KR20070076833A - Battery management system and driving method thereof - Google Patents

Abstract

A battery management system and a driving method thereof are provided to reduce a measurement error of open circuit voltage, to judge the state of charge using the open circuit voltage with a reduced measurement error, and thus calculate the state of charge precisely and exactly. The battery management system manages a battery including at least one pack, wherein the pack consists of many battery cells. The battery management system comprises: a sensing unit(10) which measures and outputs pack currents, pack voltages, and cell temperatures of the battery pack; and a main controller unit(20) which calculates internal resistance using the pack currents and pack voltages obtained from the sensing unit(10), judges output electric power corresponding to the internal resistance, calculates open circuit voltage using the output electric power, and judges the state of charge corresponding to the open circuit voltage.

Description

BATTERY MANAGEMENT SYSTEM AND DRIVING METHOD THEREOF}

1 is a view schematically showing a battery, a BMS, and a peripheral device of a BMS according to an embodiment of the present invention.

2 is a view schematically showing an MCU according to an embodiment of the present invention.

3 is a graph showing the relationship between internal resistance and output power.

4 is a graph showing the relationship between OCV and SOC.

5 is a flowchart illustrating a method of driving a battery management system according to an exemplary embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery management system, and more particularly, to a battery management system and a method of driving the same, which can be used in an automobile using electric energy.

Automobiles using internal combustion engines that use gasoline or heavy oil as their main fuels have serious effects on pollution, such as air pollution. Therefore, in recent years, in order to reduce the occurrence of pollution, much efforts have been made in the development of electric vehicles or hybrid vehicles.

An electric vehicle is a vehicle using a battery engine operated by electric energy output from a battery. Such an electric vehicle uses no battery as a main power source because a plurality of secondary cells capable of charging and discharging are used as a pack has no exhaust gas and has a very small noise.

A hybrid vehicle, on the other hand, is an intermediate vehicle between an automobile using an internal combustion engine and an electric vehicle, and a vehicle using two or more power sources such as an internal combustion engine and a battery engine. At present, a hybrid vehicle of a hybrid type has been developed, such as using a fuel cell that directly generates an electric energy by chemical reaction while continuously supplying an internal combustion engine and hydrogen and oxygen, or uses a battery and a fuel cell.

In the vehicle using electric energy as described above, the performance of the battery directly affects the performance of the vehicle. Therefore, the performance of each battery cell must be excellent, and each battery cell is measured by measuring the voltage of each battery cell, the voltage and current of the entire battery, and the like. There is an urgent need for a battery management system (BMS) capable of efficiently managing charge and discharge of cells.

In the conventional battery management system, an open loop voltage was calculated to determine a state of charge (“SOC”) of a battery. In order to calculate the open voltage, a measurement value of a battery current and voltage was required. . An error generated in the process of measuring the current and voltage value of the battery generates an error in the open voltage, and thus there is a problem in that an error occurs in the SOC of the battery. In addition, SOC errors occur due to battery deterioration.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a battery management system and a driving method thereof capable of calculating more accurate and accurate SOC.

In a battery management system in which a plurality of battery cells according to an aspect of the present invention comprises a pack and manages a battery including at least one pack, the pack current, pack voltage, and cell temperature of the battery pack are determined. Sensing unit for measuring and outputting The internal resistance is calculated using the pack current and the pack voltage input from the sensing unit, the output power corresponding to the internal resistance is determined, and the open circuit voltage (OCV) is determined using the output power. And a main controller unit (MCU) for determining an SOC corresponding to the OCV.

According to another aspect of the present invention, a method of driving a battery management system for managing a battery comprising a plurality of battery cells consisting of one pack and including at least one pack, the method comprising: a) pack current, pack voltage and cell temperature B) calculating internal resistance by recognizing the pack current and the pack voltage at a predetermined time interval, c) retrieving the internal resistance and output power data corresponding to the cell temperature, and calculating the internal resistance. Detecting an output power from the data using the same; d) calculating a current using the internal resistance and the output power and a set reference voltage, and calculating an OCV using the reference voltage, the internal resistance, and the current; e) determining the SOC from the SOC and OCV relationship data using the OCV.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention. Like parts are designated by like reference numerals throughout the specification.

Throughout the specification, when a part is "connected" to another part, this includes not only "directly connected" but also "electrically connected" with another element in between. . In addition, when a part is said to "include" a certain component, which means that it may further include other components, except to exclude other components unless otherwise stated.

1 is a view schematically showing a battery, a BMS, and a peripheral device of a BMS according to an embodiment of the present invention.

As shown in FIG. 1, an automotive system includes a BMS 1, a battery 2, a current sensor 3, a cooling fan 4, a fuse 5, a main switch 6, an engine controller unit, and an ECU. 7), an inverter 8 and a motor generator 9.

First, the battery 2 includes a plurality of subpacks 2a to 2h, an output terminal 2_OUT1, an output terminal 2_OUT2, and a subpack 2d and a subpack 2e in which a plurality of battery cells are connected in series. It includes a safety switch (2_SW) provided in. Here, the subpacks 2a to 2h are illustrated as eight by way of example, and the subpacks are merely displayed as a group of a plurality of battery cells, but are not limited thereto. In addition, the safety switch 2_SW is a switch provided between the subpack 2d and the subpack 2e and is a switch that can be manually turned on and off for the safety of the operator when replacing the battery or performing work on the battery. . In an embodiment of the present invention, a safety switch 2_SW is provided between the subpack 2d and the subpack 2e, but the present invention is not limited thereto. The output terminal 2_OUT1 and the output terminal 2_OUT2 are connected to the inverter 8.

The current sensor 3 measures the output current amount of the battery 2 and outputs it to the sensing unit 10 of the BMS 1. Specifically, the current sensor 3 may be a Hall CT (Hall current transformer) that measures current using a Hall element and outputs an analog current signal corresponding to the measured current.

The cooling fan 4 cools heat that may be generated by the charging and discharging of the battery 2 based on the control signal of the BMS 1, thereby preventing deterioration of the battery 2 and deterioration of the charging and discharging efficiency due to the temperature rise. do.

The fuse 5 prevents overcurrent from being transferred to the battery 2 by the disconnection or short circuit of the battery 2. That is, when an overcurrent occurs, the fuse 5 is disconnected to block the overcurrent from being transmitted to the battery 2.

The main switch 6 turns on and off the battery 2 based on the control signal of the BMS 1 or the ECU 7 of the vehicle when an abnormal phenomenon such as overvoltage, overcurrent, high temperature occurs.

The BMS 1 includes a sensing unit 10, a MCU (Main control unit) 20, an internal power supply unit 30, a cell balancing unit 40, a storage unit 50, a communication unit 60, and a protection circuit unit 70. , A power-on reset unit 80 and an external interface 90.

The sensing unit 10 measures a total battery pack current, a total battery pack voltage, each battery cell voltage, a cell temperature, and an ambient temperature, and transmits the same to the MCU 20.

The MCU 20 charges the battery 2 based on the digital data corresponding to the total battery pack current, the total battery pack voltage, the pack voltage of each battery cell, the cell temperature, and the ambient temperature received from the sensing unit 10. charge / discharge of the battery 2 is controlled by estimating a state of charging (hereinafter referred to as SOC) and a state of health (hereinafter referred to as SOH). In addition, the MCU 20 generates information indicating the state of the battery 2 and transmits the information to the ECU 7 of the vehicle through the communication unit 60. Therefore, the ECU 7 of the vehicle performs charging or discharging of the battery 2 based on the SOC and SOH transmitted from the MCU 20. The MCU 20 of the battery management system according to the embodiment of the present invention considers the health state SOH to accurately estimate the state of charge SOC. The MCU 20 calculates the internal resistance as a factor representing the health state (SOH) of the battery and determines the output power according to the internal resistance. The MCU 20 determines the SOH using the internal resistance and the output power. When the calculated internal resistance is larger than a predetermined reference value, or when the output power corresponding to the internal resistance is lower than the reference output power, it is determined that much deterioration has occurred and it is determined that the battery is no longer suitable for use. In addition, the MCU 20 may calculate the SOC according to the deterioration degree in consideration of the internal resistance. Specifically, the MCU 20 stores output power measurement result data and SOC and OCV relationship data according to internal resistance. The MCU 20 detects the output power Pout by measuring the internal resistance Ri and calculates an open circuit voltage (OCV) according to the output power to determine the SOC of the battery. That is, the MCU 20 calculates the internal resistance from the sensing unit 10 using the pack current and the pack voltage, and detects the output power corresponding to the internal resistance calculated from the internal resistance and the output power relation graph. The OCV value is calculated using the detected output power, and the SOC is calculated using the OCV value calculated from the SOC and OCV relationship graph.

The internal power supply unit 30 is a device that generally supplies power to the BMS 1 using an auxiliary battery.

The cell balancing unit 40 balances the state of charge of each cell. That is, a cell with a relatively high state of charge can be discharged and a cell with a relatively low state of charge can be charged.

The storage unit 50 stores the current SOC, SOH, and the like when the power of the BMS 1 is turned off. The storage unit 50 may be an EEPROM as a nonvolatile storage device that can be electrically written and erased.

The communication unit 60 transmits the SOC and SOH information received from the MCU 20 to the ECU 7.

The protection circuit unit 70 is a circuit for protecting the BMS 1 from external shock, overcurrent, low voltage, etc. using firmware.

The power-on reset unit 80 resets the entire system when the power of the BMS 1 is turned on.

The external interface 90 is a device for connecting the auxiliary devices of the BMS such as the cooling fan 4 and the main switch 6 to the MCU 20. In the present embodiment, only the cooling fan 4 and the main switch 6 are shown, but are not limited thereto.

The ECU 7 determines the torque degree based on the information of the accelerator, break, vehicle speed, etc. of the vehicle, and controls the output of the motor generator 9 to match the torque information. That is, the ECU 7 controls the switching of the inverter 8 so that the output of the motor generator 9 matches the torque information. In addition, the ECU 7 receives the SOC of the battery 2 delivered from the MCU 20 through the communication unit 60 of the BMS 1 so as to control the SOC of the battery 2 to be a target value (for example, 55%). do. For example, when the SOC transmitted from the MCU 20 is 55% or less, the switch of the inverter 8 is controlled so that the power is output in the direction of the battery 10 to charge the battery 2, and the pack current I is Can be a '+' value. On the other hand, when the SOC is 55% or more, the switch of the inverter 8 is controlled so that the power is output in the direction of the motor generator 9 so that the battery 2 is discharged. At this time, the pack current I may become a '-' value. have. In addition, the ECU 7 may receive the SOH of the battery 2 delivered from the MCU 20 through the communication unit 60 of the BMS 1 to be displayed on a display device such as an instrument panel (not shown) of a vehicle. have.

The inverter 8 causes the battery 2 to be charged or discharged based on the control signal of the ECU 7.

The motor generator 9 drives the motor vehicle based on the torque information transmitted from the ECU 7 using the electric energy of the battery 2.

Hereinafter, a battery management system for determining SOC in consideration of deterioration according to an embodiment of the present invention will be described.

2 is a diagram schematically showing the MCU 20 according to an embodiment of the present invention.

As shown in FIG. 2, the MCU 20 may include an internal resistance calculator 210, an output power determiner 220, an OCV calculator 230, an SOC determiner 240, and an SOH determiner 250. Include.

The internal resistance calculator 210 recognizes the pack current Ip and the pack voltage Vp input from the sensing unit 10 at predetermined time intervals. The internal resistance Ri is calculated using the pack current Ip1 and the pack voltage Vp1 recognized at an arbitrary time point, and the pack current Ip2 and the pack voltage Vp2 recognized after a predetermined time. Specifically, the internal resistance Ri may be calculated using Equation 1. The pack voltage Vp input to the internal resistance calculator 210 according to an exemplary embodiment of the present invention is set as the sum of the voltages of all the subpacks 2a-2e connected in series. When the battery includes a plurality of packs including a plurality of subpacks, the pack voltage Vp may be set to a sum of voltages of each of the plurality of packs.

 The output power determiner 220 receives the internal resistance value calculated from the internal resistance calculator 210. The output power determination unit 220 includes a database 225 storing the internal resistance and the output power corresponding to the calculated internal resistance. The output power determination unit 220 detects an output power corresponding to the input internal resistance value from the database 225. The output power according to the internal resistance may vary according to the cell temperature, and the database 225 according to the embodiment of the present invention may store the relationship between the internal resistance and the output power according to the cell temperature. The cell temperature may be a temperature of a specific cell of the plurality of cells or an average temperature of temperatures of each of the plurality of cells. The cell temperature according to the embodiment of the present invention is an average temperature.

Specifically, the relationship between the output power according to the internal resistance will be described with reference to FIG. 3.

3 is a graph showing the relationship between internal resistance and output power. The graph of FIG. 3 shows the output power value corresponding to the internal resistance by experiment.

As shown in FIG. 3, the deteriorated FRESH battery has an internal resistance of 0, at which time the output power is set to 100% of the output power output from the battery. As the battery is repeatedly charged and discharged, the internal resistance increases due to battery deterioration, and accordingly, output power Pout decreases. When the internal resistance value input from the internal resistance calculation unit 210 is 6 [mΩ] (Ri1), in Fig. 3, the output power corresponding to the internal resistance 6 [mΩ] (Ri1) is 70.3% (Pout1). do.

The OCV calculator 230 receives the output power Pout from the output power calculator 220 and calculates the OCV. In detail, the OCV calculator 230 sets and stores the battery lower limit voltage Vcutoff, and calculates the battery maximum discharge current value Iomax using Equation 2. The battery lower limit voltage Vcutoff means the lowest value of the voltage output from a normal battery. That is, when the voltage output from the battery is smaller than the battery lower limit voltage, the battery can no longer be used. The maximum discharge current value Iomax refers to the discharge current output from the battery when the voltage output from the battery is equal to the battery lower limit voltage.

The OCV calculator 230 calculates an OCV (Vocv) value using the battery lower limit voltage Vcutoff, the maximum discharge current value Iomax, and the internal resistance Ri. Specifically, the voltage output from the battery is equal to the sum of the OCV voltage and the voltage generated when the current generated when the load is connected to the battery flows through the internal resistance. In the embodiment of the present invention, the battery lower limit voltage Vcutoff value output from the battery is equal to the sum of the voltage generated when the maximum discharge current value Iomax flows to the internal resistance Ri1 and the OCV (Vocv) value. Equation 3 shows this as follows.

In summary, OCV (Vocv) can be calculated as shown in Equation 4.

Hereinafter, the SOC determination unit 240 will be described with reference to FIG. 4.

4 is a graph showing the relationship between OCV and SOC.

The SOC determining unit 240 determines the SOC using the OCV (Vocv) input from the OCV calculating unit 230. In detail, the SOC determination unit 240 stores data obtained by experimentally obtaining a relationship between the OCV and the SOC. This is shown in a graph, as shown in FIG. As shown in FIG. 4, the SOC (SOC1) corresponding to the OCV (Vocv) input from the OCV calculator 230 is detected.

The SOH determiner 250 receives the internal resistance and the output power from the internal resistance calculator 210 and the output power determiner 220 to determine the SOH. If the input internal resistance is larger than the predetermined internal resistance reference value or if the output power is smaller than the predetermined reference value even if the internal resistance is smaller than the predetermined reference value, it is determined as a degraded battery. A predetermined reference value for each of the internal resistance and the output power may be obtained by an experiment, and the SOH determination unit 250 may store the value obtained by the experiment and use it.

Hereinafter, a driving method of a battery management system according to an exemplary embodiment of the present invention will be described.

5 is a flowchart illustrating a method of driving a battery management system according to an exemplary embodiment of the present invention.

As shown in FIG. 5, the MCU 20 receives a pack current Ip, a pack voltage Vp, and a cell temperature Tc from the sensing unit 10 (S100). The internal resistance calculator 210 calculates the internal resistance by recognizing the pack current Ip and the pack voltage Vp at a predetermined time interval (S200).

The output power determination unit 220 retrieves the internal resistance and output power data corresponding to the input cell temperature Tc, and outputs the data from the retrieved data using the internal resistance Ri input from the internal resistance calculation unit 210. Power is detected (S300).

The OCV calculator 230 receives the internal resistance and the output power from the output power determiner 220. The battery lower limit voltage and the maximum discharge current are calculated using the output power, and the OCV is calculated using the calculated battery lower limit voltage, the maximum discharge current and the internal resistance (S400).

The SOC determination unit 240 determines the SOC from the SOC and the OCV relationship data using the OCV input from the OCV calculator 230 (S500).

The BMS 1 according to an embodiment of the present invention may repeatedly calculate the SOC in consideration of deterioration by repeating the above operation at regular time intervals.

As such, the BMS according to the embodiment of the present invention calculates the output power of the battery using the internal resistance, and calculates the OCV value using the output power. Since the SOC is determined based on the calculated OCV value, the measurement error can be prevented compared to calculating the OCV by measuring the conventional pack current and the pack voltage. Therefore, since the SOC is determined by using the OCV of which the measurement error is reduced, it is possible to provide an SOC that is more accurate than before and considers the deterioration state.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

According to an aspect of the present invention, there is provided a battery management system and a driving method thereof for determining an SOC in consideration of deterioration of a battery.

According to another aspect of the present invention, there is provided a battery management system and a method of driving the same, which can reduce the measurement error of OCV and calculate more accurate and accurate SOC by determining the SOC by using the OCV having the reduced measurement error.

Claims (10)

A battery management system in which a plurality of battery cells is configured as one pack and manages a battery including at least one pack, Sensing unit for measuring and outputting the pack current, the pack voltage and the cell temperature of the battery pack An internal resistance is calculated using the pack current and the pack voltage input from the sensing unit, an output power corresponding to the internal resistance is determined, an open circuit voltage (OCV) is calculated using the output power, and the OCV is calculated. Main controller unit (MCU) to determine corresponding SOC Battery management system comprising a. The method of claim 1, The MCU, An internal resistance calculator to calculate an internal resistance using the pack current and the pack voltage; An output power determination unit detecting an output power corresponding to the internal resistance and the cell temperature; An OCV calculator configured to calculate a current using the output power and the set voltage, and calculate an open circuit voltage (OCV) using the voltage, current, and internal resistance; And a SOC determination unit to determine an SOC using the SOC data corresponding to the OCV. The method of claim 2, The MCU, The battery management system further comprises a SOH determination unit for determining the SOH by using the calculated internal resistance and the detected output power. The method of claim 2, The internal resistance calculation unit, And a battery management system that recognizes the pack voltage and the pack current at predetermined time intervals, and calculates an internal resistance based on the pack voltage variation with respect to the pack current variation. The method of claim 2, The output power determination unit, And a battery management system using data obtained by experimentally calculating a correspondence relationship between the cell temperature, the internal resistance, and the output power in detecting an output power corresponding to the calculated internal resistance according to the cell temperature. The method of claim 2, The OCV calculation unit, Dividing the output power by the first voltage to calculate the current; And the OCV is a value obtained by subtracting a result of the product of the current and the internal resistance from the voltage. The method of claim 6, The voltage is, The battery management system is a minimum reference voltage suitable for use with the voltage output from the pack. In the driving method of a battery management system for managing a battery comprising a plurality of battery cells consisting of one pack, including at least one pack, a) receiving pack current, pack voltage and cell temperature; b) calculating the internal resistance by recognizing the pack current and the pack voltage at regular time intervals, c) retrieving the internal resistance and output power data corresponding to the cell temperature, and detecting the output power from the data using the internal resistance d) calculating current using the internal resistance and output power and a set reference voltage, and calculating OCV using the reference voltage, internal resistance and current, and e) determining a SOC from SOC and OCV relationship data using the OCV. The method of claim 8, In step d), And a value obtained by subtracting a result of the product of the current and the internal resistance from the reference voltage as the OCV. The method of claim 9, The reference voltage is, And a voltage output from the pack, the minimum reference voltage suitable for use.

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