Method of adjusting SOC for battery and battery management system using the same

A state of charge (SOC) compensation method of a battery and a battery management system using the same. A charge/discharge current of the battery is used for calculating the SOC and an SOC voltage that is a value in an OCV table, a rheobasic voltage is calculated, an error in the SOC is measured by using a difference between the SOC voltage and the rheobasic voltage, and a range of the error is determined among multiple effective ranges. Subsequently, the SOC is compensated by using a compensation SOC set in correspondence with a range in which the error is included to thereby measure a more accurate SOC of the battery.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2005-0127722, filed in the Korean Intellectual Property Office on Dec. 22, 2005, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a battery management system. More particularly, the present invention relates to a method for correcting a state of charge (SOC) of a battery in a vehicle using electrical energy, and a battery management system using the same.

2. Description of the Related Art

Vehicles with an internal combustion engine using gasoline or diesel have caused serious air pollution. Accordingly, various undertakings for developing electric or hybrid vehicles have recently been made to reduce such air pollution.

An electric vehicle is run by using electrical energy output by a battery. Since the electric vehicle mainly uses a battery formed of one battery pack including a plurality of rechargeable/dischargeable secondary cells, it produces no emission gases and generates less noise.

A hybrid vehicle is a gasoline-electric hybrid vehicle that uses gasoline to power an internal-combustion engine and a battery to power an electric motor. Recently, hybrid vehicles using an internal-combustion engine and fuel cells and hybrid vehicles using a battery and fuel cells have been developed. The fuel cells directly obtain electrical energy by generating a chemical reaction while hydrogen and oxygen are continuously provided.

Such a vehicle using electrical energy drives a generator with residual power to charge the battery when an engine outputs high power, and drives a motor by using the electric power of the battery to overcome insufficiency of power when the engine outputs low power. In this case, the battery is discharged.

Since battery performance directly affects a vehicle using electrical energy, it is generally required that each battery cell has great performance. Also, it is generally required to provide a battery management system (BMS) for measuring voltage and current of the overall battery to efficiently manage charging/discharging operations of each battery cell.

Thus, a conventional BMS measures values of a voltage, a current, and a temperature of the battery to estimate a state of charge (SOC) through an operation, and controls the SOC to improve fuel consumption efficiency of the vehicle.

The SOC is controlled to provide a balance between motor driving for power assist during acceleration and energy recovery (e.g., regenerative braking) during deceleration. In general, for example, the battery over-discharging is controlled when the SOC is decreased to 50% and the battery over-charging is controlled when the SOC is increased to 70%, to maintain the range of the SOC of the battery within 50% to 70% to thereby keep the SOC close to the center of the control.

In order to accurately control the SOC, it is essential to accurately estimate SOC of the battery in the charging/discharging state.

Conventionally, there are two SOC estimation methods. One is to measure a charge current and a discharge current (charge current has a negative (−) sign and discharge current has a positive (+) sign), multiply the current value with charge efficiency, integrate the multiplication results for a predetermined time period to calculate integration capacity, and estimate an SOC based on the integration capacity. The other method is to measure and memorize a plurality of pair data of a discharge/charge current and a corresponding terminal voltage of a rechargeable battery, obtain a one-dimensional approximation line (voltage V-current I) from the pair data, and estimate an SOC based on the no-load voltage (open circuit voltage, OCV) that is a voltage (V section of V-I approximate line) calculated in correspondence to a current value of zero.

However, in the case of the SOC estimation method that uses the integration capacity, the charge efficiency applied to the integration of the current value depends on the SOC value, the current value, and the temperature, and therefore it is difficult to estimate the most adequate charge efficiency for each condition. Moreover, it is also difficult to calculate the amount of self discharge when the battery is in a non-use state.

Therefore, the conventional SOC measuring method that uses the integration capacity cannot measure an accurate SOC because an error between an exact value and an estimated value of the SOC increases as time elapses.

SUMMARY OF THE INVENTION

In exemplary embodiments according to the present invention, a state of charge (SOC) compensation method for compensating an error of an SOC obtained by using an SOC estimation method, is provided.

In addition, exemplary embodiments of the present invention provide a battery management system for providing a more accurate SOC of a battery to an engine control unit of a vehicle by performing SOC compensation when an error of an SOC estimated by using an integration capacity exceeds a limited range.

An SOC compensation method of a battery management system according to an exemplary embodiment of the present invention compensates an SOC of a battery. The SOC compensation method includes: calculating the SOC of the battery and an SOC voltage corresponding to the SOC by using a charging/discharging current of the battery; calculating a rheobasic voltage of the battery by using the charging/discharging current of the battery, a voltage of the battery, and an internal resistance of the battery; calculating an integration error corresponding to a difference between the SOC voltage and the rheobasic voltage of the battery; determining in which effective range the integration error is included among multiple effective ranges; adding a compensation SOC to the SOC to compensate the SOC, so that the compensated SOC is included within an SOC range corresponding to the minimum effective range.

An SOC compensation method of a battery management system according to another exemplary embodiment of the present invention compensates an SOC of a battery. The SOC compensation method includes: calculating the SOC of the battery and an SOC voltage that corresponds to the SOC by using a charging/discharging current of the battery; measuring a charging/discharging voltage of the battery; calculating an integration error that corresponds to a difference between the SOC voltage and the charging/discharging voltage of the battery; determining in which effective range the integration error is included among multiple effective ranges; and adding a compensation SOC corresponding to the effective range in which the integration error is included among the multiple effective ranges to the SOC to make the compensated SOC included in an SOC range that corresponds to a minimum effective range among the multiple effective ranges.

A driving method according to another exemplary embodiment of the present invention is provided to drive a battery management system coupled to an engine control unit (ECU) of a vehicle that uses electrical energy. The driving method includes: measuring a charging/discharging current and a pack voltage of a battery; calculating an SOC of the battery and an SOC voltage that corresponds to the SOC by using the charging/discharging current of the battery; calculating a rheobasic voltage of the battery by using the charging/discharging current of the battery, a voltage of the battery, and an internal resistance of the battery; calculating an integration error that corresponds to a difference between the SOC voltage and the rheobasic voltage; determining in which effective range the calculated integration error is included among multiple effective ranges; adding a compensation SOC that corresponds to the effective range in which the integration error is included among the multiple effective ranges to the SOC to make a compensated SOC included in an SOC range that corresponds to a minimum effective range among the multiple effective ranges; and outputting the compensated SOC as a current SOC of the battery to the ECU.

In said determining in which effective range the integration error is included, the integration error may be compared with at least one of an upper threshold value or a lower threshold value of the minimum effective range among the multiple effective ranges, the effective range in which the integration error is included may be determined by repeating the comparison between the integration error and at least one of an upper threshold value or a lower threshold value of a next smallest effective range among the multiple effective ranges when the integration error exceeds the upper threshold value or the lower threshold value of the minimum effective range among the multiple effective ranges.

In said adding the compensation SOC, when the integration error exceeds an upper threshold value of a specific effective range, the compensation SOC may be subtracted from the SOC, and when the integration error exceeds a lower threshold value of the specific effective range, the compensation SOC may be added to the SOC.

The upper threshold value has a positive value and the lower threshold value has a negative value, and an absolute value of the upper threshold value and an absolute value of the lower threshold value are the same.

In said calculating the SOC, an integration current may be measured by employing a current integration method that uses a charge/discharge current of the battery, the SOC corresponding to the integration current may be calculated, and the SOC voltage may be calculated by applying the SOC to an open circuit voltage (OCV) table.

A driving method according to another exemplary embodiment of the present invention is provided to drive a battery management system coupled to an engine control unit (ECU) of a vehicle that uses electrical energy. The driving method includes: measuring a charging/discharging current and a pack voltage of a battery; calculating a state of charge (SOC) of the battery and an SOC voltage that corresponds to the SOC by using the charging/discharging current of the battery; measuring a charging/discharging voltage of the battery; calculating an integration error that corresponds to a difference between the SOC voltage and the charging/discharging voltage; determining in which effective range the calculated integration error is included among multiple effective ranges; adding a compensation SOC corresponding to the effective range in which the integration error is included among the multiple effective ranges to the SOC to make the compensated SOC included in an SOC range that corresponds to a minimum effective range among the multiple effective ranges; and outputting the compensated SOC as a current SOC of the battery to the ECU.

A battery management system according to another exemplary embodiment of the present invention is provided to manage a battery. The battery management system outputs an SOC of the battery to an engine control unit (ECU) of a vehicle that uses electrical energy. The battery management system includes an integration SOC calculator, an integration voltage calculator, a rheobasic voltage calculator, an effective range determiner, an SOC compensator, and an SOC output unit. The integration SOC calculator calculates the SOC by using a charging/discharging current of the battery. The integration voltage calculator calculates an integration voltage that corresponds to the SOC. The rheobasic voltage calculator calculates a rheobasic voltage of the battery by using a pack voltage of the battery, the charging/discharging current of the battery, and an internal resistance of the battery. The effective range determiner calculates an integration error by using the integration voltage and the rheobasic voltage, determines in which effective range the calculated integration error is included among multiple effective ranges, and outputs a specific effective range excess signal or a specific effective range below signal according to a result of the determination. The SOC compensator compensates the integration error to be included within a minimum effective range among the multiple effective ranges by adding a compensation SOC to the SOC when the output of the effective range determiner indicates that the integration error is not included in the specific effective range, the compensation SOC being set in accordance with the output of the effective range determiner. The SOC output unit outputs an output of the SOC compensator as a current SOC of the battery to the ECU.

A battery management system according to another exemplary embodiment of the present invention is provided to manage a battery. The battery management system outputs an SOC of the battery to an engine control unit (ECU) of a vehicle that uses electrical energy. The battery management system includes an integration SOC calculator, an integration voltage calculator, an effective range determiner, an SOC compensator, and an SOC output unit. The integration SOC calculator calculates the SOC by using a charging/discharging current of the battery. The integration voltage calculator calculates an integration voltage that corresponds to the SOC. The effective range determiner calculates an integration error by using the integration voltage and a charging/discharging voltage of the battery, determines in which effective range the calculated integration error is included among multiple effective ranges, and outputs a specific effective range excess signal or a specific effective range below signal according to a result of the determination. The SOC compensator compensates the integration error to be included within a minimum effective range among the multiple effective ranges by adding a compensation SOC to the SOC when the output of the effective range determiner indicates that the integration error is not included in the specific effective range, the compensation SOC being set in accordance with an output of the effective range determiner. The SOC output unit outputs an output of the SOC compensator as a current SOC of the battery to the ECU.

The effective range determiner may be adapted to compare the integration error and at least one of an upper threshold value or a lower threshold value of the minimum effective range among the multiple effective ranges, and to determine in which effective range the integration error is included by repeating the comparison between the integration error and at least one of an upper threshold value or a lower threshold value of a next smallest effective range among the multiple effective ranges when the integration error exceeds the upper threshold value or the lower threshold value of the minimum effective range among the multiple effective ranges.

The SOC compensator may be adapted to subtract the compensation SOC from the SOC when the integration error exceeds an upper threshold value of a specific effective range and to add the compensation SOC to the SOC when the integration error exceeds a lower threshold value of the specific effective range.

The integration voltage calculator may be adapted to calculate an integration voltage that corresponds to the SOC by applying the SOC to an SOC to open circuit voltage (OCV) table.

DETAILED DESCRIPTION

Throughout this specification and the claims which follow, when it is described that an element is coupled to another element, the element may be directly coupled to the other element or electrically coupled to the other element through a third element. In addition, throughout this specification and the claims which follow, unless explicitly described to the contrary, the word“comprise/include” and variations such as “comprises/includes” or“comprising/including” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements.

A method for correcting a state of charge (SOC) of a battery and a battery management system (BMS) using the method will now be described in more detail with reference to the accompanying drawings.

FIG. 1schematically shows a vehicle system that uses electrical energy according to an exemplary embodiment of the present invention.

As shown inFIG. 1, the vehicle system includes a BMS1, a battery2, a current sensing unit3, a cooling fan4, a fuse5, a main switch6, an engine control unit (ECU)7, an inverter8, and a motor generator9.

The battery2includes a plurality of sub-packs formed of a plurality of battery cells2ato2hcoupled in series with each other, output terminals2_out1and2_out2, and a safety switch2_sw provided between the sub-pack2dand the sub-pack2e. Herein, eight sub-packs2ato2hare exemplarily illustrated, and each sub-pack is formed by grouping a plurality of battery cells in one group, but this is not restrictive. In addition, the safety switch2_sw is provided between the sub-pack2dand the sub-pack2e, and is manually turned on or turned off to guarantee the safety of a worker when performing operations on the battery or replacing the battery. In a first exemplary embodiment, the safety switch2_sw is provided between the sub-pack2dand the sub-pack2e, but this is not limited thereto. The output terminals2_out1and2_out2are coupled to the inverter8.

The current sensing unit3measures the amount of output current of the battery2and outputs the measured amount to the sensing unit10of the BMS1. In more detail, the current sensing unit3may be provided as a hall current transformer (Hall CT) using a hall element to measure the amount of output current, and to output an analog current signal corresponding to the measured amount of the output current.

The cooling fan4cools down heat generated by charging/discharging the battery2in response to a control signal from the BMS1, and prevents deterioration and reduction of charge/discharge efficiency of the battery2that are caused by an increase of temperature.

The fuse5prevents an over-current, which may be caused by a disconnection or a short circuit of the battery2from being transmitted to the battery2. That is, when an over-current is generated, the fuse5is disconnected so as to interrupt the current from overflowing.

The main switch6turns on/off the battery2in response to the control signal from the BMS1or a control signal from the ECU7when an unusual phenomenon, such as, for example, an over-voltage, an over-current, and/or a high temperature, occurs.

The BMS1includes a sensing unit10, a main control unit (MCU)20, an internal power supplier30, a cell balancing unit40, a storage unit50, a communication unit60, a protection circuit unit70, a power-on reset unit80, and an external interface90.

The sensing unit10measures an overall battery pack current, an overall battery pack voltage, each battery cell voltage, each battery cell temperature, and an ambient temperature, and transmits the measured voltages and temperatures to the MCU20.

The MCU20estimates a state of charge (SOC) and a state of health (SOH) of the battery2based on the overall battery pack current, the overall battery pack voltage, each battery cell voltage, each battery cell temperature, and the ambient temperature, generates information on a state of the battery2, and transmits the information to the ECU7of the vehicle system. Accordingly, the ECU7of the vehicle system charges or discharges the battery2based on the SOC and the SOH delivered from the MCU20.

The internal power supplier30supplies power to the BMS1by using a backup battery. The cell balancing unit40balances the charging state of each cell. That is, cells that are sufficiently charged are discharged, and cells that are relatively less charged are further charged.

The storage unit50stores the current SOC data or current SOH state data when the power source of the BMS1is turned off. Here, an electrically erasable programmable read-only memory (EEPROM) may be used as the storage unit50. The communication unit60communicates with the ECU7of the vehicle system.

The protection circuit70protects the battery2from external impact, over-flowed current, or low voltages by using firmware. The power-on reset unit80resets the overall system when the power source of the BMS1is turned on. The external interface90couples BMS auxiliary devices, including the cooling fan4and the main switch6, to the MCU20. In the present exemplary embodiment, the cooling fan4and the main switch6are illustrated as the auxiliary devices of the BMS1, but this is not restrictive.

The ECU7determines the amount of torque based on vehicle information, such as an accelerator, a break, or a speed of the vehicle, etc., and controls an output of the motor generator9in accordance with the torque information. That is, the ECU7controls the output of the motor generator9in accordance with the torque information by controlling switching of the inverter8. Also, the ECU7receives the SOC of the battery2from the MCU20through the communication unit60of the BMS1and controls the SOC of the battery2to reach a target value (e.g., 55%).

For example, when the SOC level transmitted from the MCU20is lower than 55%, the ECU7controls a switch of the inverter8so as to output power toward the battery2, so as to charge the battery2. In this case, the battery pack current I is a negative (−) value. When the SOC level is greater than 55%, the ECU7controls the switch of the inverter8to output the power toward the motor generator9and discharge the battery2. In this case, the battery pack current I is a positive (+) value.

This way, the inverter8controls the battery2to be charged or discharged in response to the control signal of the ECU7.

The motor generator9uses the electrical energy of the battery2to drive the vehicle based on the torque information transmitted from the ECU7.

Accordingly, the ECU7charges and discharges the battery2based on the SOC level to prevent the battery2from being over-charged or over-discharged, and therefore the battery2can be efficiently used for a longer time. However, since it is difficult to measure an accurate SOC level of the battery2when the battery2is mounted on a vehicle, the BMS1must precisely measure the SOC level by using the battery pack current and battery pack voltage that are sensed by the sensing unit10and deliver the measured SOC to the ECU7.

The MCU20for outputting the SOC level according to the exemplary embodiment of the present invention will now be described in more detail with reference toFIG. 2.FIG. 2schematically shows the MCU20of the BMS1according to the exemplary embodiment of the present invention.

As shown inFIG. 2, the MCU20includes an integration SOC calculator21, an integration voltage calculator22, a rheobasic voltage calculator23, an effective range determiner24, an SOC compensator25, and an SOC output unit26.

The integration SOC calculator21calculates an SOC of the battery2by applying an SOC estimation method that uses integration capacity. The SOC estimation method is known to those skilled in the art. For example, the integration SOC calculator21measures and determines a charging/discharging current level provided from the sensing unit10. In this case, the charge current has a negative (−) value when the battery2is being charged, and has a positive (+) value when the battery2is being discharged. After determining the current value, the integration SOC calculator21multiplies the current value with charge efficiency, integrates a value obtained from the multiplication for a time period (e.g., a predetermined time period), calculates the integration capacity, and calculates the SOC level based on the integration capacity.

That is, the integration SOC calculator21adds the current value to a previous integration SOC level, which is given as (current integration SOC=previous integration SOC+(I*t)). Herein, I denotes a measured current and t denotes a time from a previous SOC integration to a current SOC integration (typically, t represents one cycle time of a control loop).

The integration voltage calculator22calculates the corresponding integration SOC voltage (hereinafter, referred to as an “integration voltage Vsoc”) from the integration SOC transmitted from the integration SOC calculator21by using an SOC to battery voltage value (i.e., open circuit voltage, OCV) table.

The rheobasic voltage calculator23calculates a current rheobasic voltage of the battery2by using the overall battery pack current, the overall battery pack voltage, the cell voltage, the cell temperature, and the ambient temperature, which are provided from the sensing unit10.

The rheobasic voltage Vo is obtained by adding a voltage drop due to an internal battery resistance R to a battery output voltage. Accordingly, the rheobasic voltage calculator23calculates the rheobasic voltage Vo from an output of the sensing unit10by using an equation of (rheobasic voltage Vo=battery voltage V+RI).

The effective range determiner24determines whether the integration SOC output from the integration SOC calculator21has an error component, and determines whether the error component exists within the effective range. Thus, the effective range determiner24receives an integration voltage Vsoc output from the integration voltage calculator22and the rheobasic voltage Vo output from the rheobasic voltage calculator23, calculates an error component (hereinafter, referred to as an“integration error”) from a difference between the integration voltage Vsoc and the rheobasic Voltage Vo that are received at the same time, and compares the calculated integration error and an effective range (e.g., a predetermined effective range).

An integration error ΔVo can be calculated by Equation 1.
ΔVo=VSOC−VoEquation 1

Accordingly, when the integration voltage Vsoc is greater than the rheobasic voltage Vo, the integration error ΔVo has a positive value, and when the integration voltage Vsoc is less than the OCV voltage Vo, the integration error ΔVo has a negative value.

The effective range determiner24has multiple effective ranges. The multiple effective ranges are formed of a plurality of effective ranges in the largest valid range, and the width of each valid range sequentially decreases. For example, assuming that a value A is a reference value, the multiple effective ranges according to the exemplary embodiment of the present invention satisfy K<K1<K2<K3<A<P3<P2<P1<P, and K and P, K1and P1, K2and P2, and K3and P3respectively form effective ranges. Herein, P denotes a positive threshold value, and K denotes a negative threshold value.

For better understanding, assume that the multiple effective ranges of the effective range determiner24are double effective ranges that satisfy, for example, −a<−b<ΔVo<b<a. Hereinafter, a represents a first maximum threshold value, b represents a second maximum threshold value, −a represents a first minimum threshold value, and −b represents a second minimum threshold value.

The effective range determiner24determines 1) whether the integration error ΔVo is within the effective range, 2) whether the integration voltage Vsoc is greater than the rheobasic voltage Vo so that the integration error ΔVo exceeds the first or second maximum threshold value a or b, or 3) whether the integration voltage Vsoc is less than the rheobasic voltage Vo so that the integration error ΔVo is less than the first or second minimum threshold value −a or −b, and provides an output to the SOC compensator25.

The SOC compensator25determines whether to compensate the integration SOC that has been received from the integration SOC calculator21according to the output of the effective range determiner24. When the integration SOC is determined to be compensated, the SOC compensator25adds or subtracts a compensation SOC set in correspondence with the integration error to the integration SOC. Through such SOC compensation, the integration SOC is maintained within an SOC range that corresponds to the minimum effective range among the multiple effective ranges (seeFIG. 3).

For example, except for the case where the integration error ΔVo is within the valid range, the SOC compensator25subtracts a first compensation SOC α from the integration SOC when the integration error ΔVo is not within the effective range and exceeds the first maximum threshold value a, and subtracts a second compensation SOC β from the integration SOC when the integration error ΔVo is not within the effective range and exceeds the second maximum threshold value b. In addition, the SOC compensator25adds a third compensation SOC α to the integration SOC when the integration error ΔVo exceeds the first minimum threshold value −a, and adds a fourth compensation SOC β to the integration SOC when the integration error ΔVo exceeds the second minimum threshold value −b. In this embodiment, the first compensation SOC equals the third compensation SOC, and the second compensation SOC equals the fourth compensation SOC, and the first compensation SOC and the third compensation SOC are different from each other and the second compensation SOC and the fourth compensation are different from each other.

The SOC output unit26receives the SOC output from the SOC compensator25and outputs the received SOC to the ECU7for an initial SOC reset.

FIG. 3is a graph showing a relationship between the SOC and the OCV corresponding to the SOC to OCV table. As shown inFIG. 3, by using an SOC to a rheobasic voltage Vo line (or a lookup table), when the integration voltage Vsoc or the rheobasic voltage Vo are provided, and when the integration SOC or the estimated SOC are provided, the voltage Vsoc and the rheobasic voltage Vo can be obtained.

Therefore, when a difference between the integration voltage Vsoc and the rheobasic voltage Vo is provided, a difference ΔSOC between the integration SOC and the estimated SOC (close to an actual value) can be obtained, and when the difference ΔSOC is greater than a predetermined level, the integration SOC can be compensated to be closer to the estimated SOC. The SOC compensation that compensates the SOC close to the estimated SOC maintains the difference ΔSOC to be within the predetermined level.

An SOC compensation method according to an exemplary embodiment of the present invention will now be described in more detail with reference toFIG. 4.FIG. 4sequentially shows a process for SOC compensation of the battery according to an exemplary embodiment of the present invention.

The integration SOC calculator21integrates the current values received from the sensing unit10during a period of time (e.g., a predetermined period of time) to determine the integration current, calculates the integration SOC by using the integration current, and provides the calculated integration SOC to the integration voltage calculator22and the SOC compensator25, in step S401.

At the same time, the rheobasic calculator23receives the overall battery pack current, the overall battery pack voltage, each battery cell voltage, and each battery cell temperature, and the ambient temperature from the sensing unit10, and calculates the rheobasic voltage in the state in which the current I equals a zero state in step S402.

The rheobasic calculator23provides the calculated rheobasic voltage Vo to the effective range determiner24.

After receiving the integration SOC, the integration voltage calculator22applies the integration SOC to the OCV table to determine the integration voltage Vsoc, and provides the calculated integration voltage Vsoc to the effective range determiner24, in step S403.

The effective range determiner24subtracts the rheobasic voltage Vo from the integration voltage Vsoc input at the same time, and calculates the integration error ΔVo, in step S404.

Subsequently, the effective range determiner24determines whether the integration error ΔVo is greater than the first maximum threshold value a in order to compare the integration error ΔVo and the effective range, in step S405.

When a result of the determination of step S405shows that the integration error ΔVo is greater than the first maximum threshold value a, the effective range determiner24outputs a first positive excess signal to the SOC compensator25. When the first positive excess signal is output, the SOC compensator25subtracts the first positive compensation SOC α from the integration SOC that has been currently received from the integration SOC calculator21(i.e., integration SOC—first positive compensation SOC α), and provides a compensation result SOC to the SOC output unit26, in step S406. Here, the first positive compensation SOC α is set corresponding to the first positive excess signal.

When the result of the determination in the step S405shows that the integration error ΔVo is less than the first maximum threshold value a, the effective range determiner24compares the integration error ΔVo and the second maximum threshold value b so as to determine whether the integration error ΔVo is greater than the second maximum threshold value b, in step S407.

When the determination of step S407shows that the integration error ΔVo is greater than the second maximum threshold value a, the effective range determiner24outputs a second positive excess signal to the SOC compensator25.

When the second positive excess signal is output, the SOC compensator25subtracts a second positive compensation SOC β from the integration SOC (i.e., integration SOC—second positive compensation SOC β) and provides a compensation result SOC to the SOC output unit26in step S408. Here, the second positive correction SOC β is set corresponding to the second positive excess signal.

When the determination of step S407shows that the integration error ΔVo is less than the second maximum threshold value b, the effective range determiner24compares the integration error ΔVo and the first minimum threshold value −a so as to determine whether the integration error ΔVo is less than the first minimum threshold value −a in step S409.

When the determination of step S409shows that the integration ΔVo is less than the minimum threshold value −a, the effective range determiner24outputs a first negative excess signal. When the first negative excess signal is output, the SOC compensator25adds a first negative correction SOC α to an integration SOC that has been currently received from the integration SOC calculator21(i.e., integration SOC+first negative correction SOC α), and provides a compensation result SOC to the SOC output unit26in step S410. Here, the first negative correction SOC α is set corresponding to the first negative excess signal.

When the determination of the step S409shows that the integration error ΔVo is greater than the first minimum threshold value −a, the effective range determiner24compares the integration error ΔVo and the second minimum threshold value −b so as to determine whether the integration error ΔVo is less than the second minimum threshold value −b in step S411.

When the determination of step S411shows that the integration error ΔVo is less than the second minimum threshold value −b, the effective range determiner24outputs a second negative excess signal to the SOC compensator25. When the second negative excess signal is output, the SOC compensator25adds a second negative compensation SOC β to the integration SOC that has been currently received from the integration SOC calculator21(i.e., integration SOC+second negative compensation SOC β) and provides a compensation result SOC to the output unit26in step S412. Herein, the second negative compensation SOC β is set corresponding to the second negative excess signal.

In addition, when the integration error ΔVo is less than the second maximum threshold value b and greater than the second minimum threshold value −b, the effective range determiner24determines the integration error ΔVo as the normal state and outputs a normal signal to the SOC compensator25. The SOC compensator25provides the integration SOC transmitted from the integration SOC calculator21to the SOC output unit26.

Such operations of the effective range determiner24and the SOC compensator25will be described with reference toFIG. 3. When a range of the integration error ΔVo ofFIG. 3is one of the multiple effective ranges (or multiple valid ranges) and the integration SOC leaves an effective SOC range ΔSOC corresponding to the integration error ΔVo, the compensation SOC β is added or subtracted so that the integration SOC may be maintained within the range ΔSOC.

A SOC compensation method of a battery according to another exemplary of the present invention will now be described.

The SOC compensation method according to the second exemplary embodiment is similar to the first exemplary embodiment of the present invention except that an integration SOC is compensated by using a charge/discharge voltage V of a battery rather than using a rheobasic voltage Vo.

A detailed description of the SOC compensation method according to the second exemplary embodiment of the present invention will now be provided with reference toFIG. 5andFIG. 6.FIG. 5schematically shows an MCU120of a BMS according to the second exemplary embodiment of the present invention. The MCU120has substantially the same functions as the MCU20ofFIGS. 1 and 2, and can be used in the BMS1ofFIG. 1in place of the MCU20. The MCU120is different from the MCU20in that the MCU120does not include a Rheobasic voltage calculator23. An effective range determiner124in the MCU120receives an input from the sensing unit10.

As shown inFIG. 5, the MCU120of the BMS according to the second exemplary embodiment of the present invention includes an integration SOC calculator21, an integration voltage calculator22, the effective range determiner124, an SOC compensator25, and an SOC output unit26.

The integration SOC calculator21, the integration voltage calculator22, and the SOC output unit26are the same as those in the first exemplary embodiment which has been described with reference toFIG. 2. However, the effective range determiner124and the SOC compensator125of the second exemplary embodiment have substantially the same functions as the effective range determiner24and the SOC compensator25in the first exemplary embodiment, but they have different operational processes since they have different operation processing parameters than those of the first exemplary embodiment.

That is, the effective range determiner124receives a charge/discharge voltage V of the battery2from the sensing unit10, receives an integration voltage Vsoc from the integration voltage calculator22, obtains a difference (i.e., an integration error) between the two voltages V and Vsoc, and determines where the calculated integration error is included among multiple effective ranges.

The effective range determiner124calculates the integration error ΔVo through Equation 2.
ΔV=VSOC−VEquation 2

In Equation 2, a positive integration error ΔV is output when the integration voltage Vsoc is greater than the charge/discharge voltage V, and a negative integration error ΔV is output when the integration voltage Vsoc is less than the charge/discharge voltage V.

After receiving an output that corresponds to information on a range of the integration error ΔV within the multiple effective ranges from the effective range determiner124, the SOC compensator125adds or subtracts a compensation SOC to the integration SOC corresponding to the range of the integration error ΔV. Through such a compensation, the integration SOC can be maintained within an SOC range that corresponds to the minimum effective range among the multiple effective ranges.

Here, the SOC that corresponds to an integration voltage Vsoc can be obtained from an SOC to OCV table, and the SOC that corresponds to the charge/discharge voltage V can be obtained from an SOC to charge/discharge voltage table. This implies that the integration voltage Vsoc and the charge/discharge voltage V have different SOCs respectively even though they have the same voltage level because the two voltages V and Vsoc use different SOC tables, respectively.

A compensation SOC according to the second exemplary embodiment of the present invention is set by using an SOC difference according to the SOC table difference.

An SOC compensation method of a battery according to the second exemplary embodiment of the present invention will be described with reference toFIG. 6.FIG. 6sequentially shows the SOC compensation process of the battery according to the second exemplary embodiment of the present invention. The double effective ranges ofFIG. 6are the same as those ofFIG. 4, and therefore reference numerals ofFIG. 6are the same as those ofFIG. 4.

The integration SOC calculator21integrates a current value received from the sensing unit10during a period of time (e.g., a predetermined period of time) and determines an integration current, calculates an integration SOC by using the integration current, and provides the integration SOC to the integration voltage calculator22and the SOC compensator125, in step S601.

After receiving the integration SOC, the integration voltage calculator22applies the received integration SOC to the SOC to integration voltage table to determine the integration voltage Vsoc, and provides the integration voltage Vsoc to the effective range determiner124, in step S602. At the same time, a battery charge/discharge voltage V output from the sensing unit10is provided to the effective range determiner124.

After receiving the integration voltage Vsoc from the integration voltage calculator22, the effective range determiner124determines the charge/discharge voltage V received from the sensing unit10at the same time, in step S603.

Then the effective range determiner124subtracts the charge/discharge voltage V from the integration voltage Vsoc to obtain an integration error ΔV, in step S604.

In order to compare the integration error ΔV to multiple effective ranges, the effective range determiner124determines whether the integration error ΔV is greater than a first maximum threshold value a, in step S605.

When a result of the determination of the step S605shows that the integration error ΔV is greater than the first maximum threshold value a, the effective range determiner124outputs a first positive excess signal to the SOC compensator125. When the first positive excess signal is output, the SOC compensator125subtracts a first positive compensation SOC α from the integration SOC that has been currently received from the SOC calculator21(i.e., integration SOC—first positive compensation SOC α) and provides a compensation result SOC to the SOC output unit26in step S606. Here, the first positive correction SOC α is set corresponding to the first positive excess signal.

When the result of the determination of the step S605shows that the integration error ΔV is less than the first maximum threshold value a, the effective range determiner124compares the integration error ΔV with a second maximum threshold value b and determines whether the integration error ΔV is greater than the second maximum threshold value b, in step S607.

When a result of the determination of the step S607shows that the integration error ΔV is greater than the second maximum threshold value b, the effective range determiner124outputs a second positive excess signal to the SOC compensator125. When the second positive excess signal is output, the SOC compensator125subtracts a second positive correction SOC β from the integration SOC (i.e., the integration SOC—second positive compensation SOC β), and provides a compensation result SOC to the SOC output unit26, in step S608. Here, the second positive correction SOC is set corresponding to the second positive excess signal.

When a result of the determination of the step S607shows that the integration error ΔV is less than the second maximum threshold value b, the effective range determiner24compares the integration error ΔV with a first minimum threshold value −a and determines whether the integration error ΔV is less than the first minimum threshold value −a, in step S609.

When a result of the determination of the step S609shows that the integration error ΔV is less than the first minimum threshold value −a, the effective range determiner124outputs a first negative excess signal to the SOC compensator125. When the first negative excess signal is output, the SOC compensator125adds a first negative compensation SOC α to an integration SOC that has been currently received from the integration SOC output unit21(i.e., integration SOC+first negative compensation SOC α) and provides a compensation result SOC to the SOC output unit26in step S610, wherein the first negative correction SOC is set corresponding to the first negative excess signal.

When the integration error ΔV is greater than the first minimum threshold value −a as a result of the determination in the step S609, the effective range determiner124compares the integration error ΔV to the second minimum threshold value −b and determines whether the integration error ΔV is less than the second minimum threshold value −b in step S611.

The effective range determiner124outputs a second negative excess signal to the SOC compensator125when the determination of the step S611shows that the integration error ΔV is less than the second minimum threshold value −b. When the second negative excess signal is output, the SOC compensator125adds a second negative compensation SOC β to an integration SOC that has been currently received from the integration SOC output unit21and provides a compensation result SOC to the SOC output unit26in step S612, wherein the second negative compensation SOC β is set corresponding to the second negative excess signal.

In addition, the effective range determiner124determines that the integration error ΔV is in the normal state when it is less than the second maximum threshold value b and greater than the second minimum threshold value −b and outputs a normal signal to the SOC compensator125, and the SOC compensator125provides the integration SOC that has been received from the integration SOC calculator21to the SOC output unit26.

It is known that, in general, SOC estimation by using the current integration method increases errors as time passes.

Therefore, in one embodiment, the number of compensation attempts and the compensation errors due to the SOC estimate error (seeFIG. 3) that can be estimated through the voltages Vo and V can be reduced by increasing a time interval of compensation (i.e., a compensation correction cycle time) and determining the correction SOC α and β in proportion to absolute values of the integration errors ΔVo and ΔV. This is because the SOC error corresponding to the Vo error may increase even though the Vo error is small in a middle SOC region.

For example, a cumulative error may be increased due to integration as the compensation cycle time according to an exemplary embodiment of the present invention is increased. Therefore, in one embodiment, to compensate the increase of integration error, a lot of threshold values (e.g., a, b, −a, −b) and the corresponding compensation SOC values (e.g., α and β) are set for voltages Vo and V so as to apply the largest SOC compensation value to compensate the largest integration error, thereby reducing the number of compensation performances while resulting in the same compensation effect.

The compensation SOC is a compensation value that compensates an integration SOC to be included within the effective SOC range ΔSOC.

In the present exemplary embodiment, the compensation SOC exemplarily has a predetermined value. However, the compensation SOC may have an arbitrary value corresponding to the sizes of integration errors ΔVo or ΔV.

Herein, the arbitrary compensation SOC A can be represented as given in Equation 3 using a function of the integration errors ΔVo or ΔV.
A=K×ΔV0(or ΔV)×ΔSOC+ε  Equation 3

Where K denotes a constant number, Δ SOC denotes an SOC predetermined for compensation, and ε denotes an SOC constant number.

The above-described exemplary embodiments of the present invention can be realized not only through a method and an apparatus, but also through a software program that can perform functions corresponding to configurations of the exemplary embodiments of the present invention or a recording medium storing the program, and this can be easily realized by a person skilled in the art.

As described above, when estimating an SOC by using integration capacity, an error between a real SOC value and an estimated SOC value may be generated as time passes. The error can be measured through an integration voltage and a rheobasic voltage, and an accurate SOC of the battery can be obtained by compensating the measured amount of errors.

In addition, an effective range is set for the error and thus SOC compensation can be performed without irritating a system process. In addition, multiple effective ranges are provided so that an SOC compensation value can be changed on the basis of a location of the integration error among the multiple effective ranges, thereby acquiring a more accurate SOC of the battery.