CN103389465A - Method for measuring electric quantity of battery - Google Patents

Abstract

The invention discloses a method for measuring electric quantity of a battery, which is suitable for a battery structure and comprises a three-element unit battery and at least one lithium-iron unit battery. The electric quantity measuring method firstly measures the voltage or the current of the three-element unit battery to calculate the residual electric quantity of the three-element unit battery, and then calculates the current residual electric quantity of the battery structure according to the residual electric quantity of the three-element unit battery.

Description

How to measure battery capacity

technical field

The invention relates to a battery structure and a power measurement method, in particular to a battery structure combined with a three-element unit battery and a power measurement method for obtaining the power of the whole battery structure by measuring the power of the three-element unit battery.

Background technique

Lithium-ion batteries are the main force for battery development. Lithium-ion batteries are the first choice in terms of energy density, energy efficiency, cycle life, charging time and safety. In order to maximize the performance of the battery and prolong the service life of the battery, a battery management system must be installed for detection. The main purpose of the battery management system is to obtain battery status information, performance adjustment and external protection of the battery. Among them, the battery is the most relevant to the user. Estimation of remaining power. The remaining power of the battery is called State Of Charge (SOC). The battery in an electric vehicle is equivalent to the fuel tank of a gasoline vehicle, and the residual power is equivalent to the amount of fuel. Therefore, it is especially important for customers to evaluate the remaining power. The residual capacity estimation methods in the prior art include:

(1) When the vehicle is running, use current measurement integration - use a coulomb meter to measure the current and integrate it to calculate the cumulative power consumption. (2) When the vehicle is stationary, or when the battery structure is measured separately, the open circuit voltage method (Open circuit voltage, OCV)-the measurement voltage source is analyzed through the open circuit voltage curve.

However, when the above-mentioned open-circuit voltage method is applied to a lithium-iron unit battery, there will be the following problems: (1) The open-circuit voltage curve of the lithium-iron unit battery is relatively gentle, and if the voltage value is directly measured, it may cause interpretation errors. (2) After the lithium-iron unit battery passes the cut-off voltage of charge and discharge, its voltage will continue to drift, so it is impossible to directly measure the battery terminal voltage as the judgment of the residual capacity.

Therefore, how to provide a more accurate battery power measurement mode should be considered.

Contents of the invention

The problem to be solved by the present invention is to provide a power measurement method combined with a three-element unit battery.

In order to solve the above-mentioned problem, the present invention discloses a battery power measurement method, which is applied to measure the residual power of a battery structure. The battery structure includes a three-element unit battery and at least one lithium-iron unit battery. It is characterized in that the method includes: measuring the voltage or current of the three-element unit cell to calculate the residual capacity of the three-element unit cell; and obtain the current residual capacity of the battery structure according to the residual capacity of the three-element unit cell.

In one embodiment, the three-element unit battery and at least one lithium-iron unit battery included in the battery structure are connected in series, and the current voltage value of the three-element unit battery is compared with the known minimum voltage value to calculate the three-element unit battery. The residual capacity of the element unit battery.

The feature of the present invention is that the battery structure of the present invention includes a three-element unit battery and a lithium-iron unit battery, wherein the open-circuit voltage curve of the three-element unit battery has a larger slope, and the curve change is more definite than that of a lithium-iron unit battery, and the current output It is also more stable, so it can be used as a basis for judging changes in power regardless of charging or discharging. In addition, the output voltage or output current of the three-element unit battery will not fluctuate excessively after the charge-discharge cut-off voltage, so it can be directly used as the judgment of the remaining capacity.

Description of drawings

Fig. 1A, Fig. 1B, Fig. 1C, Fig. 1D and Fig. 1E show schematic diagrams of battery series configuration of the battery structure of the embodiment of the present invention;

FIG. 2 shows a schematic diagram of another battery series connection structure according to an embodiment of the present invention;

Fig. 3 shows the flow chart of the electric quantity measurement method of the embodiment of the present invention;

FIG. 4 shows a flow chart of a battery failure determination method according to an embodiment of the present invention;

FIG. 5 shows a detailed flow chart of a method for judging a battery fault in a series connection according to an embodiment of the present invention;

Fig. 6 shows the schematic diagram of the open-circuit voltage curve of the three-element unit battery and the lithium-iron unit battery of the present invention;

Figure 7 shows a schematic diagram of the discharge curves of the three-element unit battery and the lithium-iron unit battery of the present invention; and

Fig. 8 shows a schematic diagram of the overall battery structure and the discharge curve of the lithium-iron unit battery of the present invention.

[Description of main component symbols]

10a, 10b, 10c, 10d, 10e battery structure

11 Three-element unit battery

12 Lithium iron unit battery

13 Power measurement unit

14 Display unit

15 Charging unit

T1 The first period

T2 Second Period

T3 The third period

T4 The fourth period

Steps S110-120

Steps S210-230

Detailed ways

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

First, please refer to FIG. 1A , FIG. 1B , FIG. 1C , FIG. 1D and FIG. 1E , which illustrate a schematic diagram of a battery series configuration of a battery structure according to an embodiment of the present invention.

The battery structure includes a three-element unit battery 11 and more than one lithium-iron unit battery 12. From FIG. 1A to FIG. A series connection is formed, and the arrangement order of the three-element unit cells 11 is not limited.

For example, the battery structure 10a and the battery structure 10b each have a three-element unit battery 11 and a lithium-iron unit battery 12, the order of the two is not limited, the three-element unit battery 11 can be arranged first, and then the lithium-iron unit battery 12 can be connected in series. Alternatively, the lithium-iron unit cells 12 are arranged first, and then the three-element unit cells 11 are connected in series.

In another example, the battery structure 10c, the battery structure 10d and the battery structure 10e each have a three-element unit cell 11 and more than two lithium-iron unit cells 12, and the three-element unit cell 11 and the lithium-iron unit cell 12 are connected in series. The three-element unit cells 11 are connected in series at the front ends of all the lithium-iron unit cells 12 , between any two lithium-iron unit cells 12 or at the rear ends of all the lithium-iron unit cells 12 .

Among them, the ratio of the residual power to the total power of the three-element unit battery 11 and the ratio of the residual power to the total power of each lithium-iron unit battery 12 (hereinafter referred to as the ratio of the residual power) need to be equal or very similar, so as to avoid the The difference in the proportion of residual power between different batteries is too large, which will cause the power supply burden of some batteries to be too large, thereby shortening the battery life, or causing battery damage. Secondly, the chemical composition contained in the three-element unit battery 11 is selected from the group consisting of nickel, cobalt, manganese and lithium, further, it can be a compound of nickel, cobalt, manganese and lithium, such as lithium cobaltate (LiCoO ₂ ), manganese Lithium Oxide (LiMn2O ₄ ) or Lithium Iron Phosphate (LiFePO ₄ ).

Please refer to FIG. 2 , which is a schematic diagram of another battery structure series connection according to an embodiment of the present invention. The battery structure 10 a further includes a power measuring unit 13 , a display unit 14 and a charging unit 15 . This embodiment can be implemented in any battery structure of battery arrangement in FIG. 1A to FIG. 1E , and the following embodiments will be described with the battery structure 10a, but not limited thereto.

The power measuring unit 13 is electrically connected to the three-element unit battery 11 for measuring the residual capacity of the three-element unit battery 11 . Wherein, the residual capacity ratio of the three-element unit battery 11 is equal to or greater than that of other lithium-iron unit batteries 12, and is also equal to or greater than the residual capacity ratio of the entire battery structure 10a, so the user can use the three-element unit battery 11 The power ratio is regarded as the remaining power ratio of the battery structure 10a.

The display unit 14 is electrically connected to the power measurement unit 13 for displaying the remaining power of the three-element unit battery 11 . Wherein, the display unit 14 can be a general display, a liquid crystal display, a diode structure display or other display elements that can be used to present power information.

The charging unit 15 is electrically connected to the electrodes of the entire battery structure 10 a for charging the three-element unit cells 11 and the lithium-iron unit cells 12 connected in series. The charging unit 15 and its related technologies are well known to those of ordinary skill in the technical field of the present invention, and will not be repeated here.

Please refer to FIG. 3 , which shows the flow chart of the power measurement method according to the embodiment of the present invention, and please refer to FIG. 2 at the same time for easy understanding. This method is applied to measure the power of a battery structure 10 a, which includes a three-element unit cell 11 and more than one Li-Fe unit cell 12 . This method is described as follows:

Measure the voltage or current of the three-element unit battery to calculate the residual capacity of the three-element unit battery (step S110 ). As mentioned above, the power measuring unit 13 is electrically connected to the three-element unit battery 11 to measure the residual capacity of the three-element unit battery 11 . There are two main ways to estimate the residual capacity of the battery, one is the open circuit voltage measurement method, and the other is the Coulomb integration method. The open-circuit voltage measurement method is based on the voltage of the three-element unit battery 11, and compares the current voltage value of the three-element unit battery 11 with the known minimum voltage value to calculate the remaining capacity of the three-element unit battery 11. The Coulomb integral method is By directly measuring the charge current of the three-element unit cell 11 and integrating it over time to estimate the estimated residual capacity of the three-element unit cell 11, and calculating the estimated residual capacity through ambient temperature numerical compensation to obtain The residual capacity of the three-element unit cell 11 is regarded as the residual capacity of the battery structure 10a.

Obtain the current power of the battery structure according to the power of the three-element unit battery (step S120 ). As mentioned above, the power ratio of the three-element unit cell 11 is equal to or greater than the residual capacity of other lithium-iron unit cells 12 or the entire battery structure 10a, so the power ratio of the three-element unit cell 11 can be regarded as the residual capacity of the battery structure 10a. power ratio.

Please refer to FIG. 4 for a flow chart of the method for judging a battery failure according to an embodiment of the present invention. Please also refer to FIG. 2 and FIG. 5 for a detailed flow chart of a method for judging a battery failure with a series connection structure according to an embodiment of the present invention for easy understanding. This method is described as follows:

Determine whether there is a damaged unit cell (step S210 ). Use relevant testing tools to check each battery in the battery structure 10a, and the testing tool will judge whether the three-element unit battery 11 or any lithium-iron unit battery 12 in the entire battery structure 10a is damaged according to the reaction of each unit battery . The method of judging the damaged unit battery is as follows:

As shown in Fig. 2, since the batteries of the battery structure 10a are connected in series, attention must be paid to the voltage level of each unit battery (including the three-element unit battery 11 or any lithium-iron unit battery 12) when the battery structure 10a is charging and discharging. , because each unit battery has its own voltage range.

Here, the output voltage value of each unit cell is obtained first (step S211 ). When the battery structure 10a is discharged, under the same discharge current, the output voltage of the damaged unit cell will be lower than the output voltage of other normal unit cells. Therefore, users or designers can design an example but not limited to this, such as: the lower limit of the voltage of the unit cell is more than 10% lower than the output voltage of the normal unit cell, once the output voltage of the damaged unit cell is lower than this When the lower limit of the voltage is reached, it is judged that the unit cell is faulty; after repeated charge and discharge tests, when the difference between the output voltages of the two unit cells is greater, once the output voltage difference is greater than 30%, it is judged The unit battery fails (step S212).

Alternatively, after the battery structure 10a has been charged and discharged for a long time, relevant detection tools can be used to check each battery in the battery structure 10a, and compared with the battery parameters originally stored in the power measurement unit 13, the detection tools Whether the three-element unit battery 11 or any lithium-iron unit battery 12 in the entire battery structure 10 a is damaged is determined according to the reaction of the battery.

When there is a damaged unit battery, the replacement unit battery needs to be charged or discharged first, so that the proportion of the remaining capacity of the replacement unit battery is equal to the proportion of the remaining capacity of the undamaged unit battery in the battery structure 10 a (step S220 ).

Afterwards, replace the damaged unit battery with a replacement battery (step S230 ), so as to prevent the power ratio of each battery from being too large, resulting in excessive power supply burden of some batteries, thereby shortening battery life, or causing battery damage.

Please refer to FIG. 6 which shows a schematic diagram of the open-circuit voltage curves of the three-element unit battery and the lithium-iron unit battery of the present invention. Please also refer to FIG. 2 for easy understanding. Wherein, the first time period T1 is the battery discharge time period, the second time period T2 is the discharge cut-off time period, the third time period T3 is the battery charge time period, and the fourth time period T4 is the charge cut-off time period.

During the first period T1, when the lithium-iron cell 12 is being discharged, the curve of its initial discharge open-circuit voltage (please refer to the voltage of the lithium-iron cell shown in FIG. 6 ) changes very slowly. The slope of the voltage curve increases and drops sharply. As far as power measurement is concerned, it is difficult to obtain accurate changes in battery residual power.

When the three-element unit cell 11 is discharged, not only the slope of the open circuit voltage (please refer to the voltage of the three-element unit cell shown in FIG. 6 ) curve is relatively large and obvious, but there is no large change in the slope of the open circuit voltage curve from the beginning to the end. Occurs, and the ratio of voltage drop is quite stable. As far as the power measurement operation is concerned, it is easy to obtain very accurate changes in the remaining battery capacity.

During the second period T2, the discharge cut-off voltage of the lithium-iron unit cell 12 may fluctuate excessively, and what's more, it may reversely increase to the normal voltage value before discharge. As far as the power measurement operation is concerned, it is difficult to judge whether the lithium-iron unit battery 12 is exhausted or has sufficient battery power.

However, the discharge cut-off voltage of the three-element unit cell 11 does not fluctuate, but keeps at the voltage value state after discharge. As far as the battery power measurement operation is concerned, it is easy to judge whether the three-element unit battery 11 is in a state of exhaustion or sufficient battery power.

During the third period T3, when the lithium-iron cell 12 is being charged, the open-circuit voltage curve of the initial charging rises to a certain voltage value (about 3.3~3.4V), and the open-circuit voltage changes very slowly. However, the lithium-iron cell When the residual capacity of the battery 12 is at a critical value, the slope of the open circuit voltage curve increases and rises sharply. The critical value of the lithium-iron unit battery 12 is judged by the terminal voltage of the unit battery. The terminal voltage of this critical value is the terminal voltage of the normal unit battery. More than 6% of the voltage. As far as battery power measurement is concerned, it is difficult to obtain very accurate changes in battery residual power.

When the three-element unit battery 11 is being charged, not only the slope of the open circuit voltage curve is relatively large and obvious, but there is no large change in the slope of the open circuit voltage curve from the beginning to the end, and the ratio of voltage rise is quite stable. In terms of operation, it is easy to obtain a very accurate remaining battery power.

During the fourth time period T4, the charging cut-off voltage of the lithium-iron unit battery 12 may fluctuate excessively, and what's more, it may reversely drop to the normal voltage value before charging. It is difficult to judge the remaining battery capacity of the lithium-iron unit cell 12 in terms of the battery power measurement operation.

However, the cut-off voltage of the three-element unit cell 11 does not fluctuate, but keeps at the voltage value after charging. As far as the power measurement operation is concerned, it is easy to judge the remaining battery capacity of the three-element unit battery 11 .

In this example, the three-element unit cell 11 and the lithium-iron unit cell 12 are discharged in series. Discharging is stopped when the lithium-iron unit cell 12 reaches 2.5V. When charging in series, charge in constant current mode first, and then charge the three-element unit 11 and lithium-iron unit battery 12 in constant voltage mode. The charging current is 10A. When the open circuit voltage of lithium-iron unit battery 12 is 3.6V or the charging current is less than or equal to Stop charging at 1A. During the test, the charge and discharge protection is mainly based on the battery with a lower open circuit voltage range. Observe the voltage change of the battery with a higher open circuit voltage range. Therefore, the charge and discharge protection is mainly based on the 12 voltage of the lithium-iron unit battery. The voltage of the battery 11 changes, and the lithium-iron unit battery 12 needs to be charged to 3.6V before the test, and the three-element unit battery 11 is charged to 4V to ensure that the remaining capacity of the unit battery is the highest.

Please refer to FIG. 7 which shows a schematic diagram of the discharge curves of the three-element unit battery and the lithium-iron unit battery of the present invention. Please also refer to FIG. 2 for better understanding.

As far as the lithium-iron unit cell 12 is concerned, its discharge open-circuit voltage (please refer to the average voltage of the lithium-iron battery pack shown in FIG. 7 ) curve changes quite slowly. However, when the lithium-iron unit battery 12 stops discharging, the discharge cut-off voltage will fluctuate, and the voltage value will gradually rise, which is not conducive to the measurement of the remaining battery capacity.

However, in this embodiment, the description is made on the precondition that the total electric capacity of the three-element unit battery (or battery combination) is greater than that of the lithium-iron unit battery (or battery combination). When the three-element unit cell 11 is discharged, not only the open circuit voltage (please refer to the voltage of the three-element unit cell shown in FIG. 7 ) curve has a large and obvious slope, but also the ratio of the voltage drop is quite stable. Moreover, the discharge cut-off voltage of the three-element unit cell 11 does not fluctuate, but keeps at the voltage value state after discharge.

Please refer to FIG. 8 for a schematic diagram showing the overall battery structure and the discharge curve of the lithium-iron unit battery of the present invention. Please also refer to FIG. 2 for better understanding.

Wherein, the residual capacity of the overall battery structure 10 a is obtained by measuring the entire battery structure by the power measuring unit 13 . When the overall battery residual capacity (State of Charge, SOC) gradually decreases, the open-circuit voltage (that is, the measured unit battery terminal voltage when the unit battery is not discharged) curve of the lithium-iron unit battery 12 and the overall battery structure 10a discharge will continue. decline, but very slowly. Moreover, when the lithium-iron unit cell 12 and the overall battery structure 10a stop discharging, the discharge cut-off voltage will drift, and the voltage value will gradually rise, which is not conducive to the measurement of the remaining battery capacity.

Therefore, according to Fig. 6, Fig. 7 and Fig. 8, no matter charging or discharging, the slope of the open circuit voltage curve of the three-element unit battery 11 is relatively large and obvious, and there is no large change in the slope of the open circuit voltage curve from the beginning to the end. The situation occurs, and the ratio of voltage rise and fall is quite stable. Moreover, during charging and discharging stops, there will be no voltage drift. As far as power measurement is concerned, it is easy to obtain very accurate power changes. Therefore, the three-element unit cell 11 can be used to accurately assist in measuring the residual capacity of the lithium-iron unit cell 12 or the overall battery structure 10a.

To sum up, the present invention is only described as an implementation or example of the technical means adopted to solve the problems, and it is not intended to limit the scope of the patent implementation of the present invention. That is, all equivalent changes and modifications that are consistent with the content of the claims of the present invention, or made according to the patent scope of the present invention, are all covered by the patent scope of the present invention.

Claims (10)

1. the quantity measuring method of a battery, be applied to measure the residual electric weight of battery structure, and described battery structure comprises element element cell and at least one lithium iron element cell, it is characterized in that, described method comprises:

Measure voltage or the electric current of described element element cell, to calculate the residual electric weight of described element element cell; And

Calculate the present residual electric weight of described battery structure according to the residual voltameter of described element element cell.

2. the quantity measuring method of battery according to claim 1, is characterized in that, the group that the chemical analysis that described element element cell comprises selects free nickel, cobalt, manganese and lithium to form.

3. the quantity measuring method of battery according to claim 1, it is characterized in that, measure in the described step of residual electric weight of described element element cell, to utilize the present magnitude of voltage of described element element cell and known minimum voltage value to compare, to calculate the residual electric weight of described element element cell.

4. the quantity measuring method of battery according to claim 1, it is characterized in that, measure in the described step of residual electric weight of described element element cell, that charge current by measuring described element element cell is along with the time is estimated the residual electric weight of estimating of described element element cell with its integration, and with described, estimate residual charge value by the calculating of environment temperature numerical compensation, to obtain the residual electric weight of described element element cell.

5. the quantity measuring method of battery according to claim 1, is characterized in that, the described element element cell that described battery structure comprises and described at least one lithium iron element cell are series connection.

6. the quantity measuring method of battery according to claim 5, is characterized in that, also comprises the battery failures determination step, and it comprises:

Obtain the output voltage values of element cell; And

, when the described output voltage values of the measured described element cell lower voltage limit value lower than the described element cell of correspondence, judge that described element cell is the impairment unit battery.

7. the quantity measuring method of battery according to claim 6, is characterized in that, the lower voltage limit value of described element cell is than the normal voltage value of described element cell low 10% ~ 30%.

8. a battery structure, comprise at least one lithium iron element cell, it is characterized in that, described battery structure comprises the element element cell, and described element element cell forms and connects with described at least one lithium iron element cell.

9. battery structure according to claim 8, is characterized in that, the group that the chemical analysis that described element element cell comprises selects free nickel, cobalt, manganese and lithium to form.

10. battery structure according to claim 8, it is characterized in that, when described battery structure comprises the impairment unit battery, the replacement unit battery is replaced described impairment unit battery, and the ratio of the residual electric weight of wherein said replacement unit battery and total electric weight is equal to the ratio of residual electric weight and total electric weight of the not impairment unit battery of described battery structure.

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