Safe shutdown of an inverter

Abstract

A final stage (120) for a power converter, in particular for driving an electric machine (110), comprises a half-bridge including an upper current valve (2151) and a lower current valve (2152). The upper current valve (2151) and the lower current valve (2152) of the half-bridge are connected in series between potentials of an intermediate circuit voltage, wherein the upper current valve (2151) is configured to be controlled by an upper driver (1251) and the lower current valve (2152) is configured to be controlled by a lower driver (1252). The upper current valve (2151) and the lower current valve (2152) are conducting in a de-energized control state and blocking in a current-energized control state.In the event of insufficient supply voltage to the upper driver (1251) and the lower driver (1252), either the upper driver (1251) switches the upper current valve (1251) to conduct and the lower driver (1252) switches the lower current valve (2152) to block, or the upper driver (2151) switches the upper current valve (2151) to block and the lower driver (2152) switches the lower current valve (2152) to conduct.

Description

[0001] The present invention relates to an output stage for a power converter, in particular for controlling an electrical machine. More specifically, the invention relates to the shutdown of the output stage upon loss of a supply voltage required for the controlled operation of the machine.

[0002] A motor vehicle comprises an electric motor for propulsion, which can be powered by an inverter from an electrical energy storage device. The inverter supplies the motor with three alternating currents, each 120° out of phase. The torque provided by the motor or the speed it reaches can be controlled by influencing the alternating currents.

[0003] The inverter typically comprises an output stage with three half-bridges. A half-bridge comprises two current valves connected in series between the terminals of the energy storage device, with a terminal of the electric machine connected between them. A driver opens and closes the current valves alternately with a variable duty cycle to provide a predetermined alternating current. Semiconductors, such as IGBTs or MOSFETs, are typically used as current valves. To avoid a short circuit, it is essential to ensure that both current valves are not closed at the same time.

[0004] Correct control of the current valves cannot be guaranteed if the driver's supply voltage is too low. If current valves are used that are normally closed without control (normally on), such as JFETs, they must be actively opened by a separate circuit in the event of a voltage fault when the supply voltage fails.

[0005] It has been proposed to protect a normally-on current valve using a capacitor that charges during normal operation and provides energy to close the current valve in the event of a voltage fault. However, the capacitor can be quickly discharged via the driver, so the shutdown fails or is only short-lived.

[0006] One object of the invention is to provide an improved technique for safely shutting down an inverter with a current valve that is closed without control. The invention solves this problem by means of the subject matter of the independent claims. Subclaims specify preferred embodiments. The invention ensures the establishment of a safe operating state for the machine.

[0007] An output stage for an inverter, in particular for controlling an electrical machine, comprises a half-bridge with an upper and a lower current valve, in particular which are closed when not being controlled, for example in the form of a JFET. The half-bridge comprises an upper current valve and a lower current valve. The upper current valve and the lower current valve of the half-bridge are connected in series between potentials of an intermediate circuit voltage. The upper current valve is configured to be controlled by an upper driver, and the lower current valve is configured to be controlled by a lower driver. The drivers can also be integrated with one another, so that one driver controls both current valves. The upper current valve and the lower current valve are conductive in a de-energized control state and blocking in a current-carrying control state.

[0008] If there is a lack of supply voltage to the upper driver and / or the lower driver, either the upper driver switches the upper current valve on and the lower driver switches the lower current valve off, or the upper driver switches the upper current valve off and the lower driver switches the lower current valve on.

[0009] This ensures that both flow control valves are not closed simultaneously. Furthermore, it can ensure that no short circuit occurs in the event of a driver failure, for example, if its power supply fails. This allows a safe operating state to be set for the electric machine, provided it continues to rotate due to externally applied torque. Thus, the invention can ensure that a safe operating state for the machine is established.

[0010] Preferably, an upper fuse circuit is provided on a half-bridge for actively opening the upper current valve in the event of a lack of supply voltage to the upper driver. Alternatively, a lower fuse circuit is provided on the half-bridge for actively opening the lower current valve in the event of a lack of supply voltage to the lower driver. The fuse circuit is provided on at least one, in particular on exactly one, current valve of a half-bridge. In the case of multiple half-bridges, the fuse circuits are provided either on the upper or on the lower current valves.

[0011] A flow control valve that is not assigned a safety circuit for active opening can be assigned a safety circuit for active closing.

[0012] The safety circuit is preferably implemented as a hardware solution with electrical or electronic components. It may be advantageous for the safety circuit to be implemented using software. In particular, the upper safety circuit and the lower safety circuit can be implemented using the same components and the same wiring. The functionality of the upper and lower safety circuits can differ due to different software. Thus, the software of the upper safety circuit, unlike the software of the lower safety circuit, ensures that either the upper or lower current valves are switched off when the supply voltage to the upper and lower drivers is insufficient. This ensures that no short circuit occurs.

[0013] At the same time, it can be ensured that, in the event of a fault, all terminals of the electrical machine are connected to the same potential via the closed current valves and thus short-circuited. A running electrical machine can be braked by immediately reducing the electrical voltage generated at the terminals by self-induction, which is used to build up a counter-torque on the machine.

[0014] In particular, the proposed power stage ensures that the duration of a safe shutdown of a HV system until disconnection from the high-voltage battery is comparatively short, especially compared to state-of-the-art circuits. In particular, the proposed power stage allows the use of comparatively small and inexpensive components, particularly due to low or completely absent parasitic leakage currents.

[0015] The proposed output stage can in particular enable an active short circuit by means of the, in particular self-conducting, current valves, as well as the safe shutdown of the high-voltage system due to the possibility of switching only the upper or lower current valves conductive and the lower or upper current valves blocking.

[0016] Preferably, the upper current valve and the lower current valve are each a junction field effect transistor (JFET) (or non-insulated gate FET NIGFET).

[0017] The upper driver is expediently connected to a gate terminal and to a source terminal of the upper current valve. A further field-effect transistor is expediently connected in parallel to the upper current valve in such a way that the drain terminal of the further field-effect transistor is connected to the gate terminal of the upper current valve and the source terminal of the further field-effect transistor is connected to the source terminal of the upper current valve. The lower driver is expediently connected to a gate terminal and to a source terminal of the lower current valve. A further field-effect transistor is expediently connected in parallel to the lower current valve in such a way that the drain terminal of the further field-effect transistor is connected to the gate terminal of the lower current valve and the source terminal of the further field-effect transistor is connected to the source terminal of the lower current valve.The further field-effect transistor preferably comprises a normally-on switch. Advantageously, the gate of the further field-effect transistor, in particular switch, in particular normally-on switch, is controlled by the UVLO, under voltage lock-out signal. The further field-effect transistor comprises a signal transmitter and / or signal receiver, wherein the signal indicates whether the gate voltage is sufficient to maintain the blocking state of the switch. A safe state is, for example, the conducting state of the transistor. The signal triggers the further field-effect transistor, in particular the JFET. Upon triggering, in particular the gate and the source of the upper current valve, in particular the JFET, are short-circuited. This creates a conducting state, and in particular thus a safe state.

[0018] Advantageously, the upper driver comprises the additional field-effect transistor. Advantageously, the lower driver (1252) comprises the additional field-effect transistor.

[0019] It may be appropriate for the upper driver and the lower driver to have the same hardware and / or wiring. It is advisable for the upper driver and the lower driver to have different software, so that if the supply voltage to the upper driver and the lower driver is insufficient, either the upper driver switches the upper current valve on and the lower driver switches the lower current valve off, or the upper driver switches the upper current valve off and the lower driver switches the lower current valve on.

[0020] Advantageously, the upper driver is connected to the gate terminal and the source terminal of the upper current valve. Advantageously, a resistor, in particular a pulldown resistor, is connected in parallel to the upper current valve such that the resistor is connected to the gate terminal and the source terminal of the upper field-effect transistor. Advantageously, the lower driver is connected to the gate terminal and the source terminal of the lower current valve. Advantageously, a resistor, in particular a pulldown resistor, is connected in parallel to the lower current valve such that the resistor is connected to the gate terminal and the source terminal of the lower field-effect transistor.

[0021] The output stage is preferably supplied with electrical energy from an electrical energy storage device. An intermediate circuit capacitor is preferably connected in parallel with the half-bridge. A protective device, in particular a relay, IGBT, MOSFET, and / or similar protective device, is preferably connected in series between the electrical energy storage device and the intermediate circuit capacitor. The protective device can, for example, reduce, in particular minimize, the time until the high-voltage battery is disconnected, so that a disconnected state is reliably achieved. This allows the output stage to be optimally dimensioned to safely deactivate the switches when the supply voltage fails, in particular by using small and inexpensive components.

[0022] According to a further aspect of the present invention, a power converter comprises a plurality of output stages or half-bridges as described herein. The power converter can, in particular, comprise two output stages and be used to control, for example, a DC motor. In general, the power converter can be used for the electronically controlled conversion of one input electrical current type (DC, AC) into the other, or for changing a characteristic parameter such as a voltage or frequency.

[0023] According to yet another aspect of the invention, an inverter for controlling an electrical machine comprises an output stage as described herein. The output stage can comprise one or more half-bridges, and a half-bridge can comprise one or more current control valves. Optionally, the driver for controlling current control valves is also included in the output stage. The inverter can also include an intermediate circuit capacitor for decoupling a DC voltage at which a half-bridge can be operated. Furthermore, the inverter can include a cooling system with a fluid channel in which a fluid can be moved to dissipate heat from a current control valve, a half-bridge, or the intermediate circuit capacitor.

[0024] The inverter is designed to provide one or more alternating voltages based on a direct voltage, which can in particular be provided by a rechargeable battery or another portable energy source. For use on board a motor vehicle, the direct voltage is typically approximately 400 V, approximately 800 V, or approximately 900 V, although other voltages are also possible. More preferably, the alternating voltages are coordinated with one another in such a way that they can be used to control an electrical machine, for example a permanent magnet synchronous machine. In one embodiment, the inverter is designed to provide the alternating voltages as a function of a control signal. The control signal can comprise a torque to be provided by the machine and / or a speed to be assumed by the machine.In other words, the driver can perform vector-oriented control or regulation of the electric machine. The electric machine is further preferably configured to drive a motor vehicle.

[0025] According to yet another aspect of the present invention, an electric axle drive for a motor vehicle comprises an inverter as described herein. The axle drive may comprise a fixed or switchable transmission to transmit a rotary motion of the electric motor to a drive wheel of the motor vehicle. The axle drive may be configured to be driven by another drive motor, in particular an internal combustion engine. Torques of the electric motor and the other drive motor may be coupled to one another accordingly.

[0026] According to yet another aspect of the present invention, a motor vehicle comprises an electric axle drive as described herein. The motor vehicle preferably comprises a passenger car, but may also comprise a motorcycle, a truck, or a bus.

[0027] The invention will now be described in more detail with reference to the accompanying figures, in which: Fig. 1 a motor vehicle; Fig. 2 a circuit diagram of an inverter; Fig. 3 a circuit diagram of an upper fuse circuit; Fig. 4 a circuit diagram of a lower fuse circuit; Fig. 5 a circuit diagram of an isolating circuit; and Fig. 6 shows a circuit diagram of an isolating circuit in another embodiment.

[0028] Fig. 1 shows an electric axle drive 100 on board a motor vehicle 105. The axle drive 100 comprises an electric drive motor 110 and an inverter 115, which includes an output stage 120 and a driver 125. An electrical energy storage device 130 is provided on board the motor vehicle 105, which may in particular comprise an accumulator.

[0029] Not in Fig. 1 shows an optional transmission between the electric drive motor 110 and a drive wheel of the motor vehicle 105. Optionally, a further drive motor is provided on board the motor vehicle 105, which can also be coupled to a drive wheel.

[0030] The inverter 115 is preferably configured to generate a plurality of phase-shifted alternating voltages based on a direct voltage provided by the energy storage device 130 and to provide them to the drive motor 110. The provision preferably occurs as a function of a request signal that can be provided by a driver of the motor vehicle 105.

[0031] Fig. Figure 2 shows a circuit diagram of an inverter 115 in an exemplary embodiment. The inverter 115 is connected to an energy storage device 130 and includes, for example, a DC link capacitor (DC link capacitor) 205, three half-bridges 210, each with an upper (“high-side,” shown above) current valve 2151 and a lower (“low-side,” shown below) current valve 2152.

[0032] The inverter includes driver 125. Driver 125 includes an upper driver 1251 and a lower driver 1252. Upper driver 1251 can be configured as a separate driver, i.e., independent of driver 125. Lower driver 1252 can be configured as a separate driver, i.e., independent of driver 125.

[0033] The upper driver 1251 is provided to control the upper flow control valve 2151. The lower driver 1252 is provided to control the lower flow control valve 2152. The drivers 1251, 1252 can preferably communicate with each other.

[0034] The flow control valves 2151, 2152 are each implemented as JFETs, preferably using SiC technology. Two flow control valves 2151, 2152 of a half-bridge 210 can be included in a control module 225.

[0035] By way of example, a gate terminal G, a drain terminal D, and a source terminal S are designated on one of the current valves 2152 according to the usual conventions. Two current valves 2151, 2152 of a half-bridge 210 are connected in series by connecting the source terminal of the upper current valve 2151 to the drain terminal of the lower current valve 2152. The connection between the two terminals is brought out to be connected to a phase of the electric machine 110.

[0036] The drain terminal of the upper current valve 2151 is connected to a high potential, and the source terminal of the lower current valve 2152 is connected to a low potential of the energy storage device 130. The ZKK 205 is connected in parallel to the energy storage device 130.

[0037] Driver 125 provides control voltages to the total of six current control valves 2151, 2152 to generate a predetermined voltage across the phases of the electric machine 110. In the exemplary embodiment, the upper driver 1251 provides control voltages to the total of three upper current control valves 2151, and the lower driver 1252 provides control voltages to the total of three lower current control valves 2152 to generate a predetermined voltage across the phases of the electric machine 110.

[0038] Since a current valve 2151, 2152 is closed without control, it must be actively opened by providing a suitable control voltage. The driver 125, 1251, 1252 is operated with a supply voltage that can be provided from the energy storage device 130 or another source. Should the supply voltage fail or drop below a predetermined minimum, the driver 125, 1251, 1252 can no longer function correctly and, in particular, cannot prevent both current valves 2151, 2152 of a half-bridge 210 from being closed simultaneously, which can cause a short circuit between the high and low potentials of the energy storage device 130. Typically, a protective device 230 is provided to isolate the energy storage device 130 from the inverter 115, but this may require a certain response time.

[0039] To prevent a short circuit in the event of a defect in driver 125, it is proposed to provide an upper fuse circuit 3001 on the upper current valve 2151 and a lower fuse circuit 3002 on the lower current valve 2152 of a half-bridge 210. The upper fuse circuit 3001 is provided to switch the upper current valve 2151 on when the supply voltage drops or fails. The lower fuse circuit 3002 is provided to switch the lower current valve 2152 off when the supply voltage drops or fails and to keep it off for a predetermined time.

[0040] It is understood that a half-bridge 210 can also be constructed with interchanged current valves 2101 and 2102 and / or interchanged fuse circuits 3001 and 3002. This provides a corresponding protective effect in the event of a driver 1251, 1252 failure. An active short circuit of the electrical machine 130 can be created by connecting all phases to the lower busbar 1252.

[0041] A safety circuit 3001, 3002 for actively closing a flow control valve 2151, 2152 can be omitted if it can be assumed that the associated flow control valve 2151, 2152 already closes sufficiently safely due to its design if there is no control.

[0042] For ease of reading, only the embodiment will be described below in which the upper safety circuit 3001 is provided to switch the upper flow control valve 2151 on when the supply voltage drops or fails, and the lower safety circuit 3002 is provided to switch the lower flow control valve 2152 off when the supply voltage drops or fails and to keep it off for a predetermined time. Without departing from the scope of the invention, however, a reversal of the functioning of the upper and lower safety circuits 3001, 3002 is also encompassed within the scope of the disclosure.

[0043] Fig. 3 shows a fuse circuit 3001 for protecting the upper current valve 2151. The upper driver 1251 is connected to the gate terminal and to the source terminal of the upper current valve 2151. The fuse circuit 3001 comprises a further field-effect transistor 355, which is preferably also of the normally-on type. The further field-effect transistor 355 is connected in parallel to the upper current valve 2151 such that the drain terminal of the further field-effect transistor 355 is connected to the gate terminal of the upper current valve 2151 and the source terminal of the further field-effect transistor is connected to the source terminal of the upper current valve 2151. The drain terminal of the further field-effect transistor 355 is thus also connected to the upper driver 1251. The source terminal of the further field-effect transistor 355 is thus also connected to the upper driver 1251.The gate terminal of the additional field-effect transistor 355 is controlled by a fault signal that assumes a low level in the event of a fault – a common fault signal that assumes a low level in the event of a fault (e.g., UVLO). This functionality can be referred to as a "safety turn-on." If no fault is present, the additional field-effect transistor 355 can be blocked, and the field-effect transistor 2151 can follow the control of the driver 1251. In the event of a fault, the additional field-effect transistor 355 can conduct, so that the field-effect transistor 2151 conducts independently of any control by the driver 1251.

[0044] In a further embodiment of the invention, the additional field-effect transistor 355 can be replaced by a resistor not shown in the figures, preferably a pulldown resistor, in particular between the control terminals or between the gate terminal of the upper current valve 2151 and the source terminal of the upper current valve 2151. The pulldown resistor ensures a low level at the control terminal of the current valve 2151 upon loss of supply voltage, so that the current valve is switched to the defined conducting state. If the driver 1251 is no longer working, the field-effect transistor 2151 can be switched to conduction by the pulldown resistor. A sufficiently small pulldown resistor ensures a short time constant for reliable switching on when an active short circuit is required. However, the control voltage permanently works against the pulldown resistor.If the pulldown resistor is dimensioned too small, the pulldown resistor leads to high power losses for the control.

[0045] In a further embodiment of the invention, the further field effect transistor 355 and / or the pull-down resistor can be included in the upper driver 1251.

[0046] Fig. Figure 4 shows a fuse circuit 3002 for protecting a lower current valve 2152. The gate terminal of the lower current valve 2152 is connected to the lower driver 1252. A capacitor 305 of the JFET acts between the gate terminal and the source terminal of the lower current valve 2152. A capacitor 310 and a diode 315 are connected in parallel with the capacitor 305, with a cathode of the diode facing the capacitor 310. Optionally, a resistor 320 is connected in parallel with the capacitor 310.

[0047] Another JFET 325 is connected in parallel with diode 310, with a drain terminal connected to the cathode and a source terminal connected to the anode of diode 310. The gate terminal of the additional JFET 325 is connected, for example, to an interface 330. The source terminal of the additional JFET 325 is also connected to a high potential of a voltage supply 335, which provides a supply voltage for the lower driver 1252.

[0048] During normal operation, the current direction of diode 315 allows capacitor 310 to be charged via control by lower driver 1252. The additional JFET 325 is off during normal operation. If, in the event of a fault, the signal from the gate terminal of the additional JFET 325 is removed or connected to a complementary signal, the JFET 325 closes, so that the charged capacitor 310 is located between the gate terminal and the source terminal of the lower current valve 2152. The capacitor voltage opens the lower current valve 2152 and prevents current flow through the lower current valve 2152 from the drain terminal to the source terminal.

[0049] In one embodiment, interface 330 is connected to a source of a suitable shutdown signal, for example, to a control terminal of a control module 225 that includes flow control valve 215. The signal may become active if the supply voltage drops below a predetermined threshold. The signal may have hysteresis, so that it is not deactivated until the supply voltage exceeds a second threshold that is higher than the first threshold. A resistor 340 between interface 330 and the source terminal of further JFET 325 may ensure that JFET 325 is closed when no signal is present at interface 330.

[0050] An optional circuit that is Fig. 4, can generate a suitable signal at interface 330. For this purpose, a Zener diode 345 and a resistor 350 are connected in series with the supply voltage of power supply 335. The anode of Zener diode 345 is connected to the negative potential of power supply 335. The connection between the cathode of Zener diode 345 and resistor 350 is connected to interface 330.

[0051] If there is no voltage error on the supply voltage, the negative supply voltage drops across resistor 350 and Zener diode 345. Zener diode 345 has a suitable breakdown voltage, so that in this case the voltage across resistor 350 is sufficiently high to reliably keep the additional JFET 325 open. For example, the supply voltage can be approximately -20 V. Zener diode 345 has an exemplary breakdown voltage of approximately 10 V. Thus, 10 V also drops across resistor 350, and the drive voltage of the additional JFET 325 is -10 V, so that the additional JFET 325 is open. Current valve 215 can be freely controlled by driver 125.

[0052] If the supply voltage now drops, initially only the voltage which drops across the resistor 350 is reduced, since the Zener diode 345 continues to block a predetermined voltage of 10 V here, which drops across the Zener diode 345.

[0053] If the supply voltage at resistor 350 falls below the threshold voltage of the additional JFET 325, the capacitor 310 is switched to the gate terminal of the current valve 215, so that the current valve 215 is opened. Closing of the current valve 215 can be prevented until the capacitor 310 is sufficiently discharged.

[0054] Resistor 320 can cause the lower flow control valve 2152 to close very slowly from the safely off state by discharging capacitor 310 in a controlled manner. This preferably occurs at a time when energy storage device 130 is already safely disconnected from inverter 115 by a device such as protective device 245. By gradually closing the lower flow control valve 2152, the ZKK 245 can be discharged, whereby the energy stored therein can be converted into heat at the lower flow control valve 2152.

[0055] If the supply voltage rises again, the additional JFET 325 can open again, so that the safe shutdown of the lower current valve 2152 is terminated and the lower current valve 2152 can be freely controlled by the lower driver 1252.

[0056] Fig. Figure 5 shows a circuit diagram with a lower current valve 2152 of an inverter 115, a lower fuse circuit 3002, and an isolating circuit 400. The lower driver 1252 is shown as an equivalent circuit with a first voltage source 410 and a second voltage source 415, whose supplied voltages are combined to a common terminal by a first switch 420 and a second switch 425, respectively. Such an embodiment can preferably be implemented using CMOS technology. The switches 420, 425 are alternately controlled by the lower driver 1252 to open and close the lower current valve 2152, respectively.

[0057] A first forward-biased diode 430 and, antiparallel thereto, a second reverse-biased diode 435 may be provided to provide two separate signals from the combined signal, one comprising a turn-on signal and the other a turn-off signal for the lower flow control valve 2152. Preferably, the turn-on signal and the turn-off signal each pass through a resistor 440, 441. The diodes 420, 425 and the resistors 440, 441 may be included in the lower driver 1252.

[0058] In the present embodiment, the switch-off signal is routed directly to the gate terminal of the lower current valve 2152. The switch-on signal can also be connected to the gate terminal of the lower current valve 2152 or isolated from it by means of a semiconductor switch 445. The semiconductor switch 445 is preferably designed as a field-effect transistor or a bipolar transistor. The semiconductor switch 445 opens when a sufficiently large voltage drops across a resistor 450 between its source terminal and its gate terminal. The gate terminal of the semiconductor switch 445 is connected to the fuse circuit 3002 by means of an optional Zener diode 455.

[0059] The fuse circuit 3002 responds when the supply voltage of the voltage supply 335 of the lower driver 1252 drops below a predetermined threshold and then connects the terminal of the Zener diode 455 to the source terminal of the current valve 215. This blocks the semiconductor switch 445, preventing the capacitor 310 from discharging via the switch-on signal.

[0060] Fig. 6 shows a circuit diagram according to Fig.5, however, the lower driver 1252 has a different structure and the isolation circuit 400 is adapted accordingly. The outputs of the switches 420 and 425 of the lower driver 1252 are not connected to each other here, but are led separately to the corresponding resistors 440, 441, whereby the diodes 430, 435 are omitted. Such an embodiment is known as an open collector. In this case, the isolation circuit 400 can additionally comprise a diode 505, which is arranged in the reverse direction in the signal path of the switch-off signal. The diode 505 is located here between the gate terminal of the lower current valve 2152 and the resistor 440, which leads to the second voltage source 415 via the second switch 425. Reference symbol 100 axle drive 105 Motor vehicle 110 electric drive motor 115 inverters 120 power amplifier 125 drivers 1251 upper driver 1252 lower driver 130 energy storage units 205 DC link capacitor ZKK 210 Half Bridge 2151 Upper flow valve 2152 Lower flow control valve 225 control module 230 protective device D Drain connection G Gate connection S Source connection 3001 Upper fuse circuit 3002 Lower fuse circuit 305 GS capacity 310 Capacitor 315 diode 320 resistance 325 additional JFETs 330 interface 335 Power supply 340 resistance 345 Zener diode 350 resistance 355 Additional field-effect transistor 400 isolating circuit 410 first voltage source 415 second voltage source 420 first switch 425 second switch 430 first diode 435 second diode 440 resistance 441 Resistance 445 semiconductor switch, FET 450 resistance 455 Zener diode 505 diode 605 first representation 610 second representation 615 first curve: supply voltage 620 second course: control signal flow valve 625 third curve: capacitor voltage

Claims

[1] Output stage (120) for a power converter, in particular for controlling an electrical machine (110); wherein the output stage (120) comprises a half-bridge; wherein the half-bridge comprises an upper current valve (2151) and a lower current valve (2152); wherein the upper current valve (2151) and the lower current valve (2152) of the half-bridge are connected in series between potentials of an intermediate circuit voltage; wherein the upper current valve (2151) is configured to be controlled by an upper driver (1251), and the lower current valve (2152) is configured to be controlled by a lower driver (1252); wherein the upper current valve (2151) and the lower current valve (2152) are conductive in a current-free control state and blocking in a current-carrying control state;wherein, in the event of a lack of supply voltage to the upper driver (1251) and / or the lower driver (1252), either the upper driver (1251) switches the upper flow valve (1251) to be conductive and the lower driver (1252) switches the lower flow valve (2152) to be blocking, or the upper driver (2151) switches the upper flow valve (2151) to be blocking and the lower driver (2152) switches the lower flow valve (2152) to be conductive.; [2] The output stage (120) according to claim 1, wherein the output stage (120) comprises an upper safety circuit (3001) for actively opening the upper flow control valve (2151) in the event of a lack of supply voltage to the upper driver (1251); or wherein the output stage (120) comprises a lower safety circuit (3002) for actively opening the lower flow control valve (2151) in the event of a lack of supply voltage to the lower driver (1251). [3] The output stage (120) of claim 1 or 2, wherein the upper flow control valve (2151) is a JFET; and wherein the lower flow control valve (2152) is a JFET. [4] Output stage (120) according to one of the preceding claims, wherein the upper driver (1251) is connected to a gate terminal and to a source terminal of the upper current valve (2151), and wherein a further field effect transistor (355) is connected in parallel to the upper current valve (2151) such that the drain terminal of the further field effect transistor (355) is connected to the gate terminal of the upper current valve (2151) and the source terminal of the further field effect transistor (355) is connected to the source terminal of the upper current valve (2151);and / or wherein the lower driver (1252) is connected to a gate terminal and to a source terminal of the lower current valve (2152), and wherein a further field-effect transistor (355) is connected in parallel to the lower current valve (2152) such that the drain terminal of the further field-effect transistor (355) is connected to the gate terminal of the lower current valve (2152) and the source terminal of the further field-effect transistor (355) is connected to the source terminal of the lower current valve (2152); [5] The output stage (120) of claim 4, wherein the upper driver (1251) comprises the further field effect transistor; wherein the lower driver (1252) comprises the further field effect transistor. [6] Output stage (120) according to one of the preceding claims, wherein the upper driver (1251) is connected to the gate terminal and to the source terminal of the upper current valve (2151), wherein a resistor, in particular a pull-down resistor, is connected in parallel to the upper current valve (2151) such that the resistor is connected to the gate terminal and to the source terminal of the upper field-effect transistor (2151); or wherein the lower driver (1252) is connected to the gate terminal and to the source terminal of the lower current valve (2152), wherein a resistor, in particular a pull-down resistor, is connected in parallel to the lower current valve (2152) such that the resistor is connected to the gate terminal and to the source terminal of the lower field-effect transistor (2152). [7] Output stage (120) according to one of the preceding claims, wherein the output stage (120) is supplied with electrical energy from an electrical energy store (130), wherein an intermediate circuit capacitor (205) is connected in parallel to the half-bridge, and wherein a protective device (230) is connected in series between the electrical energy store (130) and the intermediate circuit capacitor (205). [8] Power converter (115) comprising a plurality of output stages (120) according to one of the preceding claims. [9] Inverter (115) for controlling an electrical machine (110), comprising an output stage (120) according to one of the preceding claims. [10] Electric axle drive (100) for a motor vehicle (105), comprising an inverter (115) according to claim 9. [11] Motor vehicle (105) comprising an electric axle drive (100) according to claim 10.

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