Abstract:
A secondary battery capable of ensuring operator safety by checking whether a service plug is opened or closed. The secondary battery includes a battery pack having a plurality of battery cells, a service plug coupled between each of the plurality of battery cells through a pair of plug terminals for controlling interconnection of the plurality of battery cells according to whether the pair of plug terminals contact the battery cells, and a battery management system connected to the battery pack and the service plug for determining whether the service plug is opened or closed by measuring at least one selected from the group consisting of a voltage and a current of the battery pack and voltages of the plurality of battery cells connected to the service plug.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to and the benefit of Korean Patent Application No. 10-2009-0079175, filed on Aug. 26, 2009, the entire content of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    An aspect of the present invention relates to a secondary battery. 
         [0004]    2. Description of the Related Art 
         [0005]    In general, unlike primary batteries which are not rechargeable, secondary batteries can be charged and discharged. Low-capacity secondary batteries are widely employed in electronic devices such as cellular phones, laptop computers, and camcorders while large-capacity secondary batteries are typically used for driving motors of electric automobiles or hybrid automobiles. 
         [0006]    When battery cells are used in electric automobiles in particular, a problem associated with limited power capacity may arise. To address the problem, a battery pack which includes a plurality of battery cells connected to each other in series/parallel has been proposed. In such a battery pack having a number of interconnected battery cells, the overall voltage of the battery pack can be increased. Further, the battery pack can be configured to have various capacities and voltages according to the number of battery cells connected to each other, thereby improving versatility in terms of capacity and voltage outputs. 
         [0007]    Since the battery pack outputs a relatively high voltage, when operators conduct a maintenance work or the like, measures for ensuring operator safety are desirable. 
       SUMMARY OF THE INVENTION 
       [0008]    An aspect of the present invention provides a secondary battery capable of ensuring operator safety by checking whether a service plug is opened or closed. 
         [0009]    According to some aspects of the present invention, a secondary battery includes a battery pack having a plurality of battery cells; a service plug coupled between each of the plurality of battery cells via a pair of plug terminals for controlling interconnection of the plurality of battery cells according to whether the pair of plug terminals are electrically coupled to the battery cells; and a battery management system (BMS) connected to the battery pack and the service plug for determining whether the service plug is opened or closed by measuring at least one selected from the group consisting of a voltage and a current of the battery pack, and voltages of the plurality of battery cells electrically coupled to the service plug. 
         [0010]    Here, the battery management system may determine that the service plug is opened when it measures at least one selected from the group consisting of the maximum measurable value constituting the voltage of the battery pack and 0 A constituting the current of the battery pack, and when the voltage of the battery cell measured by the battery management system is the maximum measurable value. 
         [0011]    In addition, the battery management system may measure voltages of the plurality of battery cells connected to the service plug such that the pair of plug terminals of the service plug are both included in the measurement path. 
         [0012]    In addition, the battery management system may measure a voltage of the battery pack such that the pair of plug terminals of the service plug are both included in the measurement path. 
         [0013]    Further, the battery management system may determine whether the service plug is opened or closed by measuring a voltage or a current of the battery pack. 
         [0014]    In addition, when the voltage of the battery pack is the maximum measurable value and the current of the battery pack is 0 A, the battery management system may determine that the service plug is opened. 
         [0015]    The battery management system may be connected to the service plug to form a closed loop and determine whether the service plug is opened or closed by applying a current to the closed loop. When no current is applied to the closed loop, the battery management system may determine that the service plug is opened. The battery management system may output information on whether the service plug is opened or closed to an external display unit. 
         [0016]    In some embodiments, the present invention is a secondary battery including: a battery pack having a plurality of battery cells; a cell voltage measuring unit for measuring voltages of the plurality of battery cells; a pack voltage measuring unit for measuring a voltage of the battery pack; a pack current measuring unit for measuring a current of the battery pack; a temperature measuring unit for measuring a temperature of the battery pack; an internal power supply unit; a service plug coupled between each of the plurality of battery cells via a pair of plug terminals for controlling interconnection of the plurality of battery cells; a loop current measuring unit forming a closed loop with the internal power supply unit and the service plug for measuring a current of the closed loop; and a battery management system electrically coupled to the battery pack and the service plug for estimating a state of charge and a state of health of the battery pack based on the measured voltages, currents, and temperature. 
         [0017]    In some embodiments, the present invention is a secondary battery including: a battery pack having a plurality of interconnected battery cells; a service plug coupled between each of the plurality of battery cells via a pair of plug terminals for controlling interconnection of the plurality of battery cells according to a state of the pair of plug terminals; and a battery management system electrically coupled to the battery pack and the service plug for determining the state of the pair of plug terminals by measuring voltages of the plurality of battery cells electrically coupled to the service plug such that the pair of plug terminals of the service plug are both included in the measurement path. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The objects, features and advantages of the present invention will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
           [0019]      FIG. 1  shows a schematic diagram of a secondary battery, according to an exemplary embodiment of the present invention; and 
           [0020]      FIG. 2  shows a detailed diagram of a sensing unit used in the secondary battery, according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    The construction of a secondary battery according to an exemplary embodiment of the present invention will now be described in detail with reference to the accompanying drawings. 
         [0022]      FIG. 1  is a schematic diagram of a secondary battery, according to an exemplary embodiment of the present invention, and  FIG. 2  is a detailed diagram of a sensing unit used in the secondary battery, according to an exemplary embodiment of the present invention. 
         [0023]    Referring to  FIG. 1 , the secondary battery according to an exemplary embodiment of the present invention includes a battery management system (BMS)  1  and a battery pack  2 . The secondary battery may further include a current sensor  3 , a cooling fan  4 , a fuse element  5 , and a charge/discharge switch  6 . 
         [0024]    The BMS  1  includes a sensing unit  10  and a monitor control unit (MCU)  20 . The BMS  1  may further include an internal power supply unit  30 , a cell balancing unit  40 , a storage unit  50 , a communication unit  60 , a protection circuit unit  70 , a power-on reset unit  80 , and an external interface  90 . 
         [0025]    The sensing unit  10  is electrically coupled to the battery pack  2  and the current sensor  3 . 
         [0026]    The sensing unit  10  measures an overall voltage of the battery pack  2 , and voltages of subpacks  210  to  280  and/or battery cells constituting each of the subpacks  210  to  280 . In addition, the sensing unit  10  measures currents flowing through the charge and discharge lines  11  and  12  and the battery pack  2  by the current sensor  3 . 
         [0027]    To this end, the sensing unit  10  includes a cell voltage measuring unit  110  electrically coupled to the battery pack  2 , a pack voltage measuring unit  120 , a pack current measuring unit  130  electrically coupled to the current sensor  3 , and a loop current measuring unit  140  forming a closed loop with the internal power supply unit  30 . The sensing unit  10  may further include a temperature measuring unit  150  measuring a temperature of the battery pack  2  and an ambient temperature, and an A/D converter  160  converting the analog voltage and current signals measured by the cell voltage measuring unit  110  and the pack current measuring unit  130  into digital voltage and current signals. 
         [0028]    The cell voltage measuring unit  110  measures the voltages of the subpacks  210  to  280  and/or the voltages of battery cells constituting each of the subpacks  210  to  280 . In particular, as indicated by a line labeled {circle around ( 1 )}, the cell voltage measuring unit  110  measures the voltages of the subpacks  240  and  250  coupled to the service plug  290 , or the voltages of battery cells connected to the service plug  290  in the subpacks  240  and  250 . The cell voltage measuring unit  110  measures the voltages of battery cells connected to the service plug  290  such that the plug terminal  290   a  of the service plug  290  is incorporated in the cell voltage measuring unit  110 . Accordingly, when the service plug  290  is coupled between the subpacks  240  and  250 , voltages of the subpacks  240  and  250  or the battery cells connected to the service plug  290  are measured by the cell voltage measuring unit  110 . Further, when the service plug  290  is opened, that is, the service plug  290  is disconnected from the subpacks  240  and  250 , the voltage measured by the cell voltage measuring unit  110  is close to infinity. As a result, the voltage value shown on the cell voltage measuring unit  110  becomes the maximum measurable value. 
         [0029]    The pack voltage measuring unit  120  is connected to charge and discharge current lines  11  and  12  of the battery pack  2 . As indicated by a line labeled {circle around ( 2 )}, the pack voltage measuring unit  120  measures the voltage of the battery pack  2 . The service plug  290  is provided between the plurality of subpacks  210  to  280  of the battery pack  2 . Accordingly, when the service plug  290  is connected, the pack voltage measuring unit  120  may measure the voltage of the battery pack  2 . However, when the service plug  290  is opened, the voltage measured by the pack voltage measuring unit  120  is close to infinity. As a result, the voltage value shown on the pack voltage measuring unit  120  becomes the maximum measurable value. 
         [0030]    The pack current measuring unit  130  is connected to the charge and discharge current lines  11  and  12 . As indicated by a line labeled {circle around ( 3 )}, the pack current measuring unit  130  measures the current flowing in the charge and discharge current lines  11  and  12  and the current flowing in the battery pack  2  by the current sensor  3 . When the service plug  290  is coupled between the subpacks  210  to  280 , the pack current measuring unit  130  measures the current passing through the battery pack  2 . On the other hand, when the service plug  290  is opened, current is not allowed to flow in the charge and discharge current lines  11  and  12  and accordingly, the current measured by the pack current measuring unit  130  becomes 0 A. 
         [0031]    The loop current measuring unit  140  forms a closed loop  293  with the internal power supply unit  30  and the service plug  290 . The current flowing in the closed loop  293  is derived from a power supply of the internal power supply unit  30 . In some embodiments, the closed loop  293  may be formed using a separate external voltage source or a current source in addition to the internal power supply unit  30 . The loop current measuring unit  140  measures a current flowing in the closed loop  293 . When the service plug  290  is coupled between the subpacks  210  to  280 , the closed loop  293  is also maintained in a connected state, so that the loop current measuring unit  140  measures the current flowing in the closed loop  293 . On the other hand, when the service plug  290  is opened, the closed loop  293  is also opened, so that current is not allowed to flow in the closed loop  293 . Accordingly, the current measured by the loop current measuring unit  140  becomes 0 A. 
         [0032]    The temperature measuring unit  150  measures a temperature of the battery pack  2  and an ambient temperature. A signal indicative of the temperature measured by the temperature measuring unit  150  is delivered to the MCU  20 , and when the temperature of the battery pack  2  is higher than a reference level, the MCU  20  controls the charging or discharging operation of the battery pack  2 . 
         [0033]    The A/D converter  160  is connected to the cell voltage measuring unit  110 , the pack voltage measuring unit  120  and the pack current measuring unit  130 . The A/D converter  160  converts the cell voltage, subpack voltage, pack voltage and pack current analog values into digital signals. Here, the cell voltage and subpack voltage values are measured by the cell voltage measuring unit  110 , the pack voltage value is measured by the pack voltage measuring unit  120 , and the pack current value is measured by the pack current measuring unit  130 , respectively. The A/D converter  160  applies the digitally converted voltage values and current values to the MCU  20 . 
         [0034]    The MCU  20  estimates a state of charge (SOC) and a state of health (SOH) of the battery pack  2  based on the voltage values and temperature values received from the sensing unit  10 . The MCU  20  also controls charging and discharging operations of the battery pack  2 . That is, in the event of overcharging of the battery pack  2 , the MCU  20  may cut off paths of the charge and discharge current lines  11  and  12  by the main switch  6 . When the service plug  290  is opened, that is, when the service plug  290  is disconnected from the battery pack  2 , the MCU  20  outputs information on whether the service plug  290  is opened or closed to an external display unit (not shown). For example, the MCU  20  outputs a signal indicating that the service plug  290  is disconnected from the battery pack  2 . 
         [0035]    In general, the internal power supply unit  30  supplies power to the BMS  1  using an auxiliary (backup) battery (not shown). The internal power supply unit  30  may perform a charging operation through an external power supply unit. In an exemplary embodiment, in a case where the battery pack  2  of the present invention is used in a hybrid electric vehicle (HEV), or the like, the internal power supply unit  30  may be supplied with power from a lead-acid battery of a hybrid or electric vehicle to perform a charging operation. In addition, the internal power supply unit  30  may supply a constant voltage to the closed loop  293  formed by the loop current measuring unit  140  and the service plug  290 . 
         [0036]    The cell balancing unit  40  performs balancing operations between states of charge and discharge of battery cells constituting each of the subpacks  210  to  280  of the battery pack  2 . That is to say, the cell balancing unit  40  discharges over-charged cells (i.e., relatively less discharged cells) of the battery cells, and charges relatively less charged cells (i.e., over-discharged cells) of the battery cells, thereby maintaining the respective battery cells at uniform SOC levels. 
         [0037]    The storage unit  50  stores various data values, including data about SOC, SOH, etc., immediately before the BMS  1  is turned off. Accordingly, when the BMS  1  is turned on afterward, the MCU  20  can read the data values corresponding to data values stored at the time when the BMS  1  was turned off previously. The storage unit  50  stores the present levels of SOC and SOH data when the power source of the BMS  1  is turned off. To this end, an electrically erasable programmable read only memory (EEPROM) may be used as the storage unit  50 . According to some embodiments, the storage unit  50  may be an EEPROM but the present invention is not limited thereto. 
         [0038]    The communication unit  60  communicates with a motor controller (not shown), an engine control unit (not shown) on other “load control” units. The communication unit  60  allows the motor to utilize power of the battery pack  2 . In addition, the communication unit  60  may allow an engine to be driven when the motor is not driven. 
         [0039]    The protection circuit unit  70  protects the battery pack  2  from external impacts, over-current, over-voltage, etc. 
         [0040]    The power-on reset unit  80  resets the overall system when the BMS  1  is turned on. 
         [0041]    The external interface  90  allows the cooling fan  4  to be electrically coupled to the MCU  20 . In addition, the external interface  90  allows the main switch  6  of the charge and discharge current lines  11  and  12  coupled to the battery pack  2  to be coupled to the MCU  20 . 
         [0042]    The battery pack  2  includes the plurality of subpacks  210  to  280  and the service plug  290  coupled between the plurality of subpacks  210  to  280 . To supply a voltage and power suitable for a load, the battery pack  2  includes the plurality of subpacks  210  to  280 . According to some embodiments of the present invention, the battery pack  2  illustrated in  FIG. 1  includes eight subpacks  210  to  280 , each subpack including five battery cells. The present invention is not, however, limited to the exemplary embodiments shown. 
         [0043]    The service plug  290  is coupled between the subpacks  210  to  280 . In order to protect the battery pack  2  from over-charge or over-current, the service plug  290  may incorporate a safety switch  291  and a fuse  292 . The service plug  290  is normally maintained in a state in which it is coupled between the subpacks  210  to  280 . 
         [0044]    However, in an abnormal event where failures occur in the secondary battery, appropriate measures, such as maintenance, should be undertaken. In such a case, the service plug  290  is opened to prevent the current from flowing through the battery pack  2 . Here, the service plug  290  is opened by physically disconnecting one of a pair of plug terminals (see  290   a  and  290   b  of  FIG. 1 ) coupled to the subpacks  210  to  280  from the subpacks  210  to  280 . When the service plug  290  is opened, the plug terminal  290   b  which forms the closed loop  293  in cooperation with the sensing unit  10  is also disconnected from the service plug  290 . As a result, when the service plug  290  is opened, the sensing unit  10  outputs the maximum measurable values of cell voltages, subpack voltages, battery cell voltages and the current measured by the sensing unit  10  is 0 A. 
         [0045]    As described above, in the secondary battery according to the present invention, a service plug is provided between a plurality of subpacks of a battery pack, and when the service plug is opened for maintenance work, at least one of the group consisting of the battery cell voltage, subpack voltages, overall voltage and current of the battery pack are measured by a battery management system. Thus, it can be determined whether the service plug is opened or closed, ultimately ensuring operator safety. 
         [0046]    Although exemplary embodiments of the present invention have been described in detail, it should be understood that many variations and modifications of the basic inventive concept herein described, which may appear to those skilled in the art, will still fall within the spirit and scope of the exemplary embodiments of the present invention as defined by the appended claims.