Method for determining a DC current value on a DC side of an inverter

Abstract

The present invention relates to a method for determining a DC current value (DCI) on a DC side (DCS) of an inverter (110), characterised by the following steps: - detecting an AC current value (ACI) for at least two phases on an AC side (ACI) of the inverter (110), - detecting a DC voltage value (DCU) on the DC side (DCS) of the inverter (110), - determining a DC current value (DCI) on the basis of the detected AC current value (ACI) and the detected DC voltage value (DCU) using a calibrated AC-DC relationship (ADB).

Description

[0001] Determination method for determining a DC current value on a DC side of an inverter

[0002] The present invention relates to a method for determining a DC current value on a DC side of an inverter, a measuring device for determining a DC current value on a DC side of an inverter, and a computer program product for carrying out such a method of determination.

[0003] It is generally known that current measurement can be useful when operating inverters that provide conversion functionality between alternating current (AC) and direct current (DC). This is especially true when such an inverter has an electrical load on the AC side and an electrical storage device, such as a battery, on the DC side. Inverters are necessary to supply electrical loads with AC power from DC-powered batteries by converting the stored DC into AC and thus ensuring the operation of the electrical component.

[0004] To monitor the battery system during discharge and charging processes, a precise understanding of the charging and discharging currents is crucial. However, determining and measuring the current on the AC side of the inverter is a complex and costly design. Typically, a shunt resistor is used, connected in parallel with a resistor and a corresponding measuring device. Besides the increased complexity and additional components, this design also affects the currents on the DC side of the inverter. This leads not only to inaccurate DC current measurements but also to power loss.Last but not least, operating and measuring with such a shunt involves heating the resistors, necessitating additional active cooling. These disadvantages are particularly pronounced given the ever-increasing number of electrical devices, such as drones, aircraft, land vehicles, ships, and similar equipment, which often operate with very high energy storage capacities and very high operating currents.

[0005] It is therefore an object of the present invention to at least partially overcome the disadvantages described above. In particular, it is an object of the present invention to provide, in a cost-effective and simple manner, an improvement in the accuracy of a current measurement on the DC side of an inverter.

[0006] The foregoing problem is solved by a determination method with the features of claim 1, a measuring device with the features of claim 10, and a computer program product with the features of claim 13. Further features and details of the invention will become apparent from the dependent claims, the description, and the drawings. Features and details described in connection with the determination method according to the invention naturally also apply in connection with the measuring device and the computer program product according to the invention, and vice versa, so that the disclosure of the individual aspects of the invention always makes, or can make, reciprocal references.

[0007] According to the invention, a determination method serves to determine a DC current value on the DC side of an inverter. Such a determination method is characterized by the following steps:

[0008] - Recording an AC current value for at least two phases on one AC side of the inverter,

[0009] - Capturing a DC voltage value on the DC side of the inverter,

[0010] - Determining a DC current value based on the measured AC current value and the measured DC voltage value using a calibrated AC-DC relationship.

[0011] Within the scope of the present invention, a distinction is made between direct current (DC) and alternating current (AC) with regard to the measured values ​​and the sides of the inverter from an electrical perspective. The inverter can therefore also be understood, within the meaning of the present invention, as a converter between AC and DC. In particular, the inverter provides bidirectional converter functionality. Within the scope of this application, all measured values ​​determined on the DC side are designated by the abbreviation DC. Similarly, everything that occurs and is measured on the AC side is designated by the abbreviation AC.

[0012] The core concept of the invention is to provide higher accuracy in determining a DC current value. However, the current value to be determined on the DC side of the inverter, in the form of direct current, is to be measured indirectly. This indirect measurement method is based on a relationship between the DC current value and a corresponding current value on the DC side, namely the AC current value. Measurement on the AC side of the inverter is significantly simpler and more cost-effective, as determining an AC current is subject to correspondingly fewer influences. In particular, AC current measurement requires less design complexity and, especially, no or only minimal cooling capacity.In addition, current measuring devices are usually already arranged on the alternating current side of many electrical devices, and thus on the AC side of the inverter, so that the detection of an AC current value can be based on existing sensor technology.

[0013] As a second measurement, the DC voltage value is recorded according to the invention. Recording a DC voltage value is relatively simple compared to recording a DC current value, so existing technical solutions can be used. Even though this involves the DC side of the inverter, the voltage on the DC side can be recorded relatively easily and, above all, with minimal impact on the electrical conditions on the DC side of the inverter by simply taking measurements at two points. Thus, it is now possible to use two relatively simple measurement steps for the AC current value and the DC voltage value as the starting point for a determination method according to the invention.

[0014] From these two starting points, the DC current value is determined. This determination can also be understood as an indirect measurement of the DC current value, as it differs from a direct measurement using current measuring devices on the DC side of the inverter. This indirect determination can therefore be performed without any physical current measuring sensors on the DC side of the inverter. To ensure this, the determination step of a determination method according to the invention uses a calibrated AC-DC relationship. This is understood to be a relationship that establishes a connection between the measured values ​​of AC current and DC voltage and a corresponding DC current value. The significance of a calibrated AC-DC relationship lies in the fact that this calibration is specifically tailored to the respective inverter and / or the specific operating situation of an electrical device.For example, a calibrated AC-DC relationship can be established on a test bench, at the end of a production line, or through the use of simulation models. In the simplest case, the AC-DC relationship is a characteristic curve. However, algorithmic relationships, physical connections, complex algorithmic functionalities, and even the use of weighted neural networks and artificial intelligence (AI) can also be employed. The core concept is fundamentally provided by each of these approaches.

[0015] The calibrated AC-DC relationship can be provided, for example, through measurement, a combination with simulations, or by programming algorithmic and physical relationships. As explained later, it is preferable to calibrate the AC-DC relationship based on a standard relationship at the end of a production line or on a test bench and thus configure it for use in the determination procedures.

[0016] According to the invention, it is now possible to determine electrical values ​​relatively easily and cost-effectively, particularly those available from sensors already present in the electrical device for operational functionality. These values ​​are the AC current and the DC voltage. Using a calibrated AC-DC relationship, these values ​​are then used to determine the DC current. For this purpose, the acquired values, in the form of the AC current and DC voltage, are, for example, inserted into an algorithmically designed AC-DC relationship, transformed within a characteristic map, or used as input parameters for a control unit. Based on these input values—the AC current and DC voltage—this calibrated AC-DC relationship then outputs the corresponding correlated DC current as the output value.In other words, an indirect measurement of the DC current value is now possible via a direct measurement of the AC current value and the DC voltage value.

[0017] This indirect measurement method offers several advantages. Firstly, it eliminates the need for direct measurement of the DC current. This avoids the previously used shunt measurement systems and their associated complexity, weight, cost, as well as the effort required for cooling and installation. Furthermore, it achieves increased accuracy because the correlation in the calibrated AC-DC relationship results in significantly higher accuracy from the calibration procedure, for example, on a test bench, than would be possible with a direct measurement on the AC side of the inverter. In summary, this method reduces complexity and cost while simultaneously increasing the accuracy of the DC current measurement.

[0018] It can be advantageous if, in a determination method according to the invention, the AC current value is measured for at least three phases, in particular for all phases of the AC side of the inverter. If the electrical device is a high-voltage application, for example an electric vehicle, three-phase systems are typically used. Measuring the AC current value for all these phases thus extends the advantages of the invention to all phases and therefore to the entire AC side of the inverter. By considering all phases on the AC side of the inverter, the accuracy of the correlation and thus the accuracy for determining the DC current value is further increased.

[0019] Furthermore, advantages arise when the acquisition and determination steps of a determination method according to the invention are carried out repeatedly, particularly continuously. In other words, the determination method can thus serve for a repeated or even continuous determination of the DC current value. In this way, it is possible to design the determination method as a monitoring method or continuous measurement method, so that the DC current value is continuously determined and thus updated in a monitored or even continuously monitored manner. If such a determination method is to be used, for example, for a battery management system of a battery device or an electrical device, the repeated execution of the acquisition and determination steps offers the corresponding advantages of a continuous measurement method.However, this is a continuous indirect measurement method for the continuous, indirect measurement of the DC current value with the described advantages of this indirect measurement.

[0020] Further advantages can be achieved if, in a determination method according to the invention, the measured AC current value is subjected to a frequency analysis to determine AC ripple current values, wherein the determination of the DC current value is based on the determined AC ripple current values ​​and the measured DC voltage value using the calibrated AC-DC relationship. It is known that ripple currents can be obtained from multiphase current values ​​by transformation through frequency analysis. The use of the ripple currents allows for an even more precise correlation to DC current values, so that the accuracy can be further improved by frequency analysis. In this embodiment, the AC-DC relationship is calibrated accordingly to the AC ripple current values, so that, for example, when creating and calibrating the AC-DC relationship in a test bench, the frequency analysis is also part of such a calibration procedure.The conversion to AC ripple current values ​​can be performed either without transformation or with transformation, for example in a two-dimensional DQ plane. Further explanations will follow later.

[0021] Furthermore, it offers advantages if, in a determination method according to the invention for determining the DC current value, at least the measured AC current value is transformed into a two-dimensional AC current value. This applies particularly when three-phase, five-phase, or other multi-phase measurement of the AC current values ​​is required. The transformation can, for example, take place from three phases into a two-dimensional environment, so that the three phases can subsequently be represented in a two-dimensional DQ plane. As already explained, this can also be combined with the aforementioned AC ripple currents and the corresponding frequency analysis.

[0022] It is also advantageous if, in a determination method according to the invention for the calibrated AC-DC relationship, a calibration method is used at the end of a production process of an electrical device comprising the inverter. For example, at the end of a production line during the manufacture of a battery device, which is connected to at least one electrical load via an inverter, the actual currents can be measured. This electrical device can then be equipped with a temporary measuring device on the DC side of the inverter at the end of the production process and subjected to corresponding charging and / or discharging cycles.During these discharge and charge cycles of the battery device, actual measurements are taken on both the AC and DC sides, resulting in the development of a specific relationship between the AC current and DC voltage values, as well as the DC current value, for this particular electrical device. In the simplest case, the AC-DC relationship can be calibrated and configured as a characteristic map, which can then be used in subsequent determination procedures. However, it is also possible to perform these calibration procedures multiple times for several identical electrical devices. This is particularly relevant when the AC-DC relationship is based on algorithmic or functional relationships, or even simulation data, in more complex test bench trials of such an electrical device.Last but not least, test bench trials on such an electrical device can also create a sufficiently large database to carry out a training procedure and a machine learning procedure on a computer, which then forms part or the complete calibrated AC-DC relationship.

[0023] Further advantages arise when, in a determination method according to the invention, this method is used for a battery control device, in particular for controlling a battery device of at least one of the following electrical devices:

[0024] - Electric vehicle,

[0025] - Hybrid vehicle,

[0026] - aircraft,

[0027] - Electrolyzer. The preceding list is not exhaustive. In general, electrical devices suitable for use with a determination method should be those capable of handling sufficiently high currents for the charging and discharging cycles of the battery. This can be the case, for example, with the correspondingly high electrical power required for operating electric vehicles, hybrid vehicles, or aircraft. However, such situations can also arise with drones, marine applications, electrolysis systems, or fuel cell systems, where a determination method can also offer the described advantages.

[0028] A further advantage is achieved by the fact that, in a determination method according to the invention, at least one operating parameter of the inverter and / or an electrical device comprising the inverter is taken into account when determining the DC current value, in particular one of the following:

[0029] - Ageing condition,

[0030] - State of degradation.

[0031] The preceding list is not exhaustive. Naturally, several operating parameters can be used together to determine the DC current value. For example, it is known that electrochemical systems such as batteries, fuel cells, or electrolysis cells exhibit aging effects and, depending on their operating mode, are also subject to wear and tear, known as degradation. This means that such operating parameters, for example, the overall age, the number of charging cycles of the battery, as well as environmental parameters such as temperature and typical current ranges (e.g., the comparison between normal and fast charging), can have different effects on indirect measurement methods.To account for these different framework conditions, the accuracy of a determination method according to the invention can be further increased by considering these operating parameters. These parameters can be considered separately or as part of the calibrated AC-DC relationship. A particularly simple solution is to integrate this consideration of the operating parameters into the AC-DC relationship within the calibration procedure. Furthermore, it is advantageous if calibration information from a test bench trial is used for the calibrated AC-DC relationship in a determination method according to the invention. As already mentioned, test bench trials can be carried out with significantly higher accuracy and, above all, with significantly more measurement effort than actual operation at the point of use of an electrical device.Test bench trials can generate a very large amount of data, which, in addition to providing simple algorithmic or functional relationships, can also serve as a data basis for machine learning. Calibrated AC-DC relationships can thus be determined either through test bench trials and / or in combination with end-of-line calibration. In all cases, this results in the AC-DC relationship providing the desired correlation between the measured AC current value and the measured DC current value, and conversely, between the measured DC current value and the value to be determined, in a more precise and calibrated manner.

[0032] Also related to the present invention is a measuring device for determining a DC current value on the DC side of an inverter. Such a measuring device is characterized by the inclusion of a sensing module for acquiring an AC current value for at least two phases on the AC side of the inverter and for acquiring a DC voltage value on the DC side of the inverter. Furthermore, the measuring device includes a determination module for determining a DC current value based on the acquired AC current value and the acquired DC voltage value using a calibrated AC-DC relationship. The sensing module and the determination module are preferably configured for carrying out a determination method according to the invention. Thus, a measuring device according to the invention offers the same advantages as those explained in detail with reference to a determination method according to the invention.

[0033] It can be advantageous if a measuring device according to the invention is designed without a shunt on the DC side of the inverter. Even if other sensors were conceivable, those with the required accuracy would be too large and / or too expensive. This is only made possible by the determination method of the present invention, which provides an indirect measurement option. This indirect measurement option eliminates the need for a direct measurement, thus rendering the corresponding direct measuring sensors, such as a shunt, unnecessary. This clearly demonstrates once again how the costs, the number of components, and also the required installation space for a measuring device according to the invention can be reduced.

[0034] Furthermore, it is advantageous if, in a measuring device according to the invention, the detection module is at least partially integrated into the inverter. While already known systems can incorporate the corresponding sensor elements, integrating these sensor elements into the inverter is particularly advantageous. This leads to a reduction in the production effort of the measuring device and also to a reduction in the required installation space.

[0035] Another object of the present invention is a computer program product comprising instructions which, when executed by a computer, cause the computer to carry out the steps of a determination method according to the invention. Thus, a computer program product according to the invention also offers the same advantages as those explained in detail with reference to a determination method according to the invention, as well as with reference to a measuring device according to the invention.

[0036] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The drawings schematically show:

[0037] Fig. 1 shows an embodiment of an electrical device during the execution of a determination method according to the invention.

[0038] Fig. 2 a measuring device according to the invention,

[0039] Fig. 3 shows a further embodiment of a measuring device according to the invention and

[0040] Fig. 4 shows a possible use of AC ripple current values ​​and a conversion into a two-dimensional plane.

[0041] Fig. 5 Normalized amplitudes of the current oscillations are displayed against the rotor angle and shown as a vector trajectory on the DQ plane. Figure 1 schematically shows an application situation of a determination method according to the invention. For this purpose, an electrical device 100 is shown, which can be, for example, an electric vehicle. To supply a consumer 130, for example, an electric motor, with the required electrical power, current flow is necessary. The current flow, and thus the electrical energy, is provided by a battery device 120. The battery device 120 is operating in direct current mode, while the consumer 130 is operating in alternating current mode. Due to these different operating modes, an inverter 110 in the form of a converter is connected between these two components.In other words, current will now flow from the battery device 120 as direct current to the inverter 120, where it will be converted into alternating current and, as alternating current, will now provide the desired electrical power to the consumer 130, in the form of the electric motor.

[0042] For these discharge cycles, it is particularly advantageous to have the most accurate possible information about the current on the DC side, and thus on the DC side DCS of inverter 110. Figure 1 illustrates how this information can be determined without directly measuring the DC current value DCI.

[0043] To provide this information, two physical sensors are required. The first is a DC voltage measuring device 22, which can detect a voltage difference on the DC side DCS of the inverter 110. A DC voltage value DCU is thus measured and can be transmitted by the DC voltage measuring device 22 to the battery control device 122. Similarly, the AC current value ACI, particularly one with at least two phases, is determined by direct measurement using the AC current measuring device 24 and also transmitted to the battery control device 122. The battery control device 122 can include the measuring device 10 shown in more detail in Figure 2, for example.Using the calibrated AC-DC relationship, the DC current value DCI is now output as an indirect measurement and can be passed on (not shown) to, for example, a separate power meter, battery monitor, inverter control unit, or similar control modules. As can be clearly seen in Figure 1, the determination of the DC current value DCI is now carried out as an indirect measurement, without actually having to measure it on the DC side DCS of the inverter 110. Figure 2 shows a measuring device 10 for carrying out this method. In the simplest case, the two modules are provided so that, with the help of the acquisition module 20, for example with a DC voltage measuring device 22 and an AC current measuring device 24, the required input parameters in the form of the DC voltage value DC and the AC current value ACI can be acquired.These two parameters are passed on to the determination module 30, which, using the AC-DC relationship ADB, now indirectly provides a measurement in the form of a determination of the DC current value DCI.

[0044] Figure 3 further illustrates the embodiment of Figure 2. Here, an additional frequency analysis of the measured AC current value ACI is performed, resulting in a corresponding AC ripple current value ACR. The subsequent determination of the DC current value DCI is then carried out using this AC ripple current value ACR and, again, the DC voltage value DCU. Converting to an AC ripple current value enables an increase in the accuracy of the determination procedure.

[0045] Figure 4 schematically illustrates the relationships again. It shows a transformation using both an AC ripple current value transformation and a transformation into a two-dimensional plane. The upper part of the diagram shows a three-phase sinusoidal current. This current is phase-shifted, forming a three-phase current. To correlate this three-phase current with a DC side on the AC side, a transformation of the three phases into a two-phase plane, the so-called DQ plane, is performed in a first step. This plane represents the two average current values ​​resulting from the transformation of the three phases. This transformation also shows the individual AC ripple currents (ACR).These are now correlated again, which has already been determined here from an AC-DC relationship ADB (not shown in detail), and accordingly form a fluctuating DC current value curve DCI at the lower end of the diagram.

[0046] In addition to the previously shown 3-phase transformation in Figure 4, Figure 5 generalizes this in the DQ plane for any number of phases (for example, inverter designs with 5, 6, 9, and 12 phases exist). The upper part shows the normalized amplitudes of the current oscillations plotted against the rotor angle. The DC component is the fundamental part of all current phases, obtained after the Park transformation. The Id and Iq harmonics have been separated from the DC component for clarity.

[0047] The lower part of Figure 5 shows the harmonic part of the same information as a vector trajectory in the DQ plane. Increasing excitation and changing phase angles influence the vector trajectory. This allows the calibration of the AC-DC relationship (ADB) to the harmonics in the DQ plane at different amplitudes and frequencies. The preceding explanation of embodiments describes the present invention solely by way of examples.

[0048] Reference symbol list

[0049] 10 Measuring device

[0050] 20 Data acquisition module

[0051] 22 DC voltage measuring device

[0052] 24 AC current measuring device

[0053] 30 Determination module

[0054] 100 electrical devices

[0055] 110 Inverter

[0056] 120 battery device

[0057] 122 Battery control device

[0058] 130 consumers

[0059] DCI DC current value

[0060] DCU DC voltage value

[0061] DCS DC-side

[0062] ACI AC current value

[0063] ACS AC-side

[0064] ACR AC ripple current value

[0065] ADB AC-DC relationship

Claims

Patent claims 1. Determination method for determining a DC current value (DCI) on a DC side (DCS) of an inverter (110), characterized by the following steps: - Recording an AC current value (ACI) for at least two phases on one AC side (ACI) of the inverter (110), - Acquiring a DC voltage value (DCU) on the DC side (DCS) of the inverter (110), - Determining a DC current value (DCI) based on the detected AC current value (ACI) and the detected DC voltage value (DCU) using a calibrated AC-DC relationship (ADB).

2. Determination method according to claim 1, characterized in that the AC current value (ACI) is detected for at least three phases, in particular for all phases of the AC side (ACS) of the inverter (110).

3. Determination method according to one of the preceding claims, characterized in that the steps of detection and determination are carried out repeatedly, in particular continuously.

4. Determination method according to one of the preceding claims, characterized in that the recorded AC current value (ACI) is subjected to a frequency analysis to determine AC ripple current values ​​(ACR), wherein the determination of the DC current value (DCI) is carried out on the basis of the determined AC ripple current values ​​(ACR) and the recorded DC voltage value (DCU) using the calibrated AC-DC relationship (ADB).

5. Determination method according to one of the preceding claims, characterized in that, for the determination of the DC current value (DCI), at least the detected AC current value (ACI) is transformed into a two-dimensional AC current value (ACI).

6. Determination method according to one of the preceding claims, characterized in that a calibration method is used for the calibrated AC-DC relationship (ADB) at the end of a production process of an electrical device (100) comprising the inverter (110).

7. Determination method according to one of the preceding claims, characterized in that it is used for a battery control device (122), in particular for controlling a battery device (120) of at least one of the following electrical devices (100): - Electric vehicle - Hybrid vehicle - aircraft - Electrolyzer 8. Determination method according to one of the preceding claims, characterized in that at least one operating parameter of the inverter (110) and / or an electrical device (100) comprising the inverter (110) is taken into account when determining the DC current value (DCI), in particular one of the following: - Aging state - State of degradation 9. Determination method according to one of the preceding claims, characterized in that calibration information from a test bench test is used for the calibrated AC-DC relationship (ADB).

10. Measuring device (10) for determining a DC current value (DCI) on a DC side (DCS) of an inverter (110), characterized by a detection module (20) for detecting an AC current value (ACI) for at least two phases on an AC side (ACS) of the inverter (110) and for detecting a DC voltage value (DCU) on the DC side (DCS) of the inverter (110), further comprising a determination module (30) for determining a DC current value (DCI) based on the detected AC current value (ACI) and the detected DC voltage value (DCU) using a calibrated AC-DC relationship (ADB), wherein the detection module (20) and the determination module (30) are configured for an embodiment of a determination method having the features of any one of claims 1 to 9.

11. Measuring device (10) according to claim 10, characterized in that it is designed free of a shunt on the DC side (DCS) of the inverter (110).

12. Measuring device (10) according to one of claims 10 or 11 , characterized in that the detection module (20) is at least partially integrated into the inverter (110).

13. Computer program product comprising instructions which, when executed by a computer, cause the computer to perform the steps of a determination method having the features of any one of claims 1 to 9.

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