Method and device for discharging an intermediate circuit capacitor

Abstract

The invention relates to a method and a device for discharging an intermediate circuit capacitor. The intermediate circuit capacitor (106) is electrically coupled to at least one half-bridge (215), wherein the half-bridge (215) has at least two switches (225) and (227) connected in series. The method comprises at least one control step in which the switches (225) and (227) of the half-bridge (215) are controlled so that the switches (225) and (227) are closed simultaneously.

Description

Technical Field

[0001] The invention relates to a method and a device for discharging an intermediate circuit capacitor. Background Art

[0002] In most cases, intermediate circuit capacitors are installed in inverters for electric machines, which temporarily store the electrical energy to be converted in the inverter. In high-power inverters, the capacitance and / or the charging voltage can assume high values. Thus, large amounts of electrical energy are stored at a simultaneously high capacitor voltage. The combination of stored energy and voltage imposes high demands on the electrical safety of the electrical system.

[0003] In the event of a fault or when the inverter is switched off, this energy in the intermediate circuit capacitor must be discharged in order to prevent people from coming into contact with the voltage. This can occur, for example, when the inverter is to be repaired. To achieve this discharge, there are usually two methods that are used simultaneously, wherein, for example, a long-lasting slow discharge caused by passive components discharges the intermediate circuit capacitor usually within 120 seconds.

[0004] In laid-open patent application DE 10 2013 213 802 A1, a device and a method are described for overvoltage protection of active rectifiers during load shedding. Summary of the invention

[0005] Against this background, the present invention provides a better method and a better device for discharging an intermediate circuit capacitor according to the invention. Advantageous embodiments emerge from the following description.

[0006] According to the solution proposed here, the energy stored in the intermediate circuit capacitor is converted into heat by means of at least one (first) half-bridge having two switches connected in series, wherein a brief short circuit is produced via the two switches and the voltage and thus also the energy in the intermediate circuit capacitor is reduced.

[0007] A method for discharging an intermediate circuit capacitor is described, wherein the intermediate circuit capacitor is electrically coupled to at least one (first) half-bridge, which comprises at least or exactly two switches connected in series. The method comprises the step of controlling the switches of the half-bridge so that the switches are closed simultaneously. That is, the switches are switched on simultaneously. The switches can then be opened again simultaneously.

[0008] In order to actuate the respective switch for discharging the intermediate circuit capacitor, a so-called discharge pulse can be output to the respective switch. As long as the discharge pulse continues, the switch is closed. When the discharge pulse disappears, the switch is then opened again.

[0009] The intermediate circuit capacitor may be a capacitor in the intermediate circuit of a converter or inverter. A half bridge may be a circuit. A half bridge is, for example, part of an inverter or converter. Such a switch may be an electronic component, for example a transistor, such as an IGBT (insulated gate bipolar transistor) or a MOSFET (metal oxide semiconductor field effect transistor), which enables control of voltage and current. Via the half bridge, a short circuit between two connections of the intermediate circuit capacitor may be achieved by closing the switch.

[0010] Preferably, the intermediate circuit capacitor is disconnected from the DC voltage supply, for example by means of a protective device and / or a battery disconnect switch, before or simultaneously with the step of actuating the switch. The DC voltage supply is designed to supply the intermediate circuit capacitor with electrical power in normal operation.

[0011] In one embodiment, the switches can be controlled in the control step such that the switch-on time (the time between the simultaneous closing and subsequent opening of the switches) does not exceed a predetermined threshold value. In this case, the current and thermal load of the switches are kept low, whereby the switches and the intermediate circuit capacitors can be protected from damage.

[0012] In one embodiment, in the control step, the simultaneous closing and subsequent (if necessary simultaneous) opening of the switches can be repeated multiple times. In particular, the successive opening and closing of the switches are repeated at predefined (time) intervals. The predefined (time) intervals are selected such that they serve as cooling intervals after closing the switches, thereby preventing overheating of the switches in the event of repeated closing of the switches.

[0013] According to one exemplary embodiment, in the control step, the switch can be closed (continuously or repeatedly) until the intermediate circuit capacitor is discharged. In this way, it can be ensured that the risk to people can be kept as low as possible.

[0014] According to one embodiment, in the control step, a further (second) half-bridge can be controlled, which is connected in parallel with the first half-bridge. This second half-bridge also has at least or exactly two switches connected in series. The further half-bridge is implemented in particular similarly to the first half-bridge. The switches of the further half-bridge are closed simultaneously in the control step. As a result, the intermediate circuit capacitor can be discharged more quickly. Similarly to the first half-bridge, the switches of the further half-bridge can also be closed simultaneously multiple times and then opened again in each case.

[0015] According to a further embodiment, in the control step, the switches of the further half-bridge can be controlled, i.e. closed and / or opened, in a time-staggered manner relative to the switches of the first half-bridge. This makes it possible to distribute the discharge current from the intermediate circuit capacitor and the corresponding thermal load evenly over time to the half-bridges. The time tolerance of the switch-on pulses for switching on the switches of the half-bridges also has a smaller effect on the maximum current, which reduces the thermal load on the switches and also simplifies the regulation of the switch-on pulses.

[0016] One or more further such half-bridges can be provided, in particular just one third half-bridge. Thus, in particular a converter or inverter can be formed with the half-bridges. The control step can be carried out here in a similar manner to the first and / or further half-bridges. In particular, a time-staggered control of the switches of the half-bridges is achieved, so that, for example, the switches of the first half-bridge are first closed (and opened again if necessary) and only then the switches of the second half-bridge, etc. are closed (and opened again if necessary).

[0017] In one specific embodiment, a protection unit of the half-bridge, which is used to monitor the state of the switched-on switches of the half-bridge so that they are not switched on for longer than a maximum switch-on period, can be deactivated in the control step. In this way, it can be ensured that an already existing protection function for preventing a short circuit of the switches of the half-bridge does not inhibit the solution presented here for reducing the energy from the intermediate circuit capacitor.

[0018] According to one specific embodiment, in the control step, the protection unit of the half-bridge is deactivated for a predetermined period of time and activated again after the predetermined period of time has elapsed. This ensures that in a "normal" operating mode (in which a rapid drop in energy from the intermediate circuit capacitor is not required), a possibly unintentional closing of the switch of the half-bridge is prevented. This contributes to a significant increase in the operating safety in the "normal" operating mode of the intermediate circuit or the half-bridge.

[0019] In one specific embodiment, when a fault message and / or information about the presence of a generator operation of an electric machine coupled to one or more half-bridges is present, the discharge of the intermediate circuit capacitor can be controlled in the control step. In particular, the fault message is information about a fault state in the intermediate circuit and / or an overvoltage of the intermediate circuit capacitor. As a result, the electrical safety of an electrical system including an intermediate circuit capacitor can be increased.

[0020] The solution proposed here is preferably used in emergency situations, in particular load shedding situations, in which the electrical energy (voltage) from the intermediate circuit capacitor should be briefly and quickly reduced. Such emergency situations exist in particular when load shedding occurs in generator mode of an electric machine coupled to one or more half-bridges.

[0021] The specific embodiments of the proposed method can be implemented, for example, in software or hardware or in a hybrid form of software and hardware, for example in a control device, for example in an apparatus for a drive regulating device of a drive device.

[0022] Furthermore, a device is described which is designed to carry out and / or control a plurality of steps / a step of a method in a plurality of corresponding units / in a corresponding unit.

[0023] Such a device may be an electrical appliance which processes electrical signals, such as sensor signals, and outputs control signals accordingly. The device may have one or more suitable interfaces, which may be constructed in hardware and / or software. In a hardware construction, the interface may, for example, be part of an integrated circuit that implements the functions of the device. The interface may also be a suitable integrated circuit, or may be at least partially composed of discrete components. In a software construction, the interface may be a software module that exists on a microcontroller in addition to other software modules.

[0024] Also advantageous is a computer program product having a program code which can be stored on a machine-readable carrier, such as a semiconductor memory, hard disk memory or optical memory, and is used for executing the proposed method when the program is executed on a computer or device.

[0025] Furthermore, an electrical system having an electric machine is proposed, wherein the electrical system has a half-bridge coupled between the electric machine and an intermediate circuit capacitor and the described device. The electrical system is in particular an electric drive system.

[0026] The electric machine is in particular a rotary electric machine, for example in particular a synchronous machine or an asynchronous machine. The electric machine is in particular a traction motor of a vehicle, i.e. an electric motor for driving the vehicle. The vehicle is therefore in particular a vehicle which can be driven at least temporarily by means of an electric machine, for example a purely electric vehicle or a hybrid vehicle. The vehicle is in particular a motor vehicle, for example a PKW (passenger car) or a LKW (truck). The subject matter of the invention can therefore also relate to a powertrain or a drive system for such a vehicle having an electric machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] An exemplary embodiment of the solution proposed here is shown in the drawings and is explained in detail in the following description.

[0028] Figure 1 A schematic diagram of a device for discharging an intermediate circuit capacitor according to an embodiment is shown;

[0029] Figure 2 A schematic diagram of a circuit arrangement connected to an electric machine for discharging an intermediate circuit capacitor according to an exemplary embodiment is shown;

[0030] Figure 3showing a first and a second diagram with voltage and current intensity curves detected over time during the discharge of the intermediate circuit capacitor;

[0031] Figure 4 A schematic diagram of a circuit arrangement connected to an electric machine for discharging an intermediate circuit capacitor according to an exemplary embodiment is shown;

[0032] Figure 5 A schematic diagram of a protection unit of a circuit arrangement connected to an electric machine for discharging an intermediate circuit capacitor according to an exemplary embodiment is shown;

[0033] Figure 6 A schematic diagram shows a variant of a protection unit of a circuit arrangement connected to an electric machine for discharging an intermediate circuit capacitor according to an exemplary embodiment;

[0034] Figure 7 A flow chart of an exemplary embodiment of a method for discharging an intermediate circuit capacitor according to an exemplary embodiment is shown.

[0035] In the following description of preferred exemplary embodiments of the invention, identical or similar reference numerals are used for elements which are illustrated in different figures but act similarly, wherein a repeated description of these elements is omitted.

[0036] If an embodiment includes an “and / or” relationship between a first feature and a second feature, this can be interpreted as: the embodiment has the first and second features according to one embodiment, and either has only the first feature or has only the second feature according to another embodiment. DETAILED DESCRIPTION

[0037] Figure 1 A schematic diagram of a device 100 for discharging an intermediate circuit capacitor 106 according to an exemplary embodiment in cooperation with further components is shown. The device 100 is part of an electrical system 101 having an electric machine 102. The electrical system 101 can be installed, for example, in a vehicle 103, wherein an electrical energy storage device 104 can output electrical energy via an intermediate circuit 105 having an intermediate circuit capacitor 106 and an inverter 107 to the electric machine 102, for example, in order to propel the vehicle 103. The electric machine 102 is therefore in particular a traction motor of the vehicle 103. The system 101 is therefore in particular an electric drive system. The vehicle 103 is in particular a motor vehicle.

[0038] In order to prevent damage to components of the intermediate circuit 105, for example, in the event of a fault or load shedding, a device 100 is provided. For this purpose, the device is designed to carry out and / or control a method for discharging the intermediate circuit capacitor 106 in the respective unit.

[0039] The device 100 comprises a control unit 108, wherein the control unit 108 is designed, for example, to read in a fault signal 110. The fault signal 110 represents, for example, a fault message or a load shedding message, which indicates an overvoltage in the intermediate circuit 105 and / or on the intermediate circuit capacitor 106. Alternatively or additionally, the fault signal 110 may represent a generator operation of the electric machine 102, which occurs, for example, in the case of energy recovery braking of the vehicle 102. That is, if a fault occurs in the generator operation of the electric machine 102, for example due to an emergency disconnection of the energy storage device 104 to be charged by the electric machine 102 via the intermediate circuit 105, the energy provided by the electric machine 102 may cause damage to the intermediate circuit 105 or to components of the intermediate circuit 105, for example, to the intermediate circuit capacitor 106. Therefore, the control unit 108 is designed to output a control signal 115 in response to the fault signal 110.

[0040] The control signal 115 represents a command to simultaneously close and, if necessary, subsequently open the switches of the half-bridge, which will be described in more detail below. The half-bridge is preferably part of the inverter 107. In this exemplary embodiment, the discharge of the intermediate circuit capacitor 106 is therefore controlled, in particular when the fault message is an overvoltage and / or an emergency situation of the intermediate circuit capacitor.

[0041] Figure 2 A circuit arrangement 200 is shown as a schematic diagram of an electrical system 101 having a device 100 for discharging an intermediate circuit capacitor 106. The circuit arrangement 200 comprises an electric machine 102, which can be operated in generator mode and thus provides voltage and current. In addition, the electrical system 101 comprises an intermediate circuit 105 having an intermediate circuit capacitor 106, wherein the intermediate circuit 105 is connected to a high-voltage battery as an energy storage device 104 (which is generally understood here to be an electrochemical energy storage device 104). The energy storage device can be charged, for example, by the electrical energy provided by the electric machine 102, so that the electrical energy can then be output to the electric machine 102 again in order to move the vehicle 103 forward.

[0042] The electric machine 102 is currently electrically coupled to the intermediate circuit 105 by means of three phase lines 213a, 213b and 213c (U, V and W) via an inverter 107 in a manner known per se. The inverter 107 has three half bridges 215, 217, 219 (one half bridge 215, 217, 219 for each phase line U, V, W).

[0043] The half bridges 215, 217 and 219 are connected in parallel with each other in the circuit. Each half bridge 215, 217, 219 includes two switches 225 and 227, 230 and 232, 235 and 237, which are connected in series (with respect to the two poles / two joints of the intermediate circuit 105). They are high-side switches 225, 230, 235 and low-side switches 227, 232, 237.

[0044] The switches 225 and 227, 230 and 232, 235 and 237 of the half bridges 215, 217, 219 are controlled by the control unit 108 of the device 100 so that

[0045] · Close switches 225 and 227 simultaneously, and / or

[0046] Closing switches 230 and 232 simultaneously, and / or

[0047] • Close switches 235 and 237 simultaneously.

[0048] The switches 225 and 227, 230 and 232, 235 and 237 of the respective half bridge 215, 217, 219 are controlled in such a way that the switch-on period of the switches 225 and 227, 230 and 232, 235 and 237 does not exceed a predetermined (switch-on period) threshold value. In particular, the closing and subsequent opening of the switches 225 and 227, 230 and 232, 235 and 237 are repeated multiple times at predefined time intervals. This is done until the intermediate circuit capacitor 106 is completely discharged.

[0049] In particular, all switches 225 and 227, 230 and 232, 235 and 237 of the half-bridges 215, 217, 219 are actuated in this manner. However, applications are also conceivable in which only the switches 225 and 227, 230 and 232, 235 and 237 of one half-bridge 215, 217, 219 or two half-bridges 215, 217, 219 are closed and opened again in this manner. The technical function of this opening and closing is similar to the opening and closing of the switches 225 and 227, 230 and 232, 235 and 237 of all half-bridges 215, 217, 219 of the inverter 107. However, this results in a smaller current and therefore a slower discharge of the intermediate circuit capacitor 106. Also conceivable is a time-staggered activation of the switches 225 and 227 , 230 and 232 , 235 and 237 of the individual half-bridges 215 , 217 , 219 . This makes it possible to achieve a smoother curve of the current when discharging the intermediate circuit capacitor 106 .

[0050] The intermediate circuit capacitor 106 is discharged so that the electrical energy of the intermediate circuit capacitor 106 is converted into heat by means of the (briefly) short-circuited switches 225 and 227, 230 and 232, 235 and 237 of the half-bridges 215, 217, 219. According to one exemplary embodiment, the switches 225 and 227, 230 and 232, 235 and 237 are (power) transistors, for example IGBTs or MOSFETs.

[0051] When the capacitor 106 of the intermediate circuit is to be discharged, according to one embodiment, all switches 225 and 227, 230 and 232, 235 and 237 are opened and closed again with a simultaneous discharge pulse. This results in that, during the conduction period of the switches 225 and 227, 230 and 232, 235 and 237, a current flows directly from the positive potential connection of the intermediate circuit 105 or the intermediate circuit capacitor 106 to the negative potential connection of the intermediate circuit 105 or the intermediate circuit capacitor 106. This results in the discharge of the intermediate circuit capacitor 106. This current does not flow through the motor 102 in this case (as it would normally flow through in other cases) and no undesirable torque can be generated therein. In this discharge pulse, only the inductance of the current path limits the current rise. Since the inductance is usually very small, a high current rise rate can be expected. Since high currents can damage switches 225 and 227, 230 and 232, 235 and 237 of half bridges 215, 217 and 219 and intermediate circuit capacitor 106, this current increase should be kept small. This can be achieved by reducing the on-time of switches 225 and 227, 230 and 232, 235 and 237.

[0052] In most cases, the intermediate circuit capacitor 106 cannot be completely discharged by switching the switches 225 and 227, 230 and 232, 235 and 237 on and off once, since the switch-on time of the switches 225 and 227, 230 and 232, 235 and 237 should be selected to be very small. In order to increase the energy conversion, the discharge pulses are repeated sufficiently frequently at short intervals until the intermediate circuit capacitor 106 is completely or sufficiently discharged.

[0053] The advantage of using one or more half-bridges 215, 217 and 219 of the inverter 107, each with at least two switches 225 and 227, 230 and 232, 235 and 237, is that the components are generally compatible with high power losses and the heat dissipation is formed optimally. In addition, the half-bridges 215, 217 and 219 with the switches 225 and 227, 230 and 232, 235 and 237 are mostly already available and do not result in additional costs for the discharge function. The proposed solution is also characterized in that no current flows through the electric machine 102 during the discharge. As a result, no imperfect torque is provided.

[0054] Figure 3 A first and a second diagram 300 , 305 are shown with voltage and current intensity curves over time, which are detected during the discharge process of the intermediate circuit capacitor 106 using the proposed solution.

[0055] A first diagram 300 shows a time-voltage curve, wherein an x-axis 310 includes a time curve from −7.2 ms to 192.8 ms and a y-axis 315 includes voltages from 200 V to 600 V. The curve visible in the first diagram 300 describes the intermediate circuit voltage across the intermediate circuit capacitor 106. In the first diagram, the voltage is 500 V at the beginning (arrow on the left) and discharges to a voltage of 0 V after 100 ms. The voltage across the intermediate circuit capacitor 106 decreases essentially exponentially.

[0056] The second diagram 305 shows a time current intensity curve, wherein the x-axis 320 includes a time curve from -7.2 ms to 192.8 ms and the y-axis 325 includes a current intensity from -200 A to 1.4 kA. The curve visible in the second diagram 305 describes the current flowing through the half bridges 215, 217, 219 during the discharge. In the second diagram, the current intensity of the current is 1.2 kA at the beginning (arrow on the left) and decreases to a current intensity of 0 A after 100 ms. The drop in current intensity is very large at the beginning, but it becomes smaller and smaller as time increases. After a period of 50 ms, the current intensity of the current drops to less than 50%, i.e. less than 600 A (approximately 400 A).

[0057] Figure 4 A schematic diagram of a circuit arrangement 400 for discharging an intermediate circuit capacitor 106 for an electric machine 102 (not shown in detail) is shown. In the circuit arrangement 400, the intermediate circuit capacitor 106 is similar to Figure 2 The ground is electrically coupled to the three half bridges 215, 217, 219 of the inverter. The half bridges 215, 217, 219 are themselves connected in parallel with each other in the circuit. Each half bridge includes at least two switches 225 and 227, 230 and 232, 235 and 237 connected in series.

[0058] The circuit arrangement 400 further comprises phase lines U, V and W for conveying current to or from the motor 102. Each line U, V and W is coupled to two series-connected switches 225 and 227, 230 and 232, 235 and 237 of the associated half-bridge 215, 217, 219 at the central intercept point of the associated half-bridge 215, 217, 219, as also shown in FIG. Figure 2 As shown in .

[0059] The circuit arrangement 400 further comprises a half-bridge driver 405 for amplifying the actuation signal 115, which actuates the switches 225 and 227, 230 and 232, 235 and 237. The circuit arrangement 400 further comprises a microcontroller 410 for actuating the half-bridge driver 405. Figure 4 Furthermore, a coil 415 is shown in FIG. 4 , which represents the line inductance of the circuit arrangement 400 in the region of the intermediate circuit capacitor 106 .

[0060] The switches 225 and 227, 230 and 232, 235 and 237 of the half bridges 215, 217, 219 are controlled so as to execute the switching of the switches 225 and 227, 230 and 232, 235 and 237 which have been directed to Figure 2 The described simultaneous closing and subsequent opening. Thus, the switches 225 and 227, 230 and 232, 235 and 237 are controlled so that the switch-on duration does not exceed a predetermined threshold value. Closing and subsequent opening of the switches 225 and 227, 230 and 232, 235 and 237 are repeated multiple times at predefined intervals. This continues until the intermediate circuit capacitor 106 is discharged.

[0061] It is also conceivable that the discharge pulses for actuating the two switches 225 and 227, 230 and 232, 235 and 237 of the half-bridges 215, 217, 219 are either distributed to the half-bridges 215, 217, 219 in a time-staggered manner or that the discharge pulses are output simultaneously for all half-bridges 215, 217, 219. It is particularly advantageous to switch the half-bridges 215, 217 and 219 simultaneously. Since the intermediate circuit capacitor 106 contains a large part of the path inductance, This limits the maximum current increase. By switching all half-bridges 215, 217, 219 simultaneously, the maximum current that is formed is evenly distributed to the half-bridges 215, 217, 219. Therefore, the time tolerance of the switch-on pulses also has a smaller effect on the maximum current flowing. This reduces the load of the switches 225 and 227, 230 and 232, 235 and 237 on the one hand, and simplifies the regulation of the switch-on pulses on the other hand.

[0062] Figure 5 A circuit arrangement of a protection unit 500 for discharging an intermediate circuit capacitor for an electric machine by means of two switches of a half bridge, in particular switches of a half bridge of an inverter is shown. The protection unit 500 can be used in particular in Figure 2 and Figure 4 are used in the inverter shown in order to discharge the respective intermediate circuit capacitors.

[0063] The protection unit 500 comprises an input 505 for a high-side pulse width modulated signal 535 and an input 510 for a low-side pulse width modulated signal 540. The pulse width modulation is used to generate a pulse width modulated signal for opening and closing the associated switches of the half bridge. The protection unit further comprises an AND gate 515, a delay unit 520, and a high-side half-bridge driver 525 and a low-side half-bridge driver 530, which control the respective switches of the half bridge.

[0064] Usually, a protection unit is provided in the half-bridge of the inverter, which prevents the two switches of the half-bridge from being switched on for longer than the maximum switch-on duration. With such a protection unit, the solution proposed here would be hindered, because the protection unit prevents the presence of a too long switch-on pulse for closing the switch of the half-bridge. Usually, conventional protection units check for this purpose whether the high-side switch and the low-side switch are simultaneously controlled by corresponding signals on the respective inputs of the protection unit. If this is the case, both switch-on pulses are suppressed, and as a result, the two switches of the half-bridge are forcibly disconnected. However, this function would hinder the solution presented.

[0065] therefore, Figure 5 The proposed protection unit 500 is shown to be implemented in the following manner:

[0066] The protection unit 500 compares the two switching signals 535 and 540 of the inputs 505 and 510. When "high" (logic 1) is present at both inputs 505 and 510, the AND gate 515 switches its output only to "high" (logic 1). That is, if the two inputs 505 and 510 are controlled simultaneously (two logic 1s), which requires the two switches of the half bridge to be closed simultaneously, then a corresponding protection signal 545 is generated. The protection signal 545 is delayed in time by means of the delay unit 520. The protection signal 545 is output at the output of the delay unit 520 with a delay of a specific time period (delay time). Preferably, the delay time is about 500ns. The delay time is in particular at least greater than the duration of the discharge pulse for discharging the intermediate circuit capacitor. If the duration of the discharge pulse exceeds the delay time, the switch of the half bridge is forced to be cut off (again), that is, disconnected, in order to protect it. The two drivers 525 and 530 are controlled accordingly. If the discharge pulse remains shorter than the delay time, the protection unit 500 does not participate.

[0067] Figure 6 A variant of a protection unit 600 for discharging an intermediate circuit capacitor for an electric machine by means of two switches of a half-bridge, in particular switches of a half-bridge of an inverter is shown. The protection unit 600 can also be used in particular in Figure 2 and Figure 4 are used in the inverter shown in order to discharge the respective intermediate circuit capacitors.

[0068] The protection unit 600 comprises an input 505 for a high-side pulse width modulated signal 535 and an input 510 for a low-side pulse width modulated signal 540. The pulse width modulation is used to generate corresponding pulse width modulated signals with drivers 630, 635 for opening and closing the associated switches of the half bridge. The protection unit 600 further comprises three AND gates 515, 605, 610, an inverter 615, an OR gate 620 and a NAND gate 625, a delay unit 520 and a high-side switch driver 630 and a low-side switch driver 635. The drivers 630, 635 provide the necessary currents in order to actuate the respectively associated switches of the half bridge.

[0069] In one exemplary embodiment, the drivers 630 , 635 shown here have logic outputs, wherein the components 515 , 605 , 610 , 615 , 620 , 625 shown here contain the respectively mentioned logic functions.

[0070] In order for the protection unit 600 to detect signals for "high" (logic 1) and "low" (logic 0), a certain voltage range should be maintained for the potential. In order to detect "1", the input voltage should be greater than 70% of the operating voltage. In order to detect "0", the input voltage should be no greater than 30% of the operating voltage.

[0071] Inputs 505 and 510 have a locking function, which is triggered when drivers 630 and 635 should be switched on. Protection unit 600 compares two switch signals 535 and 540 at inputs 505 and 510. When at least one of the switch signals 535 and 540 is at "low" (logic 0), NAND gate 625 switches its output only to "high" (logic 1). Conversely, when both switch signals 535 and 540 are at "high" (logic 1), NAND gate 625 switches its output to "low" (logic 0).

[0072] When, for example, a microcontroller (e.g. Figure 4 The protection unit 600 can be bridged in this variant when the microcontroller 410 of the control circuit sets the request "SC_Rel" to "high" (logic 1). If this is the case, the proposed solution for discharging the intermediate circuit capacitor can be used. The delay unit 520 has the effect that the protection unit 600 is bridged only for a limited time. The delay unit 520 of the protection unit 600 and the Figure 5The delay unit 520 of the protection unit 500 operates similarly. The inverter 615 provides a negation operation on the signal present at its input. This means that after temporarily disabling the protection unit 600, the signal is set to "high" (logic 1) again through the AND gate 515. When both inputs are at "high" (logic 1), the AND gate 515 sets its output to "high" (logic 1).

[0073] Figure 7 A flow chart of an exemplary embodiment of a method 700 for discharging an intermediate circuit capacitor according to an exemplary embodiment is shown. The method 700 may be used in a Figure 1 , 2 and Figure 4 , 5 , and is implemented in the case of the equipment introduced in 6.

[0074] The method 700 comprises at least one step 705 , in which switches of a half-bridge are controlled so that the switches are closed simultaneously.

[0075] Reference numerals list

[0076] 100 devices

[0077] 101 Electrical System

[0078] 102 Motor

[0079] 103 Vehicles

[0080] 104 Energy Storage

[0081] 105 Intermediate circuit

[0082] 106 Intermediate circuit capacitor

[0083] 107 Inverter

[0084] 108 Control Unit

[0085] 110 Fault signal

[0086] 115 Control Signal

[0087] 200 Circuit Devices

[0088] 210 Motor

[0089] 213a, 213b, Phase line

[0090] 213c, U, V, W

[0091] 215 First Half Bridge

[0092] 217 Second Half Bridge

[0093] 219 The Third Half Bridge

[0094] 225 Switch

[0095] 227 Switch

[0096] 230 Switch

[0097] 232 Switch

[0098] 235 Switch

[0099] 237 Switch

[0100] 300 First graph of the time-voltage curve

[0101] 305 Second graph of time current intensity curve

[0102] 310 x-axis

[0103] 315 y-axis

[0104] 320 x-axis

[0105] 325 y-axis

[0106] 400 Circuit Devices

[0107] 405 Half-bridge Driver

[0108] 410 Microcontroller

[0109] 415 Coil

[0110] 500 protection units

[0111] 505 Input terminal for high-side pulse width modulation signal

[0112] 510 Input terminal for low-side pulse width modulation signal

[0113] 515 AND Gate

[0114] 520 Delay Unit

[0115] 525 High-Side Half-Bridge Driver

[0116] 530 Low-Side Half-Bridge Driver

[0117] 535 High-side pulse width modulated switching signal

[0118] 540 Low-side pulse width modulated switching signal

[0119] 545 Protection signal

[0120] 600 protection units

[0121] 605 AND Gate

[0122] 610 AND Gate

[0123] 615 Inverter

[0124] 620 OR Gate

[0125] 625 NAND Gate

[0126] 630 High-Side Switch Driver

[0127] 635 Low-Side Switch Driver

[0128] 700 Method for discharging an intermediate circuit capacitor

[0129] 705 Operation steps

Claims

1. A method (700) for discharging an intermediate circuit capacitor (106), wherein: The intermediate circuit capacitor (106) is electrically coupled to at least one half-bridge (215), the at least one half-bridge comprising at least two switches (225, 227) connected in series, wherein the method (700) comprises at least one of the following steps: controlling (705) the switches of the half-bridge (215) so as to close the switches (225, 227) simultaneously, wherein in the controlling (705) step a protection unit (500; 600) of the half-bridge (215) for preventing the simultaneous closing of the switches of the half-bridge in a "normal" operating mode in which the intermediate circuit capacitor does not need to be discharged is disabled, the protection unit being used to monitor the state of the switches (225, 227) of the connected half-bridge (215) so as not to be connected longer than a maximum connection duration, wherein a protection signal (545) is output at the output of a delay unit (520) of the protection unit (500; 600) with a delay of a specific delay time, the delay time being at least greater than the duration of a discharge pulse for discharging the intermediate circuit capacitor.

2. The method (700) of claim 1, wherein: In the control (705) step, the switch (225, 227) is controlled so that the switch (225, 227) is turned on for a time period that does not exceed a predetermined threshold value.

3. The method (700) of claim 1, wherein: In the control (705) step, the simultaneous closing and subsequent opening of the switches (225, 227) are repeated multiple times.

4. The method (700) of claim 3, wherein: In the manipulating (705) step, the simultaneous closing and subsequent opening of the switches (225, 227) are repeated at predefined intervals.

5. The method (700) of claim 3, wherein: In a control step (705), the switch (225, 227) is closed and then opened until the intermediate circuit capacitor (106) is discharged.

6. The method (700) according to any one of claims 1 to 5, wherein: In a control (705) step, a further half-bridge (217, 219) connected in parallel with a half-bridge (215) is controlled, wherein at least two series-connected switches (230, 232, 235, 237) of the further half-bridge (217, 219) are closed simultaneously.

7. The method (700) of claim 6, wherein: In a control step (705), switches (230, 232, 235, 237) of the other half-bridges (217, 219) are opened and / or closed in a time-staggered manner relative to switches (225, 227) of the one half-bridge (215).

8. The method (700) according to any one of claims 1 to 5, wherein: In a control (705) step, the protection unit (500; 600) is deactivated for a predetermined period of time and is activated again after the predetermined period of time has elapsed.

9. The method (700) according to any one of claims 1 to 5, wherein: If a fault message and / or information about the presence of a generator operation of an electric machine (102) coupled to the half-bridge (215) is present, a discharge of the intermediate circuit capacitor (106) is controlled in a control step (705).

10. The method (700) of claim 9, wherein: The fault message is information about a fault state in the intermediate circuit (105) and / or an overvoltage of the intermediate circuit capacitor (106).

11. A device (100) configured to carry out and / or control the steps of the method (700) according to any one of claims 1 to 10 in at least one corresponding unit (108).

12. An electrical system (101) having an electric machine (102), wherein: The electrical system (101) has a half-bridge (215) coupled between the electric machine (102) and an intermediate circuit capacitor (106) and a device (100) according to claim 11.

13. The electrical system (101) according to claim 12, wherein: The electrical system (101) is a drive system.

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