CN113189511A - Method for judging aging degree difference of battery cell and battery cell diagnosis system - Google Patents
Method for judging aging degree difference of battery cell and battery cell diagnosis system Download PDFInfo
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/396—Acquisition or processing of data for testing or for monitoring individual cells or groups of cells within a battery
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/389—Measuring internal impedance, internal conductance or related variables
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/392—Determining battery ageing or deterioration, e.g. state of health
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Abstract
The invention discloses a method for judging the difference of the aging degree of two battery cores of a battery pack which are connected in parallel, which comprises the steps of recording the branch current and the terminal voltage of each battery core when the battery pack is in a charging state or a discharging state from a rest state to a balance state, further obtaining the internal resistance of each battery core and the balance open-circuit voltage and the balance residual capacity of the battery pack, and further obtaining the open-circuit voltage and the residual capacity of each battery core at the moment before the battery pack is switched to the rest state; and obtaining the aging degree difference index of the two battery cores according to the residual capacity of each battery core at the moment before the battery pack is switched to the rest state, the branch current of each battery core at the moment after the battery pack is switched to the rest state and the rated capacity of the battery pack, thereby judging the relative aging degree of the two battery cores.
Description
Technical Field
The present invention relates to a method and a system for determining the performance of a battery pack, and more particularly, to a method and a related system for determining the difference in the degree of aging of battery cells connected in parallel.
Background
With the technological progress and social development, electric energy gradually becomes a mainstream energy source, energy storage devices capable of storing electric energy are widely used in different devices, and in order to improve the use flexibility, the most common energy storage device at present is a battery pack formed by a plurality of battery cells in a series or parallel manner, and the battery cells connected in parallel are not completely the same due to manufacturing errors, so that the attenuation degrees (or aging degrees) of the battery cells connected in parallel with each other along with the use time are not the same, and therefore, circulation currents may be generated between the battery cells connected in parallel due to the different aging degrees, and the aging speed of the battery cells and/or the whole battery pack is accelerated.
Disclosure of Invention
Therefore, an object of the present invention is to provide a method for determining a difference in the degree of aging of battery cells connected in parallel to each other of a battery pack and a related battery cell diagnosis system thereof, so as to solve the above-mentioned problems.
In order to achieve the above object, the present invention discloses a method for determining the aging difference of a plurality of battery cells connected in parallel with each other in a battery pack, the method comprises measuring and recording a plurality of branch currents and a plurality of terminal voltages of the plurality of battery cells at different time points when the battery pack goes from a charging state or a discharging state through a rest state to a balance state; obtaining a plurality of internal resistances of the plurality of battery cells according to changes in the plurality of terminal voltages and the plurality of branch currents of the plurality of battery cells between a previous time point and a subsequent time point at which the battery pack is switched from the charge state or the discharge state to the rest state; obtaining a balanced open-circuit voltage of the battery pack according to the terminal voltages of the battery cells when the battery pack is in the balanced state; obtaining the balance residual capacity of the battery pack according to the balance open-circuit voltage; obtaining a relationship of open-circuit voltages of the plurality of battery cells at the previous time point at which the battery pack switches from the charge state or the discharge state to the rest state, according to the internal resistances and the branch currents of the plurality of battery cells at the previous time point at which the battery pack switches from the charge state or the discharge state to the rest state; obtaining a plurality of residual capacities of the plurality of battery cells at the previous time point at which the battery pack was switched from the charge state or the discharge state to the rest state, from the relationship of the plurality of open-circuit voltages of the plurality of battery cells at the previous time point at which the battery pack was switched from the charge state or the discharge state to the rest state; obtaining a difference index of the degree of aging of two corresponding battery cells of the plurality of battery cells from the plurality of residual capacities of the plurality of battery cells at the previous time point at which the battery pack is switched from the charge state or the discharge state to the rest state and the plurality of branch currents of the plurality of battery cells at the subsequent time point at which the battery pack is switched from the charge state or the discharge state to the rest state; and judging the relative aging degree of the two corresponding battery cells of the plurality of battery cells according to the aging degree difference index.
In order to achieve the above object, the present invention further discloses a battery cell diagnosis system capable of determining the aging degree of a plurality of battery cells connected in parallel to each other of a battery pack, comprising a measuring device, an internal resistance calculating device, a first open circuit voltage calculating device, a first residual capacity calculating device, a second open circuit voltage calculating device, a second residual capacity calculating device, an aging degree difference index calculating device, and an aging degree determining device, wherein the measuring device is configured to measure and record a plurality of branch currents and a plurality of terminal voltages of the plurality of battery cells at different time points respectively when the battery pack is switched from a charging state or a discharging state to a balanced state through a rest state, the internal resistance calculating device is configured to determine the changes of the plurality of terminal voltages and the plurality of branch currents between a time point before and a time point after the battery pack is switched from the charging state or the discharging state to the rest state according to the changes of the plurality of terminal voltages and the plurality of terminal voltages of the plurality of terminal voltages, calculating a plurality of internal resistances of the plurality of battery cells, the first open-circuit voltage calculating means calculating a balanced open-circuit voltage of the battery pack based on the terminal voltages of the plurality of battery cells when the battery pack is in the balanced state, the first residual capacity calculating means calculating a balanced residual capacity of the battery pack based on the balanced open-circuit voltage, the second open-circuit voltage calculating means calculating a relationship between the plurality of internal resistances and the branch currents of the plurality of battery cells at the previous time point at which the battery pack is switched from the charge state or the discharge state to the rest state, the second residual capacity calculating means calculating a plurality of open-circuit voltages of the plurality of battery cells at the previous time point at which the battery pack is switched from the charge state or the discharge state to the rest state, the second residual capacity calculating means calculating a relationship between the plurality of open-circuit voltages of the plurality of battery cells at the previous time point at which the battery pack is switched from the charge state or the discharge state The relationship of the open-circuit voltages at the time point before the discharge state is switched to the rest state, a plurality of residual capacities of the battery cells at the time point before the battery pack is switched from the charge state or the discharge state to the rest state are calculated, the degradation degree difference index calculation means calculates a degradation degree difference index of two corresponding battery cells of the battery cells according to the residual capacities of the battery cells at the time point before the battery pack is switched from the charge state or the discharge state to the rest state and the branch currents of the battery cells at the time point after the battery pack is switched from the charge state or the discharge state to the rest state, the degradation degree judgment means judges the two corresponding battery cells of the battery cells according to the degradation degree difference index Relative degree of aging.
In summary, the technical solution provided by the present invention can determine the aging degree difference of the plurality of battery cells connected in parallel to each other of the battery pack, so that a user can find out a battery cell with a larger aging degree from the plurality of battery cells to replace the battery cell without replacing the whole battery pack, thereby reducing the negative effect caused by the excessively large aging degree difference and avoiding unnecessary resource waste.
Drawings
Fig. 1 is a functional block diagram of a battery cell diagnosis system according to a first embodiment of the present invention.
Fig. 2 is a flowchart of a method of determining a difference in the degree of deterioration of a first battery cell and a second battery cell of a battery pack connected in parallel according to the first embodiment of the present invention.
Fig. 3 is a current-time relationship diagram of the battery pack according to the first embodiment of the present invention.
Fig. 4 is a functional block diagram of a battery cell diagnosis system according to a second embodiment of the present invention.
Fig. 5 is a flowchart of a method of determining a difference in the degree of deterioration of a first battery cell and a second battery cell of a battery pack connected in parallel according to a second embodiment of the present invention.
Fig. 6 is a functional block diagram of a battery cell diagnosis system according to a third embodiment of the present invention.
Fig. 7 is a flowchart of a method of determining a difference in the degree of deterioration of a first battery cell and a second battery cell of a battery pack connected in parallel according to a third embodiment of the present invention.
Fig. 8 is a current-time relationship diagram of a battery pack according to a third embodiment of the present invention.
Fig. 9 is a functional block diagram of a battery cell diagnosis system according to a fourth embodiment of the present invention.
Fig. 10 is a flowchart of a method of determining a difference in the degree of deterioration of a first battery cell, a second battery cell, and a third battery cell of a battery pack connected in parallel according to a fourth embodiment of the present invention.
Wherein the reference numerals are as follows:
1A, 1B, 1C, 1D cell diagnostic system
11 measuring device
12 internal resistance calculating device
First open circuit voltage calculating means
First residual Capacity calculating device
Second open circuit voltage calculating device
Second residual capacity calculating means
17 aging degree difference index calculating device
18 aging degree judging device
19 aging degree index calculating device
2A, 2D battery pack
21 first battery cell
22 second battery cell
23 third cell
S1A-S8A, S1B-S9B, S1C-S8C and S1D-S8D
Detailed Description
The terms "coupled" or "connected" as used in the following embodiments include any direct and indirect electrical or structural connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical/structural connection, or through an indirect electrical/structural connection via other devices and connections. In addition, the "charging state" mentioned in the following embodiments means that the voltage source is connected to the battery pack and the battery pack is being charged; "discharged state" indicates that the battery pack is connected to a load source and is providing power to the load source; the "rest state" indicates that the voltage source is no longer charging the battery pack or the battery pack is no longer providing power to the load, and at this time, a circulating current is generated in the battery pack due to the mismatch of the states or physical quantities of the battery cells; the "equilibrium state" indicates that there is no circulating current in the battery pack.
Referring to fig. 1 to 3, fig. 1 is a functional block diagram of a battery cell diagnosis system 1A according to a first embodiment of the present invention, fig. 2 is a flowchart of a method for determining a difference in aging degree between a first battery cell 21 and a second battery cell 22 of a battery pack 2A connected in parallel according to the first embodiment of the present invention, and fig. 3 is a graph of a current-time relationship of the battery pack 2A according to the first embodiment of the present invention. As shown in fig. 1 to 3, the battery cell diagnosis system 1A is configured to connect the battery pack 2A to determine a difference in the degree of aging of the first battery cell 21 and the second battery cell 22, and the battery cell diagnosis system 1A includes a measuring device 11, an internal resistance calculating device 12, a first open-circuit voltage calculating device 13, a first residual capacity calculating device 14, a second open-circuit voltage calculating device 15, a second residual capacity calculating device 16, a degree of aging difference index calculating device 17, and a degree of aging determining device 18. The measuring device 11, the internal resistance calculating device 12, the first open-circuit voltage calculating device 13, the first residual capacity calculating device 14, the second open-circuit voltage calculating device 15, the second residual capacity calculating device 16, the aging degree difference index calculating device 17, and the aging degree judging device 18 may be directly or indirectly coupled to each other to perform transmission of signals, data, and/or power. The measuring device 11 is used for measuring and recording the branch current and the terminal voltage of the first battery cell 21 and the second battery cell 22 at different time points when the battery pack 2A is in a state of rest from a charging state to a balancing state; the internal resistance calculation device 12 calculates the internal resistances of the first battery cell 21 and the second battery cell 22 according to the changes of the terminal voltage and the branch current of the first battery cell 21 and the second battery cell 22 between the previous time point and the next time point when the battery pack 2A is switched from the charging state to the rest state; the first open-circuit voltage calculation means 13 calculates a balanced open-circuit voltage of the battery pack 2A from terminal voltages of the first battery cell 21 and the second battery cell 22 when the battery pack 2A is in a balanced state; the first residual capacity calculation means 14 calculates the balanced residual capacity of the battery pack 2A based on the balanced open-circuit voltage; the second open-circuit voltage calculation device 15 calculates the relationship between the open-circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state, based on the internal resistances of the first battery cell 21 and the second battery cell 22 and the branch currents of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state; the second residual capacity calculation means 16 calculates the residual capacities of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charged state to the rest state, based on the relationship between the open-circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charged state to the rest state and the balance residual capacity of the battery pack 2A; the aging degree difference index calculation device 17 calculates the aging degree difference index of the first battery cell 21 and the second battery cell 22 according to the residual capacity of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state and the branch current of the first battery cell 21 and the second battery cell 22 at the time point after the battery pack 2A is switched from the charging state to the rest state; the aging degree determination device 18 determines the relative aging degree of the first battery cell 21 and the second battery cell 22 based on the aging degree difference index.
As shown in fig. 2, the method of the battery cell diagnosis system 1A for determining the difference in the degree of deterioration of the first battery cell 21 and the second battery cell 22 of the battery pack 2A connected in parallel includes the steps of:
step S1A: when the battery pack 2A goes from the charging state to the equilibrium state through the rest state, the measuring device 11 measures and records the branch current and the terminal voltage of the first battery cell 21 and the second battery cell 22 at different time points;
step S2A: the internal resistance calculation means 12 obtains the internal resistances of the first battery cell 21 and the second battery cell 22 from the changes in the terminal voltage and the branch current between the previous time point and the subsequent time point at which the battery pack 2A is switched from the charging state to the rest state, of the first battery cell 21 and the second battery cell 22;
step S3A: the first open-circuit voltage calculation means 13 obtains the balanced open-circuit voltage of the battery pack 2A from the terminal voltages of the first battery cell 21 and the second battery cell 22 when the battery pack 2A is in the balanced state;
step S4A: the first residual capacity calculation means 14 obtains the balanced residual capacity of the battery pack 2A based on the balanced open-circuit voltage;
step S5A: the second open-circuit voltage calculation means 15 obtains the relationship between the open-circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state, based on the internal resistances of the first battery cell 21 and the second battery cell 22 and the branch currents of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state;
step S6A: the second residual capacity calculation means 16 obtains the residual capacities of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charged state to the rest state, based on the relationship between the open-circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charged state to the rest state and the balance residual capacity of the battery pack 2A;
step S7A: the aging degree difference index calculation device 17 obtains the aging degree difference index of the first battery cell 21 and the second battery cell 22 according to the residual capacity of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state and the branch current of the first battery cell 21 and the second battery cell 22 at the time point after the battery pack 2A is switched from the charging state to the rest state; and
step S8A: the aging degree determination device 18 determines the relative aging degree of the first battery cell 21 and the second battery cell 22 based on the aging degree difference index.
As described below with reference to the above steps, in step S1A, when the user wants to know the difference in the aging degree between the first battery cell 21 and the second battery cell 22 of the battery pack 2A connected in parallel, the battery pack 2A that is being charged may be powered off to switch the battery pack 2A from the charging state to the rest state, and then the battery pack 2A is left standing for a period of time (for example, at least one hour) to switch the battery pack 2A from the rest state to the balance state, and the relationship between the current and the time of the first battery cell 21 and the second battery cell 22 when the battery pack 2A is switched from the charging state to the balance state through the rest state is shown in fig. 3, and in the interval of the first time period T1A, the battery pack 2A is in the charging state, and at this time, the power source charges the first battery cell 21 and the second battery cell 22, respectively; in the interval of the second time period T2A, the battery pack 2A is in the rest state, at this time, the battery pack 2A generates a circulation current, and the branch currents of the first battery cell 21 and the second battery cell 21 are not equal to zero; during the interval of third time period T3A, battery pack 2A is in an equilibrium state, in which battery pack 2A has no circulating current, and the branch currents of first battery pack 21 and second battery pack 22 are equal to zero. During the battery pack 2A is switched from the charging state to the equilibrium state through the rest state, the measuring device 11 measures and records the branch currents and the terminal voltages of the first battery cell 21 and the second battery cell 22 at different time points, for example, as shown in table 1 below, where table 1 illustrates the corresponding relationship between the branch currents and the terminal voltages of the first battery cell 21 and the second battery cell 22 at different time point sequences and states of the battery pack 2A. Preferably, the measuring device 11 can measure and record the branch current and the terminal voltage of the first battery cell 21 and the second battery cell 22 at a specific frequency equal to or greater than 1 hz.
TABLE 1
Next, in step S2A, internal resistance calculation device 12 calculates the internal resistances of first battery cell 21 and second battery cell 22 from the changes in the terminal voltage and the branch current of first battery cell 21 and second battery cell 22 between the time point before and the time point after battery pack 2A is switched from the charged state to the rest state.
Specifically, taking table 1 above of this embodiment as an example, the branch current and the terminal voltage of the first battery cell 21 at the previous time point when the battery pack 2A is switched from the charging state to the rest state are 1.507 ampere and 3.987 volts, respectively; the branch current and the terminal voltage of the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state are 1.493 amperes and 3.969 volts, respectively; the branch current and terminal voltage of the first battery cell 21 at the later time point when the battery pack 2A is switched from the charging state to the rest state are-0.173 ampere and 3.893 volt, respectively; the branch current and the terminal voltage of the second battery cell 22 at the later time point when the battery pack 2A is switched from the charging state to the rest state are 0.173 ampere and 3.890 volt, respectively. Therefore, the internal resistance calculation means 12 can find that the difference of the terminal voltage of the first battery cell 21 at the previous time point and the latter time point at which the battery pack 2A is switched from the charged state to the rest state is 0.094 volts; the difference between the branch currents of the first battery cell 21 at the time point before and after the battery pack 2A is switched from the charging state to the rest state is 1.680 amperes; the difference between the terminal voltages of the second battery cell 22 at the time point before and after the battery pack 2A is switched from the charging state to the rest state is 0.079 volts; the difference between the branch currents of the second battery cell 22 at the time point before and after the battery pack 2A is switched from the charging state to the rest state is 1.320 amperes, and then the internal resistance calculation device 12 divides the difference between the terminal voltages of the first battery cell 21 at the time point before and after the battery pack 2A is switched from the charging state to the rest state by the difference between the branch currents of the first battery cell 21 at the time point before and after the battery pack 2A is switched from the charging state to the rest state, so as to obtain that the internal resistance of the first battery cell 21 is about 0.056 ohm; and the difference of the terminal voltage of the second cell 22 at the time point before and after the battery pack 2A is switched from the charged state to the rest state is divided by the difference of the branch current of the second cell 22 at the time point before and after the battery pack 2A is switched from the charged state to the rest state to obtain that the internal resistance of the second cell 22 is about 0.060 ohm.
In step S3A, first open circuit voltage calculation means 13 calculates the balanced open circuit voltage of battery pack 2A from the terminal voltages of first battery cell 21 and second battery cell 22 when battery pack 2A is in the balanced state. Specifically, taking the above table 1 of this embodiment as an example, when the battery pack 2A is in the balanced state, the terminal voltages of the first battery cell 21 and the second battery cell 22 are equal to each other and are 3.872 volts, and the branch currents of the first battery cell 21 and the second battery cell 22 are zero, so the first open-circuit voltage calculating device 13 can determine the balanced open-circuit voltage of the battery pack 2A according to the terminal voltages of the first battery cell 21 and the second battery cell 22 when the battery pack 2A is in the balanced state, that is, the balanced open-circuit voltage of the battery pack 2A is 3.872 volts.
In step S4A, the first residual capacity calculation means 14 calculates the balanced residual capacity of the battery pack 2A from the balanced open circuit voltage. Specifically, in this embodiment, the first residual capacity calculation means 14 may bring the balanced open circuit voltage of the battery pack 2A into a pre-established lookup table or a relationship function to find the balanced residual capacity of the battery pack 2A to be 49.8%.
In steps S5A and S6A, the second open-circuit voltage calculation device 15 calculates the relationship between the open-circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charged state to the rest state, based on the internal resistances of the first battery cell 21 and the second battery cell 22 and the branch currents of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charged state to the rest state; the second residual capacity calculation means 16 calculates the residual capacities of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charged state to the rest state, based on the relationship between the open circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charged state to the rest state and the balance residual capacity of the battery pack 2A. Specifically, the second open-circuit voltage calculation means 15 may bring the internal resistances of the first battery cell 21 and the second battery cell 22 and the branch currents of the first battery cell 21 and the second battery cell 22 at a time point before the battery pack 2A is switched from the charge state to the rest state into the terminal voltage equation (as shown in equation 1 below) to obtain the relationship between the open-circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charge state to the rest state, and then the second residual capacity calculation means 16 may perform the false value setting on the open-circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charge state to the rest state based on the relationship between the open-circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charge state to the rest state, and the corresponding residual capacities are brought into a residual capacity equation (as shown in equation 2 below) for verification, if the residual capacities of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state cannot satisfy the residual capacity equation, it indicates that the assumed values of the open-circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state are incorrect, and the assumed values need to be reset until the residual capacities of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state satisfy the residual capacity equation, so as to obtain correct open-circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state.
U1+I1R1＝U2+I2R2.. equation 1
Wherein U is1、U2A first battery cell 21 and a second battery cellAn open circuit voltage of cell core 22 at a time point before battery pack 2A is switched from the charging state to the rest state; i is1、I2Branch currents of the first battery cell 21 and the second battery cell 22 at a time point before the battery pack 2A is switched from the charging state to the rest state, respectively; r1、R2Internal resistances of the first cell 21 and the second cell 22, respectively; SoC (system on chip)bIs the equilibrium residual capacity of the battery pack 2A; SoC (system on chip)1、SoC2The residual capacities of the first battery cell 21 and the second battery cell 22 at the previous time point when the battery pack 2A is switched from the charging state to the rest state, respectively.
More specifically, in the recursive manner, the second residual capacity calculating device 16 may determine that the open circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state are 3.874 volts and 3.869 volts, respectively, and the residual capacities of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state are 50.2% and 49.4%, respectively.
In steps S7A, S8A, the aging degree difference index calculation means 17 calculates the aging degree difference index of the first battery cell 21 and the second battery cell 22 based on the residual capacity of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charged state to the rest state and the branch currents of the first battery cell 21 and the second battery cell 22 at the time point after the battery pack 2A is switched from the charged state to the rest state; the aging degree determination device 18 determines the relative aging degree of the first battery cell 21 and the second battery cell 22 based on the aging degree difference index. Specifically, in this embodiment, the aging degree difference index calculation means 17 may bring the residual capacities of the first and second battery cells 21 and 22 at the time point before the battery pack 2A is switched from the charged state to the rest state, the branch currents of the first and second battery cells 21 and 22 at the time point after the battery pack 2A is switched from the charged state to the rest state, and the rated capacity of the battery pack 2A into an aging degree difference index quantitative equation (the following equation 3) to obtain the aging degree difference index; wherein the deterioration degree judgment means 18 may judge that the first deterioration degree of the first battery cell 21 is equal to the second deterioration degree of the second battery cell 22 when the deterioration degree difference index is equal to zero; when the age difference index is less than zero, the age determination device 18 may determine that the first age of the first battery cell 21 is less than the second age of the second battery cell 22; when the age difference index is greater than zero, the age determination device 18 may determine that the first age of the first battery cell 21 is greater than the second age of the second battery cell 22.
Wherein alpha is12Is an aging degree difference index; SoC (system on chip)1、SoC2Residual capacities of the first battery cell 21 and the second battery cell 22 at a time point before the battery pack 2A is switched from the charging state to the rest state, respectively; mu is a constant; i isnThe unit of the branch current of each battery cell at the later time point of switching from the charging state to the rest state is ampere.
Mu will adjust alpha according to the state of charge or discharge of the battery12When the battery is switched from a charging state to a rest state, mu is-1, and when the battery is switched from a discharging state to the rest state, mu is + 1. In this embodiment, μ is-1, the aging degree difference index calculation means 17 brings the residual capacity of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the charging state to the rest state and the branch current of the first battery cell 21 and the second battery cell 22 at the time point after the battery pack 2A is switched from the charging state to the rest state into the aging degree difference index quantitative equation (equation 3), to obtain the aging degree difference index of-2.312%, whereby the aging degree determination means 18 can determine that the first aging degree of the first battery cell 21 is smaller than the second battery cell 22, and the user can reasonably replace the second battery cell 22 according to the determination result of the aging degree determination means 18.
In addition, it should be noted that, in practice, the measuring device may collect the terminal voltage and the branch current of each battery cell by means of specific frequency measurement, and define the previous sampling time point and the next sampling time point at which the voltage source stops supplying power to the battery pack as the previous time point and the next time point of the rest state. Taking this embodiment as an example, the measuring device 11 measures and records the branch current and terminal voltage of the first battery cell 21 and the second battery cell 22 at a specific frequency equal to 1 hz for a long time, so that the branch current and terminal voltage of the first battery cell 21 and the second battery cell 22 at a time point before the battery pack 2A is switched from the charging state to the rest state can be the last group of branch current and terminal voltage (i.e. the branch current and terminal voltage corresponding to the time point sequence of 2) measured by the battery pack 2A shown in table 1 before the voltage source is removed, the branch current and terminal voltage of the first battery cell 21 and the second battery cell 22 at a time point after the battery pack 2A is switched from the charging state to the rest state and can be the first group of branch current and terminal voltage (i.e. the branch current and terminal voltage corresponding to the time point sequence of 3) measured by the battery pack 2A shown in table 1 after the voltage source is removed, the terminal voltages of the first battery cell 21 and the second battery cell 22 when the battery pack 2A is in the equilibrium state may be the terminal voltages measured after the loop current in the battery pack 2A disappears (i.e. the branch current and the terminal voltage corresponding to the sequence of time points 3600), but the present invention is not limited thereto, and the measuring device may measure the branch current and the terminal voltage of each battery cell only at the following three time points: before the voltage source is removed (i.e. the point in time before the battery is in the rest state), after the voltage source is removed (the point in time after the battery is in the rest state, after the battery has been left to stand for at least hours (the point in time when the battery is in the equilibrium state).
Referring to fig. 4 and 5, fig. 4 is a functional block diagram of a battery cell diagnosis system 1B according to a second embodiment of the present invention, and fig. 5 is a flowchart of a method for determining a difference in aging degree of a first battery cell 21 and a second battery cell 22 of a battery pack 2A connected in parallel according to the second embodiment of the present invention. As shown in fig. 4 and fig. 5, the battery cell diagnosis system 1B of this embodiment includes a measuring device 11, an internal resistance calculating device 12, a first open-circuit voltage calculating device 13, a first residual capacity calculating device 14, a second open-circuit voltage calculating device 15, a second residual capacity calculating device 16, an aging degree difference index calculating device 17, and an aging degree determining device 18, and the structure, operation, and method flow steps S1B to S8B of the above components of this embodiment are similar to those of the first embodiment, and will not be described again. Unlike the first embodiment, the battery cell diagnosis system 1B of the present embodiment further includes an aging degree index calculation device 19 that calculates a second aging degree index of the second battery cell 22 according to the aging degree difference index and the first aging degree index of the first battery cell 21. That is, in this embodiment, when the first age index of the first battery cell 21 is known, the battery cell diagnosis system 1B may further calculate the second age index of the second battery cell 22 based on the age difference index and the first age index of the first battery cell 21 (as shown in step S9B in fig. 5). In another embodiment, when the second aging degree index of the second battery cell 22 is known, the battery cell diagnosis system may calculate the first aging degree index of the first battery cell 21 according to the aging degree difference index and the second aging degree index of the second battery cell 22.
Specifically, in this embodiment, if the first battery cell 21 is a brand-new battery cell, the first aging degree index of the first battery cell 21 is known as 100%, and the second aging degree index of the second battery cell 22 can be calculated by substituting the aging degree difference index and the first aging degree index of the first battery cell 21 into an aging degree index equation (as shown in equation 4 below).
SoH2＝SoH1+α12Equation 4
In which SoH1A first age index of the first battery cell 21; SoH2A second aging degree index of the second battery cell 22; alpha is alpha12Is an aging degree difference index; beta is a constant.
Beta will vary from one type of battery to another. In the present embodiment, β is 16.220, and the aging degree difference index and the first aging degree index of the first battery cell 21 are substituted into the aging degree index equation to obtain a second aging degree index of the second battery cell 22 of 62.5%.
In addition, the constants β, μ of this embodiment can be obtained in advance from two battery cells of which the aging degree index is known.
Referring to fig. 6 to 8, fig. 6 is a functional block diagram of a battery cell diagnosis system 1C according to a third embodiment of the present invention, fig. 7 is a flowchart of a method for determining a difference in aging degree between a first battery cell 21 and a second battery cell 22 of a battery pack 2A connected in parallel according to the third embodiment of the present invention, and fig. 8 is a current-time relationship diagram of the battery pack 2A according to the third embodiment of the present invention. As shown in fig. 6 to 8, the battery cell diagnosis system 1C of the present embodiment and the battery cell diagnosis system 1A of the first embodiment include similar components, but the measuring device 11 of the present embodiment is configured to measure and record the branch current and the terminal voltage of the first battery cell 21 and the second battery cell 22 at different time points when the battery pack 2A goes from the discharging state to the equilibrium state through the rest state, wherein the relation between the current and the time when the first battery cell 21 and the second battery cell 22 switch from the discharging state to the equilibrium state through the rest state is shown in fig. 8, the battery pack 2A is in the discharging state during the interval of the first time period T1C, and at this time, the first battery cell 21 and the second battery cell 22 respectively provide power to the load source; in the interval of the second time period T2C, the battery pack 2A is in the rest state, at this time, the battery pack 2A generates a circulation current, and the branch currents of the first battery cell 21 and the second battery cell 21 are not equal to zero; during the interval of third time period T3C, battery pack 2A is in an equilibrium state, where battery pack 2A has no circulating current and the branch currents of first battery pack 21 and second battery pack 22 are equal to zero; the internal resistance calculation device 12 calculates the internal resistances of the first battery cell 21 and the second battery cell 22 according to the changes of the terminal voltage and the branch current of the first battery cell 21 and the second battery cell 22 between the previous time point and the next time point at which the battery pack 2A is switched from the discharge state to the rest state; the first open-circuit voltage calculation means 13 calculates a balanced open-circuit voltage of the battery pack 2A from terminal voltages of the first battery cell 21 and the second battery cell 22 when the battery pack 2A is in a balanced state; the first residual capacity calculation means 14 calculates the balanced residual capacity of the battery pack 2A based on the balanced open-circuit voltage; the second open-circuit voltage calculation device 15 calculates the relationship between the open-circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the discharge state to the rest state, based on the internal resistances of the first battery cell 21 and the second battery cell 22 and the branch currents of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the discharge state to the rest state; the second residual capacity calculation means 16 calculates the residual capacity of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the discharge state to the rest state, based on the relationship between the open-circuit voltages of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the discharge state to the rest state and the balance residual capacity of the battery pack 2A; the aging degree difference index calculation device 17 calculates the aging degree difference index of the first battery cell 21 and the second battery cell 22 according to the residual capacity of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2A is switched from the discharge state to the rest state and the branch current of the first battery cell 21 and the second battery cell 22 at the time point after the battery pack 2A is switched from the discharge state to the rest state; the aging degree determination device 18 determines the relative aging degree of the first battery cell 21 and the second battery cell 22 based on the aging degree difference index. That is, the battery cell diagnosis system 1A of the first embodiment determines the relationship between the first aging degree of the first battery cell 21 and the second aging degree of the second battery cell 22 by the parameters obtained when the battery pack 2A is switched from the charge state to the equilibrium state through the rest state, but the battery cell diagnosis system 1C of this embodiment determines the relationship between the first aging degree of the first battery cell 21 and the second aging degree of the second battery cell 22 by the parameters obtained when the battery pack 2A is switched from the discharge state to the equilibrium state through the rest state (as shown in table 2 below), so μ of this embodiment is 1, and the remaining method flow steps and equations of this embodiment are similar to those of the first embodiment, and will not be described herein again.
TABLE 2
Referring to fig. 9 and 10, fig. 9 is a functional block diagram of a battery cell diagnosis system 1D according to a fourth embodiment of the present invention, and fig. 10 is a flowchart of a method for determining a difference in aging degree of a first battery cell 21, a second battery cell 22, and a third battery cell 23 of a battery pack 2D according to the fourth embodiment of the present invention. As shown in fig. 9 and 10, the battery cell diagnosis system 1D of the present embodiment and the battery cell diagnosis system 1A of the first embodiment include similar components, and the battery cell diagnosis system 1D determines the relationship between the first aging degree of the first battery cell 21, the second aging degree of the second battery cell 22, and the third aging degree of the third battery cell 23 by using the parameters (as shown in table 3 below) obtained when the battery pack 2D is switched from the charge state to the equilibrium state through the rest state.
TABLE 3
In addition, since the battery pack 2D of this embodiment includes the first battery cell 21, the second battery cell 22 and the third battery cell 23, and the battery pack 2A of the first embodiment includes only the first battery cell 21 and the second battery cell 22, equations 1, 2 and 3 of the first embodiment are modified correspondingly to include equations 5 and 6, equation 7 and another equation including equations 8, 9 and 10, respectively, below.
U1+I1R1＝U2+I2R2.. equation 5
U2+I2R2＝U3+I3R3.. equation 6
Wherein U is1、U2、U3Open circuit voltages of the first battery cell 21, the second battery cell 22, and the third battery cell 23 at a previous time point when the battery pack 2D is switched from the charging state to the rest state, respectively; i is1、I2、I3A branch current divided into the first battery cell 21, the second battery cell 22, and the third battery cell 23 at a time point before the battery pack 2D is switched from the charging state to the rest state; r1、R2、R3Internal resistances of the first cell 21, the second cell 22, and the third cell 23, respectively; SoC (system on chip)bThe equilibrium residual capacity of the battery pack 2D; SoC (system on chip)1、SoC2、SoC3Residual capacities of the first battery cell 21, the second battery cell 22, and the third battery cell 23 at a time point before the battery pack 2D is switched from the charging state to the rest state, respectively; alpha is alpha12、α13、α23The aging degree difference index of the first battery cell 21 and the second battery cell 22, the aging degree difference index of the first battery cell 21 and the third battery cell 23, and the aging degree difference index of the second battery cell 22 and the third battery cell 23 are respectively; mu is a constant; i isnThe unit of the branch current of each battery cell at the later time point of switching from the charging state to the rest state is ampere.
Similarly to the first embodiment, the second residual capacity calculating device 16 of this embodiment also obtains the open circuit voltages of the first battery cell 21, the second battery cell 22 and the third battery cell 23 at the previous time point when the battery pack 2D is switched from the charging state to the rest state as 3.8756 volts, 3.8704 volts and 3.8673 volts respectively, and the residual capacities of the first battery cell 21, the second battery cell 22 and the third battery cell 23 at the previous time point when the battery pack 2D is switched from the charging state to the rest state as 50.5%, 49.7% and 49.1% respectively, in a similar recursive manner. In this embodiment, where μ is-1, the degradation degree difference index calculation means 17 may bring the residual capacity of the first battery cell 21 and the second battery cell 22 at the time point before the battery pack 2D is switched from the charging state to the rest state and the branch currents of the first battery cell 21 and the second battery cell 22 at the time point after the battery pack 2D is switched from the charging state to the rest state into equation 8, so as to obtain a degradation degree difference index of-9.302% for the first battery cell 21 and the second battery cell 22; the residual capacities of the first battery cell 21 and the third battery cell 23 at a time point before the battery pack 2D is switched from the charge state to the rest state and the branch currents of the first battery cell 21 and the third battery cell 23 at a time point after the battery pack 2D is switched from the charge state to the rest state are substituted into equation 9, and the aging degree difference index of the first battery cell 21 and the third battery cell 23 is-16.279%; the residual capacity of the second battery cell 22 and the third battery cell 23 at the time point before the battery pack 2D is switched from the charging state to the rest state and the branch currents of the second battery cell 22 and the third battery cell 23 at the time point after the battery pack 2D is switched from the charging state to the rest state are introduced into equation 10, and the difference index of the aging degrees of the second battery cell 22 and the third battery cell 23 is-6.977%, so that the aging degree determination device 18 of this embodiment can determine that the first aging degree of the first battery cell 21 is smaller than the second aging degree of the second battery cell 22 and smaller than the third aging degree of the third battery cell 23, the second aging degree of the second battery cell 22 is smaller than the third aging degree of the third battery cell 23, and the second aging degree of the second battery cell 22 is closer to the third aging degree of the third battery cell 23, and the user can reasonably replace the second battery cell 22 and the third battery cell 23 according to the determination result of the aging degree determination device 18. In addition, if the degradation degree of any one of the first battery cell, the second battery cell and the third battery cell is known, the degradation degree of the other two battery cells of the first battery cell, the second battery cell and the third battery cell can be calculated by equation 4 in the first embodiment.
It should be noted that the present invention is not limited to the above applications, for example, as electric vehicles become popular, the number of obsolete batteries rapidly increases, and obsolete batteries after several years of use still have other application values although they cannot meet the requirements of driving vehicles, but the present invention helps users to know the aging degree of the obsolete batteries relative to each other, so as to allow the batteries matched with each other (i.e. batteries with similar aging degree) to be selected from the obsolete batteries for reuse or reuse (e.g. applied to energy storage systems), thereby reducing pollution and cost of waste disposal.
In the present invention, the battery core diagnosis system may be implemented in software, firmware, hardware or a combination thereof, for example, the battery core diagnosis system may be a computer device including a processor and a computer readable recording medium storing a program, and the processor may execute the corresponding program to implement the above functions, where the processor may be a Central Processing Unit (CPU), an application processor (application processor) or a microprocessor (microprocessor), and the like, or may be implemented by an Application Specific Integrated Circuit (ASIC), and the computer readable recording medium may be a read-only memory (ROM), a random-access memory (RAM), a Compact Disc (CDROM), a magnetic tape (magnetic tape), a floppy disk (floppy disk), a hard disk (hard disk), or an optical storage device (optical storage device), and the present invention is not limited thereto.
Compared with the prior art, the technical scheme provided by the invention can judge the aging degree difference of the plurality of battery cores of the battery pack which are connected in parallel, so that a user can find out the battery core with higher aging degree from the plurality of battery cores to replace the battery core without replacing the whole battery pack, thereby reducing the negative influence caused by the overlarge aging degree difference and avoiding unnecessary resource waste.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A method for determining a difference in aging degree between a plurality of battery cells connected in parallel to each other in a battery pack, the method comprising:
measuring and recording a plurality of branch currents and a plurality of terminal voltages of the plurality of battery cores at different time points when the battery pack is in a state of equilibrium from a charging state or a discharging state through a rest state;
obtaining a plurality of internal resistances of the plurality of battery cells according to changes in the plurality of terminal voltages and the plurality of branch currents of the plurality of battery cells between a previous time point and a subsequent time point at which the battery pack is switched from the charge state or the discharge state to the rest state;
obtaining a balanced open-circuit voltage of the battery pack according to the terminal voltages of the battery cells when the battery pack is in the balanced state;
obtaining the balance residual capacity of the battery pack according to the balance open-circuit voltage;
obtaining a relationship of open-circuit voltages of the plurality of battery cells at the previous time point at which the battery pack switches from the charge state or the discharge state to the rest state, according to the internal resistances and the branch currents of the plurality of battery cells at the previous time point at which the battery pack switches from the charge state or the discharge state to the rest state;
obtaining a plurality of residual capacities of the plurality of battery cells at the previous time point at which the battery pack was switched from the charged state or the discharged state to the rest state, based on the relationship of the plurality of open-circuit voltages of the plurality of battery cells at the previous time point at which the battery pack was switched from the charged state or the discharged state to the rest state and the balance residual capacities;
obtaining a difference index of the degree of aging of two corresponding battery cells of the plurality of battery cells from the plurality of residual capacities of the plurality of battery cells at the previous time point at which the battery pack is switched from the charge state or the discharge state to the rest state and the plurality of branch currents of the plurality of battery cells at the subsequent time point at which the battery pack is switched from the charge state or the discharge state to the rest state; and
and judging the relative aging degrees of the two corresponding battery cells of the plurality of battery cells according to the aging degree difference index.
2. The method of claim 1, wherein measuring and recording the branch currents and the terminal voltages of the battery cells at different time points respectively as the battery pack goes from the charging state or the discharging state to the equilibrium state through the rest state comprises:
measuring and recording the branch currents and the terminal voltages of the battery cells at a specific frequency when the battery pack passes from the charging state or the discharging state to the equilibrium state through the rest state.
3. The method of claim 2, wherein the particular frequency is equal to or greater than 1 hertz.
4. The method of claim 1, wherein the method further comprises:
and obtaining a second aging degree index of a second battery cell of the two corresponding battery cells of the plurality of battery cells according to the aging degree difference index and the first aging degree index of the first battery cell of the two corresponding battery cells of the plurality of battery cells.
5. The method of claim 1, wherein when the age difference index equals zero, a first aging degree of a first battery cell of the two corresponding battery cells of the plurality of battery cells is equal to a second aging degree of a second battery cell of the two corresponding battery cells of the plurality of battery cells, when the age difference index is less than zero, the first age of the first of the two corresponding battery cells of the plurality of battery cells is less than the second age of the second of the two corresponding battery cells of the plurality of battery cells, when the age difference index is greater than zero, the first age of the first of the two corresponding cells of the plurality of cells is greater than the second age of the second of the two corresponding cells of the plurality of cells.
6. A battery cell diagnosis system that can determine a difference in the degree of deterioration of a plurality of battery cells of a battery pack connected in parallel with each other, the battery cell diagnosis system comprising:
the measuring device is used for respectively measuring and recording a plurality of branch currents and a plurality of terminal voltages of the plurality of battery cores at different time points when the battery pack is in a state of balance from a charging state or a discharging state through a rest state;
internal resistance calculation means that calculates a plurality of internal resistances of the plurality of battery cells from changes in the plurality of terminal voltages and the plurality of branch currents of the plurality of battery cells between a previous time point and a subsequent time point at which the battery pack is switched from the charge state or the discharge state to the rest state;
first open circuit voltage calculation means for calculating a balanced open circuit voltage of the battery pack from the terminal voltages of the battery cells when the battery pack is in the balanced state;
a first residual capacity calculation device that calculates a balanced residual capacity of the battery pack based on the balanced open-circuit voltage;
second open-circuit voltage calculation means that calculates a relationship of open-circuit voltages of the plurality of battery cells at the previous time point at which the battery pack switches from the charge state or the discharge state to the rest state, from the plurality of internal resistances and the plurality of branch currents of the plurality of battery cells at the previous time point at which the battery pack switches from the charge state or the discharge state to the rest state;
second residual capacity calculation means for calculating a plurality of residual capacities of the plurality of battery cells at the previous time point at which the battery pack was switched from the charged state or the discharged state to the rest state, based on the relationship of the plurality of open circuit voltages of the plurality of battery cells at the previous time point at which the battery pack was switched from the charged state or the discharged state to the rest state and the equilibrium residual capacity;
an aging degree difference index calculation device that calculates an aging degree difference index of two corresponding battery cells of the plurality of battery cells, based on the plurality of residual capacities of the plurality of battery cells at the previous time point at which the battery pack switches from the charge state or the discharge state to the rest state and the plurality of branch currents of the plurality of battery cells at the subsequent time point at which the battery pack switches from the charge state or the discharge state to the rest state; and
and the aging degree judging device judges the relative aging degree of the two corresponding battery cells of the plurality of battery cells according to the aging degree difference index.
7. The battery cell diagnostic system according to claim 6, wherein the measuring device measures and records the branch currents and the terminal voltages of the battery cells at a specific frequency when the battery pack passes from the charge state or the discharge state to the equilibrium state through the rest state.
8. The battery cell diagnostic system of claim 7, wherein the particular frequency is equal to or greater than 1 hertz.
9. The battery cell diagnostic system of claim 6, further comprising:
and the aging degree index calculation device calculates a second aging degree index of a second battery cell of the two corresponding battery cells according to the aging degree difference index and a first aging degree index of a first battery cell of the two corresponding battery cells of the plurality of battery cells.
10. The battery cell diagnostic system of claim 6, wherein when the age difference index equals zero, a first aging degree of a first battery cell of the two corresponding battery cells of the plurality of battery cells is equal to a second aging degree of a second battery cell of the two corresponding battery cells of the plurality of battery cells, when the age difference index is less than zero, the first age of the first of the two corresponding battery cells of the plurality of battery cells is less than the second age of the second of the two corresponding battery cells of the plurality of battery cells, when the age difference index is greater than zero, the first age of the first of the two corresponding cells of the plurality of cells is greater than the second age of the second of the two corresponding cells of the plurality of cells.
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