Device and method for controlling the discharge of a DC link capacitor

Abstract

The invention relates to activating an active discharge of a DC link capacitor. To this end, provision is made of a discharge device which can detect a condition for activating the discharge of a DC link capacitor independently of other system components and thus can initiate an active discharge of the DC link capacitor. To this end, the voltage across the DC link capacitor is evaluated and the active discharge of the DC link capacitor is enabled if a gradient of the voltage across the DC link capacitor falls below a predefined threshold value.

Description

[0001] Description

[0002] title

[0003] Device and method for controlling the discharge of an intermediate circuit capacitor

[0004] Technical area

[0005] The present invention relates to a device and a method for controlling the discharge of an intermediate circuit capacitor, a device for discharging an intermediate circuit capacitor, an electrical power converter and an electrical drive system.

[0006] State of the art

[0007] Electrical power converters for converting an input voltage into an output voltage are used in numerous applications. For example, such power converters are used in electric drive systems, such as those found in electric vehicles. In this case, an input DC voltage of usually several hundred volts is converted by the power converter into an output voltage for driving an electrical machine. A so-called intermediate circuit capacitor is provided to stabilize the input DC voltage.

[0008] To avoid potential hazards that may arise from a charged DC link capacitor in the event of an accident or during repair work, this DC link capacitor is deliberately discharged when the electric drive system is switched off or deactivated.

[0009] For example, German patent document DE 10 2013 224 884 A1 describes a device and method for discharging such an intermediate circuit capacitor. A discharge controller is provided that discharges the intermediate circuit capacitor via an electrical load with a predetermined discharge current. Disclosure of the Invention

[0010] The present invention provides a device and a method for controlling the discharge of an intermediate circuit capacitor, a device for discharging an intermediate circuit capacitor, an electric power converter, and an electric drive system having the features of the independent patent claims. Further advantageous embodiments are the subject of the dependent patent claims.

[0011] Accordingly, it is provided:

[0012] A device for controlling the discharge of an intermediate circuit capacitor, comprising a monitoring device and a control device. The monitoring device is configured to detect an electrical voltage across the intermediate circuit capacitor. The control device is configured to determine a temporal gradient of the electrical voltage across the intermediate circuit capacitor. Furthermore, the control device is configured to enable active discharge of the intermediate circuit capacitor if the gradient of the electrical voltage across the intermediate circuit capacitor falls below a predetermined first threshold.

[0013] Furthermore, it is planned:

[0014] A device for discharging an intermediate circuit capacitor, comprising a passive discharge path, an active discharge path, and a device according to the invention for controlling the discharge of the intermediate circuit capacitor. The passive discharge path comprises an electrical resistor and / or an electrical load between a first terminal of the intermediate circuit capacitor and a second terminal of the intermediate circuit capacitor. The active discharge path comprises a switching element between the first terminal of the intermediate circuit capacitor and the second terminal of the intermediate circuit capacitor. In particular, the active discharge path can comprise a series circuit comprising the switching element and a further electrical resistor and / or a further electrical load.The device for controlling the discharge of the intermediate circuit capacitor is designed to close the switching element in the active discharge path if the active discharge of the intermediate circuit capacitor is enabled.

[0015] Furthermore, it is planned:

[0016] An electrical power converter with an input terminal, an intermediate circuit capacitor, an output terminal, and a device according to the invention for discharging the intermediate circuit capacitor. The input terminal is designed to be connected to a DC voltage source. The intermediate circuit capacitor is arranged between a first connection point and a second connection point of the input terminal. The power converter is designed, in particular, to convert a DC voltage provided at the input terminal into a predetermined output voltage and to provide this output voltage at the output terminal.

[0017] In addition, it is planned:

[0018] An electric drive system comprising an electric power converter according to the invention and an electric machine. The electric machine is electrically connected to the output terminal of the power converter.

[0019] Finally, it is planned:

[0020] A method for controlling the discharge of an intermediate circuit capacitor, comprising a step for determining an electrical voltage across the intermediate circuit capacitor, a step for determining a temporal gradient of the electrical voltage across the intermediate circuit capacitor, and a step for enabling an active discharge of the intermediate circuit capacitor if the temporal gradient of the electrical voltage across the intermediate circuit capacitor falls below a predetermined first threshold value.

[0021] Advantages of the Invention Intermediate-link capacitors, such as those found in electrical power converters, can continue to store electrical energy even after the active operation of the power converter has been switched off, so that a relatively high electrical voltage can be present across the intermediate-link capacitor for a longer period of time. To avoid potential hazards that could arise from such a high electrical voltage, it is desirable to discharge the intermediate-link capacitor as quickly as possible as soon as the electrical power converter is deactivated.

[0022] While such an active discharge of the DC link capacitor can in principle be initiated by a converter controller, it is necessary or at least desirable, for safety reasons, to provide a discharge of the DC link capacitor independent of this controller. Thus, even in the event of a failure or malfunction of the converter controller, a quick and reliable discharge of the DC link capacitor can be ensured by an additional device independent of the actual controller.

[0023] However, this requires that such a system, which is independent of the actual control system, also detects an operating state in which the intermediate circuit capacitor can be discharged as quickly and reliably as possible.

[0024] The present invention takes advantage of the fact that when the power converter is switched off and the associated disconnection of the power converter from an input voltage source, the electrical voltage across the intermediate circuit capacitor continuously decreases over time. This is generally supported by an electrical resistor provided in parallel with the intermediate circuit capacitor in a passive discharge branch. This continuously decreasing electrical voltage corresponds mathematically to a negative gradient of the electrical voltage across the intermediate circuit capacitor. In other words, if the gradient of the electrical voltage across the intermediate circuit capacitor has a negative value whose magnitude exceeds a predetermined threshold, this can be interpreted as an indication that the electrical power converter is deactivated.In such a case, an active discharge of the intermediate circuit capacitor can be initiated.

[0025] By monitoring the electrical voltage across the DC link capacitor, a simple yet highly reliable method is available for deciding whether to initiate active discharge of the DC link capacitor. In particular, this allows a decision to actively discharge the DC link capacitor to be made completely independent of the converter's control system. Thus, even in the event of a malfunction in the converter's control system, active discharge of the DC link capacitor can be initiated by an independent entity. This can increase the safety of the entire system.

[0026] A simple voltage sensor is sufficient to measure the electrical voltage across the DC link capacitor. For example, an electrical voltage divider in the form of a series connection of several electrical resistors can also be used. If necessary, such a resistor divider can also be combined with the electrical resistors in the passive discharge branch to measure the electrical voltage across the DC link capacitor. Of course, any other options for measuring the electrical voltage across the DC link capacitor are also possible.

[0027] To determine the voltage gradient across the DC link capacitor, the voltage curve can be analyzed within a predetermined time interval. For example, a current voltage across the DC link capacitor can be compared with the voltage across the DC link capacitor a predefined time period ago, such as one second, and a voltage gradient can be calculated from this. In principle, however, any other suitable time intervals are also possible. It is also possible, for example, to temporally filter the voltage curve to eliminate any short-term voltage peaks. The evaluation of the voltage curve across the DC link capacitor can be performed in any suitable manner.For example, this can be done using a microcontroller, an application-specific integrated circuit, or any other means.

[0028] According to one embodiment, the control device is designed to enable the active discharge of the intermediate circuit capacitor only if at least a predetermined period of time has elapsed since a previous active discharge of the intermediate circuit capacitor. In this way, a minimum pause time can be provided between two consecutive active discharges. This can prevent, for example, undesired activations of the discharge of the intermediate circuit capacitor from occurring in rapid succession in the case of a very dynamic voltage variation across the intermediate circuit capacitor.

[0029] According to one embodiment, the control device is designed to also enable the active discharge of the intermediate circuit capacitor if the electrical voltage across the intermediate circuit capacitor falls below a predetermined minimum voltage. For example, a minimum electrical input voltage can be specified as the threshold value for this minimum voltage. This minimum electrical input voltage can, for example, correspond to an electrical voltage that is at least expected at the input. For example, in a battery-powered voltage converter, this can correspond to a minimum battery voltage, for example, the electrical voltage of a discharged battery or a discharged battery under load.If the electrical voltage across the intermediate circuit capacitor falls below such a minimum voltage, it can be assumed that the intermediate circuit capacitor is disconnected from the voltage source and thus the conditions for discharging the intermediate circuit capacitor may be met.

[0030] According to one embodiment, the control device is designed to determine a rotational speed of an electrical machine in an electrical drive system with the intermediate circuit capacitor. In this case, the control device can be designed to enable the active discharge of the intermediate circuit capacitor if the determined rotational speed falls below a predetermined speed. If, for example, a value of zero is used as the predetermined minimum speed, this corresponds to a standstill of the electrical machine. As an alternative to a speed of zero, a speed can also be selected at which the amplitude of an induced electrical voltage generated by the electrical machine falls below a predetermined maximum value. For example, this predetermined maximum value can correspond to a value that is less than or equal to a maximum permissible electrical voltage of the discharged intermediate circuit capacitor.

[0031] According to one embodiment, the control device is designed to stop the active discharge of the intermediate circuit capacitor if the temporal gradient of the electrical voltage across the intermediate circuit capacitor exceeds a predetermined second threshold. The predetermined second threshold can, for example, correspond to the first predetermined threshold for enabling the active discharge. Alternatively, the two thresholds can differ, so that, for example, a hysteresis is provided between the first and the second threshold. If the temporal gradient of the electrical voltage across the intermediate circuit capacitor exceeds this second threshold, this can, for example, be an indication that the conditions for active discharge of the intermediate circuit capacitor are not currently met in the system with the intermediate circuit capacitor.For example, a relatively high load may have previously caused the voltage gradient across the DC link capacitor to drop below the specified value. In such cases, a voltage drop across the DC link capacitor can subsequently be compensated for by a connected voltage source. This increases the voltage gradient across the DC link capacitor. In such a case, it can be determined that a possibly initiated discharge of the DC link capacitor is inappropriate, and the discharge of the DC link capacitor can then be stopped.

[0032] According to one embodiment of the electric drive system, the device for controlling the discharge of the intermediate circuit capacitor is designed to enable the active discharge of the intermediate circuit capacitor only if a predetermined operating state has been set by the power converter. The operating states in which an active discharge of the intermediate circuit capacitor can be enabled can be, for example, so-called safe operating states such as an active short circuit or freewheeling. In this way, it can be ensured that no active discharge of the intermediate circuit capacitor occurs as long as the drive system is in an operating mode for controlling the electric machine, in which the electric machine is actively operated as a motor or generator.

[0033] The above embodiments and further developments can be combined with one another as desired, where appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention not explicitly mentioned above or described below with respect to the exemplary embodiments. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention.

[0034] Short description of the drawings

[0035] Further features and advantages of the invention are explained below with reference to the figures. These show:

[0036] Fig. 1: a schematic representation of a basic circuit diagram of an electric drive system with a device for controlling the discharge of an intermediate circuit capacitor according to an embodiment;

[0037] Fig. 2: a voltage-time diagram illustrating the control of the discharge of an intermediate circuit capacitor according to an embodiment;

[0038] Fig. 3: a voltage-time diagram illustrating the control of the discharge of an intermediate circuit capacitor according to another embodiment; and Fig. 4: a flowchart underlying a method for controlling the discharge of an intermediate circuit capacitor according to one embodiment.

[0039] Description of the embodiments

[0040] Figure 1 shows a schematic representation of a basic circuit diagram of an electric drive system with a device 1 for discharging an intermediate circuit capacitor according to one embodiment. The electric drive system comprises a power converter 2 and an electric machine 3 connected to the power converter 2. The power converter 2 can be supplied with electrical energy at an input terminal from a voltage source 4. For example, the voltage source 4 can be a DC voltage source, in particular a battery such as the traction battery of an electric vehicle. The voltage source 4 can be separated from the input terminal of the power converter 2 by means of the switching elements 41, 42. To operate the electric drive system, the two switches 41, 42 are closed.

[0041] The electrical power converter 2 can thus generate an electrical voltage suitable for driving the electrical machine 3 using the electrical energy provided by the voltage source 4. In a further operating mode, the power converter 2 can convert an electrical voltage generated by the electrical machine 3 in generator mode into an electrical voltage suitable for charging a battery 4 connected to the input terminal of the power converter 2.

[0042] To stabilize the input voltage, an intermediate circuit capacitor 20 is provided between the two connection points of the input terminal in the power converter 2. If the power converter 2 is deactivated, an electrical voltage can remain across a charged intermediate circuit capacitor 20 even if the two switching elements 41, 42 are open. In such a case, the intermediate circuit capacitor 20 can be discharged by means of the device 1 for discharging the intermediate circuit capacitor 20. The device 1 for discharging the intermediate circuit capacitor 20 comprises an active discharge path and a passive discharge path. In the passive discharge path, an electrical resistor 12 is provided between the two connection points of the input terminal of the power converter 2. It is understood that, instead of a single electrical resistor 12, a series connection and / or parallel connection of several electrical resistors can also be provided.Thus, an electrical current always flows through this electrical resistor 12 in the passive discharge path as long as an electrical voltage is applied across the intermediate circuit capacitor 20. As a result, the intermediate circuit capacitor 20 is continuously discharged with a relatively low discharge current.

[0043] In the active discharge path, a switching element 13 is provided between the two connection points of the DC voltage connection of the power converter 2. Furthermore, at least one electrical resistor 14 can be provided in series with this switching element 13. This electrical resistor 14 can limit the discharge current during an active discharge of the intermediate circuit capacitor 20. The switching element 13 is closed for this active discharge of the intermediate circuit capacitor 20. For example, the switching element 13 can be controlled by a control device 11 to initiate an active discharge of the intermediate circuit capacitor 20. The electrical resistors 12 and 14 in the passive and active discharge paths can, for example, be designed as ohmic resistors. Additionally or alternatively, it is also possible to provide another suitable electrical load.In particular, a controlled discharge of the intermediate circuit capacitor 20 via the power converter 2, in particular via so-called hot branches of the power converter 2, can also be included as an electrical consumer.

[0044] The control device 11 can operate, in particular, independently of other components of the electrical drive system, such as a control circuit for controlling the power converter 2. This allows the discharge of the intermediate circuit capacitor 20 to be activated even if a malfunction should occur in the other components of the drive system. The control device 11 of the device 1 for discharging the intermediate circuit capacitor 20 can detect the electrical voltage across the intermediate circuit capacitor 20. For this purpose, for example, a current sensor for monitoring the electrical current can be provided. The control device 11 can continuously monitor the electrical voltage across the intermediate circuit capacitor 20. For example, it is also possible to detect the electrical voltage across the intermediate circuit capacitor 20 periodically at predetermined time intervals and evaluate it as explained below.

[0045] The control device 11 evaluates the electrical voltage across the intermediate circuit capacitor 20 and, using the measured value of the electrical voltage across the intermediate circuit capacitor 20, controls the switching element 13 in the active discharge path of the device 1 for discharging the intermediate circuit capacitor 20 in order to activate or deactivate an active discharge of the intermediate circuit capacitor 20.

[0046] For example, a gradient of the voltage across the intermediate circuit capacitor 20 can be determined from the time profile of the voltage across the intermediate circuit capacitor 20. This gradient corresponds to the change in the voltage across the intermediate circuit capacitor 20 over time. A negative gradient corresponds to a decrease in the voltage across the intermediate circuit capacitor 20, while a positive gradient corresponds to an increase in the voltage across the intermediate circuit capacitor 20.

[0047] If the intermediate circuit capacitor 20 of the power converter 2 is disconnected from the voltage source 4, for example by opening the switching elements 41, 42, the electrical voltage across the intermediate circuit capacitor 20 will decrease over time, since the intermediate circuit capacitor 20 is discharged via the passive discharge path with the electrical resistor 12. Thus, the control device 11 of the device 1 for discharging the intermediate circuit capacitor 20 can detect this decrease in the electrical voltage and subsequently enable active discharge of the intermediate circuit capacitor 20 via the active discharge path. For this purpose, the control device 11 can, for example, detect that the gradient of the electrical voltage curve across the intermediate circuit capacitor 20 has a negative value that lies below a predetermined threshold. In other words, the magnitude of a negative gradient exceeds a threshold.The threshold value below which the negative gradient of the voltage curve of the electrical voltage across the intermediate circuit capacitor 20 should fall before an active discharge is triggered should be selected, for example, as a function of the discharge current through the passive discharge path with the electrical resistor 12.

[0048] Figure 2 shows a schematic representation of a voltage-time diagram to illustrate the previously described principle for enabling an active discharge of the intermediate circuit capacitor 20. In a first section I, the electric drive system is, for example, in a normal operating state. During this normal operating state, the electric drive system is supplied with electrical energy, for example, from a voltage source 4, so that the voltage U_Z across the intermediate circuit capacitor 20 is at least approximately constant at a value of approximately U_1. If the connection between the voltage source 4 and the input terminal of the power converter 2 is opened, for example by opening the switching elements 41, 42, the electrical voltage U_Z across the intermediate circuit capacitor 20 drops because the intermediate circuit capacitor 20 is discharged via the passive discharge path with the electrical resistor 12.This drop in the electrical voltage U_Z across the intermediate circuit capacitor 20 in the second phase II and the associated negative gradient can be detected, for example, by the control device 11. If the gradient of the electrical voltage U_Z across the intermediate circuit capacitor 20 falls below a predetermined threshold value, the control device 11 then enables the active discharge and closes the switching element 13 in the active discharge path. Subsequently, in the third phase III, the intermediate circuit capacitor 20 is discharged via the active discharge path with the switching element 13 and the electrical resistor 14. This discharge process is maintained, in particular, until the electrical voltage U_Z across the intermediate circuit capacitor 20 falls below a predetermined maximum value U_2 of, for example, 60 volts.The active discharge of the intermediate circuit capacitor 20 can then be terminated and the switching element 13 in the active discharge path can be opened again, so that in section IV the electrical voltage permanently falls below the maximum permissible value U2.

[0049] In addition to evaluating the gradient in the voltage curve of the electrical voltage U_Z across the intermediate circuit capacitor 20, it is also possible to additionally consider the absolute value of the electrical voltage U_Z across the intermediate circuit capacitor 20 for activating an active discharge of the intermediate circuit capacitor 20. If, for example, the electrical voltage U_Z across the intermediate circuit capacitor 20 falls below a previously specified minimum voltage, this can also be interpreted as an indication that the input of the power converter 2 and thus the intermediate circuit capacitor 20 is not electrically connected to a voltage source 4. For example, this minimum voltage can correspond to a minimum battery voltage, in particular a minimum battery voltage under load if the electrical power converter 2 is powered by a voltage source 4 with a battery.This minimum battery voltage can, for example, correspond to the minimum battery voltage of a discharged battery. If the electrical voltage U_Z across the intermediate circuit capacitor 20 falls below this previously specified minimum voltage, this can also be interpreted as an indication that the input of the voltage converter 2 is no longer connected to the DC voltage source 4. Thus, in this case, active discharge of the intermediate circuit capacitor 20 can also be enabled via the active discharge path with the switching element 13.

[0050] Furthermore, the release of active discharge can also be linked to any further conditions. For example, active discharge of the intermediate circuit capacitor 20 can only be released if the electric machine 3 of the drive system is stationary or if the speed of the electric machine 3 falls below a predetermined limit. For example, the maximum speed of the electric machine 3 can be a speed at which the electric machine, in a generator operating mode, induces an electrical voltage whose peak value falls below a predetermined maximum voltage value. Figure 3 shows a schematic representation of a voltage-time diagram of the voltage curve of the electrical voltage U_Z across the intermediate circuit capacitor 20 according to a further embodiment.Analogous to Figure 2, during normal operation of the electric drive system in phase I, the electrical voltage U_Z across the intermediate circuit capacitor 20 is at least approximately at a constant value U_l. If the voltage source 4, which feeds the input of the voltage converter 2, is subjected to a very high load, for example, due to the activation of a large load, this can also lead to the electrical voltage U_Z at the input of the DC-DC converter 2 and thus across the intermediate circuit capacitor 20 briefly dropping, causing a correspondingly negative gradient. This can, under certain circumstances, lead to an undesired activation of the active discharge of the intermediate circuit capacitor 20 in phase II.However, since the DC voltage source 4 continues to provide electrical energy, this brief voltage drop will compensate very quickly, and the electrical voltage U_Z at the input of the voltage converter and thus across the intermediate circuit capacitor 20 will rise again at least approximately to the original value U_1. In this case, the control device 11 can detect a correspondingly high positive gradient of the electrical voltage across the intermediate circuit capacitor 20. In such a case, the active discharge of the intermediate circuit capacitor 20 can be stopped by reopening the switching element 13. Thus, in the event of such a voltage drop due to the activation of a large load, the active discharge of the intermediate circuit capacitor 20 will only be activated briefly.In order to prevent excessively frequent undesired activation of the discharge of the intermediate circuit capacitor 20 in particularly dynamic systems, for example, a further activation of the active discharge of the intermediate circuit capacitor 20 can only be enabled if a predetermined period of time has elapsed since a previous activation of the active discharge.

[0051] Figure 4 shows a flowchart underlying a method for controlling the discharge of an intermediate circuit capacitor 20 according to one embodiment. The method can, in principle, comprise any desired method steps, as previously described in connection with the device 1 for discharging the intermediate circuit capacitor 20. Similarly, the previously described device 1 for discharging the intermediate circuit capacitor 20 can also comprise any desired components, as required to implement the method described below.

[0052] In a step S1, the electrical voltage U_Z across the intermediate circuit capacitor 20 is first detected. Subsequently, in step S2, a gradient of the temporal profile of the detected voltage U_Z across the intermediate circuit capacitor 20 can be determined. If the gradient of the temporal profile of the electrical voltage U_Z across the intermediate circuit capacitor 20 falls below a predetermined threshold value, i.e., if the magnitude of a negative gradient is greater than a corresponding positive threshold value, an active discharge of the intermediate circuit capacitor 20 is enabled. For such an active discharge of the intermediate circuit capacitor 20, for example, a switching element 13 can be closed in an active discharge path parallel to the terminals of the intermediate circuit capacitor 20.

[0053] To evaluate the gradient of the temporal variation of the electrical voltage U_Z across the intermediate circuit capacitor 20, it may also be possible to temporally filter the measured values ​​for the electrical voltage U_Z across the intermediate circuit capacitor 20. For example, to determine the gradient of the electrical voltage U_Z across the intermediate circuit capacitor 20, the variation of the electrical voltage U_Z over a time interval of one second can be considered. In principle, however, any other suitable time intervals are also possible.

[0054] In summary, the present invention relates to activating an active discharge of an intermediate circuit capacitor. For this purpose, a discharge device is provided which can detect a condition for activating the discharge of an intermediate circuit capacitor independently of other system components and can then initiate an active discharge of the intermediate circuit capacitor. For this purpose, the electrical voltage across the intermediate circuit capacitor is evaluated, and the active discharge of the intermediate circuit capacitor is enabled if a gradient of the electrical voltage across the intermediate circuit capacitor falls below a predetermined threshold.

Claims

Claims 1. A device for controlling a discharge of an intermediate circuit capacitor (20), comprising: a monitoring device designed to determine an electrical voltage (U_Z) across the intermediate circuit capacitor (20); a control device (11) designed to determine a temporal gradient of the electrical voltage (U_Z) across the intermediate circuit capacitor (20) and to enable an active discharge of the intermediate circuit capacitor (20) if the temporal gradient of the electrical voltage (U_Z) across the intermediate circuit capacitor (20) falls below a predetermined first threshold value.

2. Device according to claim 1, wherein the control device (11) is designed to enable the active discharge of the intermediate circuit capacitor (20) only if at least a predetermined period of time has passed since a previous active discharge of the intermediate circuit capacitor (20).

3. Device according to claim 1 or 2, wherein the control device (11) is designed to enable the active discharge of the intermediate circuit capacitor (20) if the electrical voltage (U_Z) across the intermediate circuit capacitor (20) falls below a predetermined minimum voltage.

4. Device according to one of claims 1 to 3, wherein the control device (11) is designed to determine a rotational speed of an electrical machine (3) in an electrical drive system with the intermediate circuit capacitor (20), and to enable the active discharge of the intermediate circuit capacitor (20) if the determined rotational speed falls below a predetermined rotational speed value. Device according to one of claims 1 to 4, wherein the control device is designed to stop the active discharge of the intermediate circuit capacitor if the temporal gradient of the electrical voltage (U_Z) across the intermediate circuit capacitor (20) exceeds a predetermined second threshold value.A device (1) for discharging an intermediate circuit capacitor (20), comprising: a passive discharge path arranged between a first terminal of the intermediate circuit capacitor (20) and a second terminal of the intermediate circuit capacitor (20) and comprising an electrical resistor (12) and / or an electrical load; an active discharge path arranged between a first terminal of the intermediate circuit capacitor (20) and a second terminal of the intermediate circuit capacitor (20) and comprising a switching element (13); and a device for controlling the discharge of the intermediate circuit capacitor (20) according to one of claims 1 to 5, wherein the device for controlling the discharge is designed to close the switching element (13) in the active discharge path if the active discharge of the intermediate circuit capacitor (20) is enabled.Electrical power converter (2), comprising: an input terminal designed to be connected to a DC voltage source (4); an intermediate circuit capacitor (20) arranged between a first connection point and a second connection point of the input terminal; an output terminal;. a device (1) for discharging the intermediate circuit capacitor (20) according to claim 6, wherein the power converter (2) is designed to convert a DC voltage provided at the input terminal into a predetermined output voltage and to provide it at the output terminal. An electric drive system, comprising: an electric power converter (2) according to claim 7; and an electric machine (3) electrically connected to the output terminal of the power converter (2). An electric drive system according to claim 8, wherein the device for controlling the discharge of the intermediate circuit capacitor (2) is designed to enable the active discharge of the intermediate circuit capacitor (20) only if a predetermined operating state is set by the power converter (2). A method for controlling the discharge of an intermediate circuit capacitor (2), comprising the steps: Determining (Sl) an electrical voltage across the intermediate circuit capacitor (2); Determining (S2) a temporal gradient of the electrical voltage (U_Z) across the intermediate circuit capacitor (2); Enabling (S3) an active discharge of the intermediate circuit capacitor (20) if the temporal gradient of the electrical voltage across the intermediate circuit capacitor (20) falls below a predetermined first threshold value.

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