Apparatus and method for monitoring charging/discharging capacity of battery packs as a function of time and temperature

An apparatus and a method are provided for monitoring a battery pack for accurately calculating an actual discharging or charging capacity of a secondary battery, which depends on temperature. The battery pack monitoring apparatus includes a bare cell adapted to be charged/discharged with a predetermined voltage. Sensors sense the bare cell charging/discharging voltages, charging/discharging currents, and temperature and convert them into predetermined electrical signals. A monitoring control unit converts the electrical signals from the sensors into digital signals and processes them in accordance with predetermined control commands. A storage unit stores tabulated discharging capacity-time data and charging capacity-time data as a function of the bare cell temperature, and outputs this data to the monitoring control unit. The processed data indicating a current charge/discharge capacity of the battery pack is provided to a charger or to another external system.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2005-0006762, titled APPARATUS AND METHOD FOR MONITORING BATTERY PACK, filed in the Korean Intellectual Property Office on Jan. 25, 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 an apparatus and a method for monitoring a battery pack, and more particularly to an apparatus and a method for monitoring a battery pack for accurately calculating an actual discharging or charging capacity of a secondary battery, which depends on temperature, so that the battery pack can be maintained and used in an optimum condition.

2. Description of the Prior Art

Typically, chargeable/dischargeable secondary batteries undergo conversion between chemical energy and electrical energy through electrochemical reactions in which internal active materials oxidize/reduce due to charging/discharging. Performance of the secondary batteries is affected by charging method, discharging depth, temperature during storage and service, load level, number of charging/discharging, and the like. Recent developments of secondary batteries are moving toward lithium ion batteries, lithium polymer batteries, or fuel cells, which have a high energy density and a small mass and are used as industrial, automobile, portable, or mobile power supplies.

Secondary batteries are generally classified into battery cells (also known as bare cells) and battery packs. The bare cells are simply adapted to be charged/discharged without any circuit mounted thereon. The battery packs include a bare cell and various protective and control circuits mounted on the bare cell and are packaged according to the external systems where the battery pack is used.

The circuits mainly control charging/discharging of the secondary batteries and are interrupted, when the secondary batteries are overcharged/over-discharged, to extend the life of the secondary batteries and to protect users from dangerous situations. Recently, monitoring systems are used to more accurately inform external systems of the remaining discharging capacity of battery packs.

However, conventional battery packs or monitoring systems calculate a discharging capacity simply based on a present voltage or current of bare cells and cannot inform external systems of the exact discharging capacity, which depends on temperature.

For example, when a battery pack is fully charged at room temperature and then used at a lower temperature, an external device displays remaining capacity data, which has been calculated based on the lower temperature. A remaining discharging capacity displayed at the lower temperature is smaller than an actual fully charged capacity. However, the remaining capacity data calculated based on the lower temperature is still displayed even when the battery back is again used at room temperature, although the remaining capacity must be updated based on the present temperature. As a result, the exact battery pack capacity conforming to the present temperature is not displayed.

In addition, when a battery pack is fully charged at room temperature and used at the same temperature, an external system displays remaining discharging capacity data, which has been calculated based on the present temperature. However, the remaining capacity data calculated based on room temperature is still displayed even when the battery pack is used at a lower temperature, although the remaining capacity must be updated based on the present temperature (lower temperature). As a result, the exact battery pack capacity conforming to the present temperature is not displayed.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides an apparatus and a method for monitoring a battery pack for accurately calculating an actual discharging or charging capacity of a secondary battery, which depends on temperature, and informing an external system of this capacity so that the battery pack can be maintained and used in an optimum condition.

In one embodiment of the present invention, a battery pack monitoring apparatus is provided that includes a bare cell adapted to be charged/discharged with a predetermined voltage. A voltage sensor senses the bare cell's charging/discharging voltages. A current sensor senses the bare cell's charging/discharging currents. A cell temperature sensor senses the bare cell's temperature. A monitoring control unit converts signals inputted from the voltage sensor, the current sensor, and the cell temperature sensor into digital signals and processes them in accordance with predetermined control commands. A first storage unit tabulates discharging capacity-time data and charging capacity-time data as a function of the bare cell's temperature, stores this data, and outputs them to the monitoring control unit. A second storage unit stores the bare cell's charging/discharging voltages, charging/discharging currents, and temperature processed by the monitoring control unit.

Another embodiment of the invention presents a battery pack monitoring apparatus that includes a bare cell adapted to be charged or discharged with a predetermined voltage. In this apparatus, sensors are provided for sensing bare cell charging/discharging voltages, bare cell charging/discharging currents, and bare cell temperature, and converting sensed bare cell charging/discharging voltages, bare cell charging/discharging currents, and bare cell temperature into predetermined electrical signals. The apparatus also includes first storage unit for storing bare cell discharging capacity versus time data and bare cell charging capacity versus time data as a function of the bare cell temperature. A monitoring control unit in the apparatus converts the predetermined electrical signals into digital signals, receives the tabulated data from the first storage unit, and processes the digital signals and the tabulated data in accordance with predetermined control commands to obtain a present value of the charging/discharging capacity of the battery pack and to obtain processed bare cell charging/discharging voltages, processed bare cell charging/discharging currents, and processed bare cell temperature.

In another embodiment, the apparatus may also include a voltage sensor coupled to the bare cell for sensing the bare cell charging/discharging voltages, a current sensor coupled to the bare cell for sensing the bare cell charging/discharging currents, and a cell temperature sensor for sensing the bare cell temperature. The apparatus may also include a second storage unit coupled to the monitoring control unit for storing the processed voltages, currents, and temperature received from the monitoring control unit. The apparatus may further include external terminals positioned on both ends of the bare cell for coupling the bare cell to an external system, a charging switch and a discharging switch coupled between the bare cell and the external terminals, and a switch temperature sensor coupled to the monitoring control unit for sensing a temperature of the charging switch and a temperature of the discharging switch, converting sensed switch temperatures into switch temperature electrical signals, and sending the switch temperature electrical signals to the monitoring control unit. The second storage unit may also store the sensed switch temperatures.

In another embodiment, a protective circuit unit may be included that is coupled to the charging switch and the discharging switch for receiving input of voltage sensor electrical signals or current sensor electrical signals and toggling on/off the charging switch and the discharging switch in response to the voltage sensor electrical signals or the current sensor electrical signals. A communication interface unit may be included that is coupled to the monitoring control unit to output to the external system the processed bare cell charging/discharging voltages, the processed bare cell charging/discharging currents, the processed bare cell temperature, and the sensed switch temperatures. The monitoring control unit may load discharging capacity-time data from the storage unit based on a present temperature of the bare cell when the bare cell temperature changes, re-calculate a discharging capacity with reference to the bare cell voltage and the bare cell current, and output recalculated discharging capacity to the communication interface unit.

In another embodiment, a battery pack monitoring method is provided that includes tabulating discharging capacity-time data as a function of temperature and storing the data on a storage unit, sensing a bare cell's temperature, loading discharging capacity-time data from the storage unit and calculating a discharging capacity based on the bare cell's present temperature, outputting the calculated discharging capacity to an external system, re-sensing the bare cell's temperature, determining whether or not there is a difference between the sensed temperature of the bare cell and an existing re-sensed temperature of the bare cell, loading discharging capacity-time data corresponding to the re-sensed present temperature from the storage unit, when it has been determined that there is difference in temperature, and re-calculating a discharging capacity based on the bare cell's re-sensed present temperature, and outputting the recalculated discharging capacity to the external system.

In yet another embodiment, a battery pack monitoring method is presented that includes tabulating charging capacity-time data as a function of temperature and storing the data on a storage unit, sensing a bare cell's temperature, loading charging capacity-time data from the storage unit and calculating a charging capacity based on the bare cell's sensed present temperature, outputting the calculated charging capacity to an external system, re-sensing the bare cell's temperature, determining whether or not there is a difference between the first sensed temperature of the bare cell and an existing re-sensed temperature of the bare cell, loading charging capacity-time data corresponding to the presently re-sensed temperature from the storage unit, when it has been determined that there is difference in temperature, and re-calculating a charging capacity based on the bare cell's present and re-sensed temperature, and outputting the recalculated charging capacity to the external system.

An embodiment of the invention includes a battery pack monitoring method for monitoring charging/discharging capacity of a chargeable/dischargeable bare cell included in the battery pack. Bare cell charging/discharging capacity-time data tabulated as a function of bare cell temperature are stored in a storage unit. A bare cell temperature is sensed. A charging/discharging capacity is calculated using the sensed bare cell temperature and the stored tabulated data. The calculated bare cell charging/discharging capacity are provided to an external system. The bare cell temperature is re-sensed. Then it is determined whether there is a difference between the present re-sensed bare cell temperature and the previously sensed bare cell temperature. If a difference is determined, then the bare cell charging/discharging capacity is recalculated using the re-sensed bare cell temperature and the stored tabulated data corresponding to the re-sensed bare cell temperature. The re-calculated bare cell charging/discharging capacity may then be provided to the external system. The method may also include sensing a bare cell charging/discharging voltage, and sensing a bare cell charging/discharging current. The re-calculating of the bare cell charging/discharging capacity may also include re-calculating the charging/discharging capacity using the sensed charging/discharging voltage and the sensed charging/discharging current.

DETAILED DESCRIPTION

As shown inFIG. 1, a battery pack monitoring apparatus according to the present invention may include a bare cell10, a voltage sensor20, a current sensor30, a cell temperature sensor40, a switch temperature sensor50, a monitoring control unit60, a first storage unit71, a second storage unit72, and a communication interface unit80.

At least one bare cell10is adapted to be charged or discharged with a predetermined voltage. Two or more bare cells may also be coupled in series and/or in parallel. The bare cell10is coupled between external terminals91and92. A charger or an external system200is coupled to the external terminals91and92. Therefore, the bare cell10is coupled to the charger or the external system200in parallel. The bare cell10may be any type of secondary battery. For example, the bare cell10may be a lithium ion battery, a lithium polymer battery, or a fuel cell. The external system200may include, for example, a portable electronic device, an electrical automobile, a hybrid automobile, or their equivalent.

The voltage sensor20is coupled to the bare cell10in parallel to sense a charging voltage when the bare cell10is being charged and a discharging voltage when the bare cell10is being discharged. The sensed voltage is converted into a predetermined electrical signal and is outputted to the monitoring control unit60. The bare cell10may be directly coupled to the monitoring control unit60in parallel so that the voltage of the bare cell10can be sensed by the monitoring control unit60. The structure or method for sensing the voltage of the bare cell10are not limited to those described.

A large-current path100extends between the external terminal91and the external terminal92through charging switch51or a discharging switch52, the bare cell10and the current sensor30. The current sensor30is coupled to the large-current path100between the bare cell10and the external terminal92in series to sense a charging current when the bare cell10is being charged and a discharging current when the bare cell10is being discharged. The sensed current is converted into a predetermined electrical signal and is outputted to the monitoring control unit60. Particularly, the current sensor30has a fixed resistance value and is adapted to sense a voltage applied to it, which depends on the condition of the bare cell10, to calculate the current flowing through it.

The cell temperature sensor40is positioned adjacent to the bare cell10to sense a temperature when the bare cell10is being charged/discharged. The sensed temperature is converted into a predetermined electrical signal and is outputted to the monitoring control unit60. The cell temperature sensor40may be a thermistor, a winding resistor-type sensor, a wide area resistance sensor, a semiconductor diode sensor, a metal core-type sensor, a thermocouple, or their equivalent, but not limited to these types of sensors. The cell temperature sensor40may be positioned outside the battery pack, rather than adjacent to the bare cell10, when a temperature of the pack itself needs to be sensed.

The switch temperature sensor50is positioned in the proximity of the charging and discharging switches51and52, which control charging/discharging in the large-current path100, to sense surface temperatures of the charging and discharging switches51and52when the bare cell10is being charged/discharged. The sensed surface temperatures are converted into predetermined electrical signals and are outputted to the monitoring control unit60. The charging and discharging switches51and52are coupled to the large-current path100between the bare cell10and the external terminal91. For example, the charging and discharging switches51and52may be FETs, the gate voltage of which is controlled by a separate protective circuit unit53. The protective circuit unit53receives input of voltage and current information from the voltage sensor20and the current sensor30when the bare cell10is being charged/discharged. The protective circuit unit53toggles off the charging switch51during charging when the bare cell10is overcharged, and toggles off the discharging switch52during discharging when the bare cell10is over-discharged.

The monitoring control unit60receives input of voltage and current signals of the bare cell10from the voltage sensor20and the current sensor30, respectively, and processes them. The monitoring control unit60converts signals inputted from the cell temperature sensor40and the switch temperature sensor50into digital signals and processes them based on a predetermined control order. The monitoring control unit60may include a multiplexer to properly distribute signals inputted from the voltage sensor20, the current sensor30, the cell temperature sensor40, and the switch temperature sensor50, as well as an analog/digital converter to convert analog signals inputted from the sensors into digital signals. The monitoring control unit60may further include an oscillator for providing a proper dock frequency, a voltage regulator for providing a stabilized driving voltage, registers for temporarily storing signals inputted from the sensors, and an accumulator for logical operation of data inputted from the sensors. However, components of the monitoring control unit60are not limited to those presented and alternatives understood by those skilled in the art may be used to construct an appropriate control circuit.

The first storage unit71stores tabulated data on discharging capacity versus time or discharging capacity-time data and charging capacity-time data as a function of temperature of the bare cell, which have been determined through a number of tests. Upon request from the monitoring control unit60, the first storage unit71provides the monitoring control unit60with the discharging capacity-time data and charging capacity-time data.

The second storage unit72stores data regarding the bare cell10, which has been processed by the monitoring control unit60, including charging/discharging voltages, charging/discharging currents, bare cell temperature, and switch temperature. The second storage unit72may store highest charging/discharging voltages, highest charging/discharging currents, highest bare cell temperature, and highest switch temperature, which are updated from existing data.

The first and second storage units71and72may be conventional EEPROMs, flash memories, or their equivalents, but are not limited to these devices.

The communication interface unit80is coupled to the monitoring control unit60to transmit data of the second storage unit72to the external system200or transmit a predetermined control signal from the external system200to the monitoring control unit60. The communication interface unit80may adopt a conventional RS-232C (Recommended Standard 232 Revision C) mode while including a UART chip for converting parallel data outputted from the monitoring control unit60into serial bits, a USB (Universal Serial Bus) mode, an infrared communication mode, or an equivalent of these modes or protocols. However, other modes may also be used. The communication interface unit80has a clock terminal93and a data terminal94for coupling the communication interface unit80to the external system200.

As shown inFIGS. 2aand2b,the first storage unit71of the battery pack monitoring apparatus according to the present invention stores discharging capacity-time data and charging capacity-time data, which have been experimentally obtained through a number of tests and theoretical calculations, as a function of temperature. For example, as shown inFIG. 2a,discharging capacity tends to increase as temperature rises or decrease as the temperature falls. In addition, as shown inFIG. 2b,charging capacity tends to increase as temperature rises or decrease as the temperature falls.

As shown inFIG. 3a,a method for real-time update of discharging capacity includes tabulating discharging capacity-time data as a function of temperature and storing it in a storage unit (S1); sensing a temperature of a bare cell (S2); loading the discharging capacity-time data stored in the storage unit and calculating a discharging capacity based on the present sensed temperature of the bare cell (S3); outputting the calculated discharging capacity to an external system (S4); re-sensing a temperature of the bare cell (S5); determining whether or not there is any difference between the first sensed temperature of the bare cell and an existing re-sensed temperature thereof (S6); loading discharging capacity-time data corresponding to the present temperature from the storage unit, when it has been determined that there is a difference, and recalculating a discharging capacity based on the present and re-sensed temperature of the bare cell (S7); and providing the recalculated discharging capacity to the external system (S8).

As shown inFIG. 3b,a method for real-time update of charging capacity includes tabulating charging capacity-time data as a function of temperature and storing it on a storage unit (S1); sensing a temperature of a bare cell (S2); loading the charging capacity-time data stored in the storage unit and calculating a charging capacity based on the present and sensed temperature of the bare cell (S3); outputting the calculated charging capacity to an external system (S4); re-sensing a temperature of the bare cell (S5); determining whether or not there is any difference between the sensed temperature of the bare cell and an existing re-sensed temperature thereof (S6); loading charging capacity-time data corresponding to the re-sensed temperature from the storage unit, when it has been determined that there is a difference, and re-calculating a charging capacity based on the existing re-sensed temperature of the bare cell (S7); and outputting the recalculated charging capacity to the external system (S8).

The operation of the apparatus and method for monitoring a battery pack according to the present invention will now be described.

When the Battery Pack is Being Discharged:

According to the present invention, discharging capacity-time data, which has been experimentally obtained through a number of tests and theoretical calculations, is tabulated and stored in the first storage unit71. For example, discharging capacity included in the data increases as temperature rises or decreases as the temperature falls (S1).

When the battery pack is coupled to the external system200, a current flows through a positive electrode of the bare cell10, the charging and discharging switches51and52, the external terminal91, the external system200, the external terminal92, and the current sensor30to a negative electrode of the bare cell10and the voltage sensor20. The cell temperature sensor40senses a temperature of the bare cell10. Alternatively, a temperature of the battery pack itself may be sensed, instead of that of the bare cell10. The voltage sensor20senses a discharging voltage of the bare cell10. The current sensor30senses a discharging current of the bare cell10. The switch temperature sensor50senses temperatures of the charging and discharging switches51and52. The temperature, voltage, and current of the bare cell10, as well as the temperatures of the switches51,52are stored in the second storage unit72.

Using the temperature sensed by the cell temperature sensor40, the monitoring control unit60loads discharging capacity-time data corresponding to the sensed temperature from the tabulated data stored in the first storage unit71. With reference to the discharging capacity-time data, the monitoring control unit60calculates a present discharging capacity based on the voltage and current obtained from the sensors20and30, respectively (S3). The calculated discharging capacity is stored in the second storage unit72.

The monitoring control unit60outputs information on the present discharging capacity to the external system200using the communication interface unit80(S4).

The monitoring control unit60again senses a temperature of the bare cell10or the battery pack itself using the cell temperature sensor40. The voltage sensor20senses a discharging voltage of the bare cell10, the current sensor30senses a discharging current of the bare cell10, and the switch temperature sensor50senses temperatures of the charging and discharging switches51and52. The temperature, voltage, and current of the bare cell10, as well as the temperatures of the switches51,52are stored in the second storage unit72.

The monitoring control unit60determines whether or not there is any change in temperature of the bare cell10, based on values obtained from the cell temperature sensor40(S6). If there is no difference between the present and previous sensed temperatures, then a voltage and a current of the bare cell10, as well as temperatures of the charging and discharging switches51,52are sensed again as shown by the return loop from (S6) inFIG. 3a.

For example, when the battery pack is fully charged at room temperature and then used at a lower temperature, the monitoring control unit60determines that there is temperature change. When the battery pack is fully charged at a low temperature and then used at a higher temperature (room temperature), the monitoring control unit60also determines that there is temperature change. When the monitoring control unit60determines that that there is no temperature change, the temperature of the bare cell10or the battery pack itself is repeatedly sensed using the cell temperature sensor40.

When the monitoring control unit60determines that there is a change in temperature, it refers to the temperature of the bare cell10obtained from the cell temperature sensor40and loads discharging capacity-time data corresponding to that temperature from the first storage unit71. With reference to the discharging capacity-time data, the monitoring control unit60re-calculates a present discharging capacity based on the voltage and current obtained from the sensor (S7). The re-calculated discharging capacity is stored in the second storage unit72.

The monitoring control unit60outputs information on the modified discharging capacity to the external system200using the communication interface unit80. This completes a cycle of the monitoring method of the discharging capacity versus time according to the present invention (S8). Storing discharging capacity-time data as a function of temperature (S1) is omitted in the next cycle, because storage of discharging capacity-time data is needed only one time before the battery pack is shipped.

When the Battery Pack is Being Charged:

According to the present invention, charging capacity-time data, which has been experimentally obtained through a number of tests and theoretical calculations, is tabulated and stored in the first storage unit71(S1). The increases or decreases of charging capacity as the temperature rises or falls is also reflected in the capacity versus time data that is stored in the first storage unit71(FIG. 2b).

When the battery pack is coupled to a charger, a current flows through the external terminal91, the charging and discharging switches51and52, the bare cell10, the voltage sensor20, the current sensor30, and the external terminal92. The cell temperature sensor40senses a temperature of the bare cell10. Alternatively, a temperature of the battery pack itself may be sensed instead of the temperature of the bare cell10. The voltage sensor20senses a charging voltage of the bare cell10. The current sensor30senses a charging current of the bare cell10. The switch temperature sensor50senses temperatures of the charging and discharging switches51and52(S2). The temperature, voltage, and current of the bare cell10, as well as the temperatures of the switches51,52are stored in the second storage unit72.

With reference to the temperature sensed by the cell temperature sensor40, the monitoring control unit60loads charging capacity-time data corresponding to that temperature from the first storage unit71. With reference to the charging capacity-time data, the monitoring control unit60calculates a present charging capacity based on the voltage and current obtained from the sensors20and30, respectively (S3). The calculated charging capacity is stored in the second storage unit72.

The monitoring control unit60outputs information on the present charging capacity to the external system200using the communication interface unit80(S4).

The monitoring control unit60again senses a temperature of the bare cell10or the battery pack itself using the cell temperature sensor40. The voltage sensor20senses a charging voltage of the bare cell10, the current sensor30senses a charging current of the bare cell10, and the switch sensor50senses temperatures of the charging and discharging switches51and52. The temperature, voltage, and current of the bare cell, as well as the temperatures of the switches are stored in the second storage unit72.

The monitoring control unit60determines whether or not there is any change in temperature of the bare cell10, based on values obtained from the cell temperature sensor40(S6). At the same time, a voltage and a current of the bare cell10, as well as temperatures of the charging and discharging switches are sensed.

For example, when the battery pack is fully charged at room temperature and then used at a lower temperature, the monitoring control unit60determines that there is temperature change. When the battery pack is fully charged at a low temperature and then used at a higher temperature (room temperature), in contrast, the monitoring control unit60also determines that there is temperature change. When the monitoring control unit60determines that that there is no temperature change, the temperature of the bare cell10or the battery pack itself is repeatedly sensed using the cell temperature sensor40.

When the monitoring control unit60determines that there is temperature change, it refers to the temperature of the bare cell10obtained from the cell temperature sensor40and loads charging capacity-time data corresponding to that temperature from the first storage unit71. With reference to the charging capacity-time data, the monitoring control unit60re-calculates a present charging capacity based on the voltage and current obtained from the sensor (S7). The re-calculated charging capacity is stored in the second storage unit72.

The monitoring control unit60outputs information on the modified charging capacity to the external system200using the communication interface unit80. This completes a first cycle of the monitoring method according to the present invention (S8). The storing of charging capacity-time data as a function of temperature (S1) is omitted in the next cycle, because storage of charging capacity-time is needed only one time before the battery pack is shipped.

As mentioned above, the apparatus and method for monitoring a battery pack according to the present invention have the features that, when the battery pack's temperature changes, the battery pack's charging or discharging capacity is re-calculated based on the change and is transmitted to an external system, so that the external system can always maintain and use the battery pack in an optimum condition.

In addition, information on the battery pack's present voltage, current, and temperature is transmitted to the external system in real-time so that, when the battery pack malfunctions, the exact cause can be determined more easily and the battery pack can be diagnosed more accurately.