Method for controlling expected life of battery

Abstract

The invention discloses a method for controlling the expected life of a battery. The control method comprises the following steps: acquiring a capacity limit value of charging and discharging of a battery under a given working condition; the charging and discharging capacity of the whole cycle life cycle of the battery is segmented according to the attenuation rate rule, the attenuation rate in each segment is equal, and then the charging and discharging capacity of the battery is divided to each cycle in each segment; calculating an attenuation rate corresponding to each cycle by adopting a linear interpolation method; calculating a set charging amount according to the attenuation rate corresponding to each cycle number; the charging amount of the battery is controlled by setting the charging amount, and the discharging amount of the battery is controlled by setting the cut-off voltage. According to the method, the appropriate attenuation rate is formulated based on the attenuation data when the battery circulates under the given working condition so as to determine the set value of the charging amount, the charging amount of the battery is controlled through the set electric quantity value, the discharging amount of the battery is controlled through the set cut-off voltage, and the operation life of the battery under the given working condition can be predicted and controlled.

Description

Technical Field

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

[0002] As the mainstream carrier in the field of electrochemical energy storage and the core component of energy storage equipment, the life prediction and control of lithium-ion batteries are of great practical significance, especially in industrial and commercial applications, where the stability of the charge and discharge of energy storage equipment has a direct impact on user benefits. At present, energy storage equipment using lithium-ion batteries as energy storage media controls charging and discharging by specifying a cutoff voltage. This method cannot accurately predict and control the operating life of the battery, and therefore cannot guarantee the long-term stability of the energy storage and release of the equipment, nor can it guarantee that users can obtain continuous and stable benefits; it also cannot accurately guide the use and operation of the equipment, and the battery may still be in operation even when it has reached the end of its specified life, posing a potential safety risk. Summary of the invention

[0003] In view of this, the present application provides a method for controlling the expected life of a battery, which makes the battery life predictable and controllable by formulating a corresponding attenuation rate in each charge and discharge cycle of the battery and controlling the charge amount of the battery in the corresponding cycle with the corresponding attenuation rate, so as to solve the problem that the battery life cannot be accurately predicted and controlled in the prior art. The specific scheme is:

[0004] A method for controlling the expected life of a battery, the method comprising:

[0005] S1, obtaining the charging and discharging capacity limit value of the battery under given working conditions;

[0006] S2, divide the charge and discharge capacity of the battery throughout its life cycle into segments according to the attenuation rate law, and determine the battery power attenuation rate in each segment;

[0007] S3, using linear interpolation method to calculate the decay rate corresponding to each number of cycles in each segment;

[0008] S4, calculating the set charging amount according to the decay rate corresponding to each number of cycles;

[0009] S5, in each charge and discharge cycle, the battery charge amount is controlled by the set charge amount, and the battery discharge amount is controlled by the set cut-off voltage.

[0010] Preferably, the process of controlling the battery charge amount by the attenuation rate is:

[0011] First, the set charge amount of the battery in each cycle is calculated through the decay rate;

[0012] Then, the calculated charge amount is used as the set charge amount to control the charge amount of the battery in the corresponding cycle. When the charge amount of the battery reaches the set charge amount, the battery management system issues a charge stop command and the battery stops charging.

[0013] Preferably, the charging capacity setting value corresponding to each cycle number=the charging capacity value of the battery in the first cycle*(1-the attenuation rate corresponding to the cycle number).

[0014] Preferably, the calculation process of setting the charging amount is:

[0015] First, determine the range of cycles within the charge and discharge cycle of the battery;

[0016] Then, respectively obtain the control values ​​of the charge amount corresponding to the two end points of the cycle number range of the battery; that is, obtain the maximum cycle number and the minimum cycle number in each segment, and the control values ​​of the charge amount corresponding to the maximum cycle number and the minimum cycle number;

[0017] Finally, the control value of the charge amount corresponding to the two endpoints is determined by linear interpolation to determine the control value of the charge amount corresponding to any cycle number within the cycle number range of the battery;

[0018] Repeat the above steps until the control value of the charge amount corresponding to each cycle number of the battery in the entire charge and discharge cycle is obtained, and the control value of the charge amount is the set charge amount corresponding to each cycle.

[0019] Preferably, the process of determining the range of the number of cycles is as follows:

[0020] The charging amount of a single cycle during battery operation is regulated according to the battery attenuation rate, so as to obtain the charging amount corresponding to each cycle during battery operation and a charging amount control table;

[0021] Get the current cumulative charge capacity ETx of the battery.

[0022] Then, the corresponding accumulated charge ETx is searched in the charge amount corresponding to each cycle and the charge amount control table, so as to determine the current cycle range of the battery.

[0023] Preferably, the set charging capacity for a single cycle = the charging capacity of the battery in the first cycle × (1-the decay rate in the corresponding cycle period).

[0024] Preferably, the set charging amount is controlled to be greater than the actual usage requirement and less than the capacity limit of the battery.

[0025] Preferably, the capacity limit value of the battery includes the total charge and discharge capacity value and the attenuation rate of the battery during the entire charge and discharge process.

[0026] Compared with the prior art, the beneficial effects of this application are:

[0027] The present application determines the attenuation rate of the battery in each cycle period based on the attenuation data of the battery during cycling under given operating conditions, sets a set value of the charge amount in the corresponding cycle period based on the attenuation rate, and controls the charge amount of the battery cell in the corresponding cycle period through the set value, without setting a cut-off voltage for the charge amount. The battery discharge amount is controlled through the set cut-off voltage, thereby achieving predictable and controllable operating life of the battery under given operating conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the battery cycle curve in the embodiment of this application;

[0029] Figure 2 Schematic diagram of charge capacity control value calculation in the embodiment of the present application. DETAILED DESCRIPTION

[0030] 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.

[0031] The invention provides a method for controlling the expected life of a battery.

[0032] S1, obtaining the capacity limit value of the battery under a given working condition;

[0033] S2, dividing the charge and discharge capacity of the battery throughout its life cycle into segments according to the attenuation rate law, and dividing the charge and discharge capacity of the battery into each cycle in each segment to determine the battery power attenuation rate in each cycle;

[0034] S3, using linear interpolation method to calculate the decay rate corresponding to each number of cycles in each segment;

[0035] S4, calculating the set charging amount according to the decay rate corresponding to each number of cycles;

[0036] S5, in each charge and discharge cycle, the battery charge amount is controlled by setting the charge amount, and the battery discharge amount is controlled by setting the cut-off voltage.

[0037] Furthermore, the process of controlling the battery charge amount by the attenuation rate is as follows:

[0038] First, the set charge amount of the battery in each cycle is calculated through the decay rate;

[0039] Then, the calculated charge amount is used as the set charge amount to control the charge amount of the battery in the corresponding cycle. When the charge amount of the battery reaches the set charge amount, the battery management system issues a charge stop command and the battery stops charging.

[0040] Furthermore, the charging capacity setting value corresponding to each cycle number=the charging capacity value of the battery in the first cycle*(1-the decay rate corresponding to the cycle number).

[0041] Furthermore, the calculation process of the charging amount is set as:

[0042] First, determine the range of cycles within the charge and discharge cycle of the battery;

[0043] Then, respectively obtain the control values ​​of the charging amount corresponding to the two end points of the cycle number range of the battery;

[0044] Finally, the control value of the charge amount corresponding to the two endpoints is used to determine the control value of the charge amount corresponding to any cycle number within the cycle number range of the battery by linear interpolation;

[0045] Repeat the above steps until the control value of the charge amount corresponding to each cycle of the battery in the entire charge and discharge cycle is obtained, and the control value of the charge amount is the set charge amount corresponding to each cycle.

[0046] Furthermore, the process of determining the range of the number of cycles is as follows:

[0047] According to the attenuation rate of the battery, the charge amount per unit cycle period during battery operation is regulated, so as to obtain the charge amount corresponding to each unit cycle period during battery operation and a charge amount control table;

[0048] Obtain the current cumulative charge capacity ETx of the battery;

[0049] Then, the corresponding accumulated charge amount ETx is searched in the charge amount corresponding to each unit cycle and the charge amount control table, so as to determine the current cycle range of the battery.

[0050] Furthermore, the set charging capacity per unit cycle number = the first cycle charging capacity of the battery × (1-the decay rate in the corresponding cycle period).

[0051] Furthermore, the set charging amount is controlled to be greater than the actual usage requirement and less than the capacity limit of the battery.

[0052] Furthermore, the capacity limit value of the battery includes the total charge and discharge capacity value and the attenuation rate of the battery during the entire charge and discharge process.

[0053] The present application is further explained by the following examples.

[0054] Example

[0055] This embodiment takes a lithium iron phosphate battery with a capacity of 105Ah and a power of 336Wh as an example. Figure 1 As shown in the figure, the black curve represents the cycle performance of the battery under given working conditions, with charge and discharge at the cut-off voltage, such as temperature 25°C, charge and discharge rate 0.5P, charge to 3.65V cut-off, discharge to 2.5V cut-off. The decay rate of the battery per 100 cycles can be calculated from the black curve data, and the calculation formula is:

[0056] Attenuation rate per hundred turns = (1-Q n / Q m ) / (nm)*100

[0057] Q n : The charge capacity of the nth cycle

[0058] Q m : The charge amount of the mth cycle

[0059] n, m: number of cycles

[0060] The calculation results are shown in Table 1.

[0061] Table 1 Power decay rate per 100 cycles

[0062] Cycle times range The power decay rate per 100 cycles 1-200 1.91％ 200-400 0.99％ 400-1000 0.59％ 1000-7000 0.35％

[0063] As can be seen from Table 1, the capacity decay of lithium iron phosphate batteries is fast at first and then slow. The faster capacity decay in the early stage will cause large fluctuations in the charge and discharge capacity of the energy storage device, thus affecting the user experience.

[0064] Therefore, the present application regulates the charge and discharge capacity of batteries of the same specifications by customizing the appropriate attenuation rate of the battery corresponding to each cycle number. Therefore, during the regulation, two prerequisites are considered:

[0065] The first is the cycle attenuation characteristics of the battery, that is, the attenuation law shown in the black curve and Table 1. When formulating the attenuation rate, it cannot exceed the capacity range of the battery. If the attenuation rate is set too small, the battery performance cannot be achieved. Therefore, in this application, the set charge amount control is set to be greater than the actual use demand and less than the battery capacity limit value;

[0066] Second, the total amount of electricity that the battery can provide throughout its entire life cycle is certain. By reducing the initial charge and discharge amount, the battery's power loss in the early stage of the cycle can be reduced to leave a margin for subsequent cycles, but the total amount of electricity in the entire life cycle cannot exceed the battery's performance range. Therefore, this application divides the entire charge and discharge cycle of the battery into several parts according to the number of cycles, and segments the charge and discharge capacity of the battery throughout its life cycle according to the attenuation rate law, and divides the charge and discharge capacity of the battery into each cycle in each segment to determine the battery's power attenuation rate during each cycle, and based on this, calculate the charge amount setting value of the battery during each cycle to regulate the entire charge and discharge of the battery, so that after regulation, the battery's capacity decays more smoothly during the entire charge and discharge process, as shown in the red curve. It should be noted that when the charge and discharge capacity of the battery throughout its life cycle is divided according to the number of cycles, it can be divided according to any number of cycles. In this embodiment, it is divided according to the number of cycles of 100 cycles, so as to obtain the result of the battery power attenuation rate per 100 cycles after regulation as shown in Table 2:

[0067] See Table 2:

[0068] Table 2 Battery charge attenuation rate per 100 cycles after regulation

[0069] Cycle times range Control value of power attenuation rate per 100 cycles 1-200 0.77％ 200-400 0.68％ 400-1000 0.53％ 1000-7000 0.35％

[0070] The power attenuation rate per 100 cycles after regulation is calculated based on the attenuation rate obtained in Table 2, as shown in Table 3. The charge capacity per 100 cycles of the regulated battery is shown in the third column of Table 3. Table 3 only shows the charge capacity value per 100 cycles, and the specific charge capacity is determined by linear interpolation between each 100 cycles. For example, the charge capacity control value of the first cycle is 327.36, and the charge capacity control value of the 100th cycle is 324.74. That is, if the two points (1, 327.36) and (100, 324.74) on the straight line are known, the charge capacity control value corresponding to any number of cycles between 1 and 100 can be calculated, and the same is true for other cycles.

[0071] Table 3 Power attenuation rate per 100 cycles after regulation

[0072]

[0073]

[0074]

[0075] In Table 3, the total charge capacity of the battery can be obtained by adding up the charge capacities corresponding to each cycle in each section. Before regulation, the total charge capacity of the battery after 6000 cycles was 1702996.9Wh, and after regulation, the total charge capacity of the battery after 6000 cycles was 1702589.2Wh, which did not exceed the capacity of the battery.

[0076] In this embodiment, the specific control method for regulating the charge amount of the battery by setting the charge amount in each cycle is:

[0077] The electric meter records the amount of electricity charged and discharged by the battery each time, and based on this, the cumulative charge amount ETx of the battery running to the current cycle number can be obtained;

[0078] The battery control system BMS compares ETx with the cumulative charge control value in the fourth column of Table 3, first determines the current cycle range of the battery, and then calculates the battery's next charge control value Ex. The specific calculation process is:

[0079] For example, the current battery cumulative charge capacity ETx recorded by the electric meter is 245622.0Wh. The BMS compares this value with the cumulative charge capacity control value in the fourth column of Table 3, and it can be obtained that the current battery cycle number is between 700-800 cycles. Figure 2 As shown. Then the next charge amount control value Ex can be calculated by the following formula:

[0080] Ex=Em-ΔEx=Em-(ΔE*ΔETx / ΔET).

[0081] In the above formula, Em: the charge control value of the mth lap, which can be obtained by looking up Table 3; En: the charge control value of the nth lap, which can be obtained by looking up Table 3; ΔEx: the difference between the charge control values ​​of the xth lap and the nth lap, obtained by Ex-En; ΔE: the difference between the charge control values ​​of the mth lap and the nth lap, obtained by Em-En; ΔETx: the difference between the cumulative charge control values ​​of the xth lap and the nth lap, obtained by ETx-ETn; ΔET: the difference between the cumulative charge control values ​​of the mth lap and the nth lap, obtained by ETm-ETn;

[0082] Through the above steps, the control value Ex of the battery's next charge amount can be calculated. When the next charge starts, the BMS monitors the battery's charge amount in real time through the electric meter. When the charge amount reaches Ex, the BMS issues a charge stop command, and the battery stops charging to achieve control of this charge. During discharge, the BMS monitors the battery voltage in real time through the sampling line. When the voltage reaches 2.5V, the BMS issues a charge stop command, and the battery stops discharging to achieve control of this discharge.

[0083] Through the above method, the amount of charge of the battery each time it runs can be controlled, and its life expectancy can also be controlled.

[0084] It should be noted that:

[0085] In the present application, the charge amount of the battery is controlled by formulating the corresponding attenuation rate of the battery under different cycle numbers, so as to achieve predictability and controllability of the battery service life. In the regulation of the charging and discharging process, the amount of power is controlled only according to the set value during charging, and the cut-off voltage is not set. The cut-off voltage is only set during discharging.

[0086] In this application, the attenuation rate of the battery in each stage is obtained based on the measured charge and discharge capacity of the battery under given working conditions, so that the operating life of the battery under the same environment as the given working conditions can be predicted and controlled;

[0087] In the present application, the attenuation rate is less than the measured life attenuation data of the battery and the limit value of the battery throughput, so that the battery can be replaced or retired in time when it reaches the end of its life, avoiding the safety risks caused by the continued operation of the battery beyond the life limit;

[0088] In the present application, the set charge amount corresponding to each cycle number of the battery is calculated by the actual cumulative charge amount ETx of the battery operation, thereby achieving stable and reliable energy storage and release of the energy storage device.

Claims

1. A method for controlling the expected life of a battery, characterized in that: The control method comprises: S1, obtaining the charging and discharging capacity limit value of the battery under given working conditions; S2, divide the charge and discharge capacity of the battery throughout its life cycle into segments according to the attenuation rate law, with the attenuation rates within each segment being equal, and then divide the charge and discharge capacity of the battery into each cycle in each segment to determine the battery power attenuation rate in each cycle; S3, using linear interpolation method to calculate the decay rate corresponding to each number of cycles in each segment; S4, calculating the set charging amount according to the decay rate corresponding to each number of cycles; S5, in each charge and discharge cycle, the battery charge amount is controlled by the set charge amount, and the battery discharge amount is controlled by the set cut-off voltage.

2. A method for controlling the expected battery life according to claim 1, characterized in that: The process of controlling the battery charge amount by the decay rate is as follows: First, the set charge amount of the battery in each cycle is calculated through the decay rate; Then, the calculated charge amount is used as the set charge amount to control the charge amount of the battery in the corresponding cycle. When the charge amount of the battery reaches the set charge amount, the battery management system issues a charge stop command and the battery stops charging.

3. A method for controlling the expected battery life according to claim 2, characterized in that: The set charging capacity corresponding to each cycle number = the battery's first cycle charging capacity * (1-each cycle attenuation rate).

4. The method for controlling the expected battery life according to claim 1, characterized in that: The calculation process of setting the charging capacity is: First, determine the range of cycles within the charge and discharge cycle of the battery; Then, respectively obtain the control values ​​of the charging amount corresponding to the two end points of the cycle number range of the battery; Finally, using the control values ​​of the charge amount corresponding to the two endpoints, a linear interpolation method is used to determine the control value of the charge amount corresponding to any number of cycles within the cycle number range of the battery; Repeat the above steps until the control value of the charge amount corresponding to each cycle of the battery in the entire charge and discharge cycle is obtained, and the control value of the charge amount is the set charge amount corresponding to each cycle.

5. A method for controlling the expected battery life according to claim 4, characterized in that: The process of determining the range of the number of cycles is as follows: The charging amount of each cycle of the battery operation is regulated according to the battery attenuation rate, so as to obtain the charging amount corresponding to each cycle of the battery operation and the charging amount control table; Obtain the current cumulative charge capacity ETx of the battery; Then, the corresponding accumulated charge amount ETx is searched in the charge amount corresponding to each unit cycle and the charge amount control table, so as to determine the current cycle range of the battery.

6. A method for controlling the expected battery life according to claim 2, characterized in that: The set charging capacity per unit cycle number = the first cycle charging capacity of the battery × (1-the decay rate within the corresponding cycle period).

7. A method for controlling the expected battery life according to claim 1, characterized in that: The set charging amount is controlled to be greater than the actual usage requirement and less than the capacity limit of the battery.

8. A method for controlling the expected battery life according to claim 1, characterized in that: The capacity limit of a battery includes the total charge and discharge capacity and the attenuation rate of the battery during the entire charge and discharge process.

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