JP5768914B2 - Assembled battery charge state diagnosis method - Google Patents

Description

  The present invention relates to a method for diagnosing deterioration of individual storage batteries in an assembled battery configured by combining a plurality of storage batteries.

  A storage battery represented by a lead storage battery, that is, a secondary battery, influences the reliability of electrical equipment power supplies, automatic backup power supplies for measurement equipment, uninterruptible power supplies (UPS), and electric vehicles (including hybrid vehicles). It is an important part.

However, since it is based on a chemical reaction, if it is not periodically replaced, the reliability and performance of the device using the storage battery may not be maintained, and it is also very dangerous for safety. is there. In particular, in the case of a device that operates a storage battery only in an emergency, such as a UPS, if the storage battery has deteriorated, backup cannot be performed in an emergency, not only greatly reducing the reliability of the device but also causing a serious accident. It will also be a thing.
For this reason, it is necessary to appropriately diagnose the life or deterioration of the storage battery and replace the storage battery at an appropriate time. For this purpose, a technique for diagnosing the deterioration state of the storage battery is required.

  When used as a power source, a plurality of storage batteries are often combined and used as an “assembled battery”. Since this assembled battery is composed of a plurality of storage batteries, the manufacturing conditions of each individual storage battery, the form of the assembled battery (how to combine the storage batteries in the assembled battery, etc.), and the usage environment of the assembled battery for each storage battery The difference in the degree of deterioration of the storage battery varies depending on the influence.

  In view of the above background, various methods have been proposed for diagnosing the deterioration state of the storage battery. In particular, the check (deterioration diagnosis) of the stationary VRLA battery that is always in the float charge state is the AC 1 kHz method or This has been done by a direct current discharge method (see Patent Documents 1 and 2, etc.).

JP-A-10-92472 JP-A-8-136629

However, in the DC discharge method, since the float charging is once stopped and the battery voltage is stabilized, the diagnosis is accompanied by an increase in time for stopping charging and a risk for a sudden power failure. The reason why the float charge was stopped is that the open circuit voltage depends on the specific gravity of the electrolyte and is a measure for the deterioration diagnosis of the storage battery, but the charge voltage of each cell during the float charge has a correlation with the open circuit voltage. This is because it is low and an accurate diagnosis cannot be made.
Also, neither the AC 1 kHz method nor the DC discharge method was able to diagnose the state of charge during float charging.

  Therefore, in the situation of such problems, the present invention provides an assembled battery deterioration diagnosis method that accurately measures deterioration diagnosis of individual storage batteries of the assembled battery in a short time.

The first aspect of the present invention, a battery voltage measured in any time between the time of discharge start from 0.5 seconds to the starting point to the 5 seconds, the discharge current, discharge start before the battery during float charge The internal resistance of the battery obtained by dividing the difference between the voltage and the battery voltage during discharge measured at any time between 0.001 second and 0.01 second from the start of discharge in the discharge by the discharge current A method for diagnosing the state of charge of a battery pack, wherein the state of charge of the battery is diagnosed using an addition value of the value obtained by multiplying by

  According to the present invention, even during float charging, the degradation state can be measured without waiting for the stability of the open circuit voltage (OCV) at the time of measurement without being affected by self-discharge, and required for measurement. Since the time is short, the measurement time is remarkably shortened. Furthermore, the apparatus used for the measurement can be made small and inexpensive, which has a remarkable industrial effect.

It is a figure which shows the change of the voltage of an assembled battery at the time of discharging in the state which carried out float charge. It is a test circuit diagram at the time of performing the deterioration diagnostic test of an assembled battery. It is a figure which shows the test circuit used for a deterioration diagnosis and a charge condition diagnosis. It is the figure which showed transition of the voltage when discharging with the electric current between 0.02CA and 0.2CA. It is a figure which shows the time transition of the internal resistance value (DC-IR) of a cell. Cell No. in Example It is a figure which shows transition of the discharge voltage of 0.02CA discharge of 1a-1c. Cell No. in Example It is a figure which shows transition of the discharge voltage of 0.1 CA discharge of 1a-1c. Cell No. in Example It is a figure which shows transition of the discharge voltage of 0.2CA discharge of 1a-1c. Cell No. in Example It is a figure which shows transition of the discharge voltage of 0.02CA discharge of 1d-1f. Cell No. in Example It is a figure which shows transition of the discharge voltage of 0.1 CA discharge of 1d-1f. Cell No. in Example It is a figure which shows transition of the discharge voltage of 0.2 CA discharge of 1d-1f. Cell No. in Example It is a figure which shows transition of the discharge voltage of 0.02CA discharge of 1g-1i. Cell No. in Example It is a figure which shows transition of the discharge voltage of 0.1 CA discharge of 1g-1i. Cell No. in Example It is a figure which shows transition of the discharge voltage of 0.2 CA discharge of 1g-1i. It is a figure which shows the correlation with the internal resistance value (DC-IR) of a cell, and a capacity | capacitance. It is a figure which shows the correlation with the estimated value (estimated OCV) of the open circuit voltage at the time of 0.1CA discharge, and an actual open circuit voltage (measured OCV). It is a figure which shows the correlation with the estimated value (estimated OCV) of the open circuit voltage at the time of 0.02 CA discharge, and an actual open circuit voltage (actually measured OCV). It is a figure which shows the correlation with the estimated value (estimated OCV) of the open circuit voltage at the time of 0.1CA discharge, and an actual open circuit voltage (measured OCV). It is a figure which shows the correlation with the estimated value (estimated OCV) of the open circuit voltage at the time of 0.2CA discharge, and an actual open circuit voltage (measured OCV).

The deterioration diagnosis method and charge diagnosis method of the present invention will be described below.
An outline of the deterioration diagnosis method and the charge diagnosis method of the present invention will be described with reference to FIG.
FIG. 1 is a diagram illustrating a change in voltage of a battery pack when discharging is performed in a float charge state, where the horizontal axis is “time” and the vertical axis is “voltage”.
FIG. 1 shows that when the discharge starts, the voltage drops rapidly in the initial stage, and after the rapid voltage drop, the gradual voltage drop continues. It shows that after the voltage suddenly rises, the voltage rise continues gently.

[Deterioration diagnosis]
In the deterioration diagnosis of the present invention, a voltage drop dV (value indicated by “DC-IR” in FIG. 1) at a predetermined discharge time (tdc in FIG. 1) in this discharge is measured, and the value is determined as a discharge current value. The degree of deterioration of the battery (cell) is determined by using the internal resistance rcell of the battery calculated by dividing by Idc.
The basis of the test conditions for collecting data for performing this deterioration diagnosis is shown below.

(1) Discharge Current FIG. 4 shows an example of voltage transition when one cell in the assembled battery being float charged is discharged with a current between 0.02 CA and 0.2 CA discharge current.
When discharging at any current, the voltage drops sharply immediately after the start of discharge, then gradually decreases, and once the voltage drop stabilizes, it drops linearly due to the effect of concentration polarization due to the decrease in specific gravity due to discharge. Tend to.
However, the rate of gradual decrease greatly varies depending on the magnitude of the discharge current. In the slowly decreasing part, the activation polarization is eliminated, and when discharging during float charging as in this example, the degree of polarization in each cell differs, so the time until the voltage stabilizes Will be mixed. If the discharge current is smaller than the current shown in the figure, it takes a very long time for the voltage drop to stabilize. On the other hand, if the current is large, a voltage drop due to concentration polarization occurs, and accurate measurement cannot be performed.
Therefore, the standard of the discharge current is desirably in the range of 0.02 CA or more and 0.1 CA or less.

(2) Range of measurement point of cell voltage (discharge voltage) after start of discharge for obtaining voltage drop amount dV meaning internal resistance “DC-IR” 0.001 second to 0.01 from start of discharge The reason for taking the measurement point in the range after 2 seconds is that the internal resistance “DC-IR” is stable until about 0.01 seconds from the time transition of the internal resistance value (DC-IR) of the cell shown in FIG. However, after 0.01 second, there are some that change significantly due to the effects of elimination of charge polarization and generation of activation polarization. From this, the measurement point for measuring the value of the discharge voltage for calculating the internal resistance value (DC-IR) of the cell used for diagnosis is from 0.001 second to 0.01 second from the start of discharge. The interval is desirable.
If it is less than 0.001 seconds, the amount of voltage drop due to discharge is small, and if it exceeds 0.01 seconds, the voltage drop tends to vary, and the error in the value of the obtained internal resistance becomes large.

[Charge state diagnosis]
The charge state diagnosis is a value Veocv obtained by adding a value Idc × rcell obtained by multiplying a discharge current Idc and a battery internal resistance rcell to a discharge voltage Vadc (range shown in A of FIG. 1) at a gradual voltage drop after the start of discharge. Is an estimated value of the open circuit voltage (estimated OCV) and is compared with a predetermined threshold value to diagnose the state of charge of the battery. When discharging, if an electronic load is connected to the entire assembled battery and the entire assembled battery is discharged, the charging current increases from the DC power supply to maintain the set charging voltage as soon as the discharge starts and the voltage drops. .
After all, since the current flowing through the battery is a current obtained by canceling the discharge current from the electronic load with the charging current from the DC power supply, a proper diagnosis cannot be made. Therefore, in the present invention, by discharging one of a plurality of cells constituting the assembled battery, a change in current during float charging is reduced.

  The discharge voltage Vadc (range shown in FIG. 1A) used for the charge state diagnosis is desirably a value after 0.5 to 5 seconds from the start of discharge from Table 1, and more desirably after 2 to 5 seconds. It is good to measure the discharge voltage. When the time is shorter than 0.5 seconds, as can be seen from FIG. 1, the change in the discharge voltage is still large, and a large error may occur in the charge state diagnosis by the estimated OCV. In addition, since the change is slight beyond 5 seconds, from the viewpoint of measurement accuracy and measurement efficiency, it is considered that measurement after a longer time is useless, so the above range is desirable.

[Deterioration / Charging State Diagnosis Method]
Next, in order to actually perform each diagnosis, the following test is performed to determine the internal resistance of the cell and the estimated OCV. When performing a deterioration diagnosis and a charge state diagnosis of an n-cell assembled battery in which n cells are connected in series, the test circuit shown in FIG.
In FIG. 2, 1 is an assembled battery composed of n cells, 1a to 1n are cells constituting the assembled battery, 2 is a resistor, 10 is a DC power supply, 11 is an electronic load, 12 is a data logger, 13a is a current measuring probe, 13b is a voltage measurement probe. The figure shows a state in which the i-cell (1x) is diagnosed.
The test is performed according to the following measurement procedure.

[Measurement procedure]
(1) Discharge one cell at a time under float charging under the conditions shown in Table 1, and measure the transition of voltage during discharge.
(2) The internal resistance of the cell and the estimated open circuit voltage (estimated OCV) are calculated from the measurement result of the voltage transition during discharge.
(3) A deterioration diagnosis is performed using the obtained internal resistance of the cell.
(4) The state of charge is diagnosed using the obtained estimated OCV.

A stationary battery pack is normally charged at 2.23 V / cell, and at UPS, 2.275 V / cell.
In addition, you may change atmospheric temperature according to the environment where an assembled battery is used. Further, the charging voltage and the maximum charging current are appropriately set according to the connection mode (series connection or parallel connection) of the assembled battery and the open circuit voltage of the cell of the assembled battery to be measured.
Furthermore, the voltage collection interval can be set as appropriate without sticking to the 0.0025 second (2.5 ms) interval, but the 0.001 to 0.005 second interval is preferable in consideration of the amount of data and the handling. .

Hereinafter, the present invention will be described in detail using examples.
Using the test circuit shown in FIG. 3, a deterioration test and a charge state diagnosis verification test were performed on a deteriorated battery (9-cell battery pack) in which nine VRLA batteries (cells) having a rated capacity of 500 Ah were connected in series. In FIG. 3, 1 is an assembled battery (9 cells, cells 1a to 1i), 2 is a resistor, 10 is a DC power supply, 11 is an electronic load, 12 is a data logger, 13a is a current measurement probe, and 13b is a voltage measurement probe.
The test procedure was based on the “measurement procedure” described above, but was partially changed to verify the validity. The test procedure is shown in the following (1) to (8).

(1) The capacity test of each cell in a fully charged state is performed under the conditions shown in Table 2.
(2) An assembled battery is configured using the cells 1a to 1i after the capacity test.
(3) After the completion of the recovery charge in (1), the actual open circuit voltage (actually measured OCV) (ai) of each cell (1a to 1i) is left in a state where the open circuit voltage is sufficiently stable after being left for 24 hours. Measurement is performed using the voltage measurement probe 13b.
(4) After measuring the open circuit voltage of each cell, float charging is performed on the assembled battery 1 under the conditions shown in Table 3 as an example.
(5) During charging, the batteries are discharged one by one under the conditions shown in Table 3 and the voltage transition during discharging is measured.
(6) The internal resistance of the cell and the estimated open circuit voltage (estimated OCV) are calculated from the measurement result of the voltage transition during discharge.
(7) The validity of the deterioration diagnosis is verified by comparing the obtained internal resistance of the cell with the resistance measurement result in the initial state.
(8) The obtained estimated OCV is compared with the actual OCV to verify the validity of the state of charge diagnosis.

The measurement results are shown below.
[Measurement result]
(A) Deterioration diagnosis Cell No. Table 4 shows the capacity test results of 1a to 1i.

  From Table 4, cell no. 1a, 1b, 1d, and 1g have capacities of 70% or less of the rating. The capacity of 1h and 1i was hardly deteriorated. No. 1c and 1e were capacities close to the life judgment.

Next, the result of discharging for each cell in a state where float charging is performed in the assembled battery state is shown. The voltage transitions during discharge are summarized for each three cells and shown in FIGS. 6 to 14, and the results of measurement are summarized in Tables 5 to 8. The internal resistance value used for estimation was calculated using the voltage at 2.5 seconds. Furthermore, based on this result, the internal resistance (DC-IR) of the battery was determined and listed in Tables 5-8.
Table 5 shows the discharge results at 10 A discharge, Table 6 shows the discharge results at 20 A discharge, Table 7 shows the discharge results at 50 A discharge, and Table 8 shows the discharge results at 100 A discharge.

FIG. 15 shows a correlation diagram between the capacitance and the internal resistance.
In general, a stationary VRLA battery is considered to have a lifetime when its capacity drops to 70% or less of the rated capacity. The internal resistance (DC-IR) in the initial state of the battery used in this test is 0.20 to 25 [mΩ]. The internal resistance of each cell having a capacity of 70% or less was 1 mΩ or more. Also, all the cells having a capacity of about 80% had an internal resistance of more than twice the initial value.

(B) State of charge diagnosis Based on the data of Tables 5 to 8, an estimated OCV was calculated in order to diagnose the state of charge. As the internal resistance value used for estimation, a voltage at 2.5 seconds was used.
Tables 9 to 12 show estimated OCVs obtained at times 0.5 seconds, 1 second, 2 seconds and 5 seconds after the start of discharge.
Table 9 shows the estimated OCV at the time of 10 A discharge based on Table 5, Table 10 shows the estimated OCV at the time of 20 A discharge based on Table 6, and Table 11 shows the estimated OCV at the time of 50 A discharge based on Table 7. Table 12 shows the estimated OCV during 100 A discharge based on Table 8.

In order to verify the validity of the obtained estimated OCV, the correlation between the estimated OCV and the measured OCV was examined.
The correlation diagrams are shown in FIGS. 16 to 19, and Table 13 shows the results of summarizing the correlation coefficients under the respective conditions.
The correlation coefficient between the measured OCV and the estimated OCV obtained from the discharge voltage 5 seconds after the start of discharge was 0.88 to 0.95, confirming the validity of the charge state diagnosis.

1 assembled battery 1a, 1b, 1c to 1n each cell constituting the assembled battery 2 resistance 10 DC power supply 11 electronic load 12 data logger 13a current measurement probe 13b voltage measurement probe

Claims (1)

Battery voltage measured at any time between 0.5 seconds and 5 seconds from the start of discharge;
The discharge current includes the battery voltage before the start of discharge during float charging and the battery voltage during the discharge measured at any time between 0.001 second and 0.01 second from the start of discharge in discharge. The value obtained by multiplying the internal resistance of the battery obtained by dividing the difference by the discharge current,
A method for diagnosing the state of charge of a battery using the added value of

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