Abstract:
An apparatus for identifying a position of an abnormality occurred in a secondary battery system includes an information acquisition unit for acquiring information about a module (module information) from among a plurality of modules included in a module series that accommodates a block for which the difference between a block voltage value and a block voltage value after a primary delay has changed so as to exceed a voltage threshold within a preset time before and after the point in time at which the block voltage value and series current value stopped being correlated, a notification reception unit for receiving a notification about the occurrence of an abnormality in a secondary battery, and a module specification unit for specifying at least the module corresponding to the latest module information as the module in which an abnormality occurred when the notification reception unit receives a notification.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation of International Application No. PCT/JP2014/071600 filed on Aug. 19, 2014, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-180559 filed on Aug. 30, 2013, the contents all of which are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to an apparatus (device), a method, and a non-transitory recording medium storing a program for identifying (specifying) a position of an abnormality (abnormality-occurrence area) occurred in a secondary battery system including two or more modules each accommodating one or more blocks. Each of the blocks is formed by connecting battery cells of two or more secondary batteries. 
       BACKGROUND ART 
       [0003]    In general, frequency adjustment in an electric power system and adjustment of power demands and power supplies in the electric power system are carried out using a plurality of power generators, storage batteries, etc., equipped in the electric power system. Further, in most cases, adjustment in the difference between the generated electric power from natural energy based power generators and its planned output electric power, and reduction in the changes of electric power generated by the natural energy based power generators are also performed using the power generators, storage batteries, etc. In comparison with general electric power generators, the storage batteries can change the electric power output at high speed, and can be used effectively in frequency adjustment of the electric power system, adjustment of the difference between the generated electric power from natural energy based power generators and its planned output electric power, and adjustment of power demands and power supplies in the electric power system. 
         [0004]    In this regard, as a storage battery operated at high temperature connected to the electric power system, a sodium-sulfur battery (hereinafter referred to as the NaS battery) is used, for example. This NaS battery is a high temperature secondary battery containing metal sodium and sulfur as active materials in an isolated manner using a solid electrolyte tube. When the NaS battery is heated at temperature of about 300° C., a certain amount of energy is produced by an electrochemical reaction of both of the melted active materials. Normally, the NaS battery is formed by assembling a plurality of battery cells, and used in a form of a module including a plurality of battery cells connected together. That is, the module has structure where circuits (strings) each formed by connecting a plurality of battery cells in series are connected in parallel to form a block, and at least two blocks are connected in series, and placed in a heat insulating container. 
         [0005]    As a method of reporting occurrence of an abnormality of such a module, a method of detecting an abnormality of a battery by comparing electric discharge depth of each block, and notifying the abnormality is disclosed (e.g., see Japanese Laid-Open Patent Publication No. 03-158781). In this method, the presence of the abnormality is determined for each of the blocks of the module. Therefore, in comparison with the case of detecting the abnormality for each of the individual NaS battery cells of the block, the apparatus is not complicated, and the production cost can be reduced advantageously. 
       SUMMARY OF INVENTION 
       [0006]    It is considered that failures in the battery cells, and consequently, failures in the modules are caused by internal short circuiting or external short circuiting in the battery cells. 
         [0007]    For example, external short circuiting of the battery cells may be caused by formation of an external short circuiting loop due to leakage of active materials in the battery cells. For example, internal short circuiting of the battery cells may be caused by damages, etc. of a beta tube. 
         [0008]    External short circuiting and internal short circuiting of these battery cells can be detected by checking the electric discharge depth in each block as can be seen from Japanese Laid-Open Patent Publication No 03-158781. However, the change in the electric discharge depth due to short circuiting does not occur rapidly, but occur gradually over a relatively long period of time Therefore, it is difficult to determine which module (or which block) has the abnormality, and initial response to the occurrence of the abnormality may be delayed undesirably. 
         [0009]    The present invention has been made to take the problems of this type into account, and an object of the present invention is to provide an apparatus, a method, and a non-transitory recording medium storing a program for identifying a position of an abnormality occurred in a secondary battery system in which if an abnormality occurs, it is possible to identify a module (or a block) as the abnormality source at an early stage, and it is possible to implement an initial response to the occurrence of the abnormality at an early stage. 
         [0000]    [1] An apparatus according to the first invention is an apparatus for identifying a position of an abnormality occurred in a secondary battery system. The secondary battery system includes a plurality of modules each accommodating one or more blocks. Each of the blocks is formed by connecting battery cells of two or more secondary batteries. The apparatus includes a voltage measurement unit configured to detect voltage of the secondary batteries on a block by block basis, and to output the detected voltage as a block voltage value, a string current measurement unit configured to measure electric current of a module string formed by connecting the plurality of modules in series to output the measured electric current as a string current value, an information acquisition unit configured to acquire module information of, among the plurality of modules included in the module string, a module accommodating a block where a difference between the block voltage value and the block voltage value with a first-order lag has been changed to exceed a voltage threshold value in a predetermined time period around a time point at which correlation between the block voltage value and the string current value is lost, a report reception unit configured to receive a report of an abnormality occurred in the secondary batteries, and a module identification unit configured to identify, as a module having the abnormality, the module corresponding to the module information at time of receiving the report by the report reception unit. 
         [0010]    If external short circuiting or internal circuiting occurs in any one of the battery cells, the block voltage of the block including the battery cell having the short circuiting is decreased steeply. Thereafter, in some cases, after the elapse of a certain time period, the voltage returns to the original voltage level before short circuiting. Further, if the scale of the system becomes large, the number of blocks to be monitored is increased correspondingly. Therefore, it becomes further difficult to recognize the decrease in the voltage due to short circuiting from the changes of the block voltage of all of the blocks. 
         [0011]    Further, even in the case where the block voltage value is decreased temporarily due to frequency adjustment in the power system, adjustment in the difference between the generated electric power from natural energy based power generators and its planned output electric power, adjustment of power demands and power supplies in the power system, etc., such a temporary decrease in the block voltage value may be detected erroneously as a temporary drop in the block voltage value due to short circuiting of at least one of the battery cells. 
         [0012]    However, in the present invention, among a plurality of modules, information of a module (module information) accommodating a block where the difference between the block voltage and the block voltage with a first-order lag has been changed to exceed a predetermined voltage threshold value is acquired. Consequently, it is possible to accurately detect whether or not the block voltage has been decreased, and detect occurrence of an abnormality due to short circuiting. 
         [0013]    Further, even in the case where the block voltage value is decreased temporarily due to frequency adjustment in the power system, adjustment in the difference between the generated electric power from natural energy based power generators and its planned output electric power, adjustment of power demands and power supplies in the power system, etc., such a temporary decrease in the block voltage value is not detected erroneously as a temporary drop in the block voltage value. It is because since correlation between the block voltage value and the string current value is maintained, such cases can be taken out of consideration at the time of detection. 
         [0014]    Therefore, in the present invention, by identifying the module which is the source of the abnormality, it becomes possible to send a report to a local user, a local administrator, etc. Thus, countermeasures focused on the identified abnormality source can be taken at an early stage. It becomes possible to suppress expansion of damage. 
         [0000]    [2] In the first invention, the apparatus may include a correlation determination unit configured to determine correlation between the block voltage value and the string current value. The correlation determination unit may include a differential voltage accumulation unit configured to accumulate differences between the block voltage values sampled in a predetermined fixed period and the block voltage values with the first-order lag, a differential current accumulation unit configured to accumulate differences between the string current values sampled in the fixed period and the string current values with the first-order lag, and a correlation coefficient computation unit configured to divide an accumulated differential voltage value obtained in the differential voltage accumulation unit by an accumulated differential current value obtained in the differential current accumulation unit to obtain a correlation coefficient in the fixed period. If the correlation coefficient obtained in the correlation coefficient computation unit is deviated from a predetermined range, correlation between the block voltage value and the string current value is determined as lost. In this manner, calculation becomes simple, and it is possible to confirm the presence or absence of correlation between the block voltage value and the string current value easily and promptly. It is also possible to achieve acceleration of computation.
 
[3] In this case, the predetermined range may be determined based on an I-V characteristic of the block. In this manner, it becomes easy to determine correlation between the block voltage value and the string current value.
 
[4] In the first invention, a time constant of the first-order lag may be selected in accordance with behavior where the block voltage drops temporarily due to short circuiting of at least one of the battery cells. In this manner, it is possible to improve the detection accuracy of the block having a temporary drop in the block voltage due to short circuiting of at least one of the battery cells.
 
[5] In the first invention, as the voltage threshold value, a voltage value of a temporary drop in the block voltage due to short circuiting of at least one of the battery cells may be selected. In this manner, it is possible to improve the detection accuracy of the block having a temporary drop in the block voltage due to short circuiting of at least one of the battery cells.
 
[6] In the first invention, the apparatus may further include an error output unit configured to receive the module information from the information acquisition unit, and to output the module information together with an error message. By outputting the module information together with the error message to a monitor or a printer, the position of the identified module can be recognized at a glance advantageously.
 
[7] A method according to the second invention is a method of identifying a position of an abnormality occurred in a secondary battery system. The secondary battery system includes a plurality of modules each accommodating one or more blocks. Each of the blocks is formed by connecting battery cells of two or more secondary batteries. The method includes the steps of performing voltage measurement by detecting voltage of the secondary batteries on a block by block basis, and outputting the detected voltage as a block voltage value, performing string current measurement by measuring electric current of a module string formed by connecting the plurality of modules in series to output the measured electric current as a string current value, performing information acquisition by acquiring module information of, among the plurality of modules included in the module string, a module accommodating a block where a difference between the block voltage value and the block voltage value with a first-order lag has been changed to exceed a voltage threshold value in a predetermined time period around a time point at which correlation between the block voltage value and the string current value is lost, performing report reception by receiving a report of an abnormality occurred in the secondary batteries, and performing module identification by identifying, as a module having the abnormality, the module corresponding to the module information at time of receiving the report in the report reception step.
 
[8] In the second invention, the method may include the step of performing correlation determination by determining correlation between the block voltage value and the string current value, the correlation determination step may comprise the steps of performing differential voltage accumulation by accumulating differences between the block voltage values sampled in a predetermined fixed period and the block voltage values with the first-order lag, performing differential current accumulation by accumulating differences between the string current values sampled in the fixed period and the string current values with the first order lag, and performing correlation coefficient computation by dividing an accumulated differential voltage value obtained in the differential voltage accumulation step by an accumulated differential current value obtained in the differential current accumulation step to obtain a correlation coefficient in the fixed period. If the correlation coefficient obtained in the correlation coefficient computation step is deviated from a predetermined range, correlation between the block voltage and the string current value may be determined as lost.
 
[9] In this case, the predetermined range is determined based on an I-V characteristic of the block.
 
[10] In the second invention, a time constant of the first order lag may be selected in accordance with behavior where the block voltage drops temporarily due to short circuiting of at least one of the battery cells.
 
[11] In the second invention, as the voltage threshold value, a voltage value of a temporary drop in the block voltage due to short circuiting of at least one of the battery cells may be selected.
 
[12] In the second invention, the method may include the step of performing error output by receiving the module information from the information acquisition step, and outputting the module information together with an error message.
 
[13] A non-transitory recording medium according to the third invention stores a program for a secondary battery system including a plurality of modules each accommodating one or more blocks, the blocks each being formed by connecting battery cells of two or more secondary batteries, a voltage measurement unit configured to detect voltage of the secondary batteries on a block by block basis, and to output the detected voltage as a block voltage value, and a string current measurement unit configured to measure electric current of a module string formed by connecting the plurality of modules in series to output the measured electric current as a string current value. The program is configured to allow the secondary battery system to perform functions of acquiring information (module information) of, among the plurality of modules included in the module string, a module accommodating a block where a difference between the block voltage value and the block voltage value with a first-order lag has been changed to exceed a voltage threshold value in a predetermined time period around a time point at which correlation between the block voltage value and the string current value is lost, receiving a report of an abnormality occurred in the secondary batteries, and identifying, as a module having the abnormality, the module corresponding to the module information at time of receiving the report by the report reception function.
 
         [0015]    As described above, in the apparatus, the method, and the non-transitory recording medium storing the program for identifying a position where an abnormality occurs in a secondary battery system, it is possible to identify a module (or a block) as the abnormality source at an early stage, and it is possible to implement an initial response to the occurrence of the abnormality at an early stage. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]      FIG. 1  is a diagram showing structure of a secondary battery system and an apparatus for identifying a position of an abnormality occurred in the secondary battery system according to an embodiment of the present invention; 
           [0017]      FIG. 2  is an equivalent circuit diagram showing a battery structural body included in a module; 
           [0018]      FIG. 3  is a block diagram showing structure of an information transmission unit; 
           [0019]      FIG. 4  is a diagram showing an example of a format of a transmission file; 
           [0020]      FIG. 5  is a block diagram showing structure of an information acquisition unit and an information transmission unit; 
           [0021]      FIG. 6  is a block diagram showing structure of a first voltage comparator circuit, a correlation determination circuit (second voltage comparator circuit, current comparator circuit, etc.), and a time comparator circuit; 
           [0022]      FIG. 7  is a diagram showing an example of a format of alarm information data; 
           [0023]      FIG. 8  is a flow chart showing an example of processing operation in an information acquisition unit, a module identification unit, and a report reception unit; and 
           [0024]      FIG. 9  is a flow chart showing an example of processing operation in the correlation determination unit of the information acquisition unit. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    Hereinafter, an apparatus, a method, and a non-transitory recording medium storing a program for identifying a position of an abnormality occurred in a secondary battery system according to an embodiment of the present invention will be described with reference to  FIGS. 1 to 9 . 
         [0026]    Firstly, as shown in  FIG. 1 , a secondary battery system  10  to which the apparatus, the method, and the non-transitory recording medium storing the program according to the embodiment of the present invention is applied includes a secondary battery storage unit  12 , an abnormality detection unit  14 , and a reporting unit  16 . 
         [0027]    The secondary battery storage unit  12  has structure where a plurality of box shaped packages  18  are arranged in a lateral direction. In an example of  FIG. 1 , four packages  18  (first package  18 A to fourth package  18 D) are arranged in the lateral direction. Further, the secondary battery storage unit  12  has a battery control device  20  for controlling operation of the secondary batteries. 
         [0028]    Two or more modules  22  are stacked in a vertical direction inside each of the packages  18 . Further, each of the packages  18  accommodates a module string  24  formed by connecting these two or more modules  22  in series. In the structure of the example shown in  FIG. 1 , five modules  22  are stacked to form one module string  24 . 
         [0029]    As shown in  FIG. 2 , a battery structural body included in the module  22  is formed by connecting two or more blocks  26  in series. Each of the blocks  26  is formed by connecting two or more circuits (strings  30 ) in parallel, and each of the strings  30  is formed by connecting two or more battery cells  28  as the secondary batteries in series. For example, eight battery cells  28  are connected in series to form one string  30 ,  12  strings  30  are connected in parallel to form one block  26 , and four blocks  26  are connected in series to form one module  22 . As the secondary battery, a NaS battery, a lithium ion battery, a sodium ion battery, etc. may be used. 
         [0030]    The abnormality detection unit  14  detects abnormal conditions such as a fire based on signals from sensors  32  (heat sensor, smoke sensor, etc.) provided in each of the packages  18 . 
         [0031]    The reporting unit  16  issues a report (abnormality report) indicating occurrence of an abnormality, and transmits the report to a monitoring center, etc., based on an input of an abnormality detection signal Sa (signal indicating occurrence of an abnormality) from the abnormality detection unit  14 . In this case, the report may be transmitted through a public communications network such as the Internet or a mobile phone network. Further, the report may be transmitted to a local user, a local administrator, etc, instead of and/or in addition to the monitoring center. 
         [0032]    Further, the reporting unit  16  outputs an operation stop signal Sb to the battery control device  20  in addition to the above report, based on the input of the abnormality detection signal Sa from the abnormality detection unit  14 . The battery control device  20  stops operation of the secondary batteries in accordance with a predetermined sequence for stopping operation, based on the operation stop signal Sb. 
         [0033]    Further, as shown in  FIG. 1 , an apparatus for identifying a position of an abnormality according to an embodiment of the present invention (hereinafter referred to as an abnormality identification apparatus  50 ) includes an information transmission unit  52 , an information acquisition unit  54 , a report reception unit  56 , and a module identification unit  58 . 
         [0034]    The information transmission unit  52  has a plurality of current voltage measurement units  60  provided for the respective module strings  24 . As shown in  FIG. 3 , each of the current voltage measurement units  60  includes a plurality of voltage measurement units  62  provided for the respective modules  22 , one current measurement unit  64 , and one transmission file creation unit  66 . 
         [0035]    The voltage measurement unit  62  has block voltage measurement units  68  provided for the respective blocks  26 . Each of the block voltage measurement units  68  measures the voltage across both ends of the corresponding block  26  in accordance with a predetermining monitoring cycle. For example, the block voltage measurement unit  62  measures the voltage across both ends of the corresponding block  26  at a time interval arbitrarily selected in a range from 0.2 to 2 seconds (e.g., 200 msec interval: monitoring cycle). 
         [0036]    The current measurement unit  64  measures the electric current of the corresponding module string  24  (string current value I) through a current measurement line  70  in accordance with the above described monitoring cycle. 
         [0037]    Each of the transmission file creation units  66  creates a transmission file  72  including information of the corresponding module string  24  at each monitoring cycle. For example, the information of the module string  24  includes an identification number of the module string  24  (module string information), present string current value I, information of a plurality of modules  22  included in the module string  24 , etc. For example, the information of the module  22  includes an identification number of the module  22  (module information), identification numbers of a plurality of blocks  26  included in the module  22  (block information), and the present block voltage value V corresponding to the plurality of blocks  26 , respectively. 
         [0038]    As an example of a format of a transmission file  72 , a format of the transmission file  72  associated with the first module string  24  is shown in  FIG. 4 . Specifically, in the order from the beginning, the format of the transmission file  72  includes an identification number (MR 1 ) of the first module string  24 , a present string current value I in the first module string  24 , and information of a plurality of modules  22  included in the first module string  24 . 
         [0039]    As an example of the information of the module  22 , the format of information of the first module  22  includes an identification number (M 1 ) of the first module  22 , and information of a plurality of blocks  26  included in this module  22 . 
         [0040]    For example, the information of the plurality of blocks  26  includes the following items of information:
       (a1) Identification number (B1) of the first block  26     (a2) Present block voltage value V of the first block  26     (a3) Identification number (B2) of the second block  26     (a4) Present block voltage value V of the second block  26     (a5) Identification number (B3) of the third block  26     (a6) Present block voltage value V of the third block  26     (a7) Identification number (B4) of the fourth block  26     (a8) Present block voltage value V of the fourth block  26         
 
         [0049]    In the meanwhile, with regard to the module string  24  which lost correlation between the block voltage value and the string current value, among the plurality of module strings  24 , the information acquisition unit  54  acquires information of the module  22  accommodating the block  26  which satisfies the following conditions.
       (b1) The present time is within a predetermined period around a time point at which the above described correlation is lost.   (b2) Among the plurality of modules  22  included in this module string  24 , a module  22  accommodating a block  26  where the difference (differential voltage value ΔV) between the present block voltage value V and the block voltage value Vr with a first-order lag has been changed to exceed a predetermined voltage threshold value Vth       
 
         [0052]    Specifically, as shown in  FIG. 5 , the information acquisition unit  54  includes an information request unit  74 , a voltage comparator unit  76 , correlation determination unit  78 , a time comparator unit  80 , an alarm information creation unit  82 , an alarm information storage unit  84 , and an alarm information output unit  86 . 
         [0053]    The information request unit  74  requests each of the current voltage measurement units  60  of the information transmission unit  52  to transmit information at each monitoring cycle. Upon the transmission request of information from the information request unit  74 , each of the current voltage measurement units  60  transmits the transmission file  72  including information of the corresponding module string  24 , to the information acquisition unit  54 . 
         [0054]    The voltage comparator unit  76  includes a plurality of first voltage comparator circuits  88  provided in correspondence with the plurality of blocks  26 . Likewise, the time comparator unit  80  includes a plurality of time comparator circuits  90  provided in correspondence with the plurality of blocks  26 . 
         [0055]    The first voltage comparator circuit  88  will be described taking one block  26  as an example. As shown in  FIG. 6 , the difference (differential voltage value ΔV) between the block voltage V of the block  26  included in the acquired transmission file  72  and the block voltage Vr with the first-order lag is calculated. If the differential voltage value ΔV is equal to or greater than the predetermined voltage threshold value Vth, the first voltage comparator circuit  88  outputs an event signal Se to the corresponding time comparator circuit  90 . In the first-order lag function 1−e −(t/TL) , one monitoring cycle (e.g., 200 msec) may be selected as “t”. For example, the time constant TL may be selected in accordance with the behavior where the corresponding string  30  is insulated, and the block voltage V drops temporarily due to short circuiting of one battery cell  28 . For example, a time period selected from, e.g., from 20 to 60 seconds (e.g., 40 seconds) may be adopted arbitrarily. Further, as the voltage threshold value Vth, for example, a voltage value of a temporary drop due to short circuiting of one battery cell  28 , e.g., 200 mV may be selected. 
         [0056]    As shown in  FIG. 5 , the correlation determination unit  78  includes a plurality of correlation determination circuits  92  provided in correspondence with the plurality of blocks  26  (see  FIG. 2 ). 
         [0057]    The correlation determination circuit  92  will be described taking one block  26  as an example. As shown in  FIG. 6 , the correlation determination circuit  92  includes a second voltage comparator circuit  94 , a current comparator circuit  96 , a differential voltage accumulation unit  98 , a differential current accumulation unit  100 , a correlation coefficient computation unit  102 , and a determination unit  104 . 
         [0058]    As in the case of the above described first voltage comparator circuit  88 , the second voltage comparator circuit  94  calculates the difference (differential voltage value ΔV) between the block voltage V of the block  26  included in the acquired transmission file  72  and the block voltage Vr with the first-order lag. 
         [0059]    The current comparator circuit  96  calculates the difference (differential current value Δl) between the string current value I of the module string  24  included in the acquired transmission file  72  and the string current value Ir with the first-order lag. 
         [0060]    In each of the first-order lag functions 1−e −(t/TL) , t and TL in the above described second voltage comparator circuit  94  and the current comparator circuit  96  have the same values as those of the first voltage comparator circuit  88 . Specifically, one monitoring cycle (e.g., 200 msec) may be selected as “t”. For example, 40 seconds may be selected as the time constant TL. It is a matter of course that values which are different from those of the first voltage comparator circuit  88  may be selected. For example, the first voltage comparator circuit  88  may adopt, e.g., one second as “t” of the first-order lag function, and the second voltage comparator circuit  94  and the current comparator circuit  96  may adopt, e.g., 200 msec as “t” of the first-order lag function. The first voltage comparator circuit  88  may be used as the above second voltage comparator circuit  94 , as long as the first-order lag function is the same. 
         [0061]    The differential voltage accumulation unit  98  computes the sum of the differences (differential voltage values ΔV) between the block voltage values V sampled in a predetermined fixed period Tc and the block voltage values Vr with the first-order lag. That is, the differential voltage values ΔV successively outputted from the second voltage comparator circuit  94  are accumulated over the fixed period Tc to obtain the accumulated differential voltage value ΣΔV. For example, a value in a range from 3 to 5 seconds where the number of sampling times is in a range from 10 to 30 inclusive may be selected for the fixed period Tc. 
         [0062]    The differential current accumulation unit  100  computes the sum of differences (differential current values ΔI) between the string current values I sampled in the fixed period Tc and the string current values Ir with the first-order lag. That is, the differential current values ΔI successively outputted from the current comparator circuit  96  are accumulated over the fixed period Tc to obtain the accumulated differential current value ΣΔI. 
         [0063]    The correlation coefficient computation unit  102  divides the accumulated differential voltage value ΣΔV obtained in the differential voltage accumulation unit  98  by the accumulated differential current value ΣΔI obtained in the differential current accumulation unit  100  (ΣΔV/ΣΔI)) to obtain a correlation coefficient Ra in the fixed period Tc. 
         [0064]    In the case where the correlation coefficient Ra obtained in the correlation coefficient computation unit  102  is deviated from a predetermined threshold range Rth, correlation between the block voltage value V and the string current value I is determined as lost, and the determination unit  104  outputs a time comparison instruction signal Sc to a time comparator circuit  90  corresponding to the block  26 . Preferably, the threshold value range Rth is determined based on the I-V (Current-Voltage) characteristics of the block  26 . 
         [0065]    As described above, the time comparator unit  80  (see  FIG. 5 ) includes the plurality of time comparator circuits  90  provided in correspondence with the plurality of blocks  26 . The time comparator circuit  90  will be described taking one block  26  as an example. Specifically, as shown in  FIG. 6 , a time length Ta between the time point at which the event signal Se from the corresponding first voltage comparator circuit  88  is inputted and the time point at which the time comparison instruction signal Sc from the corresponding correlation determination circuit  92  is inputted, is compared with a predetermined time length (predetermined time period Tb). If the time length Ta between these input time points is within the predetermined time period Tb, an event log signal Sel is outputted from the time comparator circuit  90  to the alarm information creation unit  82 . 
         [0066]    No event log signal Sel is outputted in the following cases (c1) to (c3). As the predetermined time period Tb, for example, a time period selected from 3 to 60 seconds (e.g., 10 seconds) may be adopted arbitrarily.
       (c1) Case where the time length Ta between the input time points exceeds the predetermined time period Tb   (c2) Case where no time comparison signal Sc is inputted even after elapse of the predetermined time period Tb from the input time point of the event signal Se from the corresponding first voltage comparator circuit  88 .   (c3) Case where no event signal Se is inputted even after elapse of the predetermined time period Tb from the input time point of the time comparison instruction signal Sc from the corresponding correlation determination circuit  92 .       
 
         [0070]    The alarm information creation unit  82  creates alarm information data  106  based on the input of the event log signal Sel outputted from the time comparator unit  80 , and transmits the alarm information data  106  to the alarm information storage unit  84  and the alarm information output unit  86 . For example, the following items of information are registered as the alarm information data  106 .
       (d1) Identification number of the module string  24  accommodating the block  26  corresponding to the time comparator circuit  90  as an output source of the event log signal Sel (module string information)   (d2) Identification number of the module  22  (module information)   (d3) Identification number of the block  26  (block information)       
 
         [0074]    For example, as shown in  FIG. 7 , as one piece of alarm information data  106 , from the beginning part, the present date (year, month, day), the present time (hour, minute), the module string information, the module information, the block information, and the present block voltage value V are stored. 
         [0075]    The alarm information storage unit  84  stores the alarm information data  106  created by the alarm information creation unit  82  in a memory  108  which adopts a stack method (last-in first-out method). Therefore, the alarm information data  106  retrieved from the memory  108  is the latest alarm information data  106 . 
         [0076]    The alarm information output unit  86  converts the alarm information data  106  transmitted successively from the alarm information creation unit  82  into display data and printing data, and outputs these items of data to a monitor  110  and a printer  112 , respectively, together with an error message (such as a message “SHORT-CIRCUITING ABNORMALITY”). Consequently, the alarm information (year, month, day, time, module string information, module information, block information, present block voltage value V) is displayed together with the error message on the monitor  110 , and printed by the printer  112  together with the error message. 
         [0077]    In the meanwhile, as shown in  FIG. 1 , the report reception unit  56  receives the report (abnormality report) indicating occurrence of an abnormality from the reporting unit  16 . Specifically, when the report reception unit  56  receives the abnormality report, the report reception unit  56  starts operation of the module identification unit  58 . 
         [0078]    The module identification unit  58  identifies, among the plurality of modules  22 , a module  22  corresponding to the module string information and the module information registered in the latest alarm information data  106  as a module  22  having the abnormality. 
         [0079]    Specifically, operation of the module identification unit  58  is started by the report reception unit  56 , and the module identification unit  58  identifies, as a module  22  having the abnormality, the module  22  corresponding to the module string information and the module information registered in the latest alarm information data  106  stored in the memory  108 . The identified module  22  is notified to, e.g., an operator by outputting the module information and the error message (for example, “ACCIDENT IN THE FIRST MODULE”) to the monitor  110  and/or the printer  112 . Further, preferably, an image with a symbol indicating occurrence of the accident may be displayed on the monitor  110 , or printed on a printing paper, together with a schematic image of the secondary battery storage unit  12 , at the position of the identified module  22 . In this manner, the position of the identified module  22  can be recognized at a glance. 
         [0080]    Next, processing operation of the abnormality identification apparatus  50  according to the embodiment of the present invention will be described with reference to flow charts in  FIGS. 8 and 9 . 
         [0081]    Firstly, in step S 1  of  FIG. 8 , the information request unit  74  requests each of the current voltage measurement units  60  of the information transmission unit  52  to transmit information. Upon the transmission request of information from the information request unit  74 , each of the current voltage measurement units  60  transmits a transmission file  72  including information of the corresponding module string  24  to the information acquisition unit  54 . 
         [0082]    In step S 2 , the information acquisition unit  54  receives the transmission file  72  from each of the current voltage measurement units  60 . 
         [0083]    In step S 3 , the voltage comparator unit  76  of the information acquisition unit  54  calculates the difference (differential voltage value ΔV) between the block voltage V and the corresponding block voltage Vr with a first-order lag for each and all of the blocks  26  in the acquired transmission file  72 . 
         [0084]    In step S 4 , the voltage comparator unit  76  outputs an event signal Se to the time comparator circuit  90  corresponding to the block  26  having the differential voltage value ΔV equal to or greater than the voltage threshold value Vth, among all of the blocks  26 . 
         [0085]    In the meanwhile, in step S 5 , the correlation determination unit  78  of the information acquisition unit  54  determines correlation between the block voltage value V and the string current value I. The correlation determination unit  78  determines the correlation between the block voltage value V and the string current value I based on the difference (differential voltage value ΔV) between the block voltage V and the corresponding block voltage Vr with the first-order lag, and the difference (differential current value ΔI) between the string current value I and the corresponding string current value Ir with the first-order lag, for each and all of the blocks  26  in the acquired transmission file  72 . 
         [0086]    Specifically, for all of the blocks  26 , processing in steps S 5   a  to S 5   f  as shown in  FIG. 9  is performed. That in step S 5   a  of  FIG. 9 , the differential voltage accumulation unit  98  accumulates differences (differential voltage values ΔV) between block voltage values V sampled in a predetermined fixed period Tc and block voltage values Vr with the first-order lag to obtain an accumulated differential voltage value ΣΔV. In step S 5   b , the differential current accumulation unit  100  accumulates the differences (differential current values ΔI) between string current values I sampled in the fixed period To and string current value Ir with the first-order lag to obtain an accumulated differential current value ΣΔI. In step S 5   c , the correlation coefficient computation unit  102  divides the accumulated differential voltage value ΣΔV by the accumulated differential current value ΣΔI to obtain the correlation coefficient Ra in the fixed period Tc. In step S 5   d , the determination unit  104  compares the correlation coefficient Ra obtained in the correlation coefficient computation unit  102  with the predetermined threshold value range Rth. In step S 5   e , if it is determined that the correlation coefficient Ra is deviated from the threshold value range Rth, the control proceeds to step S 5   f  to determine that correlation between the block voltage value V and the string current value I has been lost, and outputs a time comparison instruction signal Sc to the time comparator circuit  90  corresponding to the block. 
         [0087]    Referring back to the main routine in  FIG. 8 , in the next step S 6 , among the time comparator circuits  90  included in the time comparator unit  80 , a time comparator circuit  90  which received the inputs of the event signal Se and the time comparison instruction signal Sc compares the time length Ta between the input time point of the event signal Se and the input time point of the time comparison instruction signal Sc with the predetermined time length (predetermined time period Tb). 
         [0088]    In step S 7 , if it is determined that the time length Ta between the input time points is within the predetermined time period Tb, the control proceeds to step S 8  to output an event log signal Sel from the time comparator circuit  90  to the alarm information creation unit  82 . 
         [0089]    In step S 9 , the alarm information creation unit  82  creates the alarm information data  106 . Specifically, the alarm information creation unit  82  creates the alarm information data  106  having registrations of the following items of information or the like.
       (e1) Present date and time   (e2) Identification number of the module string  24  accommodating the block  26  corresponding to the time comparator circuit  90  as an output source of the event log signal Sel (module string information)   (e3) Identification number of the module  22  (module information)   (e4) Identification number of the block  26  (block information)       
 
         [0094]    In step S 10 , the alarm information output unit  86  converts the created alarm information data  106  into display data and printing data, and outputs these items of data to the monitor  110  and the printer  112 , respectively, together with an error message (such as a message “SHORT-CIRCUITING ABNORMALITY”). 
         [0095]    In step S 11 , the alarm information storage unit  84  stores the alarm information data  106  created by the alarm information creation unit  82  in the memory  108  which adopts a stack method (last-in first-out method). 
         [0096]    When the process in step S 11  is finished, or in step S 7 , if it is determined that the time length Ta between the input time points exceeds the predetermined time period Tb, in step S 12 , the report reception unit  56  determines whether there is any report (abnormality report) indicating occurrence of an abnormality from the reporting unit  16 . If no abnormality report has been received, the routine returns to step S 1  to repeat the processes of step S 1  and the subsequent steps. 
         [0097]    If any abnormality report has been received, the routine proceeds to the next step S 13  to perform operation in the module identification unit  58 . Specifically, the module identification unit  58  identifies, as a module  22  having the abnormality, a module  22  corresponding to the module string information and the module information registered in the latest alarm information data  106  stored in the memory  108 . Then, the module identification unit  58  outputs the module information and the error message regarding the identified module  22  to the monitor  110  and/or the printer  112 . 
         [0098]    In step S 14 , it is determined whether or not there is a request for stopping operation of the information acquisition unit  54  (e.g., end request due to interruption of the power supply, maintenance operation, etc.). If there is no request for stopping operation, the routine returns to step S 1  to repeat the processes of step S 1  and the subsequent steps. When a request for stopping operation is made, operations of the information acquisition unit  54  are stopped. 
         [0099]    As described above, in the abnormality identification apparatus  50  and the abnormality identification method according to the embodiment of the present invention, the following advantages are obtained. 
         [0100]    Specifically, normally, if external short circuiting or internal short circuiting occurs in any one of the battery cells  28 , the block voltage value V of the block  26  including the battery cell  28  having the short circuiting decreased steeply. Thereafter, in some cases, after the elapse of a few minutes, the voltage returns to the original voltage level before short circuiting. Further, if the scale of the system becomes large, the number of blocks to be monitored is increased correspondingly. Therefore, it becomes more difficult to recognize the decrease in the voltage due to short circuiting from the changes of the block voltage values V of all of the blocks  26 . 
         [0101]    Further, when the block voltage value V is decreased temporarily, e.g., by adjustment in the frequency of the electric power system, adjustment in the difference between the generated electric power from natural energy based power generators and its planned output electric power, and adjustment of power demands and power supplies in the electric power system, in some cases, this decrease in the block voltage value V may be detected erroneously as the temporary drop of the block voltage value V due to short circuiting of at least one of the battery cells  28 . 
         [0102]    However, in the embodiment of the present invention, among the plurality of modules  22  included in the module string  24 , information of a module  22  accommodating a block  26  is acquired where the difference (differential voltage value ΔV) between the block voltage value V and the block voltage value Vr with a first-order lag has been changed to exceed a predetermined voltage threshold value Vth in a predetermined time period around a time point at which correlation between the block voltage value V and the string current value I is lost. Consequently, it is possible to accurately detect whether there is a decrease in the block voltage value V, and detect occurrence of an abnormality due to short circuiting. 
         [0103]    In particular, the differences (differential voltage values ΔV) between block voltage values V sampled in a predetermined fixed period Tc and the block voltage values Vr with the first-order lag are accumulated, and the differences (differential current values ΔI) between string current values I sampled in the fixed period Tc and string current values Ir with the first-order lag are accumulated. The obtained accumulated differential voltage value ΣΔV is divided by the obtained accumulated differential current value ΣΔI to obtain the correlation coefficient Ra in the fixed period Tc. In the case where the obtained correlation coefficient Ra is deviated from the predetermined threshold range Rth, correlation between the block voltage value V and the string current value I is determined as lost. In this manner, calculation becomes simple, and it is possible to confirm the presence or absence of correlation between the block voltage value V and the string current value I easily and promptly. It is also possible to achieve acceleration of computation. 
         [0104]    Further, even in the case where the block voltage value V is decreased temporarily due to various adjustment, e.g., listed below, since correlation between the block voltage value V and the string current value I is maintained, such cases can be taken out of consideration at the time of detection, and such a detection is not recognized as the temporal drop in the block voltage value V due to short circuiting of at least one of the battery cells  28 .
       (f1) Frequency adjustment in the power system   (f2) Adjustment in the difference between the generated electric power from natural energy based power generators and its planned output electric power   (f3) adjustment of power demands and power supplies in the power system       
 
         [0108]    Further, the alarm information data  106  is created based on information of the acquired module  22 , and at the time of receiving the abnormality report in the report reception unit  56 , a module  22  corresponding to at least the latest alarm information data  106  is identified as a module  22  having the abnormality. In this manner, by identifying the module  22  which is the source of the abnormality, it becomes possible to transmit a report to a local user, a local administrator, etc. Therefore, countermeasures focused on the identified abnormality source can be taken at an early stage. It becomes possible to suppress expansion of the damage. 
         [0109]    Further, the time constant of the first-order lag is selected according to the behavior of the temporary drop in the block voltage V due to short circuiting of at least one of the battery cells  28 . Further, as the voltage threshold value Vth, for example, a voltage value for the temporary voltage drop in the block voltage V due to short circuiting of at least one of the battery cells  28  is selected. In this manner, it is possible to improve the detection accuracy of the block  26  having a temporary drop in the block voltage V due to short circuiting of at least one the battery cells  28 . 
         [0110]    It is a matter of course that the apparatus, the method, and the non-transitory recording medium storing the program for identifying a position of an abnormality occurred in a secondary battery system according to the present invention is not limited to the embodiments described above, and various structures can be adopted without deviating from the gist of the present invention.