Abstract:
Disclosed is a method and apparatus for detecting a cell voltage of a battery pack. The method comprises the steps of storing an impedance of the conductive wire from a part connected to a voltage detector to a part connected with the corresponding battery cell existing between voltage measuring points of each battery cell, detecting current of the battery pack, multiplying the impedance of the conductive wire corresponding to each battery cell and the current to calculate a voltage correction value of each battery cell, detecting voltage of each battery cell, and correcting the voltage of each battery cell, with respect to the voltage correction value of each battery cell such that the voltage correction value corresponding to the voltage of each battery cell is subtracted during charging and the voltage correction value corresponding to the voltage of each battery cell is added during discharging.

Description:
This application claims the benefit of the filing date of Korean Patent Application No. 2005-44881, filed on May 27, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a battery management system, and more particularly, to a method and apparatus for detecting voltage of a battery cell in consideration of impedance of conductive wires connecting a plurality of battery cells constituting the battery pack. 
     2. Description of the Prior Art 
     In general, voltage and current of a battery cell are separately detected in a battery management system. Lasting efforts are made to improve the precision of detecting the voltage and current of the battery cell. 
     Especially, technology of detecting the current of the battery cell is improved in precision by introducing an algorithm into the hardware, while technology of detecting the voltage of the battery cell is limited only to development of hardware technology. 
     In the battery management system, the most important factor is to calculate a state of charge (SOC) of the battery by means of accurate detection of the current. The SOC is compensated in the proximity of discharge end voltage. Because a time for this compensation is determined by reference voltage, the accurate voltage detection of the battery cell is essential to calculate the SOC of the battery. 
     A configuration of the conventional battery management system will be described with reference to  FIG. 1 . 
     Referring to  FIG. 1 , the conventional battery management system comprises a battery pack connecting a plurality of battery cells C 1 , C 2  and C 3  in series or in parallel, a voltage detector  101  detecting the voltage of the battery cells C 1 , C 2  and C 3  constituting the battery pack, a resistor  102  detecting charge/discharge current flowing through the battery pack, a current detector  103  detecting current across the resistor  102 , a controller  104  summing up and controlling the voltage and current detected through the voltage and current detectors  101  and  103 , and a communication unit  105  taking charge of communication between the controller  104  and external equipment. The voltage detector  101 , the current detector  103 , the controller  103 , and the communication unit  105  are included in a fuel gauging integrated circuit (IC) formed into one chip. 
     The battery pack connected in series by the plurality of battery cells has a cathode (+) connected with a plus terminal B+of power output terminals, and an anode (−) connected with a minus terminal B−. Further, the cathode (+) and anode (−) of the battery pack and two contacts between the plurality of battery cells C 1 , C 2  and C 3  constituting the battery pack are connected to the voltage detector  101 . 
     The voltage detector  101  is connected to each of the contacts between the plurality of battery cells C 1 , C 2  and C 3  connected in series, and detects voltage between the respective contacts without considering impedance of conductive wires connecting the battery cells. Hence, the voltage measured by the voltage detector  101  includes an error corresponding to a drop/rise value of voltage caused by the impedance of the conductive wires. 
     In this manner, conventionally, the voltage is detected without taking into consideration the impedance of the conductive wires connecting the battery cells, so that there is no alternative but to include the error caused by the impedance of the conductive wires. 
     This error lowers precision of calculating the actual SOC of the battery, which is responsible for short duration of the battery pack or abnormal protection. 
     Further, the error increases as the current flowing in the battery pack becomes higher. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention has been made to solve these various problems occurring in the prior art, and an objective of the present invention is to provide a method and apparatus of detecting voltage of a battery cell in consideration of impedance of conductive wires connecting a plurality of battery cells constituting the battery pack 
     In order to accomplish this objective, according to an aspect of the present invention, there is provided a method of detecting voltage of at least one battery cell in a battery pack, in which the battery cell is connected through a conductive wire. The method comprises the steps of: storing impedance of the conductive wire from a part connected to a voltage detector to a part connected with the corresponding battery cell; detecting current of the battery pack; multiplying the impedance of the conductive wire corresponding to each battery cell and the current to calculate a correction value of each battery cell; detecting voltage of each battery cell; and correcting the voltage of each battery cell on the basis of the correction value of each battery cell. 
     According to another aspect of the present invention, there is provided an apparatus of detecting voltage of at least one battery cell in a battery pack, in which the battery cell is connected through a conductive wire. The apparatus comprises: a voltage detector detecting the voltage of each battery cell; a memory storing impedance of the conductive wire from a part connected to a voltage detector to a part connected with the corresponding battery cell; a current detector detecting current of the battery pack; and a controller multiplying the impedance of the conductive wire corresponding to each battery cell and the current to calculate a correction value of each battery cell, and correcting the voltage of each battery cell on the basis of the correction value of each battery cell. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a configuration of a conventional battery management system. 
         FIG. 2  illustrates a configuration of a battery management system according to an exemplary embodiment of the present invention. 
         FIG. 3  is a flowchart illustrating a method of detecting voltage of each battery cell in a battery pack, according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 2  illustrates a configuration of a battery management system according to an exemplary embodiment of the present invention. 
     The battery management system  200  is provided with a battery pack, which is composed of first, second, and third battery cells BC 1 , BC 2 , and BC 3 . The first to third battery cells BC 1  to BC 3  are connected in series through first to fourth conductive wires A 1  to A 4 . Further, main current of the battery pack flows through the first to third battery cells BC 1  to BC 3 , and the first to fourth conductive wires A 1  to A 4 . 
     The first conductive wire A 1  is connected with a cathode (+) of the first battery cell BC 1  and a first terminal of a voltage detector  201 . The first terminal and the first conducive wire A 1  are connected through a first lead. Because the main current of the battery pack does not flow to the first lead, it is not necessary to consider impedance of the first lead. 
     The second conductive wire A 2  is connected between an anode (−) of the first battery cell BC 1  and a cathode (+) of the second battery cell BC 2 . A tap between the second conductive wire A 2  and the anode (−) of the first battery cell BC 1  is connected with a second terminal of the voltage detector  201  through a second lead. Because the main current of the battery pack does not flow to the second lead, it is not necessary to consider impedance of the second lead. 
     The third conductive wire A 3  is connected between an anode (−) of the second battery cell BC 2  and a cathode (+) of the third battery cell BC 3 . A tap between the third conductive wire A 3  and the cathode (+) of the third battery cell BC 3  is connected with a third terminal of the voltage detector  201  through a third lead. Because the main current of the battery pack does not flow to the third lead, it is not necessary to consider impedance of the third lead. 
     The fourth conductive wire A 4  is connected with an anode (−) of the third battery cell BC 3  and a fourth terminal of the voltage detector  201 . The fourth terminal and the fourth conducive wire A 4  are connected through a fourth lead. Because the main current of the battery pack does not flow to the fourth lead, it is not necessary to consider impedance of the fourth lead. 
     With respect to the first battery cell BC 1 , the voltage detector  201  measures voltage between an end terminal of the first conductive wire A 1  and the anode of the first battery cell BC 1 . In this case, the voltage of the first battery cell BC 1  should take into consideration a voltage drop or rise caused by the impedance of the first conductive wire A 1 . 
     With respect to the second battery cell BC 2 , the voltage detector  201  measures voltage between the anode of the first battery cell BC 1  and the cathode of the third cell BC 3 . In this case, the voltage of the second battery cell BC 2  should take into consideration a voltage drop or rise caused by the impedance of the second and third conductive wires A 2  and A 3 . 
     Finally, with respect to the third battery cell BC 3 , the voltage detector  201  measures voltage between the cathode of the third battery cell BC 3  and an end terminal of the fourth conductive wire A 4 . In this case, the voltage of the third battery cell BC 3  should take into consideration a voltage drop or rise caused by the impedance of the fourth conductive wire A 4 . 
     In this manner, the voltage detector  201  detects the voltage of each of the first to third battery cells BC 1  to BC 3 , and provides the detected results to a controller  204 . 
     A current detector  203  detects current flowing through a current detection resistor  202 , and provides the detected result to the controller  204 . 
     The controller  204  creates various pieces of information for controlling the battery pack on the basis of the voltage and current measurement values of the battery cells which are measured through the voltage and current detectors  201  and  203 . Particularly, according to an exemplary embodiment of the present invention, the controller  204  corrects the voltage measurement values of the battery cells using impedance measurement values of the conductive wires corresponding to the first to third battery cells BC 1  to BC 3 , wherein the impedance measurement values are stored in a memory  206 . 
     A communication unit  205  takes charge of communication between the controller  204  and external equipment. Particularly, the communication unit  205  receives the impedance measurement values of the conductive wires corresponding to the first to third battery cells BC 1  to BC 3 , and provides the received results to the controller  204 . 
     The memory  206  stores various pieces of information including processing programs of the controller  204 . Particularly, according to an exemplary embodiment of the present invention, the memory  206  stores the impedance measurement values of the conductive wires corresponding to the first to third battery cells BC 1  to BC 3  as shown in Table 1. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Conductive Wire 
                 Impedance 
               
               
                   
                   
               
             
             
               
                   
                 Conductive wire A1 
                 First impedance 
               
               
                   
                 corresponding to first 
                 Impedance_Voltage_B1 
               
               
                   
                 battery cell BC1 
               
               
                   
                 Conductive wires A2 and A3 
                 Second impedance 
               
               
                   
                 corresponding to second 
                 Impedance_Voltage_B2 
               
               
                   
                 battery cell BC2 
               
               
                   
                 Conductive wire A4 
                 Third impedance 
               
               
                   
                 corresponding to third 
                 Impedance_Voltage_B3 
               
               
                   
                 battery cell BC3 
               
               
                   
                   
               
             
          
         
       
     
     In Table 1, the first impedance Impedance_Voltage_B 1  is the impedance of the first conductive wire A 1 , the second impedance Impedance_Voltage_B 2  is the sum of the impedance of the second conductive wire A 2  and the impedance of the third conductive wire A 3 , and the third impedance Impedance_Voltage_B 3  is the impedance of the fourth conductive wire A 4 . 
     Here, the first, second, and third impedances Impedance_Voltage_B 1 , Impedance_Voltage_B 2 , and Impedance_Voltage_B 3 , which correspond to the first, second, and third battery cells BC 1 , BC 2 , and BC 3  respectively, are measured through a milliohm meter (not shown), and provided to the controller  204  through the communication unit  205 . The controller  204  instructs the memory  206  to store the impedances. 
     Further, the voltage detector  201 , the current detector  203 , the controller  204 , the communication unit  205 , and the memory  206  can be included in a fuel gauging integrated circuit (IC) formed into one chip. 
     Now, a method of detecting a voltage of a battery cell, which can be applied to the battery management system, will be described with reference to a flowchart of  FIG. 3 . 
     The controller  204  measures voltage of each of the first, second, and third battery cells BC 1 , BC 2 , and BC 3  constituting the battery pack through the voltage detector  201 . Each measured voltage is as shown in Table 2, and temporarily stored in the memory  206  (S 300 ). 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Voltage of Battery Cell 
                 Measured Voltage Variable 
               
               
                   
                   
               
             
             
               
                   
                 Voltage of first battery 
                 Real_Voltage_B1 
               
               
                   
                 cell BC1 
               
               
                   
                 Voltage of second battery 
                 Real_Voltage_B2 
               
               
                   
                 cell BC2 
               
               
                   
                 Voltage of third battery 
                 Real_Voltage_B3 
               
               
                   
                 cell BC3 
               
               
                   
                   
               
             
          
         
       
     
     Thereafter, the controller  204  measures current of the battery pack through the current detector  203  (S 302 ), and reads out the first, second, and third impedances Impedance_Voltage_B 1 , Impedance_Voltage_B 2 , and Impedance_Voltage_B 3 , which correspond to the first, second, and third battery cells BC 1 , BC 2 , and BC 3  respectively, and are stored in the memory  206  in advance (S 304 ). 
     Then, the controller  204  multiplies the first, second, and third impedances Impedance_Voltage_B 1 , Impedance_Voltage_B 2 , and Impedance_Voltage_B 3 , which correspond to the first, second, and third battery cells BC 1 , BC 2 , and BC 3  and are stored in the memory  206 , by the current value detected through the current detector  203 , thereby creating a correction value of each of the first, second, and third battery cell BC 1 , BC 2 , and BC 3 . Here, the correction values are created by Equation
 
First Impedance (Impedance_Voltage —   B 1)×Current=Correction Value of First Battery Cell ( BC 1);
 
Second Impedance (Impedance_Voltage —   B 2)×Current=Correction Value of Second Battery Cell ( BC 2); and
 
Third Impedance (Impedance_Voltage —   B 3)×Current=Correction Value of Third Battery Cell ( BC 3)  Equation 1
 
     When the creation of the correction values based on Equation 1 is completed, the controller  204  checks whether the battery pack is in a charged state or in a discharged state on the basis of the current value detected through the current detector  203  (S 308 ). 
     As a result of the checking on the basis of the current value, if the battery pack is in a discharged state, the controller  204  adds the calculated correction value of each of the first, second, and third battery cells BC 1 , BC 2 , and BC 3  to the measured voltage of each of the first, second, and third battery cells BC 1 , BC 2 , and BC 3 , thereby calculating final voltage of each of the first, second, and third battery cells BC 1 , BC 2 , and BC 3 . Here, the final voltage of each of the battery cells is obtained by Equation 2.
 
Measured Voltage (Real_Voltage —   B 1) of First Battery Cell  BC 1+Correction Value of First Battery Cell  BC 1=Final Voltage (Correction_Voltage —   B 1) of First Battery Cell  BC 1;
 
Measured Voltage (Real_Voltage —   B 2) of Second Battery Cell  BC 2+Correction Value of Second Battery Cell  BC 2=Final Voltage (Correction_Voltage —   B 2) of Second Battery Cell  BC 2; and
 
Measured Voltage (Real_Voltage —   B 3) of Third Battery Cell  BC 3+Correction Value of Third Battery Cell  BC 3=Final Voltage (Correction_Voltage —   B 3) of Third Battery Cell  BC 3  Equation 2
 
     As a result of the checking on the basis of the current value in step S 308 , if the battery pack is in the charged state, the controller  204  subtracts the calculated correction value of each of the first, second, and third battery cells BC 1 , BC 2 , and BC 3  from the measured voltage of each of the first, second, and third battery cells BC 1 , BC 2 , and BC 3 , thereby calculating final voltage of each of the first, second, and third battery cells BC 1 , BC 2 , and BC 3 , Here, the final voltage of each of the battery cells when charged is obtained by Equation 3.
 
Measured Voltage (Real_Voltage —   B 1) of First Battery Cell  BC 1−Correction Value of First Battery Cell  BC 1=Final Voltage (Correction_Voltage —   B 1) of First Battery Cell  BC 1;
 
Measured Voltage (Real_Voltage —   B 2) of Second Battery Cell  BC 2−Correction Value of Second Battery Cell  BC 2=Final Voltage (Correction_Voltage —   B 2) of Second Battery Cell  BC 2; and
 
Measured Voltage (Real_Voltage —   B 3) of Third Battery Cell  BC 3−Correction Value of Third Battery Cell  BC 3=Final Voltage (Correction_Voltage —   B 3) of Third Battery Cell  BC 3  Equation 3
 
     As described above, the voltage of each battery cell is corrected in consideration of the voltage drop or rise caused by the impedance of each of the conductive wires connecting the battery cells. Thereby, it is possible to accurately measure the voltage of each battery cell. 
     The embodiment of the present invention comprises computer readable media including program commands for executing operation implemented by various computers. The computer readable media may include a program command, a data file, a data structure, etc. in individual or combination. The program command of the media may be one designed or constructed especially for the present invention or an available one well-known to those skilled in the computer software field. 
     INDUSTRIAL APPLICABILITY 
     As can be seen from the foregoing, the voltage of each battery cell is detected in consideration of the impedance of each of the conductive wires connecting the plurality of battery cells constituting the battery pack. As a result, when various pieces of information for battery management, such as a measurement of the SOC of the battery, are estimated, the estimated reliability can be improved. 
     Although exemplary embodiments of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.