Method for determining the capacity of an electrical energy store

Abstract

The invention relates to a method for determining the capacity of an electrical energy storage unit, comprising the steps: a) determining a first capacity value of the electrical energy storage unit based on at least the age and / or the charge flux of the electrical energy storage unit using a first mathematical model; b) determining a second capacity value of the electrical energy storage unit based on at least a second charge flux value of the electrical energy storage unit and a state-of-charge difference derived from the state-of-charge at two different points in time using a second mathematical model; c) determining a correction factor for determining the capacity value using the first mathematical model based on the determined first capacity value and the determined second capacity value; d) determining a third capacity value of the electrical energy storage unit based on at least the determined correction factor and the age of the electrical energy storage unit and / or a third charge flux value of the first electrical energy storage unit using the first mathematical model.

Description

Technical Field

[0001] This invention relates to a method for determining the capacity of an electrical energy storage unit according to the present invention. Background Technology

[0002] With increasing electrification, particularly in the vehicle or automotive sector, mobile electrical energy storage systems are becoming more and more common. Especially with the increasing use of lithium-ion technology, it is crucial to adhere to pre-defined limits, such as voltage and state-of-charge limits, to ensure the safety and lifespan of these systems. Furthermore, it is essential for users of such systems to accurately know the capacity, or storage performance, of the electrical energy storage cells. Therefore, the battery management system updates the capacity values ​​of the electrical energy storage cells at largely irregular intervals. These capacity values ​​allow the user to view, for example, the remaining effective mileage of an electrically powered vehicle. The more frequently these updates are performed, the more accurately the vehicle's effective mileage can be displayed to the user. Moreover, the accuracy of the mathematical models used to calculate the capacity can be improved through corresponding feedback.

[0003] Document CN 108196200 describes a method for determining the capacity of lithium-ion batteries.

[0004] Document CN 103399277 describes a method for determining the capacity of a battery. Summary of the Invention

[0005] This invention discloses a method according to the present invention.

[0006] The methods for determining capacity include the steps described below.

[0007] Here, a first mathematical model is used to determine the first capacity value of the electrical energy storage unit, wherein the first model is based at least on the usage time of the electrical energy storage unit and / or the charge flux (Ladungsdurchsatz) of the electrical energy storage unit. Here, the usage time of the electrical energy storage unit specifically refers to the time the electrical energy storage unit is installed in the electrical energy storage system. The charge flux of the electrical energy storage unit can be obtained, for example, by integrating the time of current flowing into and out of the electrical energy storage unit.

[0008] The first mathematical model is preferably an empirical model, which is created by laboratory experiments and, for example, illustrates the relationship between the capacity of an electrical energy storage unit and its usage time and charge flux.

[0009] Furthermore, a second mathematical model is used to determine the second capacity value of the electrical energy storage unit, wherein the first and second mathematical models differ. Here, the second model is based at least on the second charge flux value and the state-of-charge difference of the electrical energy storage unit. The state-of-charge difference is calculated here from the state-of-charge values ​​at two different time points.

[0010] The second mathematical model is preferably one that uses current and voltage measurements to determine the capacity. It is important to note that the voltage measurements should preferably refer to the voltage of the electrical energy storage unit in a quiescent state.

[0011] In order to correct the capacity value obtained using the first mathematical model, a correction factor (Korrekturfaktor) is obtained based on the obtained first capacity value and the obtained second capacity value, so as to improve the capacity value obtained using the first mathematical model.

[0012] The third capacity value of the electrical energy storage unit is then obtained using the first mathematical model, which is based on the usage time and / or charge flux of the electrical energy storage unit and the obtained correction factor used to improve the result.

[0013] The method is advantageous because it yields a more accurate value for the capacity by combining two different methods for determining the capacity. This is particularly advantageous when the correction factor is determined once for the first mathematical model within a certain timeframe, and then only this model is used to determine the capacity, since there is no need to determine a suitable quiescent voltage value for the second model.

[0014] Other advantageous embodiments of the invention are other subjects described in this disclosure.

[0015] The state of charge at different time points can be determined by appropriately using the open-circuit voltage value of the modeled open-circuit voltage characteristic curve. This allows for a faster determination of the second capacity value because it is not necessary to wait for the electrical energy storage unit to reach its static state or be fully operational before determining the second capacity value, as the corresponding quiescent voltage value may not have been reached due to prolonged use of the electrical energy storage unit.

[0016] The modeled no-load voltage characteristic curve is appropriately divided into different ranges. There exists a first range where the no-load voltage values ​​are used to determine the state of charge (SOC), and a second range where the no-load voltage values ​​are not used. In these second ranges, the measured values ​​of the voltage of the electrical energy storage unit are used instead to determine the SOC. This is advantageous because the first range (in which the simulation of the no-load voltage curve of the electrical energy storage unit is rarely wrong) is therefore used to determine the capacity, while the second range (in which the simulation is more prone to error) is not used. This improves the accuracy of the capacity determination.

[0017] The first range suitably includes open-circuit voltage ranges of 4 volts to 3.8 volts and 3.7 volts to 3.6 volts. Within these ranges, a low-error simulation of the open-circuit voltage characteristic curve is achieved, thus enabling accurate determination of the capacity value.

[0018] The method is suitably implemented continuously to continuously improve capacity determination and thus achieve more accurate results in each repetition. This is particularly important for electrical energy storage units with long operating and usage durations, in order to always provide current and accurate capacity values.

[0019] The method can be implemented, for example, in a computer-based manner.

[0020] Furthermore, a computer program is also the subject of this disclosure, which sets up all the steps for implementing the above-described methods. Therefore, the aforementioned advantages can be achieved.

[0021] Furthermore, a machine-readable storage medium on which the computer program is stored is also the subject of this disclosure.

[0022] Furthermore, an apparatus for determining the capacity of an electrical energy storage unit is also the subject of this disclosure. This apparatus includes at least one device configured to implement all the steps of the described method. Therefore, the aforementioned advantages can be achieved. The at least one device can be, in particular, an electronic control unit.

[0023] At least one device may include, for example, a battery management controller and corresponding power electronics, such as an inverter, as well as a current sensor and / or a voltage sensor and / or a temperature sensor. An electronic control unit, particularly in the case of a battery management controller, may also be such a device. The electronic control unit may specifically refer to an electronic controller, which may include, for example, a microcontroller and / or application-specific hardware components, such as an ASIC, but may also be a memory-programmable control mechanism.

[0024] Furthermore, an electrical energy storage system is also the subject of this disclosure, which includes an electrical energy storage unit and the described apparatus. Therefore, the aforementioned advantages can be achieved.

[0025] An electrical energy storage unit can specifically refer to an electrochemical battery cell and / or a battery module containing at least one electrochemical battery cell and / or a battery pack containing at least one battery module. An electrical energy storage unit can, for example, be a lithium-based battery cell, a lithium-based battery module, or a lithium-based battery pack. An electrical energy storage unit can particularly be a lithium-ion battery cell, a lithium-ion battery module, or a lithium-ion battery pack. Furthermore, the battery cell can be a lithium-polymer battery, a nickel-cyanide battery, a lead-acid battery, a lithium-air battery, or a lithium-sulfur battery, or generally a battery of any electrochemical composition. Attached Figure Description

[0026] Advantageous embodiments of the invention are shown in the accompanying drawings and explained in more detail in the following description. The drawings show: Figure 1 A flowchart of the disclosed method according to one embodiment is shown; Figure 2 A schematic diagram of the no-load voltage characteristic curve with two first ranges and three second ranges is shown. Figure 3 A schematic diagram showing the capacity variation curve of an electrical energy storage unit according to a first mathematical model, along with correction factors, is presented; and Figure 4 A schematic diagram of a disclosed electrical energy storage system according to one embodiment is shown. Detailed Implementation

[0027] The same reference numerals are used to label the same device parts or the same method steps in all the figures.

[0028] Figure 1 A flowchart of a disclosed method for determining the capacity of an electrical energy storage unit according to one embodiment is shown.

[0029] Here, in the first step S11, the first capacity value of the electric energy storage unit is obtained using a first mathematical model based at least on the usage time and / or charge flux of the electric energy storage unit.

[0030] The first mathematical model can take the following form: .

[0031] Here we assume that the capacity C(t) of the electrical energy storage unit is linearly related to the usage time t. As the usage time increases, the capacity therefore decreases linearly. C2 and C1 are the capacity values, and t2 and t1 are the corresponding usage times, for which these capacity values ​​are recorded, where t2 marks a later time point than t1. This model can be determined, for example, in laboratory experiments. Therefore, the first capacity value of the electrical energy storage unit can be obtained using this first mathematical model.

[0032] In the second step S12, the second capacity value of the electrical energy storage unit is determined using a second mathematical model, based at least on the second charge flux value and the state of charge difference of the electrical energy storage unit. Here, the state of charge difference is derived from the state of charge at two different points in time.

[0033] The second mathematical model can, for example, take the following form: .

[0034] Here, Qcell is used to calculate the capacity value through a second mathematical model, and time points t3 and t4 are two distinct time points. To determine the net charge flow, the current is integrated over the time interval between t3 and t4. The second capacity value is then obtained by dividing by the difference in state of charge between t3 and t4.

[0035] In the third step S13, a correction factor is then calculated based on the obtained first capacity value and the obtained second capacity value, which is used to calculate the capacity value using the first mathematical model. This also... Figure 3 This is explained in the text.

[0036] In the fourth step S14, the third capacity value of the electric energy storage unit is obtained using the first mathematical model, which is based on the obtained correction factor for the first mathematical model and the usage time and / or the third charge flux value of the first electric energy storage unit.

[0037] The third capacity value thus obtained can be used, for example, in electronic control units to improve lifespan and / or effective mileage predictions, as well as to improve the prediction of available power, thereby enabling the electrical energy storage unit to operate in an improved manner.

[0038] Figure 2 A schematic diagram of the no-load voltage characteristic curve 21, modeled with two first ranges Δ1 and Δ2 and three second ranges, is shown. The no-load voltage values ​​in the two first ranges are used to determine the state of charge, while the no-load voltage values ​​in the three second ranges are not used to determine the state of charge. The no-load voltage values ​​are plotted on the vertical axis OCV (volts) and the state of charge values ​​are plotted on the horizontal axis SOC, thus deriving the no-load voltage characteristic curve 21.

[0039] Figure 3 A schematic diagram is shown of the capacity variation curve 31 of the electrical energy storage unit according to the first mathematical model, along with a correction factor 32, wherein the correction factor is obtained at two different time points t1 and t2. The capacity value of the electrical energy storage unit is marked on the vertical axis CAP, as it is derived from the first mathematical model, and the usage time of the electrical energy storage unit is marked on the horizontal axis t, thereby deriving the capacity variation curve 31.

[0040] The exemplary model used above is accompanied by a correction factor in the following form: .

[0041] Here, Label the corresponding correction factors. For Figure 3 This means that, The value is positive because the first mathematical model overestimates the capacity loss over time. The model can be improved using the disclosed method, which yields a more accurate capacity value.

[0042] Figure 4 A schematic diagram of a disclosed electrical energy storage system 40 according to one embodiment is shown. The electrical energy storage system 40 has an electrical energy storage unit 41 and a device 42 for determining the capacity of the electrical energy storage unit. Here, the device 42 includes a component 44 that provides steps for implementing the disclosed method. The device 44 further controls a power electronics component 43, which, for example, regulates the energy delivery to an electric motor.

Claims

1. A method for determining the capacity of an electrical energy storage unit (41), the method comprising the following steps: a) The first capacity value of the electric energy storage unit (41) is determined using a first mathematical model based at least on the usage time and charge flux of the electric energy storage unit (41); b) The second capacity value of the electric energy storage unit (41) is determined using a second mathematical model based at least on the second charge flux value of the electric energy storage unit (41) at two different time points and the difference in charging state derived from the charging state at the corresponding time points; c) Based on the obtained first capacity value and the obtained second capacity value, obtain the correction factor (32) to modify the first mathematical model; d) The third capacity value of the electric energy storage unit (41) is determined using the modified first mathematical model, based at least on the determined correction factor (32) and the usage time of the electric energy storage unit (41) and the third charge flux value of the first electric energy storage unit (41).

2. The method according to claim 1, wherein, In step b), the no-load voltage value of the modeled no-load voltage characteristic curve (21) is used to determine the charging state.

3. The method according to claim 2, wherein, The modeled no-load voltage characteristic curve (21) is divided into different ranges, wherein there is at least one first range (△1, △2), the no-load voltage value of the at least one first range is used to determine the charging state, and wherein there is at least one second range, the no-load voltage value of the at least one second range is not used to determine the charging state, but instead the measured value of the voltage of the electrical energy storage unit (41) is used to determine the charging state.

4. The method according to claim 3, wherein, The at least one first range (△1, △2) includes an open-circuit voltage range of 4 volts to 3.8 volts and an open-circuit voltage range of 3.7 volts to 3.6 volts.

5. The method according to any one of claims 1 to 4, wherein, Repeat the method described above to improve capacity retrieval.

6. A computer program product comprising a computer program configured to perform all steps of the method according to any one of claims 1 to 5.

7. A machine-readable storage medium having stored thereon the computer program of the computer program product according to claim 6.

8. A device (42) for determining the capacity of an electrical energy storage unit (41), the device comprising at least one device (44) configured to perform the steps of the method according to any one of claims 1 to 5.

9. An electric energy storage system (40) comprising an electric energy storage unit (41) and the device (42) according to claim 8.

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