Patent Publication Number: US-2013249488-A1

Title: Battery pack charging system and method of controlling the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of Provisional Patent Application No. 61/615,685 filed in the U.S. Patent and Trademark Office on Mar. 26, 2012, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     One or more embodiments of the present invention relate to a battery pack charging system and a method of controlling the same. 
     2. Description of the Related Technology 
     In general, unlike primary batteries, which are not rechargeable, secondary batteries are rechargeable and dischargeable. According to the types of external devices to which the secondary batteries are applied, the secondary batteries are used as a single battery or in the form of a battery module in which a plurality of batteries are connected as a unit. 
     In some systems, a lead storage battery is used as a power supply unit for starting up an engine. Recently, to improve fuel efficiency, an Idle Stop &amp; Go (ISG) system (or start-stop or stop-start) systems have been developed, and the use of these systems is gradually increasing. A power supply unit that supports a start-stop system, which is aimed at limiting the amount of time an engine spends idling, has to maintain strong charging or discharging characteristics despite high output characteristics for engine start up and frequent start ups, and has a long life span. However, charging or discharging characteristics of lead storage batteries may deteriorate due to repeated engine stops or restart-ups under the start-stop system, and cannot be used for a long time. 
     In an electrical device using electricity, when a system is turned off, power related to basic operations of the electrical device is turned off. However, when the device is turned on again, a current for immediately starting an operation of the electrical device and continuing the basic operations of the electrical device is supplied and is referred to as a dark current. 
     SUMMARY OF CERTAIN INVENTIVE ASPECTS 
     One aspect of the invention is a method of charging a battery pack including determining a need for charging the battery pack, sending a signal to a motor based on a determined need to charge the battery pack, and initiating charging of the battery pack after receipt of the signal. 
     In some embodiments, determining the need for charging the battery may be based on monitoring a state of charge (SOC) of the battery. 
     In some embodiments, determining the need for charging the battery may be based on the SOC being below a threshold 
     In some embodiments, determining the need for charging the battery may be based on passage of a predetermined time period. 
     In some embodiments, the predetermined time period may be based on discharge characteristics of the battery. 
     In some embodiments, the motor may be connected to a generator. 
     In some embodiments, the generator may be operated to charge the battery pack when the signal is sent to the motor. 
     In some embodiments, the signal may be indicative of the determined need for charging the battery 
     In some embodiments, determining a need for charging the battery pack may include determining whether the battery pack is connected to an engine that is turned off; and the signal may be sent to the motor if the battery pack is connected to an engine that is turned off. 
     Another aspect of the invention is a method of charging a battery pack including monitoring a state of charge of a battery pack, determining a need for charging the battery pack based on the monitored state of charge of the batter and triggering charging of the battery pack by sending a signal indicative of the need for charging the battery pack based on the determined need for charging the battery pack. 
     In some embodiments, determining the need for charging the battery pack includes determining the need when the monitored state of charge of the battery pack crosses a predetermined threshold value. 
     In some embodiments, the predetermined threshold value includes a percentage of a level associated with a completely charged battery pack. 
     In some embodiments, the triggering charging of the battery pack is further based on a predetermined time period. 
     In some embodiments, the predetermined time period is based on a linear discharge characteristic of the battery pack. 
     Another aspect of the invention is a battery pack including a controller configured to monitor a state of charge of a battery, a processor configured to determine a need for charging the battery based on the state of charge of the battery, and circuitry configured to trigger charging of the battery based on the determined need for charging the battery, where the circuitry is further configured to send a signal indicative of the need for charging the battery to a starter motor. 
     In some embodiments, the battery pack may be at least one of a lithium ion battery pack and a nickel metal hydride battery pack. 
     In some embodiments, the signal sent to the starter motor may be configured to automatically drive the power generator to charge the battery. 
     Another aspect of the invention is a vehicle including a battery pack including a controller configured to monitor a state of charge of a battery pack, a processor configured to determine a need for charging the battery pack based on the state of charge of the battery pack, and circuitry configured to trigger charging of the battery pack based on the determined need for charging the battery pack, where the circuitry is further configured to send a first signal indicative of the need for charging the battery pack to a starter motor, the starter motor electrically connected to the battery pack, the starter motor configured to receive the first signal indicative of the need for charging the battery pack, and a generator connected to the battery pack, the generator configured to charge the battery pack. 
     In some embodiments, the circuitry is configured to send the first signal when the monitored state of charge of the battery is below a predetermined threshold value. 
     In some embodiments, the circuitry is configured to send a second signal to the starter motor when the monitored state of charge of the battery is above a predetermined threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating a structure of a battery pack according to an embodiment of the present invention and a connection between the battery pack and external peripheral devices; 
         FIG. 2  is a graph showing a state-of-charge (SOC) of a battery module when an engine of a vehicle is stopped; 
         FIG. 3  is a graph showing an SOC of a battery module according to an embodiment of the present invention, when the battery module is automatically charged; 
         FIG. 4  is a graph showing an SOC of a battery module according to another embodiment of the present invention, when the battery module is automatically charged; 
         FIG. 5  is a flowchart illustrating a method of controlling a battery charging system, according to an embodiment of the present invention; and 
         FIG. 6  is a flowchart illustrating a method of controlling a battery charging system, according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN INVENTIVE EMBODIMENTS 
     The present invention will now be described more fully with reference to the accompanying drawings, in which certain embodiments of the invention are shown. The embodiments will be described in detail such that one of ordinary skill in the art may easily work the present invention. It should be understood that the embodiments of the present invention may vary but do not have to be mutually exclusive. For example, particular shapes, structures, and properties according to a predetermined embodiment described in this specification may be modified in other embodiments without departing from the spirit and scope of the prevent invention. In addition, positions or arrangement of individual components of each of the embodiments may also be modified without departing from the spirit and scope of the present invention. Accordingly, the detailed description below should not be construed as having limited meanings but construed to encompass the scope of the claims and any equivalent ranges thereto. In the drawings, like reference numerals generally denote like elements in various aspects. 
     Hereinafter, the present invention will now be described more fully with reference to the accompanying drawings, in which certain embodiments of the present invention are shown such that one of ordinary skill in the art may easily work the invention. 
       FIG. 1  is a schematic view illustrating a structure of a battery pack  100  according to an embodiment of the present invention and a connection between the battery pack  100  and external peripheral devices. 
     The battery pack  100  includes a battery module  110  that is connected between first and second terminals P 1  and P 2  to receive charging power and output discharging power. The battery pack  100  may be electrically connected in parallel to a power generation module  210 , an engine  240 , and a starter motor  220  via the first and second terminals P 1  and P 2 . Also, as illustrated in  FIG. 1 , the battery pack  100  includes a battery management system (BMS)  120 . 
     The battery pack  100  may store charging power generated from the power generation module  210  and supply discharging power to the starter motor  220 . For example, the power generation module  210  may be connected to engine  240  to provide power thereto, and may be connected to a driving axis of the engine  240  to convert rotational motive power into an electrical output. Charging power generated by the power generation module  210  may be stored in the battery module  110  via the first and second terminals P 1  and P 2  of the battery pack  100 . For example, the power generation module  210  may include a direct current (DC) generator (not shown) or an alternating current (AC) generator (not shown) and a rectifying unit (not shown), and may supply power of about 15 V DC. 
     For example, the battery pack  100  may be used as a power unit for starting up engine  240 . In some embodiments, the engine  240  may operate in a start-stop system, in which the start-stop function is implemented to improve fuel efficiency. In the start-stop system, as the engine  240  is repeatedly and frequently stopped and restarted, charging and discharging of the battery pack  100  are repeated. 
     A lead storage battery applied to existing start-stop systems may have a decrease in durability and a life span and a decrease in charging and discharging characteristics due to frequent repetition of charging and discharging operations. In such systems, starting up of an engine may be degraded, and an exchange cycle of the lead storage battery is shortened. 
     In some embodiments, the battery module  110  includes a lithium ion battery which maintains relatively uniform charging or discharging characteristics, and thus, has little deterioration and may be suitable for a start-stop system where stopping and re-startup of an engine  240  is repeated. Compared to a lead storage battery of the same charging capacity, the battery module  110  according to embodiments of the present invention obtains the same charging capacity with less volume than the lead storage battery, and thus, a mounting space of the battery module  110  may be reduced. In some embodiments, a nickel metal hydride (NiMH) battery may be used as the battery module  110 . 
     The battery module  110  may include a plurality of battery cells (not shown) that are connected serially or parallel, and a rated charging voltage and a charging capacity of the battery cells may be adjusted through combinations of serial and parallel connections. 
     The battery module  110  is a general name of a structure including a plurality of battery sub-units. For example, when the battery pack  100  is a battery rack including a plurality of battery trays, the battery rack may be regarded as the battery module  110 . Also, when a battery tray includes a plurality of battery cells, the battery tray may be regarded as the battery module  110 . 
     The BMS  120  monitors a battery state and controls charging and discharging operations thereof. In some embodiments, the BMS  120  may include a controller, a sensor, or the like. In some embodiments, the BMS  120  monitors a state-of-charge (SOC) of the battery module  110  and automatically drives the starter motor  220  to determine whether to receive charging power from the power generation module  210  or not. The function and operation of the BMS  120  is described below. 
     The power generation module  210  may function like an alternator of a vehicle. An alternator not only supplies charging power to the battery pack  100  but also power to an electrical load  230  while the engine  240  is driven, as described below. 
     In some embodiments, when an SOC of the battery module  110  is reduced to a predetermined value or lower, the power generation module  210  receives rotational driving power from the engine  240  by automatic driving of the starter motor  220  to supply charging power to the battery pack  100 . 
     Next, the starter motor  220  is driven when the engine  240  of a vehicle is started up, and may provide an initial rotational motive power that rotates a driving axis of the engine  240 . For example, the starter motor  220  may receive stored power via the first and second terminals P 1  and P 2  of the battery pack  100  and rotate a driving axis of the engine  240  when the engine  240  is started up or when the engine  240  is restarted after an idle stop, thereby re-driving the engine  240 . When a user starts up a vehicle or at a moment of an idle go, the starter motor  220  provides an initial rotational motive power of the engine  240 . In some embodiments, while the engine  240  is operated by the starter motor  220 , the power generation module  210  may be driven to generate charging power. 
     As described above, as the starter motor  220  receives an initial ignition motive power via the first and second terminals P 1  and P 2  of the battery pack  100 , when the battery module  110  is completely discharged, the engine  240  may not be operated or operated again via the starter motor  220 . In particular, in the case of a start-stop vehicle, re-operation of the engine  240  is to be performed frequently, and thus, if the battery module  110  is completely discharged, and thus, the starter motor  220  is not to be operated, serious problems may occur, for example, the vehicle may not be able to start in an idle stop state. 
     According to some embodiments, if an SOC of the battery module  110  is decreased to a discharging limit or below, the starter motor  220  may be automatically operated. The starter motor  220  may be connected to the BMS  120 , and when a signal indicating that an SOC of the battery module  110  is decreased to a discharging limit or below is received from the BMS  120 , the starter motor  220  automatically operates to work the engine  240 , thereby driving the power generation module  210 . 
     As described above, as the BMS  120  monitors an SOC of the battery module  110  so as to automatically operate the starter motor  220 , the SOC of the battery module  110  may be always maintained at a discharging limit or higher. That is, the power generation module  210  is driven to supply charging power to the battery module  110 , and thus, even when the battery is discharged while operation of the engine  240  is stopped, a charging value of the battery module  110  for starting or restarting the engine  240  may always be maintained. 
     Together with the power generation module  210  and the starter motor  220 , the electrical load  230  may be connected to the battery pack  100 . The electrical load  230  consumes power stored in the battery pack  100 , may receive stored discharging power via the first and second terminals P 1  and P 2 , and may include various components for electrical devices. 
     Examples of the electrical load  230  include an air conditioner for vehicles, a radio, a remote reception terminal, or the like, but are not limited thereto; the electrical load  230  may refer to any type of a load that operates upon receiving power from the power generation module  210  or the battery module  110 . 
     The electrical load  230  may generate a dark current while the engine  240  is stopped. In a vehicle, if the engine  240  is stopped, a flow of a current supplied to a starting device and other loading apparatuses is stopped in a battery, but a current for immediately starting up engine  240  is supplied by starter motor  220  or a current of a battery is supplied to the electrical load  230  such as other types of controllers, that is, a dark current, is continuously supplied electrical load  230 . 
     The dark current consumed by the electrical load  230  as described above is consumed while the engine  240  is stopped, and thus the power generation module  210  does not supply charging power to the battery module  110 , and there is a risk of completely discharging the battery module  110 . In particular, when a lithium ion battery is used in a vehicle in which a start-stop mode is applied, due to low capacity thereof, a battery may be completely discharged by a dark current while the engine  240  of the vehicle is stopped. 
     According to some embodiments of the present invention as described above, if an SOC of the battery module  110  is decreased to a discharging limit or below due to the dark current, the starter motor  220  is automatically driven to thereby charge the battery module  110 . 
     Hereinafter, a typical function of the BMS  120  and a method in which the BMS  120  charges the battery module  110  by monitoring an SOC of the battery module  110  and transmitting a control signal to the above-described peripheral devices is described. 
     The BMS  120  is connected to the battery module  110 , and controls charging and discharging operations of the battery module  110 . In addition, the BMS  120  may perform functions such as overcharge protection function, over-discharge protection function, over-current protection function, over-voltage protection function, overheating protection function, and cell balancing. To this end, the BMS  120  may include a measuring unit that measures a voltage, a current, a temperature, a remaining amount of power, a lifespan, an SOC, or the like, from the battery module  110 , and may generate a control signal based on a measurement result to control external devices such as the starter motor  220  and the power generation module  210 . 
     The BMS  120  determines a limit of an SOC so that the starter motor  220  may drive itself. In existing start-stop vehicles, a user has to start up engine  240  himself or herself or only the starter motor  220  may drive the engine  240 , or the starter motor  220  drives engine  240  only in an idle go state, and the engine drives the power generation module  210 . However, according to embodiments of the present invention, the starter motor  220  may be automatically driven by a control signal of the BMS  120 . 
     In a start-stop vehicle, when a lithium ion battery is used as the battery module  110 , advantages such as high output characteristics for implementing the same charging capacity with less volume and shorter charging time than a lead storage battery are available but since the capacity of the battery module  110  is smaller than that of a lead storage battery, the battery module  110  may be discharged quickly. 
     As a result, a period in which a lithium ion battery is completely discharged may be shorter than in a lead storage battery due to the electrical load  230  which requires power supply of a battery. In particular, like a dark current that is generated by the electrical load  230  which requires power even when turning off the engine  240  of the vehicle, the lithium ion battery is highly likely to completely discharge due to a dark current that consumes power uniformly even in a section where the vehicle is not driven. A lithium ion battery may be completely discharged within two or three weeks while the engine  240  of the vehicle is not started. 
     According to embodiments of the present invention, in order to solve this problem, the BMS  120  may monitor an SOC of the battery module  110  and sense when the SOC is decreased to a discharging limit or below. The discharging limit is a reference value for charging the battery module  110  by automatically driving the power generation module  210 ; for example, the discharging value is a value indicating to start charging the battery module  110  when a voltage value has reached the discharging limit, by determining that there is a risk of completely discharging the battery module  110 . 
     The BMS  120  may generate a control signal for driving the starter motor  220  when the SOC has reached the discharging limit. When the starter motor  220  is driven by the control signal, the power generation module  210  is driven by rotation of the engine  240 , thereby supplying charging power to the battery module  110 . 
     In addition, the BMS  120  may set a charging limit to determine a power section to be used by the battery module  110 . That is, the BMS  120  receives charging power from the power generation module  210  to charge the battery module  110  as described above, and when the BMS  120  senses that the SOC has reached a charging limit, the BMS  120  may generate a control signal indicating to stop driving of the power generation module  210  to end the charging. 
     The charging limit and the discharging limit set by the BMS  120  may be an SOC or another parameter for determining an SOC. Thus, in order to determine an SOC, the BMS  120  may use an SOC determination method such as a voltage measuring method, a current integration method, a current integration, and a Calman filter application method. The methods of determining the SOC are not limited to the above examples. 
     Also, as other parameters for determining an SOC, a charging limit and a discharging limit may be voltages. That is, the BMS  120  may measure a voltage of the battery module  110  by using any one of the above-described measuring units, and may determine whether the battery module  110  has reached the charging limit or the discharging limit according to the measured voltage. 
     According to another embodiment of the present invention, a predetermined period after the engine  240  of the vehicle is stopped, the BMS  120  may automatically generate a control signal for driving the starter motor  220  to charge the battery module  110 . Accordingly, when the battery module  110  has linear SOC characteristics, the BMS  120  may charge the battery module  110  for a standard time period after the engine  240  is stopped, without having to monitor the SOC. 
     For example, the battery module  110  has linear SOC characteristics when a material of a battery includes soft carbon. The BMS  120  may set a time when an SOC (of the battery module) reaches a discharging limit by using characteristics of the battery module  110  after the engine  240  is stopped, and may generate a control signal for starting charging of the battery module  110  automatically at the previously set time. Likewise, the BMS  120  may set a time when (the SOC) reaches a charging limit after starting the charging, and may generate a control signal for automatically ending the charging of the battery module  110  at the previously set time. 
       FIG. 2  is a graph showing an SOC of a battery module when engine  240  of a vehicle is stopped. 
     Referring to  FIG. 2 , the horizontal axis denotes time, and the vertical axis denotes SOC. Referring to  FIG. 2 , an SOC of the battery module  110  continuously decreases with time due to a dark current even when the engine  240  is stopped. 
     As described above, when a lithium ion battery is used in a start-stop vehicle, the lithium ion battery has lower capacity than a conventional lead storage battery, and thus, a graph of SOC in % may abruptly converge to 0. Accordingly, due to the complete discharging of the battery, the engine  240  may not be started up or restarted. 
       FIG. 3  is a graph showing an SOC of a battery module according to an embodiment of the present invention, when the battery module is automatically charged. 
     Also, referring to  FIG. 3 , a discharging limit of the battery module  110  is set as L. For example, a discharging limit L may be 30% when a completely charged SOC is 100%. In other embodiments, the limit L may be 70%, 60%, 40% or any other percentage of the completely charged SOC. The BMS  120  may monitor an SOC of the battery module  110 , and when the SOC decreases to an L value or below, the starter motor  220  may be driven to thereby automatically drive the power generation module  210 . 
     When the power generation module  210  is driven to supply charging power to the battery module  110 , the BMS  120  generates a control signal for stopping driving of the power generation module  210  when an SOC is increased by a charging limit value H. Referring to  FIG. 3 , when the SOC corresponds to the discharging limit L, the power generation module  210  is driven to charge the battery module  110 , and the driving of the power generation module  210  is stopped at a time t 2  where the SOC of the battery module  110  reaches the charging limit H so as to detect discharging of the battery module  110  again. 
     For reference, the SOC is slightly decreased after a time t 1  in  FIG. 3  and then charging starts because the battery module  110  supplies driving power to the starter motor  220 . Accordingly, a discharging limit L may be greater than power used to start up an engine  240  by the driving of the starter motor  220 . 
       FIG. 4  is a graph showing an SOC of a battery module according to another embodiment of the present invention, when the battery module is automatically charged. 
     Referring to  FIG. 4 , an SOC of the battery module  110  according to another embodiment of the present invention has linear characteristics. Likewise, when the SOC graph has linear characteristics, even when the BMS  120  does not monitor the SOC of the battery module  110 , it may be determined based on a previously provided reference value whether charging of the battery module  110  is necessary when a predetermined period of time passes. 
     For example, when it is known that the SOC has reached a discharging limit L at the time t 1  due to a dark current based on the battery module  110  having linear SOC characteristics, the BMS  120  does not have to monitor an SOC but may drive the starter motor  220  at the time t 1  after the engine  240  of the vehicle is stopped so that the power generation module  210  may charge the battery module  110 . 
     Likewise, when the power generation module  210  charges the battery module  110 , when it is known that an SOC has reached the charging limit H at a time t 2  due to the battery characteristics, the BMS  120  may stop driving of the power generation module  210  at the time t 2  without having to monitor an SOC, thereby stopping charging of the battery module  110 . 
       FIG. 5  is a flowchart illustrating a method of controlling a battery charging system, according to an embodiment of the present invention. 
     Referring to  FIG. 5 , first, a discharging limit of the BMS  120  is set when manufacturing a battery pack or by a user, in operation S 11 . 
     Next, the BMS  120  monitors an SOC of the battery module  110  that is discharged by a dark current after an engine of the vehicle is stopped, in operation S 12 . 
     Next, the BMS  120  senses whether an SOC of the battery module  110  is decreased to a discharging limit L or below in operation S 13 . If the SOC of the battery module  110  does not decrease to a discharging limit L, the BMS  20  continuously monitors an SOC of the battery module  110 . 
     Otherwise, if the SOC is decreased to a discharging limit L or below, the BMS  120  generates a control signal indicating to drive the starter motor  220  so as to drive the power generation module  210  in operation S 14 . 
     Next, in operation S 15 , the power generation module  210  supplies charging power to the battery module  110 . 
     Also, while charging continues, the BMS  120  senses whether the SOC of the battery module  110  exceeds a charging limit H in operation S 16 . If the BMS  120  does not exceed the charging limit H, the BMS  120  further monitors the SOC of the battery module  110 . 
     Otherwise, if the SOC exceeds the charging limit H, the BMS  120  transmits a signal to the power generation module  210  to stop the driving thereof, thereby ending the charging of the battery module  110 , in operation S 17 . 
       FIG. 6  is a flowchart illustrating a method of controlling a battery charging system, according to another embodiment of the present invention. 
     Referring to  FIG. 6 , first, in operation S 21 , a time t 1  where an SOC becomes a discharging limit and a time t 2  where an SOC becomes a charging limit are obtained by using characteristics of a battery module. Here, referring to  FIG. 6 , the battery module has linear SOC characteristics. 
     Next, discharging of a battery module is performed by a dark current, and an SOC of the battery module decreases linearly in operation S 22 . 
     Next, in operation S 23 , the BMS  120  senses whether the time t 1  has been reached after the engine  240  is stopped. If the time t 1  has not been reached, discharging of the battery module is further performed. 
     Otherwise, if the time t 1  has been reached, the BMS  120  generates a control signal indicating to drive the starter motor  220 , thereby driving the power generation module  210  in operation S 24 . 
     Next, in operation S 25 , the power generation module  210  supplies charging power to the battery module  110 . 
     Next, in operation S 26 , the BMS  120  senses whether the time t 2  has been reached. If the time t 2  has not been reached, charging of the battery module  110  is further performed. 
     In operation S 27 , if the time t 2  has been reached, the BMS  120  transmits a signal to the power generation module  210  to stop the driving thereof, thereby ending the charging of the battery module  110 . 
     While this invention has been particularly shown and described with reference to certain embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The described embodiments should be considered in descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention. 
     EXPLANATION OF REFERENCE NUMERALS 
       100 : battery pack 
       110 : battery module 
       120 : BMS 
       210 : power generation module 
       220 : starter motor 
       230 : electrical load 
       240 : engine