Patent Publication Number: US-2013241480-A1

Title: Battery control device, battery system, electric vehicle, movable body, power storage device, and power supply device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT/JP2011/001287, filed on 4 Mar. 2011. Priority under 35 U.S.C. §119(a) and 35 U.S.C. §365(b) is claimed from Japanese Application No. 2010-050788, filed 8 Mar. 2010, the disclosure of which are also incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a battery control device, and a battery system, an electric vehicle, a movable body, a power storage device, and a power supply device including the same. 
     BACKGROUND ART 
     In movable bodies such as an electric automobile including a plurality of battery cells capable of charge and discharge, a battery control device for controlling charge and discharge of the battery cells is provided. The battery control device includes a voltage detector that detects a terminal voltage of the battery cell and a controller that performs various control operations based on the terminal voltage detected by the voltage detector (see, e.g., Patent Document 1). 
     [Patent Document 1] JP 2000-173674 A 
     SUMMARY OF INVENTION  
     Technical Problem 
     In the above-mentioned battery control device, a configuration for detecting the terminal voltage of the battery cell becomes complicated. 
     An object of the present invention is to provide a battery control device capable of preventing the precision of charge/discharge control of a battery cell from decreasing while being prevented from becoming complex in configuration and increasing in cost, and a battery system, an electric vehicle, a movable body, a power storage device, and a power supply device including the same. 
     Solution to Problem 
     According to an aspect of the present invention, a battery control device for performing charge/discharge control of a plurality of battery cells includes a voltage detector that detects a terminal voltage of each of the plurality of battery cells, and a controller that is connected to the voltage detector via a communication line, in which the controller includes a voltage calculator that calculates, based on currents respectively flowing through the plurality of battery cells, a terminal voltage of each of the battery cells, and a control value calculator that calculates a control value for controlling charge or discharge of the plurality of battery cells using one of the terminal voltage detected by the voltage detector and the terminal voltage calculated by the voltage calculator. 
     In the battery control device, the terminal voltage detected by the voltage detector is fed to the controller via the communication line. In the controller, the voltage calculator calculates, based on the currents flowing through the plurality of battery cells, the terminal voltage of each of the battery cells. The control value calculator calculates the control value for controlling the charge/discharge of the plurality of battery cells using one of the terminal voltage detected by the voltage detector and the terminal voltage calculated by the voltage calculator. 
     In this case, one of the terminal voltage detected by the voltage detector and the terminal voltage calculated by the voltage calculator can be selectively used. Even when the terminal voltage detected by the voltage detector cannot be used because the communication line is disconnected, for example, the control value can be calculated using the terminal voltage calculated based on the currents flowing through the plurality of battery cells by the voltage calculator. As a result, the reliability of the battery control device can be improved. 
     The control value calculator may calculate the control value using the terminal voltage calculated by the voltage calculator when it cannot receive the terminal voltage detected by the voltage detector. 
     In this case, the control value calculator can calculate the control value using the terminal voltage detected by the voltage detector when it can receive the terminal voltage detected by the voltage detector. The control value calculator can reliably calculate the control value in a simple configuration using the terminal voltage calculated by the voltage calculator even when it cannot receive the terminal voltage detected by the voltage detector because the communication line is disconnected, for example. 
     According to another aspect of the present invention, a battery control device for performing charge/discharge control of a plurality of battery cells includes a voltage calculator that calculates, based on currents respectively flowing through the plurality of battery cells, a terminal voltage of each of the battery cells, and a control value calculator that calculates a control value for controlling charge/discharge of the plurality of battery cells using the terminal voltage calculated by the voltage calculator. 
     In the battery control device, the voltage calculator calculates, based on the currents flowing through the plurality of battery cells, the terminal voltage of each of the battery cells. The control value calculator calculates the control value for controlling the charge/discharge of the plurality of battery cells using the terminal voltage calculated by the voltage calculator. 
     Thus, the control value can be calculated, based on the currents flowing through the plurality of battery cells, using the terminal voltage of each of the battery cells calculated in a simple configuration without providing the battery control device with the voltage detector for detecting the terminal voltage of the battery cell. Therefore, the precision of the charge/discharge control of each of the battery cells can be prevented from decreasing while preventing the battery control device from becoming complex in configuration and increasing in cost. 
     The battery control device may further include a range determiner that determines whether the terminal voltage of each of the plurality of battery cells belongs to a predetermined voltage range, and the voltage calculator may correct the terminal voltage of each of the battery cells based on a result of the determination by the range determiner. 
     In this case, the calculated terminal voltage is corrected based on the result of the determination whether the voltage of each of the battery cells belongs to the predetermined voltage range. Thus, a more accurate terminal voltage of each of the battery cells can be obtained while preventing the battery control device from becoming complex in configuration and increasing in cost. 
     The range determiner may determine whether the terminal voltage of each of the battery cells belongs to the voltage range based on a comparison result between a reference voltage and the terminal voltage of the battery cell. 
     In this case, it can be determined whether the terminal voltage of each of the battery cells belongs to the voltage range by adding the reference voltage in an existing configuration used to compare an upper-limit voltage at which the battery cell is not overcharged or a lower-limit voltage at which the battery cell is not overdischarged with the terminal voltage of the battery cell, for example. Thus, the configuration of the battery control device can be prevented from becoming complex. 
     The range determiner may compare the upper-limit voltage at which each of the battery cells is not overcharged and the terminal voltage of the battery cell while comparing the lower-limit voltage at which the battery cell is not overdischarged and the terminal voltage of the battery cell, and the battery control device may further include a stop controller that controls the stop of the charge/discharge of the plurality of battery cells based on a comparison result by the range determiner. 
     In this case, each of the plurality of battery cells can be prevented from being overcharged and overdischarged by stopping the charge/discharge of the plurality of battery cells at the time point where the terminal voltage of at least one of the battery cells has reached the upper-limit voltage or the lower-limit voltage. Thus, the safety of each of the battery cells can be ensured. 
     The common range determiner can determine whether the terminal voltage of each of the battery cells belongs to a predetermined voltage range while determining whether the terminal voltage of at least one of the battery cells has reached the upper-limit voltage or the lower-limit voltage. Thus, each of the battery cells can be prevented from being deteriorated by being overcharged or overdischarged while preventing the battery control device from becoming complex in configuration and increasing in cost. 
     According to still another aspect of the present invention, a battery system includes a plurality of battery cells, and the above-mentioned battery control device for performing charge/discharge control of the plurality of battery cells. 
     In the battery system, the above-mentioned battery control device calculates the control value for performing charge/discharge control of the plurality of battery cells based on currents flowing through the plurality of battery cells. Thus, the reliability of the battery control device can be improved while preventing the battery control device from becoming complex in configuration and increasing in cost. Alternatively, the precision of the charge/discharge control of each of the battery cells can be prevented from decreasing while preventing the battery control device from becoming complex in configuration and increasing in cost. 
     According to still another aspect of the present invention, an electric vehicle includes a plurality of battery cells, the above-mentioned battery control device for performing charge/discharge control of the plurality of battery cells, a motor that is driven with electric power from the plurality of battery cells, and a drive wheel that rotates with a torque generated by the motor. 
     In the electric vehicle, the motor is driven with the electric power from the plurality of battery cells. The drive wheel rotates with the torque generated by the motor so that the electric vehicle moves. 
     The above-mentioned battery control device calculates the control value for controlling charge/discharge of the plurality of battery cells based on currents flowing through the plurality of battery cells. Thus, the reliability of the battery control device can be improved while preventing the battery control device from becoming complex in configuration and increasing in cost. Alternatively, the precision of the charge/discharge control of each of the battery cells can be prevented from decreasing while preventing the battery control device from becoming complex in configuration and increasing in cost. As a result, the traveling performance of the electric vehicle can be improved. 
     According to still another aspect of the present invention, a movable body includes the above-mentioned battery system, a main movable body, a power source that converts electric power from the battery system into drive power upon receipt of the electric power, and a driver that moves the main movable body with the drive power obtained in the conversion by the power source. 
     In the movable body, the power source converts the electric power from the above-mentioned battery system into the drive power, and the driver moves the main movable body with the drive power. In this case, the above-mentioned battery system is used so that the precision of the charge/discharge control of each of the battery cells can be prevented from decreasing while preventing the battery control device from becoming complex in configuration and increasing in cost. 
     According to still another aspect of the present invention, a power storage device includes the above-mentioned battery system, and a system controller that performs control relating to charge or discharge of the plurality of battery cells in the battery system. 
     In the power storage device, the system controller performs control relating to the charge or discharge of the plurality of battery cells. Thus, the plurality of battery cells can be prevented from being degraded, overcharged, and overdischarged. 
     The above-mentioned battery system is used so that the precision of the charge/discharge control of each of the battery cells can be prevented from decreasing while preventing the battery control device from becoming complex in configuration and increasing in cost. 
     According to still another aspect of the present invention, a power supply device connectable to an external object includes the above-mentioned power storage device, and a power conversion device that is controlled by the system controller in the power storage device and converts electric power between the plurality of battery cells in the power storage device and the external object. 
     In the power supply device, the power conversion device performs electric power conversion between the plurality of battery cells and the external object. The system controller in the power storage device controls the power conversion device so that control relating to the charge or discharge of the plurality of battery cells is performed. Thus, the plurality of battery cells can be prevented from being deteriorated, overdischarged, and overcharged. 
     The above-mentioned battery system is used so that the precision of the charge/discharge control of each of the battery cells can be prevented from decreasing while preventing the battery control device from becoming complex in configuration and increasing in cost. 
     Advantageous Effects of Invention 
     According to the present invention, the precision of charge/discharge control of each of battery cells can be prevented from decreasing while preventing a battery control device from becoming complex in configuration and increasing in cost. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating a configuration of a battery control device according to a first embodiment and a battery system including the same. 
         FIG. 2  is a block diagram illustrating a configuration of a voltage detector. 
         FIG. 3  is a block diagram illustrating a configuration of a range determiner, a voltage calculator, and a current detector. 
         FIG. 4  is a flowchart illustrating voltage range determination processing performed by a determination controller. 
         FIG. 5  is a diagram illustrating a state of each switching element. 
         FIG. 6  is a diagram illustrating a relationship between a terminal voltage of a battery cell and a voltage range. 
         FIG. 7  is a diagram illustrating a relationship between a comparison result of a comparator and a voltage range. 
         FIG. 8  is a block diagram illustrating a configuration of an overcharge/overdischarge detector illustrated in  FIG. 3 . 
         FIG. 9  is a flowchart illustrating SOC calculation processing performed by a battery control device. 
         FIG. 10  is a flowchart illustrating SOC calculation processing performed by a battery control device. 
         FIG. 11  is a flowchart illustrating SOC calculation processing performed by a battery control device. 
         FIG. 12  illustrates a relationship between an SOC and an OCV of an i-th battery cell. 
         FIG. 13  is a flowchart illustrating battery control value calculation processing performed by a control value calculator. 
         FIG. 14  is a flowchart illustrating battery control value calculation processing performed by a control value calculator. 
         FIG. 15  is a block diagram illustrating a configuration of a battery control device according to a second embodiment and a battery system including the same. 
         FIG. 16  is a block diagram illustrating a configuration of a battery control device according to a third embodiment and a battery system including the same. 
         FIG. 17  is a block diagram illustrating a configuration of an electric automobile according to a fourth embodiment. 
         FIG. 18  is a block diagram illustrating a configuration of a power supply device according to a fifth embodiment. 
         FIG. 19  is a perspective view of a rack that houses a plurality of battery systems  500 . 
         FIG. 20  is a diagram illustrating an arrangement example of a service plug. 
         FIG. 21  is a diagram illustrating another arrangement example of a service plug. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The embodiments of the present invention will be described in detail referring to the drawings. The embodiments below describe a battery control device, a battery system, an electric vehicle, a movable body, a power storage device, and a power supply device. The battery control device according to the present embodiment is used as one of constituent elements of the battery system installed in an electric vehicle or a power supply device using electric power as a driving source. The electric vehicle includes a hybrid electric vehicle, a battery electric vehicle, and a plug-in hybrid electric vehicle. In the present embodiment, the electric vehicle is a hybrid electric vehicle. 
     In the following description, an amount of electric charges stored in a battery cell in a full charge state is referred to as a full charging capacity. An amount of electric charges stored in the battery cell in any state is referred to as a remaining capacity. Further, the ratio of the remaining capacity to the full charging capacity of the battery is referred to as a state of charge (SOC). 
     (1) First Embodiment 
     A battery control device and a battery system according to a first embodiment of the present invention will be described. 
     (1-1) Configuration of Battery Control Device and Battery System 
       FIG. 1  is a block diagram illustrating a configuration of a battery control device according to a first embodiment and a battery system including the same. In the present embodiment, a battery system  500  includes a plurality of battery modules  100 , a battery electronic control unit (hereinafter referred to as a battery ECU)  101 , a contactor  102 , and a current sensor  103 , and is connected to a main controller  300  in an electric vehicle. 
     The plurality of battery modules  100  are connected to one another, respectively, via power supply lines  501 . Each of the battery modules  100  includes a plurality of battery cells  10  and a detection unit  20 . A secondary battery such as a lithium-ion battery is used as the battery cell  10 . The plurality of battery cells  10  in each of the battery modules  100  are connected in series. The detection unit  20  includes a range determiner  201  and a voltage detector  202 . A positive electrode terminal and a negative electrode terminal of each of the battery cells  10  are respectively connected to the range determiner  201  and the voltage detector  202  via terminals T 1  of the detection unit  20 . The range determiner  201  is connected to a terminal T 2 , and the voltage detector  202  is connected to a terminal T 3 . Details of the range determiner  201  and the voltage detector  202  will be described below. 
     Power supply lines  501  are respectively connected to the battery cells  10  arranged at both ends of each of the battery modules  100 . Thus, all the battery cells  10  in each of the plurality of battery modules  100  are connected in series. The current sensor  103  and the contactor  102  are inserted into the power supply line  501  connected to the battery module  100  at one end. When the contactor  102  is turned off, no current flows through all the battery cells  10 . The power supply line  501  connected to the battery module  100  at the one end and the power supply line  501  connected to the battery module  100  at the other end are connected to a load such as a motor of the electric vehicle. 
     The range determiner  201  and the voltage detector  202  in each of the detection units  20  are provided on a common circuit board. The battery ECU  101  is provided on another circuit board. One end of a transmission line D 1  is connected to the terminal T 2  of the detection unit  20  in each of the battery modules  100 . The other end of the transmission line D 1  is connected to each of terminals T 5  of the battery ECU  101 . One end of a communication line D 2  is connected to the terminal T 3  of the detection unit  20  in each of the battery modules  100 . The other end of each of the plurality of communication lines D 2  is connected to one end of a communication line D 3 . The other end of the communication line D 3  is connected to a terminal T 6  of the battery ECU  101 . The terminal T 3  of each of the detection units  20  may be cascade-connected to the terminal T 6  of the battery ECU  101  via a bus serving as a communication line. The terminal T 3  of each of the detection units  20  may be connected to the terminal T 6  of the battery ECU  101  in another connection format such as a star connection. The current sensor  103  is connected to a terminal T 7  of the battery ECU  101  via a transmission line D 4 . 
     The battery ECU  101  includes a control value calculator  211 , a voltage calculator  212 , a current detector  213 , a storage  214 , and a stop controller  215 , and is connected to the main controller  300  in the electric vehicle. The battery ECU  101  controls ON/OFF of the contactor  102  while giving a value for charge/discharge control of each of the battery cells  10  to the main controller  300  in the electric vehicle. Details of the battery ECU  101  will be described below. 
     In the battery system  500  illustrated in  FIG. 1 , the detection units  20  in the plurality of battery modules  100 , the battery ECU  101 , the transmission lines D 1 , and the communication lines D 2  and D 3  constitute a battery control device  400 . 
     (1-2) Voltage Detector 
       FIG. 2  is a block diagram illustrating a configuration of the voltage detector  202  illustrated in  FIG. 1 . As illustrated in  FIG. 2 , the voltage detector  202  includes a plurality of differential amplifiers  321 , a multiplexer  322 , and an A/D converter (Analog-to-Digital Converter)  323 . 
     Each of the differential amplifiers  321  has two input terminals and an output terminal. Each of the differential amplifiers  321  differentially amplifies voltages respectively input to the two input terminals, and outputs the amplified voltages from the output terminal. The two input terminals of each of the differential amplifiers  321  are respectively connected to a positive electrode terminal and a negative electrode terminal of each of the battery cells  10  via terminals T 1 . 
     Each of the differential amplifiers  321  differentially amplifies a voltage at each of the battery cells  10 . Respective output voltages of the plurality of differential amplifiers  321  are fed to the multiplexer  322 . The multiplexer  322  sequentially outputs the output voltages of the plurality of differential amplifiers  321  to the A/D converter  323 . The A/D converter  323  converts an output voltage of the multiplexer  322  into a digital value. The digital value obtained by the A/D converter  323  represents a terminal voltage of each of the battery cells  10 . 
     Thus, the voltage detector  202  has the function of detecting the terminal voltage of each of the battery cells  10  with high precision. The detected terminal voltage is transmitted for each predetermined period of time (e.g., several milliseconds) to the control value calculator  211  in the battery ECU  101  via the communication lines D 2  and D 3  illustrated in  FIG. 1 . 
     (1-3) Details of Range Determiner, Voltage Calculator, and Current Detector 
       FIG. 3  is a block diagram illustrating a configuration of the range determiner  201 , the voltage calculator  212 , and the current detector  213  illustrated in  FIG. 1 . In an example illustrated in  FIG. 3 , only the range determiner  201  in one of the plurality of battery modules  100  is illustrated for simplicity of illustration. In the example illustrated in  FIG. 3 , the battery module  100  includes two battery cells  10 . V 1  denotes a terminal voltage of one of the battery cells  10 , and V 2  denotes a terminal voltage of the other battery cell  10 . 
     As illustrated in  FIG. 3 , the current detector  213  includes an A/D (Analog-to-Digital) converter  231  and a current value calculator  232 . The current sensor  103  outputs a value of a current flowing through each of the battery modules  100  as a voltage. The A/D converter  231  converts an output voltage of the current sensor  103  into a digital value. The current value calculator  232  calculates the value of the current based on the digital value obtained by the A/D converter  231 . 
     The range determiner  201  includes a reference voltage unit  221 , a differential amplifier  222 , a comparator  223 , a determination controller  224 , a plurality of switching elements SW 01 , SW 02 , SW 11 , SW 12 , SW 21 , SW 22 , SW 31 , SW 32 , and SW 100 , and a capacitor C 1 . Each of the switching elements SW 01 , SW 02 , SW 11 , SW 12 , SW 21 , SW 22 , SW 31 , SW 32 , and SW 100  is composed of a transistor, for example. 
     The differential amplifier  222  has two input terminals and an output terminal. The switching element SW 01  is connected between the positive electrode terminal of one of the battery cells  10  and a node N 1 , and the switching element SW 02  is connected between the positive electrode terminal of the other battery cell  10  and the node N 1 . The switching element SW 11  is connected between the negative electrode terminal of one of the battery cells  10  and a node N 2 , and the switching element SW 12  is connected between the negative electrode terminal of the other battery cell  10  and the node N 2 . The switching element SW 21  is connected between the node N 1  and a node N 3 , and the switching element SW 22  is connected between the node N 2  and a node N 4 . The capacitor C 1  is connected between the node N 3  and the node N 4 . The switching element SW 31  is connected between the node N 3  and one of the input terminals of the differential amplifier  222 , and the switching element SW 32  is connected between the node N 4  and the other input terminal of the differential amplifier  222 . The differential amplifier  222  differentially amplifies voltages respectively input to the two input terminals, and outputs the amplified voltages from the output terminal. An output voltage of the differential amplifier  222  is fed to one of input terminals of the comparator  223 . 
     The switching element SW 100  has a plurality of terminals CP 0 , CP 1 , CP 2 , CP 3 , and CP 4 . The reference voltage unit  221  includes four reference voltage outputters  221   a,    221   b,    221   c,  and  221   d . The reference voltage outputters  221   a  to  221   d  respectively output a lower-limit voltage Vref_UV, a lower-side intermediate voltage Vref 1 , an upper-side intermediate voltage Vref 2 , and an upper-limit voltage Vref_OV as reference voltages to the terminals CP 1 , CP 2 , CP 3 , and CP 4 . The upper-limit voltage Vref_OV is higher than the upper-side intermediate voltage Vref 2 , the upper-side intermediate voltage Vref 2  is higher than the lower-side intermediate voltage Vref 1 , and the lower-side intermediate voltage Vref 1  is higher than the lower-limit voltage Vref_UV. The lower-side intermediate voltage Vref 1  is 3.70 [V], for example, and the upper-side intermediate voltage Vref 2  is 3.75 [V], for example. 
     The switching element SW 100  is switched so that one of the plurality of terminals CP 1  to CP 4  is connected to the terminal CP 0 . The terminal CP 0  of the switching element SW 100  is connected to the other input terminal of the comparator  223 . The comparator  223  compares the magnitudes of the voltages input to the two input terminals, and outputs a signal representing a comparison result from the output terminal. 
     In this example, when the output voltage of the differential amplifier  222  is not less than a voltage at the terminal CP 0 , the comparator  223  outputs a logical “1” (e.g., high-level) signal. When the output voltage of the differential amplifier  222  is lower than the voltage at the terminal CP 0 , the comparator  223  outputs a logical “0” (e.g., low-level) signal. 
     The determination controller  224  controls switching among the plurality of switching elements SW 01 , SW 02 , SW 11 , SW 12 , SW 21 , SW 22 , SW 31 , SW 32 , and SW 100  while determining in which of a plurality of voltage ranges a voltage of the battery cell  10  in the battery module  100  exists based on the output signal of the comparator  223 . Voltage range determination processing for the battery cell  10  will be described below. 
     The voltage calculator  212  includes an accumulator  242 , an SOC calculator  243 , an OCV estimator  244 , a voltage estimator  245 , and a voltage corrector  246 . 
     The accumulator  242  acquires respective values of the currents flowing through the plurality of battery cells  10  from the current detector  213  for each predetermined period of time, and accumulates the acquired values of the currents to calculate a current accumulated value. 
     The SOC calculator  243  calculates, based on the SOC of each of the battery cells  10  stored in the storage  214  and the current accumulated value calculated by the accumulator  242 , a value of the SOC at the current time point of the battery cell  10 . The SOC calculator  243  then calculates, based on a value of the SOC fed from the voltage corrector  246 , described below, and the current accumulated value calculated by the accumulator  242 , the SOC at the current time point of each of the battery cells  10 . 
     The OCV estimator  244  estimates, based on the SOC of each of the battery cells  10 , which has been calculated by the SOC calculator  243 , an open voltage (OCV) at the current time point of the battery cell  10 . 
     The voltage estimator  245  estimates, based on the value of the current flowing through each of the plurality of battery cells  10 , which has been calculated by the current value calculator  232 , and the OCV of the battery cell  10 , which has been estimated by the OCV estimator  244 , the terminal voltage at the current time point of the battery cell  10 . 
     The voltage corrector  246  includes a timer (not illustrated). The voltage corrector  246  corrects, based on the voltage range of each of the battery cells  10 , which has been determined by the determination controller  224 , the terminal voltage at the current time point of the battery cell  10 , which has been estimated by the voltage estimator  245 , corrects the OCV at the current time point based on the corrected terminal voltage, and corrects the SOC at the current time point of the battery cell  10  based on the corrected OCV. The voltage corrector  246  feeds the corrected SOC at the current time point of each of the battery cells  10  to the SOC calculator  243  while resetting the current accumulated value calculated by the accumulator  242 . 
     In the present embodiment, the determination controller  224  is implemented by hardware such as a CPU and a memory, and software such as a computer program. In this case, the CPU executes a computer program stored in the memory, to implement functions of the determination controller  224 . A part or the whole of the determination controller  224  may be implemented by hardware such as ASIC (Application Specific Integrated Circuits). 
     Similarly, in the present embodiment, the voltage calculator  212 , the current value calculator  232 , a control value calculator  211 , described below, and a stop controller  215 , described below, are implemented by hardware such as a CPU (Central Processing Unit) and a memory, and software such as a computer program. The accumulator  242 , the SOC calculator  243 , the OCV estimator  244 , the voltage estimator  245 , the voltage corrector  246 , the current value calculator  232 , the control value calculator  211 , and the stop controller  215  correspond to a module of the computer program. In this case, the CPU executes the computer program stored in the memory, to implement functions of the accumulator  242 , the SOC calculator  243 , the OCV estimator  244 , the voltage estimator  245 , the voltage corrector  246 , the current value calculator  232 , the control value calculator  211 , and the stop controller  215 . Some or all of the accumulator  242 , the SOC calculator  243 , the OCV estimator  244 , the voltage estimator  245 , the voltage corrector  246 , the current value calculator  232 , the control value calculator  211 , and the stop controller  215  may be implemented by hardware. 
     (1-4) Voltage Range Determination Processing for Battery Cell 
     Voltage range determination processing for the battery cell  10  by the determination controller  224  will be described.  FIG. 4  is a flowchart illustrating the voltage range determination processing by the determination controller  224 . In the present embodiment, the CPU constituting the determination controller  224  executes a voltage range determination processing program stored in the memory so that the voltage range determination processing is performed.  FIG. 5  is a diagram illustrating states of the switching elements SW 01 , SW 02 , SW 11 , SW 12 , SW 21 , SW 22 , SW 31 , SW 32 , and SW 100 . The determination controller  224  previously stores states illustrated in  FIG. 5  as data. The voltage range determination processing illustrated in  FIG. 4  is started when the determination controller  224  receives a voltage range acquisition signal from the voltage calculator  212 , as described below. 
     As illustrated in  FIGS. 4 and 5 , the determination controller  224  sets the switching elements SW 01 , SW 02 , SW 11 , SW 12 , SW 21 , SW 22 , SW 31 , SW 32 , and SW 100  to states ST 1 , ST 2 , and ST 3  in this order (step S 9 - 1 ). In the states ST 1 , ST 2 , and ST 3 , the switching element SW 100  is switched to the terminal CP 2 . Thus, the lower-side intermediate voltage Vref 1  from the reference voltage outputter  221   b  is fed to the comparator  223 . 
     In the state ST 1 , the switching elements SW 01 , SW 11 , SW 21 , and SW 22  are turned on, and the switching elements SW 02 , SW 12 , SW 31 , and SW 32  are turned off. Thus, the capacitor C 1  is charged with the terminal voltage V 1  of one of the battery cells  10 . 
     In the state ST 2 , the switching elements SW 21  and SW 22  are then turned off. Thus, the capacitor C 1  is separated from the battery cell  10 . 
     Then, in the state ST 3 , the switching elements SW 31  and SW 32  are turned on. Thus, a voltage of the capacitor C 1  is fed as the terminal voltage V 1  of one of the battery cells  10  to the comparator  223 . 
     In this case, the comparator  223  compares the lower-side intermediate voltage Vref 1  and the terminal voltage V 1  of one of the battery cells  10 , and outputs a logical “1” or “0” signal representing a comparison result L 11 . The determination controller  224  acquires the comparison result L 11  of the lower-side intermediate voltage Vref 1  and the terminal voltage V 1  of one of the battery cells  10  (step S 9 - 2 ). 
     The determination controller  224  then sets the switching SW 100  to a state ST 4  (step S 9 - 3 ). In the state ST 4 , the switching element SW 100  is switched to the terminal CP 3 . Thus, the upper-side intermediate voltage Vref 2  from the reference voltage outputter  221   c  is fed to the comparator  223 . 
     In this case, the comparator  223  compares the upper-side intermediate voltage Vref 2  and the terminal voltage V 1  of one of the battery cells  10 , and outputs a logical “1” or “0” signal representing a comparison result L 12 . The determination controller  224  acquires the comparison result L 12  of the upper-side intermediate voltage Vref 2  and the terminal voltage V 1  of one of the battery cells  10  (step S 9 - 4 ). 
     The determination controller  224  then sets the switching elements SW 01 , SW 02 , SW 11 , SW 12 , SW 21 , SW 22 , SW 31 , SW 32 , and SW 100  to states ST 5 , ST 6 , ST 7 , and ST 8  in this order (step S 9 - 5 ). In the state ST 5 , the switching elements SW 01 , SW 02 , SW 11 , SW 12 , SW 21 , SW 22 , SW 31 , and SW 32  are set to OFF. Thus, the capacitor C 1  is separated from the battery cell  10 . 
     In the state ST 6 , the switching elements SW 02 , SW 12 , SW 21 , and SW 22  are turned on. Thus, the capacitor C 1  is charged with the terminal voltage V 2  of the other battery cell  10 . 
     In the state ST 7 , the switching elements SW 21  and SW 22  are then turned off. Thus, the capacitor C 1  is separated from the other battery cell  10 . 
     Then, in the state ST 8 , the switching elements SW 31  and SW 32  are turned on. Thus, a voltage of the capacitor C 1  is fed as the terminal voltage V 2  of the other battery cell  10  to the comparator  223 . 
     In this case, the comparator  223  compares the upper-side intermediate voltage Vref 2  and the terminal voltage V 2  of the other battery cell  10 , and outputs a logical “1” or “0” signal representing a comparison result L 22 . The determination controller  224  acquires the comparison result L 22  of the upper-side intermediate voltage Vref 2  and the terminal voltage V 2  of the other battery cell  10  (step S 9 - 6 ). 
     The determination controller  224  then sets the switching SW 100  to a state ST 9  (step S 9 - 7 ). In the state ST 9 , the switching element SW 100  is switched to the terminal CP 2 . Thus, the lower-side intermediate voltage Vref 1  from the reference voltage outputter  221   b  is fed to the comparator  223 . 
     In this case, the comparator  223  compares the lower-side intermediate voltage Vref 1  and the terminal voltage V 2  of the other battery cell  10 , and outputs a logical “1” or “0” signal representing a comparison result L 21 . The determination controller  224  acquires the comparison result L 21  of the lower-side intermediate voltage Vref 1  and the terminal voltage V 2  of the other battery cell  10  (step S 9 - 8 ). 
     The determination controller  224  then sets the switching elements SW 01 , SW 02 , SW 11 , SW 12 , SW 21 , SW 22 , SW 31 , SW 32 , and SW 100  to a state ST 10  (step S 9 - 9 ). In the state ST 10 , the switching elements SW 01 , SW 02 , SW 11 , SW 12 , SW 21 , SW 22 , SW 31 , and SW 32  are set to OFF. Thus, the capacitor C 1  is separated from the battery cell  10 . 
     Finally, the determination controller  224  determines the voltage range LI of one of the battery cells  10  from the acquired comparison results L 11  and L 12  while determining the voltage range L 2  of the other battery cell  10  from the acquired comparison results L 21  and L 22  (step S 9 - 10 ). 
       FIG. 6  is a diagram illustrating a relationship between the terminal voltage of the battery cell  10  and a voltage range. As illustrated in  FIG. 6 , a voltage range “0” is less than the lower-side intermediate voltage Vref 1 , a voltage range “1” is in a range of not less than the lower-side intermediate voltage Vref 1  and less than the upper-side intermediate voltage Vref 2 , and the voltage range “2” is not less than the upper-side intermediate voltage Vref 2 .  FIG. 7  is a diagram illustrating a relationship between a comparison result of the comparator  223  and a voltage range. 
     In  FIG. 7 , n is a positive integer for specifying each of the plurality of battery cells  10 . In this example, Ln 1  and Ln 2  are respectively the comparison results L 11  and L 12  corresponding to one of the battery cells  10  or the comparison results L 21  and L 22  corresponding to the other battery cell  10 , and Vn is the terminal voltage V 1  of one of the battery cells  10  or the terminal voltage V 2  of the other battery cell  10 . 
     If both the comparison results Ln 1  and Ln 2  of the comparator  223  are logical “0”, as illustrated in  FIG. 7 , the determination controller  224  determines that the voltage range Ln is “0”. This indicates that the terminal voltage Vn of the battery cell  10  is less than the lower-side intermediate voltage Vref 1 . 
     If the comparison result Ln 1  of the comparator  223  is logical “1”, and the comparison result Ln 2  thereof is logical “0”, the determination controller  224  determines that the voltage range Ln is “1”. This indicates that the terminal voltage Vn of the battery cell  10  is not less than the lower-side intermediate voltage Vref 1  and less than the upper-side intermediate voltage Vref 2 . 
     Further, if both the comparison results Ln 1  and Ln 2  of the comparator  223  are logical “1”, the determination controller  224  determines that the voltage range Ln is “2”. This indicates that the terminal voltage Vn of the battery cell  10  is the upper-side intermediate voltage Vref 2  or more. 
     If the comparison result Ln 1  of the comparator  223  is logical “0”, and the comparison result Ln 2  thereof is logical “1”, the determination controller  224  does not determine the voltage range Ln. This indicates that the terminal voltage Vn of the battery cell  10  exceeds the upper-side intermediate voltage Vref 2  while being less than the lower-side intermediate voltage Vref 1 . Such a situation is considered to occur when the reference voltage unit  221 , the differential amplifier  222 , or the comparator  223  is broken down. 
     In step S 9 - 10  illustrated in  FIG. 4 , it is determined in which of the voltage ranges “0”, “1”, and “2” the terminal voltage V 1  of one of the battery cells  10  and the terminal voltage V 2  of the other battery cell  10  exist based on the relationship illustrated in  FIG. 7 . A determination result of the voltage range of each of the battery cells  10  by the determination controller  224  is transmitted to the voltage calculator  212  in the battery ECU  101  via the transmission line D 1  illustrated in  FIG. 1 . 
     In this example, the range determiner  201  includes an overcharge/overdischarge detector  201   b  that detects overcharge and overdischarge of the battery cell  10 .  FIG. 8  is a block diagram illustrating a configuration of the overcharge/overdischarge detector  201   b.  As illustrated in  FIG. 8 , the overcharge/overdischarge detector  201   b  includes reference voltage outputters  221   a  and  221   d,  a differential amplifier  222 , a comparator  223 , a determination controller  224 , a plurality of switching elements SW 01 , SW 02 , SW 11 , SW 12 , SW 21 , SW 22 , SW 31 , SW 32 , and SW 100 , and a capacitor C 1 . 
     The switching element SW 100  is switched to a terminal CP 1  so that a lower-limit voltage Vref_UV from the reference voltage outputter  221   a  is fed to the comparator  223 . In this state, the terminal voltage of each of the battery cells  10  is fed to the comparator  223  via the capacitor C 1  and the differential amplifier  222  so that the lower-limit voltage Vref_UV and the terminal voltage of each of the battery cells  10  are compared with each other. Similarly, the switching element SW 100  is switched to a terminal CP 4  so that an upper-limit voltage Vref_OV from the reference voltage outputter  221   d  is fed to the comparator  223 . In this state, the terminal voltage of each of the battery cells  10  is fed to the comparator  223  via the capacitor C 1  and the differential amplifier  222  so that the upper-limit voltage Vref_OV and the terminal voltage of each of the battery cells  10  are compared with each other. 
     If the terminal voltage of the battery cell  10  is lower than the lower-limit voltage Vref_UV, the battery cell  10  is in an overdischarge state. If the terminal voltage of the battery cell  10  is higher than the upper-limit voltage Vref_OV, the battery cell  10  is in an overcharge state. 
     If a comparison result indicating that the terminal voltage of at least one of the battery cells  10  has reached the lower-limit voltage Vref_UV or the upper-limit voltage Vref_OV is output from the comparator  223 , the determination controller  224  feeds a charge/discharge stop signal to the stop controller  215  ( FIG. 1 ) in the battery ECU  101  via the transmission line D 1 . In this case, the stop controller  215  turns off the contactor  102  in response to the charge/discharge stop signal from the determination controller  224 . Thus, the charge or discharge of each of the battery cells  10  is stopped. As a result, the safety of each of the battery cells  10  by overdischarge or overcharge can be ensured. 
     The overcharge/overdischarge detector  201   b  having the above-mentioned configuration has been conventionally used to detect the overcharge and overdischarge of the battery cell  10 . In this example, the conventional overcharge/overdischarge detector  201   b  is diverted into the range determiner  201  by adding the reference voltage outputter  221   b  that outputs the lower-side intermediate voltage Vref 1  and the upper-side intermediate voltage Vref 2  that outputs the upper-side intermediate voltage Vref 2  to the conventional overcharge/overdischarge detector  201   b.  This prevents the battery control device  400  from becoming complex in configuration and increasing in cost. 
     Further, the voltage calculator  212  can calculate the terminal voltage of each of the battery cells  10  using a determination result of the voltage range transmitted from the range determiner  201 . Thus, the charge/discharge control of each of the battery cells  10  can be performed with sufficient precision while preventing the battery control device  400  from becoming complex in configuration and increasing in cost. More specifically, the terminal voltage of each of the battery cells  10  can be calculated based on the current flowing through each of the battery cells  10 . Further, the calculated terminal voltage can be corrected using the determination result of the voltage range of each of the battery cells  10  by the range determiner  201 . Thus, the precision of the charge/discharge control of each of the battery cells  10  can be prevented from decreasing as compared with when an A/D converter or the like capable of detecting a terminal voltage of each of battery cells  10  with high precision is used. 
     (1-5) SOC Calculation Processing for Battery Cell 
     SOC calculation processing for the battery cell  10  by the battery calculator  212  and the current value calculator  232  will be described below.  FIGS. 9 to 11  are flowcharts illustrating the SOC calculation processing by the voltage calculator  212  and the current value calculator  232 . In the present embodiment, the CPU executes an SOC calculation processing program stored in the memory so that SOC calculation processing is performed. 
     As illustrated in  FIGS. 9 and 10 , when an ignition key of a start instructor  607  ( FIG. 17 , described below) in the vehicle is turned on, the battery system  500  is started, and the voltage corrector  246  resets a current accumulated value calculated by the accumulator  242  (step  51 ). The SOC calculator  243  then acquires the SOC of each of the battery cells  10  from the storage  214  (step S 2 ). The storage  214  stores a value of the SOC acquired when the ignition key is turned off in the previous SOC calculation processing. The voltage corrector  246  sets a timer (step S 3 ). Thus, the timer starts to measure an elapsed time. The timer is set so that a measured value t becomes zero. 
     Then, the current value calculator  232  acquires values of the currents respectively flowing through the plurality of battery cells  10  (step S 4 ). The accumulator  242  accumulates the values of the currents acquired by the current value calculator  232 , to calculate a current accumulated value (step S 5 ). The SOC calculator  243  calculates the SOC at the current time point based on the calculated current accumulated value and the acquired SOC (step S 6 ). When a value of the SOC at the previous time point of the i-th battery cell  10  is SOC(i) [%], the current accumulated value is ΣI [Ah], and a full charging capacity of the i-th battery cell  10  is C(i) [Ah], a value SOC_new(i) of the SOC at the current time point of the i-th battery cell  10  is calculated by the following equation (1), for example, where i is any integer from 1 to a value representing the number of battery cells  10 : 
       SOC_new( i )=SOC( i )+Σ I/C ( i ) [%]  (1)
 
     The OCV estimator  244  then estimates the OCV at the current time point of each of the battery cells  10  from the calculated SOC at the current time point (step S 7 ).  FIG. 12  illustrates a relationship between respective values of the SOC and the OCV of the i-th battery cell  10 . The relationship illustrated in  FIG. 12  is previously stored in the OCV estimator  244 . The OCV of each of the battery cells  10  is estimated by referring to the relationship illustrated in  FIG. 12 , for example. The relationship between the SOC and the OCV of the battery cell  10  may be stored as a function or may be stored in a tubular form. 
     The voltage estimator  245  estimates the terminal voltage at the current time point of each of the battery cells  10  from the OCV at the current time point (step S 8 ). When a value of the OCV at the current time point of the i-th battery cell  10  is V 0 ( i ) [V], a value of the current flowing through each of the plurality of battery cells  10  is I [A], and an internal impedance of the i-th battery cell  10  is Z(i) [Ω], a value Vest(i) of a terminal voltage at the current time point of the i-th battery cell  10  is estimated by the following equation (2), for example: 
         V est( i )= V 0( i )+ I×Z ( i ) [ V]   (2)
 
     Here, the value I of the current is positive at the time of charge, and is negative at the time of discharge. A previously measured value, for example, is used as the internal impedance of each of the battery cells  10 . In this case, the internal impedance is stored in the storage  214 . 
     The voltage corrector  246  then transmits a voltage range acquisition signal to the determination controller  224  in each of the battery modules  100  (step S 9 ). Each of the determination controllers  224  performs the voltage range determination processing illustrated in  FIG. 4  when it receives the voltage range acquisition signal from the voltage corrector  246 . Each of the determination controllers  224  transmits a determination result of voltage ranges of the corresponding plurality of battery cells  10  to the voltage corrector  246 . 
     The voltage corrector  246  then determines whether the determination result of the voltage ranges from all the determination controllers  224  has been received (step S 10 ). If the determination result of the voltage ranges from all the determination controllers  224  is not received, the voltage corrector  246  waits until the determination result of the voltage ranges from all the determination controllers  224  is received. 
     If the determination result of the voltage ranges from all the determination controllers  224  is received, the voltage corrector  246  determines whether the voltage range of each of the battery cells  10  is “1” (step S 11 ). If the voltage range of each of the battery cells  10  is “1”, i.e., if the terminal voltage of each of the battery cells  10  is not less than the lower-side intermediate voltage Vref 1  and less than the upper-side intermediate voltage Vref 2 , the voltage corrector  246  corrects the terminal voltage at the current time point of each of the battery cells  10  in the following method (step S 12 ). Letting a be a smoothing coefficient, a value Vest_new(i) of the terminal voltage after the correction of the i-th battery cell  10  is calculated by the following equation (3), for example. The smoothing coefficient α is not less than zero nor more than one: 
         V est_new( i )=α× V est( i )+(1−α)×( V ref1+ V ref2)/2 [ V]   (3)
 
     The voltage corrector  246  corrects the OCV at the current time point of each of the battery cells  10  in the following method based on the corrected terminal voltage at the current time point of the battery cell  10  (step S 13 ). A value V 0 _new(i) of the OCV after the correction of the i-th battery cell  10  is calculated by the following equation (4), for example. 
         V 0_new( i )= V 0( i )+( V est_new( i )− V est( i )) [ V]   (4)
 
     Further, the voltage corrector  246  corrects the SOC at the current time point of each of the battery cells  10  based on the corrected OCV at the current time point (step S 14 ). The SOC at the current time point after the correction is found by referring to the relationship illustrated in  FIG. 12 , for example. 
     The voltage corrector  246  then resets the current accumulated value calculated by the accumulator  242  (step S 15 ). The voltage corrector  246  feeds the terminal voltage at the current time point of each of the battery cells  10 , which has been corrected in step S 12 , to the control value calculator  211  illustrated in  FIG. 1  (step S 16 ). 
     Then, the voltage corrector  246  waits until the measured value t of the timer reaches a predetermined time T (step S 17 ). When the measured value t of the timer reaches the predetermined time T, the voltage corrector  246  returns to the processing in step S 3 . The SOC of each of the battery cells  10 , which is stored in the storage  214 , is replaced with the SOC at the current time point of the battery cell  10 , which has been corrected by the voltage corrector  246 , to repeat the processing from step S 3  to step S 17 . 
     If the voltage range of each of the battery cells  10  is not “1” in step S 11 , i.e., if the voltage range is “0” (if the terminal voltage of the battery cell  10  is less than the lower-side intermediate voltage Vref 1 ) or is “2” (if the terminal voltage of the battery cell  10  is the upper-side intermediate voltage Vref 2  or more), the terminal voltage of the battery cell  10  cannot be appropriately corrected by the foregoing equation (3). Therefore, the voltage corrector  246  proceeds to the processing in step S 16  without correcting the terminal voltage, correcting the OCV, and correcting the SOC. In step S 16 , the terminal voltage at the current time point, which has been estimated by the voltage estimator  245  in step S 8 , is fed to the control value calculator  211  illustrated in  FIG. 1 . 
     On the other hand, when the ignition key of the start instructor  607  in the electric vehicle ( FIG. 17 , described below) is turned off, the SOC calculator  243  stores the SOC at the current time point of each of the battery cells  10  in the storage  214  (step S 20 ), as illustrated in  FIG. 11 . In this case, the SOC stored in the storage  214  is updated to the SOC at the current time point. Then, the battery system  500  is stopped. 
     (1-6) Control Value Calculator 
     As described above, the terminal voltage of each of the battery cells  10 , which has been detected by the voltage detector  202  in each of the battery modules  100 , is transmitted to the control value calculator  211  in the battery ECU  101  illustrated in  FIG. 1  via the communication lines D 2  and D 3 . The terminal voltage of each of the battery cells  10 , which has been calculated by the voltage calculator  212 , is fed to the control value calculator  211 . The terminal voltage of each of the battery cells  10 , which has been detected by the voltage detector  202 , is referred to as a detection voltage, and the terminal voltage of each of the battery cells  10 , which has been calculated by the voltage calculator  212 , is referred to as a calculation voltage. 
     The control value calculator  211  includes a timer (not illustrated), and calculates a value for charge/discharge control (hereinafter referred to as a battery control value) of each of the battery cells  10  using one of the detection voltage and the calculation voltage and gives the value to the main controller  300  in the electric vehicle. The battery control value represents a capacity, which can be charged from the current time point until the terminal voltage of at least one of the battery cells  10  reaches the upper-limit voltage Vref_OV, or a capacity, which can be discharged from the current time point until the terminal voltage of at least one of the battery cells  10  reaches the lower-limit voltage Vref_UV. 
       FIGS. 13 and 14  are flowcharts of battery control value calculation processing by the control value calculator  211 . In the present embodiment, the CPU executes a battery control value calculation processing program stored in the memory, to perform the battery control value calculation processing. When an ignition key of a start instructor  607  ( FIG. 17 , described below) in the electric vehicle is turned on, as illustrated in  FIG. 13 , the battery system  500  is started. Thus, the control value calculator  211  starts the battery control value calculation processing. First, the control value calculator  211  resets first and second counter values stored in the storage  214  (step S 51 ). The first counter value is a value, which is added every time the processing passes through step S 60 , described below, and the second counter value is a value, which is added every time the processing passes through step S 66 , described below. 
     The control value calculator  211  then resets the timer (step S 52 ). The timer starts to measure an elapsed time from this time point. The control value calculator  211  then determines whether the first counter value has reached a predetermined value T 1  (step S 53 ). If the first counter value does not reach the predetermined value T 1 , the control value calculator  211  determines whether detection voltages from all the voltage detectors  202  have been received (step S 54 ). If the battery ECU  101  and each of the battery modules  100  are normally connected to each other via the communication lines D 2  and D 3 , the control value calculator  211  receives the detection voltage from each of the voltage detectors  202 . 
     If the detection voltages from all the voltage detectors  202  are received, the control value calculator  211  updates a voltage Vp stored in the storage  214  to the detection voltage (step S 55 ). The voltage Vp corresponds to a terminal voltage of each of the battery cells  10  at the current time point. 
     The control value calculator  211  then resets the first counter value stored in the storage  214  (step S 56 ). The control value calculator  211  then calculates the battery control value using the voltage Vp stored in the storage  214 , and outputs the calculated battery control value (step S 57 ). The battery control value output from the control value calculator  211  is given to the main controller  300  in the electric vehicle. 
     The control value calculator  211  then waits until a measurement time by the timer reaches a predetermined period of time T 2  (step S 58 ). When the measurement time by the timer reaches the predetermined period of time T 2 , the control value calculator  211  returns to the processing in step S 52 . 
     On the other hand, if the battery ECU  101  and each of the battery modules  100  are not normally connected to each other via the communication lines D 2  and D 3 , the control value calculator  211  may not receive the detection voltage from at least one of all the voltage detectors  202 . As described above, the detection voltage is transmitted for each predetermined period of time from each of the voltage detectors  202 . The control value calculator  211  determines, when a state where the detection voltage is not received for a predetermined period of time longer than the predetermined period of time is maintained, that the detection voltage from the voltage detector  202  is not received in step S 54 . 
     Examples of a case where the detection voltage is not received include a case where a value of the voltage is not received in a predetermined data format (e.g., header information or a data series), a state where a value corresponding to a power supply voltage or a ground voltage is continuously received, a case where an indefinite value is received, a case where a received value vibrates, and a case where a receiving interval is a predetermined period of time or more. 
     If the detection voltages from all the voltage detectors  202  are not received in step S 54 , the control value calculator  211  maintains the voltage Vp stored in the storage  214  at a value updated in the previous step S 55  (step S 59 ). The control value calculator  211  adds one to the first counter value stored in the storage  214  (step S 60 ), and proceeds to the processing in step S 57 . 
     When the state where the detection voltage is not received is maintained, one is repeatedly added to the first counter value in step S 60 . If the first counter value has reached the predetermined value T 1  in step S 53 , the control value calculator  211  determines whether the second counter value has reached a predetermined value T 3  (step S 61 ), as illustrated in  FIG. 14 . If the second counter value has not reached the predetermined value T 3 , the control value calculator  211  determines whether the calculation voltage has been acquired (step S 62 ). If the battery ECU  101  and each of the battery modules  100  are normally connected to each other via the transmission line D 1 , the control value calculator  211  acquires the calculation voltage. 
     If the calculation voltage has been acquired, the control value calculator  211  updates the voltage Vp stored in the storage  214  to the calculation voltage (step S 55 ). The control value calculator  211  resets the second counter value, and proceeds to the processing in step S 57  illustrated in  FIG. 13 . 
     On the other hand, if the battery ECU  101  and each of the battery modules  100  are not normally connected to each other via the transmission line D 1 , a determination result of the voltage ranges by all the range determiners  201  is not obtained in step S 10  illustrated in  FIG. 10 . Thus, the voltage calculator  212  cannot calculate the calculation voltage. Therefore, the control value calculator  211  cannot acquire the calculation voltage. Examples of a case where the calculation voltage is not acquired include a case where a value of the voltage is not acquired in a predetermined data format (e.g., header information or a data series), a case where a value corresponding to a power supply voltage or a ground voltage is continuously acquired, a case where an indefinite value is acquired, a case where the acquired value vibrates, and a case where an acquisition interval is a predetermined period of time or more. 
     If the calculation voltage has not been acquired in step S 62  illustrated in  FIG. 14 , the control value calculator  211  maintains the voltage Vp stored in the storage  214  at a value updated in the previous step S 55  or step S 63  (step S 65 ). The control value calculator  211  adds one to the second counter value stored in the storage  214  (step S 66 ), and proceeds to the processing in step S 57  illustrated in  FIG. 13 . 
     When the state where the calculation voltage is not acquired is maintained, one is repeatedly added to the second counter value in step S 66 . If the second counter value has reached the predetermined value T 3  in step S 61 , the control value calculator  211  causes the stop controller  215  to turn off the contactor  102  (step S 67 ), and ends the battery control value calculation processing. 
     If the control value calculator  211  can neither receive the detection voltage from at least one of the voltage detectors  202  nor acquire the calculation voltage from the voltage calculator  212 , the control value calculator  211  cannot calculate appropriate battery control values relating to all the battery cells  10 . Thus, the main controller  300  cannot appropriately perform charge/discharge control of each of the battery cells  10 . In this case, the contactor  102  is turned off, to enter a state where no current flows through each of the battery cells  10 . Thus, each of the battery cells  10  can be sufficiently prevented from being overcharged and overdischarged. 
     When the ignition key of the start instructor  607  ( FIG. 17 , described below) in the electric vehicle is turned off, as illustrated in  FIG. 11 , the battery system  500  is stopped. At this time, the battery control value calculation processing by the control value calculator  211  ends. 
     (1-7) Effects of First Embodiment 
     Thus, in the battery control device  400  in the battery system  500  according to the first embodiment, if the control value calculator  211  can receive the detection voltages from all the voltage detectors  202 , the battery control value is calculated using the detection voltages. As described above, the voltage detector  202  can detect the terminal voltage of each of the battery cells  10  with high precision. Thus, the control value calculator  211  can calculate an accurate battery control value by using the detection voltage. 
     On the other hand, the control value calculator  211  calculates the battery control value using the calculation voltage if it cannot receive the detection voltage from at least one of the voltage detectors  202 . Thus, even if the communication lines D 2  and D 3  are disconnected, the control value calculator  211  can calculate the battery control value. Therefore, the reliability of the battery control device  400  is improved. 
     Even if the voltage detector  202  is not provided, the battery control value can be calculated using the calculation voltage. Thus, it is possible to simplify the configuration of the battery control device  400  (prevent the battery control device  400  from becoming complex in configuration) and reduce the cost thereof. 
     The voltage calculator  212  calculates the calculation voltage using the determination result of the voltage range of each of the battery cells  10  by the range determiner  201 . In this case, the terminal voltage of each of the battery cells  10  is not detected so that the calculation voltage can be calculated in a simple configuration. Therefore, the reliability of the battery control device  400  can be improved while preventing the battery control device  400  from becoming complex in configuration and increasing in cost. 
     When the calculation voltage is calculated, the range determiner  201  determines whether the terminal voltage of each of the battery cells  10  belongs to the predetermined voltage range “1”, and the voltage calculator  212  corrects the terminal voltage calculated based on the current if the terminal voltage of the battery cell  10  belongs to “1”. Thus, the accurate calculation voltage can be obtained while preventing the battery control device  400  from becoming complex in configuration and increasing in cost. 
     The range determiner  201  determines whether the terminal voltage of each of the battery cells  10  belongs to the voltage range “1” by comparing the terminal voltage of the battery cell  10  with the lower-side intermediate voltage Vref 1  and the upper-side intermediate voltage Vref 2 . Thus, the accurate calculation voltage of each of the battery cells  10  can be obtained without complicating the configuration of the battery control device  400 . 
     The common range determiner  201  can determine the voltage range of each of the battery cells  10 , and determine whether the terminal voltage of at least one of the battery cells  10  has reached the upper-limit voltage Vref_OV or the lower-limit voltage Vref_UV. This further prevents the battery control device  400  from becoming complex in configuration and increasing in cost. 
     (1-8) Modified Example 
     While in the above-mentioned first embodiment, the control value calculator  211  calculate, when it cannot communicate with at least one of the voltage detectors  202 , the battery control value using the calculation voltage with respect to all the battery cells  10 , the present invention is not limited to this. If the control value calculator  211  cannot communicate with some of the voltage detectors  202 , for example, the control value calculator  211  may calculate the battery control value using the detection voltage from the voltage detector  202  with respect to the battery cell  10  corresponding to the voltage detector  202  with which it can communicate and using the calculation voltage with respect to the battery cell  10  corresponding to the voltage detector  202  with which it cannot communicate. 
     (2) Second Embodiment 
     (2-1) Configuration of Battery Control Device and Battery System 
       FIG. 15  is a block diagram illustrating a configuration of a battery control device according to a second embodiment and a battery system including the same. The battery control device  400   a  illustrated in  FIG. 15  will be described by referring to differences from the battery control device  400  illustrated in  FIG. 1 . 
     In the battery control deice  400   a  in a battery system  500   a  illustrated in  FIG. 15 , a detection unit  20  in each of battery modules  100  is provided with a plurality of range determiners  201   a  corresponding to a plurality of battery cells  10 . The range determiner  201   a  is not provided with switching elements SW 01 , SW 02 , SW 11 , and SW 12  illustrated in  FIG. 3 . 
     (2-2) Effects of Second Embodiment 
     In the battery control device  400   a  in the battery system  500   a  according to the second embodiment, when a voltage range of each of the battery cells  10  is determined, the switching elements SW 01 , SW 02 , SW 11 , and SW 12  need not be switched. The plurality of range determiners  201   a  can simultaneously determine voltage ranges of the plurality of battery cells  10 . Thus, a period of time required to determine the voltage ranges can be significantly shortened. 
     (3) Third Embodiment 
     (3-1) Configuration of Battery Control Device and Battery System 
       FIG. 16  is a block diagram illustrating a configuration of a battery control device according to a third embodiment and a battery system including the same. A battery control device  400   b  illustrated in  FIG. 16  will be described by referring to differences from the battery control device  400  illustrated in  FIG. 1 . 
     In the battery control deice  400   b  in a battery system  500   b  illustrated in  FIG. 16 , a detection unit  20  in each of battery modules  100  is not provided with a voltage detector  202 . A control value calculator  211  in a battery ECU  101  calculates a battery control value using a calculation voltage from a voltage calculator  212 . 
     (3-2) Effects of Third Embodiment 
     In the battery control device  400   b  in the battery system  500   b  according to the third embodiment, the control value calculator  211  calculates the battery control value using the calculation voltage calculated based on a current value at the time of charge/discharge by a range determiner  201  and the voltage calculator  212  without detecting a terminal voltage of each of battery cells  10 . Thus, charge/discharge control of each of the battery cells  10  can be performed with sufficient precision while preventing the battery control device  400   b  from becoming complex in configuration and increasing in cost. More specifically, the precision of the charge/discharge control of each of the battery cells  10  can be prevented from decreasing as compared with when an ND converter or the like capable of detecting a terminal voltage of each of battery cells  10  with high precision is used. 
     In the battery control device  400   b  according to the third embodiment, each of the battery modules  100  may be provided with a plurality of range determiners  201   a,  which are similar to those in the second embodiment, instead of the range determiner  201 . 
     (4) Fourth Embodiment 
     An electric vehicle according to a fourth embodiment will be described below. The electric vehicle according to the present embodiment includes a battery system  500  according to the first embodiment. An electric automobile will be described as an example of the electric vehicle. 
     (4-1) Configuration and Operation 
       FIG. 17  is a block diagram illustrating a configuration of an electric automobile according to the fourth embodiment. As illustrated in  FIG. 17 , an electric automobile  600  according to the present embodiment includes a vehicle body  610 . The vehicle body  610  is provided with a battery system  500  and an electric power converter  601  illustrated in  FIG. 1 , and a motor  602 M serving as the load illustrated in  FIG. 3 , a drive wheel  603 , an accelerator device  604 , a brake device  605 , a rotational speed sensor  606 , a start instructor  607 , and a main controller  300 . If the motor  602 M is an alternating current (AC) motor, the electric power converter  601  includes an inverter circuit. The battery system  500  includes a battery control device  400  illustrated in  FIG. 1 . 
     The battery system  500  is connected to the motor  602 M via the electric power converter  601  while being connected to the main controller  300 . 
     A battery control value is given to the main controller  300  from a battery ECU  101  ( FIG. 1 ) in the battery control device  400 . The accelerator device  604 , the brake device  605 , the rotational speed sensor  606  are connected to the main controller  300 . The main controller  300  includes a CPU and a memory, or a microcomputer, for example. Further, the start instructor  607  is connected to the main controller  300 . 
     The accelerator device  604  includes an accelerator pedal  604   a  included in the electric automobile  600  and an accelerator detector  604   b  that detects an operation amount (a depression amount) of the accelerator pedal  604   a.    
     When a user operates the accelerator pedal  604   a  with an ignition key of the start instructor  607  turned on, an accelerator detector  604   b  detects the operation amount of the accelerator  604   a  using a state where the user does not operate the accelerator pedal  604   a  as a basis. The detected operation amount of the accelerator pedal  604   a  is fed to the main controller  300 . 
     The brake device  605  includes a brake pedal  605   a  included in the electric automobile  600  and a brake detector  605   b  that detects an operation amount (a depression amount) of the brake pedal  605   a  by the user. When the user operates the brake pedal  605   a  with the ignition key turned on, the brake detector  605   b  detects the operation amount. The detected operation amount of the brake pedal  605   a  is given to the main controller  300 . The rotational speed sensor  606  detects a rotational speed of the motor  602 M. The detected rotational speed is given to the main controller  300 . 
     As described above, the battery control value, the operation amount of the accelerator pedal  604   a,  the operation amount of the brake pedal  605   a,  and the rotational speed of the motor  602 M are given to the main controller  300 . The main controller  300  performs charge/discharge control of a battery module  100  and electric power conversion control of the electric power converter  601  based on these information. When the electric automobile  600  is started and accelerated based on an accelerator operation, for example, electric power from the battery module  100  is supplied to the electric power converter  601  from the battery system  500 . 
     Further, the main controller  300  calculates a torque (a command torque) to be transmitted to the drive wheel  603  based on the given operation amount of the accelerator pedal  604   a,  and feeds a control signal based on the command torque to the electric power converter  601 . 
     The electric power converter  601 , which has received the above-mentioned control signal, converts electric power supplied from the battery system  500  to electric power (driving electric power) required to drive the drive wheel  603 . Thus, the driving electric power, which has been obtained in the conversion by the electric power converter  601 , is supplied to the motor  602 M, and a torque generated by the motor  602 M based on the driving electric power is transmitted to the drive wheel  603 . 
     On the other hand, the motor  602 M functions as a power generation device when the electric automobile  600  is decelerated based on a brake operation. In this case, the electric power converter  601  converts regenerated electric power, which has been generated by the motor  602 M, into electric power suitable for charge of the plurality of battery cells  10 , and feeds the electric power to the plurality of battery cells  10 . Thus, the plurality of battery cells  10  are charged. 
     (4-2) Effects of Fourth Embodiment 
     In the electric automobile  600  according to the fourth embodiment, the battery system  500  including the battery control device  400  according to the first embodiment is provided. 
     The battery system  500  according to the first embodiment is provided so that the battery control value can be calculated based on a current value at the time of charge/discharge even if the communication lines D 2  and D 3  are disconnected, for example. Therefore, the reliability of the electric automobile  600  is improved. 
     In the electric automobile  600  illustrated in  FIG. 17 , a battery system  500  including the battery control device  400   a  according to the second embodiment may be provided instead of the battery system  500  including the battery control device  400  according to the first embodiment. In this case, a plurality of range determiners  201   a  can simultaneously determine the voltage ranges of the plurality of battery cells  10 . Thus, a period of time required to determine the voltage ranges can be significantly shortened. 
     In the electric automobile  600  illustrated in  FIG. 17 , a battery system  500   b  including the battery control device  400   b  according to the third embodiment may be provided instead of the battery system  500  including the battery control device  400  according to the first embodiment. In this case, charge/discharge control of each of the battery cells  10  can be performed with sufficient precision while preventing the battery control device  400   b  from becoming complex in configuration and increasing in cost. More specifically, the precision of the charge/discharge control of each of the battery cells  10  can be prevented from decreasing as compared with when an ND converter or the like capable of detecting a terminal voltage of each of battery cells  10  with high precision is used. Therefore, the cost of the electric automobile  600  can be reduced. 
     (4-3) Another Movable Body 
     While an example in which the battery system  500  illustrated in  FIG. 1  is loaded into the electric vehicle has been described above, the battery system  500  may be loaded into another movable body such as a ship, an airplane, an elevator, or a walking robot. 
     The ship, which is loaded with the battery system  500 , includes a hull instead of the vehicle body  610  illustrated in  FIG. 17 , includes a screw instead of the drive wheel  603 , includes an accelerator inputter instead of the accelerator device  604 , and includes a deceleration inputter instead of the brake device  605 , for example. An operator operates the acceleration inputter instead of the accelerator device  604  in accelerating the hull, and operates the deceleration inputter instead of the brake device  605  in decelerating the hull. In this case, the hull corresponds to a main movable body, the motor corresponds to a power source, and the screw corresponds to a driver. In such a configuration, the motor converts electric power from the battery system  500  into power upon receipt of the electric power, and the screw is rotated with the power so that the full moves. 
     Similarly, the airplane, which is loaded with the battery system  500 , includes an airframe instead of the vehicle body  610  illustrated in  FIG. 17 , includes a propeller instead of the drive wheel  603 , includes an acceleration inputter instead of the accelerator device  604 , and includes a deceleration inputter instead of the brake device  605 , for example. In this case, the airframe corresponds to a main movable body, the motor corresponds to a power source, and the propeller corresponds to a driver. In such a configuration, the motor converts electric power from the battery system  500  into power, and the propeller is rotated with the electric power so that the airframe moves. 
     The elevator, which is loaded with the battery system  500 , includes a cage instead of the vehicle body  610  illustrated in  FIG. 17 , includes a hoist rope, which is attached to the cage, instead of the drive wheel  603 , includes an accelerator inputter instead of the accelerator device  604 , and includes a deceleration inputter instead of the brake device  605 , for example. In this case, the cage corresponds to a main movable body, the motor corresponds to a power source, and the hoist rope corresponds to a driver. In such a configuration, the motor converts electric power from the battery system  500  into power upon receipt of the electric power, and the hoist rope is wound up with the power so that the cage moves up and down. 
     The walking robot, which is loaded with the battery system  500 , includes a body instead of the vehicle body  610  illustrated in  FIG. 17 , includes a foot instead of the drive wheel  603 , includes an acceleration inputter instead of the accelerator device  604 , and includes a deceleration inputter instead of the brake device  605 , for example. In this case, the body corresponds to a main movable body, the motor corresponds to a power source, and the foot corresponds to a driver. In such a configuration, the motor converts electric power from the battery system  500  into power upon receipt of the electric power, and the foot is driven with the power so that the body moves. 
     Thus, in the movable body, which is loaded with the battery system  500 , a power source converts the electric power from the battery system  500  into power, and the driver moves the main movable body with the power obtained in the conversion by the power source. 
     (5) Fifth Embodiment 
     A power supply device according to a fifth embodiment of the present invention will be described below. 
     (5-1) Overall Configuration 
       FIG. 18  is a block diagram illustrating a configuration of a power supply device according to the fifth embodiment. As illustrated in  FIG. 18 , a power supply device  700  includes a power storage device  710  and a power conversion device  720 . The power storage device  710  includes a battery system group  711  and a controller  712 . The battery system group  711  includes a plurality of battery systems  500 , and a plurality of switching units SU respectively corresponding to the plurality of battery systems  500 . Each of the battery systems  500  has a similar configuration to that of the battery system  500  illustrated in  FIG. 1 . The plurality of battery systems  500  may be connected in parallel, or may be connected in series. When each of the switching units SU is turned on, the corresponding battery system  500  is electrically connected to the other battery system  500 . When each of the switching units SU is turned off, the corresponding battery system  500  is electrically separated from the other battery system  500 . 
     The controller  712  is an example of a system controller, and includes a CPU and a memory, or a microcomputer, for example. The controller  712  is connected to the battery ECUs  101  ( FIG. 1 ) in the battery systems  500  and the switching units SU. A battery control value is given to the controller  712  from the battery ECU  101  in each of the battery systems  500 . The controller  712  performs control relating to discharge or charge of the plurality of battery cells included in each of the battery systems  500  by controlling the power conversion device  720  and each of the switching units SU based on the battery control value given from the battery ECU  101 . 
     The power conversion device  720  includes a DC/DC (direct current/direct current) converter  721  and a DC/AC (direct current/alternating current) inverter  722 . The DC/DC converter  721  has input/output terminals  721   a  and  721   b,  and the DC/AC inverter  722  has input/output terminals  722   a  and  722   b.  The input/output terminal  721   a  of the DC/DC converter  721  is connected to the battery system group  711  in the power storage device  710 . The input/output terminal  721   b  of the DC/DC converter  721  and the input/output terminal  722   a  of the DC/AC inverter  722  are connected to each other while being connected to an electric power outputter PU 1 . The input/output terminal  722   b  of the DC/AC inverter  722  is connected to an electric power outputter PU 2  while being connected to another electric power system. Each of the electric power outputters PU 1  and PU 2  has an outlet, for example. Various loads, for example, are connected to the electric power outputters PU 1  and PU 2 . The other electric power system includes a commercial power supply or a solar battery, for example. The electric power outputters PU 1  and PU 2  and the other electric power system are examples of an external object connected to the power supply device. 
     The controller  712  controls the DC/DC converter  721  and the DC/AC inverter  722  so that the battery system group  711  is discharged and charged. 
     When the battery system group  711  is discharged, the DC/DC converter  721  performs DC/DC (direct current/direct current) conversion of electric power fed from the battery system group  711 , and the DC/AC inverter  722  further performs DC/AC (direct current/alternating current) conversion thereof. 
     Electric power obtained in the DC/DC conversion by the DC/DC converter  721  is supplied to the electric power outputters PU 1 . Electric power obtained in the DC/AC conversion by the DC/AC inverter  722  is supplied to the electric power outputter PU 2 . DC electric power is output to the external object from the electric power outputter PU 1 , and AC electric power is output to the external object from the electric power outputter PU 2 . AC electric power obtained in the conversion by the DC/AC inverter  722  may also be supplied to another electric power system. 
     The controller  712  performs the following control as an example of control relating to discharge of the plurality of battery cells  10  included in each of the battery systems  500 . When the battery system group  711  is discharged, the controller  712  determines whether discharge of the battery system group  711  is stopped based on the battery control value from each of the battery ECUs ( FIG. 1 ), and controls the power conversion device  720  based on a determination result. More specifically, when the charged capacity of any one of the plurality of battery cells  10  ( FIG. 1 ) included in the battery system group  711  becomes smaller than a predetermined threshold value, the controller  712  controls the DC/DC converter  721  and the DC/AC inverter  722  so that the discharge of the battery system group  711  is stopped or the discharging current (or discharging electric power) is limited. Thus, each of the battery cells  10  is prevented from being overdischarged. 
     On the other hand, when the battery system group  711  is charged, the DC/AC inverter  722  performs AC/DC (alternating current/direct current) conversion of AC electric power fed from another electric power system, and the DC/DC converter  721  further performs DC/DC (direct current/direct current) conversion thereof. Electric power is fed from the DC/DC converter  721  to the battery system group  711  so that the plurality of battery cells  10  ( FIG. 1 ) included in the battery system group  711  are charged. 
     The controller  712  performs the following control as an example of control relating to charge of the plurality of battery cells  10  included in each of the battery systems  500 . When the battery system group  711  is charged, the controller  712  determines whether the charge of the battery system group  711  is stopped based on the battery control value from each of the battery ECUs ( FIG. 1 ), and controls the power conversion device  720  based on a determination result. More specifically, when the charged capacity of any one of the plurality of battery cells  10  ( FIG. 1 ) included in the battery system group  711  becomes larger than a predetermined threshold value, the controller  712  controls the DC/DC converter  721  and the DC/AC inverter  722  so that the charge of the battery system group  711  is stopped or the charging current (or charging electric power) is limited. Thus, each of the battery cells  10  is prevented from being overcharged. 
     If electric power can be supplied between the power supply device  700  and the external object, the power conversion device  720  may include only either one of the DC/DC converter  721  and the DC/AC inverter  722 . If electric power can be supplied between the power supply device  700  and the external object, the power conversion device  720  need not be provided. 
     If the communication lines D 2  and D 3  ( FIG. 1 ) in any one of the battery systems  500  may be disconnected, a communication line disconnection signal is fed to the controller  712  from the battery ECU  101  ( FIG. 1 ) in the battery system  500 . 
     More specifically, if a first counter value reaches a predetermined value T 1  in step S 53  illustrated in  FIG. 13 , the control value calculator  211  ( FIG. 1 ) feeds the communication line disconnection signal to the controller  712 . The controller  712  specifies the battery system  500  in which the communication lines D 2  and D 3  may be disconnected (hereinafter referred to as the defective battery system  500 ) based on the fed communication line disconnection signal. 
     The controller  712  causes a presentation unit (not illustrated) to present the specified defective battery system  500  to the user. The presentation unit includes a liquid crystal display and a speaker, for example, and visually and acoustically presents the defective battery system  500  to the user. Thus, the user can quickly recognize that the defective battery system  500  occurs, and can quickly maintain the defective battery system  500 . 
     The controller  712  may turn off the switching unit SU corresponding to the defective battery system  500 . In this case, the defective battery system  500  is electrically separated from the other battery system  500 . Thus, the other battery system  500  can be continuously used while reliably preventing the defective battery system  500  from being overdischarged and overcharged. 
     If the defective battery system  500  is electrically separated from the other battery system  500  when the battery system group  711  is charged, the controller  712  may control the power conversion device  720  so that electric power fed to the battery system group  711  from the external object decreases by an amount corresponding to the defective battery system  500 . In this case, the other battery system  500  is prevented from being overcharged. 
     Similarly, if the defective battery system  500  is electrically separated from the other battery system  500  when the battery system group  711  is discharged, the controller  712  may control the power conversion device  720  so that electric power fed from the battery system group  711  to the external object decreases by an amount corresponding to the defective battery system  500 . In this case, the other battery system  500  is prevented from being overdischarged. 
     In the battery control device  400  ( FIG. 1 ) in each of the battery systems  500 , the battery control value can be calculated using the calculation voltage even if the communication lines D 2  and D 3  are disconnected. Thus, the defective battery system  500  can be continuously used without being repaired. 
     (5-2) Installation of Battery System 
     In the present embodiment, the plurality of battery systems  500  are housed in a common rack.  FIG. 19  is a perspective view of the rack that houses the plurality of battery systems  500 . 
     As illustrated in  FIG. 19 , a rack  750  includes side surface portions  751  and  752 , an upper surface portion  753 , a bottom surface portion  754 , a back surface portion  755 , and a plurality of partition portions  756 . The side surface portions  751  and  752  vertically extend parallel to each other. The upper surface portion  753  horizontally extends to connect upper ends of the side surface portions  751  and  752 , and the bottom surface portion  754  horizontally extends to connect lower ends of the side surface portions  751  and  752 . The back surface portion  755  vertically extends perpendicularly to the side surface portions  751  and  752  along one side of the side surface portion  751  and one side of the side surface portion  752 . The plurality of partition portions  756  are equally spaced apart from one another parallel to the upper surface portion  753  and the bottom surface portion  754  between the upper surface portion  753  and the bottom surface portion  754 . A plurality of housing spaces  757  are provided among the upper surface portion  753 , the plurality of partition portions  756 , and the bottom surface portion  754 . Each of the housing spaces  757  opens toward a front surface of the rack  750  (a surface opposite to the back surface portion  755 ). 
     The battery system  500  illustrated in  FIG. 1  is housed in a box-shaped casing  550 . The casing  550  that houses the battery system  500  is housed in each of the housing spaces  757  from the front surface of the rack  750 . 
     All the battery systems  500  may be housed in one rack  750 , or may be separately housed in a plurality of racks  750 . All the battery systems  500  may be individually installed without being housed in the rack  750 . 
     To easily maintain the battery system  500 , each of the battery systems  500  is preferably provided with a service plug that shuts off a current path. If each of the battery systems  500  includes four battery modules  100  ( FIG. 1 ), for example, the service plug is provided between the two battery modules  100  connected in series and the other two battery modules  100  connected in series. The service plug is turned on so that the four battery modules  100  are connected in series. On the other hand, the service plug is turned off so that the two battery modules  100  and the other two battery modules  100  are electrically separated from each other. Thus, a current path between the plurality of battery modules  100  is shut off. Therefore, the battery system  500  can be maintained easily and safely. 
       FIG. 20  is a diagram illustrating an arrangement example of a service plug. In the example illustrated in  FIG. 20 , a service plug  510  is provided along one side surface of a casing  550  positioned on a front surface of a rack  750 . In this case, a user can switch ON and OFF of the service plug  510  from the front surface of the rack  750  with a battery system  500  housed in a housing space  757 . As a result, the battery system  500  can be easily and safely maintained. 
       FIG. 21  is a diagram illustrating another arrangement example of a service plug. In the example illustrated in  FIG. 21 , a service plug  510  is provided along one side surface of a casing  550  opposite to a back surface portion  755  in a rack  750 . In the back surface portion  755  in the service plug  510 , an ON/OFF switcher  764  is provided at a position that overlaps the service plug  510 . In this case, a battery system  500  is housed in a housing space  757  in the rack  750  so that the service plug  510  is connected to the ON/OFF switcher  764 , and the service plug  510  is turned on. On the other hand, the battery system  500  is taken out of the housing space  757  in the rack  750  so that the service plug  510  and the ON/OFF switcher  764  are separated from each other, and the service plug  510  is turned off. 
     Thus, a current path between the plurality of battery modules  100  is shut off with the battery system  500  not housed in the housing space  757  in the rack  750 . Therefore, the battery system  500  can be easily and safely maintained. 
     (5-3) Effects 
     In the power supply device  700  according to the present embodiment, the controller  712  performs control relating to discharge or charge of the battery system group  711  based on the battery control value from each of the battery systems  500 . Thus, each of the battery cells  10  included in the battery system group  711  can be prevented from being overdischarged and overcharged. 
     In each of the battery systems  500 , even if the communication lines D 2  and D 3  are disconnected, for example, the battery control value can be calculated based on the current value at the time of charge/discharge. Therefore, the reliability of the power supply device  700  is improved. 
     (5-4) Another Example of Power Supply Device 
     In the power supply device  700  illustrated in  FIG. 18 , the controller  712  may have a similar function to that of the battery ECU  101  instead of providing each of the battery systems  500  with the battery ECU  101 . In this case, the controller  712  is connected to the range determiner  201  and the voltage detector  202  in each of the battery modules  100  in each of the battery systems  500  while being connected to the current sensor  103  in the battery system  500 . The controller  712  calculates a battery control value using the detection voltage or the calculation voltage, and performs control relating to discharge or charge of the battery system group  711  based on the calculated battery control value. Thus, a configuration of each of the battery systems  500  is simplified. 
     In the power supply device  700  illustrated in  FIG. 18 , the battery system  500  illustrated in  FIG. 1  may be replaced with the battery system  500   a  illustrated in  FIG. 15 . In this case, the plurality of range determiners  201   a  can simultaneously determine voltage ranges of the plurality of battery cells  10 . Thus, a period of time required to determine the voltage ranges can be significantly shortened. 
     In the power supply device  700  illustrated in  FIG. 18 , the battery system  500  illustrated in  FIG. 1  may be replaced with the battery system  500   b  illustrated in  FIG. 16 . In this case, charge/discharge control of each of the battery cells  10  can be performed with sufficient precision while preventing the battery control device  400   b  from becoming complex in configuration and increasing in cost. More specifically, the precision of the charge/discharge control of each of the battery cells  10  can be prevented from decreasing as compared with when an A/D converter or the like capable of detecting a terminal voltage of each of battery cells  10  with high precision is used. Therefore, the cost of the power supply device  700  can be reduced. 
     (6) Another Embodiment 
     As each of constituent elements in the claims, other types of constituent elements having configurations or functions described in the claims can be used in addition to the constituent elements described in the above-mentioned first to fifth embodiments. 
     (6-1) While in the range determiner  201  according to the above-mentioned embodiment, the terminal voltages V 1  and V 2  of the battery cells  10  are fed to the comparator  223  after the capacitor Cl is charged with the terminal voltages V 1  and V 2 , the present invention is not limited to this. If a temporal change in the terminal voltages V 1  and V 2  of the battery cells  10  is small, the terminal voltages V 1  and V 2  of the battery cells  10  may be directly fed to the comparator  223 . In this case, the switching elements SW 21 , SW 22 , SW 31 , SW 32 , and the capacitor C 1  are not required. Thus, the switching elements SW 21 , SW 22 , SW 31 , and SW 32  need not be switched, and the capacitor C 1  need not be charged. Therefore, a period of time required to determine voltage ranges can be further shortened. 
     (6-2) In the above-mentioned embodiments, the control value calculator may calculate any of an SOC, a remaining capacity, a depth of discharge (DOD), a current accumulated value, and a difference in amount of stored electric charges of each of the battery cells  10  as a battery control value. 
     The DOD is the ratio of a chargeable capacity (a capacity obtained by subtracting the remaining capacity of the battery cell  10  from the full charging capacity thereof) to the full charging capacity of the battery cell  10 . The difference in amount of stored electric charges is a difference between the SOC at the current time point and a predetermined reference SOC (e.g., SOC 50 [%]). 
     INDUSTRIAL APPLICABILITY 
     The present invention is applicable to various movable bodies, a power storage device, a mobile equipment, and others using electric power as a driving source.