Battery system

A battery system includes a battery circuit group in which a plurality of battery circuits, each including a plurality of battery units including a battery and a switching unit connected in series, are connected in parallel, and a control unit that controls the switching unit. The switching unit switches a state of the battery unit between a first state, in which the battery is connected between a positive electrode end and a negative electrode end of the battery unit, and a second state, in which the positive electrode end and the negative electrode end are connected without the battery. When discharging, the control unit controls the switching unit such that the state of the battery unit including the battery determined to be not fully discharged becomes the first state, and the state of the battery unit including the battery determined to be fully discharged becomes the second state.

TECHNICAL FIELD

The present invention relates to a battery system.

BACKGROUND ART

Conventionally, as a battery system mentioned above, a storage battery system which judges the degradation of a battery and can replace the degraded battery with a spare battery is known (Patent Literature 1).

By the way, a used battery may be mounted as a battery mentioned above. The state of deterioration of the used battery differs depending on the usage of the user. In general, a battery whose deterioration has advanced has a reduced battery capacity, and therefore, a power capacity capable of charging and discharging is smaller than that of a battery which is not deteriorated.

If batteries in different deterioration states are mixed and connected in series, the batteries that have deteriorated during charge/discharge will be initially fully charged or fully discharged. In this case, even if the remaining capacity of the other batteries remains, charging and discharging must be stopped, and there is a problem that the battery capacity cannot be used up.

Therefore, conventionally, a new battery system has been configured by selecting batteries having the same deterioration state. In this case, a battery system composed of batteries in different deterioration states is difficult to be realized as a product because the battery capacity of the battery system is different. Therefore, it was necessary to collect batteries with the same degradation state to support the number of products manufactured. In this case, a battery system composed of batteries in different deterioration states also occurs, and it was necessary to consider different products corresponding to these. From the above, it is necessary to have a large storage for sorting and pooling batteries, which makes cost reduction difficult.

PRIOR ART DOCUMENT

Patent Literature

Patent Literature 1: JP 2013-240155 A

SUMMARY OF INVENTION

Technical Problem

For example, in the case of the battery system having the configuration shown inFIG. 1, the capacity of all the batteries can be sufficiently used even if the batteries in different deterioration states are mixed. In this battery system, a switch for blocking is arranged in series with each battery, and a switch for bypass is arranged in parallel with each battery. Therefore, when the battery is fully charged or fully discharged, it is possible to separate it from other batteries by cutting off the fully charged or fully discharged battery with the switch turned off, and with the switch for bypass turned on. Even if some batteries are fully charged or fully discharged, it is possible to continue charging and discharging other batteries.

However, in the above-described battery system, during discharge, while the operation of disconnecting the fully discharged battery is being performed, that is, until the cutoff switch is turned off and the bypass switch is turned on, power supply to the load will stop.

The present invention has been made in view of the above background, and an object of the present invention is to provide a battery system capable of continuing to supply power to a load even while operating to disconnect a fully discharged battery.

Solution to Problem

According to one aspect of the present invention, there is provided a battery system comprising:a battery circuit group in which a plurality of battery circuits connected in parallel, each including a plurality of battery units connected in series, each including a positive electrode end, a negative electrode end, a battery and a switching unit; anda control unit that determines a charge state of the battery and controls the switching unit based on the determined charge state,wherein in each of the battery units, the switching unit switches a state of the battery unit between a first state, in which the battery is connected between the positive electrode end and the negative electrode end, and a second state, in which the positive electrode end and the negative electrode end are connected without the battery,wherein when discharging of the battery circuit group, the control unit controls the switching unit such that the state of the battery unit including the battery determined to be not fully discharged becomes the first state, and the state of the battery unit including the battery determined to be fully discharged becomes the second state, andwherein each of the battery circuits has a diode connected in series with the plurality of battery units such that a discharge direction of the battery is a forward direction.

Preferably, the control unit determines that the battery is not fully discharged when a voltage across the battery is greater than a predetermined discharge termination voltage, and determines that the battery is fully discharged when the voltage across the battery is less than or equal to the predetermined discharge termination voltage.

Preferably, each of the plurality of battery circuits further includes a bypass switch connected in parallel with the diode, andthe control unit controls the switching unit such that when charging of the battery circuit group, the state of the battery unit including the battery determined to be not fully charged becomes the first state, and the state of the battery unit including the battery determined to be fully charged becomes the second state.

Preferably, the control unit determines that the battery is not fully charged when the voltage across the battery is less than a predetermined charge termination voltage, and determines that the battery is fully charged when the voltage across the battery is equal to or greater than the predetermined charge termination voltage.

Preferably, the control unit controls the bypass switches such that only one bypass switch of the battery circuit is turned on, and controls the bypass switch so as to sequentially charge the plurality of battery circuits by controlling the bypass switch such that the bypass switch is turned off when it is determined that all the batteries in the battery circuit in which the bypass switch is on are fully charged.

Effect of the Invention

According to the aspect described above, it is possible to provide a battery system capable of continuing to supply power to a load even while operating to disconnect a fully discharged battery.

DESCRIPTION OF EMBODIMENTS

First Embodiment

Hereinafter, a first embodiment of the present invention will be described based onFIG. 1. A battery system1shown inFIG. 1is, for example, a device mounted on an EV or HEV vehicle driven by an electric motor and supplying power to the electric motor.

As shown inFIG. 1, the battery system1includes a plurality of battery units11ato11e, a plurality of voltage measurement units12ato12e, and a control unit13. The plurality of battery units11ato11ehas the same configuration. In the present embodiment, the battery unit11awill be described as a representative. Incidentally, in the battery units11bto11e, “a” in the description of the battery unit11acan be replaced with “b” to “e” respectively, and the detailed description will be omitted.

The battery unit11aincludes a battery111aand a switching unit112a.

The battery111ais a chargeable/dischargeable storage battery, and may be configured of one cell or may be configured of a plurality of cells. In the present embodiment, the used batteries used on a vehicle are used as the batteries111ato111eprovided in the plurality of battery units11ato11e. The deterioration state of the used battery used for the vehicle is measured, and the batteries111ato111eare sorted so that the total capacity of the plurality of batteries111ato111ebecomes a desired capacity. At this time, the battery deterioration degrees of the batteries111ato111edo not have to be the same, and the total capacity of the batteries111ato111emay be a desired capacity.

The switching unit112ais provided switchably between a connected state in which the corresponding battery111ais used as a power supply and a non-connected state not used as a power supply. More specifically, the batteries switched to the connected state by the switching units112ato112eare connected in series, and the batteries switched to the unconnected state by the switching units112ato112eare disconnected from the connected batteries.

The switching unit112aincludes a first switch SW1aconnected in series to the battery111a, and a second switch SW2aconnected in parallel to the battery111aand the first switch SW1a. Now, one end T11of the first switch SW1ais connected to one electrode (for example, positive electrode) of the corresponding battery111a. One end T21of the second switch SW2ais connected to the other electrode (for example, negative electrode) of the corresponding battery111a, and the other end T22is connected to the other end T12of the first switch SW1a.

The battery units11ato11edescribed above are connected in series, and both ends thereof are connected to a DC/AC converter14that converts direct current into alternating current. That is, the other end T12of the first switch SW1aand the other end T22of the second switch SW2aprovided in the battery unit11aon one side (the left side inFIG. 1) in an arrangement direction of the battery units11ato11eare connected to the DC/AC converter14. Further, the other electrode of the battery111eand one end T21of the second switch SW2eprovided in the battery unit11eon the other end side (the right side inFIG. 1) in the arranging direction are connected to the DC/AC converter.

According to the above configuration, when the second switch SW2ais turned off and the first switch SW1ais turned on, the battery111ais in the connected state. when the first switch SW1ais turned off, and the second switch SW2ais turned on, the battery111ais in the disconnected state.

The plurality of voltage measurement units12ato12emeasures the voltages across the corresponding batteries111ato111e, and outputs the measurement results to the control unit13described later.

The control unit13includes well-known CPU, ROM, and RAM, and controls the entire battery system1. The control unit13turns on and off the first switches SW1ato SW1eand the second switches SW2ato SW2ebased on the voltages across the batteries111ato111e.

Next, the operation of the battery system1configured as described above will be described with reference to the flowcharts ofFIGS. 2 and 3. First, when charging of the battery system1is started, the control unit13starts the charging process shown inFIG. 2. First, the control unit13turns on the first switches SW1ato SW1eafter turning off the second switches SW2ato SW2eof all the battery units11ato11e(step S10). As a result, all the batteries111ato111eare connected in series, and charged.

Next, the control unit13measures the voltages across the batteries111ato111eusing the voltage measurement units12ato12e(step S11). The control unit13determines whether there is any of the plurality of batteries111ato111ethat has reached a predetermined charge termination voltage (step S12). If there is no battery that has reached the charge termination voltage (N in step S12), the control unit13determines that none of the batteries111ato111eis fully charged, and returns to step S11.

On the other hand, if there is any of batteries111ato111ethat has reached the charge termination voltage (Y in step S12), the control unit13determines that the any of batteries111ato111eis fully charged, and any of the first switches SW1ato SW1eis turned off, and any of the second switches SW2ato SW2eis turned on corresponding to the fully charged battery (step S13). Thus, any of the batteries111ato111ein the fully charged state are switched to the non-connected state, and the charging is stopped. Thereafter, the control unit13proceeds to step S14.

In step S14, the control unit13determines whether or not charging has ended. If the charging is ended (Y in step S14), the control unit13ends the charging process. On the other hand, if the charging is not ended (N in step S14), the control unit13returns to step S11again.

Further, when the discharge of the battery system1is started, the control unit13starts the discharging process shown inFIG. 3. First, the control unit13turns on the first switches SW1ato SW1eafter turning off the second switches SW2ato SW2eof all the battery units11ato11e(step S20). As a result, all the batteries111ato111eare connected in series, and discharged.

Next, the control unit13measures the voltages across the batteries111ato111eusing the voltage measurement units12ato12e(step S21). The control unit13determines whether there is any of the plurality of batteries111ato111ethat has reached a predetermined discharge termination voltage (step S22). If there is no battery that has reached the discharge termination voltage (N in step S22), the control unit13determines that none of the batteries111ato111eis fully discharged, and returns to step S21.

On the other hand, if there is any of batteries111ato111ethat has reached the discharge termination voltage (Y in step S22), the control unit13determines that the any of batteries111ato111eis fully discharged, and any of the first switches SW1ato SW1eis turned off, and any of the second switches SW2ato SW2eis turned on corresponding to the fully discharged battery (step S23). Thus, any of the batteries111ato111ein the fully discharged state are switched to the non-connected state, and the discharging is stopped. Thereafter, the control unit13proceeds to step S24.

In step S24, the control unit13determines whether or not discharging has ended. If the discharging is ended (Y in step S24), the control unit13ends the discharging process. On the other hand, if the discharging is not ended (N in step S24), the control unit13returns to step S21again.

Next, an example of the operation of the above-described battery system1will be described assuming that the deterioration progresses from the battery111ato the battery111e. When the battery system1is charged, the control unit13firstly turns off the second switches SW2ato SW2e, and then turns on the first switches SW1ato SW1eof all the battery units11ato11e. Thus, at the start of charging, all the batteries111ato111eare charged. Thereafter, since the voltage across the most advanced deterioration battery111ereaches the charge termination voltage, the control unit13turns off the first switch SW1eand turns on the second switch SW2e. As a result, the battery111eis disconnected, and charging is continued as the battery system1configured by the batteries111ato111d.

Next, since the voltage across the battery111din which the battery deterioration has advanced second reaches the charge termination voltage, the control unit13turns off the first switch SW1dand turns on the second switch SW2d. As a result, the battery111dis also disconnected, and charging is continued as the battery system1configured of the battery111ato the battery111c. By repeating this process up to one battery, charging can be performed until the states of charge SOC of all the batteries111ato111ereach 100% (=full charge state).

On the other hand, when the battery system1is discharged, the control unit13first turns off the second switches SW2ato SW2eof all the battery units11ato11eand then turns on the first switches SW1ato SW1e. Thus, at the start of the discharge, all the batteries111ato111eare discharged. Thereafter, since the voltage across the most advanced deterioration battery111ereaches the discharge termination voltage, the control unit13turns off the first switch SW1eand turns on the second switch SW2e. As a result, the battery111eis disconnected, and the discharge is continued as the battery system1configured of the batteries111ato111d.

Next, since the voltage across the battery111din which the battery deterioration has advanced second reaches the discharge termination voltage, the control unit13turns off the first switch SW1dand turns on the second switch SW2d. As a result, the battery111dis also disconnected, and the discharge is continued as the battery system1configured of the battery111ato the battery111c. By repeating this process up to one battery, discharge can be performed until the state of charge SOC of all the batteries111ato111ebecomes 0% (=full discharge state).

According to the above-described first embodiment, the control unit13controls the plurality of switching units112ato112eto be in the connected state in a normal state, and controls the switching units112ato112ecorresponding to the batteries111ato111edetermined to be fully charged during charging or fully discharged during discharging to be disconnected. Thus, as described above, all the batteries111ato111ecan be charged to full charge, and all the batteries111ato111ecan be discharged to the end of discharge. Therefore, the battery system1, capable of sufficiently using the capacities of all the batteries111ato111eeven if the batteries111ato111ein different deterioration states are mixed, can be provided at low cost.

Further, according to the first embodiment described above, the switching unit112ais configured of the first switch SW1aconnected in series to the battery111a, and the second switch SW2aconnected in parallel to the battery111aand the first switch SW1a(for the switching units112bto112e, “a” is read as “b” to “e”). Thus, the batteries111ato111ecan be easily switched between the connected state and the disconnected state using the switches SW1ato SW1eand SW2ato SW2e.

Second Embodiment

Next, a second embodiment of the present invention will be described based onFIG. 4. A significant difference between the first embodiment and the second embodiment is the configuration of the switching units112ato112e. In this embodiment, the switching unit112awill be described as a representative. Incidentally, in the switching units112bto112e, “a” in the description of the switching unit112acan be replaced with “b” to “e”, respectively, and the detailed description will be omitted. In the first embodiment described above, the switching unit112ais configured of two on/off switches SW1aand SW2a, but in the second embodiment, the switching unit112ais configured of one changeover switch SW3a.

Incidentally, inFIG. 4, the same components as those inFIG. 1already described in the above-described first embodiment are given the same reference signs, and the details thereof are omitted.

The switching unit112aconsists of a changeover switch SW3athat switches the connection of the first contact C1between the second contact C2connected to one electrode of the battery111aand the third contact C3connected to the other electrode of the battery111a. Incidentally, the first contact C1of the changeover switch SW3ais connected to the DC/AC converter14. The first contacts C1of the changeover switches SW3bto SW3eare respectively connected to the adjacent batteries111ato111d.

According to the above configuration, when the changeover switches SW3ato SW3eare switched to the second contact C2side, the connected state is established, and when the changeover switches SW3ato SW3eare switched to the third contact C3side, the disconnected state is established.

Next, the operation of the battery system1configured as described above will be described. The operation of the second embodiment is substantially the same as the first embodiment described above with reference toFIGS. 2 and 3. The difference is that in the first embodiment, the control unit13turns on the first switches SW1ato SW1eand turns off the second switches SW2ato SW2ein steps S10and S20, but in the second embodiment, the changeover switches SW3ato SW3eare switched to the second contact C2side. Further, in the first embodiment, in steps S13and S23, the control unit13turns off the first switches SW1ato SW1eand turns on the second switches SW2ato SW2ecorresponding to the batteries111ato111ein the fully charged or fully discharged state, but in the second embodiment, the corresponding changeover switches SW3ato SW3eare switched to the third contact C3side.

Further, according to the second embodiment described above, the switching units112ato112eare configured by the changeover switches SW3ato SW3e. Thereby, the batteries111ato111ecan be easily switched between the connected state and the disconnected state using the changeover switches SW3ato SW3e. Further, a short circuit due to erroneous switching of the first switches SW1ato SW1eand the second switches SW2ato SW2eis prevented.

Third Embodiment

Next, a third embodiment will be described based onFIG. 5. In the third embodiment, a battery circuit group in which a plurality of battery circuits510, each having a plurality of battery units11ato11econnected in series, are connected in parallel is provided. Further, a charge control unit520and a load530are connected in parallel to both ends of the battery circuit510. Although not shown inFIG. 5, in the third embodiment, voltage measurement units12ato12efor measuring the voltage across the batteries111ato111eare provided similar to the first and second embodiments.

Similar to the first embodiment, each of the battery circuits510includes switching units112ato112econsisting of first switches SW1ato SW1eand second switches SW2ato SW2e. Then, similar to the first embodiment, when the batteries111ato111eare neither fully charged nor fully discharged, the first switches SW1ato SW1eare turned on and the second switches SW2ato SW2eare turned off. Thus, the battery units11ato11eare in a state (first state) in which the batteries111ato111eare connected between the positive electrode ends113ato113eand the negative electrode ends114ato114eof the battery units11ato11e. The batteries111ato111eare connected in series to the batteries111ato111eof the battery units11ato11ein the other first state, and are used as power supplies. Further, when it is determined that the batteries111ato111ehave reached the fully charged or fully discharged state, the first switches SW1ato SW1eare turned off and the second switches SW2ato SW2eare turned on. As a result, the positive electrode ends113ato113eand the negative electrode ends114ato114eof the battery units11ato11eare connected without the batteries111ato111e(second state). The batteries111ato111eare separated from the batteries111ato111eof the battery units11ato11ein the other first state, and are not used as power supplies.

Incidentally, inFIG. 5, the switching units112ato112eare configured by first switches SW1ato SW1eand second switches SW2ato SW2e. However, instead of this, similar to the second embodiment, the switching units112ato112emay be configured by the switching switches SW3ato SW3e. In this case, when the batteries111ato111eare neither fully charged nor fully discharged, the contact C1is connected to the contact C2in the changeover switches SW3ato SW3e. Thus, the battery units11ato11eare in a state (first state) in which the batteries111ato111eare connected between the positive electrode ends113ato113eand the negative electrode ends114ato114eof the battery units11ato11e. The batteries111ato111eare connected in series to the batteries111ato111eof the battery units11ato11ein the other first state, and are used as power supplies. In addition, when it is determined that the batteries111ato111ehave reached the fully charged state or the fully discharged state, the contact C1is connected to the contact C3in the changeover switches SW3ato SW3e. As a result, the positive electrode ends113ato113eand the negative electrode ends114ato114eof the battery units11ato11eare connected without the batteries111ato111e(second state). The batteries111ato111eare separated from the batteries111ato111eof the battery units11ato11ein the other first states, and are not used as power supplies.

In the first embodiment, during the discharge operation, power supply to the load is stopped while the battery in the fully discharged state is being disconnected, that is, until the first switches SW1ato SW1eare turned off and the second switches SW2ato SW2eare turned on. Further, also in the second embodiment, during the discharging operation, power supply to the load is stopped while the battery in the fully discharged state is being disconnected, that is, until the changeover switches SW3ato SW3eare switched from the second contact C2to the third contact C3.

Therefore, in the third embodiment, a plurality of battery circuits510having the batteries111ato111econnected in series is connected in parallel. As a result, even if one of the battery circuits510operates to disconnect the fully discharged battery at the time of discharge, current flows through the other battery circuits510. Therefore, the power supply to the load530is not stopped while the operation of disconnecting the fully discharged battery is performed.

Further, in the third embodiment, in each of the plurality of battery circuits510, the diode511is connected in series with the plurality of battery units11ato11esuch that the discharge direction of the batteries111ato111eis the forward direction. For example, inFIG. 5, the positive electrode end113aof the battery unit11ais connected to the anode of the diode510. Therefore, even if the total voltage of each of the plurality of battery circuits510is different by disconnecting the battery in the fully discharged state, it is possible to prevent the flow of current from the battery circuit510having a high total voltage to the battery circuit510having a low total voltage when discharging.

When the plurality of battery circuits510is configured as described above, the direction of the current for charging the batteries111ato111eis reverse to the forward direction of the diode511, and the current for charging the batteries111ato111ecannot pass through the diode511. Thus, in the third embodiment, as illustrated inFIG. 5, each of the plurality of battery circuits510includes a bypass switch512connected in parallel to the diode511. By turning on the bypass switch512at the time of charging, the current for charging the batteries111ato111ecan bypass the diode511, and the current for charging the batteries111ato111ecan be supplied.

In addition, the control unit13controls the bypass switches512such that the plurality of battery circuits510are sequentially charged one by one at the time of charging. That is, the control unit13turns on only one bypass switch512among the plurality of battery circuits510, turns off the bypass switch512of the other battery circuits510, and charges only the battery circuit510in which the bypass switch512is turned on. Then, when charging is completed, the bypass switch512is turned off, and only one bypass switch512of the other uncharged battery circuits510is turned on to charge this battery circuit510. By continuing such control, the control unit13charges the battery circuit510sequentially. Therefore, the battery circuits510are not connected to each other at the time of charging. Therefore, in the third embodiment, even if the total voltage of each of the plurality of battery circuits510is different by disconnecting the fully charged battery, no current flows into the circuit510of the battery having a low total voltage from the circuit510of the battery having a high total voltage.

FIG. 6is a flowchart showing the operation at the time of discharge in the third embodiment. All of the first switches SW1ato SW1e, the second switches SW2ato SW2e, and the bypass switch512are turned off (step S601). The first switches SW1ato SW1eare turned on (step S602). Thereafter, the discharge is started (step S603).

Next, the control unit13measures the voltages across the batteries111ato111e(step S604). The control unit13determines whether there is any of the plurality of batteries111ato111ethat has reached a predetermined discharge termination voltage (step S605). If there is no battery111ato111ethat has reached the discharge termination voltage (N in step S605), the control unit13determines that none of the batteries111ato111eis fully discharged, and returns to step S604.

On the other hand, if there is a battery111ato111ethat has reached the discharge termination voltage (Y in step S605), the control unit13determines that this one of the batteries111ato111eis in the fully discharged state, and one of the first switches SW1ato SW1eis turned off, and the one of the second switches SW2ato SW2eis turned on corresponding to this one of the batteries111ato111e(step S606). As a result, the connection of any of the batteries111ato111ein the fully discharged state is switched to the disconnected state, and the discharge of any of the batteries111ato111ein the fully discharged state is stopped. Thereafter, the control unit13proceeds to step S607.

In step S607, the control unit13determines whether the discharge of all the batteries111ato111ehas been stopped, that is, whether the discharge of all the batteries111ato111ehas ended. If the discharge of all the batteries111ato111eis ended (Y in step S607), the control unit13stops the discharge (S608), and all of the first switches SW1ato SW1e, the second switches SW2ato SW2e, and the bypass switches512are turned off (step S609), and the first switches SW1ato SW1eare turned on (step S610). On the other hand, if the discharge of all the batteries111ato111eis not ended (N in step S606), the control unit13returns to step S604again.

FIG. 7is a flowchart showing the operation at the time of charging in the third embodiment. All of the first switches SW1ato SW1e, the second switches SW2ato SW2e, and the bypass switches512are turned off (step S701). The first switches SW1ato SW1eare turned on, and only the bypass switch512of one battery circuit510among the battery circuits510not yet charged is turned on (step S702). Thereafter, charging is started (step S703).

Next, the control unit13measures the voltage across the batteries111ato111e(step S704). The control unit13determines whether there is any of the plurality of batteries111ato111ethat has reached a predetermined charge termination voltage (step S705). If there is no battery111ato111ethat has reached the charge termination voltage (N in step S705), the control unit13determines that none of the batteries111ato111eis fully charged, and returns to step S704.

On the other hand, if there is any of batteries111ato111ethat has reached the charge termination voltage (Y in step S705), the control unit13determines that this one of the battery111ato111eis fully charged, and the first switches SW1ato SW1eare turned off, and the second switches SW2ato SW2eare turned on corresponding to this one of the batteries111ato111e(step S706). Thereby, the connection of any of the batteries111ato111ein the fully charged state is switched to the disconnected state, and the charging is stopped. Thereafter, the control unit13proceeds to step S707.

In step S707, the control unit13determines whether charging of all the batteries111ato111eof the battery circuit510in which the bypass switch512is on is stopped or not, that is, whether charging of the battery circuit510with the bypass switch512turned on has ended (S707). If the charging of the battery circuit510in which the bypass switch512is on has been ended (Y in step S707), the control unit13proceeds to step S708. If the charging of the battery circuit510for which the bypass switch512is on has not been ended (N in step S707), the process returns to step S704again.

In step S708, the control unit determines whether charging of all the battery circuits510has ended. If charging of all the battery circuits510is ended (Y in step S708), the control unit13stops the discharge (S709), and all of the first switches SW1ato SW1e, the second switches SW2ato SW2e, the bypass switches512are turned off (step S710), and the first switches SW1ato SW1eare turned on (step S711). On the other hand, if the discharge of all the batteries111ato111eis not ended (N in step S708), the control unit13returns to step S701again.

Incidentally, the present invention is not limited to the above embodiments. That is, various modifications can be made without departing from the scope of the present invention.

REFERENCE SIGNS LIST

C1first contact

C2second contact

C3third contact

520charge control unit