Patent Description:
Recently, there has been a rapid increase in the demand for portable electronic products such as laptop computers, video cameras and mobile phones, and with the extensive development of electric vehicles, accumulators for energy storage, robots and satellites, many studies are being made on high performance batteries that can be recharged repeatedly.

Currently, commercially available batteries include nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, lithium batteries and the like, and among them, lithium batteries have little or no memory effect, and thus they are gaining more attention than nickel-based batteries for their advantages that recharging can be done whenever it is convenient, the self-discharge rate is very low and the energy density is high.

A battery undergoes a cycle state and a rest state repeatedly. The cycle state refers to a state in which the charge/discharge of the battery is ongoing. The rest state refers to a state in which the charge/discharge of the battery is interrupted (stopped), i.e., a charge current and a discharge current do not flow through the battery.

Even in the rest state of the battery, the State Of Charge (SOC) of the battery may not be constantly maintained due to charge/discharge history in the cycle state, self-discharge of the battery and power consumption of a battery management system. Accordingly, it is necessary to monitor the SOC of the battery even in the rest state of the battery.

Meanwhile, conventionally, an Open Circuit Voltage (OCV) curve widely used to estimate the SOC of the battery is a dataset defining a relationship between OCV and SOC of the battery when hysteresis is completely removed with a lapse of a sufficiently long time after the charge/discharge of the battery was stopped.

However, in case that the rest state is not maintained for a sufficiently long time after the battery's shift from the cycle state to the rest state, it is impossible to sufficiently remove the hysteresis generated by the charge/discharge history in the cycle state.

Accordingly, SOC estimation based on only the OCV curve from the start time of the rest state (i.e., the ending time of the cycle state) without considering the period of time during which the battery is kept in the rest state results in low accuracy.

<CIT> relates to an electronic control unit that is configured to: i) calculate the surface stress from a use history of the secondary battery; ii) calculate the amount of change in OCV from the calculated surface stress iii) correct an estimated OCV with the use of the amount of change in OCV; the estimated OCV being estimated from a voltage value and current value of the secondary battery; and iv) estimate an SOC corresponding to the corrected estimated OCV as the SOC of the secondary battery.

<CIT> relates to a State of Charge (SOC) estimation device for a secondary battery in which a correlation curve indicating a relationship between an SOC and Open Circuit Voltage (OCV) differs between a charging process and discharging process.

<CIT> relates to method of estimating a battery state that includes determining whether a previous state to a rest state of a battery is a charging state or a discharging state; selecting a current profile comprising one or both of a charging pulse and a discharging pulse based on the previous state of the battery; stabilizing an open circuit voltage (OCV) of the battery by applying the current profile to the battery; and measuring the stabilized OCV.

<CIT> relates to a state-of-charge estimation device that includes a voltage measuring unit which measures a closed circuit voltage in a battery, a charge estimation unit which estimates a state of charge in a charge mode by referring to charge mode information that associates a closed circuit voltage with a state of charge in the battery, and a discharge estimation unit which estimates a state of charge in a discharge mode by referring to discharge mode information that associates a closed circuit voltage generated by use of a discharge pattern of the battery with a state of charge in the battery by use of the measured closed circuit voltage.

The present disclosure is designed to solve the above-described problem, and therefore the present disclosure is aimed at accurately determining a State Of Charge (SOC) of a battery while the battery is resting by changing an Open Circuit Voltage (OCV) curve defining a relationship between OCV and SOC, according to the period of time during which the battery is kept in the rest state after the battery's shift from the cycle state to the rest state.

These and other objects and advantages of the present disclosure may be understood by the following description and will be apparent from the embodiments of the present disclosure. In addition, it will be readily understood that the objects and advantages of the present disclosure may be realized by the means set forth in the appended claims and a combination thereof.

A battery management system according to a first aspect is provided in claim <NUM>.

The control circuit may be configured to determine the first standby time and the first shift time based on a reference SOC and a reference temperature in case that the battery is being discharged when the key-off signal is received. The reference SOC indicates a SOC of the battery when the key-off signal is received. The reference temperature indicates a temperature of the battery when the key-off signal is received.

The memory may be further configured to store a third OCV curve defining a third relationship indicating an average of the first relationship and the second relationship. The control circuit may be configured to estimate the SOC of the battery at the predetermined time interval from the second time point based on the battery voltage measured at the predetermined time interval and the third OCV curve in case the battery is being discharged when the key-off signal is received.

The control circuit may be configured to estimate the SOC of the battery at the predetermined time interval from a third time point to a fourth time point based on the battery voltage measured at the predetermined time interval and the second OCV curve in case that the battery is being charged when the key-off signal is received. The third time point is a time point when a second standby time has passed since the key-off signal was received. The fourth time point is a time point when a second shift time has passed since the key-off signal was received, the second shift time being longer than the second standby time.

The control circuit may be configured to determine the second standby time and the second shift time based on a reference SOC and a reference temperature in case that the battery is being discharged when the key-off signal is received. The reference SOC indicates a SOC of the battery when the key-off signal is received. The reference temperature indicates a temperature of the battery when the key-off signal is received.

The memory may be further configured to store a third OCV curve defining a third relationship indicating an average of the first relationship and the second relationship. The control circuit may be configured to estimate the SOC of the battery at the predetermined time interval from the fourth time point based on the battery voltage measured at the predetermined time interval and the third OCV curve in case that the battery is being charged when the key-off signal is received.

A battery pack according to another aspect of the present disclosure includes the battery management system.

An electric vehicle according to still another aspect of the present disclosure includes the battery pack.

A battery management method according to further another aspect is provided in claim <NUM>.

According to at least one of the embodiments of the present disclosure, it is possible to accurately determine a State Of Charge (SOC) of a battery while the battery is resting by changing an Open Circuit Voltage (OCV) curve defining a relationship between OCV and SOC, according to the period of time during which the battery is kept in the rest state after the battery's shift from the cycle state to the rest state.

The effects of the present disclosure are not limited to the effects mentioned above, and these and other effects will be clearly understood by those skilled in the art from the appended claims.

Unless the context clearly indicates otherwise, it will be understood that the term "comprises" when used in this specification, specifies the presence of stated elements, but does not preclude the presence or addition of one or more other elements. Additionally, the term "control unit" as used herein refers to a processing unit of at least one function or operation, and may be implemented by hardware and software either alone or in combination.

<FIG> is a diagram exemplarily showing a configuration of an electric vehicle <NUM> according to the present disclosure.

Referring to <FIG>, the electric vehicle <NUM> includes a vehicle controller <NUM>, a battery pack <NUM>, a switch <NUM>, an inverter <NUM> and an electric motor <NUM>.

The vehicle controller <NUM> is configured to generate a key-on signal in response to an engine start button (not shown) provided in the electric vehicle <NUM> being shifted to ON-position by a user. The vehicle controller <NUM> is configured to generate a key-off signal in response to the engine start button being shifted to OFF-position by the user.

The switch <NUM> is installed on a power line <NUM> for the battery pack <NUM>. While the switch <NUM> is in an on state, power may be transferred from any one of the battery pack <NUM> and the inverter <NUM> to the other through the power line <NUM>. The switch <NUM> may include any one of well-known switching devices such as a relay and a Field Effect Transistor (FET) or a combination thereof.

The inverter <NUM> converts the direct current power supplied from a battery B to alternating current power and supplies to the electric motor <NUM>. The electric motor <NUM> converts the alternating current power from the inverter <NUM> to kinetic energy for the electric vehicle <NUM>.

The battery pack <NUM> includes the battery B and a battery management system <NUM>.

The battery B includes at least one battery cell. The battery cell is not limited to a particular type, and includes any type of rechargeable battery or cell, for example, a lithium ion cell.

The battery management system <NUM> includes a voltage sensor <NUM>, a memory <NUM> and a control circuit <NUM>. The battery management system <NUM> may further include at least one of a temperature sensor <NUM>, a current sensor <NUM> or a communication circuit <NUM>.

The voltage sensor <NUM> is provided to be electrically connectable to a positive electrode terminal and a negative electrode terminal of the battery B. The voltage sensor <NUM> is configured to measure a voltage across the battery B (hereinafter referred to as a 'battery voltage') at a predetermined time interval, and output a signal indicating the measured battery voltage to the control circuit <NUM>.

The temperature sensor <NUM> is positioned within a predetermined distance from the battery B. For example, a thermocouple may be used as the temperature sensor <NUM>. The temperature sensor <NUM> is configured to measure a temperature of the battery B (hereinafter referred to as 'battery temperature') at the predetermined time interval and output a signal indicating the measured battery temperature to the control circuit <NUM>.

The current sensor <NUM> is installed on the power line <NUM>. The current sensor <NUM> is provided to be electrically connectable to the battery B in series through the power line <NUM>. For example, the current sensor <NUM> may include a shunt resistor or a hall effect device. The current sensor <NUM> is configured to measure an electric current flowing through the power line <NUM> (hereinafter referred to as a 'battery current') at the predetermined time interval, and output a signal indicating the measured battery current to the control circuit <NUM>. The battery current measured during the discharge of the battery B may be referred to as a 'discharge current' and the battery current measured during the charge of the battery B may be referred to as a 'charge current'.

The memory <NUM> is configured to store programs and data necessary to perform battery management methods according to the embodiments as described below. The memory <NUM> may include, for example, at least one type of storage medium of flash memory type, hard disk type, Solid State Disk (SSD) type, Silicon Disk Drive (SDD) type, multimedia card micro type, random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM) or programmable read-only memory (PROM).

The control circuit <NUM> is operably coupled to the vehicle controller <NUM>, the switch <NUM>, the voltage sensor <NUM>, the temperature sensor <NUM>, the current sensor <NUM>, the memory <NUM> and the communication circuit <NUM>. The operably coupled refers to connection to enable unidirectional or bidirectional signal transmission and reception. The control circuit <NUM> may be implemented in hardware using at least one of application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), microprocessors or electrical units for performing other functions.

The communication circuit <NUM> may be coupled to the vehicle controller <NUM> of the electric vehicle <NUM> to enable communication between. The communication circuit <NUM> may transmit a message from the vehicle controller <NUM> to the control circuit <NUM>, and transmit a message from the control circuit <NUM> to the vehicle controller <NUM>. The communication between the communication circuit <NUM> and the vehicle controller <NUM> may use, for example, a wired network such as a local area network (LAN), a controller area network (CAN) and a daisy chain and/or a near-field wireless network such as Bluetooth, Zigbee, WiFi or the like.

The control circuit <NUM> may determine the SOC of the battery B based on the battery voltage, the battery current and/or the battery temperature. The determination of the SOC during the charge/discharge of the battery B may use well-known methods such as ampere counting, Kalman filter or the like. The determination of the SOC of the battery B while the battery B is resting will be described in detail below.

<FIG> is a diagram for describing hysteresis by charge/discharge history in the cycle state of the battery B.

Referring to <FIG>, a curve <NUM> defines a first relationship between OCV and SOC of the battery B during the discharge of the battery B and may be referred to as a 'first OCV curve' or a 'discharge OCV curve'. The curve <NUM> may be data pre-acquired from a discharge testing process by repeating the constant current discharge and the rest in an alternating manner from full charge to full discharge of another battery (batteries) having the same specification as the battery B in an environment in which a predetermined reference temperature (for example, <NUM>) is maintained. For example, during the discharge test, the discharg using a predetermined current rate (for example, <NUM> C) over a first test time (for example, <NUM>) and the rest over a second test time (for example, <NUM>) may be repeated. In this case, the OCV of the curve <NUM> may indicate the battery voltage each time the battery B rests for the second test time during the discharge test.

A curve <NUM> defines a second relationship between OCV and SOC of the battery B during the charge of the battery B, and may be referred to as a 'second OCV curve' or a 'charge OCV curve'. The curve <NUM> may be data pre-acquired from the discharge testing process by repeating the constant current charge and the rest from full discharge to full charge of another battery (batteries) having the same specification as the battery B in an environment in which the predetermined reference temperature (for example, <NUM>) is maintained. For example, during the charge test, the charge using the predetermined current rate (for example, <NUM> C) over a third test time (for example, <NUM>) and the rest over a fourth test time (for example, <NUM>) may be repeated. In this case, the OCV of the curve <NUM> may indicate the battery voltage each time the battery B rests for the fourth test time during the charge test.

A curve <NUM> defines a third relationship indicating an average of the first relationship and the second relationship and may be referred to as a 'third OCV curve' or an 'average OCV curve'. By averaging the first relationship and the second relationship, the hysteresis induced by discharge and the hysteresis induced by charge cancel each other out. Accordingly, the third relationship may indicate the OCV and SOC of the battery B when the hysteresis of the battery B is completely removed.

At the same SOC, the OCV of the curve <NUM> is lower than the OCV of the curve <NUM> due to the hysteresis generated by the discharge, while the OCV of the curve <NUM> is higher than the OCV of the curve <NUM> due to the hysteresis generated by the charge. For example, where SOC = A [%], OCV V<NUM> of the curve <NUM> is lower than OCV V<NUM> of the curve <NUM>, and OCV V<NUM> of the curve <NUM> is higher than OCV V<NUM> of the curve <NUM>. For reference, since the curve <NUM> is an average of the curve <NUM> and the curve <NUM>, V<NUM> = (V<NUM> +V<NUM>)/<NUM>.

By the same reason, at the same OCV, the SOC of the curve <NUM> is higher than the SOC of the curve <NUM>, while the SOC of the curve <NUM> is lower than the SOC of the curve <NUM>. For example, where OCV = V<NUM> [V], SOC A [%] of the curve <NUM> is higher than SOC B [%] of the curve <NUM>, and SOC C [%] of the curve <NUM> is lower than SOC B [%] of the curve <NUM>.

<FIG> is a diagram for describing a phenomenon in which the hysteresis generated by the discharge of the battery B is reduced in the rest state.

Referring to <FIG>, in response to a key-off signal received during the discharge of the battery B, the battery B enters the rest state from a time point T<NUM>. For convenience of description, assume that the actual SOC of the battery B at the time point T<NUM> is A [%].

Referring to <FIG> and <FIG>, as the hysteresis by the discharge is resolved from the time point T<NUM>, the battery voltage gradually rises. At a time point T<NUM>, the battery voltage reaches OCV V<NUM> of the curve <NUM>. The time point T<NUM> may be a time point when a predetermined time has passed since the time point T<NUM>. With a lapse of a sufficient time from the time point T<NUM>, the battery voltage reaches OCV V<NUM> of the curve <NUM>.

At a time point T<NUM> after the time point T<NUM>, the battery voltage Vx is between V<NUM> and V<NUM>. When a reference is made to the curve <NUM>, the SOC at the time point T<NUM> is determined as D [%]. In contrast, when a reference is made to the curve <NUM>, the SOC at the time point T<NUM> is determined as E [%].

While the battery B is resting, Vx gradually rises to V<NUM>, and thus a difference between Vx and V<NUM> increases, while a difference between Vx and V<NUM> decreases, as can be seen from <FIG> and <FIG>. Additionally, while the battery B is resting, a difference ΔE<NUM> between A and D increases, while a difference ΔE<NUM> between A and E decreases.

When ΔE<NUM> is smaller than ΔE<NUM>, the SOC determined based on the curve <NUM> is closer to the actual SOC than the SOC determined based on the curve <NUM>. In contrast, when ΔE<NUM> is larger than ΔE<NUM>, the SOC determined based on the curve <NUM> is closer to the actual SOC than the SOC determined based on the curve <NUM>.

In view of this, the control circuit <NUM> may be configured to determine a first shift time ΔtC1 as an estimated time required until ΔE<NUM> equals ΔE<NUM>. The control circuit <NUM> may determine the SOC at a predetermined time interval based on the curve <NUM> from a time point when a first standby time ΔtR1 has passed since the time point T<NUM>, and determine the SOC at the predetermined time interval based on the curve <NUM> from a time point when the first shift time ΔtC1 has passed since the time point T<NUM>.

<FIG> is a diagram for describing a phenomenon in which the hysteresis generated by the charge of the battery B is reduced in the rest state.

Referring to <FIG>, in response to a key-off signal received during the charge of the battery B, the battery B goes into the rest state from a time point T<NUM>. For convenience of description, assume that the actual SOC of the battery B at the time point T<NUM> is A [%].

Referring to <FIG> and <FIG>, as the hysteresis by the charge is resolved after the time point T<NUM>, the battery voltage gradually drops. At a time point T<NUM>, the battery voltage reaches OCV V<NUM> of the curve <NUM>. The time point T<NUM> may be a time point when a predetermined time has passed since the time point T<NUM>. With a lapse of a sufficient time from the time point T<NUM>, the battery voltage reaches OCV V<NUM> of the curve <NUM>.

At a time point T<NUM> after the time point T<NUM>, the battery voltage Vy is between V<NUM> and V<NUM>. When a reference is made to the curve <NUM>, the SOC at the time point T<NUM> is determined as F [%]. In contrast, when a reference is made to the curve <NUM>, the SOC at the time point T<NUM> is determined as G [%].

While the battery B is resting, Vy gradually drops to V<NUM>, and thus a difference between Vy and V<NUM> increases, while a difference between Vy and V<NUM> decreases, as can be seen from <FIG> and <FIG>. Additionally, while the battery B is resting, a difference ΔE<NUM> between A and F increases, while a difference ΔE<NUM> between A and G decreases.

In view of this, the control circuit <NUM> may be configured to determine a second shift time ΔtC2 as an estimated time required until ΔE<NUM> equals ΔE<NUM>. The control circuit <NUM> may determine the SOC at the predetermined time interval based on the curve <NUM> from a time point when a standby time ΔtR2 has passed since the time point T<NUM>, and may determine the SOC at the predetermined time interval based on the curve <NUM> from a time point when the second shift time ΔtC2 has passed since the time point T<NUM>.

<FIG> is a flowchart illustrating a battery management method according to a first embodiment of the present disclosure, and <FIG> illustrates data tables for the method of <FIG>. The method of <FIG> may start by a key-off signal from the vehicle controller <NUM> during the discharge of the battery B.

Referring to <FIG>, <FIG> and <FIG>, in step S510, the control circuit <NUM> stores a reference SOC and a reference temperature in the memory <NUM>. The reference SOC indicates the SOC of the battery B when the key-off signal is received. The reference temperature indicates the battery temperature when the key-off signal is received.

In step S520, the control circuit <NUM> interrupts a flow of current through the battery B. That, the control circuit <NUM> turns off the switch <NUM>. Thus, the battery B is shifted from the cycle state to the rest state.

In step S530, the control circuit <NUM> determines the first standby time ΔtR1 and the first shift time ΔtC1 based on the reference SOC and the reference temperature.

The first standby time ΔtR1 is a length of time required since the key-off signal was received to determine the SOC of the battery B using the curve <NUM>. At the early stage of the rest state, the battery voltage rises fast, so it is undesirable to determine the SOC of the battery B using the curve <NUM> from the start of the rest state. According to the invention, the first standby time ΔtR1 is an estimated time required until the rate at which the battery voltage rises equals a predetermined threshold rate (for example, <NUM> V/minute) from the start time of the rest state.

The first shift time ΔtC1 is longer than the first standby time ΔtR1. The first shift time ΔtC1 is a length of time required since the key-off signal was received to determine the SOC of the battery B using the curve <NUM> instead of the curve <NUM>.

Referring to <FIG>, a data table <NUM> and a data table <NUM> are stored in the memory <NUM>. The data table <NUM> defines a relationship between the reference SOC, the reference temperature and the first standby time ΔtR1. The data table <NUM> defines that the lower reference temperature is associated with the longer first standby time ΔtR1 at the same reference SOC. For example, when the reference SOC is <NUM> [%] and the reference temperature is <NUM>[°C], <NUM> minute is determined as the first standby time ΔtR1, and when the reference SOC is <NUM> [%] and the reference temperature is <NUM>[°C], <NUM> minutes is determined the first standby time ΔtR1. Additionally, the data table <NUM> defines the lower reference SOC is associated with the longer or equal first standby time ΔtR1 at the same reference temperature. For example, when the reference SOC is <NUM> [%] and the reference temperature is <NUM>[°C], <NUM> minutes is determined as the first standby time ΔtR1, and when the reference SOC is <NUM> [%] and the reference temperature is <NUM>[°C], <NUM> minutes is determined as the first standby time ΔtR1.

The data table <NUM> defines a relationship between the reference SOC, the reference temperature and the first shift time ΔtC1. The data table <NUM> defines that the lower reference temperature is associated with the longer first shift time ΔtC1 at the same reference SOC. Additionally, the data table <NUM> defines that the lower reference SOC is associated with the longer or equal first shift time ΔtC1 at the same reference temperature.

The numeric values in the data table <NUM> and the data table <NUM> are provided by way of example to help understanding.

Alternatively, each of the first standby time ΔtR1 and the first shift time ΔtC1 may be preset to a particular value irrespective of the SOC and the temperature. In this case, the steps S510 and S530 may be omitted from the method of <FIG>.

In step S540, the control circuit <NUM> measures the battery voltage.

In step S550, the control circuit <NUM> determines whether the first standby time ΔtR1 has passed since the key-off signal was received. When a value of the step S550 is "Yes", step S560 is performed.

In the step S560, the control circuit <NUM> determines whether the first shift time ΔtC1 has passed since the key-off signal was received. When a value of the step S560 is "No", step S570 is performed. When the value of the step S560 is "Yes", step S580 is performed.

In the step S570, the control circuit <NUM> determines the SOC of the battery B based on the battery voltage and the first OCV curve <NUM>.

In the step S580, the control circuit <NUM> determines the SOC of the battery B based on the battery voltage and the third OCV curve <NUM>.

The control circuit <NUM> may determine the SOC of the battery B at the predetermined time interval by repeating the steps S540 to S580 until a key-on signal is received from the vehicle controller <NUM>.

<FIG> is a flowchart illustrating a battery management method according to a second embodiment of the present disclosure, and <FIG> illustrates data tables for the method of <FIG>. The method of <FIG> may start by a key-off signal from the vehicle controller <NUM> during the charge of the battery B.

Referring to <FIG>, <FIG>, <FIG>, <FIG> and <FIG>, in step S710, the control circuit <NUM> stores the reference SOC and the reference temperature in the memory <NUM>. The reference SOC indicates the SOC of the battery B when the key-off signal is received. The reference temperature indicates the battery temperature when the key-off signal is received.

In step S720, the control circuit <NUM> interrupts a flow of current through the battery B. That is, the control circuit <NUM> turns off the switch <NUM>. Thus, the battery B is shifted from the cycle state to the rest state.

In step S730, the control circuit <NUM> determines the second standby time ΔtR2 and the second shift time ΔtC2 based on the reference SOC and the reference temperature.

The second standby time ΔtR2 is a length of time required since the key-off signal was received to determine the SOC of the battery B using the curve <NUM>. At the early stage of the rest state, the battery voltage drops fast, so it is undesirable to determine the SOC of the battery B using the curve <NUM> from the start of the rest state. For example, the second standby time ΔtR2 is an estimated time required until the rate at which the battery voltage drops equals a predetermined threshold rate (for example, <NUM> V/minute) from the start time of the rest state.

The second shift time ΔtC2 is a length of time required since the key-off signal was received to determine the SOC of the battery B using the curve <NUM> instead of the curve <NUM>.

Referring to <FIG>, a data table <NUM> and a data table <NUM> are stored in the memory <NUM>. The data table <NUM> defines a relationship between the reference SOC, the reference temperature and the second standby time ΔtR2. The data table <NUM> defines that the lower reference temperature is associated with the longer second standby time ΔtR2 at the same reference SOC. For example, when the reference SOC is <NUM> [%] and the reference temperature is <NUM>[°C], <NUM> minutes is determined as the second standby time ΔtR2, and when the reference SOC is <NUM> [%] and the reference temperature is <NUM>[°C], <NUM> minutes is determined as the second standby time ΔtR2. Additionally, the data table <NUM> defines that the higher reference SOC is associated with the longer or equal second standby time at the same reference temperature. For example, when the reference SOC is <NUM> [%] and the reference temperature is <NUM>[°C], <NUM> minutes is determined as the second standby time, and when the reference SOC is <NUM> [%] and the reference temperature is <NUM>[°C], <NUM> minutes is determined as the second standby time.

The data table <NUM> defines a relationship between the reference SOC, the reference temperature and the second shift time ΔtC2. The data table <NUM> defines that the lower reference temperature is associated with the longer second shift time ΔtC2 at the same reference SOC. Additionally, the data table <NUM> defines that the higher reference SOC is associated with the longer or equal second shift time ΔtC2 at the same reference temperature.

Alternatively, each of the second standby time ΔtR2 and the second shift time ΔtC2 may be preset to a particular value irrespective of the SOC and the temperature. In this case, the steps S710 and S730 may be omitted from the method of <FIG>.

In step S740, the control circuit <NUM> measures the battery voltage.

In step S750, the control circuit <NUM> determines whether the second standby time ΔtR2 has passed since the key-off signal was received. When a value of the step S750 is "Yes", step S760 is performed.

In the step S760, the control circuit <NUM> determines whether the second shift time ΔtC2 has passed since the key-off signal was received. When a value of the step S760 is "No", step S770 is performed. When the value of the step S760 is "Yes", step S780 is performed.

In the step S770, the control circuit <NUM> determines the SOC of the battery B based on the battery voltage and the second OCV curve <NUM>.

In the step S780, the control circuit <NUM> determines the SOC of the battery B based on the battery voltage and the third OCV curve <NUM>.

The control circuit <NUM> may determine the SOC of the battery B at the predetermined time interval by repeating the steps S740 to S780 until a key-on signal is received from the vehicle controller <NUM>.

The embodiments of the present disclosure described hereinabove are not implemented only through the apparatus and method, and may be implemented through programs that perform functions corresponding to the configurations of the embodiments of the present disclosure or recording media having the programs recorded thereon, and such implementation may be easily achieved by those skilled in the art from the disclosure of the embodiments previously described.

While the present disclosure has been hereinabove described with regard to a limited number of embodiments and drawings, the present disclosure is not limited thereto and it is obvious to those skilled in the art that various modifications and changes may be made thereto within the technical aspects of the present disclosure and the equivalent scope of the appended claims.

Claim 1:
A battery management system (<NUM>), comprising:
a memory (<NUM>) configured to store a first Open Circuit Voltage, OCV, curve and a second OCV curve;
a voltage sensor (<NUM>) configured to measure a battery voltage which is a voltage across a battery (B); and
a control circuit (<NUM>) coupled to the memory (<NUM>) and the voltage sensor (<NUM>),
wherein the first OCV curve defines a first relationship between OCV and State Of Charge, SOC),of the battery (B) during discharge of the battery,
the second OCV curve defines a second relationship OCV and SOC of the battery (B) during charge of the battery,
the control circuit (<NUM>) is configured to:
interrupt a flow of current through the battery (B) so that the battery is in a rest state when the control circuit (<NUM> receives a key-off signal, and
estimate a SOC of the battery (B) at a predetermined time interval from a first time point to a second time point based on the battery voltage measured at the predetermined time interval and the first OCV curve in case that the battery (B) is being discharged when the key-off signal is received,
the first time point is a time point when a first standby time has passed since the key-off signal was received, and
the second time point is a time point when a first shift time has passed since the key-off signal was received, the first shift time being longer than the first standby time,
wherein the first standby time is an estimated time required until the rate at which the battery voltage rises equals a predetermined threshold rate from the start time of the rest state.