, in particular a DC link circuit, having a high-side DC voltage level, an input, and an output. The electronic circuit comprises a DC link capacitor and a switch-on circuit for limiting an input current to a predetermined level, wherein the switch-on circuit is connected between a supply line of the DC link capacitor and the input. The switch-on circuit comprises a charging resistance element, a switching element connected in parallel with the charging resistance element, and a control means for controlling the switching element, wherein the control means is configured to switch the switching element on when the input current falls below a predetermined current level.The control means further comprises a trigger control element configured to detect a differential voltage across the switching element and to turn off the switching element when the detected differential voltage rises above a predetermined threshold voltage.

[0005] The invention is based on the object of enabling the safest possible discharge of an electrical network or an electrically operated unit of such an electrical network.

[0006] This object is achieved according to the invention by a discharge device for active discharging having the features of claim 1. Furthermore, this object is achieved according to the invention by an electrically operated unit having the features of claim 9. Furthermore, the object is achieved according to the invention by a discharge method having the features of claim 10. Advantageous and partly inventive embodiments and developments of the invention are set out in the subclaims and the following description.

[0007] The discharge device according to the invention serves to actively discharge an electrical network, in particular a high-voltage network, or an electrically operated unit, which is preferably part of such a high-voltage network or comprises such a network. The discharge device has a discharge circuit via which, in particular during discharge operation, a component of the high-voltage network (also: "vehicle electrical system") or of the electrically operated unit to be discharged is connected to a reference potential (preferably ground potential). For this purpose, the discharge circuit has a resistor, referred to below as a "current-limiting resistor," and a first switch, referred to below as a "discharge switch." The discharge switch serves to connect, in particular reversibly, this component to be discharged to the reference potential indirectly via the current-limiting resistor.The discharge circuit is designed such that, when the discharge switch is closed (i.e., switched on or conductive), the high-voltage network or at least the electrically operated unit (in particular, at least the component to be discharged) is electrically conductively connected to the reference potential via the current-limiting resistor. Furthermore, the discharge device has a limiting circuit arranged on the control terminal side of the discharge switch and preferably conductively connected to it, which serves to monitor and limit heating occurring at the discharge switch and / or at the current-limiting resistor during discharge operation. The limiting circuit has an NTC resistor (also referred to as a "thermistor"), the resistance of which consequently decreases in the heated state. This NTC resistor is thermally coupled to the discharge switch and / or the current-limiting resistor.

[0008] Preferably, the NTC resistor is only thermally coupled to the discharge switch.

[0009] A high-voltage network, in particular a high-voltage on-board network of a vehicle, is understood here and below to mean in particular an (on-board) network that is operated with an operating voltage with a voltage value greater than or equal to 60 volts.

[0010] Preferably, the NTC resistor is wired in such a way that, in the heated state of the NTC resistor—thus, in the "good" conducting state of the NTC resistor; where a heated state is understood to mean, in particular, a temperature value of more than 80, preferably more than 100, in particular more than 150 degrees Celsius—a direct or indirect reduction of a control voltage or a control current required to switch through the discharge switch occurs. This, in turn, leads to a reduction of a (discharge) current flowing through the discharge switch and / or to the shutdown of the discharge circuit, the latter in particular by the discharge switch being opened due to a lack of a sufficiently high control voltage or a sufficiently high control current.

[0011] During discharge operation, the discharge switch and usually also the current-limiting resistor heat up due to the power loss. This can lead to the failure of at least one of the two components, which in turn can destroy the high-voltage network and / or the electrically operated unit. The fact that the NTC resistor is thermally coupled to the discharge switch or the current-limiting resistor advantageously enables monitoring and, in particular, reduction of the heat introduced into the discharge circuit before it is (at least thermally) overloaded. Particularly in the event that the high-voltage network or the electrically operated unit has an energy storage device, such as a capacitor, as the component to be discharged, this enables comparatively safe discharge operation even in the event of a failure of a higher-level monitoring system, particularly of the vehicle.

[0012] In a preferred embodiment, the discharge switch is formed in particular by a power transistor, preferably by an insulated-gate bipolar transistor (IGBT) or by a metal-oxide-semiconductor field-effect transistor (MOS-FET). In particular, the discharge switch thus represents a voltage-controlled switch. In particular, the discharge switch has a collector or drain terminal, an emitter or source terminal, and a gate terminal, wherein the gate terminal is the aforementioned control terminal. Further preferably, the discharge switch is integrated into the high-voltage network in such a way that the collector or drain terminal is (at least indirectly) linked to the part (component) of the high-voltage network to be discharged or to the electrically operated unit to be discharged.The emitter or source terminal is preferably connected to the reference potential, particularly with the aforementioned current-limiting resistor interposed. The voltage drop across the current-limiting resistor (during discharge operation) feeds back to the control voltage applied to the control terminal, which in turn limits the discharge current flowing through the discharge switch. Depending on the choice of current-limiting resistor, the maximum discharge current can be preset.

[0013] In order to enable disproportionate current limitation in the discharge switch, particularly above normal temperature, in a practical embodiment of the invention, the NTC resistor is connected to the control terminal of the discharge switch and, in particular, preferably inseparably and, in particular, indirectly, to the reference potential. Preferably, the NTC resistor is also connected (in particular in series) to an "additional resistor," which serves, in particular, to specify, in particular, to set, a temperature threshold above which the limitation of the discharge current becomes effective. This additional resistor is preferably connected between the NTC resistor and the reference potential.Due to this connection of the NTC resistor, the (thus disproportionate) limitation of the control voltage at the control terminal of the discharge switch (preferably designed as an IGBT or MOS-FET) and thus of the discharge current occurs when the NTC resistor heats up and its conductivity increases, particularly above the temperature threshold specified by the additional resistor. Above the temperature threshold (and thus independent of the additional resistor), the limitation is optionally also disproportionate or linear, depending on the temperature behavior of the NTC resistor.

[0014] In a practical embodiment, the discharge device, preferably the limiting circuit, comprises a particularly controllable or at least adjustable voltage reference, e.g., a controllable Zener diode, which is connected between the control terminal of the discharge switch and the reference potential. The NTC resistor is also connected—in addition to its above-described connection to the control terminal of the discharge switch, in particular to its other terminal—to a control input of the voltage reference. Due to the voltage reference, the limiting circuit can advantageously be designed (configured) better, in particular more precisely and / or more simply. The NTC resistor, preferably in combination with the above-described additional resistor, provides a target value for the voltage reference (and thus also serves as a temperature threshold above which the reduction of the discharge current begins).The voltage reference preferably influences the control voltage at the control terminal of the discharge switch. As the NTC resistor heats up, its increasing conductivity causes a reduction in the control voltage at the control terminal of the discharge switch, particularly indirectly via the voltage reference. This, in turn, reduces the current flowing through the discharge switch (discharge current), so that the power loss in the discharge switch decreases. The temperature of the discharge switch can thus advantageously be kept within a temperature range that is not critical for the discharge circuit - especially with a suitable design of the NTC resistor, the additional resistor, etc. If the discharge switch cools down, the NTC resistor also cools down due to the thermal coupling. This reduces the conductivity of the NTC resistor and, in turn, increases the control voltage at the control terminal of the discharge switch.This allows the intended discharge to resume fully or, if necessary, at least to a greater extent (than with a warmer NTC resistor) via the discharge switch and the current-limiting resistor. In principle, the NTC resistor can be used without the voltage reference. However, in this case, the NTC resistor would have to be selected with a comparatively low resistance, which would in turn result in greater self-heating of the NTC resistor (particularly due to current).

[0015] In an expedient embodiment of the invention, which is particularly alternative to the embodiment described above, the limiting circuit has a second switch. The NTC resistor is connected to the control terminal of this second switch. Furthermore, the second switch is connected such that, when the second switch is fully switched on (i.e., "switched through"), the control terminal of the discharge switch is connected to the reference potential. Thus, when the second switch is fully switched on—specifically, when the discharge switch is configured as an IGBT or MOS-FET—the control voltage at the control terminal of the discharge switch drops to zero or at least to such a low value ("switching value") that the discharge switch opens. In this case, the discharge circuit is "deactivated" or switched off.In an optional variant, the NTC resistor is also designed and / or thermally coupled to the discharge switch or the current-limiting resistor in such a way that, with increasing heating and thus increasing conductivity of the NTC resistor, a limit value of an assigned second control voltage or, if applicable, a second control current required for the complete conduction of the second switch is exceeded. Optionally, this limit value can also be adjusted accordingly (in particular via the selection of the second switch). In this case, the control voltage at the control terminal of the discharge switch is indirectly reduced, in particular switched off, by means of the second switch.

[0016] Because the discharge switch is opened when the second switch is fully switched through, the discharge switch and, if applicable, the current limiting resistor can cool down (again) to a non-critical temperature value. Due to the thermal coupling of the NTC resistor with the discharge switch, the NTC resistor also cools down, reducing its conductivity and, accordingly, opening the second switch again. This continues the intended discharge of the electrically operated unit or the high-voltage network via the discharge switch and the current limiting resistor. In an alternative variant, the operating point of the second switch and / or in particular the thermal coupling of the discharge switch orThe current-limiting resistor and the NTC resistor are advantageously selected such that, even with increasing heating and thus increasing conductivity of the NTC resistor, the limit value required for the complete conduction of the second switch is not exceeded, but rather, in particular, is only increasingly approached. As a result, with increasing heating of the NTC resistor, the second switch is advantageously in partially conducting mode (in particular, with a correspondingly increasing conductivity of the second switch), so that only a partial reduction of the control voltage at the control terminal of the discharge switch (preferably above its switching value) occurs, and thus the discharge switch is not fully opened.

[0017] In a preferred embodiment, the second switch described above is formed by a field-effect transistor, in particular a MOSFET, and is thus particularly voltage-controlled. In this case, the NTC resistor is connected in particular to a gate terminal of the field-effect transistor, in particular the MOSFET.

[0018] In each of the embodiments described above, in a preferred embodiment, the discharge device comprises a control circuit, which in turn comprises circuit means for reversibly connecting the control terminal of the discharge switch to the reference potential. In particular, this control circuit serves to keep the discharge switch in its open state and thus maintain the intended operation—in particular, the intended continuous operation—of the high-voltage network or the electrically operated unit.

[0019] In a preferred embodiment, the circuit means comprise a further (optionally third) switch, in particular a transistor, preferably a bipolar transistor. This switch is coupled (in particular on the collector side) to the control terminal of the discharge switch. Particularly in the case where the limiting circuit comprises the second switch, this third switch is preferably directly coupled to the control terminal of the discharge switch. The third switch thus serves directly to connect the control terminal of the discharge switch to the reference potential.

[0020] Preferably, the control circuit also comprises a controller for controlling the switching means, in particular the third switch.

[0021] Preferably, the third switch is switched through in each of the cases described above for intended continuous operation, so that the discharge switch is open. If the control circuit is switched off or fails, the third switch is opened in any case, thus advantageously automatically switching through the discharge switch and initiating the discharge operation. This enables a comparatively fail-safe and, in particular, automatically initiated discharge operation.

[0022] The electrically operated unit according to the invention is preferably part of a vehicle and in particular configured for high-voltage operation. Thus, the electrically operated unit is part of a high-voltage network described above or forms such a high-voltage network itself. The electrically operated unit according to the invention has the discharge device described above. For example, the electrically operated unit comprises a traction motor of the vehicle, an air conditioning compressor, a coolant or lubricant pump, a water pump, a steering drive, or the like. In particular, the electrically operated unit also comprises an energy storage device, in particular a capacitor, which must preferably be discharged automatically in certain cases (e.g., accident, vehicle repair, etc.).

[0023] The discharge method according to the invention serves, in particular, for the active discharge of the above-described electrical (high-voltage) network or the above-described electrically operated unit. The discharge method is carried out, in particular, automatically by means of the above-described discharge device. The discharge circuit connects the component to be discharged to the reference potential via the current-limiting resistor and the discharge switch. The NTC resistor thermally coupled to the discharge switch and / or the current-limiting resistor heats up. This reduces the discharge current flowing through the current-limiting resistor and the discharge switch.

[0024] The electrically operated unit according to the invention and the discharging method according to the invention thus also share the advantages of the discharging device described above.

[0025] The conjunction "and / or" is to be understood here and in the following in particular in such a way that the features linked by this conjunction can be formed both together and as alternatives to one another.

[0026] Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. In the drawings: Fig. 1 in a schematic circuit diagram of a discharge device for an electrically operated unit of a vehicle, and Fig. 2 in view according to Fig. 1 an alternative embodiment of the unloading device.

[0027] Corresponding parts are always provided with the same reference symbols in all figures.

[0028] In Figure 1A schematic block diagram shows part of a high-voltage electrical network of an electrically operated unit 1. The electrically operated unit 1 comprises, as components, an electric motor (not shown in detail) and an energy storage device formed by a capacitor 4 for stabilizing an operating voltage value required to operate the electric motor. In order to be able to discharge the capacitor 4 in certain cases, the electrically operated unit 1 has a discharge device 6. The discharge device 6, in turn, has a discharge circuit 8, which is connected in parallel to the capacitor 4. The discharge circuit 8 has a first switch, referred to as "discharge switch 10", and a current-limiting resistor 12 connected in series with it, i.e., to an emitter terminal 11 of the discharge switch 10. The discharge switch 10 is formed by an IGBT.In the closed or "switched-on" state of the discharge switch 10 (thus in "discharge mode"), the capacitor 4 is connected via the discharge switch 10, specifically its collector terminal 13, to a reference potential, specifically ground potential 14. Thus, in discharge mode, a discharge current flows from the capacitor 4 via the discharge switch 10 and the current-limiting resistor 12 to ground potential 14.

[0029] In an alternative embodiment, the discharge switch 10 is formed by a MOS-FET.

[0030] To prevent the discharge switch 10 from being heated above its load limit and thereby destroyed due to the discharge current during discharge operation, the discharge device 6 also has a limiting circuit 16. This limiting circuit 16 is connected to a control terminal 18 of the discharge switch 10. The limiting circuit 16 has an NTC resistor 20, which is specifically connected to the control terminal 18. The NTC resistor 20 is also thermally coupled to the discharge switch 10 in a manner not shown in detail. For example, the NTC resistor 20 is arranged on a housing of the discharge switch 10. In addition, the limiting circuit 16 has a further resistor, referred to as "additional resistor 22," which is connected in series with the NTC resistor 20, specifically between it and ground potential 14.In addition, the limiting circuit 16 has an adjustable voltage reference 23, which is connected in the form of a controllable Zener diode (i.e., a Zener diode with an additional control input) between the control terminal 18 and ground potential 14. A control input of the voltage reference 23 is connected between the NTC resistor 20 and the additional resistor 22.

[0031] The discharge device 6 also has a control circuit 24, which serves to keep the discharge switch 10 in its open state during the intended operating state of the electrically operated unit 1, thus preventing the discharge of the capacitor 4. For this purpose, the control circuit 24 comprises a controller 26 and circuit means in the form of another switch, referred to here as "control switch 30," which can be actuated (also: switched) directly or indirectly by the controller 26. The control switch 30 is formed by a bipolar transistor (or alternatively by a MOS-FET or the like), whose control terminal is connected to the controller 26. In the intended operating state, the controller 26 closes the control switch 30, thereby connecting the control terminal 18 of the discharge switch 10 to ground potential 14, so that the discharge switch 10 is open.

[0032] During discharge operation—i.e., when the control switch 30 is open—the voltage drop across the voltage reference 23 is so high that a voltage (hereinafter referred to as the "control voltage") applied from the capacitor 4 to the control terminal 18 via a further gate charging resistor 32 (also referred to as "pull-up") exceeds a switching value required to switch the discharge switch 10 through, thus turning the discharge switch 10 on. Due to the discharge current flowing through the discharge switch 10 and the current-limiting resistor 12, these heat up. Due to the thermal coupling of the discharge switch 10 to the NTC resistor 20, the NTC resistor 20 also heats up. This increases the electrical conductivity of the NTC resistor 20, which in turn reduces the voltage across the voltage reference 23 and thus also the control voltage at the control terminal 18 of the discharge switch 10.This limits the discharge current flowing through the discharge switch 10, which in turn reduces (limits) the power loss in the discharge switch 10 and thus also its heating. In particular, this creates a control of the "discharge temperature" of the discharge switch 10, which is determined by the discharge current.

[0033] The discharge device 6 also includes a Zener diode 33 connected in parallel with the voltage reference 23. This prevents the control voltage at the control terminal 18 of the discharge switch 10 from exceeding a maximum value permissible for the discharge switch 10 at low temperatures.

[0034] In Figure 2An alternative embodiment of the electrically operated unit 1, specifically the limiting circuit 16 and the control circuit 24, is shown. The NTC resistor 20 of the discharge circuit 16 is also thermally coupled to the discharge switch 10 in this embodiment. However, the limiting circuit 16 additionally comprises a switch, which in the present embodiment is designed as a field-effect transistor, specifically as a MOS-FET 34. This MOS-FET 34 is connected between the control terminal 18 of the discharge switch 10 and ground potential 14. A gate terminal 36 of the MOS-FET 34, serving as a control terminal, is connected between the NTC resistor 20 and the additional resistor 22. The NTC resistor 20 is also connected to the capacitor 4 via a further gate charging resistor 38.If the NTC resistor 20 heats up during discharge operation, the control voltage at the gate terminal 36 of the MOS-FET 34 increases due to the decreasing resistance of the NTC resistor 20. When a conduction value of the MOS-FET 34 is reached, the control terminal 18 of the discharge switch 10 is connected to ground potential 14, so that the discharge switch 10 opens again and thus the discharge of the capacitor 4 is prevented. Once the discharge switch 10 and thus also the NTC resistor 20 have cooled sufficiently, the MOS-FET 34 opens again and thus the discharge switch 10 closes.

[0035] In a further embodiment, the circuit of which is similar to that in Fig. 2illustrated embodiment, the MOS-FET 34 and the NTC resistor 20 are tuned in such a way that when the NTC resistor heats up, the conduction value for fully switching the MOS-FET 34 is not reached. Rather, the MOS-FET 34 in this case goes into a partially conducting mode, within which its conductivity (with increasing heating of the NTC resistor) also increases further. As a result, the control voltage at the control terminal 18 of the discharge switch 10 is only reduced, so that the latter does not open completely. Therefore, the circuit according to Fig. 2 the discharge current flowing through the discharge switch 10 is limited, which in turn leads to the power loss in the discharge switch 10 and thus also its heating being reduced (limited).

[0036] The subject matter of the invention is not limited to the exemplary embodiments described above. Rather, further embodiments of the invention can be derived by those skilled in the art from the above description. In particular, the individual features of the invention and their design variants described with reference to the various exemplary embodiments can also be combined with one another in other ways. List of reference symbols

[0037] 1 Electrically operated unit 4 Capacitor 6 Discharge device 8 Discharge circuit 10 Discharge switch 11 Emitter terminal 12 Current limiting resistor 13 Collector terminal 14 Ground potential 16 Limiting circuit 18 Control terminal 20 NTC resistor 22 Additional resistor 23 Voltage reference 24 Control circuit 26 Controller 30 Control switch 32 Gate charging resistor 33 Zener diode 34 MOS-FET 36 Gate terminal 38 Gate charging resistor

Claims

1. Discharging device (6) for actively discharging an electrical network or an electrically operated unit (1), comprising - a discharging circuit (8) which has a current limiting resistor (12) and a first switch (10) for connecting a component (4) to be discharged of the network or of the electrically operated unit (1) to a reference potential (14) indirectly via the current limiting resistor (12), and - a limiting circuit (16) which is arranged on the control connection side of the first switch (10) and is intended to limit heating which occurs at the first switch (10) and / or at the current limiting resistor (12) in the discharging mode, wherein the limiting circuit (16) has an NTC thermistor (20) which is thermally coupled to the first switch (10) and / or to the current limiting resistor (12).

2. Discharging device (6) according to Claim 1, wherein the first switch (10) is formed by a power transistor, in particular an IGBT or a MOSFET.

3. Discharging device (6) according to Claim 1 or 2, wherein the NTC thermistor (20) is connected to a control connection (18) of the first switch (10).

4. Discharging device (6) according to Claim 3, having a voltage reference (23) which is connected between the control connection (18) of the first switch (10) and the reference potential (14), wherein the NTC thermistor (20) is also connected to a control input of the voltage reference (23).

5. Discharging device (6) according to Claim 1 or 2, wherein the limiting circuit (16) has a second switch (34), to the control connection (36) of which the NTC thermistor (20) is connected, wherein the second switch (34) connects the control connection (18) of the first switch (10) to the reference potential (14) in the fully switched-on state.

6. Discharging device (6) according to Claim 5, wherein the second switch is formed by a field effect transistor (34), in particular a MOSFET.

7. Discharging device (6) according to one of Claims 1 to 6, having a control circuit (24) which has circuit means (26, 30) in order to reversibly connect the control connection (18) of the first switch (10) to the reference potential (14).

8. Discharging device (6) according to Claim 7, wherein the circuit means comprise a third switch, in particular a transistor (30), which is coupled to the control connection (18) of the first switch (10).

9. Electrically operated unit (1) for a vehicle, which unit comprises the discharging device (6) according to one of Claims 1 to 8.

10. Discharging method for actively discharging an electrical network or an electrically operated unit (1) by means of the discharging device (6) according to one of Claims 1 to 8, wherein the discharging circuit (8) is used to connect the component (4) to be discharged of the network or of the electrically operated unit (1) to be discharged to the reference potential (14) via the current limiting resistor (12) and the first switch (10), wherein the NTC thermistor (20) of the limiting circuit (16) arranged on the control connection side of the first switch (10), which NTC thermistor is thermally coupled to the first switch (10) and / or to the current limiting resistor (12), heats up, and wherein the discharge current flowing via the current limiting resistor (12) and the first switch (10) is reduced as a result.