Patent Publication Number: US-2021184481-A1

Title: Battery management system and cell supervising circuit

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application of PCT International Application No. PCT/JP2019/033494 filed on Aug. 27, 2019, designating the United States of America, which is based on and claims priority of Japanese Patent Application No. 2018-160143 filed on Aug. 29, 2018. The entire disclosures of the above-identified applications, including the specifications, drawings and claims are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present disclosure relates to a battery management system and a cell supervising circuit included in the same. 
     BACKGROUND 
     PTL 1 relates to a battery system including a plurality of battery cells, and particularly relates to a cell balancing system for a battery system including a plurality of battery cells and a method in a traditional technique for balancing the battery cells. 
     CITATION LIST 
     Patent Literature 
     PTL 1: U.S. Pat. No. 9,153,973 
     SUMMARY 
     Technical Problem 
     The present disclosure provides a battery management system which can suppress a failure of cell balancing caused by a variation in operating power among cell supervising circuits, and a cell supervising circuit included in the same. 
     Solution to Problem 
     The battery management system according to one aspect of the present disclosure includes cell supervising circuits connected to an alternating current power line; and a management device connected to the alternating current power line. The management device includes an information processor which instructs at least one of the cell supervising circuits to control a state of charge of a storage cell monitored by the at least one of the cell supervising circuits, based on pieces of information in the cell supervising circuits, the information indicating a state of charge of a storage cell monitored by each of the cell supervising circuits. 
     The cell supervising circuit according to one aspect of the present disclosure is a cell supervising circuit which monitors a storage cell, the cell supervising circuit including an insulating element for receiving electric power through an alternating current power line in a non-contact manner; a communication circuit which receives an instruction to control a state of charge of the storage cell from a management device which manages the state of the storage cell, the management device being connected to the alternating current power line via the insulating element; and a circuit which controls the state of charge of the storage cell based on the instruction. 
     Advantageous Effects 
     The present disclosure implements a battery management system which can suppress the failure of cell balancing in operating power among the cell supervising circuits, and a cell supervising circuit included in the same. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other advantages and features will become apparent from the following description thereof taken in conjunction with the accompanying Drawings, by way of non-limiting examples of embodiments disclosed herein. 
         FIG. 1  is a diagram illustrating an outline of the functional configuration of the BMS according to Embodiment 1. 
         FIG. 2  is a flowchart illustrating the operation of the BMS according to Embodiment 1. 
         FIG. 3  is a diagram illustrating an outline of the functional configuration of the BMS according to Embodiment 2. 
         FIG. 4  is a flowchart illustrating the operation of the BMS according to Embodiment 2. 
         FIG. 5  is a diagram illustrating an outline of the functional configuration of the BMS according to Embodiment 3. 
         FIG. 6  is a flowchart illustrating the operation of the BMS according to Embodiment 3. 
         FIG. 7  is a diagram illustrating an outline of the functional configuration of the BMS according to Embodiment 4. 
         FIG. 8  is a flowchart illustrating the operation of the BMS according to Embodiment 4. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiment 1 
     [Configuration] 
     The battery management system (BMS) according to Embodiment 1 will now be described. Initially, the configuration of the BMS according to Embodiment 1 will be described.  FIG. 1  is a diagram illustrating an outline of the functional configuration of the BMS according to Embodiment 1. 
     BMS  100  according to Embodiment 1 is mounted on a vehicle such as an electric vehicle, for example. BMS  100  includes battery management unit (BMU)  10 , secondary battery cells  21 , and cell supervising circuits (CSCs)  30  corresponding to secondary battery cells  21 . Although two second battery cells  21  and two cell supervising circuits  30  are illustrated in  FIG. 1 , the number of secondary battery cells  21  and that of cell supervising circuits  30  are not limited to two, and may be three or more. Alternatively, BMS  100  may include only one secondary battery cell  21  and only one cell supervising circuit  30 . BMU  10  and cell supervising circuits  30  are connected to alternating current power line  50  via a transformer. 
     BMU  10  supervises the states of secondary battery cells  21  and performs charge control of secondary battery cells  21 . Secondary battery cell  21  is one example of a storage cell. Specifically, secondary battery cell  21  is a lithium ion battery, and may be another battery such as a nickel hydrogen battery. Secondary battery cells  21  are connected in serial, for example. Part or all of them may be connected in parallel. Secondary battery cells  21  constitute an assembled battery. 
     Instead of secondary battery cells  21 , BMS  100  may include energy storage capacitor cells. The energy storage capacitor cell is another example of the storage cell. Specifically, the energy storage capacitor cell is an electrical double-layer capacitor, and may be a lithium ion capacitor or the like. 
     Specifically, BMU  10  includes communication circuits  11 , alternating current power supply  12 , control microcomputer  13 , and transformer  14 . To be noted, it is sufficient that BMU  10  includes at least control microcomputer  13 . 
     Communication circuit  11  is one example of a second communication circuit, which allows BMU  10  to communicate with each of cell supervising circuits  30  via alternating current power line  50 . Communication circuit  11  specifically includes a transmission circuit for transmitting a signal, a filter, an amplification circuit, a reception circuit for receiving a signal, a filter, and an amplification circuit. Alternating current power line  50  used in communication is a power line shared with BMU  10  and cell supervising circuits  30 , and is connected to BMU  10  and cell supervising circuits  30  via transformers. Alternating current power line  50  is used to feed electric power from alternating current power supply  12  to cell supervising circuits  30 . 
     Alternating current power supply  12  feeds AC power to each of cell supervising circuits  30  via alternating current power line  50 . Thus, in BMS  100 , the AC power is fed from BMU  10  to each of cell supervising circuits  30  across the galvanic isolation boundary. In other words, each cell supervising circuit  30  operates by the power fed from alternating current power supply  12  but not from assembled battery  20 . 
     Control microcomputer  13  supervises the states of secondary battery cells  21 , and controls a plurality of assembled batteries  20 . Control microcomputer  13  is one example of an information processor. 
     Cell supervising circuits  30  are circuits having one-to-one correspondence with secondary battery cells  21 . In other words, one cell supervising circuit  30  supervises only one secondary battery cell  21 . Cell supervising circuit  30  is a circuit module, and is formed by packaging circuit parts on a substrate. Specifically, cell supervising circuit  30  includes measuring circuit  31 , communication circuit  37 , transformer  38 , converting circuit  39 , clock generating circuit  40 , and charge circuit  41 . 
     Measuring circuit  31  measures the state of charge of the target secondary battery cell  21 . Specifically, measuring circuit  31  measures the voltage of the target secondary battery cell  21  as a parameter indicating the state of charge of the target secondary battery cell  21 . Measuring circuit  31  includes switching element  32 , AD converter  34 , storage  35 , and control circuit  36 . To be noted, it is sufficient that measuring circuit  31  measures the parameter directly or indirectly indicating the state of charge. 
     Switching element  32  turns on secondary battery cell  21  connected thereto to cause secondary battery cell  21  to discharge. Thus, the state of charge is adjusted. 
     AD converter  34  converts an analog voltage of secondary battery cell  21  into a digital voltage. 
     Storage  35  is a nonvolatile semiconductor memory, for example, and stores an address for distinguishing cell supervising circuit  30  from other cell supervising circuits  30  (in other words, identification information or an identification code). This address can also be considered as the identification information for distinguishing secondary battery cell  21  from other secondary battery cells  21 . Although storage  35  is illustrated as part of measuring circuit  31  (in other words, is included in measuring circuit  31 ) in the example of  FIG. 1 , storage  35  may be disposed as a component separated from measuring circuit  31 . 
     Control circuit  36  generates information including the value of the digital voltage output from AD converter  34  and the address stored in storage  35  (also referred to as information indicating the state of charge measured by measuring circuit  31 ), and outputs the generated information to communication circuit  37 . In other words, control circuit  36  is a control logic circuit. 
     Communication circuit  37  is one example of a first communication circuit, and transmits the information indicating the state of charge measured by measuring circuit  31  to BMU  10 , which manages the state of second battery cell  21 , via transformer  38 . Specifically, communication circuit  37  includes a transmission circuit for transmitting a signal, a filter, an amplification circuit, a reception circuit for receiving a signal, a filter, and an amplification circuit. 
     Transformer  38  is an insulating element which enables measuring circuit  31  to receive power supply in a non-contact manner from alternating current power supply  12 , which is a power supply different from second battery cell  21 . Instead of transformer  38 , cell supervising circuit  30  may include another coil element as the insulating element. 
     Converting circuit  39  converts the AC power, which is fed from alternating current power supply  12  via transformer  38 , to the DC power to feed the DC power to measuring circuit  31 , communication circuit  37 , clock generating circuit  40 , and charge circuit  41 . Specifically, converting circuit  39  includes a full-wave rectification circuit, a smoothing circuit, and a regulator. 
     The frequency of the AC power fed by alternating current power supply  12  is several hundreds kilohertz (kHz), for example, and more specifically, 350 kHz, for example. The effective value of the AC voltage is 5 V, for example. The frequency and the effective value of alternating current power supply  12  are not particularly limited. 
     Clock generating circuit  40  generates a clock signal in synchronization with the frequency of the AC power. Measuring circuit  31  measures the voltage of secondary battery cell  21  based on the generated clock signal. Specifically, clock generating circuit  40  is implemented by a phase synchronization circuit (or a phase locked loop (PLL) circuit). Clock generating circuit  40  can synchronize the system clocks of cell supervising circuits  30 . 
     Charge circuit  41  charges secondary battery cell  21  with the DC power output by converting circuit  39 . The operation of charge circuit  41  is controlled by control circuit  36 , for example. 
     [Differences from Configuration of Standard BMS] 
     To suppress heat generation, ignition, explosion, and degradation caused by overcharge of secondary battery cell  21  and to maximize the states of charge of the secondary battery cells, a standard BMS performs cell balancing processing to balance the states of charge (SOC) of the secondary battery cells, and then charges assembled battery  20 . At this time, the BMU performs daisy-chain (string) communication with the cell supervising circuits to manage the states of charge of the secondary battery cells (in other words, the voltages of the secondary battery cells). 
     In such a standard BMS, electric power is fed to each of cell supervising circuits  30  from the secondary battery cell, which is the target to be monitored by the cell supervising circuit. In such a configuration, the cell balancing is failed due to a variation in operating power among the cell supervising circuits. In particular, a variation in operating power caused by the difference in frequency of communication among the cell supervising circuits is a significant cause to fail the cell balancing. 
     To suppress the failure of cell balancing, a method of feeding electric power to a cell supervising circuit from another power supply different from the secondary battery cell (such as a 12 V battery in applications where the BMS is mounted on a vehicle) is considered. In this method, the another power supply should be galvanically isolated from the secondary battery cell. The method of feeding electric power from another power supply to the cell supervising circuit is specifically feeding of electric power to the cell supervising circuit by an insulating DC-DC converter using a transformer. 
     However, when the method of feeding electric power from another power supply to the cell supervising circuit is used in the standard BMS, a power supply path (such as a wiring or a harness) should be disposed between a plurality of cell supervising circuits and the BMU. This causes new problems such as an increase in the number of parts and an increase in weight. 
     In contrast, BMS  100  also uses the power supply path (alternating current power line  50  and transformer  38 ) of alternating current power supply  12  as the communication path for BMU  10  and cell supervising circuits  30 . Thus, it is unnecessary to separately dispose another power supply path. In other words, BMS  100  can suppress an increase in the number of parts and an increase in weight and can suppress the failure of cell balancing caused by a variation in operating power among cell supervising circuits  30 . 
     The frequency bandwidth used in communication is higher than the frequency of the AC power. In other words, communication circuit  11  and communication circuit  37  communicate using a frequency bandwidth higher than the frequency of the AC power. The carrier wave frequency of communication is 20 MHz, for example. 
     The frequency bandwidth used in communication may be divided into a plurality of frequency channels. For example, each of cell supervising circuits  30  uses part of the frequency bandwidth as a communication channel assigned to cell supervising circuit  30 . Thereby, the communication rate and the communication quality can be improved. 
     [Operation] 
     BMS  100  can easily perform an active cell balancing processing. Hereinafter, such an operation of BMS  100  will be described.  FIG. 2  is a flowchart illustrating the operation of BMS  100 . 
     First, each of cell supervising circuits  30  transmits the information indicating the state of charge of secondary battery cell  21 , which is measured by measuring circuit  31 , through communication circuit  37 . Communication circuit  11  in BMU  10  receives the pieces of information indicating the states of charge of secondary battery cells  21 , which are the targets monitored by cell supervising circuits  30 , from cell supervising circuits  30 , respectively (S 11 ). As described above, each information contains an address, and BMU  10  (control microcomputer  13 ) can distinguish the states of charge of secondary battery cells  21 . 
     Next, based on the received pieces of information, control microcomputer  13  in BMU  10  instructs at least one of cell supervising circuits  30  to charge secondary battery cell  21  using the AC power obtained through alternating current power line  50  (S 12 ). 
     Specifically, based on the pieces of information indicating the states of charge, which are received in step S 11 , control microcomputer  13  specifies secondary battery cell  21  having the highest state of charge as the target cell. Subsequently, control microcomputer  13  instructs cell supervising circuit  30  which monitors another secondary battery cell  21  other than the target cell to charge another secondary battery cell  21  monitored by another cell supervising circuit  30  until the state of charge of another secondary battery cell  21  is substantially equal to the state of charge of the target cell. This instruction is performed through the communication between communication circuit  11  and communication circuit  37  (i.e., communication using alternating current power line  50 ), and control circuit  36  of cell supervising circuit  30  which receives the instruction causes charge circuit  41  to charge secondary battery cell  21 . 
     As described above, by charging secondary battery cells  21 , BMS  100  can successfully provide cell balancing among secondary battery cells  21  connected to cell supervising circuits  30 , respectively. The active cell balancing processing implemented by BMS  100  can suppress heat generation, which is a problem in a passive cell balancing processing where secondary battery cells  21  are forcibly discharged to perform conversion to thermal energy. 
     Embodiment 2 
     [Configuration] 
     The BMS according to Embodiment 2 will now be described. Initially, the configuration of the BMS according to Embodiment 2 will be described.  FIG. 3  is a diagram illustrating an outline of functional configuration of the BMS according to Embodiment 2. In Embodiment 2, differences from Embodiment 1 will be mainly described, and the description of the contents described in Embodiment 1 will be appropriately omitted or simplified. 
     BMS  100   a  according to Embodiment 2 includes BMU  10 , assembled batteries  20 , and cell supervising circuits  30   a  corresponding to assembled batteries  20 . 
     Unlike cell supervising circuit  30 , cell supervising circuit  30   a  monitors assembled battery  20  including a plurality of secondary battery cells  21 . Secondary battery cells  21  are connected to one another in series, and may be partially connected in parallel. Assembled battery  20  may include any number of secondary battery cells  21 . 
     For such cell supervising circuit  30   a  which monitors a plurality of secondary battery cells  21 , measuring circuit  31   a  included in cell supervising circuit  30   a  includes a plurality of switching elements  32  and multiplexer  33 . 
     By selectively turning on switching elements  32 , multiplexer measures the voltage across secondary battery cell  21  corresponding to switching element  32  turned on. For example, by selectively turning on switching elements  32  in a predetermined order, multiplexer  33  measures the voltage of each of secondary battery cells  21  included in one assembled battery  20 . 
     Cell supervising circuit  30   a  includes charge circuit  42 , rather than charge circuit  41 . Charge circuit  42  includes converting circuit  42   a  and selecting circuit  42   b.    
     Converting circuit  42   a  converts the AC power obtained through alternating current power line  50  to the DC power. Specifically, converting circuit  42   a  includes a transformer, a full-wave rectification circuit which converts the AC power fed via this transformer into the DC power (DC voltage), and a smoothing circuit which smooths the DC voltage output from the full-wave rectification circuit. Converting circuit  42   a  is a converting circuit different from converting circuit  39 . 
     Selecting circuit  42   b  is a circuit which selectively charges secondary battery cells  21 , which are the targets monitored by cell supervising circuit  30   a . Specifically, selecting circuit  42   b  switches two output terminals of the full-wave rectification circuit included in converting circuit  42   a  to be electrically connected to one of secondary battery cells  21 . In other words, selecting circuit  42   b  switches secondary battery cells  21  as the target to be charged. Selecting circuit  42   b  is implemented by a plurality of switching elements, and on/off control of the switching elements is performed by control circuit  36 , for example. 
     Usually, when the cell supervising circuit monitors a plurality of secondary battery cells connected in series, these secondary battery cells have different reference potentials. For this reason, to selectively charge the secondary battery cells, charging should be performed by raising the reference voltage from the lowest potential (GND) of the cell supervising circuit using an inverter, a DC-DC converter, or a charge pump. In other words, voltage shift should be performed. 
     In contrast, in BMS  100   a , the AC power is fed to cell supervising circuit  30   a . Charge circuit  42  can easily perform voltage shift utilizing the feed of the AC power according to the circuit configuration above. 
     [Operation] 
     The operation of BMS  100   a  will now be described.  FIG. 4  is a flowchart illustrating the operation of BMS  100   a.    
     Initially, each of cell supervising circuits  30   a  transmits pieces of information indicating the states of charge of secondary battery cells  21 , which are measured by measuring circuit  31 , to communication circuit  37 . Communication circuit  11  in BMU  10  receives the pieces of information indicating the states of charge of secondary battery cells  21 , which are the targets monitored by each of cell supervising circuits  30   a , from each of cell supervising circuits  30   a  (S 21 ). As described above, each information contains an address. Thus, BMU  10  (control microcomputer  13 ) can specify cell supervising circuit  30   a  (assembled battery  20 ) which transmits the pieces of information. Each cell supervising circuit  30   a  sequentially transmits the pieces of information indicating the states of charge of secondary battery cells  21 . Secondary battery cells  21  as the targets monitored by cell supervising circuit  30   a  (i.e., secondary battery cells  21  included in one assembled battery  20 ) are distinguished in this order, for example. 
     Next, based on the received pieces of information, control microcomputer  13  in BMU  10  instructs at least one of cell supervising circuits  30   a  to charge secondary battery cells  21  using the AC power obtained through alternating current power line  50  (S 22 ). 
     Specifically, based on the pieces of information indicating the states of charge, which are received in step S 21 , control microcomputer  13  specifies secondary battery cell  21  having the highest state of charge as the target cell. Subsequently, control microcomputer  13  instructs another cell supervising circuit  30   a  which monitors another secondary battery cell  21  other than the target cell to charge another secondary battery cell  21  monitored by another cell supervising circuit  30   a  until the state of charge of another secondary battery cell  21  is substantially equal to the state of charge of the target cell. This instruction is performed through communication between communication circuit  11  and communication circuit  37  (i.e., communication using alternating current power line  50 ), and control circuit  36  of cell supervising circuit  30   a  which receives the instruction to cause charge circuit  42  to charge secondary battery cell  21 . In other words, based in the instruction from BMU  10 , charge circuit  42  performs discharge from secondary battery cell  21  to alternating current power line  50 . 
     As described above, BMS  100   a  can successfully provide cell balancing among secondary battery cells  21  by charging secondary battery cell  21 . The active cell balancing processing implemented by BMS  100   a  can suppress heat generation, which is a problem in the passive cell balancing processing. 
     Embodiment 3 
     [Configuration] 
     The BMS according to Embodiment 3 will now be described. Initially, the configuration of the BMS according to Embodiment 3 will be described.  FIG. 5  is a diagram illustrating an outline of the functional configuration of the BMS according to Embodiment 3. In Embodiment 3, differences from Embodiments 1 and 2 will be mainly described, and the description of the contents described in Embodiments 1 and 2 will be appropriately omitted or simplified. 
     BMS  100   b  according to Embodiment 3 includes BMU  10 , assembled batteries  20 , cell supervising circuits  30   b  corresponding to assembled batteries  20 , and assembled battery charge circuit  60 . 
     Unlike cell supervising circuit  30   a , cell supervising circuit  30   b  includes discharge circuit  43  rather than charge circuit  42 . Discharge circuit  43  includes selecting circuit  43   a  and converting circuit  43   b.    
     Selecting circuit  43   a  is a circuit for selectively discharging a plurality of secondary battery cells  21 , which are the targets monitored by cell supervising circuit  30   b . Specifically, selecting circuit  43   a  switches two input terminals of converting circuit  43   b  to be electrically connected to one of secondary battery cells  21 . In other words, selecting circuit  43   a  switches secondary battery cells  21  as the discharge target. Selecting circuit  43   a  is implements by a plurality of switching elements, and on/off control of the switching elements is performed by control circuit  36 , for example. 
     Converting circuit  43   b  converts the DC power obtained through discharge of secondary battery cell  21  into the AC power, and outputs the AC power to alternating current power line  50 . Specifically, converting circuit  43   b  is an inverter circuit configured of four switching elements. On/off control of the four switching elements is performed by control circuit  36 , for example. 
     BMS  100   b  includes assembled battery charge circuit  60 . Assembled battery charge circuit  60  is a circuit for charging assembled batteries  20  each including a plurality of secondary battery cells  21  (more specifically, assembled batteries  20  connected in series) using the AC power obtained through alternating current power line  50  by the discharge operation by discharge circuit  43 . Specifically, assembled battery charge circuit  60  includes a transformer connected to alternating current power line  50 , a full-wave rectification circuit which converts the AC power fed via this transformer to the DC power, a smoothing circuit which smooths the DC voltage output by the full-wave rectification circuit, and a charge controller which performs on/off control of charge. 
     [Operation] 
     The operation of BMS  100   b  will now be described.  FIG. 6  is a flowchart illustrating the operation of BMS  100   b.    
     Initially, each of cell supervising circuits  30   b  transmits pieces of information indicating the states of charge of secondary battery cells  21 , which are measured by measuring circuit  31 , through communication circuit  37 . Communication circuit  11  in BMU  10  receives the pieces of information indicating the states of charge of secondary battery cells  21 , which are the targets monitored by each of cell supervising circuits  30   b , from each of cell supervising circuits  30   b  (S 31 ). As described above, each information contains an address, and BMU  10  (control microcomputer  13 ) can specify cell supervising circuit  30   b  (assembled battery  20 ) which transmits the information. 
     Each cell supervising circuit  30   b  sequentially transmits the pieces of information indicating the states of charge of secondary battery cells  21 . Secondary battery cells  21  as the targets monitored by each cell supervising circuit  30   b  (i.e., secondary battery cells  21  included in one assembled battery  20 ) are distinguished in this order, for example. 
     Next, based on the received pieces of information, control microcomputer  13  in BMU  10  instructs at least one of cell supervising circuits  30   b  to discharge secondary battery cells  21  using the AC power obtained through alternating current power line  50  (S 32 ). 
     Specifically, based on the pieces of information indicating the states of charge, which are received in step S 31 , control microcomputer  13  specifies secondary battery cell  21  having the lowest state of charge as the target cell. Subsequently, control microcomputer  13  instructs another cell supervising circuit  30   b  which monitors another secondary battery cell  21  other than the target cell to discharge secondary battery cell  21  monitored by another cell supervising circuit  30   b  until the state of charge of another secondary battery cell  21  is substantially equal to the state of charge of the target cell. This instruction is performed through communication between communication circuit  11  and communication circuit  37  (i.e., communication using alternating current power line  50 ), and control circuit  36  of cell supervising circuit  30   b  which receives the instruction causes discharge circuit  43  to discharge secondary battery cell  21 . In other words, based on the instruction from BMU  10 , discharge circuit  43  performs discharge from secondary battery cell  21  to alternating current power line  50 . 
     When discharge to alternating current power line  50  (in other words, addition of the AC power) is performed by discharge circuit  43 , the frequency and the phase of the discharged energy should be matched with those of alternating current power supply  12 . In BMS  100   b , the AC power is fed to cell supervising circuit  30   b  via transformer  38 . For this reason, by monitoring the AC power and controlling discharge circuit  43 , cell supervising circuit  30   b  (specifically, control circuit  36  or the like) can readily match the frequency and the phase of the discharged energy with those of alternating current power supply  12 . In addition of the AC power, the direction of the current of the discharged energy is appropriately adjusted using an ammeter (the component represented by symbol “A” in  FIG. 5 ). 
     Here, although the electric power discharged to alternating current power line  50  by discharge circuit  43  may be used in any manner, the electric power is regenerated to assembled battery  20  in BMS  100   b . In other words, assembled battery  20  is charged (S 33 ). Specifically, for example, assembled battery charge circuit  60  (charge controller) is turned on by an instruction transmitted by BMU  10  (control microcomputer  13 ) via the communication path (not illustrated in  FIG. 5 ) using alternating current power line  50 . 
     As described above, BMS  100   b  can successfully provide cell balancing among secondary battery cells  21  by discharging secondary battery cell  21 . The active cell balancing processing implemented by BMS  100   b  can suppress heat generation, which is a problem in the passive cell balancing processing. 
     Although the standard active cell balancing processing has a problem in treatment of the discharged energy, BMS  100   b  can readily regenerate the discharged energy to assembled battery  20  by outputting the discharged energy to alternating current power line  50 . 
     To be noted, it is more preferred that BMS  100   b  match the total of the discharged energy (the electric power added in the cell balancing processing) and the AC power output by alternating current power supply  12  with the electric power consumed by the entire system. 
     Embodiment 4 
     [Configuration] 
     The BMS according to Embodiment 4 will now be described. Initially, the configuration of the BMS according to Embodiment 4 will be described.  FIG. 7  is a diagram illustrating an outline of the functional configuration of the BMS according to Embodiment 4. In Embodiment 4, the differences from Embodiments 1 to 3 will be mainly described, and the description of the contents described in Embodiments 1 to 3 will be appropriately omitted or simplified. 
     BMS  100   c  according to Embodiment 4 includes BMU  10 , assembled batteries  20 , cell supervising circuits  30   b  corresponding to assembled batteries  20 , and battery charge circuit  70 . 
     Unlike BMS  100   b , BMS  100   c  includes battery charge circuit  70  rather than assembled battery charge circuit  60 . 
     Battery charge circuit  70  is a circuit for charging battery  80  different from assembled batteries  20  (secondary battery cells  21 ) using the AC power obtained through alternating current power line  50  by discharging discharge circuit  43 . Battery  80  is a 12 V battery mounted on vehicles, for example, and is galvanically isolated from assembled batteries  20 . Specifically, battery charge circuit  70  includes a transformer connected to alternating current power line  50 , a full-wave rectification circuit which converts the AC power fed via the transformer to the DC power, a smoothing circuit which smooths the DC voltage output by the full-wave rectification circuit, and a charge controller which controls on/off of charge. 
     [Operation] 
     The operation of BMS  100   c  will now be described.  FIG. 8  is a flowchart illustrating the operation of BMS  100   c.    
     Initially, communication circuit  11  in BMU  10  receives pieces of information indicating the states of charge of secondary battery cells  21  monitored by each of cell supervising circuits  30   b  from each of cell supervising circuits  30   b  (S 41 ). The processing in step S 41  is the same as that in step S 31 . 
     Next, based on the received pieces of information, control microcomputer  13  in BMU  10  instructs at least one of cell supervising circuits  30   b  to discharge secondary battery cells  21  using the AC power obtained through alternating current power line  50  (S 42 ). The processing in step S 42  is the same as that in step S 32 . 
     In BMS  100   c , the electric power discharged by discharge circuit  43  to alternating current power line  50  is regenerated across the galvanic isolation boundary to battery  80  different from assembled battery  20 . In other words, battery  80  is charged (S 43 ). Specifically, for example, battery charge circuit  70  (charge controller) is turned on by an instruction transmitted by BMU  10  (control microcomputer  13 ) via a communication path (not illustrated in  FIG. 7 ) using alternating current power line  50 . 
     As described above, BMS  100   c  can successfully provide cell balancing among secondary battery cells  21  by discharging secondary battery cells  21 . The active cell balancing processing implemented by BMS  100   c  can suppress heat generation, which is a problem in the passive cell balancing processing. 
     Although the standard active cell balancing processing has a problem in treatment of the discharged energy, BMS  100   c  can readily regenerate the discharged energy to battery  80  (i.e., regeneration of the electric power across the galvanic isolation boundary) by outputting the discharged energy to alternating current power line  50 . 
     To be noted, it is more preferred that BMS  100   c  match the total of the discharged energy (the electric power added in the cell balancing processing) and the AC power output by alternating current power supply  12  with the electric power consumed by the entire system. 
     SUMMARY 
     As described above, BMS  100  includes cell supervising circuits  30  connected to alternating current power line  50 , and BMU  10  connected to alternating current power line  50 . BMU  10  includes control microcomputer  13  which instructs at least one of cell supervising circuits  30  to control the state of charge of secondary battery cell  21  monitored by the at least one of cell supervising circuits  30 , based on the pieces of information in cell supervising circuits  30 , the information indicating the state of charge of storage cell  21  monitored by each of cell supervising circuits  30 . Transformer  38  and transformer  14  are one example of the insulating element, and BMU  10  is one example of the management device. Secondary battery cell  21  is one example of the storage cell, and control microcomputer  13  is one example of the information processor. Control of the state of charge means adjustment of the state of charge in other words. 
     Such BMS  100  can successfully provide cell balancing among secondary battery cells  21  connected to cell supervising circuits  30 , respectively. BMS  100  can suppress the failure of cell balancing caused by a variation in operating power among cell supervising circuits  30  because cell supervising circuits  30  can operate by the electric power fed from alternating current power supply  12 , which is a power supply different from secondary battery cells  21 . 
     Moreover, each of cell supervising circuits  30  includes communication circuit  37  which transmits the information, for example. BMU  10  further includes communication circuit  11  which receives the information. Communication circuit  37  and communication circuit  11  communicate with each other via alternating current power line  50 . Communication circuit  37  is one example of the first communication circuit, and communication circuit  11  is one example of the second communication circuit. 
     Such BMS  100  also uses the power supply path from alternating current power supply  12  (which is a power supply different from secondary battery cells  21 ) to cell supervising circuits  30  as a communication path between BMU  10  and cell supervising circuits  30 . For this reason, BMS  100  can prevent addition of components related with communication, and can suppress the failure of cell balancing caused by a variation in operating power among cell supervising circuits  30 . 
     Moreover, each of cell supervising circuits  30  monitors only one secondary battery cell  21 , for example. 
     Such BMS  100  can successfully provide cell balancing among secondary battery cells  21  connected to cell supervising circuits  30 , respectively. 
     Moreover, control microcomputer  13  gives an instruction for charge as control of the state of charge, for example. Each of cell supervising circuits  30  includes converting circuit  39  which controls the AC power obtained through alternating current power line  50  to the DC power, and charge circuit  41  for charging secondary battery cell  21  using the DC power, secondary battery cell  21  being monitored by cell supervising circuit  30 . 
     Such BMS  100  can successfully provide cell balancing among secondary battery cells  21  connected to cell supervising circuits  30 , respectively, by charging secondary battery cell  21 . 
     Moreover, in BMS  100   a , each of cell supervising circuits  30   a  monitors a plurality of secondary battery cells  21 , for example. 
     Such BMS  100   a  can successfully provide cell balancing among pluralities of secondary battery cells  21  connected to cell supervising circuits  30   a , respectively, and among each of the pluralities of secondary battery cells  21  connected to its corresponding cell supervising circuit  30   a.    
     Moreover, in BMS  100   a , control microcomputer  13  gives an instruction for charge as the control of the state of charge, for example. Each of cell supervising circuits  30   a  includes converting circuit  42   a  which converts the AC power obtained through alternating current power line  50  to the DC power, and selecting circuit  42   b  for selectively charging the plurality of secondary battery cells  21  monitored by cell supervising circuit  30   a.    
     By charging secondary battery cell  21 , such BMS  100   a  can successfully provide cell balancing among pluralities of secondary battery cells  21  connected to cell supervising circuits  30   a , respectively, and among each of the pluralities of secondary battery cells  21  connected to its corresponding cell supervising circuit  30   a.    
     Moreover, in BMS  100   b , control microcomputer  13  gives an instruction for discharge as the control of the state of charge, for example. Each of cell supervising circuits  30   b  includes selecting circuit  43   a  for selectively discharging a plurality of secondary battery cells  21  monitored by cell supervising circuit  30   b , and converting circuit  43   b  which converts the DC power obtained by the discharging to the AC power, and outputs the AC power to alternating current power line  50 . 
     By discharging secondary battery cell  21 , BMS  100   a  can successfully provide cell balancing among pluralities of secondary battery cells  21  connected to cell supervising circuits  30   a , respectively, and among each of the pluralities of secondary battery cells  21  connected to its corresponding cell supervising circuit  30   a.    
     Moreover, in BMS  100   b , control microcomputer  13  gives an instruction for discharge to alternating current power line  50  as the control of the state of charge, for example. BMS  100   b  further includes assembled battery charge circuit  60  for charging assembled battery  20  including secondary battery cells  21  using the AC power obtained through alternating current power line  50  by the discharge. 
     By discharging secondary battery cell  21 , such BMS  100   b  can successfully provide cell balancing among pluralities of secondary battery cells  21  connected to cell supervising circuits  30   b , respectively, and can regenerate the discharged energy to assembled battery  20 . 
     Moreover, in BMS  100   c , control microcomputer  13  gives an instruction for discharge to alternating current power line  50  as the control of state of charge, for example. BMS  100   c  further includes battery charge circuit  70  for charging battery  80  different from secondary battery cell  21  using the AC power obtained through alternating current power line  50  by the discharge. 
     By discharging secondary battery cell  21 , such BMS  100   b  can successfully provide cell balancing among pluralities of secondary battery cells  21  connected to cell supervising circuits  30   b , respectively, and can regenerate the discharged energy to battery  80 . 
     Moreover, cell supervising circuit  30  which monitors secondary battery cell  21  includes transformer  38  for receiving electric power through alternating current power line  50  in a non-contact manner, communication circuit  37  which receives an instruction to control the state of charge of secondary battery cell  21  from BMU  10  which manages the states of secondary battery cells  21 , BMU  10  being connected to transformer  14  via alternating current power line  50 , and a circuit which controls the state of charge of secondary battery cell  21  based on the instruction. 
     Such cell supervising circuit  30  can suppress the failure of cell balancing caused by a variation in operating power among cell supervising circuits  30  because cell supervising circuit  30  can operate by the electric power fed by alternating current power supply  12 , which is a power supply different from secondary battery cell  21 . 
     Moreover, in cell supervising circuit  30 , the circuit is charge circuit  41  which charges secondary battery cell  21  based on the instruction using the AC power obtained through alternating current power line  50 , for example. In cell supervising circuit  30   a , the circuit is charge circuit  42  which charges secondary battery cell  21  based on the instruction using the AC power obtained through alternating current power line  50 . 
     By charging secondary battery cell  21  based on the instruction, such cell supervising circuit  30  can successfully provide cell balancing between secondary battery cell  21  and secondary battery cells  21  connected to other cell supervising circuits  30 . The same applies to cell supervising circuit  30   a.    
     Moreover, in cell supervising circuit  30   b , the circuit is discharge circuit  43  which performs discharge from secondary battery cell  21  to alternating current power line  50  based on the instruction, for example. 
     By discharging secondary battery cell  21  based on the instruction, such cell supervising circuit  30   b  can successfully provide cell balancing between secondary battery cell  21  and secondary battery cells  21  connected to other cell supervising circuits  30   b.    
     Other Embodiments 
     The embodiments have been described above, but these embodiments should not be construed as limitations to the present disclosure. 
     For example, although the communication between the BMU and each of the cell supervising circuits is performed using the alternating current power line in the embodiments above, the communication may be performed using a dedicated communication line different from the alternating current power line. In other words, the communication performed using the alternating current power line is not essential. 
     Embodiments 1 to 4 above may be arbitrarily combined. For example, in the configuration where one cell supervising circuit monitors only one secondary battery cell, the cell supervising circuit may include a discharge circuit. Alternatively, the cell supervising circuit may include both of the discharge circuit and the charge circuit. 
     For example, although the transformer is exemplified as the insulating element in the embodiments above, the insulating element may be another insulating element such as an electromagnetic resonance coupler. 
     Although the assembled battery used in electric vehicles are managed in the embodiments above, the BMS may manage batteries used in any application. 
     The circuit configurations described in the embodiments above are exemplary, and these circuit configurations should not be construed as limitations to the present disclosure. In other words, the present disclosure also covers circuits which can implement the functions characteristic to the present disclosure, as well as the circuit configurations above. For example, the present disclosure covers circuits where an element such as a switching element (transistor), a resistor element, or a capacitive element is connected to an element in series or in parallel in the range enabling the same functions as those of the circuit configurations above. 
     The components included in the cell supervising circuit may be integrated in any manner in the embodiments above. For example, the measuring circuit and the communication circuit may be implemented as a single integrated circuit, or may be implemented as separate integrated circuits. 
     The cell supervising circuit is implemented by hardware in the embodiments above. However, part of the components included in the cell supervising circuit may be implemented by executing software programs suitable for the components. Part of the components included in the cell supervising circuit may be implemented by a program executor such as a central processing unit (CPU) or a processor, which reads out and executes software programs recorded on a recording medium such as a hard disk or a semiconductor memory. 
     The information processor is implemented by a microcomputer in the embodiments above. In other words, the functions of the information processor are implemented by a program executor such as a CPU or a processor, which reads out and executes software programs recorded on a recording medium such as a hard disk or a semiconductor memory. However, the information processor may be partially implemented by hardware. 
     Moreover, the processing executed by the specific processor in the embodiments above may be executed by another processor. In the operations described in the embodiments above, the order of processings may be changed, or several processings may be performed in parallel. 
     Besides, the present disclosure also covers embodiments obtained by performing a variety of modifications conceived by persons skilled in the art on the embodiments above or embodiments including any combination of the components and the functions in the embodiments above without departing the gist of the present disclosure. 
     For example, the present disclosure may be implemented as a BMU, a storage capacitor management system, or a storage capacitor management unit. The present disclosure may be implemented as a vehicle (such as an electric vehicle) on which the cell supervising circuit or the BMS according any one of the embodiments above is mounted. The present disclosure may be implemented as an apparatus other than vehicles on which the cell supervising circuit or the BMS according to any one of the embodiments above is mounted. 
     INDUSTRIAL APPLICABILITY 
     The BMS according to the present disclosure and the cell supervising circuit included in the same can be used in broad applications such as applications to vehicles.