Method for determining the capacitance in an intermediate circuit of an electric drive system

Abstract

The invention relates to a method for determining the capacitance in an intermediate circuit (2) of an electric drive system (100). The electric drive system (100) comprises: at least one first electrical energy source (10) which supplies the intermediate circuit (2); a drive unit (80) having an inverter (20) and an electrical load (30), wherein the inverter (20) is electrically connected to the intermediate circuit (2) on the input side and to the electrical load (30) on the output side; and a DC voltage converter (40) which is electrically connected to the intermediate circuit (2) and measures the voltage in the intermediate circuit (2) by high-frequency sampling. According to the invention, the capacitance in the intermediate circuit (2) is determined from the voltage in the intermediate circuit (2) measured by the DC voltage converter (40). The invention also relates to a motor vehicle comprising an electric drive system (100) which is configured to carry out the method according to the invention.

Description

Technical Field

[0001] The invention relates to a method for determining the capacitance in an intermediate circuit of an electric drive system. The electric drive system comprises: at least one first electrical energy source, which supplies the intermediate circuit; a drive unit, which has an inverter and an electrical consumer, wherein the inverter is electrically connected to the intermediate circuit on the input side and to the electrical consumer on the output side; and a DC voltage converter, which is electrically connected to the intermediate circuit and measures the voltage in the intermediate circuit by high-frequency sampling. The invention also relates to a motor vehicle, which comprises an electric drive system, which is configured to carry out the method according to the invention. Background Art

[0002] It is apparent that electrically driven motor vehicles will be increasingly used in the future. Such electrically driven motor vehicles, such as electric vehicles and hybrid vehicles, each include an electric drive system having an intermediate circuit and a plurality of electric units electrically connected directly or indirectly to the intermediate circuit. The intermediate circuit here includes a plurality of intermediate circuit capacitors, which are each assigned to an electric unit electrically connected directly to the intermediate circuit.

[0003] The above-mentioned electrical unit which is directly electrically connected to the intermediate circuit comprises, for example: an inverter, in particular a pulse inverter, which is used to control and drive an electric motor, such as a traction motor; and a DC voltage converter, which is used to convert a DC voltage supplied at the input into a DC voltage with a higher, lower or inverted voltage level.

[0004] Intermediate circuit capacitors, in particular those assigned to an inverter, are often overdimensioned for various reasons, such as manufacturing precision, capacitance drift at high temperatures and aging. Therefore, there is no need for state monitoring of the intermediate circuit capacitors, which, for example, determines the current capacitance in the intermediate circuit or in the intermediate circuit capacitor, in particular the current capacitance of the intermediate circuit capacitor assigned to the inverter.

[0005] US 2013 / 278190 A1 discloses a method for regulating the voltage of a DC voltage intermediate circuit, as well as a battery and a battery system having a DC voltage intermediate circuit, which are designed to carry out the method.

[0006] Document US 2018 / 054151 A1 discloses an electric power adaptation system and a control method for the electric power adaptation system. In the electric power adaptation system, the characteristics of the ripple current are changed by changing the number of drive phases and / or the voltage ratio of the multi-phase converter. Summary of the invention

[0007] A method for determining the capacitance in an intermediate circuit of an electric drive system is proposed. The electric drive system comprises: at least one first electrical energy source, which supplies the intermediate circuit; a drive unit, which has an inverter and an electrical load, wherein the inverter is electrically connected to the intermediate circuit on the input side and to the electrical load on the output side; and a DC voltage converter, which is electrically connected to the intermediate circuit and measures the voltage in the intermediate circuit by means of high-frequency sampling.

[0008] The DC voltage converter has a device for measuring the voltage in the intermediate circuit. The device can be designed, for example, as an A / D converter (analog-digital converter). Preferably, the sampling frequency is greater than 10 kHz.

[0009] According to the invention, the capacitance in the intermediate circuit is determined as a function of the voltage in the intermediate circuit measured by the DC voltage converter.

[0010] The electric drive system may also have at least one second electrical energy source, which is electrically connected to the intermediate circuit via a DC voltage converter and has a voltage level different from that of the first electrical energy source. Preferably, the first electrical energy source has a higher voltage level than the second electrical energy source.

[0011] The electric drive system may include other electric units. For example, the electric drive system may have a first other electric consumer, wherein the first other electric consumer has one or more electric units and is electrically connected to the intermediate circuit via a DC voltage converter, and a second other electric consumer has one or more electric units and is directly electrically connected to the intermediate circuit.

[0012] The intermediate circuit has a plurality of intermediate circuit capacitors which are respectively assigned to electrical units directly electrically connected to the intermediate circuit. For example, the intermediate circuit comprises intermediate circuit capacitors which are respectively assigned to an inverter, a DC voltage converter and, if applicable, also to a second electrical load.

[0013] The first and second electrical energy sources can be designed as energy storage devices, such as batteries, in particular lithium-ion batteries (LIB), supercapacitors (SC) or hybrid supercapacitors (HSC), or as energy converters, such as fuel cells.

[0014] According to an advantageous embodiment of the present invention, the method according to the present invention comprises the following steps:

[0015] - detecting the ripple of the voltage in the intermediate circuit when measuring the voltage in the intermediate circuit by means of a DC voltage converter;

[0016] - measure the current of electrical appliances;

[0017] - simulation of the ripple of the input current of the inverter based on the measured current of the load and with the aid of a model of the drive unit;

[0018] The capacitance in the intermediate circuit is determined with the aid of a dynamic intermediate circuit model from the measured ripple of the voltage in the intermediate circuit and the simulated ripple of the input current of the inverter.

[0019] In this case, the measured values ​​of the current of the electrical load are used as the starting point for the model of the drive unit for simulating the ripple of the input current of the inverter. The DC voltage converter and, if necessary, other units directly electrically connected to the intermediate circuit are also inactive in this case, i.e., no current flows through the DC voltage converter and other units directly electrically connected to the intermediate circuit.

[0020] In this case, the load is controlled by the inverter according to a switching pattern. For example, the inverter for controlling a load designed as a three-phase motor can be controlled according to so-called space vector modulation, which is based on pulse width modulation. In this case, the ripple of the input current of the inverter can be simulated during the duration of the voltage vector by means of a model of the inverter and a model of the motor, wherein the duration of the voltage vector depends on the switching frequency of the space vector modulation.

[0021] Here, the dynamic intermediate circuit model includes: the inductance and resistance of all cables electrically connected to the intermediate circuit; and the capacitance of all intermediate circuit capacitors assigned to the corresponding electrical units directly electrically connected to the intermediate circuit. Dynamic should be understood as: these model parameters are dynamic and frequency-dependent. In order to be able to determine the capacitance according to the dynamic intermediate circuit model, the ripple of the voltage in the intermediate circuit detected by the DC voltage converter and the simulated ripple of the input current of the inverter must exist synchronously. This synchronization can be carried out, for example, by: the ripple of the voltage in the intermediate circuit detected by the DC voltage converter is synchronized with the voltage measured by the inverter in the intermediate circuit. In order to control the electrical appliance, the voltage in the intermediate circuit is also measured by sampling by the inverter, wherein this sampling performed by the inverter has a lower sampling frequency than the sampling performed by the DC voltage converter. The sampling performed by the inverter is not suitable for simulating the ripple of the voltage in the intermediate circuit.

[0022] Preferably, the dynamic intermediate circuit model can be adjusted by measuring the voltage in the intermediate circuit or determined by a change factor of the capacitance in the intermediate circuit or a change factor of the ripple of the voltage in the intermediate circuit. The dynamic intermediate circuit model can be adjusted when there is sufficient capacitance in the intermediate circuit. In this case, the capacitance in the intermediate circuit, the resistance and inductance of all cables electrically connected to the intermediate circuit can be adjusted.

[0023] For example, the dynamic intermediate circuit model can be adjusted by comparing the capacities in the intermediate circuit obtained by multiple executions of the method according to the invention. Alternatively, the dynamic intermediate circuit model can be adjusted by comparing the following ripples of the voltage in the intermediate circuit, wherein the ripples are obtained by multiple executions of the method according to the invention at the same ripple of the input current of the inverter. In the case of a smaller capacity in the intermediate circuit, a greater ripple of the voltage is generated in the intermediate circuit. However, the dynamic intermediate circuit model can also be adjusted by comparing the ripples of the input current of the inverter, wherein the ripples are obtained by multiple executions of the method according to the invention at the same ripple of the voltage in the intermediate circuit.

[0024] Preferably, the amplitude of the ripple of the voltage in the detected intermediate circuit is stored in a storage medium. Here, the stored amplitude of the detected ripple of the voltage in the intermediate circuit can be used to adjust the intermediate circuit model. The storage medium is to be understood as a medium that is suitable for storing data. The storage medium can be a memory card. However, it is also conceivable that a cloud storage can be used to store data online. Information about the capacity in the intermediate circuits of other electric drive systems can also be stored in the cloud storage. The information can be used to adjust the dynamic intermediate circuit model.

[0025] According to another advantageous embodiment of the present invention, the method according to the present invention comprises the following steps:

[0026] - detecting a voltage change in the intermediate circuit within a time period during which the voltage in the intermediate circuit is measured by the DC voltage converter;

[0027] - measuring the charging current or discharging current of the intermediate circuit during this time period;

[0028] - Determining the capacitance in the intermediate circuit from the voltage change detected in the intermediate circuit during the time period and the charging or discharging current measured during the time period with the aid of the equation I=C*du / dt.

[0029] In this case, I is the charging or discharging current of the intermediate circuit and C is the capacity to be determined in the intermediate circuit. du / dt in this case denotes the voltage change in the intermediate circuit within the time period.

[0030] Preferably, the electric drive system has at least one second electrical energy source, which is electrically connected to the intermediate circuit via a DC voltage converter. In this case, the intermediate circuit can be charged by the second electrical energy source via the DC voltage converter and the first electrical energy source is switched off when the intermediate circuit is charged to a predetermined voltage level.

[0031] The intermediate circuit can also be discharged via the DC voltage converter. If the second electrical energy source is an electrical energy storage device, the second electrical energy source can be charged via the DC voltage converter by the discharge current of the intermediate circuit.

[0032] When determining the capacitance in the intermediate circuit, for example, only the initial value and the final value of the voltage measured in the intermediate circuit within the time period need to be taken into account.

[0033] Preferably, the capacitance in the intermediate circuit is determined multiple times. Subsequently, an average value of the capacitances determined multiple times in the intermediate circuit is formed. The multiple determinations of the capacitance in the intermediate circuit are carried out during a charging or discharging process.

[0034] In this case, the capacitance in the intermediate circuit can advantageously be determined as a function of the temperature. This enables additional information about the aging of the intermediate circuit capacitors in the intermediate circuit, which are assigned to the respective electrical units directly electrically connected to the intermediate circuit. Furthermore, the influence of the temperature on the capacitance in the intermediate circuit can be determined or calculated as a function of the temperature using the measurement of the capacitance in the intermediate circuit.

[0035] The method according to the invention makes it possible to determine the capacitance of the intermediate circuit capacitor assigned to the inverter. In this case, the intermediate circuit can include a plurality of intermediate circuit capacitors, which are respectively assigned to an electrical unit directly connected to the intermediate circuit. For this purpose, the capacitance of the intermediate circuit capacitor assigned to the inverter is significantly greater than the sum of the capacitances of the intermediate circuit capacitors respectively assigned to the other electrical units directly connected to the intermediate circuit.

[0036] Furthermore, a motor vehicle is proposed which comprises an electric drive system which is designed to carry out the method according to the invention.

[0037] Advantages of the present invention

[0038] The intermediate circuit usually comprises a plurality of intermediate circuit capacitors. For example, the intermediate circuit may comprise a first intermediate circuit capacitor, which is assigned to the inverter, and a second intermediate circuit capacitor, which is assigned to the DC voltage converter. The intermediate circuit may have further intermediate circuit capacitors, which are assigned to further electrical units or consumers which are directly electrically connected to the intermediate circuit.

[0039] The method according to the invention makes it possible to utilize the high-frequency sampling voltage measurement of the DC voltage converter of the electric drive system. Thus, the capacitance in the intermediate circuit of the electric drive system can be determined cost-effectively.

[0040] Since the capacitance of the intermediate circuit capacitor assigned to the DC voltage converter and the capacitance of the intermediate circuit capacitor assigned to other electrical units is significantly smaller than the capacitance of the intermediate circuit capacitor assigned to the inverter, the capacitance of the intermediate circuit capacitor assigned to the inverter can be determined in an approximate manner using the method according to the invention.

[0041] The method according to the invention makes it possible to permanently monitor the state of an intermediate circuit capacitor associated with an inverter.

[0042] Advantageously, the method according to the invention makes it possible to determine the aging mechanisms of the intermediate circuit capacitors assigned to the inverter by collecting measurement signals, such as voltage, current and temperature.

[0043] The method according to the invention also makes it possible to adapt control parameters, such as current control, to the state of an intermediate circuit capacitor assigned to the inverter in order to be able to extend the service life of the intermediate circuit capacitor assigned to the inverter.

[0044] Furthermore, the intermediate circuit capacitor assigned to the inverter can be designed smaller using the method according to the invention and thus avoids oversizing the intermediate circuit capacitor assigned to the inverter. Thus, the construction space and manufacturing costs of the intermediate circuit capacitor assigned to the inverter or the inverter are reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Embodiments of the present invention are further described with reference to the accompanying drawings and the following description.

[0046] Figure 1 The diagram shows a schematic diagram of an electric drive system which is set up to determine a capacitance in an intermediate circuit. DETAILED DESCRIPTION

[0047] In the following description of embodiments of the invention, identical or similar elements are denoted by the same reference numerals, wherein a repeated description of these elements in individual cases is omitted. The figures merely schematically illustrate the subject matter of the invention.

[0048] Figure 1 1 . A schematic diagram of an electric drive system 100 is shown which is configured to determine a capacitance in an intermediate circuit 2 .

[0049] The electric drive system 100 includes a first electric energy source 10, which is electrically connected to the intermediate circuit 2 through a main switch 12 and supplies the intermediate circuit 2. The first electric energy source 10 can be configured as an energy storage device, such as a battery pack, in particular a lithium-ion battery pack (LIB), a supercapacitor (SC) or a hybrid supercapacitor (HSC). However, the first electric energy source 10 can also be configured as an energy converter, such as a fuel cell.

[0050] The electric drive system 100 further includes a drive unit 80, which has an inverter 20 and an electrical load 30, wherein the inverter 20 is electrically connected to the intermediate circuit 2 on the input side. On the output side, the inverter 20 is electrically connected to the electrical load 30. Depending on the electrical load 30 electrically connected to the inverter 20, the inverter 20 is configured as a single-phase or three-phase. The electrical load 30 can be configured as a three-phase motor.

[0051] The electric drive system 100 further comprises a DC voltage converter 40 which is electrically connected to the intermediate circuit 2 and measures the voltage in the intermediate circuit 2 by means of high-frequency sampling.

[0052] In addition, the electric drive system 100 has a second electrical energy source 50, which is electrically connected to the intermediate circuit 2 via a DC voltage converter 40. The second electrical energy source 50 can be configured as an energy storage device, such as a battery, in particular a lithium-ion battery (LIB), a supercapacitor (SC) or a hybrid supercapacitor (HSC). However, the first electrical energy source 10 can also be configured as an energy converter, such as a fuel cell.

[0053] The first electrical energy source 10 and the second electrical energy source 50 have different voltage levels. Preferably, the first electrical energy source 10 has a higher voltage level than the second electrical energy source 50.

[0054] The electric drive system 100 further comprises a first further electrical consumer 60 which is electrically connected to the DC voltage converter 40 and via the DC voltage converter to the intermediate circuit 2. The first further electrical consumer 60 is to be understood as a group of electrical units.

[0055] The electric drive system 100 further comprises a second further electrical consumer 70, which is directly electrically connected to the intermediate circuit 2. The second further electrical consumer 70 is also to be understood as a group of electrical units.

[0056] In this case, the intermediate circuit 2 comprises a plurality of intermediate circuit capacitors which are respectively assigned to the inverter 20 , the DC voltage converter 40 and the second further electrical load 70 .

[0057] In order to determine the capacitance in the intermediate circuit 2 , the voltage in the intermediate circuit 2 is measured by means of high-frequency sampling via a DC voltage converter 40 .

[0058] According to an advantageous embodiment of the invention, the ripple of the voltage in the intermediate circuit 2 is detected when the voltage in the intermediate circuit 2 is measured by a DC voltage converter. In order to be able to detect the ripple of the voltage in the intermediate circuit 2, the sampling frequency is preferably greater than 10 kHz.

[0059] In this case, the ripple of the input current of the inverter 20 is simulated with the aid of a model of the drive unit 80. In this case, other electrical units such as the DC voltage converter 40 or the second further electrical load 70 are not active.

[0060] In this case, the current of the load 30 is measured, wherein the measured value of the current of the load 30 is used as a starting point for a model of the drive unit 80 for simulating the ripple of the input current of the inverter 20 .

[0061] The load 30 can be controlled by the inverter 20 according to the switching pattern. For example, the load 30 can be controlled by the inverter 20 according to so-called space vector modulation, wherein the load is designed as a three-phase motor, wherein the space vector modulation is based on pulse width modulation. In this case, the ripple of the current of the motor can be simulated during the duration of the voltage vector by means of a model of the inverter 20 and a model of the motor, wherein the duration of the voltage vector depends on the switching frequency of the space vector modulation.

[0062] After the ripple of the voltage in the intermediate circuit 2 is detected and the ripple of the input current of the inverter 20 is simulated, the capacitance in the intermediate circuit 2 is determined according to a dynamic intermediate circuit model. Here, the dynamic intermediate circuit model includes: the inductance and resistance of all cables electrically connected to the intermediate circuit 2; and the capacitance of all intermediate circuit capacitors assigned to the corresponding electrical units directly electrically connected to the intermediate circuit 2, wherein the electrical units are currently the inverter 20, the DC voltage converter 40 and the second other electrical consumer 70. In order to be able to determine the capacitance in the intermediate circuit 2 according to the dynamic intermediate circuit model, the ripple of the voltage in the intermediate circuit 2 detected by the DC voltage converter 40 and the simulated ripple of the input current of the inverter 20 must exist synchronously. This synchronization can be performed, for example, by: the ripple of the voltage in the intermediate circuit 2 detected by the DC voltage converter 40 is synchronized with the voltage measured by the inverter 20 in the intermediate circuit 2. In order to control the load 30, the voltage in the intermediate circuit 2 is also measured by means of sampling via the inverter 20, wherein this sampling by the inverter 20 has a lower sampling frequency than the sampling by the DC voltage converter 40. The sampling by the inverter 20 is not suitable for simulating the ripple of the voltage in the intermediate circuit 2.

[0063] The dynamic intermediate circuit model can be adjusted by measuring the voltage in the intermediate circuit 2 or can be determined by a change factor of the capacitance in the intermediate circuit 2 or a change factor of the ripple of the voltage in the intermediate circuit 2. The adjustment of the dynamic intermediate circuit model can be carried out with sufficient capacitance in the intermediate circuit 2. With a smaller capacitance in the intermediate circuit 2, a greater ripple of the voltage in the intermediate circuit 2 is produced.

[0064] Preferably, the amplitude of the ripple of the voltage in the intermediate circuit 2 detected is stored in a storage medium. Here, the stored amplitude of the ripple of the voltage in the intermediate circuit 2 detected can be used to adjust the dynamic intermediate circuit model. The storage medium can be a memory card. However, it is also conceivable that a cloud storage can be used to store the data online. Information about the capacity in the intermediate circuit 2 of other electric drive systems 100 can also be stored in the cloud storage. This information can be used to adjust the dynamic intermediate circuit model.

[0065] According to a further advantageous embodiment of the invention, a voltage change in the intermediate circuit 2 is detected during the time period during which the voltage in the intermediate circuit 2 is measured by the DC voltage converter 40 .

[0066] In this case, the charging current or discharging current of the intermediate circuit 2 is measured during this time period. The intermediate circuit 2 can be charged by the second electrical energy source 50 via the DC voltage converter 40, and when the intermediate circuit 2 is charged to a predetermined voltage level, the first electrical energy source 10 is disconnected from the intermediate circuit 2 by the main switch 12.

[0067] The intermediate circuit 2 can also be discharged via the DC voltage converter. If the second electrical energy source 50 is an electrical energy storage device, the second electrical energy source 50 can be charged by the discharge current of the intermediate circuit 2 via the DC voltage converter 40 .

[0068] The capacitance in the intermediate circuit 2 is determined from the voltage change detected in the intermediate circuit 2 during the time period and the charging or discharging current measured during the time period by means of the equation I=C*du / dt. In this case, I is the charging or discharging current of the intermediate circuit 2 and C is the capacitance to be determined in the intermediate circuit 2. du / dt in this case denotes the voltage change in the intermediate circuit 2 during the time period.

[0069] Preferably, electric drive system 100 is an electric drive system of a motor vehicle, in particular an electric vehicle or a hybrid vehicle.

[0070] Here, the electrical consumer 30 is configured as an electric motor, such as a traction engine. The first electrical energy source 10 can be configured as an energy storage device, such as a traction battery pack or an energy converter, such as a fuel cell. The first electrical energy source 10 can, for example, have a voltage level of 48 volts or even higher. The second electrical energy source 50 can, for example, be a battery pack with a low voltage, such as a 12V battery pack.

[0071] The first further electrical consumer 60 may include, for example, an entertainment device, such as a radio or a screen.

[0072] The second further electrical consumers 70 may include, for example, a heating, ventilation and air conditioning system.

[0073] When the motor vehicle is started, the intermediate circuit 2 is charged. The time period of this charging is observed here. During this charging time period, the voltage in the intermediate circuit 2 is measured by the DC voltage converter 40 .

[0074] When the motor vehicle is started, the intermediate circuit 2 is charged. The charging time period is observed. During this charging time period, the voltage in the intermediate circuit 2 is measured by the DC voltage converter 40. Together with the charging current of the intermediate circuit 2 measured during this charging time period, the capacitance in the intermediate circuit 2 can be determined.

[0075] In contrast, the intermediate circuit 2 is discharged when the motor vehicle is parked. The time period of this discharge is observed. During this time period of discharge, the voltage in the intermediate circuit 2 is measured by the DC voltage converter 40. Together with the discharge current of the intermediate circuit 2 measured during the time period of discharge, the capacitance in the intermediate circuit 2 can be determined.

[0076] When determining the capacitance in the intermediate circuit 2 , for example, only the initial value and the final value of the measured voltage in the intermediate circuit 2 within the time period need to be taken into account.

[0077] Preferably, the capacitance in the intermediate circuit 2 is determined multiple times. Subsequently, a mean value formation is carried out of the capacitances determined multiple times in the intermediate circuit 2. The multiple determination of the capacitance in the intermediate circuit 2 takes place during a charging or discharging process.

[0078] Advantageously, the capacitance in the intermediate circuit 2 can be determined as a function of the temperature. This provides additional information about the aging of the intermediate circuit capacitors in the intermediate circuit 2, which are assigned to the respective electrical units directly electrically connected to the intermediate circuit 2. Furthermore, the influence of the temperature on the capacitance in the intermediate circuit 2 can be determined or calculated as a function of the temperature using the measurement of the capacitance in the intermediate circuit 2.

[0079] If the motor vehicle has been parked for a long enough time, the capacitance in the intermediate circuit 2 can be determined based on the temperature, especially when the motor vehicle is started. In this case, the temperature of the intermediate circuit 2 or the temperature of the intermediate circuit capacitor in the intermediate circuit 2 corresponds to the temperature of the coolant or the temperature of the surroundings.

[0080] Since the capacitance of the intermediate circuit capacitor assigned to the DC voltage converter 40 and the capacitance of the intermediate circuit capacitor assigned to the second further electrical consumer 70 are significantly smaller than the capacitance of the intermediate circuit capacitor assigned to the inverter 20 , the capacitance of the intermediate circuit capacitor assigned to the inverter 20 can be determined in an approximate manner using the method according to the invention.

[0081] The invention is not limited to the embodiments described here and the aspects highlighted therein, but rather numerous variations are possible within the scope of the invention as described by the claims and within the purview of a person skilled in the art.

Claims

1. A method for determining a capacitance in an intermediate circuit (2) of an electric drive system (100), wherein the electric drive system (100) comprises: at least one first electrical energy source (10), which supplies the intermediate circuit (2); A drive unit (80) comprising an inverter (20) and an electrical load (30), wherein the inverter (20) is electrically connected to the intermediate circuit (2) on the input side and is electrically connected to the electrical load (30) on the output side; and A DC voltage converter (40) is electrically connected to the intermediate circuit (2) and measures the voltage in the intermediate circuit (2) by high-frequency sampling, wherein the intermediate circuit (2) has a plurality of intermediate circuit capacitors, and the plurality of intermediate circuit capacitors are respectively allocated to the inverter (20) and the DC voltage converter (40), wherein the inverter (20) and the DC voltage converter (40) are directly electrically connected to the intermediate circuit (2), characterized in that: The capacitance in the intermediate circuit (2) is determined based on the voltage in the intermediate circuit (2) measured by the DC voltage converter (40), wherein the method further comprises the following steps: - detecting the ripple of the voltage in the intermediate circuit (2) when measuring the voltage in the intermediate circuit (2) by means of the DC voltage converter (40); - measuring the current of the electrical consumer (30); - simulating the ripple of the input current of the inverter (20) based on the measured current of the electrical load (30) and with the aid of a model of the drive unit (80); - Determining the capacitance in the intermediate circuit (2) with the aid of a dynamic intermediate circuit model based on the detected ripple of the voltage in the intermediate circuit (2) and the simulated ripple of the input current of the inverter (20), wherein the ripple of the voltage in the intermediate circuit (2) detected by the DC voltage converter (40) is synchronized with the voltage in the intermediate circuit (2) measured by the inverter (20).

2. The method according to claim 1, characterized in that The dynamic intermediate circuit model is adjusted by measuring the voltage in the intermediate circuit (2), or is determined by a change factor of the capacitance in the intermediate circuit (2) or a change factor of the ripple of the voltage in the intermediate circuit (2).

3. The method according to claim 1 or 2, characterized in that: The detected amplitude of the ripple of the voltage in the intermediate circuit (2) is stored in a storage medium.

4. The method according to claim 1, comprising the steps of: - detecting a voltage change in the intermediate circuit (2) during a time period when the voltage in the intermediate circuit (2) is measured by the DC voltage converter (40); - measuring the charging current or the discharging current of the intermediate circuit (2) during the time period; - determining the capacitance in the intermediate circuit (2) based on the voltage change in the intermediate circuit (2) detected during the time period and the charging current or discharging current measured during the time period.

5. The method according to claim 4, characterized in that The electric drive system (100) comprises at least one second electric energy source (50), which is electrically connected to the intermediate circuit (2) via the DC voltage converter (40).

6. The method according to claim 4 or 5, characterized in that: The capacitance in the intermediate circuit (2) is determined multiple times, and an average value of the capacitances determined multiple times in the intermediate circuit (2) is formed.

7. The method according to any one of claims 4 to 6, characterized in that: The capacitance in the intermediate circuit (2) is determined as a function of temperature.

8. The method according to any one of claims 1 to 7, wherein: The capacitance of an intermediate circuit capacitor assigned to the inverter (20) is determined.

9. A motor vehicle comprising an electric drive system (100) which is configured to carry out the method according to any one of claims 1 to 8.

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