Calculation method of battery attenuation rate

Abstract

The invention belongs to the technical field of electrochemical energy storage, and particularly discloses a method for calculating the attenuation rate of a battery. Comprising the steps that the charging and discharging capacity of the whole cycle life cycle of a battery is divided into a plurality of sections according to attenuation rates, the attenuation rates in the sections are equal, and the set charging amount corresponding to each cycle in each section is determined based on the attenuation rates, so that battery charging is regulated and controlled; establishing a comparison table of the number of battery charging and discharging cycles, the corresponding charging amount regulation and control values and the charging amount accumulative regulation and control values; determining the current cycle number range of the battery by comparing the actual accumulative charge quantity with the accumulative charge quantity regulation value; calculating an actual regulation and control value EX of the next charging amount of the battery; and correspondingly calculating the attenuation rate of the battery through the actual regulation value EX. The actual regulation and control value EX of next operation of the battery is calculated based on the actual accumulative charging amount of the battery, and then the actual attenuation rate of the battery is calculated according to the actual regulation and control value Ex, so that the actual health degree of battery operation is accurately reflected.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical energy storage, and in particular to a method for calculating a battery attenuation rate. Background Art

[0002] With the construction of new energy systems such as photovoltaic and wind power, the supporting energy storage technologies are also developing rapidly. Among many electrochemical energy storage technologies, lithium-ion battery energy storage currently occupies a dominant position. As the core component of energy storage equipment, its SOH calculation has very important practical value for energy storage systems. In the prior art, the battery attenuation rate SOH in the energy storage system is usually calculated based on the current charge and discharge amount setting or the initial charge and discharge amount.

[0003] The disadvantages of this calculation method are that, first, the decay rate SOH may be greater than 100%, which cannot accurately reflect the health of the battery and is easy to cause misunderstanding; second, when the operating conditions on a certain day are not fully charged and discharged (charge and discharge both reach the pre-set cutoff conditions), the decay rate SOH cannot be calculated in this way, resulting in data gaps. Especially when the battery is running to the end of its life, the lack of SOH monitoring will bring risks to the safe operation of the energy storage system. Summary of the invention

[0004] In view of this, the present application provides a method for calculating the battery attenuation rate to solve the defects in the above-mentioned prior art.

[0005] The specific plan is:

[0006] A method for calculating a battery attenuation rate, comprising:

[0007] S1, the charge and discharge capacity of the battery in the entire cycle life cycle is divided into several sections according to the attenuation rate, and the attenuation rate in each section is equal. The charge capacity control value corresponding to each cycle is calculated based on the attenuation rate, and a comparison table of the number of battery cycles, the corresponding charge capacity control value and the cumulative charge capacity control value is formulated;

[0008] S2, regulating the charge amount of the battery during each cycle according to the charge amount control value corresponding to each cycle;

[0009] S3, obtaining the actual cumulative charge capacity ETx of the battery up to the current time;

[0010] S4, in the comparison table, by comparing the actual cumulative charge capacity ETx with the cumulative charge capacity control value, determine the current cycle range of the battery;

[0011] S5, based on the charge control values ​​and the cycle number at the two end points of the current cycle range of the battery, calculate the actual control value E of the next charge of the battery within the current cycle range X ;

[0012] S6, based on the actual control value E of the battery's next charge capacity X , correspondingly calculate the battery decay rate SOH;

[0013] The battery decay rate SOH = the actual control value E of the battery charge X / The actual charge value of the battery during the first cycle.

[0014] Preferably, the process of determining the current cycle range of the battery is as follows:

[0015] First, the accumulated charge capacity ETx of the battery up to the current time is obtained;

[0016] Then, the cycle number range corresponding to the cumulative charge amount ETx is found in the comparison table, and this cycle number range is the cycle number range of the battery currently.

[0017] Preferably, the current cumulative charge capacity ETx of the battery is the sum of the charge capacity values ​​of the battery from the first cycle to the current cycle.

[0018] Preferably, the actual adjustment control value Ex of the next battery charge amount is calculated by the following formula:

[0019] Ex=Em-ΔEx=Em-(ΔE*ΔETx / ΔET)

[0020] Wherein, Em: is the charge capacity control value corresponding to the maximum number of cycles within the cycle range of the battery; En: is the charge capacity control value corresponding to the minimum number of cycles within the cycle range of the battery; ΔEx: is the difference between the number of cycles corresponding to the next charge within the cycle range of the battery and the charge capacity control value of the minimum number of cycles, ΔEx=Ex-En; ΔE: is the difference between the charge capacity control values ​​corresponding to the maximum number of cycles and the minimum number of cycles within the cycle range of the battery, ΔE=Em-En; ΔETx: is the difference between the cumulative charge capacity control values ​​corresponding to the number of cycles corresponding to the next charge within the cycle range of the battery and the minimum number of cycles, ΔETx=ETx-ETn; ΔET: is the difference between the cumulative charge capacity control values ​​corresponding to the maximum number of cycles and the minimum number of cycles within the cycle range of the battery, ΔET=ETm-ETn.

[0021] Preferably, the capacity limit of the battery includes the total charge and discharge capacity value and attenuation rate of the battery during the entire charge and discharge process.

[0022] Preferably, the capacity limit of the battery is obtained through measured life attenuation data of the battery under given operating conditions.

[0023] Compared with the prior art, the beneficial effects of this application are:

[0024] In this application, based on the actual cumulative charge amount ETx of the battery running to the present, the actual control value E of the battery for the next operation is calculated. X , further calculate the actual decay rate SOH of the battery according to the actual control value Ex. Since the decay rate SOH corresponding to each charge and discharge cycle is calculated based on the actual cumulative charge amount ETx of the battery, it can accurately reflect the actual health of the battery;

[0025] In the present application, the calculation of the actual battery attenuation rate is based on the actual cumulative charge amount ETx of the previous charge and discharge cycle, that is, when the device is running, whether it is fully charged or not, the corresponding attenuation rate SOH in each cycle can be calculated, and there will be no data gaps, so as to achieve continuous and stable state monitoring of the battery during operation; avoid the inability to calculate the attenuation rate SOH during the entire charging and discharging process of the battery due to incomplete charging and discharging (both charging and discharging reach the preset cutoff conditions), resulting in data gaps, especially when the battery is running to the end of its life, the lack of monitoring of the attenuation rate SOH will bring risks to the safe operation of the energy storage system;

[0026] At the same time, in the present application, the calculation of the battery attenuation rate SOH is based on a comparison table, and the comparison table is obtained by dividing the battery's capacity limit throughout its life cycle into each charge and discharge cycle according to the attenuation rate law, thereby avoiding the situation where SOH>100% cannot accurately reflect the health of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the battery cycle curve in the embodiment of this application;

[0028] Figure 2 Schematic diagram of calculation of charging value of a battery after any number of cycles in an embodiment of the present application. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] S1, obtain the measured life attenuation data of the battery under given working conditions, that is, obtain the charge and discharge capacity of the battery in the entire cycle life cycle, that is, the capacity limit value. Among them, the capacity limit value includes the attenuation rate of the battery in the entire charge and discharge process and the total charge and discharge capacity of the battery.

[0031] S2, dividing the charge and discharge capacity of the battery in the entire cycle life cycle into several segments according to the attenuation rate law, with the attenuation rate being equal in each segment, calculating the charge capacity control value corresponding to each cycle based on the attenuation rate, and formulating a comparison table of the number of battery cycles, the corresponding charge capacity control value, and the cumulative charge capacity control value;

[0032] S3, regulating the charge amount of the battery in each cycle according to the charge amount control value corresponding to each cycle;

[0033] S4, obtain the actual cumulative charge capacity ETx of the battery under the same environment as the given working condition and the actual charge capacity of the first cycle of the battery to calculate the decay rate SOH corresponding to the current cycle of the battery. The specific calculation process is:

[0034] 1) Obtain the actual cumulative charge capacity ETx of the battery up to the current time;

[0035] 2) In the comparison table, by comparing the actual cumulative charge capacity ETx with the cumulative charge capacity control value, determine the current cycle range of the battery;

[0036] 3) Based on the charge control values ​​and cycle numbers at both ends of the current cycle range of the battery, calculate the actual control value E of the next charge of the battery within the current cycle range X ;

[0037] 4) The actual control value E based on the battery's next charge capacity X , correspondingly calculate the battery decay rate SOH;

[0038] The battery decay rate SOH = the actual control value E of the battery charge X / The actual charge value of the battery during the first cycle.

[0039] Furthermore, the process of determining the current cycle range of the battery is as follows:

[0040] First, the accumulated charge capacity ETx of the battery up to the current time is obtained;

[0041] Then, the cycle number range corresponding to the cumulative charge amount ETx is found in the comparison table, and this cycle number range is the cycle number range of the battery currently.

[0042] Furthermore, the current cumulative charge capacity ETx of the battery is the sum of the charge capacity values ​​corresponding to each cycle number when the battery runs from the first cycle to the current cycle number.

[0043] Furthermore, the actual adjustment control value Ex of the next battery charge amount is calculated by the following formula:

[0044] Ex=Em-ΔEx=Em-(ΔE*ΔETx / ΔET)

[0045] Wherein, Em: is the charge capacity control value corresponding to the maximum number of cycles within the cycle range of the battery; En: is the charge capacity control value corresponding to the minimum number of cycles within the cycle range of the battery; ΔEx: is the difference between the number of cycles corresponding to the next charge within the cycle range of the battery and the charge capacity control value of the minimum number of cycles, ΔEx=Ex-En; ΔE: is the difference between the charge capacity control values ​​corresponding to the maximum number of cycles and the minimum number of cycles within the cycle range of the battery, ΔE=Em-En; ΔETx: is the difference between the cumulative charge capacity control values ​​corresponding to the number of cycles corresponding to the next charge within the cycle range of the battery and the minimum number of cycles, ΔETx=ETx-ETn; ΔET: is the difference between the cumulative charge capacity control values ​​corresponding to the maximum number of cycles and the minimum number of cycles within the cycle range of the battery, ΔET=ETm-ETn.

[0046] The present invention is further explained by the following examples.

[0047] Example

[0048] like Figure 1 As shown, this embodiment takes a lithium iron phosphate battery with a capacity of 105Ah and a power of 336Wh as an example. The black curve represents the cycle performance of the battery under given working conditions and the charge and discharge according to the cut-off voltage, such as temperature 25°C, charge and discharge rate 0.5P, charging to 3.65V cut-off, and discharging to 2.5V cut-off. The present invention regulates the charge and discharge amount of the battery by formulating a suitable attenuation rate, as shown in the red curve. By reducing the initial charge amount, the power loss of the battery in the early stage of the cycle is reduced, leaving a margin for subsequent cycles.

[0049] The charge control value corresponding to each cycle of the battery after regulation is shown in the second column of Table 1, where the specific charge capacity is determined by linear interpolation method between every hundred cycles. For example, the charge control value of the 200th cycle is 322.3, and the charge control value of the 300th cycle is 320.1. That is, if the two points (200, 322.3) and (300, 320.1) on the straight line are known, the charge control value corresponding to any cycle number between 200-300 can be calculated, and the same is true for other cycles. In this way, the charge control value corresponding to each cycle number of the battery can be calculated.

[0050] The cumulative charge control value of the battery for any number of cycles can be obtained by summing up the charge control values ​​corresponding to all cycles from the first cycle to the current cycle. For example, to find the cumulative charge control value when the battery runs to the 100th cycle, it is necessary to add the charge control values ​​of each cycle between 1 and 100 to get the cumulative charge control value at the 100th cycle. The calculation results are shown in the third column of Table 1.

[0051] The battery attenuation rate SOH is calculated by (the charging capacity of the battery at the current number of cycles / the charging capacity of the first cycle). The calculation results for every 100 cycles are shown in the fourth column of Table 1.

[0052] Table 1 Comparison table of the cycle number range, corresponding charging capacity and setting value of charging capacity control value of each unit charge and discharge cycle

[0053]

[0054]

[0055]

[0056] The charge value corresponding to the current number of cycles of the battery (i.e. the charge value corresponding to any number of cycles) can be calculated as follows:

[0057] The amount of electricity charged and discharged each time by the battery is recorded by the electric meter, based on which the cumulative charge capacity ETx of the battery running to the current cycle number can be obtained. The battery control system BMS compares ETx with the cumulative charge capacity control value in the third column of Table 1, first determines the current cycle range of the battery, and then calculates the actual charge capacity control value E for the next time. X For example, the current battery cumulative charge capacity ETx recorded by the electric meter is 978152.0Wh. The BMS compares this value with the cumulative charge capacity control value in the third column of Table 1, and it can be obtained that the current battery cycle number is between 3200-3300 cycles, such as Figure 2 As shown. Then the next charge amount control value Ex can be calculated by the following formula:

[0058] Ex=Em-ΔEx=Em-(ΔE*ΔETx / ΔET).

[0059] Wherein, Em: is the charge capacity control value of the mth hundredth cycle (i.e., the maximum cycle number within the nmth cycle number range), which can be obtained by looking up Table 1;

[0060] En: is the charge control value of the nth cycle (i.e. the minimum cycle number within the nmth cycle number range), which can be obtained by looking up Table 1;

[0061] ΔEx: the difference between the charge control values ​​of the xth and nth hundredth cycles within the nmth cycle number range, obtained by Ex-En; ΔE: the difference between the charge control values ​​of the mth and nth hundredth cycles within the nmth cycle number range, obtained by Em-En;

[0062] ΔETx: The difference between the cumulative charge control values ​​of the xth and nth hundredth cycles within the nmth cycle number range, obtained by ETx-ETn;

[0063] ΔET: The difference between the cumulative charge control values ​​of the mth and nth hundredth cycles within the nmth cycle number range, obtained by ETm-ETn;

[0064] After Ex is calculated, the attenuation rate SOH of the battery when it cycles to any number of cycles within the nmth cycle number range = Ex / first cycle charge value = Ex / 372.4. In the present application, the charge amount of each cycle of the battery operation is first regulated by a specific charge amount control method, and the charge amount and cumulative charge amount control table corresponding to the battery running to any number of cycles can be obtained, and then the charge amount value Ex of the battery cycled to the next arbitrary number of cycles is calculated according to the data in the control table, so as to calculate the SOH of the battery cycled to the next arbitrary number of cycles. That is, the method for calculating the SOH corresponding to each cycle number of the battery in the present application is to first determine the charge amount control value and charge amount corresponding to each cycle number of the battery according to the capacity limit of the battery, and first realize the control of the charge amount according to the determined charge amount control value, and then directly calculate according to the actual cumulative charge amount of the battery, without measuring other parameters, and there is no error problem of fitting function, and the accuracy is higher.

Claims

1. A method for calculating battery attenuation rate, characterized in that: include: S1, the charge and discharge capacity of the battery in the entire cycle life cycle is divided into several sections according to the attenuation rate, and the attenuation rate in each section is equal. The charge capacity control value corresponding to each cycle is calculated based on the attenuation rate, and a comparison table of the number of battery cycles, the corresponding charge capacity control value and the cumulative charge capacity control value is formulated; S2, regulating the charge amount of the battery in each cycle according to the charge amount control value corresponding to each cycle; S3, obtaining the actual cumulative charge capacity ETx of the battery up to the current time; S4, in the comparison table, by comparing the actual cumulative charge capacity ETx with the cumulative charge capacity control value, determine the current cycle range of the battery; S5, based on the charge control values ​​and the cycle number at the two end points of the current cycle range of the battery, calculate the actual control value E of the next charge of the battery within the current cycle range X ; S6, based on the actual control value E of the battery's next charge capacity X , correspondingly calculate the battery decay rate SOH; The battery decay rate SOH = the actual control value E of the battery charge X / The actual charge value of the battery during the first cycle.

2. The method for calculating the battery attenuation rate according to claim 1, characterized in that: The process of determining the current cycle range of the battery is as follows: First, the accumulated charge capacity ETx of the battery up to the current time is obtained; Then, the cycle number range corresponding to the cumulative charge amount ETx is found in the comparison table, and this cycle number range is the cycle number range of the battery currently.

3. The method for calculating the battery attenuation rate according to claim 2, characterized in that: The cumulative charge capacity ETx of the battery up to the present is the sum of the charge values ​​of the battery from the first cycle to the current cycle.

4. The method for calculating battery attenuation rate according to claim 1, characterized in that: The actual adjustment control value Ex of the battery's next charge capacity is calculated by the following formula: Ex=Em-ΔEx=Em-(ΔE*ΔETx / ΔET) Wherein, Em: is the charge capacity control value corresponding to the maximum number of cycles within the cycle range of the battery; En: is the charge capacity control value corresponding to the minimum number of cycles within the cycle range of the battery; ΔEx: is the difference between the number of cycles corresponding to the next charge within the cycle range of the battery and the charge capacity control value of the minimum number of cycles, ΔEx=Ex-En; ΔE: is the difference between the charge capacity control values ​​corresponding to the maximum number of cycles and the minimum number of cycles within the cycle range of the battery, ΔE=Em-En; ΔETx: is the difference between the cumulative charge capacity control values ​​corresponding to the number of cycles corresponding to the next charge within the cycle range of the battery and the minimum number of cycles, ΔETx=ETx-ETn; ΔET: is the difference between the cumulative charge capacity control values ​​corresponding to the maximum number of cycles and the minimum number of cycles within the cycle range of the battery, ΔET=ETm-ETn.

5. The method for calculating battery attenuation rate according to claim 1, characterized in that: The capacity limit of the battery includes the total charge and discharge value and the attenuation rate of the battery during the entire charge and discharge process.

6. The method for calculating battery attenuation rate according to claim 1, characterized in that: The capacity limit of the battery is obtained through the measured life attenuation data of the battery under given operating conditions.

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