KR101238478B1 - The Measurment Method of Battery SOC - Google Patents

Abstract

In order to solve the problems of the prior art, the present invention calculates the estimated OCV in the state of considering the charging and discharging current, and discharged through the total amount of electricity charged in the battery and driving. The SOC is calculated by adding or subtracting the cumulative accumulated amount of SOC% unit of charge/discharge current. However, when the full charge condition is reached or a predetermined correction point is reached, the table of SOC values is periodically corrected based on the estimated OCV voltage to charge/discharge. It is possible to provide a method for more accurately measuring the SOC value by preventing the error of the calculated value of the SOC from continuously accumulating as the cycle increases.

Description

The remaining battery capacity measurement method {The Measurment Method of Battery SOC}

In recent years, the demand for batteries that can accumulate and use electrical energy in addition to the demand for alternative energy due to depletion of oil resources and environmental pollution is spreading to various fields such as alternative energy storage systems such as fuel cells.

For electric vehicles such as hybrid (HEV) vehicles, electric vehicles, electric bicycles, and golf-carts, the power density of high-capacity lithium ions, lithium polymers, and nickel-metal hydride batteries is high for the purpose of increasing driving speed and maximum driving distance. The utilization of the battery line is also increasing.

On the other hand, in the case of a gasoline vehicle, since the engine is driven using fuel, there is no great difficulty in measuring the amount of fuel, but in the case of a battery that is a power source of an electric vehicle, it is difficult to measure the residual energy accumulated therein. However, it is very important for the driver of the electric vehicle to know how much energy is left and how much more driving is possible in the future.

The state of charge of the battery means how much energy is left at present. It is used in the current state of charge compared to the maximum capacity that can be stored by charging the battery full. The percentage of possible storage (residual) capacity is defined as "SOC (%)", and a small number of documents also refer to SOC as charged residual capacity.

Since an electric vehicle is a vehicle that is driven by energy charged in a battery, it is very important to determine the remaining capacity ((SOC %)) charged in the battery, and it is important to know the remaining capacity of the battery while driving to obtain information such as the driving distance. Several techniques are being developed to inform people.

The battery charging state (SOC) measurement algorithm is based on various research results, and the representative one is to measure the OCV voltage of the battery and rely on the correlation graph between the OCV voltage and the state of charge (SOC) to calculate the remaining capacity. The second method is a method of calculating the remaining capacity of the battery by adding or subtracting the total amount of electricity charged in the battery and the total amount of electricity discharged through driving. Also, in some cases, the two methods were mixed and used.

As a patent for this, the SOC estimation method of the battery filed in Korea on October 20, 2005 and published on April 25, 2007 and the patent for the battery management system using the same (application number 10-2005-0099088), total A method for estimating SOC of a current battery is proposed using the total battery capacity corresponding to the accumulated discharge amount.

Many attempts have been made to properly set the initial value of the remaining capacity of the battery prior to driving the vehicle. At this time, the initial value of the remaining capacity is usually set based on the open circuit voltage (OCV). In this method, the OCV becomes an absolute reference value of the remaining capacity on the premise that the environment does not change.

In addition, the patent for a method for measuring the remaining battery capacity and its device, filed in Korea on December 13, 2000, and published on May 7, 2001, corrects the accuracy of calculating the total residual amount change according to the actual deterioration of individual batteries. , It provides a method for measuring the remaining battery capacity that can reflect changes in the characteristics of a battery by utilizing it as cycle count data that changes depending on the battery usage state.

In addition, it has been proposed to configure the OCV and SOC at various temperatures as a table to set the initial value of the battery (Korean Patent Application No. 2005-19487). However, the OCV (Open Circuit Voltage) indicates the no-load voltage in a stable state of the battery, but the OCV voltage cannot be measured at the battery terminal when the battery is loaded (discharge current flows). There is a problem that it cannot be used during the discharge time.

Conventional techniques mainly calculate the remaining capacity by relying on a correlation table between the OCV voltage (no-load voltage) and SOC (State Of Charge) of the battery, and measure the OCV voltage, which is the no-load voltage, at the beginning of discharge of the battery. SOC is calculated from the relationship between voltage and SOC.

However, even if the external environment of the device in which the battery is mounted, specifically, the change in the external temperature is not considered or considered, an SOC value is calculated based on the battery voltage before the battery reaches a stable OCV voltage, and thus an error occurs. In addition, in order to reduce the measurement error, SOC was initialized based on the terminal voltage (OCV) without the battery, so it was difficult to trust the SOC measurement.

Second, there is a method of calculating the SOC (recharge remaining capacity) of the battery by adding or subtracting the total amount of electric current charged and discharged through the total amount of electricity charged in the battery and driving.

Also, to improve measurement accuracy In some cases, the above two methods were mixed and used.

However, even though the above two methods of correcting the remaining capacity of the battery are calculated by using the correlation table between the battery OCV voltage and SOC to increase the measurement accuracy, and adding and subtracting the total amount of accumulated and discharged current, SOC is calculated. , OCV voltage can be changed according to the environment (especially temperature), and after a certain period of time after charging or discharging, it can be stabilized to an accurate value, which also hinders accurate measurement of SOC value.

In addition, when the SOC value is calculated based on the accumulated amount of charge and discharge current, if the SOC value is not corrected every appropriate period, the error of the calculated value of the SOC may continuously accumulate as the charge and discharge cycle increases.

The present invention has been proposed to solve the problems of the prior art, and calculates the estimated OCV voltage based on the internal resistance of the battery and the battery charge and discharge current, discharged through the total amount of electricity charged in the battery and driving, etc. The SOC value is calculated and calculated by adding or subtracting the total current accumulation amount, but when the full charge condition is reached or when a predetermined SOC correction point is reached, the charging/discharging cycle is performed by periodically correcting the SOC value mapping table based on the estimated OCV voltage. Since it is possible to prevent the error of the calculated value of the SOC from continuously accumulating as it increases, it is possible to provide a method capable of accurately measuring the SOC value than the conventional method.

Hereinafter, in the detailed description of the present invention, the battery means a battery unit cell or a battery pack in which battery unit cells are connected in series. Therefore, the present invention is used to measure SOC of a battery unit cell or a battery pack in which battery unit cells are connected in series. It is possible to apply.

In more detail with respect to the technical solution in the present invention,

1) experimentally calculating a correlation table of estimated OCV voltage and SOC values corresponding to the passage of discharge time and storing them in a memory of a BMS (battery management system);

2) When the state of charge of the battery becomes a full charge condition, the battery terminal voltage is measured to calculate the estimated OCV voltage, and in step 1), the estimated OCV voltage corresponding to the stored SOC 100% is measured. Correcting the calculated value and proportionally correcting a correlation table corresponding to the passage of time by a predetermined calculation formula accordingly;

3) after the full charge, measuring and calculating the estimated OCV voltage according to the elapse of charge and discharge time, and calculating the SOC value by the charge and discharge current integration amount.

4) When the SOC value calculated in step 3) reaches a predetermined correction point, the calculation operation of the charge/discharge current integrated amount is separately started from the point when the correction point is reached, and the estimated OCV voltage from the point at which it is the correction point. Calculating an accumulated charge/discharge current amount during a section at which the discharge end voltage is reached;

5) It is preferable to further include a step of correcting an error in the correlation table (data) corresponding to the SOC value corresponding to the accumulated charge/discharge current amount and the SOC value obtained at the correction point in step 4). .

The correlation table of the estimated OCV voltage and SOC value may include one or more of a correlation function, a correlation equation, or a correlation graph capable of mapping the correlation data of the estimated OCV voltage and SOC of the battery in a predetermined time elapsed unit.

In addition, it is preferable to designate the first correction point when the SOC value is 20% based on the discharge depth 80%, which is generally used when the battery is discharged. In addition Depending on the type of battery and charging/discharging characteristics, A plurality of correction points are additionally set between the point corresponding to the full charge condition and the predetermined first correction point, the discharge depth of 80% (ie, SOC corresponds to 100% to 20%), and the additionally set correction In this regard, a method for further correcting an error in the correlation table (data) of the SOC It may be advantageous in terms of further improving SOC measurement accuracy.

In addition, the correlation table preferably further includes any one or more of the battery temperature and the internal resistance in addition to the estimated OCV voltage and SOC value in units of charging and discharging time, thereby making the battery according to the temperature change or long-term use of the battery The SOC value may be corrected in consideration of the capacity reduction factor.

As described above, according to the present invention, the estimated OCV voltage can be calculated based on the internal resistance of the battery and the charge/discharge current, and the SOC value can be accurately calculated based on this, and also the full charge condition or SOC value or the estimated OCV voltage When the measured value arrives at a predetermined correction point, by periodically calibrating the correlation table of the SOC value, it is possible to prevent repeatedly accumulating the error of the SOC operation value as charge/discharge time or cycle elapses. SOC values can be measured more accurately. In addition, the SOC value can be corrected in consideration of not only a change in temperature of the battery but also a decrease in capacity due to aging, and thus an effect of reducing measurement errors due to environmental changes can be obtained.

1 is a correlation graph between the battery terminal voltage and SOC value according to the discharge load size.
2 is a view showing a correlation between the no-load voltage OCV and the terminal voltage according to the discharge current size of the battery cell.
3 is an SOC estimation table mapped in response to an elapsed time as an embodiment of the present invention
4 is a graph showing the results of calibration of the SOC mapping table for the estimated OCV voltage, which is an embodiment of the present invention.

SOC% is a value that represents the ratio between the'amount of usable storage energy' and'the maximum capacity that can be fully charged' when the battery is currently charged, and corresponds to the fuel gauge of the engine vehicle. can do.

식 (1)

Equation (1)

Where C _o (Battery Capacity) refers to the capacity of the battery and becomes a reference value (corresponding to SOC 100%) in obtaining SOC %. It means the total amount of discharged electric charge when discharged with a constant current (eg, 1.0C), that is, the total accumulated (accumulated) amount of discharge current according to the elapse of discharge time.

When the battery has been used for a long time and aged, the capacity that can be charged when fully charged C _o (Battery Capacity) can be reduced to about 80% of the new rated design capacity.

On the other hand, the accumulated amount of charge and discharge current is essential data for estimating the state of charge (SOC) of the battery. In the present invention, the SOC value is calculated based on the correlation table of the accumulated amount of current measured over time during charging and discharging of the battery and the estimated OCV voltage corresponding thereto, and the SOC correction algorithm is appropriately implemented to achieve SOC Re-calibration of the correlation table of values and SOC values can be easily read out if necessary.

1 shows a correlation graph between the battery terminal voltage (V) and SOC according to the discharge load size.

Referring to FIG. 1, as the battery discharge progresses, the battery terminal voltage V and SOC gradually decrease, and as the SOC of the battery decreases, the battery electromotive force E has the same slope in relation to the battery terminal voltage V. You can see that it is strong. In general, a secondary battery, such as a lead-acid battery or a lithium-ion-based battery, rapidly decreases in terminal voltage (V) at the beginning of discharge, and then discharges (from 1 to 2 minutes after the start of discharge after full charge). It has a discharge characteristic that gradually decreases and the terminal voltage (V) decreases rapidly from the end of discharge (the point where the SOC value is approximately 10% or less), but in the case of a lithium iron phosphate (LFP) battery, the SOC value as discharge elapses It is known that the terminal voltage in the interval of about 98% to 10% has a discharge characteristic that is hardly reduced compared to other types of lithium-based batteries.

FIG. 2 shows the correlation between the internal resistance of the battery cell and the no-load voltage OCV or terminal voltage according to the discharge current size.

As shown in FIG. 2, the graph as shown in FIG. 2 can be obtained by measuring the load current and the terminal voltage of the battery while increasing the discharge current (eg, from 0 to 2.0C). The voltage shown in the voltmeter in FIG. 2 is a potential difference between two pole terminals of the battery when a discharge current flows in the battery, which indicates the terminal voltage of the battery. Also, it can be seen that the slope of the straight line is the same as the internal resistance of the battery (cell).

Even if the storage energy capacity (Ah) of the battery is constant, the voltage drop due to the internal resistance of the battery occurs as the discharge current increases, so the battery terminal voltage is lowered in proportion to the increase in the discharge current. When the discharge current flows in this way, even if the battery's electromotive force E does not change due to the constant storage energy capacity (Ah) of the battery, a voltage drop due to the internal resistance of the battery occurs and the terminal voltage of the battery decreases.

In the graph of FIG. 2, the terminal voltage when the straight line extends to meet the voltage V-axis is the OCV voltage of the battery when the discharge current is 0. That is, when the discharge current is 0, there is no voltage drop due to the internal resistance, and the electromotive force E of the battery at this time becomes the same value as the open circuit voltage (OCV), which is the no-load terminal voltage.

In general, the battery OCV voltage is slightly changed depending on the factors related to the charging and discharging conditions immediately after charging, so it is preferable to measure it after a stable period.

When a battery is used in the field, the magnitude of the discharge current varies from time to time as the discharge time elapses, and the voltage of the battery terminal also changes depending on the size of the discharge current. On the other hand, since the voltage E corresponding to the internal electromotive force (energy) of the battery is constant regardless of the size of the discharge current, focusing on these characteristics, it does not change according to the size of the discharge current and has a direct correlation with SOC. OCV voltage' can be set virtually. The'estimated OCV voltage' has an intrinsic value correlated to each charge and discharge current according to the elapsed time of charge and discharge, and the battery has no load. The estimated OCV voltage becomes the same value as the terminal voltage when the battery is not loaded, and is a value corresponding to the electromotive force E of the battery.

The estimated OCV voltage set as a virtual value in the above is not a value that can be measured at the actual external terminal of the battery, but can be calculated from the battery terminal voltage in consideration of the magnitude of the discharge current, and is not related to the magnitude of the load current. It can be effectively mapped so that only the voltage and SOC values can be correlated 1:1, and the SOC value corresponding to the estimated OCV voltage can be easily read from the 1:1 mapped table.

Hereinafter, a method of calculating the estimated OCV required for mapping the correlation table will be described.

As described above, the estimated OCV voltage can be obtained from a correlation between the battery terminal voltage at load and the internal resistance of the battery and the current flowing through the battery, and has the same meaning as the electromotive force E of the battery.

If the electromotive force of the battery is E (the same as the terminal voltage at no load as described above), the battery terminal voltage during actual discharge is V , the internal resistance of the battery is r , and the discharge current flowing through the battery is I , then Equation 2 Relationships are established.

(식 2)

(Equation 2)

Here, the battery electromotive force E is equal to the estimated OCV voltage.

Thus, random At the time of charge and discharge elapsed time t , when the charge and discharge current It flows, the estimated OCV voltage of the battery can be expressed as OCVt , which is a function having a time variable as shown in Equation 3. Where Vt is Battery terminal voltage.

(식 3)

(Equation 3)

In addition, the internal resistance r of the battery slightly increases as the battery temperature decreases, and the battery capacity decreases as the charge/discharge cycle increases, so that the battery electromotive force E decreases somewhat. Accordingly, Equation 3 may be extended as Equation 4 so that SOC can be more accurately calculated in consideration of such cases.

(식 4)

(Equation 4)

Here, Equation 4 is the characteristic coefficient k ₁ And k ₂ It is important to note that the voltage of the battery terminal is greater than the estimated OCV voltage during charging because it becomes equal to Eq. 3 when all conditions are 1 and the current It has a negative (-) sign when charging the battery.

In addition, in Equation 4, Vt is the battery terminal voltage at any time t , k ₁ Is the temperature coefficient of the internal resistance r , k ₂ The It is a factor for aging change as charge/discharge cycles increase. The internal resistance r may be preferably applied to Eq. (3) or Eq. (4) by periodically measuring in a battery management device (BMS) according to a known inner resistance measurement method such as a DC discharge measurement method or an AC impedance measurement method. have.

k ₁ Is a constant corresponding to a capacity derating factor due to an increase in the internal resistance r depending on the ambient temperature during charging and discharging, and can be expressed as a function of the battery usage temperature or usage time. Storage battery manufacturers disclose this as a graph showing the reduction coefficient, as a function of ambient temperature or usage time, or as a data table.

k ₂ Is a constant that varies depending on the electrode plate material, thickness or electrolyte of the cell constituting the battery cell, and further, the manufacturing method. For example, in the case of a sealed lead battery, it is around 0.9. The degree of decrease in the maximum full charge capacity of a lithium ion or lithium polymer battery decreases by a few percent as the charge/discharge cycle (time) progresses, but the internal resistance changes approximately twice (k ₂ Is increased to 2.0 level).

As shown in Equation 3 or Equation 4 above, since the size of the discharge current is not constant and varies depending on the size of the load during discharge of the battery, such as when driving an electric vehicle, by measuring the battery terminal voltage Vt and It over time Estimated OCVt over time The voltage can be calculated from Equation 3 or Equation 4.

Meanwhile, as the charge/discharge cycles increase, the maximum capacity (Ah) that can be fully charged becomes a power fade. The energy storage (remaining) energy amount (Ah) usable in the current state of charge in a battery having a maximum capacity is depleted when the discharge end voltage is reached with a predetermined load current size after the battery is fully charged. It corresponds to the total accumulated amount of discharge current discharged to (Ah unit).

Hereinafter, a method for calculating SOC of a battery, which is a preferred embodiment of the present invention, will be described.

In order to accurately calculate the SOC based on the accumulated amount of the discharge current amount of the battery equipped with the BMS, first, the battery terminal voltage is measured by Equation 3 or Equation 4 to calculate the estimated OCV voltage and corresponds to various estimated OCV voltages. The SOC correlation table consisting of SOC values is experimentally obtained and stored in the non-volatile memory of the BMS.

At this time, the capacity reduction coefficient k ₁ depending on the ambient temperature, internal resistance, or temperature of the battery I Capacity reduction coefficient k ₂ It may be desirable to separately obtain and store it in advance, and read the OCVt voltage corresponding to the passage of time from Equation 4 at the necessary time to take this into account when calculating the OCVt voltage. You will be able to measure accurately.

To summarize the embodiments of the present invention step by step,

Mapping a correlation table of estimated OCV and SOC values corresponding to charging and discharging time lapses; Calculating SOC by adding or subtracting the total accumulated charge/discharge current of the battery; And when the full charge condition arrives or the calculated SOC value arrives at a predetermined correction point, periodically correcting the correlation table of the SOC value.

4 is a graph showing a SOC mapping table curve corresponding to an estimated OCV voltage and a corrected result of the SOC mapping table according to an embodiment of the present invention.

More specifically, curve ① represents the graph of the SOC mapping table for the estimated OCV voltage before calibration, ② is the graph of the mapping table for the estimated OCV voltage corrected after the full charge, and ③ is the first This is a graph of the mapping table for the estimated OCV voltage corrected at the correction point.

First, when the start operation key is started and the BMS control unit of the battery management system requests the SOC% value at the present time, the SOC correlation table maps the SOC value corresponding to the estimated OCVt voltage for each elapsed time t as shown in curve ①. Therefore, the terminal voltage of the battery according to the current load current is measured and the corresponding OCV is estimated. It is possible to calculate the voltage and read the SOC value at the current time corresponding to the estimated OCV value obtained as a result from the mapped SOC correlation table. In this case, if there is no mapping data that exactly matches the elapsed time of charge and discharge, the SOC value can be newly calculated by adding or subtracting the accumulated amount of current according to the elapse of charge and discharge time.
Meanwhile In the case of a lithium iron phosphate (LFP) battery, unlike other types of lithium-based batteries, as the discharge time elapses from about 1 to 2 minutes after the start of discharge (the SOC value is about 98% to 10%), Even when the depth of discharge gradually increases, the terminal voltage has a small discharge characteristic. As such, in the case of a lithium iron phosphate (LFP) battery, Since the slope of the proportional curve between estimated OCVs compared to SOC values is very low, An accurate OCV value can be accurately obtained by accurately measuring a minute voltage change of a battery terminal, and an accurate SOC value at the current time can be read and calculated based on the estimated OCV value from the mapped SOC correlation table.
In addition, In general, in the case of a lithium-based battery, since the consumption by self-discharge in the standby state is extremely small and the SOC value is hardly changed, it may be preferable to re-read and use the SOC value read immediately before the standby state.

If charging/discharging continues after starting, the maximum capacity that can fully charge the accumulated charge/discharge current (unit: Amps.Hour) for the elapsed time from the starting point to the current point C _o It is divided into (Battery Capacity) to obtain the converted value in SOC units, and this value is added or subtracted (+, -) to the SOC value read in the previous step to newly calculate the SOC value according to the charging and discharging time.

Subsequently, when a full charge state is detected because the charge and discharge time continues, the estimated OCV voltage is calculated from the measured battery terminal voltage, and the estimated OCV voltage corresponding to SOC 100% in the correlation table of the pre-calibration step is The estimated OCV voltage mapped to be equal to the calculation result value is newly corrected. The estimated OCV voltage obtained at this time will be almost the same as the battery terminal voltage since the charging current is close to 0 (zero).

In detail in FIG. 4 through the curve ② which is the “mapping table graph for the estimated OCV voltage corrected after full charge”, from the horizontal axis to the point of the curve ② When the full charge state is reached, the estimated OCV of the table mapped in the immediately preceding step The voltage Vo(to) It is corrected by substituting the value of V1(to) , which is the estimated OCV value under full charge condition.

In addition, the discharge elapsed time (t 1 , t2 , t3) immediately or after the estimated OCV voltage is newly corrected in the above step. ...Number tn Correct the estimated OCV voltages for all intervals of ). Even after calibration, the estimated OCV ( tn ) value corresponding to the end point of the discharge must be the Vo ( tn ) value to be the same as the value before calibration, so that an equation such as Equation (5) can be derived by these conditions, and the discharge elapsed time ( t 1 , t2 , t3 .... tn It is desirable to correct each OCV ( ti ) voltage corresponding to) according to equation (5).

식 (5)

Equation (5)

Where OCV' ( ti ) is an estimate corrected over the discharge time The OCV (t) value is displayed, and the curve ②, which is the graph after the correction, is compared with the curve ① before and after calibration, and the size difference for each estimated OCV (t) value before and after calibration is proportional to the discharge time. As it decreases gradually, the graphs before and after calibration have a shape that is collected at the same level (position) at the end of discharge.

If charging/discharging continues afterwards, a new SOC is added or subtracted by adding (+,-) the accumulated amount of charging/discharging current in SOC units to the SOC reference value read from the mapping table corrected in the previous step over time. The value can be calculated and displayed, and it may also be desirable to re-calibrate the estimated OCV voltage and SOC values corrected in the previous step in consideration of the percentage of charge and discharge current integration.

If the battery is not charged/discharged for a long time without being charged or restarted after the start operation key is increased, the estimated OCV voltage is calculated based on the battery terminal voltage, and the recently corrected SOC correlation is based on the calculated value. The SOC value corresponding to the estimated OCV voltage can be read back from the table.

Subsequently, when the charging/discharging period is continued and the SOC value currently calculated reaches a predetermined correction point (corresponding to point A, which is the first correction point in the embodiment of FIG. 4), the calculation operation of the accumulated charge/discharge current is separately calculated. It starts. At the same time, it may be desirable to reset the accumulated charge/discharge current calculated to date.

In addition, since the discharge continues after the correction point, the estimated OCV value is the discharge end voltage. When ( Vo(tn) ) is reached , the The accumulated charge/discharge current during the discharge period ( tm ~ tn ) after the correction point is calculated and converted into SOC values (hereinafter, converted into SOC units of charge/discharge current accumulated amounts). At the same time, the SOC value corresponding to the time point tn when the estimated OCV value reaches the discharge end voltage Vo(tn ) is corrected to 0 (zero).

If, based on the full charge, the SOC unit conversion value of the accumulated charge/discharge current during the discharge period (tm ~ tn) according to the curve ② corrected in the immediately preceding step does not have an error and is correct, the charge/discharge The SOC unit conversion value of the current accumulation amount will be the same as the SOC value at the correction point (point A) of the elapsed time tm .

curve ③ is a graph for the estimated OCV voltage table corrected based on the first correction point when there is an error in the SOC unit conversion value of the above-mentioned charge and discharge current integration amount as an embodiment of the present invention. When comparing the SOC value corresponding to the correction point A and the SOC unit conversion value of the accumulated charge/discharge current during the discharge periods tm to tn, the curve ③ indicates that the estimated OCV voltage corresponding to the SOC unit conversion value is V1 _{( tk )} -V1 _{( ttm )} than the estimated OCV value corresponding to the point A. It will be appreciated that this is an embodiment for the increased case.

As described above, the accumulated charge and discharge current accumulated during the discharge period ( tm ~ tn ) in the curve ② is When the SOC unit conversion value is measured to be larger than the SOC value at a predetermined correction point obtained from the SOC correlation table, the magnitude of the estimated OCV voltage corresponding to the SOC unit conversion value of the accumulated charge and discharge current accumulation amount is A in curve ② Than the estimated OCV voltage value corresponding to the point location ( V1 _(tk) -V1 _(ttm) ) It should be increased by, and thus it will correspond to the estimated OCV value at point B corresponding to the elapsed time tk in curve ②. Of course, when the SOC unit conversion value at the correction point is measured to be less than the SOC value corresponding to the A point, the elapsed time is increased, ie, moves along the curve ② between elapsed times tm and tn opposite to the B point. And the estimated OCV voltage corresponding to the shifted time point will be further reduced.

If an error occurs in the SOC value obtained in the previous step as described above, the estimated OCV corresponding to the correction point (point A) To the value ( V1 _{( tm )} ) From above As much as the size of the error ( V1 _(tk) -V1 _(tm) ) Estimated OCV after correction corresponding to time tm by adding or subtracting (+,-) The value is corrected to the value corresponding to point A'of the curve ③, and the estimated OCV value is calculated according to equation (6) or equation (7). By correcting the discharge time The mapped correlation table can be corrected to have the shape of the curve ③.

가

이면 SOC=100% 에 해당되고, 교정후의 추정 OCV 전압

은 교정전의 추정 OCV 전압

과 같도록 교정되게 한다.Where elapsed time

end

SOC = 100%, the estimated OCV voltage after calibration

Is the estimated OCV voltage before calibration

It is calibrated to be equal to.

가 t1 에서 tm 사이인

경우이면, 교정후의 추정 OCV 전압인

를 식 (6)에 의하여 교정되게 한다.Also elapsed time

Is between t1 and tm

If yes, the estimated OCV voltage after calibration

To be corrected by equation (6).

식 (6)

Equation (6)

가 tm 에서 tn 사이인

경우이면, 교정후의 추정 OCV 전압인

를 식 (7)에 의하여 교정되게 한다.Also elapsed time

Is between tm and tn

If yes, the estimated OCV voltage after calibration

To be corrected by equation (7).

식 (7)

Equation (7)

가

이면 SOC=0 %인 경우에 해당되고, 교정후의 추정 OCV 전압

은, 교정전의 추정 OCV 전압인

와 같도록 교정한다.Also elapsed time

end

If it is SOC=0%, the estimated OCV voltage after calibration

Is the estimated OCV voltage before calibration

Correct as follows.

If charging and discharging continues even after the calibration, the calibration process is repeatedly executed, and in this way, it is possible to correct an error in the SOC value that can be accumulated periodically during calculation.

As the predetermined correction point, in reality, the depth of discharge (DOD) of the battery is mainly used at 80%, so it is preferable to select the point at which the SOC value is 20% as the first correction point.

In the charging and discharging elapsed time (t1, t2, t3 to tn), the data mapping interval is selected from a few seconds to several minutes in consideration of the total charging and discharging time of the battery to be measured to ensure sufficient measurement accuracy or resolution. desirable. In other words, if you consider that the battery is fully discharged within 30 minutes for rapid discharge use, at least hundreds of data must be secured to ensure accuracy and resolution, so several seconds (eg, 5 seconds) depending on the elapsed time of charging and discharging. ) Mapping data will be needed at intervals.

Further, the correlation table of the estimated OCV voltage and SOC value may include any one of a correlation function, a correlation equation, or a correlation graph capable of mapping correlation data of the estimated OCV voltage and SOC value.

The correlation table, in addition to the estimated OCV voltage and SOC values in a predetermined time elapsed unit, the reduction coefficient k ₁ according to the temperature, internal resistance, and temperature of the battery Or over the discharge cycle time Abatement factor k ₂ It is preferable to further include at least any one of.

In addition, in addition to the predetermined first correction point in the above step, the estimated OCV voltage corresponding to the depth of discharge that may appear in the course of the actual charge/discharge cycle is additionally set as a correction point, and is described above based on the additionally set correction point. It would be desirable to recalibrate the SOC value according to one method to increase the measurement accuracy, but it should be considered that the SOC measurement algorithm may be more complicated.

In addition, if the battery capacity is relatively small or the accuracy of measurement and computation is low, and there is no problem in use, it may be desirable to calculate the estimated OCV voltage according to Equation 3 according to the judgment of the operator.

In addition, in order to optimize the calculation time or calculation algorithm, the estimated OCV voltage and SOC values mapped corresponding to the discharge time lapse are calculated based on the battery rated charge/discharge current size in order to meet the actual situation of the site. It should be, and it would be desirable to perform it so that it can be further corrected based on the capacity reduction coefficient according to changes in battery temperature or battery age.

In the present invention below Briefly step-by-step summarizing or calibrating the SOC method over time as the battery charge/discharge time passes,

First, OCVt is measured and calculated for each elapsed time t according to the elapse of charge and discharge time (100),
An SOC correlation table having SOC values corresponding to the various OCVt is experimentally obtained, mapped by elapsed time, and stored in the memory of the BMS. (101)

If the BMS control unit requests the SOC% value at the present time, the SOC value at the present time is read from the stored SOC correlation table. (102)

Subsequently, the accumulated charge/discharge current amount for the elapsed time from the starting point to the current point is divided by the full charge capacity to obtain a value converted in SOC units, and this value is added to or subtracted from the SOC value read in the previous step (102). ,-) to calculate the SOC value over time. (103)

When the state of full charge is reached, the estimated OCV voltage is calculated, and the estimated OCV voltage corresponding to SOC 100% in the SOC correlation table of the previous step (102 or 103) is corrected to the current calculated value, and the discharge elapsed time (t 1) , t2 , t3 ...Number tn Correct the estimated OCV voltages for the section according to equation (5). (104)

The discharge continues after the predetermined correction point, and the estimated OCV value is the discharge end voltage. When reached (Vo (tn)), the charge for the subsequent predetermined correction point discharge interval (tm ~ tn). Obtaining the amount of discharge current integration and converts it to a SOC value unit (105)

The SOC value obtained in the previous step 104 is compared with the value converted in SOC units for the accumulated charge/discharge current during the discharge period ( tm ~ tn ) in step 105, and if an error occurs, as much as the OCV voltage error generated. Add or subtract (+,-), in the previous step 104 The corrected SOC correlation table is re-calibrated through an operation according to equation (6) or equation (7). (106)

As described above, the present invention has been described with reference to preferred embodiments, but the present invention is not limited to the above-described embodiments or the foregoing, and those skilled in the art to which the present invention pertains can make various modifications and modifications from these descriptions. Deformation is possible. Accordingly, the spirit of the present invention will be said to be within the scope of the spirit of the invention, both equivalent or equivalent modifications thereof.

The battery SOC measurement technology of the present invention can be used to display the state of charge or the remaining battery charge during use or charging in a home electronic device such as a mobile phone, PDA, or laptop. In particular, in an electric vehicle such as a hybrid vehicle, an EV electric vehicle, an electric bicycle, or a golf cart, which uses a series of batteries having a high power density such as lithium ion and lithium polymer as the main power source, the driver can use the battery as a fuel gauge. It is expected that the industrial capacity will be very high because the remaining capacity (SOC) of the vehicle needs to be notified to the driver to provide information such as the remaining mileage more accurately.

Claims (10)

In calculating the SOC from the estimated OCV and SOC correlation of the battery,
Ⅰ) Arbitrary according to charging and discharging time Every elapsed time t Calculating an estimated OCV voltage ( OCVt ) corresponding to the charge and discharge current amount;
Ii ) calculating and mapping a correlation table of SOC values corresponding to the estimated OCV voltage ( OCVt );
Iii) When the full charge state is reached, the battery terminal voltage is measured to calculate the estimated OCV voltage, and the estimated OCV voltage corresponding to SOC 100% mapped in the immediately preceding step is corrected to the estimated OCV voltage of the calculated full charge state, Correcting the correlation table of each OCV voltage ( OCVt ) according to the charging and discharging time according to the correction result; And
Iii) Before or after the step iii), measuring and calculating an estimated OCV voltage at a required time point, and calculating an SOC value from the correlation table. According to claim 1,
When the measured and calculated SOC value reaches a predetermined correction point,
a) separately measuring and accumulating charge and discharge currents over time.
b) measuring and calculating the accumulated amount of charge/discharge current disclosed in the step (a) until a point in time at which the estimated OCV voltage reaches the discharge end voltage and converting the accumulated amount into SOC value units;
c) The accumulated and accumulated charge/discharge current in SOC units measured and computed in step (b) and SOC values at SOC correction points measured before step (b) are compared to each other, and the corresponding correlation table has an error. SOC calibration method further comprising the step of correcting. A battery management system is provided, and SOC is calculated by integrating charge and discharge currents.
a) estimated OCV Experimentally obtaining an SOC correlation table having SOC values corresponding to and mapping the charge/discharge elapsed time periods and storing them in a memory of a battery management system (BMS) (101);
b) if the SOC% value at the present time is requested, reading the SOC value at the present time from the stored SOC correlation table;
c) The accumulated cumulative charge/discharge current over the charging/discharging time is divided by the full charge capacity to obtain the converted value in SOC units, and this value is added (+,-) to the SOC value read in step (b). SOC calculation method comprising; calculating the SOC value over time again. The method of claim 1 or 3,
The correlation table,
SOC calculation method comprising a correlation function, a correlation equation or a correlation graph capable of mapping the correlation data of the estimated OCV and SOC in a predetermined time unit. According to claim 1,
Step ii) of mapping the correlation table comprises:
a) Chung. Experimentally calculating correlation table data of estimated OCV and SOC values corresponding to discharge time lapse; And
b) storing the data calculated in step a) in the memory of the battery management system; SOC calculation method comprising a. According to claim 1,
To calibrate the correlation table, the calculation formula for the estimated OCV voltage OCV' ( ti ) after the calibration at the charge and discharge elapsed time ti is:
Equation 5

SOC calculation method characterized in that the.
(Where, OCV ( ti ) is the estimated OCV voltage of the pre-calibration phase at the elapsed time ti , Vo ( to ) is the estimated OCV voltage of the pre-calibration phase to the elapsed time to , V1 ( to ) is the elapsed time to the full-charge state Estimated OCV voltage at, tn indicates the elapsed time corresponding to the end point of discharge) According to claim 2,
To calibrate the Singi Correlation Table, the equation for the estimated OCV voltage OCV “( ti ) after the calibration at the charge and discharge elapsed time ti is
Equation 6

or
Equation 7

SOC calculation method characterized in that the.
(Where OCV' ( ti ) is the estimated OCV voltage before step (c) at the elapsed time ti , tm is a predetermined The elapsed time to the correction point, tn is the elapsed time until the discharge end voltage is reached, and V1 ( tm ) is The estimated OCV voltage at the elapsed time tm , ( V1 _(tk) -V1 _(tm) ), is the charge during the elapsed time ( tm to tn ) at which the SOC value at the predetermined correction point ( tm ) and the discharge end voltage are reached. .Displays the error for the estimated OCV value generated mutually with the converted value of S OC unit for the accumulated accumulation amount of discharge current) The method of claim 1 or 3,
The estimated OCV includes charging and discharging currents depending on the elapsed time t of charging and discharging; Battery internal resistance; And a battery temperature, an internal resistance temperature coefficient, or a reduction coefficient according to aging change. The method of claim 4,
The SOC correlation table may include a battery temperature, an internal resistance, a reduction coefficient according to a temperature, or a discharge cycle time elapsed in units of a predetermined elapsed time. Reduction factor SOC calculation method characterized in that the SOC of each estimated OCV voltage is mapped by further including at least one or more coefficients. According to claim 2,
The SOC correction method characterized in that the predetermined correction point of the SOC value includes a point where the measured SOC value becomes 20% as the first correction point.

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