WO2020054924A1

WO2020054924A1 - Apparatus and method for diagnosing state of battery in cell unit

Info

Publication number: WO2020054924A1
Application number: PCT/KR2019/001215
Authority: WO
Inventors: 최진혁; 임지훈
Original assignee: 한국전력공사
Priority date: 2018-09-12
Filing date: 2019-01-29
Publication date: 2020-03-19
Also published as: KR101990042B1

Abstract

The present invention relates to an apparatus and a method for diagnosing the state of a battery. The apparatus for diagnosing the state of a battery in a cell unit, according to the present invention, comprises: a power transform unit for applying a predetermined pulse waveform to the battery; a measurement unit for measuring the maximum voltage value and the minimum voltage value in a cell unit of the battery according to the applied predetermined pulse waveform; and a control unit for calculating the cell-unit internal resistance value of the battery on the basis of the difference between the maximum voltage value and the minimum voltage value.

Description

Apparatus and method for diagnosing the state of the battery in units of cells

The present invention relates to an apparatus and method for diagnosing the condition of a battery.

As the use time for charging and discharging becomes longer for an electric vehicle battery or an energy storage battery, the use time is reduced due to deterioration due to an increase in internal resistance.

In the prior art, in order to measure the life deterioration of the energy storage system, the capacity deterioration is mainly measured. In this case, there is a problem that the test time is excessively taken during periodic inspection.

Currently, in electric vehicles and energy storage systems, a state of charge (SOC) range (a state of use of a charged state) is specified for normal operation of a required output when charging and discharging a battery. However, since the method for measuring the exact degree of deterioration is not applied, there is no method to check whether the required output is normally operated according to the SOC. In addition, the available SOC range due to system degradation is not considered in the operating algorithm.

In particular, in the prior art, since the degree of deterioration of individual unit cells constituting the battery system cannot be measured, maintenance costs such as replacement of the entire system are excessively required during maintenance, and there is a problem that the replacement unit cannot be minimized.

The present invention aims to solve the above and other problems. Another object is to calculate the internal resistance based on the difference between the maximum voltage value and the minimum voltage value generated when a predetermined pulse waveform is applied, and predict the battery in advance to facilitate the operation, maintenance, and maintenance of the battery. It is an object of the present invention to provide an apparatus and method for diagnosing the state of a battery to be cell-by-cell.

According to an aspect of the present invention to achieve the above or another object, a power conversion unit for applying a predetermined pulse waveform to the battery; A measuring unit measuring a maximum voltage value and a minimum voltage value in units of cells of the battery as the predetermined pulse waveform is applied; And based on the difference between the maximum voltage value and the minimum voltage value, a control unit for calculating the internal resistance value of each cell of the battery; provides a device for diagnosing the state of the battery in a cell unit.

In an embodiment, the controller may repeatedly calculate the internal resistance value of each cell of the battery while adjusting the state of charge (SOC) of the battery.

In another embodiment, the controller may calculate the internal resistance value of each cell of the battery based on a difference between a maximum voltage value and a minimum voltage value measured as the predetermined pulse waveform is applied at a predetermined SOC value. have.

In another embodiment, the controller increases the predetermined SOC value by a predetermined value, and then, based on the difference between the maximum voltage value and the minimum voltage value measured as the predetermined pulse waveform is applied, the battery It is possible to calculate the internal resistance value per cell.

In another embodiment, the controller may detect a cell that deviates from a standard deviation value for the internal resistance value by applying a predetermined statistical analysis to the internal resistance value of each cell of the battery.

In addition, according to another aspect of the invention, applying a predetermined pulse waveform to the battery; Measuring the maximum voltage value and the minimum voltage value in units of cells of the battery as the predetermined pulse waveform is applied; And based on the difference between the maximum voltage value and the minimum voltage value, calculating the internal resistance value of each cell of the battery; provides a method for diagnosing the state of the battery in units of cells.

In an embodiment, while adjusting the state of charge (SOC) of the battery, repeatedly calculating an internal resistance value of each cell of the battery.

In another embodiment, applying a predetermined statistical analysis to the internal resistance value of each cell of the battery, the step of detecting a cell outside the standard deviation value for the internal resistance value may include.

The effects of the apparatus and method for diagnosing the state of a battery according to the present invention in units of cells are as follows.

According to at least one of the embodiments of the present invention, since the output deterioration degree is directly measured at a system level without relying on the state of health (SOH) calculated in the BMS, the stability and performance of the entire system are diagnosed. Can judge.

In addition, it is possible to predict and manage the abnormality of the entire battery system in advance, periodically monitor the degree of deterioration of the entire battery system, and predict the output of the battery using the measured degree of deterioration.

When the reliability of the SOH value measured in the battery management system is low, it can be used as comparative information, and when the reliability of the SOH value is high, it can be used as information for determining the state of contact resistance on the system. This can be very useful diagnostic information.

In addition, according to at least one of the embodiments of the present invention, battery maintenance intervals and units can be optimized by measuring and analyzing not only the deterioration degree of the entire battery system, but also the deterioration degree of individual cells, and the replacement unit is minimized when replacement is required. can do.

In addition, when the deterioration degree of each battery cell is indicated on the energy storage device operating system and the electric vehicle charger or operator screen, it can be effectively used for condition inspection, maintenance, and replacement.

As another example, the measured charging and discharging maximum outputs can be utilized and reflected in the operating algorithm, thereby being used for optimal operation of the energy storage system.

The energy storage system can be used by reflecting the available range in the operating algorithm depending on the battery SOC. Depending on the application purpose, such as peak reduction operation and frequency adjustment operation, the available output described in the embodiment of the present invention can be applied in the available SOC range.

In addition, since the available output value in the SOC range decreases (deteriorates) as the usage time elapses, the available output according to the SOC range can be calculated and reflected in the operating algorithm, and the SOC range in which the required output can be expressed normally Can be confirmed. This enables long life operation.

The battery exhibits output characteristics for each SOC range depending on the material or design. Therefore, the charge output characteristics and the discharge output characteristics are different depending on the manufacturer or design differences. Accordingly, by applying the apparatus and method of the present invention, the optimal operating SOC range can be set and mounted in the operating system.

And, when applied to an electric vehicle charger, the internal resistance value can be used to present a quantitative value for the battery deterioration to the user, and it can be checked as needed at every charge, so information on maintenance intervals and replacement units There is an advantage that the user can grasp.

Further scope of applicability of the present invention will become apparent from the following detailed description. However, various changes and modifications within the spirit and scope of the present invention may be clearly understood by those skilled in the art, and thus, it should be understood that specific embodiments such as detailed description and preferred embodiments of the present invention are given as examples only.

1 is a block diagram illustrating an embodiment of an apparatus for diagnosing a battery state in units of cells according to the present invention.

2 is a graph for explaining an embodiment of a predetermined pulse waveform applied to the battery and the output accordingly.

3 and 4 are graphs showing embodiments of internal resistance and available output change for each SOC.

5 is a flowchart for explaining an embodiment of a method of diagnosing a battery state in units of cells according to the present invention.

6 is a table for explaining an example of measuring the open circuit voltage of a cell before / after the output test for each SOC.

Hereinafter, exemplary embodiments disclosed herein will be described in detail with reference to the accompanying drawings, but the same reference numerals will be assigned to the same or similar elements regardless of reference numerals, and redundant descriptions thereof will be omitted. The suffixes "modules" and "parts" for the components used in the following description are given or mixed only considering the ease of writing the specification, and do not have meanings or roles distinguished from each other in themselves. In addition, in describing the embodiments disclosed in the present specification, when it is determined that detailed descriptions of related known technologies may obscure the gist of the embodiments disclosed herein, detailed descriptions thereof will be omitted. In addition, the accompanying drawings are only for easy understanding of the embodiments disclosed in the present specification, and the technical spirit disclosed in the specification is not limited by the accompanying drawings, and all modifications included in the spirit and technical scope of the present invention , It should be understood to include equivalents or substitutes.

Terms including ordinal numbers such as first and second may be used to describe various components, but the components are not limited by the terms. The terms are used only for the purpose of distinguishing one component from other components.

When an element is said to be "connected" or "connected" to another component, it is understood that other components may be directly connected to or connected to the other component, but other components may exist in the middle. It should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that no other component exists in the middle.

Singular expressions include plural expressions unless the context clearly indicates otherwise.

In this application, the terms "comprises" or "have" are intended to indicate the presence of features, numbers, steps, actions, components, parts or combinations thereof described herein, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. Not all embodiments of the present invention are disclosed in the following description. The invention can be implemented in a wide variety of forms, and should not be construed as limited to the embodiments disclosed herein. These embodiments are provided to meet legal requirements for filing. The same reference numerals are used throughout the same components.

Referring to FIG. 1, an apparatus for diagnosing a state of a battery according to the present invention in units of cells may include a power conversion unit, a measurement unit, and a control unit.

The power conversion unit may apply a predetermined pulse waveform to the battery.

As the predetermined pulse waveform is applied, the measurement unit may measure a maximum voltage value and a minimum voltage value in units of cells of the battery.

The controller may calculate the internal resistance value of each cell of the battery based on the difference between the maximum voltage value and the minimum voltage value. The control unit may include a battery management system (BMS).

Specifically, the controller may calculate a cell unit internal resistance value of the battery based on a difference between a maximum voltage value and a minimum voltage value measured as the predetermined pulse waveform is applied at a predetermined SOC value.

Subsequently, the controller increases the predetermined SOC value by a predetermined value, and then, based on a difference between a maximum voltage value and a minimum voltage value measured as the predetermined pulse waveform is applied, the internal resistance value of each battery cell unit. Can be calculated.

In addition, by adding a device for measuring AC-impedance to the output control system, by measuring AC-impedance in addition to the DC resistance calculated through the application of the existing pulse current, it is possible to improve the accuracy of the system internal degradation measurement.

As described above, a predetermined pulse waveform may be applied to the battery.

Referring to FIG. 2, test methods and calculation formulas for measuring DC internal resistance and maximum charge output and maximum discharge output are expressed.

First, after adjusting the output characteristics to the SOC (charged state) to be calculated, discharge for 10 seconds with a current of 4 times the battery capacity (Ah or Wh) and charge for 10 seconds with a current of 3.75 times, DC internal resistance and maximum discharge And the charging output can be calculated by the following equation.

Where R _dis is the discharge internal resistance value, OCV _dis is the voltage of the battery at the start of discharge (means the open circuit voltage at the start of discharge), V _dis is the voltage of the battery at the end of discharge, and I _dis is the discharge current. It means size.

When the discharge internal resistance value is calculated, the controller may calculate the maximum discharge output according to Equation 2 below based on the calculated discharge internal resistance value.

Here, Discharge Power is the maximum discharge power and V _MIN is the minimum discharge voltage.

When the maximum discharge output is calculated according to Equation 2 above, before calculating the maximum charging output, the controller converts the power for a predetermined idle time for the voltage of the battery to reach the Open Circuit Voltage (OCV). Stop controlling for wealth.

The idle time is the time required for the voltage of the battery to reach an open circuit voltage and enter a stable state. When the battery is not in a stable state, there is an error in the maximum discharge output and maximum charging output calculated based on the voltage and current of the battery. Since it is present, the control unit waits until the voltage of the battery reaches the open circuit voltage. This dwell time is applied even before calculating the maximum discharge power.

When the voltage of the battery reaches the open circuit voltage, the control unit controls the power conversion unit as shown in FIG. 2 to generate a charging current having a predetermined size (eg, 3.75 times the current (3.75C rate) of the battery capacity). The battery can be charged by supplying it to the battery for a set time (eg, 10 seconds). At this time, the control unit may calculate a charging internal resistance value based on the voltage of the battery at the start of charging, the voltage of the battery at the completion of charging, and the charging current.

That is, since the amount of voltage rise when the battery is charged depends on the product of the magnitude of the charging current supplied to the battery and the value of the charging internal resistance, the value of the charging internal resistance can be calculated according to Equation 3 below.

Where R _chg is the charge internal resistance value, OCV _chg is the voltage of the battery at the start of charging (meaning the open circuit voltage at the start of charging), V _chg is the voltage of the battery at the completion of charging, and I _chg is the charge current. It means size.

When the charging internal resistance value is calculated, the controller may calculate the maximum charging output according to Equation 4 below based on the calculated charging internal resistance value.

Here, Charge Power is the maximum charging output, and V _MAX is the maximum charging voltage.

As shown in FIG. 2, when using a pulse for measuring the internal DC resistance, not only the overall internal DC resistance of the battery system, but also the voltage data of the battery management system (BMS, Battery Monitoring System) is used, or a separate measurement system is used. By measuring the DC resistance of individual cells, each degree of degradation can be diagnosed. It can be used to set the replacement unit and cycle, and can be used as a selection criterion when recycling.

Using the above data, it is possible to calculate the charge and discharge internal resistance and the maximum charge and discharge power in the SOC of the battery system, and the measurement standard SOC sequentially performs pulse discharge and charge tests between 90% and 10%, Sufficient downtime should be provided to reach OCV prior to the start of each test.

As an embodiment, the pulse pattern for this test may be utilized by inputting a pattern to a power converter (PCS) of an energy storage system.

As a result of periodically performing this test, as shown in FIGS. 3 and 4, the output deterioration and available power can be evaluated by using the amount of change in the DC internal resistance after initial and 2000 cycles for each state of charge (SOC). You can.

The available SOC range at each charge / discharge can be calculated and compared to the system request output and reflected in the energy storage system operation algorithm.

In the case of FIG. 3, after performing a pulse pattern test in an environment of 15 ° C., 25 ° C., and 30 ° C., the results of the discharged internal resistance are respectively calculated, and the results of a cell used for more than 2000 cycles (Used) are shown as an example. .

As can be seen in Figure 3, it can be seen that the internal resistance is significantly increased in the case of a used cell in three temperature environments (15 ° C, 25 ° C, 30 ° C).

Figure 4 is an example comparing the available output of the Fresh cell and the Used cell at each temperature condition (15 ℃, 25 ℃, 30 ℃). In the case of a used cell, it can be seen that the available output is greatly reduced.

Referring to FIG. 5, a step (S510) of setting a range of SOC (SOC_Start, SOC_End) is performed. Accordingly, an initial SOC is set (S520), and a predetermined pulse is applied from the initial SOC to measure V, I, and T in units of cells (S530). As described above, the pulse of FIG. 2 may be applied.

Subsequently, a step (S540) of calculating the degree of deterioration (internal resistance, available output) of the cell is performed based on the measured value. As an embodiment, the deterioration degree of a cell may be calculated by the above-described equations.

Thereafter, a step (S550) of determining whether the SOC value is a predetermined final value (SOC_End, n%) is performed.

If the SOC value is not the final value, after adding 10% to the SOC value, steps S530, S540, and S550 are repeated.

If the SOC value is the final value, step S560 of determining whether there is an abnormality in a cell unit by applying a statistical analysis to the internal resistance is performed. For example, through statistical analysis of measured and calculated internal resistance values, it is possible to perform screening, maintenance, and replacement for cells with high internal resistance significantly out of the standard deviation value.

As another embodiment, the resistance value for calculating the internal resistance of each cell may be measured by using a separate measurement sensor or by using BMS (Battery Management System) information previously applied to the battery system.

As a result, when the internal resistance value exceeds the reference value, it is possible to improve the convenience of application by adding a method indicating the location of the cell in the operating system (BMS or PMS (Power Management System)) of the energy storage device. For example, in the case of a battery system applied to an electric vehicle, the present system can be applied by using a charger.

Referring to FIG. 6, an open circuit voltage (OCV) for each cell before and after an output test for each SOC is shown, and a variation in DC internal resistance for each cell can be evaluated using a periodic change in this value.

Referring to the test results, SOC was measured by changing SOC from 10 to 90 in increments of 10, and the maximum voltage, minimum voltage, and the difference between the maximum voltage and the minimum voltage of a predetermined number of cells constituting the battery system before and after the test. (△ V) can be confirmed.

As the battery system deteriorates, the voltage drop value can be checked using the voltage values before and after the application of the pulse waveform in each cell, and the internal resistance can be calculated using the above-described equation.

On the other hand, the battery system applied by the present invention is a single cell, a single cell is a module connected in series and parallel, a rack in which modules are connected in series and parallel, a system in which the racks are connected in series and parallel, evaluates the output characteristics and measures the degree of degradation. The pulse current or pulse output applied to each can be calculated and applied from the total capacity (Ah) or energy (Wh).

Whether the output deterioration degree proposed in the present invention is determined is based on the output required by the rating of the applied cell, module, rack, and system, and performs replacement or maintenance through comparison with the maximum output calculated through the pulse charge / discharge test. It is possible to compare and verify the degree of deterioration by changing the maximum output and internal resistance values calculated through periodic pulse charge and discharge tests.

In addition, it is possible to predict and manage the abnormality of the entire battery system in advance, periodically monitor the degree of deterioration of the entire battery system, and predict the battery output using the measured degree of deterioration.

When the SOH value measured in the battery management system is not reliable, it can be used as comparative alternative information. When the SOH value is high, it can be used as information to determine the state of contact resistance on the system. Can be

As another example, the measured charging and discharging maximum outputs can be utilized and reflected in the operating algorithm, thereby being utilized for optimal operation of the energy storage system.

In addition, since the available output value in the SOC range decreases (deteriorates) as the usage time elapses, the available output according to the SOC range can be calculated and reflected in the operating algorithm, and the SOC range in which the required output can be expressed normally Able to know. This enables long life operation.

The above detailed description should not be construed as limiting in all respects, but should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the equivalent scope of the present invention are included in the scope of the present invention.

Claims

A power conversion unit that applies a predetermined pulse waveform to the battery;

A measuring unit measuring a maximum voltage value and a minimum voltage value in units of cells of the battery as the predetermined pulse waveform is applied; And

And a controller configured to calculate an internal resistance value of each cell of the battery based on the difference between the maximum voltage value and the minimum voltage value.
According to claim 1,

The control unit,

The apparatus for diagnosing the state of a battery in units of cells, by repeatedly calculating an internal resistance value of each unit of cells of the battery while adjusting a state of charge (SOC) of the battery.
According to claim 2,

The control unit,

Diagnosing the state of the battery in units of cells, characterized in that an internal resistance value of each cell of the battery is calculated based on a difference between a maximum voltage value and a minimum voltage value measured as the predetermined pulse waveform is applied at a predetermined SOC value. Device.
According to claim 3,

The control unit,

After increasing the predetermined SOC value by a predetermined value, the internal resistance value of each battery cell is calculated based on a difference between a maximum voltage value and a minimum voltage value measured as the predetermined pulse waveform is applied. Device that diagnoses the state of the battery to be cell-by-cell.
According to claim 1,

The control unit,

Apparatus for diagnosing the state of the battery in units of cells, characterized by detecting a cell outside the standard deviation value for the internal resistance value by applying a predetermined statistical analysis to the internal resistance value of each unit of the battery.
Applying a predetermined pulse waveform to the battery;

Measuring the maximum voltage value and the minimum voltage value in units of cells of the battery as the predetermined pulse waveform is applied; And

And calculating a cell unit internal resistance value of the battery based on the difference between the maximum voltage value and the minimum voltage value.
The method of claim 6,

And repeatedly calculating an internal resistance value of each cell of the battery while adjusting a state of charge (SOC) of the battery.
The method of claim 6,

And applying a predetermined statistical analysis to the internal resistance value of each cell of the battery to detect a cell outside the standard deviation value for the internal resistance value.