Abstract:
A battery pack in which an increase in size is restrained even if the battery pack includes plural battery modules with fuses is to be provided. In order to solve the foregoing problem, a battery pack according to the invention includes at least two or more battery modules, each battery module having a battery cell and a first fuse connected in series with the battery cell, the battery cell and the first fuse being housed in a casing. A positive electrode terminal provided in one battery module and a negative electrode terminal provided in another battery module are connected to each other via a second fuse. The second fuse has a higher rated voltage than the first fuse.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a battery system equipped with a fuse. 
         [0003]    2. Description of the Related Art 
         [0004]    A battery system that is recently under development can be used for various purposes, and the scale of the battery system varies depending on the purpose of use. Particularly, a battery system used to restrain load fluctuation and cope with blackouts at a server center or the like, or to stabilize a large-scale system such as a regenerative energy storage system for railways, renewable energy system or nuclear power station, is of a large scale. In this large-scale battery system, plural battery modules as minimum units of use are connected in series to form a battery pack, and plural such battery packs are connected in parallel. Such a large-scale battery system is assumed to be used for a long period and therefore maintenance is needed. 
         [0005]    The above maintenance is carried out, for example, by inspecting the state of deterioration of the currently used battery module and determining whether the battery module is approaching a limit of use or is already beyond the limit of use. The battery module that is approaching the limit of use or is already beyond the limit of use is to be replaced. Meanwhile, as disclosed in JP-A-2010-122194, the battery module that is assumed to be replaced when necessary is provided with a fuse so that the battery module can tolerate a maximum voltage of the system and hence can be protected from overcurrent and overvoltage due to wiring errors at the time of replacement. 
         [0006]    However, according to the invention disclosed in JP-A-2010-122194, a fuse with a high voltage resistance needs to be installed within the module and this causes an increase in the volume of the battery module itself when constructing a large-scale battery system. Therefore, there is a problem that the battery system itself is increased in size. 
       SUMMARY OF THE INVENTION 
       [0007]    Thus, it is an object of the invention to provide a battery pack in which an increase in size is restrained even if the battery pack includes plural battery modules with fuses. 
         [0008]    In order to solve the foregoing problem, a battery pack according to an aspect of the invention includes at least two or more battery modules, each battery module having a battery cell and a first fuse connected in series with the battery cell, the battery cell and the first fuse being housed in a casing. A positive electrode terminal provided in one battery module and a negative electrode terminal provided in another battery module are connected to each other via a second fuse. The second fuse has a higher rated voltage than the first fuse. 
         [0009]    Moreover, in order to solve the foregoing problem, a battery system according to an aspect of the invention includes a plural number of the battery packs connected in parallel and a resistance element corresponding to each of the plural battery packs. 
         [0010]    By carrying out the invention, an increase in size can be restrained even if the battery pack includes plural battery modules with fuses. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows a power generation system according to the invention. 
           [0012]      FIG. 2  is a block diagram of a battery system according to the invention. 
           [0013]      FIG. 3  is a circuit diagram of a battery module according to the invention. 
           [0014]      FIG. 4  shows the configuration of the battery module according to the invention. 
           [0015]      FIG. 5  is a circuit diagram of the battery system according to the invention. 
           [0016]      FIG. 6  is a perspective view of a battery pack according to the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    Hereinafter, an embodiment of the invention will be described with reference to the drawings. First, a power generation system according to the invention will be described with reference to  FIG. 1 . A power generation system  101  includes a power generation device  103 , an electric power system  102 , an electric wire  105  connecting the electric power system  102  and the power generation device  103 , and a battery system  201  connected to the electric wire  105  via an inverter  104 . The power generation device  103  is, for example, a wind power generation facility, hydroelectric generation facility, solar power generation facility or another type of power generation facility. 
         [0018]    The battery system  201  charges with generated electric power when the power generation device  103  generates excess power that is greater than electric power required by the electric power system  102 , and the battery system  201  discharges electric power when the amount of power generation by the power generation device  103  is smaller than electric power required by the electric power system  102 , thus realizing stable supply of electric power. When the battery system  201  charges and discharges, electric power is supplied and received after the inverter  104  carries out AC-DC and DC-AC conversion. Next, a block diagram of the battery system  201  is shown in  FIG. 2 . The battery system  201  according to the invention includes a battery module  30  as a minimum unit, a battery pack  40  including plural battery modules  30 , and a battery block  50  including plural battery packs  40 . 
         [0019]    First, the configuration of the battery module  30  will be described specifically. The battery module  30  has plural battery cell groups  20 , a cell control unit (CCU)  210  which collects battery information of the battery cell groups  20  (for example, current information, voltage information, temperature information, state of charge and the like of battery cells), and a battery module control unit (BMCU)  31 . The cell control unit  210  also performs balancing control between battery cells, which will be described later. The battery information collected by the cell control unit  210  is sent to the battery module control unit (BMCU)  31 . The battery module control unit (BMCU)  31  calculates an average state of charge of the battery cell groups  20  in the battery module  30 , adds the battery information of the average state of charge of the battery cell groups  20  to the above battery information, and transmits the battery information to a higher-level battery pack control unit (BPCU)  230 . 
         [0020]    The battery pack  40  has plural battery modules  30  and a battery pack control unit  230 . The battery pack control unit  230  collects battery information outputted from each battery module control unit  31  and calculates information of an average state of charge of the battery modules  30 , which is the average of the states of charge of the battery modules  30  in the battery pack  40 . The information of the average state of charge of the plural battery modules  30  is added to the battery information acquired from the battery module control unit  31 , and the battery information is outputted to a battery block control unit  240 , which is on a still higher level. 
         [0021]    The battery block  50  has plural battery packs  40  and a battery block control unit  240 . The battery block control unit  240  collects battery information outputted from each battery pack control unit  230  and calculates information of an average state of charge of the battery packs  40 , which is the average of the states of charge of the battery packs  40  in the battery block  50 . The information of the average state of charge of the plural battery packs  40  is added to the battery information acquired from the battery pack control unit  230 , and the battery information is outputted to a system control unit  250 , which is on a still higher level. In this description, there are plural battery packs  40  in the battery block  50 . However, only one battery pack  40  may form the battery block  50 . In such a case, the battery block control unit  240  outputs the battery information outputted from the battery pack control unit  230 , directly to the system control unit  250 . 
         [0022]    According to the invention, since the states of batteries are thus monitored in plural hierarchical levels, the battery system  201  has a high level of safety. Also, since each of the battery module  30 , the battery pack  40  and the battery block  50  according to the invention can be replaced on the respective levels, the battery system is easy to maintain. 
         [0023]    Next, the specific circuit configuration of the battery module  30  will be described with reference to  FIG. 3 . The battery module  30  is provided with a power-supply circuit  25  in which plural battery cell groups  20  are connected in series, and a fuse  32  connected in series with the power-supply circuit. 
         [0024]    The side of the fuse  32  that is not connected to the power-supply circuit  25  is connected to a positive electrode-side terminal  1 , which is connected to another device (including another battery module  30 ) arranged outside this battery module  30 . 
         [0025]    Meanwhile, a negative electrode side of the power-supply circuit  25  is connected to a negative electrode-side terminal  2 . The negative electrode-side terminal  2 , too, is connected to another device (including another battery module  30 ). 
         [0026]    The battery cell group  20  includes plural battery cells Bn 1 , Bn 2  . . . BnX connected in parallel (where n is greater than 1 and is the number of battery cell groups  20  connected in series, and X is the number of cells). Also, a resistance element  21  and a switch element  22  are connected parallel to the battery cell group  20 . The resistance element  21  and the switch element  22  are for taking balance, for example, among battery cells B 11 , B 12  . . . B 1 X when voltage and state of charge vary among the battery cells B 11 , B 12  . . . B 1 X. 
         [0027]    The cell control unit  210  acquires battery information of each battery cell Bn 1 , Bn 2  BnX and outputs the battery information to the battery module control unit  31 . The battery module control unit  31  calculates the state of charge (SOC) of each battery cell based on the battery information outputted from each cell control unit  210  and outputs the information of the state of charge to the cell control unit  210 . For example, the cell control unit  210 , after receiving the information of the state of charge, outputs a signal to turn on the switch element  22  when the difference in the state of charge among the battery cells Bn 1 , Bn 2  . . . BnX in the battery cell group  20  monitored by the cell control unit  210  becomes 10% or greater, thus taking balance among the battery cells Bn 1 , Bn 2  . . . BnX. 
         [0028]    Also, a configuration in which plural battery modules  30  are connected in series will be described with reference to  FIG. 4 . In  FIG. 4 , a configuration in which three battery modules  30   a,    30   b  and  30   c  are connected in series is used to simply the explanation. However, the number of the battery modules  30  connected in series is not limited to this number. 
         [0029]    As described with reference to  FIG. 3 , the battery module  30  has the power-supply circuit  25  and the fuse  32  connected in series with the power-supply circuit  25 , inside a casing  35 . Also, the positive electrode-side terminal  1  and the negative electrode-side terminal  2  are provided on the casing  35 . 
         [0030]    Here, the connection of the battery module  30   b  as a center unit to each of the battery modules  30   a  and  30   c  will be described specifically. The positive electrode-side terminal  1  of the battery module  30   b  is connected to the negative electrode-side terminal  2  of the neighboring battery module  30   a  via a fuse  33  ( 33   a ), using a connection line  34  such as bus bar. Also, the battery module  30   c  next to the battery module  30   b  is connected using a similar configuration to the connection between the battery module  30   b  and the battery module  30   a.    
         [0031]    The fuse  33  has a higher voltage resistance than the fuse  32  provided inside the battery module  30  and has a greater volume than the fuse  32 . Therefore, by providing the fuse  32  with a lower voltage resistance (rated voltage) than the fuse  33 , within the battery module, a smaller size can be realized than in the case where a high voltage-resistance fuse is provided inside the battery module  30 , while minimum necessary safety of the battery module  30  is secured. Also, by providing the fuse  33  with a high voltage resistance, that is, with a high rated voltage between the battery modules  30  after the small-size fuse  32  is provided in the battery modules  30 , the battery modules  30  can be miniaturized while sufficient safety as the battery system is secured. 
         [0032]    Moreover, by configuring the high voltage-resistance fuse  33  to break at a lower current than the low voltage-resistance fuse  32 , the high voltage-resistance fuse  33  can be made to break first when an abnormality occurs. With this configuration, even when an abnormality occurs in the battery system or when a maintenance worker makes an error in wiring, the fuse  33  arranged outside the battery module  30  breaks and therefore it suffices to replace the fuse  33  alone instead of replacing the battery module  30 . Thus, ease of maintenance is improved further. 
         [0033]    The voltage resistance (rated voltage) of the low voltage-resistance fuse  32  is equal to or higher than the maximum voltage of the battery module  30 , and the fuse  32  is made to break, for example, when an external short circuit is formed in the battery module alone. As the fusing current (rated current), the fuse  32  is made to break approximately at twice the maximum current specified in the specifications of the battery module  30 , or greater. As an example of the voltage resistance (rated voltage) and fusing current (rated current) of the low voltage-resistance fuse  32 , when the maximum voltage of the battery module  30  is 30 V, the rated voltage is 30 V or higher, and when the maximum current specified in the specifications of the battery module  30  is  20 A, the fusing current (rated current) is  40 A or higher. 
         [0034]    Meanwhile, the voltage resistance (rated voltage) of the high voltage-resistance fuse  33  is equal to or higher than the maximum voltage of the battery pack  40 , and the fuse  33  is made to break, for example, when there is an overload in the operation of the battery system. As the fusing current (rated current), the fuse  33  is made to break at a current equal to or higher than the maximum current specified in the specifications of the battery pack  40  and lower than the rated current of the low voltage-resistance fuse. As an example of the voltage resistance (rated voltage) and fusing current (rated current) of the high voltage-resistance fuse  33 , when the maximum voltage of the battery pack  40  is 480 V, the rated voltage is 480 V or higher, and when the maximum current specified in the specifications of the battery pack  40  is  20 A, the fusing current (rated current) is  20 A or higher and lower than  40 A. 
         [0035]    With such a configuration, the battery system as a whole can be miniaturized while ease of maintenance is improved. Thus, higher safety can be secured. 
         [0036]    Next, the circuit configuration of the battery system  201  will be described with reference to  FIG. 5 .  FIG. 5  shows the battery system  201  in which plural battery blocks  50  are connected in parallel, each battery block  50  having battery packs  40  each of which includes plural battery modules  30 . 
         [0037]    First, the configuration of the battery block  50  will be described. The battery block  50  has the battery packs  40  a pre-charge circuit  55  connected in series with the battery packs  40 . The battery blocks  50  are connected parallel to each other and are connected to a positive electrode side of the inverter  104  via a switch unit  251  and to a negative electrode side of the inverter  104  via a switch unit  252 . 
         [0038]    The pre-charge circuit  55  includes a switch element  51 , and a resistance element  52  and a switch element  53  which are connected parallel to the switch element  51 . When there is a difference in the state of charge or voltage from the other battery blocks  50 , the pre-charge circuit  55  maintains a certain period during which the switch unit  251  and the switch unit  252  are off, the switch element  51  is off and the switch element  53  is on. Thus, the difference in the state of charge or voltage among the individual battery blocks  50  can be reduced, using cross-current. 
         [0039]    The battery block  50  also has switch elements  54   a   1  ( 54   a ),  54   a   2  ( 54   a ) . . .  54   an  ( 54   a ) (where n is the number of battery packs  40  connected in parallel within the battery block  50 ) connected in series corresponding to each battery pack  40 . When a problem occurs in each battery pack  40 , the switch element  54   a  corresponding to the battery pack  40  with the problem is opened and this battery pack  40  can thus be disconnected from the other battery packs  40 . Also, with such a configuration, at the time of maintenance, overvoltage can be prevented from being applied to the battery packs  40  by opening the switch elements  54   a.  Therefore, safety in operation is secured at the time of maintenance of the battery packs  40  and double protection of the battery system as a whole is possible with the fuses  32  and  33 . Thus, safety and ease of maintenance are improved further. 
         [0040]    Finally, a perspective view of the battery pack  40  is shown in  FIG. 6 . The battery pack  40  has a module installation table  120  where plural battery modules  30  are installed, the battery pack control unit  230 , and a battery rack  110  in which these units are installed. In this embodiment, the battery pack control unit  230  is arranged in a lower part of the battery rack  110 . However, the battery pack control unit  230  may be arranged in an upper part. Also, by arranging the battery modules  30  closely to each other, the battery pack  40  as a whole can be further miniaturized, utilizing the battery modules  30  which are miniaturized with the high voltage-resistance fuses  33  arranged outside of the casings  35  of the battery modules. Even if the battery modules  30  are slightly spaced from each other instead of being in tight contact with each other, the battery pack  40  has a small size because the battery modules  30  themselves are small in size. 
         [0041]    The plural battery modules  30  are connected to the neighboring battery modules  30  via the connection line  34 . Here, if the battery modules are connected in such a way that the negative electrode-side terminal  2  of the one battery module  30   a  and the positive electrode-side terminal  1  of the next battery module  30   b  are laid side by side, the fuse  33  arranged on the upper side of the battery module  30  and the fuse  33  arranged on the lower side of the battery module become alternate with respect to a direction substantially parallel to an installation surface of the module installation table  120 , as shown in  FIG. 6 . With such an arrangement, even in the battery pack  40  in which the small-size battery modules are arranged in tight contact with each other to save space, sufficient work space to replace the fuse  33  can be secured. Thus, a battery system in which ease of maintenance and safety are improved while the battery pack  40  is miniaturized as a whole by the miniaturization of the battery module  30  can be provided.