METHOD FOR PLASIBILITIZING A CURRENT MEASUREMENT BETWEEN AN ELECTRICAL ENERGY STORAGE SYSTEM AND AN ELECTRICAL CONSUMER

Description

[0001] The present invention is based on a method for verifying the plausibility of a current measurement between an electrical energy storage system and an electrical consumer. State of the art

[0002] Electrical energy storage systems, especially batteries, with lithium iron phosphate (LFP) chemistry can be particularly useful for certain battery systems due to their low voltage level, such as 12V vehicle electrical systems with a typical voltage range of 9V-16V, which is covered by four LFP cells. Furthermore, LFP cells are particularly safe, especially in the event of overtemperature or short circuits.

[0003] For the use of LFP batteries for safety-critical applications in vehicles that require a reliable prediction of the currently available battery performance and remaining battery energy, the SOC must be reliably determined, in particular the currently lowest possible state of charge must be known.

[0004] The electrochemical properties of LFP chemistry prevent SOC determination via OCV curve measurement over a wide range of charge levels, because the OCV voltage hardly changes when the charge level changes, for example, due to current draw. This results from the flat open-circuit voltage characteristic of LFP chemistry.

[0005] It is therefore advisable to continuously measure the current drawn from a battery using a battery management system. This means monitoring the current in every mode of the battery management system, including standby mode, where current draws may also be required. For example, this may be necessary for a 12V battery to supply the vehicle with standby power.

[0006] The worst-case state of charge (SOC), which is important for safety-critical applications—that is, the lowest possible remaining energy—is thus directly influenced by the current measurement accuracy. For longer periods of standby mode, even small measurement inaccuracies have a significant impact on the worst-case SOC and only allow a very conservative estimate. As a result, the battery's actually available power cannot be released to the vehicle or consumer and thus cannot be used.

[0007] A key cause of limited measurement accuracy in current measurements (for the relevant case of low current amplitudes considered here) is, in particular, the EMC deviation of the sensor technology or a temperature-dependent offset inaccuracy of the analog-to-digital converter. These are therefore inaccuracies in the current measurement that must be maintained at all times, even though the conditions leading to the inaccuracy are not always present, in particular the aforementioned EMC interference or particularly low temperature ranges.

[0008] The document US 2013 / 0335100 describes a method for checking the proper functioning of a current sensor.

[0009] The document DE102014219806A1 describes a device and a method for testing the functionality of a current sensor. Disclosure of the invention Advantages of the invention

[0010] A method for checking the plausibility of a current measurement between an electrical energy storage system and an electrical consumer is disclosed, with the features of the independent patent claim, wherein a capacitor and a switching element are arranged between the electrical energy storage system and the electrical consumer.

[0011] A first current value is determined by measuring an electrical current between the electrical energy storage system and the electrical consumer.

[0012] Furthermore, the switching element is controlled to separate the electrical energy storage system from the electrical consumer, so that the electrical consumer is supplied with electrical energy from the capacitor.

[0013] A first electrical voltage is then determined across the capacitor, as well as a second current value depending on the determined voltage.

[0014] The current measurement is then checked for plausibility by comparing the first current value with the second current value.

[0015] The method is advantageous because, in addition to the actual current measurement, a plausibility check of the measured first current value is performed, which checks whether a current is actually flowing or whether a measured value is merely caused by EMC interference or an analog-to-digital converter offset. Based on the voltage across the capacitor, a current flow can be inferred. The goal of the plausibility check is to reduce the accuracy buffer maintained during current value acquisition during times of low current flow. Therefore, the method is intended for use in times of low current flow, for example, in a standby situation.

[0016] Further advantageous embodiments of the present invention are the subject of the subclaims.

[0017] A suitable switching element can be, for example, a transistor, in particular a MOSFET, or comprise one.

[0018] In particular, the method can also be implemented by computer.

[0019] It is advisable to adjust the measurement uncertainties to be considered in the current measurement depending on the second current value. This is advantageous because, especially at low current flow, the state of charge can be estimated less conservatively due to the adjusted measurement uncertainties of the current measurement.

[0020] The functionality of the switching element is conveniently tested based on the first electrical voltage detected on the capacitor. Depending on the type and measurement location of the first electrical voltage, the functionality of the switching element is determined if the voltage exceeds or falls below a predefined value. This is advantageous for ensuring its functionality.

[0021] The first current value is expediently compared with a predefined first current limit, with activation taking place depending on the comparison. For example, it can be provided that the switching element is only activated when the current falls below the predefined first current limit. Additionally, it can be provided that the current must have been below the predefined first current limit for a predefined first period of time before the switching element is only activated. This is advantageous because the method is particularly advantageous at low power consumption, as mentioned above, and furthermore, switching at high current due to possible wear of the switching element is avoided.

[0022] Conveniently, the switching element is controlled to connect the electrical energy storage system to the load, so that the electrical load is supplied with electrical energy from the electrical energy storage system. This is advantageous because the capacitor can typically store a smaller amount of energy than the electrical energy storage system and can therefore only supply the load for a shorter period of time, so that the supply is secured again by connecting it.

[0023] The switching element for connection is expediently controlled depending on a second electrical voltage on the capacitor. This is advantageous, for example, to connect the electrical energy storage system directly to the load when a predefined voltage limit is exceeded or undershot, which can occur particularly in the case of a high energy demand from the load.

[0024] Furthermore, the invention relates to a computer program configured to execute all steps of the method described above. Thus, the aforementioned advantages can be achieved.

[0025] Furthermore, the invention relates to a machine-readable storage medium on which the aforementioned computer program is stored. Thus, the above-mentioned advantages can be achieved.

[0026] Furthermore, the invention relates to an electronic control unit configured to carry out all steps of the above-mentioned method. Thus, the above-mentioned advantages can be achieved.

[0027] Furthermore, the invention relates to a device comprising an electronic control unit according to the invention, an electrical energy storage system and an electrical consumer, wherein a capacitor and a switching element are arranged between the two. Short description of the drawings

[0028] Advantageous embodiments of the invention are illustrated in the figures and explained in more detail in the following description.

[0029] They show: Figure 1 shows a flowchart of a method according to the invention according to a first embodiment; Figure 2 shows a flowchart of a method according to the invention according to a second embodiment; Figure 3 shows a flowchart of a method according to the invention according to a third embodiment; Figure 4 shows a schematic representation of a device according to the invention according to an embodiment. Embodiments of the invention

[0030] The same reference numerals designate the same device components or the same process steps in all figures.

[0031] Figure 1 shows a flowchart of the method according to the invention for checking the plausibility of a current measurement between an electrical energy storage system and an electrical consumer, wherein a capacitor and a switching element are arranged between the two, according to a first embodiment.

[0032] In a first step S11, an electrical current between the electrical energy storage system and the electrical load is measured, thus determining a first current value. This makes it possible, for example, to determine whether the energy storage system is in a low-energy consumption state.

[0033] In a second step S12, the switching element is activated to separate the electrical energy storage system from the electrical load. Once the switching element has separated the two components, the electrical load is supplied with electrical energy from the capacitor.

[0034] In a third step S13, a first electrical voltage is determined at the capacitor. This can occur, in particular, after a predefined period of time following the disconnection of the electrical energy storage system from the electrical load.

[0035] In a fourth step S14, a second current value is determined based on the measured voltage. Using the measured voltage and, if applicable, the predefined time period, the flowing current can be inferred.

[0036] In a fifth step S15, the current measurement is then validated by comparing the first current value with the second current value. Depending on the determined second current value, corresponding safety margins or intended measurement uncertainties for the current measurement or for the current value determination can be reduced, since, for example, interference from electrical or electromagnetic interference or from a converter offset during the second voltage measurement can be considered insignificant, since a voltage change preferably occurs in the volt range.

[0037] Figure 2shows a flowchart of the inventive method according to a second embodiment. Steps S21 to S25 correspond to the steps S11 to S15 described above. Additionally, a sixth step S26 is executed.

[0038] In the sixth step S26, the functionality of the switching element is checked depending on the determined first electrical voltage across the capacitor. This takes advantage of the fact that, depending on the specific measuring points carried out, the first electrical voltage drops when functioning correctly, for example upon disconnection, and rises again upon a subsequent connection of the electrical energy storage system to the consumer. If this is not the case, the switching element is not functioning correctly. For this purpose, for example, the first electrical voltage can be compared with a predefined voltage limit, which can be used to differentiate between functional integrity. The sixth step S26 can also be carried out at a different point, as long as the step of determining the first electrical voltage across the capacitor was carried out beforehand, for example directly after this step.

[0039] Figure 3 shows a flowchart of the method according to the invention according to a second embodiment. The first step S31 corresponds to the first step S11 described above.

[0040] In a second step S32, the first current value thus determined is compared with a predefined first current limit. If, for example, the first current value is below the predefined first current limit, the system continues with the next third step S33. Otherwise, the system continues with the first step S31.

[0041] The third step S33 corresponds to the second step S12 described above. This is followed by a fourth step S34, a fifth step S35, and a sixth step S36, which correspond to the above-described steps S13, S14, and S15.

[0042] In a subsequent step S37, the switching element is controlled again, this time to connect the electrical energy storage system to the consumer so that the consumer is again supplied with energy by the electrical energy storage system.

[0043] Alternatively and / or additionally, in all embodiments, it can be provided that if the determined first voltage at the capacitor falls below or exceeds a predefined voltage limit, the switching element for connecting the electrical energy storage system is immediately activated to prevent an interruption in the power supply. This could, for example, result from excessive discharge of the capacitor due to increased energy consumption by the consumer.

[0044] Figure 4shows a schematic representation of a device 40 according to the invention according to one embodiment. The device 40 comprises an electrical energy storage system 41 and an electrical load 42. Between the two components, a capacitor 43 and a switching element 44 are arranged for isolating the electrical energy storage system 41 from the electrical load 42, so that the electrical load 42 is supplied with electrical energy when it is separated from the capacitor 43. Figure 4 The switching element 44 is shown in the connected state. Furthermore, the device 40 comprises an electronic control unit 45, which is configured to carry out all steps of a method according to the invention.

Claims

1. Method for checking the plausibility of a current measurement between an electrical energy storage system (41) and an electrical consumer (42), wherein a capacitor (43) and a switching element (44) are arranged between the two, comprising the steps of: a) ascertaining a first current value by measuring an electrical current between the electrical energy storage system (41) and the electrical consumer (42); b) actuating the switching element (44) to disconnect the electrical energy storage system (41) from the electrical consumer (42) so that the electrical consumer (42) is supplied with electrical energy by the capacitor (43); c) ascertaining a first electrical voltage across the capacitor (43); d) ascertaining a second current value on the basis of the ascertained voltage; e) checking the plausibility of the current measurement by comparing the first current value with the second current value.

2. Method according to the preceding claim, furthermore comprising: f) adapting measurement uncertainties to be taken into account in the current measurement, on the basis of the second current value.

3. Method according to either of the preceding claims, furthermore comprising: g) checking the operability of the switching element (44) on the basis of the ascertained first electrical voltage across the capacitor (43).

4. Method according to one of the preceding claims, furthermore comprising: h) comparing the first current value with a predefined first current limit value, wherein the switching element (44) is actuated to disconnect on the basis of the comparison.

5. Method according to one of the preceding claims, furthermore comprising: i) actuating the switching element (44) to connect the electrical energy storage system (41) to the consumer so that the electrical consumer (42) is supplied with electrical energy by the electrical energy storage system (41).

6. Method according to the preceding claim, wherein the actuation is performed on the basis of a second electrical voltage across the capacitor (43).

7. Computer program which is configured to carry out all the steps of the method according to one of the preceding claims.

8. Machine-readable storage medium on which the computer program according to the preceding claim is stored.

9. Electronic control unit (45) which is configured to carry out all the steps of the method according to one of Claims 1 to 5.

10. Apparatus (40) comprising an electrical energy storage system (41) and an electrical consumer (42), wherein a capacitor (43) and a switching element (44) are arranged between the two, and an electronic control unit (45) according to the preceding claim.