CN110168839B - Method and system for detecting fault currents in a battery - Google Patents
Method and system for detecting fault currents in a battery Download PDFInfo
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- CN110168839B CN110168839B CN201780079554.7A CN201780079554A CN110168839B CN 110168839 B CN110168839 B CN 110168839B CN 201780079554 A CN201780079554 A CN 201780079554A CN 110168839 B CN110168839 B CN 110168839B
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Abstract
The invention relates to a method for detecting a fault current in a rechargeable electrical energy storage unit, in particular in a storage battery of a rechargeable battery unit. The method comprises the following steps: -continuously determining the respective state of charge (S1.1) of the accumulator at a prescribed moment in the respective operating cycle of the accumulator unit; -determining the relative capacitance (S1.2) of the respective accumulator; -predicting the state of charge of at least one battery by means of the determined relative capacitances of the batteries at defined moments of the determined cycle (S4.1); and-identifying a fault current in the at least one battery by comparing the determined state of charge of the at least one battery with the predicted state of charge at a prescribed moment of the determined cycle (S4.2). The invention also relates to a corresponding identification system and a corresponding computer program product.
Description
Technical Field
The invention relates to a method for detecting a fault current in a rechargeable electrical energy storage unit, in particular in a storage battery of a rechargeable battery unit. The invention also relates to a corresponding identification system and a corresponding computer program product.
Background
From document EP 2 336 794 A2, a method for detecting leakage currents of a battery by means of a potentioless capacitor for voltage detection at the terminals of the battery is known. A bleed-off resistance is calculated based on the detected voltage, and the bleed-off resistance is compared with an insulation resistance standard value to determine whether leakage current or leakage current occurs.
Batteries are often used as a current source in vehicles. Lithium ion batteries are mainly used in hybrid vehicles and electric vehicles. To achieve higher voltages, multiple cells are typically connected in series. Typically, multiple cells are combined into one module and multiple modules are combined into one package. In order to improve safety, battery packs and modules are equipped with large-scale electronic devices. Different physical variables, such as current, voltage and temperature, are detected by means of sensors. In addition, the electronic device includes one or more controllers on which the battery management system is implemented. The battery management system is composed of different software algorithms in which, in particular, the limit values for the permissible currents and voltages are calculated. Another important task of the battery management system is to identify faults in the battery cells or the electronic devices.
One type of fault is an internal short circuit. If an internal short circuit is not recognized in time, damage to the cell can increase. In extreme cases, so-called "thermal runaway" occurs. In this case, the cells heat up very strongly and eventually fire.
There are different types of internal shorts that develop differently quickly and act on the dynamics of the battery in different ways. One type is the so-called slow short circuit. The slow short circuit is characterized by improving the self-discharge rate of the battery. Self-discharge causes a slow decay of the state of charge (soc=state of charge). Slow self-discharge is difficult to detect.
If the battery is discharged by an external consumer or charged by means of an external current source, for example during driving of the vehicle, a significantly greater current flows in the battery. The state of charge, SOC, of a battery is typically estimated by means of an algorithm for battery state identification. There are a number of different methods for determining SOC. Common to these methods is that they have only limited accuracy. If the battery is separated from the external current source and the consumers after a load, for example, charging, discharging or the entire driving cycle, a stable voltage (OCV: open Circuit Voltage, open circuit voltage) occurs for each cell after some time. Due to the chemical and physical processes in the cell, the cell voltage after current flow, but also frequently varies over several hours. The voltage can furthermore be determined only with limited measurement accuracy. The increased self-discharge causes a slow voltage drop of the cell. For this reason, it is very difficult to distinguish the voltage drop due to the increased self-discharge from other phenomena, thereby identifying the slow short circuit.
Disclosure of Invention
The method according to the invention with the features mentioned in claim 1 and the system according to the invention with the features mentioned in claim 8 provide the advantage that it is possible to identify a slow decay of the state of charge due to a fault current in the cell.
In a method for detecting a fault current in a rechargeable electrical energy storage unit, in particular in a rechargeable battery cell, over a plurality of operating cycles, the following steps are provided according to the invention:
(i) Continuously determining a respective state of charge SOC of the battery at a defined time during a respective operating cycle of the energy storage unit;
(ii) Determining a relative capacitance c rel of the corresponding battery;
(iii) Predicting the state of charge of at least one battery at a defined time t 2 of the defined period by means of a defined relative capacitance c rel of the battery; and
(Iv) The fault current in the at least one battery is identified by comparing the determined state of charge of the at least one battery with the predicted state of charge at a defined time t2 of the determined cycle. Optionally, a corresponding output value is then output (v), which in the simplest case is to send information about the identification of the fault current outwards. The unit can be a module, such as a battery module, or a pack, such as a battery pack.
According to a preferred embodiment of the invention, the relative capacitance c rel of the respective battery j is determined in the step of determining it by: a ratio of a change in the state of charge SOC of the battery between one of the cycles, i.e. the prescribed time t 2 of the cycle k and the prescribed time t 1 of the cycle k-1 preceding the cycle, to a change in the state of charge SOC of the battery of the unit defined as the reference cell i between the one cycle, i.e. the prescribed time t 2 of the cycle k and the prescribed time t 1 of the cycle k-1 preceding the cycle k, which ratio describes the relative capacitance c rel of the respective battery j, is determined. In other words, the relative capacitance c rel of the corresponding battery j is derived according to the following equation:
according to a further preferred embodiment of the invention, it is provided that the state of charge of the respective battery is predicted at a defined time of a cycle according to the following equation:
Here, SOC j,Prog is the predicted state of charge of the respective battery, and SOC i is the determined state of charge of the reference cell.
According to a further preferred embodiment of the invention, the respective state of charge SOC of battery j at defined time t 2 is determined according to the following equation:
Here, I is current, I kurzschluss,j is short-circuit current, konst is constant and Δ Modell-undMessfehler is inaccuracy due to model and measurement errors.
It is furthermore advantageously provided that the respective state of charge SOC of the battery is determined by measuring the respective steady voltage or no-load voltage (OCV: open circuit voltage).
According to a further preferred embodiment of the invention, the operating cycle (a) is a charge/discharge cycle of the rechargeable electrical energy storage unit or a driving cycle of the rechargeable electrical energy storage unit of the vehicle.
According to a further preferred embodiment of the invention, the fault current is an internal short-circuit current of the energy storage unit or of the battery.
In a corresponding system for detecting a fault current in a rechargeable electrical energy storage unit, in particular in a storage battery of a rechargeable battery unit, it is provided according to the invention that the system is designed to carry out the following steps:
(i) Continuously determining a respective state of charge SOC of the battery at a defined time during a respective operating cycle of the energy storage unit;
(ii) Determining a relative capacitance c rel of the corresponding battery;
(iii) Predicting the state of charge of at least one battery at a defined time t 2 of the defined period by means of a defined relative capacitance c rel of the battery;
(iv) Identifying a fault current in the at least one battery by comparing the determined state of charge of the at least one battery with the predicted state of charge at a prescribed time t2 of the determined cycle; and
(V) And outputting a corresponding output value.
The system is in particular a system for performing the above-described method.
According to a preferred embodiment of the system according to the invention, the system has a computer device with:
(a) Processor and method for controlling the same
(B) At least one data memory
(C) At least one interface.
The computer device has means preferably for performing the above steps.
The invention also relates to a computer program product for executing the above method on a computer device comprising a processor and a data memory.
Additional advantages and advantageous embodiments of the subject matter according to the invention are illustrated by the following examples and the following figures and are set forth in the description which follows, wherein the described features can be the subject matter of the invention individually or in any combination, provided that the contrary is not explicitly drawn from the context. It is noted herein that the drawings have merely descriptive characteristics and are not to be construed as limiting the invention in any way.
Examples:
in the static phase, where no current flows, the state of charge of each cell is determined and stored after a suitable waiting time. After the following load phase, the state of charge is re-determined and a difference is formed for each cell. For a larger number of cells, for example, cells in a module or a package, the OCV (open circuit voltage) of each cell in the package or module is determined and the SOC is calculated therefrom. At a later time when the OCV can be determined with high accuracy, such as after the end of a driving cycle or other working cycle, the SOC value is determined again by means of the OCV. The SOC difference is proportional to the total extracted or added charge amount for each cell. The SOC of cell j at time k is calculated as follows:
The variable c j represents the capacitance of cell j. The current I kurzschluss,j is very small and negligible for the "healthy" Shan Chilai. In the average, the variables have only minor significance for a cell without defects. The SOC also contains a deviation Δsoc relax from the regulated voltage OCV, related to the dynamics of the current in the final load phase and the elapsed waiting time.
The relative capacitance is determined for each cell by means of the following calculation rules:
N is the number of cells.
The variable c rel.j (k) is stored. Additionally, the cell voltage at the end of the rest phase is stored and the value c rel.j (k) is recalculated in the next phase. For each cell, the value c rel.j is filtered in an appropriate manner over a number of cycles. Over a longer period, the divergence of values between Shan Chi jcrel.j (k) and the divergence of single Chi kcrel.j (k) over multiple periods is observed.
According to equations (1) and (2), the SOC of a cell without a fault can be predicted by means of the learned value c rel.j. For this, the SOC values of all other cells must be known:
。
the predicted value deviates from the actual measured value due to measurement accuracy and various other effects. With the relative divergences Δ jcrel.j (k) and Δ kcrel.j (k) determined in the earlier measurements, the predicted statistical error can be given:
If the deviation is significantly greater than the expected statistical divergence, this indicates an increased leakage or short-circuit current I kurzschluss,j according to equation (1). This means that when the following condition is satisfied; output failure for cell j:
Example embodiments:
for illustration, a module consisting of 4 cells was observed. The state of charge of the cell was observed in three rest phases and the following values were obtained:
。
During the second rest phase, the following values of the relative capacitance are calculated:
。
The divergence Δc rel is 0.0498.
For the third stationary phase, the following SOC values are predicted for cell 2 based on this:
The estimated statistical deviation is:
The actual deviation is 31% -20% = 11% and thus significantly larger than the statistical deviation. This represents a defect in cell 2.
Drawings
The application of the method for detecting a fault current in a battery of a rechargeable electrical energy storage unit in the previously described example is shown in the drawings.
Wherein:
Fig. 1 shows a block diagram of a method according to a preferred embodiment.
Detailed Description
Fig. 1 shows a block diagram of a schematic flow of a method in the scope of an example of a previous process, said method comprising four steps S1, S2, S3, S4. Step S1 here comprises two substeps S1.1, S1.2 and step S4 also comprises two substeps S4.1, S4.2.
In step S1, it is first checked whether the current I is on. In this case, if no current flows (i=0), waiting until the current flows (I > 0). Thus, for example, the beginning of a working cycle is determined. The start is thus for example the start of a discharge cycle or a driving cycle. Before the current is switched on, in particular directly before the current is switched on, a state of charge value (SOC value) should be determined and if necessary stored—substep S1.1. The relative capacitance c rel is then determined/calculated, in particular by means of filtering the already "learned" values—substep S1.2.
In step S2, the end of the discharge or travel portion of the duty cycle is determined. This is waited for when current > 0 until current=0.
In step S3, a relaxation time is also introduced. For this purpose, for the case of current=0, it is also waited until a predefined relaxation time, for example, one hour (1 h), is reached.
In step S4, the SOC value is then predicted based on the relative capacitance c rel in the first sub-step S4.1, and then a diagnosis is performed in the second sub-step S4.2.
Hereinafter, the core of the present invention should be described again in other expressions in terms of a battery having a plurality of cells:
The quiescent voltage of a plurality of battery cells, such as all cells in a module or package, is measured over a plurality of cycles consisting of rest and load. The relative capacitances of the cells are determined by statistical comparison of the cells. After a load phase, e.g. a charge, discharge or driving cycle, a certain time is waited for in a subsequent rest phase and then the average SOC of the cell is determined. By means of the learned relative capacitances and the stored state of charge at the end of the last stationary phase, the SOC can be estimated for each cell. If the difference between the estimated and actual values is too large, this indicates an increased self-discharge or leakage current.
Unlike the usual methods for determining the state of aging or health (soh_g), which determine the remaining residual capacity, the method is independent of the current measurement and thus of the measurement accuracy of the current measurement.
The magnitude of the change in state of charge during the relaxation phase is similarly large for all cells. The systematic errors are eliminated by relatively observing the state of charge.
The learned relative unit Chi Dianrong changes only very slowly due to battery aging. The value changes more slowly than soh_c of the module/package. The system effects that also relate to the entire cell are eliminated here.
By detecting multiple cells and observing over a longer period of time, the divergence of the relative cell capacitance can be detected. In this way, it is possible to distinguish significant changes from random noise.
Claims (10)
1. A method for identifying fault currents in a battery of a rechargeable electrical energy storage unit, having the steps of:
-continuously determining the respective state of charge (S1.1) of the battery at a prescribed moment in the respective operating cycle of the accumulator unit;
-determining the relative capacitance (S1.2) of the respective accumulator;
-predicting the state of charge of at least one of the batteries by means of the determined relative capacitances of the batteries at defined moments of the determined cycle (S4.1); and
Identifying a fault current in the at least one battery by comparing the determined state of charge of the at least one battery with the predicted state of charge at a defined moment of the determined cycle (S4.2),
Wherein the relative capacitance of the respective battery is derived by: determining a ratio of a change in the state of charge of the battery between a prescribed time of one of the cycles and a prescribed time of a cycle preceding the cycle to a change in the state of charge of the battery of the unit defined as a reference cell between the prescribed time of the one cycle and the prescribed time of the cycle preceding the cycle;
Wherein the state of charge of the respective battery is predicted at a prescribed time of the one cycle according to the following equation:
SOCj,Prog(t2)＝SOCj(t1)+crel,j×(SOCi(t2)-SOCi(t1))
Where j is the footmark of the corresponding battery, i is the footmark of the reference cell, t 2 is the prescribed time of the one cycle, t 1 is the prescribed time of the cycle preceding the cycle, SOC j,Prog is the predicted state of charge of the corresponding battery, SOC j is the determined state of charge of the corresponding battery, and SOC i is the determined state of charge of the reference cell;
wherein the relative capacitance c rel of the corresponding battery j is derived according to the following equation:
2. the method according to claim 1,
Characterized in that the rechargeable electrical energy storage unit is a rechargeable battery unit.
3. The method according to claim 1,
It is characterized in that the method comprises the steps of,
The corresponding state of charge SOC of battery j at defined time t 2 is determined according to the following equation:
SOC j(t2)＝SOCj(t1)+cj×∫Idt+konst×∫IKurzschluss,jdt+ΔModell-und Messfehler where j is the subscript of the corresponding battery, t 2 is the prescribed time of the one cycle, t 1 is the prescribed time of the cycle preceding the cycle, SOC j is the determined state of charge of the corresponding battery, I is the current, I kurzschluss,j is the short circuit current, konst is constant and Δ Modell-undMessfehler is inaccuracy due to model and measurement errors.
4. The method according to claim 1 to 3,
It is characterized in that the method comprises the steps of,
The respective state of charge of the battery is determined by measuring the respective no-load voltage.
5. The method according to claim 1 to 3,
It is characterized in that the method comprises the steps of,
The duty cycle is a charge/discharge cycle or a driving cycle of a rechargeable electric energy storage unit of the vehicle.
6. The method according to claim 1 to 3,
It is characterized in that the method comprises the steps of,
The fault current is a short-circuit current inside the energy storage unit or the battery.
7. A system for identifying fault currents in a battery of a rechargeable electrical energy storage unit, wherein the system is designed for performing the steps of:
-continuously determining the respective state of charge of the battery at a prescribed moment in the respective operating cycle of the accumulator unit;
-determining the relative capacitances of the respective accumulators;
-predicting the state of charge of at least one of said batteries by means of the determined relative capacitances of said batteries at defined moments of the determined cycle;
-identifying a fault current in the at least one battery by comparing the determined state of charge of the at least one battery with the predicted state of charge at a prescribed moment t 2 of the determined cycle; and
-Outputting a corresponding output value of the output signal,
Wherein the relative capacitance of the respective battery is derived by: determining a ratio of a change in the state of charge of the battery between a prescribed time of one of the cycles and a prescribed time of a cycle preceding the cycle to a change in the state of charge of the battery of the unit defined as a reference cell between the prescribed time of the one cycle and the prescribed time of the cycle preceding the cycle;
Wherein the state of charge of the respective battery is predicted at a prescribed time of the one cycle according to the following equation:
SOCj,Prog(t2)＝SOCj(t1)+crel,j×(SOCi(t2)-SOCi(t1))
Where j is the footmark of the corresponding battery, i is the footmark of the reference cell, t 2 is the prescribed time of the one cycle, t 1 is the prescribed time of the cycle preceding the cycle, SOC j,Prog is the predicted state of charge of the corresponding battery, SOC j is the determined state of charge of the corresponding battery, and SOC i is the determined state of charge of the reference cell;
wherein the relative capacitance c rel of the corresponding battery j is derived according to the following equation:
8. the system according to claim 7,
Characterized in that the rechargeable electrical energy storage unit is a rechargeable battery unit.
9. The system according to claim 7 or 8,
It is characterized in that the method comprises the steps of,
A computer device is provided, the computer device having:
The processor is configured to perform the steps of,
At least one data memory, and
-At least one interface.
10. A computer program product for executing the method according to any of claims 1 to 6 on a computer device comprising a processor and a data memory.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE102016225988.1A DE102016225988A1 (en) | 2016-12-22 | 2016-12-22 | Method and system for detecting fault currents in memory cells |
| DE102016225988.1 | 2016-12-22 | ||
| PCT/EP2017/078222 WO2018114107A1 (en) | 2016-12-22 | 2017-11-03 | Method and system for detecting fault currents in storage cells |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN110168839A CN110168839A (en) | 2019-08-23 |
| CN110168839B true CN110168839B (en) | 2024-07-16 |
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