Patent Publication Number: US-2023155401-A1

Title: Power storage pack, electric moving body, charging device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a power storage pack capable of being mounted to and unmounted from an electric moving body, an electric moving body, and a charging device. 
     BACKGROUND ART 
     In recent years, electric motorcycles (electric scooters) and electric bicycles have become widespread. Usually, a portable battery pack capable of being mounted and unmounted is used in the electric motorcycle or the electric bicycle. When a battery is used as a power source of the motorcycle (scooter), a time required for energy supply is longer than that in a case where a liquid fuel such as gasoline is used (a charging time is longer than a fueling time). 
     Then, it is considered to construct a mechanism for shortening the time required for energy supply by exchanging a battery pack charged in advance with a battery pack having reduced remaining capacity at the nearest charging stand when the remaining capacity of the battery pack decreases. 
     In order to reduce the number of terminals of the battery pack, it is conceivable to transmit and receive control signals between the battery pack and the vehicle or the charger by wireless communication. In the above mechanism involving exchange of the battery pack, when a battery pack that transmits and receives control signals by wireless communication is used, a circumstance where a plurality of vehicles or a plurality of chargers exist in a range where wireless communication with the battery pack is possible can occur. 
     Under such a circumstance, there is a possibility that a controller of a certain vehicle erroneously controls a battery pack mounted into another adjacent vehicle. There is a possibility that a controller of a charger does not control a battery pack that is supposed to be controlled and is mounted into a certain charging slot but erroneously controls a battery pack that is not supposed to be controlled and is mounted into another charging slot. In such a case, safety and security of the entire charging system cannot be secured. 
     Therefore, the inventors of the present invention have developed a method of correctly identifying a battery pack mounted to a vehicle or a charging device by transmitting identification information from the vehicle or the charging device to the battery pack via a power line, and looping back the identification information from the battery pack to the vehicle or the charging device by wireless communication. In this method, when the identification information is transmitted via the power line, the power line and the high-voltage unit are interrupted, and the power line is used as a low-voltage signal line. 
     PTL 1 discloses a method of suppressing consumption of a battery by making a voltage dividing resistor of an overvoltage protection circuit that monitors the battery separable by a switch. This overvoltage protection circuit protects the battery so as not to apply an overvoltage to the battery, and does not protect a low-voltage controlling circuit from a high-voltage unit in a state where a power line interrupted from the high-voltage unit such as the battery is used as a low-voltage signal line. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL 1: Unexamined Japanese Patent Publication No. 2000-152510 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     The present disclosure has been made in view of such a circumstance, and an object of the present disclosure is to provide a technique for safely performing communication using a power line between a power storage pack and an electric moving body or a charging device. 
     Solution to Problem 
     In order to solve the above problems, a power storage pack of an aspect of the present disclosure includes: a power storage unit for supplying power to an electric moving body; a power line connecting between the power storage unit and a power source terminal for charging and discharging; a first switch inserted into the power line; a controller that communicates with a controller of the electric moving body in a state where the power storage pack is mounted to the electric moving body or communicate with a controller of a charging device in a state where the power storage pack is mounted to a charging slot of the charging device; a communication wiring that connects between a node of the power line on the power source terminal side relative to the first switch and the controller of the power storage pack; a second switch inserted into the communication wiring; and an overvoltage protection circuit that protects a controller of the power storage pack from overvoltage. A controller of the power storage pack controls the first switch to be turned off and the second switch to be turned on when performing communication with a controller of the electric moving body or a controller of the charging device using the power line and the communication wiring, and the overvoltage protection circuit turns off the second switch when detecting an overvoltage of the power line during communication between a controller of the power storage pack and a controller of the electric moving body or a controller of the charging device. 
     Advantageous Effect of Invention 
     According to the present disclosure, it is possible to safely perform communication using a power line between a power storage pack and an electric moving body or a charging device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a conceptual diagram of a vehicle system using an exchangeable battery pack according to an exemplary embodiment. 
         FIG.  2    is a view illustrating a configuration example of a charging device according to the exemplary embodiment. 
         FIG.  3    is a view illustrating a configuration example of a vehicle according to the exemplary embodiment. 
         FIG.  4    is a view illustrating a system configuration example of a battery pack equipped in the vehicle and a vehicle controller according to the exemplary embodiment. 
         FIG.  5    is a view illustrating a basic concept of processing of authenticating, by a vehicle controller, a battery pack mounted into a mounting slot of the vehicle. 
         FIG.  6    is a view schematically illustrating a flow of granting ID to an exchanged battery pack when the battery pack mounted into the mounting slot of the vehicle is exchanged. 
         FIG.  7    is a sequence diagram illustrating a detailed processing flow when a battery pack mounted into the mounting slot of the vehicle is exchanged. 
         FIG.  8    is a sequence diagram illustrating a detailed processing flow when a battery pack mounted into the mounting slot of the vehicle is exchanged. 
         FIG.  9    is a view for explaining configuration example 1 of an overvoltage protection circuit of a first battery pack of  FIG.  4    and a first overvoltage protection circuit of a vehicle. 
         FIG.  10    is a view for explaining configuration example 2 of the overvoltage protection circuit of the first battery pack of  FIG.  4    and the first overvoltage protection circuit of the vehicle. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
       FIG.  1    is a conceptual diagram of vehicle system  1  using exchangeable battery pack  10  according to an exemplary embodiment. In vehicle system  1 , a plurality of battery packs  10 , at least one charging device  20 , and a plurality of vehicles  30  are used. In the present exemplary embodiment, an electric motorcycle (electric scooter) is assumed as vehicle  30 . 
     Battery pack  10  is a portable or exchangeable battery pack capable of being mounted and unmounted, and can be mounted into a mounting slot of vehicle  30  and a charging slot of charging device  20 . Battery pack  10  is charged in a state of being mounted into the charging slot of charging device  20 . Charged battery pack  10  is taken out by a user (usually, a driver of vehicle  30 ) and is mounted into the mounting slot of vehicle  30 . Battery pack  10  mounted into the mounting slot of vehicle  30  discharges during travelling of vehicle  30 , and a remaining capacity is reduced with the discharge. Battery pack  10  having the reduced remaining capacity is taken out by the user and is mounted into the charging slot of charging device  20 . The user takes out charged battery pack  10  from another charging slot of charging device  20  and mounts the charged battery pack into the mounting slot of vehicle  30 . By this work, battery pack  10  having the reduced remaining capacity is exchanged with charged battery pack  10 . Due to this, the user does not need to wait while battery pack  10  is charged, and can resume travelling of vehicle  30  in a short time. 
     In this method, since the mounting and unmounting of battery pack  10  frequently occur, degradation of a connector part of battery pack  10  coming into contact with a connector part of the mounting slot of vehicle  30  or a connector part of the charging slot of charging device  20  easily progresses. As a countermeasure against this, in the present exemplary embodiment, transmission and reception of control signals between vehicle  30  or charging device  20  and battery pack  10  by wireless communication. This can eliminate a terminal for a communication line from a connector. It is sufficient to provide a terminal for a power line in the connector. In the present exemplary embodiment, since wired communication via a connector is not used for the transmission and reception of control signals, it is possible to prevent control signals from being interrupted due to connector failure. 
     Near-field communication is used for wireless communication between vehicle  30  and battery pack  10 , wireless communication between charging device  20  and battery pack  10 , and wireless communication between vehicle  30  and charging device  20 . Bluetooth (registered trademark), Wi-Fi (registered trademark), infrared communication, and the like can be used as the near-field communication. Hereinafter, in the present exemplary embodiment, it is assumed that Bluetooth (registered trademark) Low Energy (BLE) is used as the near-field communication. 
     The BLE is one of extended standards of Bluetooth (registered trademark), and is a low-power-consumption near-field communication standard using a 2.4 GHz band. Since the BLE has low power consumption to such an extent that the battery pack can be driven for several years with one button cell, it is suitable for battery driving, and the influence on the remaining capacity of battery pack  10  can be considered almost ignored. Since many modules for BLE communication are shipped to the market, the modules can be obtained at low cost. The BLE has high affinity with a smartphone, and can provide various services in cooperation with the smartphone. 
     When a general class II device is used, radio wave coverage of the BLE becomes about 10 m. Therefore, a state where there are the plurality of vehicles  30 , the plurality of battery packs  10 , and charging device  20  within a communication range of the BLE can occur. Since charging device  20  is provided with the plurality of charging slots, charging device  20  needs to wirelessly communicate with the plurality of battery packs  10  mounted into the plurality of charging slots. That is, a 1:N network is established between charging device  20  and the plurality of battery packs  10 . Similarly, when vehicle  30  is provided with the plurality of mounting slots, vehicle  30  needs to wirelessly communicate with the plurality of battery packs  10  mounted into the plurality of mounting slots. That is, a 1:N network is established between vehicle  30  and the plurality of battery packs  10 . 
     Therefore, a mechanism for ensuring that battery pack  10  mounted into a specific charging slot of charging device  20  and battery pack  10  of a specific communication partner of charging device  20  are identical is required. Similarly, a mechanism for ensuring that battery pack  10  mounted into a specific mounting slot of vehicle  30  and battery pack  10  of a specific communication partner of vehicle  30  are identical is required. In the present exemplary embodiment, the identity between battery pack  10  physically connected and battery pack  10  connected by wireless communication is confirmed by using identification information (ID). This identification information (ID) is sufficient to be temporal identification information. The identification information (ID) may include identification information unique to each device. 
       FIG.  2    is a view illustrating a configuration example of charging device  20  according to the exemplary embodiment. Charging device  20  includes charging stand  21 , controller  22 , display unit  27 , operation unit  28 , and charging unit  29 . Controller  22  at least includes processor  23 , antenna  25 , and wireless communication unit  26 . 
     Charging stand  21  has a plurality of charging slots SLc 1  to SLc 8  for mounting the plurality of battery packs  10 . Although the number of charging slots is eight in the example illustrated in  FIG.  2   , the number of charging slots may be two or more, and may be four, for example. 
     Each of charging slots SLc 1  to SLc 8  has a connector including a positive-electrode terminal and a negative-electrode terminal, and when battery pack  10  is mounted, the charging slots are conducted to the positive-electrode terminal and the negative-electrode terminal included in the connector of battery pack  10 . A negative-electrode terminal part included in the connector of each of charging slots SLc 1  to SLc 8  and a negative-electrode terminal part included in the connector of battery pack  10  each may include solid GND. In this case, pins included in the connector of battery pack  10  can be integrated with one positive-electrode terminal pin, and the number of projection parts of the connector where defects are likely to occur can be reduced. 
     Processor  13  (see  FIG.  4   ) of each battery pack  10  mounted into charging stand  21  transmits and receives a control signal to and from processor  23  in controller  22  by using the near-field communication and a power line. A specific transmission and reception method for the control signal between both will be described later. 
     The positive-electrode terminal and the negative-electrode terminal of each of charging slots SLc 1  to SLc 8  are connected to a positive-electrode terminal and a negative-electrode terminal of charging unit  29 , respectively. Charging unit  29  is connected to commercial power system  2 , and can charge battery pack  10  mounted into charging stand  21 . Charging unit  29  generates DC power by performing full-wave rectifying of AC power supplied from commercial power system  2  and smoothing it by a filter. 
     A relay not illustrated is provided between the positive-electrode terminal and the negative-electrode terminal of charging unit  29  and between the positive-electrode terminal and the negative-electrode terminal of each of charging slots SLc 1  to SLc 8 . Processor  23  controls conduction or interruption of each of charging slots SLc 1  to SLc 8  by performing control of on (close) or off (open) of the relay. 
     A DC/DC converter not illustrated may be provided between the positive-electrode terminal and the negative-electrode terminal of charging unit  29  and between the positive-electrode terminal and the negative-electrode terminal of each of charging slots SLc 1  to SLc 8 . In this case, by controlling the DC/DC converter, processor  23  controls a charging voltage or a charging current of each battery pack  10 . For example, constant current (CC) charging or constant voltage (CV) charging can be performed. The DC/DC converter may be provided in battery pack  10 . When an AC/DC converter is equipped in battery pack  10 , battery pack  10  can be charged with AC power from charging unit  29 . 
     Processor  23  includes, for example, a microcomputer. Wireless communication unit  26  executes near-field communication processing. In the present exemplary embodiment, wireless communication unit  26  includes a BLE module, and antenna  25  includes a chip antenna or a pattern antenna built in the BLE module. Wireless communication unit  26  outputs, to processor  23 , data received by the near-field communication, and transmits, by the near-field communication, data input from processor  23 . 
     Processor  23  can acquire battery state information from battery pack  10  mounted into charging stand  21 . As the battery state information, information on at least one of voltage, current, temperature, state of charge (SOC), and state of health (SOH) of a plurality of cells E 1  to En (see  FIG.  4   ) in battery pack  10  can be acquired. 
     Display unit  27  includes a display, and displays, on the display, guidance to the user (usually, the driver of vehicle  30 ) who uses charging device  20 . Operation unit  28  is a user interface such as a touchscreen, and accepts an operation from the user. Charging device  20  may further include a speaker (not illustrated) to output audio guidance from the speaker to the user. 
       FIG.  3    is a view illustrating a configuration example of vehicle  30  according to the exemplary embodiment. Vehicle  30  includes battery mounting unit  31 , vehicle controller  32 , instrument panel  39 , inverter  310 , motor  311 , and tire  312 . Vehicle controller  32  at least includes processor  33 , antenna  35 , and wireless communication unit  36 . 
     Battery mounting unit  31  has at least one of mounting slots SLa 1  and SLa 2  for mounting at least one battery pack  10 . Although the number of mounting slots is two in the example illustrated in  FIG.  3   , the number of mounting slots may be one or three or more. 
     Each of mounting slots SLa 1  and SLa 2  has a connector including a positive-electrode terminal and a negative-electrode terminal, and when battery pack  10  is mounted, the mounting slots are conducted to the positive-electrode terminal and the negative-electrode terminal included in the connector of battery pack  10 . A negative-electrode terminal part included in the connector of each of mounting slots SLa 1  and SLa 2  may include solid GND. 
     Processor  13  (see  FIG.  4   ) of each battery pack  10  mounted into battery mounting unit  31  transmits and receives a control signal to and from processor  33  in vehicle controller  32  by using the near-field communication and a power line. A specific transmission and reception method for the control signal between both will be described later. 
     The plurality of positive-electrode terminals of the plurality of mounting slots SLa 1  and SLa 2  are each connected to a positive-side power bus, and the plurality of negative-electrode terminals are each connected to a negative-side power bus. Therefore, the plurality of battery packs  10  mounted into the plurality of mounting slots SLa 1  and SLa 2  have a relationship where they are electrically connected in parallel. Therefore, as the number of battery packs  10  mounted into battery mounting unit  31  increases, the capacity increases. The plurality of battery packs  10  mounted into the plurality of mounting slots SLa 1  and SLa 2  may be electrically connected in series. In that case, an output voltage can be increased. 
     A positive-electrode terminal and a negative-electrode terminal of battery mounting unit  31  are connected to a positive-electrode terminal and a negative-electrode terminal of inverter  310  via main relay RYm. Main relay RYm functions as a contactor between vehicle  30  and battery pack  10 . Processor  33  controls conduction or interruption between vehicle  30  and battery pack  10  by performing control of on or off of main relay RYm. 
     Inverter  310  converts DC power supplied from battery pack  10  mounted into battery mounting unit  31  into AC power and supplies the AC power to motor  311  at the time of power running. The inverter converts AC power supplied from motor  311  into DC power and supplies the DC power to battery pack  10  mounted into battery mounting unit  31  at the time of regeneration. Motor  311  is a three-phase AC motor, and rotates in accordance with the AC power supplied from inverter  310  at the time of power running. The motor converts rotational energy by deceleration into AC power and supplies the AC power to inverter  310  at the time of regeneration. A rotary shaft of motor  311  is coupled to a rotary shaft of tire  312  of a rear wheel. A transmission may be provided between the rotary shaft of motor  311  and the rotary shaft of tire  312 . 
     Vehicle controller  32  is a vehicle electronic control unit (ECU) that controls entire vehicle  30 . Processor  33  of vehicle controller  32  includes a microcomputer. Wireless communication unit  36  executes near-field communication processing. In the present exemplary embodiment, wireless communication unit  36  includes a BLE module, and antenna  35  includes a chip antenna or a pattern antenna built in the BLE module. Wireless communication unit  36  outputs, to processor  33 , data received by the near-field communication, and transmits, by the near-field communication, data input from processor  33 . 
     Processor  33  can acquire battery state information from battery pack  10  mounted into battery mounting unit  31 . As the battery state information, information on at least one of voltage, current, temperature, SOC, and SOH of the plurality of cells E 1  to En (see  FIG.  4   ) in battery pack  10  can be acquired. Processor  33  can acquire speed of vehicle  30 . 
     Instrument panel  39  displays state information of vehicle  30 . For example, the instrument panel displays the speed of vehicle  30  and the remaining capacity (SOC) of battery pack  10 . The driver can judge the necessity of exchange of battery pack  10  by looking at the remaining capacity (SOC) of battery pack  10  displayed on instrument panel  39 . 
       FIG.  4    is a view illustrating a system configuration example of battery pack  10  equipped in vehicle  30  and vehicle controller  32  according to the exemplary embodiment. The example illustrated in  FIG.  4    presents a state where two battery packs  10   a  and  10   b  are mounted into battery mounting unit  31  of vehicle  30  (see  FIG.  3   ). 
     Battery pack  10  includes battery module  11  and battery controller  12 . Battery module  11  is connected on a power line internally connecting positive-electrode terminal Tp and negative-electrode terminal Tm of battery pack  10 . Positive-electrode terminal Tp of battery pack  10  is connected to the positive-side power bus via slot relay RYs, and negative-electrode terminal Tm of battery pack  10  is connected to the negative-side power bus. The positive-side power bus and the negative-side power bus are connected to inverter  310  via main relay RYm (see  FIG.  3   ). 
     Battery module  11  includes the plurality of cells E 1  to En connected in series. Battery module  11  may be configured such that a plurality of battery modules are connected in series or in series-parallel. For the cell, a lithium ion battery cell, a nickel metal hydride battery cell, a lead battery cell, or the like can be used. Hereinafter, the present description assumes an example of use of a lithium ion battery cell (nominal voltage: 3.6 V to 3.7 V). The number of series connections of cells E 1  to En is decided in accordance with a drive voltage of motor  311 . 
     A communication path is branched from node N 1  between positive-electrode terminal Tp of battery pack  10  and battery module  11 . Power relay RYp is inserted between node N 1  and battery module  11 . Current sensor  17  is installed on a power line internally connecting positive-electrode terminal Tp and negative-electrode terminal Tm of battery pack  10 . Current sensor  17  is installed at a position closer to negative-electrode terminal Tm relative to power relay RYp. Current sensor  17  measures a current flowing through battery module  11 , and outputs the measured current value to processor  13  of battery controller  12 . Current sensor  17  can include, for example, a combination of a shunt resistor, a differential amplifier, and an A/D converter. A Hall element may be used in place of the shunt resistor. 
     Battery controller  12  includes processor  13 , voltage measurer  14 , antenna  15 , and wireless communication unit  16 . A plurality of voltage measurement lines connect between voltage measurer  14  and each node of the plurality of cells E 1  to En connected in series. Voltage measurer  14  measures voltage of each of cells E 1  to En by measuring each voltage between adjacent two voltage measurement lines. Voltage measurer  14  transmits the measured voltage value of each of cells E 1  to En to processor  13 . 
     Voltage measurer  14  is high in voltage with respect to processor  13 , and therefore voltage measurer  14  and processor  13  are connected in an insulated state by a communication line. Voltage measurer  14  can be configured using an application specific integrated circuit (ASIC) or a general-purpose analog front-end IC. Voltage measurer  14  includes a multiplexer and an A/D converter. The multiplexer outputs a voltage between adjacent two voltage measurement lines to the A/D converter in order from the top. The A/D converter converts, into a digital value, an analog voltage to be input from the multiplexer. 
     Although not illustrated in  FIG.  4   , at least one temperature sensor is installed near the plurality of cells E 1  to En. The temperature sensor measures the temperature of the plurality of cells E 1  to En, and outputs the measured temperature value to processor  13 . The temperature sensor can include, for example, a combination of a thermistor, a voltage dividing resistor, and an A/D converter. 
     In a case where an A/D converter is equipped in processor  13  and an analog input port is installed in processor  13 , output values of current sensor  17  and the temperature sensor can be input to processor  13  as analog values. 
     Fitting detector  18  detects a fitting state between the connector of battery pack  10  and the connector of battery mounting unit  31  of vehicle  30 . For example, the connector on battery pack  10  may be a female connector, and the connector on battery mounting unit  31  of vehicle  30  may be a male connector. Fitting detector  18  outputs seizing signals corresponding to connection states of both to processor  13 . The seizing signal is defined by a binary signal, and an on signal is output in a state where both are connected, and an off signal is output in a state where both are separated. Fitting detector  18  can include, for example, a reed switch. In this case, fitting detector  18  magnetically determines presence or absence of connection between both. A sensor that mechanically detects the presence or absence of connection between both may be used. 
     Wireless communication unit  16  executes near-field communication processing. In the present exemplary embodiment, wireless communication unit  16  includes a BLE module, and antenna  15  includes a chip antenna or a pattern antenna built in the BLE module. Wireless communication unit  16  outputs, to processor  13 , data received by the near-field communication, and transmits, by the near-field communication, data input from processor  13 . 
     Node N 1  between positive-electrode terminal Tp of battery pack  10  and battery module  11  and processor  13  are connected by communication wiring Lc 1 . Pack-side communication switch SWc is inserted on communication wiring Lc 1 . A fuse (not illustrated) may be inserted on communication wiring Lc 1  in series with pack-side communication switch SWc. The fuse functions as a protection element for preventing an overcurrent from flowing into processor  13  from power line Lp 1 . 
     Processor  13  includes a microcomputer. Processor  13  is activated when the seizing signal input from fitting detector  18  is turned on, and is shut down when the seizing signal is turned off. Instead of shutdown, transition to a standby state or a sleep state may be performed. 
     Processor  13  controls conduction or interruption of communication wiring Lc 1  between node N 1  and processor  13  by performing control of on or off of pack-side communication switch SWc. Processor  13  manages states of the plurality of cells E 1  to En based on the voltage values, the current values, and the temperature values of the plurality of cells E 1  to En measured by voltage measurer  14 , current sensor  17 , and the temperature sensor. For example, when overvoltage, undervoltage, overcurrent, high-temperature abnormality, or low-temperature abnormality occurs, processor  13  turns off power relay RYp to protect the plurality of cells E 1  to En. 
     Processor  13  can estimate the SOC and the SOH of each of the plurality of cells E 1  to En. Processor  13  can estimate the SOC by using an open circuit voltage (OCV) method or a current integration method. The SOH is defined as a ratio of current full charge capacity to initial full charge capacity, and a lower value (closer to 0%) indicates that degradation has progressed more. The SOH may be obtained by measuring the capacity through full charging and discharging, or may be obtained by adding storage degradation and cycle degradation. The storage degradation can be estimated based on the SOC, the temperature, and a storage degradation speed. The cycle degradation can be estimated based on the SOC range to be used, the temperature, the current rate, and the cycle degradation speed. The storage degradation speed and the cycle degradation speed can be derived preliminarily by an experiment or simulation. The SOC, the temperature, the SOC range, and the current rate can be obtained by measurement. 
     The SOH can also be estimated based on a correlation with an internal resistance of the cell. The internal resistance can be estimated by dividing, by the current value, a voltage drop occurring when a predetermined current flows through the cell for a predetermined time. The internal resistance has a relationship of decreasing as the temperature rises, and increasing as the SOH decreases. 
     In the system configuration example illustrated in  FIG.  4   , vehicle controller  32  includes processor  33 , relay controller  34 , antenna  35 , wireless communication unit  36 , and pack detector  37 . Relay controller  34  performs control of on and off of each of main relay RYm, first slot relay RYsa, and second slot relay RYsb in response to an instruction from processor  33 . 
     Node Na between positive-electrode terminal Tp of first battery pack  10   a  and first slot relay RYsa and processor  33  of vehicle controller  32  are connected by communication wiring Lca. First vehicle-side communication switch SWca is inserted onto communication wiring Lca. A fuse (not illustrated) may be inserted on communication wiring Lca in series with first vehicle-side communication switch SWca. Processor  33  controls conduction or interruption of communication wiring Lca between node Na and processor  33  by performing control of on or off of first vehicle-side communication switch SWca. 
     Similarly, node Nb between positive-electrode terminal Tp of second battery pack  10   b  and second slot relay RYsb and processor  33  of vehicle controller  32  are connected by communication wiring Lcb. Second vehicle-side communication switch SWcb is inserted onto communication wiring Lcb. A fuse (not illustrated) may be inserted on communication wiring Lcb in series with second vehicle-side communication switch SWcb. Processor  33  controls conduction or interruption of communication wiring Lcb between node Nb and processor  33  by performing control of on or off of second vehicle-side communication switch SWcb. 
     When battery mounting unit  31  of vehicle  30  is provided with three or more mounting slots, three or more slot relays RYs and three or more vehicle-side communication switches SWc on communication wiring Lc are provided in parallel. 
     First fitting detector  38   a  detects a fitting state between the connector of first mounting slot SLa 1  of battery mounting unit  31  and the connector of first battery pack  10   a , and outputs, to pack detector  37 , a detection signal indicating presence or absence of fitting. Similarly, second fitting detector  38   b  detects a fitting state between the connector of second mounting slot SLa 2  of battery mounting unit  31  and the connector of second battery pack  10   b , and outputs, to pack detector  37 , a detection signal indicating presence or absence of fitting. First fitting detector  38   a  and second fitting detector  38   b  may detect presence or absence of connection with the connector on battery pack  10  side by a magnetic method or a mechanical method. 
     Pack detector  37  outputs, to processor  33 , seizing signals corresponding to a plurality of detection signals input from the plurality of fitting detectors  38   a  and  38   b . In a case where at least one of the plurality of detection signals indicates a connection state, pack detector  37  outputs a seizing signal including a slot number of the connection state. In a case where all of the plurality of detection signals indicate a non-connection state, pack detector  37  controls the seizing signal to be in an off state. 
     Processor  33  is activated when the seizing signal input from pack detector  37  is turned on, and is shut down when the seizing signal is turned off. Instead of shutdown, transition to a standby state or a sleep state may be performed. 
     In the system configuration example described above, processor  33  of vehicle controller  32  can transmit and receive control signals to and from processor  13  of battery controller  12  by using near-field communication. 
     Processor  33  of vehicle controller  32  can transmit a control signal to processor  13  of battery controller  12  via a wired path. When communicating with processor  13  of first battery pack  10   a  via wire, processor  33  of vehicle controller  32  turns off first slot relay RYsa and turns on first vehicle-side communication switch SWca. Processor  13  of first battery pack  10   a  turns off power relay RYp in first battery pack  10   a  and turns on pack-side communication switch SWc. In this state, the wired path between processor  33  of vehicle controller  32  and processor  13  of first battery pack  10   a  is conducted in a state of being insulated from vehicle  30  and a high-voltage unit of battery pack  10 . In this state, serial communication of a low voltage (for example, 5 V) corresponding to the operating voltage of the processor can be performed between processor  33  of vehicle controller  32  and processor  13  of first battery pack  10   a.    
     Similarly, when communicating with processor  13  of second battery pack  10   b  via wire, processor  33  of vehicle controller  32  turns off second slot relay RYsb and turns on second vehicle-side communication switch SWcb. Processor  13  of second battery pack  10   b  turns off power relay RYp in second battery pack  10   b  and turns on pack-side communication switch SWc. In this state, the wired path between processor  33  of vehicle controller  32  and processor  13  of second battery pack  10   b  is conducted in a state of being insulated from vehicle  30  and a high-voltage unit of battery pack  10 . In this state, serial communication of a low voltage (for example, 5 V) corresponding to the operating voltage of the processor can be performed between processor  33  of vehicle controller  32  and processor  13  of second battery pack  10   b.    
     In the system configuration example illustrated in  FIG.  4   , overvoltage protection circuit  19  for protecting processor  13  of battery pack  10  from overvoltage is provided. Overvoltage protection circuit  19  turns off pack-side communication switch SWc when detecting overvoltage of the power line during communication between processor  13  of battery pack  10  and processor  33  of vehicle  30  using the power line. The section of the power line used for communication is a section between power relay RYp and slot relay RYs in battery pack  10 . Overvoltage protection circuit  19  detects the voltage in the section of the power line. In  FIG.  4   , the voltage in the section of power line Lp 1  in battery pack  10  between power relay RYp and positive-electrode terminal Tp is detected. 
     First overvoltage protection circuit  39   a  and second overvoltage protection circuit  39   b  for protecting processor  33  of vehicle  30  from overvoltage are provided. First overvoltage protection circuit  39   a  turns off first vehicle-side communication switch SWca when detecting overvoltage of the power line during communication between processor  13  of battery pack  10  and processor  33  of vehicle  30  using the power line. First overvoltage protection circuit  39   a  detects the voltage in a section of the power line between power relay RYp and first slot relay RYsa. In  FIG.  4   , the voltage in the section of power line Lpa on vehicle  30  side between positive-electrode terminal Tp and first slot relay RYsa is detected. 
     Similarly, second overvoltage protection circuit  39   b  turns off second vehicle-side communication switch SWcb when detecting overvoltage of power line Lpb during communication between processor  13  of battery pack  10  and processor  33  of vehicle  30  using the power line. Second overvoltage protection circuit  39   b  detects the voltage in a section of the power line between power relay RYp and second slot relay RYsb. In  FIG.  4   , the voltage in the section of power line Lpb on vehicle  30  side between positive-electrode terminal Tp and second slot relay RYsb is detected. Detailed configuration examples of overvoltage protection circuit  19  of battery pack  10 , and first overvoltage protection circuit  39   a  and second overvoltage protection circuit  39   b  of vehicle  30  will be described later. 
     In the system configuration example illustrated in  FIG.  4   , at least one of main relay RYm, slot relay RYs, and power relay RYp may be replaced with a semiconductor switch. Communication switch SWc may be replaced with a relay. 
     Although not illustrated in  FIG.  2   , a similar configuration to that of vehicle controller  32  illustrated in  FIG.  4    is also provided in controller  22  of charging device  20 . In the case of vehicle  30 , the connection destination of the power bus is inverter  310 , but in the case of charging device  20 , the connection destination of the power bus is charging unit  29 . In charging device  20 , the number of slots connected to the power bus is usually larger than that of vehicle  30 . 
     Processor  23  of charging device  20  can transmit and receive control signals to and from processor  13  of battery controller  12  via the near-field communication between wireless communication unit  26  of charging device  20  and wireless communication unit  16  of battery controller  12 . Processor  23  of charging device  20  can transmit a control signal to processor  13  of battery controller  12  via a wired path. 
       FIG.  5    is a view illustrating a basic concept of processing of authenticating, by vehicle controller  32 , battery pack  10  mounted into mounting slot SLa of vehicle  30 . Vehicle controller  32  identifies battery pack  10  basically by searching for a radio wave of near-field communication transmitted from battery pack  10 . Specifically, when battery pack  10  is mounted into mounting slot SLa, vehicle controller  32  transmits ID 1  via wire. Upon receiving ID 1  from vehicle controller  32  via wire, battery controller  12  of battery pack  10  transmits a signal including ID 1  by near-field communication. 
     Upon receiving the signal of the near-field communication, vehicle controller  32  collates ID included in the received signal with ID 1  previously transmitted via wire. When both match, vehicle controller  32  authenticates that battery pack  10  mounted into mounting slot SLa and the communication partner of the near-field communication are identical. When both do not match, vehicle controller  32  determines that battery pack  10  mounted into mounting slot SLa and the communication partner of the near-field communication are not identical, and does not authenticate battery pack  10  of the communication partner. For example, when a signal including ID 2  is received, since ID does not match ID 1  transmitted via wire, battery pack  10  of the transmission destination of the signal including ID 2  is not authenticated. 
     By transmitting ID by the near-field communication, and collate the transmitted ID with ID received from battery controller  12  of battery pack  10  via wire, vehicle controller  32  may judge the identity between battery pack  10  mounted into mounting slot SLa and the communication partner of the near-field communication. 
     Although the basic concept of the processing of authenticating, by vehicle controller  32 , battery pack  10  mounted into mounting slot SLa of vehicle  30  has been described above, the same applies to a case where controller  22  of charging device  20  authenticates battery pack  10  mounted into charging slot SLc of charging device  20 . 
       FIG.  6    is a view schematically illustrating the flow of granting ID to exchanged battery pack  10  when battery pack  10  mounted into mounting slot SLa of vehicle  30  is exchanged. In state  1 , first charging slot SLc 1  of charging device  20  is an empty slot, and charged second battery pack  10   b  is mounted into second charging slot SLc 2 . First battery pack  10   a  having a reduced remaining capacity is mounted into first mounting slot SLa 1  of vehicle  30 . First battery pack  10   a  includes a vehicle ID authenticated by vehicle controller  32 . The vehicle ID ensures the identity between first battery pack  10   a  as a physical connection partner and first battery pack  10   a  as a connection partner of wireless communication as viewed from vehicle  30  side. 
     In state  2 , the user (usually, the driver of vehicle  30 ) unmounts first battery pack  10   a  from first mounting slot SLa 1  of vehicle  30 , and mounts unmounted first battery pack  10   a  into first charging slot SLc 1  of charging device  20 . When first battery pack  10   a  is rented, a work of returning first battery pack  10   a  to charging device  20  is performed. When first battery pack  10   a  is unmounted from first mounting slot SLa 1  of vehicle  30 , battery controller  12  of first battery pack  10   a  deletes the retained vehicle ID. 
     In state  3 , second battery pack  10   b  is unmounted from second charging slot SLc 2  of charging device  20 , and is mounted into first mounting slot SLa 1  of vehicle  30  by the user. By this work, battery pack  10  mounted into first mounting slot SLa 1  of vehicle  30  is physically exchanged. 
     In state  4 , vehicle controller  32  grants a new vehicle ID to second battery pack  10   b  mounted into first mounting slot SLa 1 . This new vehicle ID ensures the identity between second battery pack  10   b  as a physical connection partner and second battery pack  10   b  as a connection partner of wireless communication as viewed from vehicle  30  side. 
       FIG.  7    is a sequence diagram illustrating a detailed processing flow when battery pack  10  mounted into mounting slot SLa of vehicle  30  is exchanged (part  1 ).  FIG.  8    is a sequence diagram illustrating a detailed processing flow when battery pack  10  mounted into mounting slot SLa of vehicle  30  is exchanged (part  2 ). In horizontal lines in the following sequence diagrams, a thin dotted line indicates wireless communication, a thin solid line indicates wired communication, a thick dotted line indicates physical movement of the battery pack, and a thick solid line indicates charge and discharge of the battery pack. 
     First charging slot SLc 1  of charging device  20  is an empty slot, and second battery pack  10   b  is mounted into second charging slot SLc 2 . Second battery pack  10   b  includes charging ID 1  authenticated by controller  22  of charging device  20 . Charging ID 1  ensures the identity between second battery pack  10   b  as a physical connection partner and second battery pack  10   b  as a connection partner of wireless communication as viewed from charging device  20  side. 
     Charging device  20  charges second battery pack  10   b  mounted into second charging slot SLc 2 . That is, a charging current flows from charging unit  29  to second battery pack  10   b  mounted into second charging slot SLc 2 . When the SOC of second battery pack  10   b  reaches an upper limit value, charging ends. The upper limit value may be an SOC corresponding to a full charge capacity or an SOC (for example, 90%) lower than the full charge capacity. 
     First battery pack  10   a  is mounted into first mounting slot SLa 1  of vehicle  30 . First battery pack  10   a  includes a vehicle ID authenticated by vehicle controller  32 . The vehicle ID ensures the identity between first battery pack  10   a  as a physical connection partner and first battery pack  10   a  as a connection partner of wireless communication as viewed from vehicle  30  side. While vehicle  30  is travelling, a discharging current flows from first battery pack  10   a  to motor  311  via inverter  310 . The SOC of first battery pack  10   a  decreases with travel of vehicle  30 . 
     When an ignition-off operation is performed by the user (usually, the driver of vehicle  30 ), vehicle controller  32  accepts the ignition-off operation (P 1   a ). Upon accepting the ignition-off operation, vehicle controller  32  transmits a shutdown instruction to battery controller  12  of first battery pack  10   a  by the near-field communication. Upon receiving the shutdown instruction from vehicle controller  32 , battery controller  12  of first battery pack  10   a  is shut down (P 1   b ). 
     When first battery pack  10   a  is unmounted from first mounting slot SLa 1  of vehicle  30  and first battery pack  10   a  is mounted into first charging slot SLc 1  of charging device  20  by the user, fitting detector  18  of first battery pack  10   a  detects fitting with first charging slot SLc 1  (P 1   c ), and battery controller  12  of first battery pack  10   a  is activated (P 1   e ). Controller  22  of charging device  20  detects that battery pack  10  is mounted into first charging slot SLc 1  (P 1   d ). Battery controller  12  of first battery pack  10   a  deletes the vehicle ID when recognizing to be unmounted from first mounting slot SLa 1 . 
     Controller  22  of charging device  20  transmits, via wire, charging ID 2  to battery controller  12  of first battery pack  10   a  mounted into first charging slot SLc 1 , and writes charging ID 2  to battery controller  12  of first battery pack  10   a  (P 1   f ). Upon receiving charging ID 2 , battery controller  12  of first battery pack  10   a  serves as a beacon terminal (peripheral terminal) and executes advertising of the near-field communication (P 1   g ). Specifically, battery controller  12  transmits, at regular time intervals, an advertising packet including charging ID 2  received via wire as a beacon packet. The advertising packet functions as a signal for notifying controller  22  of charging device  20  or vehicle controller  32  of vehicle  30  as a central terminal of the presence of itself. 
     Upon receiving the advertising packet, controller  22  of charging device  20  collates the charging ID included in the received advertising packet with the charging ID previously transmitted via wire (P 1   h ). In the example illustrated in  FIG.  7   , the collation succeeds if the charging ID included in the received advertising packet is charging ID 2 , and the collation fails if the charging ID is not charging ID 2 . When the collation fails, controller  22  of charging device  20  continues scanning of the advertising packet. When the collation succeeds, controller  22  of charging device  20  starts connection processing with battery controller  12  of first battery pack  10   a  (P 1   i ). 
     First, controller  22  of charging device  20  transmits a connection request to battery controller  12  of first battery pack  10   a . Next, encryption parameters (for example, the number of digits of an encryption key and an encryption level) are exchanged between controller  22  of charging device  20  and battery controller  12  of first battery pack  10   a . Battery controller  12  of first battery pack  10   a  generates an encryption key for use in encryption of communication data based on the exchanged encryption parameters (P 1   j ). Controller  22  of charging device  20  generates an encryption key for use in encryption of communication data based on the exchanged encryption parameters (P 1   k ). Finally, the generated encryption key is exchanged between controller  22  of charging device  20  and battery controller  12  of first battery pack  10   a . Due to this, pairing between controller  22  of charging device  20  and battery controller  12  of first battery pack  10   a  is completed (P 1   m ). With the completion of the pairing of both, returning processing of first battery pack  10   a  to charging device  20  is completed. 
     Controller  22  of charging device  20  selects another battery pack  10  to be exchanged with first battery pack  10   a  (P 1   n ). Specifically, controller  22  of charging device  20  selects one of charged battery packs  10  mounted into the plurality of charging slots SLc of charging stand  21 . In the example illustrated in  FIG.  7   , charged second battery pack  10   b  mounted into second charging slot SLc 2  is selected. 
     Controller  22  of charging device  20  transmits a shutdown instruction to battery controller  12  of selected second battery pack  10   b  by the near-field communication, and executes disconnection processing with battery controller  12  of second battery pack  10   b  (P 1   o ). Upon receiving the shutdown instruction from controller  22  of charging device  20 , battery controller  12  of second battery pack  10   b  is shut down (P 1   p ). Battery controller  12  of second battery pack  10   b  transmits a shutdown completion notification to controller  22  of charging device  20  immediately before the shutdown. 
     Upon receiving the shutdown completion notification from battery controller  12  of second battery pack  10   b , controller  22  of charging device  20  instructs the user of vehicle  30  to remove second battery pack  10   b  mounted into second charging slot SLc 2  (P 1   q ). For example, controller  22  of charging device  20  causes display unit  27  to display a message instructing to remove second battery pack  10   b  mounted into second charging slot SLc 2 . At this time, controller  22  of charging device  20  may output audio guidance from the speaker (not illustrated) to the user. Controller  22  may light or blink only a lamp (not illustrated) of second charging slot SLc 2 . Controller  22  may light only the lamp (not illustrated) of second charging slot SLc 2  in a color different from color of a lamp of another charging slot. 
     When the user removes second battery pack  10   b  from second charging slot SLc 2  and mounts second battery pack  10   b  into first mounting slot SLa 1  of vehicle  30 , fitting detector  18  of second battery pack  10   b  detects fitting with first mounting slot SLa 1  (P 1   r ), and battery controller  12  of second battery pack  10   b  is activated (P 1   t ). When fitting detector  38  of vehicle  30  detects that battery pack  10  is mounted into first mounting slot SLa 1  (PIs), vehicle controller  32  is activated (P 1   u ). Battery controller  12  of second battery pack  10   b  deletes charging ID 2  when recognizing to be unmounted from second charging slot SLc 2 . 
     Controller  22  of charging device  20  starts charging control of first battery pack  10   a  mounted into first charging slot SLc 1  (P 1   v ). Specifically, controller  22  of charging device  20  transmits a charging instruction to battery controller  12  of first battery pack  10   a  by the near-field communication, and turns on second slot relay RYsb. Upon receiving the charging instruction, battery controller  12  of first battery pack  10   a  turns on power relay RYp. Due to this, a charging current flows from charging unit  29  of charging device  20  to first battery pack  10   a  mounted into first charging slot SLc 1 . 
     Vehicle controller  32  transmits, via wire, the vehicle ID to second battery pack  10   b  mounted into first mounting slot SLa 1 , and writes the vehicle ID to battery controller  12  of second battery pack  10   b  (P 1   y ). Upon receiving the vehicle ID, battery controller  12  of second battery pack  10   b  serves as a beacon terminal and executes advertising of the near-field communication (P 1   z ). Specifically, battery controller  12  transmits, at regular time intervals, an advertising packet including the vehicle ID received via wire as a beacon packet. 
     Upon receiving the advertising packet, vehicle controller  32  collates the vehicle ID included in the received advertising packet with the vehicle ID previously transmitted via wire (P 1 A). When the collation of the vehicle ID fails, vehicle controller  32  continues scanning of the advertising packet. When the collation of the vehicle ID succeeds, vehicle controller  32  starts connection processing with battery controller  12  of second battery pack  10   b  (P 1 B). 
     First, vehicle controller  32  transmits a connection request to battery controller  12  of second battery pack  10   b . Next, encryption parameters are exchanged between vehicle controller  32  and battery controller  12  of second battery pack  10   b . Battery controller  12  of second battery pack  10   b  generates an encryption key for use in encryption of communication data based on the exchanged encryption parameters (P 1 C). Vehicle controller  32  generates an encryption key for use in encryption of communication data based on the exchanged encryption parameters (P 1 D). Finally, the generated encryption key is exchanged between vehicle controller  32  and battery controller  12  of second battery pack  10   b . Due to this, pairing between vehicle controller  32  and battery controller  12  of second battery pack  10   b  is completed (P 1 F). After the pairing is completed, vehicle controller  32  transmits a shutdown instruction to battery controller  12  of second battery pack  10   b  by the near-field communication. Upon receiving the shutdown instruction from vehicle controller  32 , battery controller  12  of second battery pack  10   b  is shut down (PIG). 
       FIG.  9    is a view for explaining configuration example 1 of overvoltage protection circuit  19  of first battery pack  10   a  of  FIG.  4    and first overvoltage protection circuit  39   a  of vehicle  30 . The circuit diagram illustrated in  FIG.  9    illustrates a configuration related to wired communication between processor  13  of first battery pack  10   a  and processor  33  of vehicle  30 , and appropriately omits a configuration not related to the wired communication. 
     A serial port of processor  33  of vehicle  30  is connected to the positive wiring of power line Lpa via first vehicle-side communication switch SWca. In configuration example 1 illustrated in  FIG.  9   , first vehicle-side communication switch SWca includes an N-channel MOSFET. The drain terminal of first vehicle-side communication switch SWca is connected to the positive wiring of power line Lpa, the source terminal is connected to the serial port of processor  33 , and the gate terminal is connected to an output terminal of first overvoltage protection circuit  39   a.    
     First overvoltage protection circuit  39   a  includes first resistor R 11 , second resistor R 12 , third resistor R 13 , first NPN transistor Q 13 , second NPN transistor Q 14 , fourth resistor R 14 , and photocoupler PC. First resistor R 11  and second resistor R 12  are first voltage dividing resistors connected in series between the positive wiring and the negative wiring of power line Lpa. The emitter terminal of first NPN transistor Q 13  is connected to the negative wiring of power line Lpa, the collector terminal of first NPN transistor Q 13  is connected to the positive wiring of power line Lpa via third resistor R 13 , and the base terminal of first NPN transistor Q 13  is connected to the voltage dividing point of the first voltage dividing resistor. The base terminal of second NPN transistor Q 14  is connected to the collector terminal of first NPN transistor Q 13 , the emitter terminal of second NPN transistor Q 14  is connected to the negative wiring of power line Lpa, and the collector terminal of second NPN transistor Q 14  is connected to the positive wiring of power line Lpa via fourth resistor R 14  and a light emitting diode of photocoupler PC. As an output of first overvoltage protection circuit  39   a  from an emitter of a phototransistor that serves as a light-receiving element of photocoupler PC, an emitter terminal of the phototransistor is connected to a gate terminal of an N-channel MOSFET that serves as first vehicle-side communication switch SWca. Fifth resistor R 15  for flowing a discharging current for turning off the N-channel MOSFET is connected between the gate terminal and the source terminal of the N-channel MOSFET. 
     Processor  33  of vehicle  30  includes microcomputer  33   a  that transmits a control signal to processor  13  of first battery pack  10   a , and an insulated DC/DC converter  33   b  that supplies a positive power source voltage (for example, +5 V) to the collector of the phototransistor of photocoupler PC of first overvoltage protection circuit  39   a  and supplies a negative power source voltage (for example, GND) to the source terminal of the N-channel MOSFET. The phototransistor of photocoupler PC and the N-channel MOSFET are floated from power line Lpa by the DC/DC converter  33   b.    
     A serial port of processor  13  of first battery pack  10   a  is connected to the positive wiring of power line Lp 1  via comparator CP 1 , the second voltage dividing resistor configured by a series circuit of seventh resistor R 7  and eighth resistor R 8 , and pack-side communication switch SWc. In configuration example 1 illustrated in  FIG.  9   , pack-side communication switch SWc is configured by a PNP transistor. The emitter terminal of pack-side communication switch SWc is connected to the positive wiring of power line Lp 1 , the collector terminal is connected to the negative wiring of power line Lp 1  via the second voltage dividing resistor, and the base terminal is connected to the output terminal of overvoltage protection circuit  19 . A non-inverting input terminal of comparator CP 1  is connected to reference voltage source Vref, an inverting input terminal is connected to a voltage dividing point of the second voltage dividing resistor, and an output terminal is connected to a serial port of processor  13 . 
     Overvoltage protection circuit  19  includes first resistor R 1 , second resistor R 2 , third resistor R 3 , and PNP transistor Q 3 . First resistor R 1  and second resistor R 2  are first voltage dividing resistors connected in series between the positive wiring and the negative wiring of power line Lp 1 . The emitter terminal of PNP transistor Q 3  is connected to the positive wiring of power line Lp 1 , the collector terminal is connected to the negative wiring of power line Lp 1  via third resistor R 3 , and the base terminal is connected to the voltage dividing point of the first voltage dividing resistor. As an output of overvoltage protection circuit  19 , the collector terminal of PNP transistor Q 3  is connected to the base terminal of pack-side communication switch SWc. 
     In the above circuit configuration, when a control signal is transmitted from processor  33  of vehicle  30  to processor  13  of first battery pack  10   a , processor  33  of vehicle  30  turns off first slot relay RYsa and turns on first vehicle-side communication switch SWca. Processor  13  of first battery pack  10   a  turns off power relay RYp in first battery pack  10   a  and turns on pack-side communication switch SWc. Due to this, the section between power relay RYp of the power line and first slot relay RYsa is insulated from high-voltage battery module  11  and inverter  310  of vehicle  30 . While power relay RYp and first slot relay RYsa are off, the section between power relay RYp and first slot relay RYsa can be diverted as low-voltage communication wiring. 
     Hereinafter, an example is assumed where the voltage of battery module  11  is 48 V, and the voltage for use in serial communication between processor  33  of vehicle  30  and processor  13  of first battery pack  10   a  is 5 V. In serial communication of 5 V, 1 (high level) is transferred at 5 V, and 0 (low level) is transmitted at 0 V. 
     Comparator CP 1  connected to the preceding stage of processor  13  on the reception side outputs, to processor  13 , high level when a voltage higher than 2.5 V is input and outputs low level when a voltage lower than 2.5 V is input. Comparator CP 1  is not provided at the preceding stage of processor  13 , and the voltage of the positive wiring of power line Lp 1  may be configured to be input to an analog input port of processor  13  as it is. While  FIG.  9    illustrates the configuration where unidirectional communication is performed from processor  33  of vehicle  30  to processor  13  of first battery pack  10   a , a configuration where bidirectional communication is possible with a configuration where processor  33  of vehicle  30  and processor  13  of first battery pack  10   a  are symmetric. 
     When 5 V serial communication is performed between processor  33  of vehicle  30  and processor  13  of first battery pack  10   a , there is a possibility that 48 V is applied, due to malfunction, to a section (hereinafter, called power line communication section) of a power line diverted as low-voltage communication wiring. For example, power relay RYp or first slot relay RYsa may be turned on at an unintended timing due to noise, vibration, a bug in firmware, or the like. In that case, a high voltage is applied to processor  13  of first battery pack  10   a  and processor  33  of vehicle  30 , and defects such as breakdown in withstand voltage and abnormal heat generation occur. 
     As a countermeasure, it is conceivable to adopt a processor having a high withstand voltage, but in that case, the cost and the circuit area increase. When the voltage of battery module  11  is 100 V or more, the cost and the circuit area further increase. 
     In the circuit configuration illustrated in  FIG.  9   , a mechanism where overvoltage protection circuit  19  automatically turns off pack-side communication switch SWc when a high voltage is applied to the communication section of the power line, and a mechanism where first overvoltage protection circuit  39   a  automatically turns off first vehicle-side communication switch SWca are introduced. 
     In overvoltage protection circuit  19 , the voltage dividing ratio between first resistor R 1  and second resistor R 2  constituting the first voltage dividing resistor is set such that the base current does not flow when the voltage in the communication section of the power line is low and the base current flows when the voltage is high. In a general bipolar transistor, a base current flows when the voltage between the base and the emitter exceeds 0.6 V to 0.7 V. 
     Hereinafter, a specific operation of overvoltage protection circuit  19  of first battery pack  10   a  will be described. For example, the voltage dividing ratio between first resistor R 1  and second resistor R 2  is set to 0.9. When the voltage in the communication section of the power line is 5 V, the base potential of PNP transistor Q 3  becomes 4.5 V, the emitter potential is 5 V, and therefore, the voltage between the base and the emitter becomes 0.5 V, where the base current does not flow. In this case, PNP transistor Q 3  is not conducted, and the base terminal of pack-side communication switch SWc is connected to the negative wiring of power line Lp 1  via third resistor R 3 . Due to this, pack-side communication switch SWc is conducted. 
     On the other hand, when the voltage in the communication section of the power line is 48 V, the base potential of PNP transistor Q 3  is about to become 43.2 V, the emitter potential is 48 V, and therefore, the voltage between the base and the emitter is clamped to about 0.6 V as a result of the base current flowing. In this case, PNP transistor Q 3  is conducted, and the base terminal of pack-side communication switch SWc is connected to the positive wiring of power line Lp 1  via PNP transistor Q 3 . Due to this, first vehicle-side communication switch SWca is interrupted. 
     In first overvoltage protection circuit  39   a  of vehicle  30 , the voltage dividing ratio between first resistor R 11  and second resistor R 12  constituting the first voltage dividing resistor is set such that the base current does not flow when the voltage in the communication section of the power line is low and the base current flows when the voltage is high. For example, the voltage dividing ratio between first resistor R 11  and second resistor R 12  is set to 0.1. When the voltage in the communication section of the power line is 5 V, the base potential of NPN transistor Q 13  becomes 0.5 V, the emitter potential is 0 V, and therefore, the voltage between the base and the emitter becomes 0.5 V, where the base current does not flow. In this case, NPN transistor Q 13  is not conducted, the base potential of NPN transistor Q 14  becomes 5 V, the emitter potential is 0 V, and therefore, NPN transistor Q 14  has the voltage between the base and the emitter of 5 V, and enters a conductive state. Therefore, the light emitting diode of photocoupler PC becomes conductive and enters a light-emitting state. Due to this, the phototransistor of photocoupler PC enters a conductive state, a positive power source voltage and a negative power source voltage of the DC/DC converter  33   b  are applied between the gate and the source of the MOSFET of first vehicle-side communication switch SWca, and first vehicle-side communication switch SWca enters a conductive state. 
     On the other hand, when the voltage in the communication section of the power line is 48 V, the base potential of NPN transistor Q 13  is about to become 4.8 V, the emitter potential is 0 V, and therefore the voltage between the base and the emitter is clamped to about 0.6 V as a result of the base current flowing. Therefore, NPN transistor Q 13  is conducted, and the voltage between the base and the emitter of NPN transistor Q 14  becomes less than 0.6 V of the conduction voltage of NPN transistor Q 14 . Therefore, NPN transistor Q 14  is not conductive, and the light emitting diode of photocoupler PC is not conducted and is in a state of being turned off. Due to this, the phototransistor of photocoupler PC is not conducted, and first vehicle-side communication switch SWca is interrupted. 
     Therefore, when the voltage in the communication section of the power line is 5 V, pack-side communication switch SWc and first vehicle-side communication switch SWca are conducted, and communication is possible between processor  13  of first battery pack  10   a  and processor  33  of vehicle  30 . On the other hand, when the voltage in the communication section of the power line is 48 V, pack-side communication switch SWc and first vehicle-side communication switch SWca are interrupted, and processor  13  of first battery pack  10   a  and processor  33  of vehicle  30  are protected from overvoltage. 
       FIG.  10    is a view for explaining configuration example 2 of overvoltage protection circuit  19  of first battery pack  10   a  of  FIG.  4    and first overvoltage protection circuit  39   a  of vehicle  30 . The configuration and the operation of first overvoltage protection circuit  39   a  of vehicle  30  are similar to those in configuration example 1 illustrated in  FIG.  9   . 
     In configuration example 2, overvoltage protection circuit  19  includes first resistor R 1 , second resistor R 2 , fourth resistor R 4 , fifth resistor R 5 , first NPN transistor Q 4 , and second NPN transistor Q 5 . First resistor R 1  and second resistor R 2  are first voltage dividing resistors connected in series between the positive wiring and the negative wiring of power line Lp 1 . The emitter terminal of first NPN transistor Q 4  is connected to the negative wiring of power line Lp 1 , the collector terminal is connected to the positive wiring of power line Lp 1  via fourth resistor R 4 , and the base terminal is connected to the voltage dividing point of the first voltage dividing resistor. The emitter terminal of second NPN transistor Q 5  is connected to the negative wiring of power line Lp 1 , the collector terminal is connected to the positive wiring of power line Lp 1  via fifth resistor R 5 , and the base terminal is connected to the collector terminal of first NPN transistor Q 4 . As an output of overvoltage protection circuit  19 , the collector terminal of second NPN transistor Q 5  is connected to the base terminal of pack-side communication switch SWc via sixth resistor R 6 . 
     Hereinafter, a specific operation of overvoltage protection circuit  19  of first battery pack  10   a  will be described. For example, the voltage dividing ratio between first resistor R 1  and second resistor R 2  is set to 0.1. When the voltage in the communication section of the power line is 5 V, the base potential of first NPN transistor Q 4  becomes 0.5 V, the emitter potential is 0 V, and therefore, the voltage between the base and the emitter becomes 0.5 V, where the base current does not flow. In this case, first NPN transistor Q 4  is not conducted, and the base terminal of second NPN transistor Q 5  is connected to the positive wiring of power line Lp 1  via fourth resistor R 4 . Due to this, second NPN transistor Q 5  is conducted. When second NPN transistor Q 5  is conducted, the voltage drop by fifth resistor R 5  exceeds the conduction voltage between the base and the emitter of pack-side communication switch SWc, and the base terminal of pack-side communication switch SWc is connected to the negative wiring of power line Lp 1  via sixth resistor R 6  and second NPN transistor Q 5 . Due to this, pack-side communication switch SWc is conducted. 
     On the other hand, when the voltage in the communication section of the power line is 48 V, the base potential of first NPN transistor Q 4  is about to become 4.8 V, the emitter potential is 0 V, and therefore, the voltage between the base and the emitter is clamped to about 0.6 V as a result of the base current flowing. In this case, first NPN transistor Q 4  is conducted, and the base terminal of second NPN transistor Q 5  is connected to the negative wiring of power line Lp 1  via first NPN transistor Q 4 . Due to this, second NPN transistor Q 5  is interrupted. When second NPN transistor Q 5  is interrupted, the base terminal of pack-side communication switch SWc is connected to the positive wiring of power line Lp 1  via fifth resistor R 5  and sixth resistor R 6 . Due to this, pack-side communication switch SWc is interrupted. 
     Therefore, when the voltage in the communication section of the power line is 5 V, pack-side communication switch SWc and first vehicle-side communication switch SWca are conducted, and communication is possible between processor  13  of first battery pack  10   a  and processor  33  of vehicle  30 . On the other hand, when the voltage in the communication section of the power line is 48 V, pack-side communication switch SWc and first vehicle-side communication switch SWca are interrupted, and processor  13  of first battery pack  10   a  and processor  33  of vehicle  30  are protected from overvoltage. 
     As described above, in the present exemplary embodiment, ID is written from vehicle  30  or charging device  20  to battery pack  10  via wire, and the ID is looped back from battery pack  10  to vehicle  30  or charging device  20  by the near-field communication. Due to this, vehicle  30  or charging device  20  that controls battery pack  10  by using the near-field communication can correctly identify mounted battery pack  10 . There is no longer malfunctions such as erroneous control of battery pack  10  mounted in another nearby vehicle  30  by vehicle controller  32  of certain vehicle  30 , and the safety and security of entire vehicle system  1  using charging device  20  and exchangeable battery pack  10  can be secured. The user can cause vehicle  30  to safely travel only by taking out battery pack  10  mounted into charging device  20  and mounting the battery pack in vehicle  30 . 
     The number of pins included in the connector of battery pack  10  can be reduced by performing, by the near-field communication, transmission and reception of control signals between vehicle  30  or charging device  20  and battery pack  10 . This makes it possible to reduce mechanical connection failure between vehicle  30  or charging device  20  and battery pack  10 . The firmware used in battery controller  12  of battery pack  10  can be updated via wireless communication, and update of the firmware becomes easy. 
     By providing the overvoltage protection circuit, it is possible to safely perform communication between battery pack  10  and vehicle  30  or charging device  20  using the power line. That is, even when a high voltage is applied to a communication section of the power line during low-voltage communication using the communication section of the power line, each processor can be protected from overvoltage. This overvoltage protection is hardware control using a self-control type switch, and has high reliability. 
     The present disclosure has been described above based on the exemplary embodiment. It is to be understood by the person of ordinary skill in the art that the exemplary embodiment is an example, that combinations of its configuration elements and processing processes can have various modified examples, and that such modified examples are also within the scope of the present disclosure. 
     The NPN transistor in the above-described exemplary embodiment may be appropriately replaced with an N-channel FET, and the PNP transistor may be appropriately replaced with a P-channel FET. In that case, it is necessary to appropriately adjust the connection position of each resistor and the value of each resistor in accordance with the threshold voltage and the gate capacitance of the FET to be used. 
     In the above-described exemplary embodiment, an example of using battery pack  10  incorporating battery module  11  including the lithium ion battery cell, the nickel hydrogen battery cell, and the lead battery cell has been described. In this regard, a capacitor pack incorporating a capacitor module including an electric double layer capacitor cell and a lithium ion capacitor cell may be used. In this description, a battery pack and a capacitor pack are collectively called a power storage pack. 
     In the above-described exemplary embodiment, an electric motorcycle (electric scooter) is assumed as vehicle  30  using exchangeable battery pack  10  as a power source. In this regard, vehicle  30  may be an electric bicycle. Vehicle  30  may be a four-wheeled electric vehicle (EV). The electric vehicles include not only full-standard electric vehicles but also low-speed electric vehicles such as golf carts and golf cars used in shopping malls and entertainment facilities. 
     An electric moving body using exchangeable battery pack  10  as a power source is not limited to vehicle  30 . For example, the electric moving bodies also include electric ships. For example, a power source of a water bus or a water taxi may be exchangeable battery pack  10 . The electric moving bodies also include trains. For example, a train equipped with exchangeable battery pack  10  can be used instead of a diesel train used in a non-electrified railway line. The electric moving bodies also include electric flying objects. The electric flight objects include multicopters (drones). The multicopters include so-called flying cars. Any electric moving body can shorten an energy supply time. 
     The exemplary embodiment may be specified by the following items. 
     [Item 1] 
     Power storage pack ( 10 ) including: power storage unit ( 11 ) for supplying power to electric moving body ( 30 ); power line (Lp 1 ) connecting between power storage unit ( 11 ) and power source terminal (Tp) for charging and discharging; first switch (RYp) inserted into power line (Lp 1 ); controller ( 12 ) that communicates with controller ( 32 ) of electric moving body ( 30 ) in a state where power storage pack ( 10 ) is mounted to electric moving body ( 30 ) or communicate with controller ( 22 ) of charging device ( 20 ) in a state where power storage pack ( 10 ) is mounted to charging slot (SLc 1 ) of charging device ( 20 ); communication wiring (Lc 1 ) that connects between a node of power line (Lp 1 ) on power source terminal (Tp) side relative to first switch (RYp) and controller ( 12 ) of power storage pack ( 10 ); second switch (SWc) inserted into communication wiring (Lc 1 ); and overvoltage protection circuit ( 19 ) that protects controller ( 12 ) of power storage pack ( 10 ) from overvoltage, in which controller ( 12 ) of power storage pack ( 10 ) controls first switch (RYp) to be turned off and second switch (SWc) to be turned on when performing communication with controller ( 32 ) of electric moving body ( 30 ) or controller ( 22 ) of charging device ( 20 ) using power line (Lp 1 ) and communication wiring (Lc 1 ), and overvoltage protection circuit ( 19 ) turns off second switch (SWc) upon detecting an overvoltage of power line (Lp 1 ) during communication between controller ( 12 ) of power storage pack ( 10 ) and controller ( 32 ) of electric moving body ( 30 ) or controller ( 22 ) of charging device ( 20 ). 
     This makes it possible to protect controller ( 12 ) of power storage pack ( 10 ) from an overvoltage of power line (Lp 1 ). 
     [Item 2] 
     Power storage pack ( 10 ) according to Item 1, in which overvoltage protection circuit ( 19 ) includes voltage dividing resistor (R 1  or R 2 ) for detecting a voltage of the node of power line (Lp 1 ), and third switch (Q 3 ) that turns on second switch (SWc) when a divided voltage of the voltage dividing resistor (R 1  or R 2 ) exceeds a threshold voltage. 
     This makes it possible to highly accurately protect controller ( 12 ) of power storage pack ( 10 ) from an overvoltage by hardware control using self-control type switch (SWc). 
     [Item 3] 
     Power storage pack ( 10 ) according to Item 2, in which second switch (SWc) and third switch (Q 3 ) are PNP transistors, voltage dividing resistor (R 1  or R 2 ) is connected between a positive wiring and a negative wiring of power line (Lp 1 ), an emitter of third switch (Q 3 ) is connected to a positive wiring of power line (Lp 1 ), a collector of third switch (Q 3 ) is connected to a negative wiring of power line (Lp 1 ) via a resistor (R 3 ), and a base of third switch (Q 3 ) is connected to a voltage dividing point of voltage dividing resistor (R 1  or R 2 ), and an emitter of second switch (SWc) is connected to a positive wiring of power line (Lp 1 ), a collector of second switch (SWc) is connected to controller ( 12 ) of power storage pack ( 10 ), and a base of second switch (SWc) is connected to a collector of third switch (Q 3 ). 
     This makes it possible for a two-stage PNP transistor to highly accurately protect controller ( 12 ) of power storage pack ( 10 ) from overvoltage. 
     [Item 4] 
     Power storage pack ( 10 ) according to any one of Items 1 to 3, in which upon receiving identification information from controller ( 32 ) of electric moving body ( 30 ) or controller ( 22 ) of charging device ( 20 ) via power line (Lp 1 ) and communication wiring (Lc 1 ), controller ( 12 ) of power storage pack ( 10 ) transmits a signal including the identification information by near-field communication, and a signal transmitted in the near-field communication is used by controller ( 32 ) of electric moving body ( 30 ) or controller ( 22 ) of charging device ( 20 ) to authenticate whether or not power storage pack ( 10 ) mounted into electric moving body ( 30 ) or charging slot (SLc 1 ) and a communication partner of the near-field communication are identical. 
     This makes it possible for controller ( 32 ) of electric moving body ( 30 ) or controller ( 22 ) of charging device ( 20 ) to accurately authenticate whether or not power storage pack ( 10 ) mounted into electric moving body ( 30 ) or charging slot (SLc 1 ) and the communication partner of the near-field communication are identical. 
     [Item 5] 
     Electric moving body ( 30 ) including: motor ( 311 ); power line (Lpa) that connects between motor ( 311 ) and power source terminal (Tp) that receives power supplying from an outside; first switch (RYsa) inserted into power line (Lpa); controller ( 32 ) that communicates with controller ( 12 ) of power storage pack ( 10 ) in a state where power storage pack ( 10 ) for supplying power to motor ( 311 ) is mounted to electric moving body ( 30 ); communication wiring (Lca) that connects between a node of power line (Lpa) on power source terminal (Tp) side relative to first switch (RYsa) and controller ( 32 ) of electric moving body ( 30 ); second switch (SWca) inserted into communication wiring (Lca); and overvoltage protection circuit ( 39   a ) that protects controller ( 32 ) of electric moving body ( 30 ) from overvoltage, in which controller ( 32 ) of electric moving body ( 30 ) controls first switch (RYsa) to be turned off and second switch (SWca) to be turned on when performing communication with controller ( 12 ) of power storage pack ( 10 ) using power line (Lpa) and communication wiring (Lca), and overvoltage protection circuit ( 39   a ) turns off second switch (SWca) upon detecting an overvoltage of power line (Lpa) during communication between controller ( 32 ) of electric moving body ( 30 ) and controller ( 12 ) of power storage pack ( 10 ). 
     This makes it possible to protect controller ( 32 ) of electric moving body ( 30 ) from overvoltage of power line (Lpa). 
     [Item 6] 
     Electric moving body ( 30 ) according to Item 5, in which controller ( 32 ) of electric moving body ( 30 ) transmits identification information to controller ( 12 ) of power storage pack ( 10 ) via power line (Lpa) and communication wiring (Lca) when power storage pack ( 10 ) is mounted to electric moving body ( 30 ), and collates whether or not identification information included in a received signal matches the transmitted identification information when receiving a signal transmitted by near-field communication, and authenticates that power storage pack ( 10 ) mounted to electric moving body ( 30 ) and a communication partner of the near-field communication are identical when the identification information included in the received signal matches the transmitted identification information. 
     This makes it possible for controller ( 32 ) of electric moving body ( 30 ) to accurately authenticate whether or not power storage pack ( 10 ) mounted to electric moving body ( 30 ) and the communication partner of the near-field communication are identical. 
     [Item 7] 
     Charging device ( 20 ) including: charging slot (SLc 1 ); power line (Lpa) that connects between charging source ( 29 ) and power source terminal (Tp) of charging slot (SLc 1 ); first switch (RYsa) inserted into power line (Lpa); controller ( 22 ) that communicates with controller ( 12 ) of power storage pack ( 10 ) in a state where power storage pack ( 10 ) is mounted into charging slot (SLc 1 ); communication wiring (Lca) that connects between a node of power line (Lpa) on power source terminal (Tp) side relative to first switch (RYsa) and controller ( 22 ) of charging device ( 20 ); second switch (SWca) inserted into communication wiring (Lca); and overvoltage protection circuit ( 39   a ) that protects controller ( 22 ) of charging device ( 20 ) from overvoltage, in which controller ( 22 ) of charging device ( 20 ) controls first switch (RYsa) to be turned off and second switch (SWca) to be turned on when performing communication with controller ( 12 ) of power storage pack ( 10 ) using power line (Lpa) and communication wiring (Lca), and overvoltage protection circuit ( 39   a ) turns off second switch (SWca) upon detecting an overvoltage of power line (Lpa) during communication between controller ( 22 ) of charging device ( 20 ) and controller ( 12 ) of power storage pack ( 10 ). 
     This makes it possible to protect controller ( 22 ) of charging device ( 20 ) from overvoltage of power line (Lpa). 
     [Item 8] 
     Charging device ( 20 ) according to Item 7, in which controller ( 22 ) of charging device ( 20 ) transmits identification information to controller ( 12 ) of power storage pack ( 10 ) via power line (Lpa) and communication wiring (Lca) when power storage pack ( 10 ) is mounted to charging slot (SLc 1 ), and collates whether or not identification information included in a received signal matches the transmitted identification information when receiving a signal transmitted by near-field communication, and authenticates that power storage pack ( 10 ) mounted to charging slot (SLc 1 ) and a communication partner of the near-field communication are identical when the identification information included in the received signal matches the transmitted identification information. 
     This makes it possible for controller ( 22 ) of charging device ( 20 ) to accurately authenticate whether or not power storage pack ( 10 ) mounted into charging slot (SLc 1 ) and the communication partner of the near-field communication are identical. 
     REFERENCE MARKS IN THE DRAWINGS 
     
         
         
           
               1 : vehicle system 
               2 : commercial power system 
               10 : battery pack 
               11 : battery module 
             E 1 -En: cell 
               12 : battery controller 
               13 : processor 
               14 : voltage measurer 
               15 : antenna 
               16 : wireless communication unit 
               17 : current sensor 
               18 : fitting detector 
               19 : overvoltage protection circuit 
               20 : charging device 
               21 : charging stand 
             SLc: charging slot 
               22 : controller 
               23 : processor 
               25 : antenna 
               26 : wireless communication unit 
               27 : display unit 
               28 : operation unit 
               29 : charging unit 
               30 : vehicle 
               31 : battery mounting unit 
             SL 1 : mounting slot 
               32 : vehicle controller 
               33 : processor 
               33   a : microcomputer 
               33   b : DC/DC converter 
               34 : relay controller 
               35 : antenna 
               36 : wireless communication unit 
               37 : pack detector 
               38 : fitting detector 
               39 : instrument panel 
               39   a : first overvoltage protection circuit 
               39   b : second overvoltage protection circuit 
               310 : inverter 
               311 : motor 
               312 : tire 
             RYm: main relay 
             RYs: slot relay 
             RYp: power relay 
             SWc: pack-side communication switch 
             SWca: first vehicle-side communication switch 
             SWcb: second vehicle-side communication switch 
             Q 3 : PNP transistor 
             Q 4 , Q 5 , Q 13 , Q 14 : NPN transistor 
             R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 11 , R 12 , R 13 , R 14 , R 15 : resistor 
             PC: photocoupler 
             CP 1 : comparator 
             Tp: positive-electrode terminal 
             Tm: negative-electrode terminal