Patent Publication Number: US-2016223618-A1

Title: Voltage correction method of battery cell, battery monitoring device, semiconductor chip, and vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese patent application No. 2015-015446, filed on Jan. 29, 2015, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     The present invention relates to a voltage correction method of a battery cell, a battery monitoring device, a semiconductor chip, and a vehicle. 
     A battery such as a lithium-ion battery is used, for example, in an electric vehicle, a hybrid electric vehicle and the like. When the lithium-ion battery is in a state of being overcharged in which charging is continued beyond the capacity of a battery cell or in a state of being overdischarged in which discharging is continued to about the lower limit of the capacity of the battery cell, electric properties of the battery cell are degraded, which may cause the capacity and the output voltage to be reduced. Further, when overcharge occurs, in particular, the amount of heat generated in the battery cell becomes large, which may reduce safety. 
     Therefore, in the charge/discharge control of the battery cell, a battery monitoring system measures the voltage of the battery cell to monitor the charging state. The battery monitoring system controls charge and discharge of the battery cell to prevent overcharge and overdischarge based on the upper-limit value of the voltage for the charging and the lower-limit value of the voltage for the discharging that have been set. 
     When there is an error in the voltage measurement, however, even when the battery cell is overcharged or overdischarged, the state of the overcharge or overdischarge cannot be normally detected. In a battery used in a power supply system of a vehicle in particular, overcharge and overdischarge should be definitely avoided to secure safety. 
     Therefore, the upper-limit value for the charging is set lower and the lower-limit value for the discharging is set higher in consideration of the error of the voltage measurement. It is therefore possible to prevent the overcharge and the overdischarge due to the measurement error. 
     Typically, the voltage of the battery cell is converted from an analog signal that has been measured into a digital signal via an analog/digital converter in a battery monitoring IC (Integrated Circuit). At this time, a reference voltage used to conduct this conversion varies depending on the temperature of the analog/digital converter, which causes a voltage measurement error. 
     In Japanese Unexamined Patent Application Publication No. 2013-254359, secondary temperature characteristics of a reference voltage are subjected to an analog correction. Further, in Japanese Unexamined Patent Application Publication No. 8-181610, when analog/digital conversion is conducted, the temperature of the analog/digital converter is detected and the reference voltage is corrected based on the temperature that has been detected. 
     SUMMARY 
     When the upper-limit value for charging is set lower and the lower-limit value for discharging is set higher in consideration of the error of the voltage measurement as stated above, the error of the voltage measurement is taken under control as a margin, whereby the larger the expected error becomes, the narrower the operating voltage region of the battery cell becomes. It is therefore impossible to fully use the capacity of the battery cell, resulting in a shorter travelable distance in the vehicle according to the error margin. Therefore, in order to improve the travelable distance while securing safety, it is required to reduce the error of the voltage measurement of the battery cell. 
     When the analog correction is performed as disclosed in Japanese Unexamined Patent Application Publication No. 2013-254359, if the number of correction points is increased to improve the accuracy of the analog correction, the size of the circuit increases. Further, while a large number of battery monitoring ICs are provided to monitor the voltage of the battery cell, according to the technique disclosed in Japanese Unexamined Patent Application Publication No. 8-181610, each battery monitoring IC performs a correction operation, which increases the size of the circuit. The other problems of the prior art and the novel characteristics of the present invention will be made clear from the description of the specification and the accompanying drawings. 
     One embodiment includes a process of calculating a correction value of a voltage of a battery cell based on a temperature of a battery monitoring unit and voltage correction data to correct a voltage measurement error of the battery cell according to a change in the temperature of the battery monitoring unit and correcting the voltage of the battery cell based on the correction value in a second semiconductor chip. 
     According to one embodiment, an operation unit of a second semiconductor chip calculates a correction value of a voltage of a battery cell based on a temperature of a battery monitoring unit and voltage correction data to correct a voltage measurement error of the battery cell according to a change in the temperature of the battery monitoring unit and corrects the voltage of the battery cell based on the correction value. 
     One embodiment includes an output terminal to output a voltage of a battery cell and a temperature of a battery monitoring unit. 
     According to the embodiment, it is possible to measure the voltage of the battery cell with a high accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, advantages and features will be more apparent from the following description of certain embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram showing a vehicle according to a first embodiment; 
         FIG. 2  is a block diagram showing a power supply system according to the first embodiment; 
         FIG. 3  is a block diagram showing a battery monitoring unit in a battery monitoring device according to the first embodiment; 
         FIG. 4  is a diagram showing a relation between temperature measured by a temperature measurement unit and an output voltage of the temperature measurement unit; 
         FIG. 5  shows in (a) a relation between a voltage of the temperature measurement unit and a reference voltage and in (b) a relation between an output voltage of the temperature measurement unit and a voltage of a battery cell; 
         FIG. 6  is a diagram showing a relation between the output voltage of the temperature measurement unit and a voltage approximate value of the battery cell; 
         FIG. 7  is a flowchart of processing of a voltage correction method of a battery cell according to the first embodiment; 
         FIG. 8  is a diagram showing an order for measuring the voltage of the temperature measurement unit and the battery cell in the voltage correction method of the battery cell according to the first embodiment; 
         FIG. 9  is a conceptual diagram that corrects a result of measuring the voltage of the battery cell using voltage correction data; 
         FIG. 10  is a block diagram showing a battery monitoring device having a configuration in which each first semiconductor chip performs a voltage correction operation; 
         FIG. 11  is a flowchart showing processing of a voltage correction method of a battery cell according to a second embodiment; 
         FIG. 12  is a diagram showing an order for measuring a voltage of a temperature measurement unit and a battery cell according to a third embodiment; 
         FIG. 13  is a diagram showing an order for measuring a voltage of a temperature measurement unit and a battery cell according to a fourth embodiment; and 
         FIG. 14  is a diagram showing an order for measuring a voltage of a temperature measurement unit and a battery cell according to a fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     A voltage correction method of a battery cell, a battery monitoring device, a semiconductor chip, and a vehicle according to this embodiment will be described. First, the vehicle according to this embodiment will be described.  FIG. 1  is a block diagram showing the vehicle according to this embodiment. 
     A vehicle  1  is typically a hybrid vehicle or an electric vehicle, for example. As shown in  FIG. 1 , the vehicle  1  according to this embodiment includes a power supply system  2 , an inverter  3 , a motor  4 , an ECU  5  (Electronic Control Unit), and meters  6 . 
     While the details of the power supply system  2  will be described later, the power supply system  2  controls power of the vehicle  1  based on a control signal input from the ECU  5 . The inverter  3  converts DC power supplied from the power supply system  2  into AC power having a predetermined voltage based on the control signal input from the ECU  5  and supplies the AC power to the motor  4 . 
     The motor  4  is mounted to the vehicle  1  as one type of driving sources of the vehicle  1 . The driving force of the motor  4  is transmitted to wheels  9  via a transmission  7  and a drive shaft  8 . The ECU  5  is a control device to control the power supply system  2 , the inverter  3 , the motor  4 , the transmission  7  and the like. 
     The meters  6  output power information on the vehicle  1  and output information on the motor  4  to allow a user of the vehicle  1  to check these information. The power supply system  2 , the inverter  3 , the motor  4 , the ECU  5 , the meters  6 , and the transmission  7  are connected via a bus  10 . The bus  10  may be, for example, a CAN (Controller Area Network) bus. 
     Next, the power supply system  2  according to this embodiment will be described.  FIG. 2  is a block diagram showing the power supply system according to this embodiment. As shown in  FIG. 2 , the power supply system  2  includes a battery  21 , a battery management unit  22 , an AC/DC converter  23 , and switches  24  and  25 . 
     The battery  21  includes a plurality of battery cells  21   a  ( 21   a _ 1 ˜ 21   a _N: N is a natural number) and is a secondary battery such as a lithium-ion battery. The battery  21  supplies power to each element such as the motor  4 , the ECU  5 , and the meters  6 . 
     The battery management unit  22  operates to charge the battery  21  and supply power to each element that operates the vehicle  1  from the battery  21 . The battery management unit  22  according to this embodiment includes a battery monitoring device  26  and a battery control device  27 . 
     The battery monitoring device  26  measures the voltage of the battery cell  21   a  and outputs a signal indicating the measurement result to the battery control device  27 . The details of the battery monitoring device  26  will be described later. 
     The battery control device  27  controls the AC/DC converter  23  and the switch  24  to charge the battery  21  based on the signal indicating the measurement result input from the battery monitoring device  26 . Further, the battery control device  27  controls the switch  25  to supply power to the motor  4 . While the battery control device  27  includes a semiconductor chip  28  including a storage unit  28   a , an operation unit  28   b , and a communication unit  28   c  like general integrated circuits, the detailed descriptions of the battery control device  27  will be omitted. 
     The AC/DC converter  23  converts the AC power input from a charging device  11  into DC power having a predetermined voltage to convert the power input from the external charging device  11  into charge power of the battery  21  and supplies the DC power to the battery  21 . The AC/DC converter  23  operates based on a control signal input from the battery control device  27 . 
     The charging device  11  is, for example, an external AC power supply. The power supplied from the charging device  11  is supplied to the vehicle  1  via a connection terminal  1   a  of the vehicle  1 . 
     The switch  24  is arranged between the AC/DC converter  23  and the battery  21  and operates based on the control signal input from the battery control device  27 . 
     The switch  25  is arranged between the inverter  3  and the battery  21  and operates based on the control signal input from the battery control device  27 . 
     In the vehicle  1  stated above, when the signal indicating the measurement result is input to the battery control device  27  from the battery monitoring device  26  first, the battery control device  27  determines whether the result of measuring the voltage of the battery  21  which is the measurement result is lower than a predetermined voltage. 
     When the result of measuring the voltage of the battery  21  is lower than the predetermined voltage, the battery control device  27  determines whether the charging device  11  is connected to the connection terminal  1   a  of the vehicle  1 . When the charging device  11  is connected to the connection terminal  1   a  of the vehicle  1 , the battery control device  27  outputs the control signal to the AC/DC converter  23  and the switch  24  to accumulate the power supplied from the charging device  11  in the battery  21 . 
     The AC/DC converter  23  converts the AC power supplied from the charging device  11  into the DC power having a predetermined voltage based on the control signal input from the battery control device  27 . Further, the switch  24  is switched on based on the control signal input from the battery control device  27 . At this time, the switch  25  has been turned off. It is therefore possible to accumulate the power supplied from the charging device  11  in the battery  21 . 
     On the other hand, when the charging device  11  is not connected to the connection terminal  1   a  of the vehicle  1 , the battery control device  27  turns off the switch  25  to interrupt the power supply from the battery  21  to the motor  4 . At this time, the switch  24  is also turned off. 
     In other cases, the battery control device  27  outputs the control signal to the switch  25  to supply power from the battery  21  to the motor  4 . 
     The switch  25  is turned on based on the control signal input from the battery control device  27 . At this time, the switch  24  has been turned off. Further, the inverter  3  converts the DC power supplied from the battery  21  into the AC power having a predetermined voltage based on the control signal input from the ECU  5 . Therefore, the power from the battery  21  is supplied to the motor  4 . 
     While a configuration in which the power generated by the motor  4  is supplied to the battery  21  is not employed in this embodiment, such a configuration can be employed, similar to general hybrid vehicles. 
     Next, the battery monitoring device  26  according to this embodiment will be described in detail.  FIG. 3  is a block diagram showing a battery monitoring unit in the battery monitoring device according to this embodiment.  FIG. 4  is a diagram showing a relation between the temperature measured by the temperature measurement unit and the output voltage of the temperature measurement unit. 
     The battery monitoring device  26  includes a first semiconductor chip  31  and a second semiconductor chip  32 . The first semiconductor chip  31  is arranged for each of the plurality of battery cells  21   a , as shown in  FIG. 2 . As a result, the battery monitoring device  26  according to this embodiment includes a plurality of first semiconductor chips ( 31 _ 1 ˜ 31 _N: N is a natural number). 
     For example, the battery monitoring device  26  includes a battery  21  including 96 battery cells  21   a , and one first semiconductor chip  31  is provided for every 12 battery cells  21   a , which means eight first semiconductor chips  31  are included in the battery  21  in total. The first semiconductor chip  31  includes, as shown in  FIG. 2 , a storage unit  31   a , a battery monitoring unit  31   b , and a communication unit  31   c.    
     While the details will be described later, the storage unit  31   a  stores voltage correction data to correct a voltage measurement error of the battery cell  21   a  according to a change in the temperature of the battery monitoring unit  31   b . The battery monitoring unit  31   b  monitors the voltage of the battery cell  21   a  and the temperature of the battery monitoring unit  31   b . The battery monitoring unit  31   b  according to this embodiment includes, as shown in  FIG. 3 , a voltage measurement unit  31   d , a temperature measurement unit  31   e , and an analog/digital converter  31   f.    
     The voltage measurement unit  31   d  measures the voltage of each battery cell  21   a  based on a signal indicating a read command input from the second semiconductor chip  32  and outputs a signal indicating the measurement result to the analog/digital converter  31   f.    
     The temperature measurement unit  31   e  measures the temperature of the battery monitoring unit  31   b  and eventually the temperature of the analog/digital converter  31   f  based on a signal indicating a read command input from the second semiconductor chip  32  and outputs a signal indicating the measurement result to the analog/digital converter  31   f.    
     Typically, a relation between the temperature measured by the temperature measurement unit  31   e  and the output voltage of the temperature measurement unit  31   e  is shown in  FIG. 4 . In this embodiment, the signal indicating the measurement result of the output voltage of the temperature measurement unit  31   e  is output to the analog/digital converter  31   f  as the signal indicating the measurement temperature of the battery monitoring unit  31   b.    
     The analog/digital converter  31   f  analog/digital converts the signal indicating the measurement result input from the voltage measurement unit  31   d  based on a reference voltage and outputs the converted signal indicating the measurement result to the communication unit  31   c . Further, the analog/digital converter  31   f  analog/digital converts the signal indicating the measurement result input from the temperature measurement unit  31   e  and outputs the converted signal indicating the measurement result to the communication unit  31   c.    
     The communication unit  31   c  achieves communications with the second semiconductor chip  32 . Specifically, the communication unit  31   c  outputs the signal indicating the result of measuring the voltage of the battery cell  21   a , the signal indicating the result of measuring the voltage of the temperature measurement unit  31   e , and the signal indicating the voltage correction data to the second semiconductor chip  32 . That is, an output unit  31   g  of the communication unit  31   c  serves as an output terminal of the first semiconductor chip  31 . Further, the signal indicating the read command is input to the communication unit  31   c  from the second semiconductor chip  32 . 
     Note that the communication unit  31   c  according to this embodiment is configured to be able to communicate with the communication unit  31   c  of another first semiconductor chip  31  and outputs the signal indicating the result of measuring the voltage of the battery cell  21   a , the signal indicating the result of measuring the voltage of the temperature measurement unit  31   e , and the signal indicating the voltage correction data to the second semiconductor chip  32  via the other first semiconductor chip  31 . Each of the first semiconductor chips  31  may be directly communicated with the second semiconductor chip  32 . 
     The second semiconductor chip  32  includes, as shown in  FIG. 2 , a communication unit  32   a , a storage unit  32   b , and an operation unit  32   c . The communication unit  32   a  achieves communications with the communication unit  31   c  of the first semiconductor chip  31 . Specifically, the communication unit  32   a  outputs the signal indicating the read command to the communication unit  31   c  of the first semiconductor chip  31 . Further, the signal indicating the result of measuring the voltage of the battery cell  21   a , the signal indicating the result of measuring the voltage of the temperature measurement unit  31   e , and the signal indicating the voltage correction data are input to the communication unit  32   a  from the first semiconductor chip  31 . 
     A program for implementing the voltage correction method of the battery cell  21   a  described later and the like are stored in the storage unit  32   b.    
     The operation unit  32   c  executes the program read out from the storage unit  32   b . While the details of the operation unit  32   c  will be described later, the operation unit  32   c  calculates the correction value of the result of measuring the voltage of the battery cell  21   a  based on the voltage correction data and the result of measuring the voltage of the temperature measurement unit  31   e  and corrects the result of measuring the voltage of the battery cell  21   a  based on the correction value that has been calculated. 
     Now, a procedure for setting the voltage correction data according to this embodiment will be described.  FIG. 5( a )  is a diagram showing a relation between the voltage of the temperature measurement unit and the reference voltage. FIG.  5 ( b ) is a diagram showing a relation between the output voltage of the temperature measurement unit and the voltage of the battery cell.  FIG. 6  is a diagram showing a relation between the output voltage of the temperature measurement unit and a voltage approximate value of the battery cell. 
     First, the battery cell  21   a  having a predetermined voltage (expected value) is prepared, the voltage of the battery cell  21   a  is measured by the voltage measurement unit  31   d  and the output voltage of the temperature measurement unit  31   e  is measured while the temperature of the analog/digital converter  31   f  is being changed to obtain  FIGS. 5( a ) and 5( b ) . 
     Next, the result of measuring the voltage of the battery cell  21   a  with respect to the output voltages at a plurality of points (three points in this embodiment) in the temperature measurement unit  31   e  is extracted, and the following a, b, and c in &lt;Expression 1&gt; are introduced based on the error between the result of measuring the voltage of the battery cell  21   a  that has been extracted and the expected value of the battery cell  21   a  to obtain  FIG. 6 . 
     That is, it can be said that  FIG. 6  shows the error between the result of measuring the voltage of the battery cell  21   a  that has been extracted and the expected value of the battery cell  21   a  with respect to the voltage of the temperature measurement unit  31   e . While the result of measuring the voltage of the battery cell  21   a  with respect to the output voltages at three points in the temperature measurement unit  31   e  is extracted, the number of points is not particularly limited as long as the number is plural. 
         y=ax   2   +bx+c   &lt;Expression 1&gt;
 
     Note that x represents the result of measuring the voltage of the temperature measurement unit  31   e,  y represents the correction value of the result of measuring the voltage of the battery cell  21   a , and a, b, and c represent correction coefficients. 
     &lt;Expression 1&gt; thus introduced is set as the voltage correction data. The voltage correction data when the reference voltage has secondary temperature characteristics has been introduced in this embodiment. When the reference voltage has primary temperature characteristics, a and b of the following &lt;Expression 2&gt; may be introduced and &lt;Expression 2&gt; may be set as the voltage correction data. 
         y=ax+b   &lt;Expression 2&gt;
 
     Next, the voltage correction method of the battery cell according to this embodiment will be described.  FIG. 7  is a flowchart of processing of the voltage correction method of the battery cell according to this embodiment.  FIG. 8  is a diagram showing an order for measuring the voltages of the battery cell and the temperature measurement unit in the voltage correction method of the battery cell according to this embodiment.  FIG. 9  is a conceptual diagram for correcting the result of measuring the voltage of the battery cell using the voltage correction data.  FIG. 10  is a block diagram showing a battery monitoring device having a configuration in which each first semiconductor chip performs the voltage correction operation. 
     First, the voltage correction data set as stated above is stored in the storage unit  31   a  of the first semiconductor chip  31 . Next, in the second semiconductor chip  32 , the operation unit  32   c  reads out and executes the program for implementing the voltage correction method of the battery cell  21   a  from the storage unit  32   b  and outputs the signal indicating the read command from the communication unit  32   a  at a predetermined timing (S 1 ). 
     In the first semiconductor chip  31 , the signal indicating the read command is input to the communication unit  31   c  (S 2 ). In the first semiconductor chip  31 , the voltage measurement unit  31   d  measures the voltage of the battery cell  21   a  and the signal indicating the result of measuring the voltage of the battery cell  21   a  is output to the analog/digital converter  31   f . Further, in the first semiconductor chip  31 , the temperature measurement unit  31   e  measures the temperature of the analog/digital converter  31   f  and measures the output voltage of the temperature measurement unit  31   e  at this time, and outputs the signal indicating the result of measuring the voltage of the temperature measurement unit  31   e  to the analog/digital converter  31   f . In this embodiment, as shown in  FIG. 8 , first, after the output voltage of the temperature measurement unit  31   e  is measured, the voltages of the plurality of battery cells  21   a  are measured by the voltage measurement unit  31   d.    
     Next, in the first semiconductor chip  31 , the analog/digital converter  31   f  analog/digital converts the signal indicating the result of measuring the voltage of the battery cell  21   a  and the signal indicating the result of measuring the voltage of the temperature measurement unit  31   e  and outputs the converted signals to the communication unit  31   c.    
     Next, in the first semiconductor chip  31 , when the signal indicating the result of measuring the voltage of the battery cell  21   a  and the signal indicating the result of measuring the voltage of the temperature measurement unit  31   e  are input to the communication unit  31   c , the communication unit  31   c  reads out the signal indicating the voltage correction data from the storage unit  31   a  (S 3 ). 
     Next, in the first semiconductor chip  31 , the communication unit  31   c  outputs the signal indicating the result of measuring the voltage of the battery cell  21   a , the signal indicating the result of measuring the voltage of the temperature measurement unit  31   e , and the signal indicating the voltage correction data (S 4 ). 
     In the second semiconductor chip  32 , the signal indicating the result of measuring the voltage of the battery cell  21   a , the signal indicating the result of measuring the voltage of the temperature measurement unit  31   e , and the signal indicating the voltage correction data are input to the communication unit  32   a  (S 5 ). 
     Next, in the second semiconductor chip  32 , the operation unit  32   c  introduces the voltage measurement error of the battery cell  21   a  based on the result of measuring the voltage of the temperature measurement unit  31   e  and the voltage correction data and as shown in  FIG. 9 , the voltage measurement error that has been introduced is subtracted from the result of measuring the voltage of the battery cell  21   a  to correct the result of measuring the voltage of the battery cell  21   a  (S 6 ). The operation unit  32   c  then calculates the remaining amount of the battery based on the corrected result of measuring the voltage of the battery cell  21   a  and displays the remaining amount of the battery on the meters  6 . 
     As described above, in this embodiment, as shown in  FIG. 10 , for example, instead of performing the correction operation of the result of measuring the voltage of the battery cell  21   a  by each of the first semiconductor chips  31 , the operation unit  32   c  of the second semiconductor chip  32  collectively performs the correction operation of the result of measuring the voltage of the battery cell  21   a . It is therefore possible to reduce the size of the circuit of the first semiconductor chip  31 , which results in a reduction in the size of the battery monitoring device  26 . Further, since the overlapping functions are omitted, the battery monitoring device  26  can be manufactured at a reduced cost. 
     Further, the battery monitoring device  26  according to this embodiment uses a merged process of a high withstand voltage and a low withstand voltage in which the first semiconductor chip  31  deals with a high voltage and the second semiconductor chip  32  deals with a low voltage. Since the calculation processing is not performed in the first semiconductor chip  31 , the battery monitoring device  26  according to this embodiment is able to use the merged process of the inexpensive low withstand voltage process and high withstand voltage process. Since the merged process becomes expensive when the low withstand voltage process becomes a fine process, the advantage of mounting the operation unit to the second semiconductor chip  32  is large. 
     Further, since the voltage correction data showing a relation between the result of measuring the voltage of the temperature measurement unit  31   e  and the voltage measurement error of the battery cell  21   a  is set in advance and the result of measuring the voltage of the battery cell  21   a  is corrected based on the voltage correction data, a high measurement accuracy can be obtained. It is therefore possible to suppress overcharge and overdischarge of the battery  21  and improve the safety of the battery  21 . Moreover, compared to the case in which the error of the voltage measurement is taken under control as a margin, the operating voltage region of the battery cell  21   a  can be made wider and the capacity of the battery cell  21   a  can be used. In the vehicle  1 , it is possible to increase the travelable distance while maintaining the security of the battery cell  21   a.    
     To be more specific, although it is possible to decrease the fluctuations of the reference voltage in the technique disclosed in Japanese Unexamined Patent Application Publication No. 2013-254359, it is impossible to suppress the error of the reference voltage. Meanwhile, the battery monitoring device  26  according to this embodiment is able to suppress the error of the reference voltage. Therefore, the battery monitoring device  26  according to this embodiment is able to measure the voltage of the battery cell  21   a  more accurately than the technique disclosed in Japanese Unexamined Patent Application Publication No. 2013-254359. 
     When the voltage correction data is once sent to the second semiconductor chip  32  from the first semiconductor chip  31  and the voltage correction data is stored in the storage unit  32   b  of the second semiconductor chip  32 , the following correction of the result of measuring the voltage of the battery cell  21   a  may be performed using the voltage correction data of the storage unit  32   b.    
     When there is a variation in the voltage of the battery cell  21   a  after the correction, this voltage is preferably smoothed or an alarm of the overcharge or the overdischarge is preferably set up. 
     Second Embodiment 
     In this embodiment, a voltage correction method of the battery cell  21   a  different from that of the first embodiment will be described.  FIG. 11  is a flowchart of processing of the voltage correction method of the battery cell according to this embodiment. 
     The voltage correction method of the battery cell  21   a  according to this embodiment is substantially equal to the voltage correction method of the battery cell  21   a  according to the first embodiment. Therefore, overlapping descriptions will be omitted. In this embodiment, the voltage correction data is stored in the storage unit  32   b  of the second semiconductor chip  32  in advance. In accordance therewith, in this embodiment, the readout of the voltage correction data in the first semiconductor chip  31  and the input/output of the signal indicating the voltage correction data between the first semiconductor chip  31  and the second semiconductor chip  32  are omitted. 
     When the result of measuring the voltage of the battery cell  21   a  is corrected using the voltage correction data, the operation unit  32   c  reads out the voltage correction data from the storage unit  32   b  (S 26 ). In the following process, the result of measuring the voltage of the battery cell  21   a  is corrected, similar to the process in the first embodiment. 
     As described above, in this embodiment, the voltage correction data is stored in the storage unit  32   b  of the second semiconductor chip  32  in advance. Therefore, there is no need to output the signal indicating the voltage correction data to the second semiconductor chip  32  from the first semiconductor chip  31  and the amount of signals to be output to the second semiconductor chip  32  from the first semiconductor chip  31  can be reduced. It is therefore possible to obtain the corrected result of measuring the voltage of the battery cell  21   a  in a short time, whereby it is possible to detect an abnormality in the battery cell  21   a  at an earlier stage and contribute to an improvement in the safety of the battery  21 . 
     Third Embodiment 
     In this embodiment, the voltages of the battery cell  21   a  and the temperature measurement unit  31   e  are measured in an order different from the order described in the first embodiment.  FIG. 12  is a diagram showing an order for measuring the voltages of the battery cell and the temperature measurement unit according to this embodiment. Note that the number of battery cells  21   a  whose voltages are measured by the voltage measurement unit  31   d  of one first semiconductor chip  31  is N. 
     In this embodiment, as shown in  FIG. 12 , first, the voltage measurement unit  31   d  measures the voltages of the N/2 battery cells  21   a  and then measures the output voltage of the temperature measurement unit  31   e . After that, the voltage measurement unit  31   d  measures the voltages of the remaining N/2 battery cells  21   a . In this way, the output voltage of the temperature measurement unit  31   e  may be measured in the middle of measuring the voltages of the plurality of battery cells  21   a  by the voltage measurement unit  31   d.    
     Fourth Embodiment 
     In this embodiment, the voltages of the battery cell  21   a  and the temperature measurement unit  31   e  are measured in an order different from the orders described in the first and third embodiments.  FIG. 13  is a diagram showing an order for measuring the voltages of the battery cell and the temperature measurement unit according to this embodiment. Note that the number of battery cells  21   a  whose voltages are measured by the voltage measurement unit  31   d  of one first semiconductor chip  31  is N. 
     In this embodiment, as shown in  FIG. 13 , the output voltage of the temperature measurement unit  31   e  is measured before and after the voltage measurement unit  31   d  measures the voltages of all the N battery cells  21   a  and the average value of the measured values is output as the result of measuring the voltage of the temperature measurement unit  31   e . In this way, the output voltage of the temperature measurement unit  31   e  is measured a plurality of times and the average value of the measured values is output as the result of measuring the voltage of the temperature measurement unit  31   e , whereby the output voltage of the temperature measurement unit  31   e  can be accurately measured. 
     Fifth Embodiment 
     In this embodiment, the voltages of the battery cell  21   a  and the temperature measurement unit  31   e  are measured in an order different from the orders described in the first, third, and the fourth embodiments.  FIG. 14  is a diagram showing an order for measuring the voltages of the battery cell and the temperature measurement unit according to this embodiment. Note that the number of battery cells  21   a  whose voltages are measured by the voltage measurement unit  31   d  of one first semiconductor chip  31  is N. 
     In this embodiment, as shown in  FIG. 14 , the output voltage of the temperature measurement unit  31   e  is measured before the voltage of the battery cell  21   a  is measured in the voltage measurement unit  31   d . Further, after the voltages of the N/2 battery cells  21   a  are measured by the voltage measurement unit  31   d , the output voltage of the temperature measurement unit  31   e  is measured. Then, after the voltages of the remaining N/2 battery cells  21   a  are measured by the voltage measurement unit  31   d , the output voltage of the temperature measurement unit  31   e  is measured and the average value of the results of measuring the voltage of the temperature measurement unit  31   e  three times is output as the result of measuring the voltage of the temperature measurement unit  31   e . In this way, according to this embodiment as well, the output voltage of the temperature measurement unit  31   e  is measured a plurality of times and the average value is output as the result of measuring the voltage of the temperature measurement unit  31   e , whereby it is possible to accurately measure the output voltage of the temperature measurement unit  31   e.    
     While the invention made by the present inventors have been specifically described based on the embodiments, needless to say, the present invention is not limited to the embodiments already stated above and may be changed in various ways without departing from the spirit of the present invention. 
     For example, the program stated above can be stored and provided to a computer using any type of non-transitory computer readable media. Non-transitory computer readable media include any type of tangible storage media. Examples of non-transitory computer readable media include magnetic storage media (such as flexible disks, magnetic tapes, hard disk drives, etc.), optical magnetic storage media (e.g., magneto-optical disks), Compact Disc Read Only Memory (CD-ROM), CD-R, CD-R/W, and semiconductor memories (such as mask ROM, Programmable ROM (PROM), Erasable PROM (EPROM), flash ROM, Random Access Memory (RAM), etc.). The program may be provided to a computer using any type of transitory computer readable media. Examples of transitory computer readable media include electric signals, optical signals, and electromagnetic waves. Transitory computer readable media can provide the program to a computer via a wired communication line (e.g., electric wires, and optical fibers) or a wireless communication line. 
     The first to fifth embodiments can be combined as desirable by one of ordinary skill in the art. 
     While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention can be practiced with various modifications within the spirit and scope of the appended claims and the invention is not limited to the examples described above. 
     Further, the scope of the claims is not limited by the embodiments described above. 
     Furthermore, it is noted that, Applicant&#39;s intent is to encompass equivalents of all claim elements, even if amended later during prosecution.