阅读说明：本技术 锂电池微短路的识别方法及电池管理系统 (Identification method for micro short circuit of lithium battery and battery management system ) 是由 张颖 韩冠超 高攀龙 于 2019-08-29 设计创作，主要内容包括：本发明涉及动力电池技术领域,提供一种锂电池微短路的识别方法及电池管理系统,解决了现有技术中在采用电压降、温升的方法提前预判微短路时,由于检测时间长且在有负载电流干扰的情况下,难以准确的判断电池微短路是否发生的问题。本发明所述的锂电池微短路的识别方法包括：实时采集锂电池中每个电芯的电压和电流；根据每个电芯的电压和电流,利用联合卡尔曼滤波方法,得到每个电芯的短路电阻；根据每个电芯的短路电阻与预设短路阻值范围的比较结果,确定每个电芯的内短路级别。本发明实施例适用于锂电池微短路的预判过程。(The invention relates to the technical field of power batteries, provides a method for identifying a micro short circuit of a lithium battery and a battery management system, and solves the problem that in the prior art, when the micro short circuit is pre-judged in advance by adopting a voltage drop and temperature rise method, whether the micro short circuit of the battery occurs or not is difficult to accurately judge due to long detection time and under the condition of load current interference. The method for identifying the micro short circuit of the lithium battery comprises the following steps: acquiring the voltage and current of each battery cell in the lithium battery in real time; obtaining the short-circuit resistance of each battery cell by using a combined Kalman filtering method according to the voltage and the current of each battery cell; and determining the internal short circuit level of each battery cell according to the comparison result of the short circuit resistance of each battery cell and the preset short circuit resistance range. The embodiment of the invention is suitable for the prejudging process of the micro short circuit of the lithium battery.)

1. A method for identifying a micro short circuit of a lithium battery is characterized by comprising the following steps:

acquiring the voltage and current of each battery cell in the lithium battery in real time;

obtaining the short-circuit resistance of each battery cell by using a combined Kalman filtering method according to the voltage and the current of each battery cell;

and determining the internal short circuit level of each battery cell according to the comparison result of the short circuit resistance of each battery cell and the preset short circuit resistance range.

2. The method for identifying the micro short circuit of the lithium battery as claimed in claim 1, wherein after the step of collecting the voltage and the current of each cell in the lithium battery in real time, the method for identifying the micro short circuit of the lithium battery further comprises the steps of:

obtaining the SOC value of each battery cell by using a combined Kalman filtering method according to the voltage and the current of each battery cell;

averaging the SOC values of all the battery cores in the lithium battery to obtain an average SOC value of the lithium battery;

obtaining the SOC value ratio of each battery cell according to the ratio of the SOC value of each battery cell to the average SOC value;

comparing the SOC value ratio of each battery cell with a preset threshold value;

and determining the battery cell with the SOC value ratio larger than the preset threshold value as the battery cell with the micro short circuit, and obtaining the short circuit resistance of the battery cell by using a combined Kalman filtering method according to the voltage and the current of the battery cell.

3. The method for identifying the micro short circuit of the lithium battery as claimed in claim 1, wherein after the step of collecting the voltage and the current of each cell in the lithium battery in real time, the method for identifying the micro short circuit of the lithium battery further comprises the steps of:

comparing the voltage of each battery cell with a preset voltage limit value;

when the voltage of the battery cell is smaller than the preset voltage limit value, outputting a power-off command;

and when the voltage of the battery cell is larger than or equal to the preset voltage limit value, determining that the battery cell is an internal short circuit battery cell, and obtaining the short circuit resistance of the battery cell by using a combined Kalman filtering method according to the voltage and the current of the battery cell.

4. The method for identifying the micro short circuit of the lithium battery according to claim 1, wherein the preset short circuit resistance range includes a first short circuit resistance range, a second short circuit resistance range and a third short circuit resistance range, the three short circuit resistance ranges have resistance values in a sequence of a first short circuit resistance range < a second short circuit resistance range < a third short circuit resistance range, and determining the internal short circuit level of each battery cell according to a comparison result between the short circuit resistance of each battery cell and the preset short circuit resistance range includes:

judging which one of the preset short-circuit resistance value ranges the short-circuit resistance of each battery cell belongs to;

when the short-circuit resistance of the battery cell is judged to belong to the first short-circuit resistance value range, the internal short-circuit level of the battery cell is a serious level internal short circuit;

when the short-circuit resistance of the battery cell is judged to belong to the second short-circuit resistance value range, the internal short-circuit level of the battery cell is a medium-level internal short circuit;

and when the short-circuit resistance of the battery cell is judged to belong to the third short-circuit resistance value range, the internal short-circuit level of the battery cell is a slight-level internal short circuit.

5. The method for identifying the micro short circuit of the lithium battery according to claim 4, wherein after the determining the internal short circuit level of each cell, the method for identifying the micro short circuit of the lithium battery further comprises:

when the internal short circuit level of the battery cell is determined to be a serious level internal short circuit, reducing the power of the lithium battery to a first power value;

when the internal short circuit level of the battery cell is determined to be a medium-level internal short circuit, reducing the power of the lithium battery to a second power value;

and when the internal short circuit level of the battery cell is determined to be a slight-level internal short circuit, reducing the power of the lithium battery to a third power value, wherein the first power value < the second power value < the third power value.

6. A battery management system for performing the method for identifying a micro short circuit of a lithium battery according to any one of claims 1 to 5.

Technical Field

The invention relates to the technical field of power batteries, in particular to a method for identifying micro short circuit of a lithium battery and a battery management system.

Background

The lithium battery is widely applied to new energy automobiles due to high cyclic utilization rate and high energy density. However, the lithium battery brings high economic benefit and has certain risk problem. The most obvious safety problem is the battery micro short circuit. The micro short circuit of the lithium battery is a micro short circuit phenomenon between the electric core and the electric core in the lithium battery or in a single electric core. The micro short circuit can cause abnormal discharge of the battery, abnormal heat generation and even spread of a thermal runaway phenomenon, and cause the ignition and explosion of the battery. In the prior art, a battery management system in a new energy automobile generally adopts a voltage drop and temperature rise method to pre-judge a micro short circuit in advance for the prevention and control of the micro short circuit, but the detection time is long and whether the micro short circuit of the battery occurs or not is difficult to accurately judge under the condition of load current interference.

Disclosure of Invention

In view of the above, the present invention is directed to a method for identifying a micro short circuit of a lithium battery and a battery management system, so as to at least partially solve the above technical problems.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a method for identifying a micro short circuit of a lithium battery comprises the following steps: acquiring the voltage and current of each battery cell in the lithium battery in real time; obtaining the short-circuit resistance of each battery cell by using a combined Kalman filtering method according to the voltage and the current of each battery cell; and determining the internal short circuit level of each battery cell according to the comparison result of the short circuit resistance of each battery cell and the preset short circuit resistance range.

Further, after the real-time collection of the voltage and the current of each electric core in the lithium battery, the identification method of the micro short circuit of the lithium battery further includes: obtaining the SOC value of each battery cell by using a combined Kalman filtering method according to the voltage and the current of each battery cell; averaging the SOC values of all the battery cores in the lithium battery to obtain an average SOC value of the lithium battery; obtaining the SOC value ratio of each battery cell according to the ratio of the SOC value of each battery cell to the average SOC value; comparing the SOC value ratio of each battery cell with a preset threshold value; and determining the battery cell with the SOC value ratio larger than the preset threshold value as the battery cell with the micro short circuit, and obtaining the short circuit resistance of the battery cell by using a combined Kalman filtering method according to the voltage and the current of the battery cell.

Further, after the real-time collection of the voltage and the current of each electric core in the lithium battery, the identification method of the micro short circuit of the lithium battery further includes: comparing the voltage of each battery cell with a preset voltage limit value; when the voltage of the battery cell is smaller than the preset voltage limit value, outputting a power-off command; and when the voltage of the battery cell is larger than or equal to the preset voltage limit value, determining that the battery cell is an internal short circuit battery cell, and obtaining the short circuit resistance of the battery cell by using a combined Kalman filtering method according to the voltage and the current of the battery cell.

Further, the preset short-circuit resistance range includes a first short-circuit resistance range, a second short-circuit resistance range and a third short-circuit resistance range, and the resistance values in the three short-circuit resistance ranges are in sequence that the first short-circuit resistance range is smaller than the second short-circuit resistance range and smaller than the third short-circuit resistance range, and the internal short-circuit level of each battery cell is determined to include according to the comparison result between the short-circuit resistance of each battery cell and the preset short-circuit resistance range: judging which one of the preset short-circuit resistance value ranges the short-circuit resistance of each battery cell belongs to; when the short-circuit resistance of the battery cell is judged to belong to the first short-circuit resistance value range, the internal short-circuit level of the battery cell is a serious level internal short circuit; when the short-circuit resistance of the battery cell is judged to belong to the second short-circuit resistance value range, the internal short-circuit level of the battery cell is a medium-level internal short circuit; and when the short-circuit resistance of the battery cell is judged to belong to the third short-circuit resistance value range, the internal short-circuit level of the battery cell is a slight-level internal short circuit.

Further, after determining the internal short circuit level of each cell, the method for identifying a micro short circuit of a lithium battery further includes: when the internal short circuit level of the battery cell is determined to be a serious level internal short circuit, reducing the power of the lithium battery to a first power value; when the internal short circuit level of the battery cell is determined to be a medium-level internal short circuit, reducing the power of the lithium battery to a second power value; and when the internal short circuit level of the battery cell is determined to be a slight-level internal short circuit, reducing the power of the lithium battery to a third power value, wherein the first power value < the second power value < the third power value.

Compared with the prior art, the method for identifying the micro short circuit of the lithium battery has the following advantages:

the method for identifying the micro short circuit of the lithium battery adopts a combined Kalman method, eliminates load current interference, reduces the error of the estimated short circuit resistance, and improves the estimation precision, thereby improving the safety of the lithium battery.

Another object of the present invention is to provide a battery management system for performing the method for identifying a micro short circuit of a lithium battery as described above.

Compared with the prior art, the battery management system and the identification method of the micro short circuit of the lithium battery have the same advantages, and are not repeated herein.

Additional features and advantages of the invention will be set forth in the detailed description which follows.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention.

In the drawings:

fig. 1 is a schematic flow chart of a method for identifying a micro short circuit of a lithium battery according to an embodiment of the present invention;

fig. 2 is a schematic circuit diagram of an intra-cell short circuit provided in an embodiment of the present invention;

fig. 3 is a schematic flow chart of a method for identifying a micro short circuit of a lithium battery according to an embodiment of the present invention.

Detailed Description

In addition, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.

The present invention will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.

Fig. 1 is a schematic flow chart of a method for identifying a micro short circuit of a lithium battery according to an embodiment of the present invention. As shown in fig. 1, the method is applied to a Battery Management System (BMS), and the method for identifying a micro short circuit of a lithium Battery includes:

step 101, acquiring voltage and current of each battery cell in a lithium battery in real time;

102, obtaining the short-circuit resistance of each battery cell by using a combined Kalman method according to the voltage and the current of each battery cell;

and 103, determining the internal short circuit level of each battery cell according to the comparison result of the short circuit resistance of each battery cell and the preset short circuit resistance value range.

As shown in fig. 2, the normal internal resistance in the battery cell is R_fNormal current is I₁Normal voltage in the cell is V_ocIt can be seen that when no internal short circuit occurs in the cell, the voltage V of the cell_t＝V_oc. When an internal short circuit occurs in the battery cell, the short circuit resistance is R_SCThe current I is I₁+I₂I.e. equal to the normal current I₁And short-circuit current I₂Sum, voltage V in the cell_t＝V_oc+R_fI₁。

By acquiring the voltage V of each battery cell in the lithium battery on line in real time_tAnd the current I is obtained, and then the short circuit resistance of each battery cell is obtained by adopting a combined Kalman filtering method according to the voltage and the current of each battery cell.

The combined Kalman filtering method is improved on the basis of the Kalman filtering method, aiming at the condition that the model parameters are not fixed, the changed parameters and the model state variables can be combined together to apply an extended Kalman filtering algorithm, so that the more accurate minimum variance estimation of the state variables is realized, and the method is suitable for a nonlinear system. When new data comes, the new state variable at the current moment can be calculated according to the new data, the state estimation value at the previous moment, the state transition equation of the system and the basic recursion formula of Kalman filtering.

Obtaining a state equation in the joint Kalman filtering method through formula (1):

wherein x is_kFor the SOC value, u, of the cell at the kth acquisition time_kR of cell for kth acquisition time_fVoltage of (internal resistance voltage), theta_kFor the current of the cell at the kth acquisition time,short-circuit resistance, X, of the cell for the kth acquisition time_k+1Equation of state for the k +1 th acquisition time, y_kFor the observation equation, the voltage of the cell at the kth acquisition time is expressed, X is_k+1And y_kThe combinations are state variables. For example, the current and voltage acquired at the kth acquisition time of each cell are used, a state equation in a joint kalman filtering method is used to calculate and obtain a voltage and current estimation value at the (k + 1) th acquisition time of each cell, an estimation error at the (k + 1) th acquisition time is obtained by actually acquiring the voltage and current values at the (k + 1) th acquisition time of each cell, a filtering gain is combined to correct the current value of each cell at the (k + 1) th acquisition time, and an optimal estimation value of the short-circuit internal resistance corresponding to the (k + 1) th acquisition time of each cell is obtained, that is, the short-circuit resistance of each cell is obtained by using the joint kalman filtering method according to the voltage and current of each cell.

In step 103, after the short-circuit resistance of each battery cell is obtained, the internal short-circuit level of each battery cell may be determined according to the comparison result between the short-circuit resistance of each battery cell and the preset short-circuit resistance value range. Specifically, the preset short circuit resistance value range includes a first short circuit resistance value range, a second short circuit resistance value range and a third short circuit resistance value range, and the resistance values in the three short circuit resistance value ranges are sequentially the first short circuit resistance value rangeRange of<Second short circuit resistance value range<A third short resistance range. The first short-circuit resistance range, the second short-circuit resistance range and the third short-circuit resistance range can be obtained by respectively setting the following short-circuit points in four internal short-circuit conditions in the lithium battery: the method includes creating a short circuit point between the anode and the cathode, creating a short circuit point between the anode current collector and the cathode, creating a short circuit point between the anode and the cathode current collector, and creating a short circuit point between the anode current collector and the cathode current collector. And carrying out short circuit simulation experiments through the different short circuit types to obtain three short circuit resistance value ranges. For example, the first short circuit resistance range is less than 1 ohm, the second short circuit resistance range is greater than or equal to 1 ohm and less than or equal to 50 ohm, the third short circuit resistance range is greater than 50 ohm, and the corresponding internal short circuit levels are a severe level internal short circuit, a medium level internal short circuit and a slight level internal short circuit respectively. First, it is determined which of the short-circuit resistance value ranges the short-circuit resistance of each cell belongs to. When the short-circuit resistance of the battery cell is judged to belong to the first short-circuit resistance range, the internal short-circuit level of the battery cell is a serious level internal short circuit, namely when R is within the range_SCWhen the voltage is less than 1 omega, the battery cell is in a serious-grade internal short circuit; when the short-circuit resistance of the battery cell is judged to belong to the second short-circuit resistance range, the internal short-circuit level of the battery cell is a medium-level internal short circuit, namely when R is more than or equal to 1 omega_SCWhen the voltage is less than or equal to 50 omega, the battery cell is short-circuited in a medium level; when the short-circuit resistance of the battery cell is judged to belong to the third short-circuit resistance range, the internal short-circuit level of the battery cell is slight internal short circuit, namely when R is within the range_SCAnd when the voltage is higher than 50 omega, the battery cell is slightly internally short-circuited.

In an implementation manner of the embodiment of the present invention, after the internal short circuit level of each battery cell is determined, in order to reduce the risk level of the internal short circuit and improve the safety control method, the power of the lithium battery may be correspondingly reduced. Specifically, when the internal short circuit level of the battery cell is determined to be a serious level internal short circuit, reducing the power of the lithium battery to a first power value; when the internal short circuit level of the battery cell is determined to be a medium-level internal short circuit, reducing the power of the lithium battery to a second power value; when the internal short circuit level of the battery core is determined to be a slight-level internal short circuit, reducing the power of the lithium battery to a third power value, and enabling the first power value < the second power value < the third power value, for example, the first power value is a rated power reduced by 50%, the second power value is a rated power reduced by 20%, and the third power value is a rated power reduced by 10%.

In another implementation manner of the embodiment of the present invention, in order to pre-determine whether the lithium battery has a micro short circuit, the determination may be performed according to the SOC value. Specifically, after the voltage and the current of each battery cell in the lithium battery are collected in real time, the SOC value of each battery cell is obtained by using a joint kalman filtering method according to the voltage and the current of each battery cell. The current and the voltage acquired at the kth acquisition time of each battery cell are calculated to obtain a current estimation value at the kth +1 acquisition time of each battery cell by using a state equation in a combined Kalman filtering method, namely the formula (1), the estimation error at the kth +1 acquisition time is obtained by using the actual acquisition current value at the kth +1 acquisition time of each battery cell, the SOC value of each battery cell at the kth +1 acquisition time is corrected by combining filtering gain according to the actually measured voltage and current at the current moment, and the optimal estimation value of the SOC value corresponding to the kth +1 acquisition time of each battery cell is obtained, namely the SOC value of each battery cell is obtained by using the combined Kalman filtering method according to the voltage and the current of each battery cell. Then, the SOC values of all the battery cores in the lithium battery are averaged to obtain an average SOC value of the lithium battery, and the SOC value ratio of each battery core is obtained according to the ratio of the SOC value of each battery core to the average SOC value. And then, comparing the SOC ratio of each battery cell with a preset threshold, for example, 0.15, determining that a micro short circuit exists in the corresponding battery cell when the SOC ratio is greater than the preset threshold, and determining that a micro short circuit does not exist in the corresponding battery cell if the SOC ratio is less than or equal to the preset threshold. For the battery cell with the micro short circuit, the short circuit resistance of the battery cell can be obtained by using a combined Kalman filtering method according to the voltage and the current of the battery cell with the micro short circuit.

In another real-time manner of the embodiment of the present invention, in order to further determine the type of the micro short circuit, after the voltage and the current of each battery cell in the lithium battery are collected in real time, whether the type of the micro short circuit is an external short circuit or an internal short circuit may be determined according to a comparison result between the voltage of each battery cell and a preset voltage limit value. Specifically, the voltage of each cell is compared with the preset voltage limit, for example, the preset voltage limit is a safety voltage limit of the cell. And when the voltage of the battery cell is smaller than the preset voltage limit value, determining that the battery cell is in an external short circuit, and directly outputting a power-off command to require the emergency power-off of the lithium battery. When the voltage of the battery cell is larger than or equal to the preset voltage limit value, the battery cell is determined to be an internal short circuit battery cell, and then the short circuit resistance of the battery cell can be obtained by using a combined Kalman filtering method according to the voltage and the current of the internal short circuit battery cell.

To facilitate understanding of the embodiment of the present invention, fig. 3 is a schematic flow chart of a method for identifying a micro short circuit of a lithium battery according to the embodiment of the present invention. As shown in fig. 3, the method for identifying a micro short circuit of a lithium battery includes the following steps:

step 301, acquiring voltage and current of each battery cell in a lithium battery in real time;

step 302, obtaining an SOC value of each battery cell by using a combined Kalman filtering method according to the voltage and the current of each battery cell;

step 303, averaging the SOC values of all the battery cells in the lithium battery to obtain an average SOC value of the lithium battery;

step 304, obtaining the SOC value ratio of each battery cell according to the ratio of the SOC value of each battery cell to the average SOC value;

step 305, judging whether the SOC value of each battery cell is greater than or equal to a preset threshold, determining that the battery cell with the SOC value greater than or equal to the preset threshold is a battery cell with a micro short circuit, executing step 306, if the battery cell with the SOC value less than the preset threshold does not have the micro short circuit, returning to step 301, and continuously collecting the voltage and the current of the battery cell without the micro short circuit in real time;

step 306, judging whether the voltage of the electric core with the micro short circuit is smaller than a preset voltage limit value, determining that an external short circuit exists for the electric core with the voltage smaller than the preset voltage limit value, executing step 307, and executing step 308 for the electric core with the voltage larger than or equal to the preset voltage limit value;

step 307, outputting a power-off command, wherein the lithium battery is powered off emergently;

308, obtaining the short-circuit resistance of each battery cell by using a combined Kalman filtering method according to the voltage and the current of the battery cell with the internal short circuit;

309, judging which of the preset short-circuit resistance value ranges the short-circuit resistance of each battery cell belongs to;

step 310, when the short-circuit resistance of the battery cell is judged to belong to the first short-circuit resistance value range, the internal short-circuit level of the battery cell is a serious level internal short circuit, and the power of the lithium battery is reduced to a first power value;

step 311, when it is determined that the short-circuit resistance of the battery cell belongs to the second short-circuit resistance value range, the internal short-circuit level of the battery cell is a medium-level internal short circuit, and the power of the lithium battery is reduced to a second power value;

step 312, when it is determined that the short-circuit resistance of the battery cell belongs to the third short-circuit resistance range, the internal short-circuit level of the battery cell is a slight-level internal short circuit, and the power of the lithium battery is reduced to a third power value, where resistance values in the three short-circuit resistance ranges are sequentially a first short-circuit resistance range < a second short-circuit resistance range < a third short-circuit resistance range, and the first power value < the second power value < the third power value.

According to the embodiment of the invention, aiming at the condition that the model parameters are not fixed, the variable parameters are combined with the model state variables by using a combined Kalman filtering method, the short-circuit resistance of the internal short-circuit battery core is estimated, the load current interference can be eliminated, the estimation error of the short-circuit resistance is reduced, the micro short-circuit of the lithium battery is detected in advance, and the risk of the micro short-circuit is reduced by changing the power of the lithium battery according to the identified internal short-circuit grade.

Correspondingly, the embodiment of the invention also provides a battery management system, and the battery management system is used for executing the identification method of the micro short circuit of the lithium battery in the embodiment.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.