Battery management system and driving method thereof

In a battery management system and a driving method thereof, the system includes a sensor and a micro control unit (MCU). The sensor senses a voltage and a current of a battery, and generates an estimation current of the battery using a result of cumulatively calculating the battery current by a unit of a predetermined period. The MCU receives the battery voltage and the estimation current, sets a voltage of the battery in a key-on state as a first voltage, sets a voltage of the battery after a first period as a second voltage, and calculates an internal resistance of the battery using a difference between the first and second voltages and an average value of the estimation current.

CLAIM OF PRIORITY

This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C.§119 from an application for BATTERY MANAGEMENT SYSTEM AND DRIVING METHOD THEREOF earlier filed in the Korean Intellectual Property Office on the 26 day of Sep. 2006 and there duly assigned Serial No. 10-2006-0093589.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a battery management system. More particularly, the present invention relates to a battery management system used in a vehicle using electrical energy, and a driving method thereof.

2. Related Art

A vehicle using an internal combustion engine, and using gasoline or heavy oil as a main fuel, has a serious influence on the generation of environmental pollution, such as air pollution. In recent years, much effort has been made to develop an electric vehicle or a hybrid vehicle so as to reduce the generation of environmental pollution.

The electric vehicle is a vehicle which uses a battery engine which operates by means of electrical energy output from a battery. The electric vehicle uses a battery in which a plurality of rechargeable secondary cells is provided as one pack and as its main power source. Thus, the electric vehicle has advantages in that there is no discharge gas, and the noise is very small.

The hybrid vehicle is an intermediary vehicle between the vehicle using an internal combustion engine and the electric vehicle. The hybrid vehicle uses two or more power sources, for example, an internal combustion engine and a battery engine. At present, a hybrid vehicle which uses an internal combustion engine and a fuel cell for continuously supplying hydrogen and oxygen while inducing a chemical reaction to directly obtain electrical energy, or which uses a battery and a fuel cell, is being developed.

In the vehicle using the battery engine, secondary battery cells are increasing in number so as to improve the power source, and a plurality of connected cells have a direct influence on the performance of the vehicle. Thus, there is a requirement for a battery management system (BMS) in which each battery cell should not only be excellent in performance, but also a BMS in which the voltage of each battery cell and the voltage and current of the entire battery are measured, and charge and discharge of each battery cell is effectively managed.

In particular, the internal resistance of the battery has a direct relation to an output reduction and a fatigue state of the battery, and it is used as a reference for determining the lifespan and the state of health (SOH) of the battery. Thus, there is a requirement to more accurately measure the internal resistance of the battery so as to determine the lifespan and the SOH of the battery having the direct influence on the performance of the vehicle.

The information disclosed above is only for enhancement of an understanding of the invention, and thus it does not necessarily form the prior art already known to a person of ordinary skill in the art.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide a battery management system and a driving method thereof having the advantage of more accurately calculating an internal resistance of a battery.

An exemplary embodiment of the present invention provides a battery management system which includes a sensor and a micro control unit (MCU). The sensor senses a voltage and a current of a battery, and generates an estimation current of the battery using a result of cumulatively calculating the battery current by a unit of a predetermined period. The MCU receives the battery voltage and estimation current, sets a voltage of the battery in a key-on state as a first voltage, sets a voltage of the battery after a first period as a second voltage, and calculates an internal resistance of the battery using the difference between the first and second voltages and an average value of the estimation current. The estimation current is generated by cumulatively calculating the battery current by a unit of a second period, and dividing the calculated result by a time corresponding to the second period. The MCU samples the battery estimation current of the first period, and calculates the average value of the estimation current. The MCU calculates the battery internal resistance using the following equation:

Rb=V2-V1Iave×1000⁢[m⁢⁢Ω]
whereV1is the battery voltage in the key-on state,V2is the battery voltage after the first period, andIaveis the average value of the estimation current.

The sensor includes an electric current estimator for comparing the battery current with a reference current, cumulatively calculating a deviation based on the comparison result, dividing the calculated result by the time corresponding to the second period, and generating the estimation current.

Another embodiment of the present invention provides a method for driving a battery management system managing a battery. The method includes: setting a voltage of the battery in a key-on state as a first voltage; setting a voltage of the battery after a first period as a second voltage; calculating an average value of an estimation current of the battery of the first period; and calculating an internal resistance of the battery using a difference between the first and second voltages and the average value of the estimation current. The calculation of the average value includes: cumulatively calculating the battery current by a unit of a second period, dividing the calculated result by a time corresponding to the second period, and generating the estimation current of the battery. The calculation of the average value of the estimation current is performed by sampling the battery estimation current of the first period. The calculation of the internal resistance is performed using the following equation:

Rb=V2-V1Iave×1000⁢[m⁢⁢Ω]
whereV1is the battery voltage in the key-on state,V2is the battery voltage after the first period, andIaveis the average value of the estimation current.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the entire specification, “connecting” any part with another part not only includes “directly connecting”, but also includes “electrically connecting” with a different constituent element interposed therebetween. Also, “including” a constituent element in a part signifies further including, not excluding, another constituent element if there is no specific reference to the contrary.

FIG. 1is a schematic diagram illustrating a battery, a battery management system (BMS), and a peripheral device of the BMS according to an exemplary embodiment of the present invention.

As shown inFIG. 1, a vehicle system includes the BMS1, the battery2, an electric current sensor3, a cooling fan4, a fuse5, a main switch6, a motor control unit (MTCU)7, an inverter8, and a motor generator9.

The battery2includes: a plurality of sub-packs2ato2hin which a plurality of battery cells are coupled in series; output terminals (2_OUT1and2_OUT2); and a safety switch (2_SW) provided between the sub-pack2dand the sub-pack2e. The sub-packs2ato2hare exemplarily eight in number indicating the plurality of battery cells in one group, and are not intended to limit the scope of the present invention. The safety switch (2_SW) refers to a switch provided between the sub-pack2dand the sub-pack2e. The safety switch (2_SW) can be manually switched on/off for the sake of a worker's safety when the battery is replaced or when work on the battery is being carried out. In an exemplary embodiment of the present invention, the safety switch (2_SW) is provided between the sub-pack2dand the sub-pack2e, but it is not intended to limit the scope of the present invention. The output terminals (2_OUT1and2_OUT2) are connected to the inverter8through electric current sensor3and through fuse5and switch6, respectively.

The electric current sensor3measures the amount of electric current output from the battery2, and outputs the measured current amount to a sensor10of the BMS1. The electric current sensor3can be a Hall current transformer (CT) for measuring the current using a Hall device and outputting an analog current signal associated with the measured current, or a shunt resistor for outputting a voltage signal corresponding to an electric current flowing through a resistor inserted into a load line.

The cooling fan4dissipates heat caused by charge and discharge of the battery2on the basis of a control signal of the BMS1, thereby preventing the battery2from being degenerated due to an increase in temperature, and preventing efficiency of the charge and discharge from being reduced.

The fuse5disconnects or short-circuits the battery2, thereby preventing an overcurrent from being transmitted to the battery2. In other words, when an overcurrent is generated, the fuse5is disconnected, thereby preventing the overcurrent from being transmitted to the battery2.

When an abnormal overvoltage, overcurrent, or high temperature occurs, the main switch6switches on/off the battery2on the basis of a control signal from the BMS1or the MTCU7of the vehicle.

The BMS1includes the sensor10, a Micro Control Unit (MCU)20, an internal power supplying unit30, a cell balancing unit40, a storage unit50, a communication unit60, a protective circuit70, a power-on reset unit80, and an external interface90.

The sensor10senses and transmits a battery voltage, a battery current, and a battery temperature to the MCU20.

The MCU20estimates a state of charge (SOC) and a state of health (SOH) of the battery2using the battery voltage, the battery current, and the battery temperature received from the sensor10, and controls the charge and discharge of the battery2. Particularly, the MCU20calculates the internal resistance of the battery2, and determines the life span and the SOH of the battery2using the calculated internal resistance of the battery2. Since the internal resistance has a close connection to the output reduction and the fatigue state of the battery2, it can be a reference for determining the lifespan and the SOH of the battery2. While the vehicle runs, it is difficult to detect a time point where an open circuit voltage (OCV) is detected, and the electric current suddenly varies. Therefore, the MCU20calculates the internal resistance of the battery2soon after the key-on state. Factors necessary for calculating the internal resistance of the battery2are the battery voltage (V1) soon after the key-on state, the battery voltage (V2) measured after a first period for which the battery2is charged or discharged, and an average value (Iave) of an estimation current flowing through the battery2for the first period. According to an exemplary embodiment of the present invention, the first period refers to a period arbitrarily set among a battery charge or discharged period after the key-on state. The first period can be set according to a condition for controlling the vehicle. For example, according to the condition for controlling the vehicle, the vehicle is operated by only a gasoline engine for a prescribed period after the key-on-state. Then, the first period is set to be below the prescribed period. In detail, the MCU20sets a voltage received from the sensor10soon after the key-on state, as the battery voltage (V1) of the key-on state, in order to calculate the internal resistance of the battery2. The MCU20sets a voltage, received from the sensor10after the first period for which the battery2is charged or discharged, as the battery voltage (V2). The MCU20calculates a difference (V2−V1) between the battery voltage (V2) after the first period and the battery voltage (V1) of the key-on state. The MCU20calculates the average value (Iave) of the estimation current of the battery2, using the estimation current (i) flowing through the battery2for the first period for which the battery2is charged or discharged. The MCU20divides the calculated voltage difference (V2−V1) by the average value (Iave) of the estimation current of the battery2, calculates the internal resistance of the battery2, and determines the lifespan and the SOH of the battery2using the calculated internal resistance of the battery2. According to an exemplary embodiment of the present invention, the battery management system compares a presently measured battery current with a reference current, and cumulatively calculates a deviation between the battery current and the reference current by a unit of a second period. The estimation current is an electric current calculated by dividing the cumulatively calculated result by a time corresponding to the second period. The second period refers to a time period for which a variation of the battery current is measured. As the time corresponding to the second period gets shorter, the battery current can be more accurately measured.

The internal power supplying unit30supplies power to the BMS1using a sub battery. The cell balancing unit40balances the state of charge of each cell. In other words, the cell balancing unit40can discharge a cell having a relatively high charged state, and can charge a cell having a relatively low charged state. The storage unit50stores data of the SOC and SOH when the BMS1is in a power-off state. The storage unit50can be a nonvolatile storage unit which is an electrically erasable programmable read only memory (EEPROM). The communication unit60communicates with the MTCU7of the vehicle. The communication unit60transmits information on the SOC and the SOH from the BMS1to the MTCU7, or receives information on the vehicle state from the MTCU7and transmits the received information to the MCU20. The protective circuit70refers to a secondarily added circuit to protect the battery2from overcurrent and overvoltage using hardware. Before that, the protective circuit70primarily protects the battery2using firmware provided within the MCU20. The power-on reset unit80resets the entire system when the BMS1is in a power-on state. The external interface90connects sub devices of the BMS1, such as the cooling fan4and the main switch6, to the MCU20. In an exemplary embodiment of the present invention, only the cooling fan4and the main switch6are shown, but this is not intended to limit the scope of the present invention.

The MTCU7detects an in-running state of the vehicle on the basis of information on the accelerator, the brake, and the speed of the vehicle, and determined necessary information such as the degree of torque. The in-running state of the vehicle refers to the key-on state for starting the engine, a key-off state for stopping the engine, a coasting state, and an acceleration running state. The MTCU7transmits the information on the vehicle state to the communication unit60of the BMS1. The MTCU7controls the motor generator9so that it has an output based on torque information. In other words, the MTCU7controls switching of the inverter8, and controls the motor generator9to have an output based on the torque information. The MTCU7receives the SOC of the battery2from the MCU20through the communication unit60of the BMS1, and controls the SOC of the battery2to reach a target value (e.g., 55%). For example, receiving an SOC of 55% or less from the MCU20, the MTCU7controls a switch of the inverter8to output power toward the battery2, thereby charging the battery2. At this time, the battery current can be set to a positive (+) value. Receiving an SOC of 55% or more, the MTCU7controls the switch of the inverter8to output the power toward the motor generator9, thereby discharging the battery2. At this time, the battery current can be set to a negative (−) value.

The inverter8enables the battery2to be charged or discharged on the basis of the control signal of the MTCU7.

The motor generator9uses the electrical energy of the battery2to drive the vehicle on the basis of the torque information received from the MTCU7.

As a result, the MTCU7charges and discharges the battery2as much as a rechargeable power on the basis of the SOC, thereby preventing the battery2from being overcharged and over discharged, and making it possible to efficiently use the battery2for a long time. However, when the battery2is installed in the vehicle, it is difficult to measure the actual SOC of the battery2. Therefore, the BMS1should accurately estimate the SOC, using the battery current, the battery voltage, and the cell temperature sensed in the sensor10, and transmit the estimated SOC to the MTCU7.

A method for calculating the internal resistance of the battery according to an exemplary embodiment of the present invention will be described in detail with reference toFIGS. 2 and 3.

FIG. 2is a schematic diagram illustrating the sensor and the micro control unit (MCU) ofFIG. 1according to an exemplary embodiment of the present invention, andFIG. 3is a graph for describing the process of calculating an average value of an estimation current of a battery according to an exemplary embodiment of the present invention. It is shown that the batter is charged for the first period inFIG. 3. But the battery can be discharged for the first period.

As shown inFIG. 2, according to an exemplary embodiment of the present invention, the MCU20calculates the internal resistance of the battery2using the battery voltage (V) sensed by the sensor10and the battery estimation current (i). The sensor10includes a battery voltage sensor110, a battery current sensor120, an electric current estimator130, and an analog-to-digital (A/D) converter140. The MCU20includes an internal resistance calculator210and an SOH determiner220.

The battery voltage sensor110senses and transmits, to the A/V converter140, an analog voltage value between the output terminals (2_out1and2_out2) of the battery2.

The battery current sensor120receives an electric current value sensed by the current sensor3, and transmits it to the electric current estimator130.

The current estimator130compares the present battery current, received from the battery current sensor120, with the reference current. The current estimator130cumulatively calculates the deviation of the current based on the comparison result, by a unit of a second period. The current estimator130divides the cumulatively calculated current value by the time corresponding to the second period, and generates the estimation current (i) of the battery. According to an exemplary embodiment of the present invention, the reference current is an arbitrarily set electric current that is compared with the presently measured battery current. The reference current can be different depending on the user's setting.

The A/D converter140converts analog data, received from the battery voltage sensor110and the current estimator130, into digital data, and transmits the converted digital data to the MCU20.

A method for calculating the internal resistances of the elements and the battery of the MCU20will be described in detail below.

The battery internal resistance calculator210receives the battery voltage measured by the sensor10soon after the key-on state, and the battery estimation current (i), and sets the received voltage as the battery voltage (V1). The battery internal resistance calculator210sets the voltage, received from the sensor10after the first period for which the battery is charged, as the battery voltage (V2). Thus, the battery internal resistance calculator210calculates the difference (V2−V1) between the battery voltages (V2) measured after the first period and the battery voltage (V1) of the key-on state. The battery internal resistance calculator210calculates the average value (Iave) of the estimation current using the battery estimation current (i) of the first period. The process of calculating the average value (Iave) of the estimation current of the battery according to an exemplary embodiment of the present invention will be described in detail with reference toFIG. 3.

The battery internal resistance calculator210samples the battery estimation current (i) of the first period for which the battery is charged. The battery internal resistance calculator210sums up estimation current values corresponding to respective sampling time durations (T1to Tn). The battery internal resistance calculator210divides a sum of the estimation currents by the sampling number of times (n), and calculates the average value (Iave) of the battery estimation currents of the first period. Thus, the battery internal resistance calculator210divides the voltage difference (V2−V1) of the battery by the average value (Iave) of the battery estimation current, and calculates the battery internal resistance using Equation 1 below.

Rb=V2-V1Iave×1000⁢[m⁢⁢Ω](Equation⁢⁢1)
whereV1is battery voltage in the key-on state,V2is battery voltage after first period for which battery is charged, andIaveis average value of estimation current of the first period for which battery is charged.

The battery internal resistance calculator210transmits the calculated internal resistance of the battery to the SOH determiner220. According to an exemplary embodiment of the present invention, the internal resistance of the battery has a unit of milliohms (mΩ) because the amount of variation of the battery voltage is very small in magnitude compared to the magnitude of the battery current, but it is not intended to limit the scope of the present invention. The resistance unit used in the above equation can vary depending on the amount of variation of the battery voltage and current.

The SOH determiner220determines the SOH using the battery internal resistance. The SOH determiner220receives the battery internal resistance from the battery internal resistance calculator210, and compares the received internal resistance with a reference resistance. When the battery internal resistance is greater than the reference resistance, the SOH determiner220determines that the SOH of the battery is low, and that the lifespan of the battery has expired. However, when the battery internal resistance is less than the reference resistance, the SOH determiner220determines that the SOH of the battery is high, and the lifespan of the battery is in a normal range. According to an exemplary embodiment of the present invention, the reference resistance can be the battery internal resistance when the battery in use provides an output which is 80% of the output of a fresh battery. However, it is not intended to limit the scope of the present invention, and the reference resistance can be different depending on the user's setting.

FIG. 4is a flowchart illustrating the method for calculating the internal resistance of the battery according to an exemplary embodiment of the present invention.

A determination as to whether or not the MCU20is in a key-on state is made (S100).

When it is determined in step S100that the MCU20is not in the key-on state, step S100is repeated. When it is determined in step S100that the MCU20is in the key-on state, the MCU20sets the voltage received from the sensor10in the key-on state as the battery voltage (V1) (S200). The battery is charged or discharged during the first period (V1) (S300).

After the first period for which the battery is charged or discharged, the MCU20sets the voltage received from the sensor10as the battery voltage (V2) (S400). Then, the MCU20calculates the difference (V2−V1) between the battery voltage (V2) and the battery voltage (V1) of the key-on state. The MCU20samples the battery estimation current (i) during the first period, and sums up the estimation current values corresponding to the respective sampling time durations (T1to Tn). The MCU20divides the sum of the estimation currents by the sampling number of times (n), and calculates the average value (Iave) of the battery estimation current of the first period (S500).

Upon completion of the calculation of the average value (Iave) of the battery estimation current in step S500, the MCU20divides the voltage difference (V2−V1) by the average value (Iave) of the battery estimation current, and calculates the battery internal resistance using Equation 1 which is repeated below.

The MCU20compares the calculated internal resistance of step S600with the reference resistance (S700).

When the calculated battery internal resistance is less than the reference resistance as a result of the comparison of step S700, the MCU20determines that the SOH of the battery is high, and the lifespan of the battery is in the normal range (S800). When the calculated battery internal resistance is greater than the reference resistance as a result of step S700, the MCU20determines that the SOH of the battery is low, and that the lifespan of the battery has expired (S900).

As described above, in the method for calculating the battery internal resistance using the average value (Iave) of the battery estimation current according to an exemplary embodiment of the present invention, calculation is performed in consideration of the dynamically varying electric current. Therefore, the calculation can be more accurately performed, and thus the lifespan and the SOH of the battery can be more accurately determined in comparison to a conventional method for calculating the internal resistance.

In the battery management system and the driving method thereof according to an exemplary embodiment of the present invention, the internal resistance of the battery can be more accurately calculated using the average value of the estimation current of the battery.