KR102597670B1 - Device and method for estimating life expectancy of a used battery pack - Google Patents

Abstract

According to the present invention, the life of a battery pack including a cell voltage measuring unit that measures the cell voltage of each battery cell constituting the battery pack, and a control unit that controls the time of one cycle of repeatedly charging and discharging each battery cell. The estimation device includes an SOH calculation unit that calculates the life expectancy (SOH: State of Health) of the battery pack based on information about the trend of the discharge end voltage gradually decreasing during a preset discharge time. A device for estimating the lifespan of a battery pack after use is provided. According to the present invention, the expected lifespan is estimated by monitoring the change in discharge end voltage through a charging and discharging cycle test for a short period of time for the battery recovered after use of an electric vehicle, so it is possible to provide data for determining whether or not to reuse. This has the effect of making it possible to objectively determine the degree of aging of batteries for which the initial use history has not been secured.

Description

Method and device for estimating the lifespan of a used battery pack {DEVICE AND METHOD FOR ESTIMATING LIFE EXPECTANCY OF A USED BATTERY PACK}

The present invention relates to a method and device for estimating the life expectancy (SOH, State of Health) of a battery pack that has already been used for a certain period of time based on a test that repeats charging and discharging.

Recently, as interest in environmental protection has increased, electric vehicles (EV, HEV, PHEV) have been in the spotlight, and due to the expanded use of new and renewable energy and increased demand for electricity, smart grid projects using energy storage systems (ESS) are attracting attention. is receiving.

Across industries, including electric vehicles and new and renewable energy fields, the adoption and use of secondary batteries capable of stable power supply and charging is expanding. Accordingly, battery management is required to use and manage batteries more efficiently. The importance of system-related technology is also gradually increasing.

Basically, batteries age as they are repeatedly charged and discharged, and the aging of the battery may progress faster due to various other factors (battery temperature, charging method, current change, depth of discharge, etc.). In order for a battery management system to optimally manage and operate the battery, it is necessary to accurately estimate the battery's aging lifespan. In particular, in order for a battery management system to properly adjust the battery's charging or discharging output and remaining capacity (State of Charging; SOC) usage strategy, it must be able to accurately predict the battery's life (State of Health; SOH).

Prior technologies for estimating the life of a battery include the following technologies.

As prior art 1, Korean Patent Publication No. 2015-0045600 "Battery Tester and Control Method" is a technology that counts the number of charge and discharge times of a battery and predicts the aging degree and lifespan of the battery in comparison to the number of charge and discharge guaranteed by the battery manufacturer. am. However, batteries used in actual mechanical devices do not end in a clear charge/discharge cycle in the form of full charge and complete discharge, and are sometimes discharged while partially charged, or partially discharged, and then recharged, making it impossible to accurately count the number of charge/discharge times. . Therefore, there are limitations in accurately estimating the aging degree and lifespan of a battery based on the number of battery charge and discharge cycles.

As prior art 2, Korean Patent Publication No. 2011-0084633, “Battery life prediction device and method,” uses OCV (Open Circuit Voltage) and SOC corresponding to the voltage, current, and temperature measured using the OCV-SOC Table of the battery. (State Of Charge) is calculated and the lifespan of the battery is predicted using the accumulated current of the battery over a certain period of time and the calculated SOC. However, in this prior art 2, since the OCV-SOC table of the battery may vary depending on the capacity deterioration state of the battery, it is impossible to accurately estimate the life expectancy of the battery due to the uncertainty of the OCV-SOC table depending on the deterioration state of the battery. There is.

As prior art 3, Korean Patent No. 0740113, “Battery life determination method and battery management system using the same,” measures the pack current and pack voltage for a battery pack in which a plurality of battery cells are formed into one pack, and determines the pack internal resistance. The maximum output of the battery pack is calculated using the calculated pack internal resistance, and the lifespan of the battery is estimated by comparing the calculated maximum output with the reference output.

As prior art 4, Republic of Korea Publication Application No. 2012-0075756, “Method and Apparatus for Calculating Remaining Life of Secondary Battery,” calculates the life of the battery using parameters such as internal resistance, remaining capacity (SOC), and conductance of the battery. The technology is described.

However, the internal resistance calculated based on the battery current and battery voltage consists of the actual internal resistance and contact resistance, and the contact resistance is based on the current and voltage because it varies depending on the contact state of the battery and wiring, not the deterioration of the battery. Therefore, it is very difficult to accurately calculate the internal resistance due to battery deterioration. Additionally, it is very difficult to calculate the remaining capacity or accurately estimate the life of the battery based on its internal resistance.

Prior Art 5, Republic of Korea Patent Publication No. 10-2015-0084354 “Battery pack life estimation device” infers the degree of aging based on the number of cells and the number of cell balancing that constitutes the battery pack.

The battery life estimation devices are a method of gradually inferring the aging of the battery as the usage increases during the production of the battery by the manufacturer. By recovering batteries that have already been used for the first time for any purpose, they are used in an environment without existing usage data. Since this method is not suitable for predicting the remaining lifespan, a more rapid, accurate, and highly reliable method of estimating the lifespan of the battery is needed to reuse the battery.

The present invention was derived to solve the above-mentioned problems, and relates to estimating the remaining expected life of a battery pack that has been used to a certain extent. When reusing a battery after using an electric vehicle, the expected life is estimated within a short period of time and the expected life is estimated for use at the time of reuse. The goal is to provide a method and device for estimating life expectancy (SOH, State of Health) that ensures decision-making and safety.

Additionally, the purpose of the present invention is to provide a method of inferring the expected lifespan of a battery pack recovered from an electric vehicle for which no usage history is given through a short cycle test.

According to one aspect of the present invention, a battery including a cell voltage measurement unit that measures the cell voltage of each battery cell constituting a battery pack, and a control unit that controls the time of one cycle of repeatedly charging and discharging each battery cell. A life estimation device for a pack, comprising an SOH calculation unit that calculates the life expectancy (SOH: State Of Health) of the battery pack based on information about the trend of the discharge end voltage gradually decreasing during a preset discharge time. A device for estimating the lifespan of a battery pack after use is provided.

According to the present invention, the expected lifespan is estimated by monitoring the change in discharge end voltage through a charging and discharging cycle test for a short period of time for batteries recovered after electric vehicle use, which has the effect of providing data to determine whether or not to reuse. there is.

In addition, according to the present invention, it is possible to objectively determine the degree of aging of a battery whose initial use history has not been secured.

1 is a block diagram schematically showing the configuration of an apparatus for estimating the lifespan of a used battery pack according to an embodiment of the present invention.
Figure 2 is an operation flowchart illustrating a method for estimating the lifespan of a battery pack after use according to an embodiment of the present invention.
Figure 3 is a graph of a test performed on [Battery A] after 150 charge/discharge cycles.
Figure 4 is a graph of a test performed on [Battery B] after 150 charge/discharge cycles.

Since the present invention can be modified in various ways and can have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all transformations, equivalents, and substitutes included in the spirit and technical scope of the present invention.

In describing the present invention, if it is determined that a detailed description of related known technologies may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. In addition, numbers (eg, first, second, etc.) used in the description of this specification are merely identifiers to distinguish one component from another component.

In addition, throughout the specification, when a component is referred to as "connected" or "connected" to another component, the component may be directly connected or directly connected to the other component, but in particular Unless there is a contrary description, it should be understood that it may be connected or connected through another component in the middle. In addition, throughout the specification, when a part "includes" a certain element, this means that it may further include other elements rather than excluding other elements, unless specifically stated to the contrary.

1 is a block diagram schematically showing the configuration of an apparatus for estimating the lifespan of a used battery pack according to an embodiment of the present invention. Hereinafter, in the description of FIG. 1, FIGS. 3 and 4 will be referred to together. Here, Figure 3 is a graph of a test performed on [Battery A] after 150 charge/discharge cycles, and Figure 4 is a graph of a test performed on [Battery B] after 150 charge/discharge cycles.

Referring to FIG. 1, a device for estimating the lifespan of a used battery pack may include a cell voltage measurement unit 210, a control unit 220, a history storage unit 230, and an SOH calculation unit 240.

The cell voltage measurement unit 210 can measure the voltage of each cell in real time while a charge/discharge test is performed on the used battery pack 10 under the control of the control unit 220. Accordingly, the obtained cell voltage measurement value and discharge time may be stored in the history storage unit 230.

The control unit 220 can control the operations of the charging device 100 and the discharging device 110 to perform a charging and discharging test on the battery pack 10 after use. At this time, the control unit 220 can control the cycle time for repeatedly charging and discharging each battery cell for a simple charging and discharging test. In one embodiment, the charging and discharging experiment is performed by repeating 12 minutes of charging, 1 minute of rest, and 12 minutes of discharging. You can proceed. Also, at this time, the control unit 220 can control the charging current amount during the charge/discharge test to be adjusted to a preset constant current amount. In one embodiment, charge/discharge is performed at 20% of the battery's rated capacity, that is, at 0.2C-rate for the same time. and short rest periods can be repeated.

At this time, the charging time and discharging time are set to the same time, and one test cycle combining charging time, rest time, and discharging time is set to not exceed 30 minutes, which previously took about 6 months to predict lifespan. can be reduced to about 2 weeks.

The device for estimating the lifespan of a used battery pack according to an embodiment of the present invention monitors the charging and discharging power amounts to maintain a constant current amount while the charging device 100 and the discharging device 110 perform a charge and discharge cycle test. Additional parts (not shown) may be included.

The SOH calculation unit 240 uses the cell voltage measurement value and the discharge time stored in the history storage unit 230 to determine the used battery based on information about the trend of the discharge end voltage gradually decreasing during the discharge time. The SOH (State Of Health) of the pack can be calculated.

According to the prior art, the battery life test or cycle test is usually performed 150 to 500 times by repeating charging and discharging for the battery's rated capacity (for example, 4.8V), and then the capacity before the cycle test is performed. Since it is based on a method of comparing the capacity after the cycle test, several months of test time is required and the expected lifespan of a new battery is presented. However, the test method through the present invention is a method of comparing the battery recovered within a short test time as described above. The expected lifespan can be predicted.

Hereinafter, a detailed description of the method of predicting the expected lifespan of the battery pack 10 after use in the SOH calculation unit 240 is as follows. That is, the SOH calculation unit 240 can predict the life expectancy (SOH) of the battery pack after use through Equation 1 below.

Here, N is a weight according to the charge/discharge current. Also here: is the discharge end voltage (i.e., the end voltage when the preset discharge time has elapsed) at the time of the first discharge test (during one discharge test) and at the time of the final discharge test (e.g., when 500 charge/discharge tests are set). In this case, it means the slope between the discharge end voltages (at the time of 500 discharges).

At this time, the N may be given different weights depending on the type of battery pack by manufacturer or the characteristics of the battery pack. Also, in general, when the charge/discharge current is set to a low value, there will not be a significant difference in the slope between each discharge end voltage during the first and last discharge tests compared to when the charge/discharge current is set to a high value. Since there is a possibility, the weight N is set in order to secure reliability in the life expectancy estimation by setting an appropriate weight by the designer according to the type and characteristics of the battery pack.

Based on Equation 1 above, as shown in the graph in FIG. 3, in the case of a specific battery A, the change in voltage at the end of discharge (discharge end voltage) is large as the charge/discharge cycle test progresses, but the test under the same conditions is specific. Looking at the graph of FIG. 4 for battery B, it can be seen that the range of change is not large compared to FIG. 3. As in the case of FIG. 4, when there is no trend of change in discharge end voltage, the life expectancy (SOH, State of Health) is calculated as 100, and as in the case of FIG. 3, the life expectancy (SOH) in the charge/discharge cycle test suggested by the manufacturer is calculated as 100. When the slope between each discharge end voltage is about 30 degrees, the life expectancy can be predicted as 100 * (1 - N * cos30) %.

Through the method described above, the aging of the battery pack after use can be measured by the change trend (slope) of the final voltage at the end of discharge (discharge end voltage), which decreases as the charge/discharge cycle test progresses.

Figure 2 is an operation flowchart illustrating a method for estimating the lifespan of a battery pack after use according to an embodiment of the present invention.

Referring to FIG. 2, the cycle period for predicting the lifespan of the battery pack being used is set (S210), a charge/discharge test for the battery pack is determined (S220), and charging is performed using a preset charging power amount. Perform (S230) (e.g., for 12 minutes at 0.2C-rate charging current), have a pause for a preset time (S240) (e.g., 1 minute), and discharge by the preset discharge power amount. (S250) (e.g., for 12 minutes), after testing for a pre-specified number of cycle tests (e.g., 150, 500, etc.) (S260), the initial discharge end voltage and By recording the final discharge end voltage (S270) and outputting the SOH calculated from the recorded voltage trend (S280), it can be determined whether the battery pack is reusable.

According to the above-described method, according to the method of estimating the lifespan of a used battery pack according to an embodiment of the present invention, the change in discharge end voltage is monitored by charging and discharging the battery recovered after use of the electric vehicle for a short period of time to estimate the expected lifespan of the battery pack. Because it estimates the lifespan, it can provide data to determine whether or not to reuse, and it can also be possible to objectively determine the degree of aging for batteries for which the history of initial use has not been secured.

Although the present invention has been described above with reference to embodiments, those skilled in the art can modify the present invention in various ways without departing from the spirit and scope of the present invention as set forth in the claims below. It will be easy to understand that and can be changed.

Claims (4)

A device for estimating the lifespan of a battery pack after use,
A cell voltage measurement unit that measures the cell voltage of each battery cell constituting the battery pack;
a control unit that controls the time of one cycle of repeatedly charging and discharging each battery cell;
An SOH calculation unit that calculates the expected lifespan (SOH: State of Health) of the battery pack based on information about the trend of the discharge end voltage that gradually decreases during the preset discharge time,
The control unit,
The charging and discharging test is conducted with a current of 0.2C-rate, which is equivalent to 20% of the rated capacity of the battery pack. The charging time and discharging time are set to the same time, and the charging time, rest time, and discharge time are added to 1. Set the test cycle to not exceed 30 minutes,
The SOH calculation unit is a device for estimating the life expectancy of a used battery pack, wherein the SOH calculation unit calculates the life expectancy (SOH) of the used battery pack using Equation 1 below.

[Equation 1]


Here, N is a weight according to the charge/discharge current, means the slope angle between the discharge end voltage during the first discharge test (end voltage when the preset discharge time has elapsed) and the discharge end voltage during the final discharge test.
delete According to paragraph 1,
A history storage unit that stores the voltage of each cell measured in real time by the cell voltage measurement unit while performing a charge/discharge test on the used battery pack; and
A monitoring unit that monitors the amount of charging power and discharging power of the used battery pack in order to check whether the amount of current applied to the charging device and discharging device used in the charging and discharging test of the used battery pack maintains a constant current amount;
A device for estimating the lifespan of a used battery pack, further comprising:
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