Abstract:
Provided are a cell balance device for protecting a switch circuit from an overcurrent flow. The cell balance device includes: a plurality of electric accumulator connection terminals each connected to one of a node and two terminals of electric accumulators connected in series; a voltage hold device connection terminal connected to a voltage hold device; a plurality of first switch circuits provided between the plurality of electric accumulator connection terminals and the voltage hold device; a control circuit for controlling ON/OFF of the plurality of first switch circuits based on a synchronization signal; and an overcurrent detection circuit for detecting an overcurrent flowing through each of the plurality of first switch circuits.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2011-180446 filed on Aug. 22, 2011, the entire content of which is hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a cell balance device for achieving a cell balance of secondary batteries connected in series and to a battery system including the cell balance devices, and more particularly, to a cell balance device capable of preventing a switch circuit of the cell balance device from being broken down by an overcurrent and to a battery system including the cell balance devices. 
         [0004]    2. Description of the Related Art 
         [0005]      FIG. 5  illustrates a circuit diagram of a conventional cell balance adjusting circuit. A cell balance device including the conventional cell balance adjusting circuit is provided with a battery pack portion, in which a plurality of secondary battery cells (hereinafter, referred to as cells)  401  to  406  as basic components are connected in series, and switches  411  to  462  each having one contact connected to a node between the cells. The other contact of each of the switches  411 ,  421 ,  431 ,  441 ,  451 , and  461  is connected to one electrode of a capacitor  407  which is a voltage hold device. The other contact of each of the switches  412 ,  422 ,  432 ,  442 ,  452 , and  462  than the one contact on the cell side is connected to the other electrode of the voltage hold device  407 . A load circuit or a charging circuit  408  is connected across the battery pack. 
         [0006]    Open/close signals for the respective switches are connected so that the switch  411  and the switch  412  may operate simultaneously. Signals are similarly connected so that the switch  421  and the switch  422 , the switch  431  and the switch  432 , the switch  441  and the switch  442 , the switch  451  and the switch  452 , and the switch  461  and the switch  462  may be open/closed simultaneously each as a switch of a set of corresponding two switches. 
         [0007]    Further, the switch open/close signals sequentially turn ON/OFF the switches  411  to  451  and the switches  412  to  462 . Then, after finishing turning ON/OFF the switch  461  and the switch  462 , repetitive switch open/close operations are continuously performed by returning to the first ON/OFF operation of the switch  411  and the switch  412 . 
         [0008]    Next, an operation of the conventional cell balance adjusting circuit is described. The conventional cell balance adjusting circuit scans switches sequentially in one direction so that the switches are switched over while forming parallel connections between the series-connected adjacent cells and the voltage hold device  407 . 
         [0009]    The switches  411  and  412  are configured to receive signals for simultaneous open/close operation, and the switch  421  and the switch  422  are also configured to be open/closed simultaneously. The same is applied to the other switches, and the simultaneous open/close operation is performed in each combination of the switch  431  and the switch  432 , the switch  441  and the switch  442 , the switch  451  and the switch  452 , and the switch  461  and the switch  462 . 
         [0010]    The switches are controlled in this way, to thereby form parallel connections sequentially between all the series-connected cells and the voltage hold device  407 . After completion of the formation of parallel connections to all control target cells in the battery pack, the same switching operation is repeatedly performed from the first cell, thereby adjusting a cell balance. 
         [0011]    In the conventional technology, however, when an overcurrent flows through the switch, the switch is broken down, and hence there is a problem in that the reliability of the cell balance device is lowered. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention has been devised in view of the above-mentioned problem, and provides a cell balance device capable of protecting a switch when an overcurrent flows through the switch so as to prevent the switch from being broken down, and a battery system including the cell balance devices. 
         [0013]    In order to solve the conventional problem, the cell balance device according to the present invention is configured as follows. 
         [0014]    There is provided a cell balance device for a battery system for adjusting a cell balance of a plurality of electric accumulators connected in series, the cell balance device including: a plurality of electric accumulator connection terminals to be each connected to one of a node and two terminals of the plurality of electric accumulators connected in series; a voltage hold device connection terminal to be connected to a voltage hold device; a plurality of first switch circuits provided between the plurality of electric accumulator connection terminals and the voltage hold device; a receiving terminal for receiving a synchronization signal; a transmitting terminal for transmitting the synchronization signal; a control circuit for controlling ON/OFF of the plurality of first switch circuits based on the synchronization signal; and an overcurrent detection circuit for detecting an overcurrent flowing through each of the plurality of first switch circuits. 
         [0015]    There is also provided a battery system, including: a plurality of electric accumulators connected in series; a plurality of voltage hold devices connected in series; a clock generation circuit for outputting a synchronization signal; and a plurality of the cell balance devices, in which the plurality of the cell balance devices each include a plurality of electric accumulator connection terminals connected to one of a node and two terminals of the plurality of electric accumulators connected in series, and a voltage hold device connection terminal connected to one of a node and two terminals of the plurality of voltage hold devices connected in series. 
         [0016]    According to the present invention, when an overcurrent flows through the switch circuit, the overcurrent can be detected and the switch circuit can be turned OFF, to thereby prevent the switch circuit from being broken down. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    In the accompanying drawings: 
           [0018]      FIG. 1  is a circuit diagram of a battery system including cell balance devices according to an embodiment of the present invention; 
           [0019]      FIG. 2  is a circuit diagram of the cell balance devices according to the embodiment of the present invention; 
           [0020]      FIG. 3  is a timing chart of signals in the cell balance devices according to the embodiment of the present invention; 
           [0021]      FIG. 4  is a circuit diagram of an overcurrent detecting circuit of the cell balance device according to the embodiment of the present invention; and 
           [0022]      FIG. 5  is a circuit diagram of a cell balance device including a conventional cell balance adjusting circuit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]      FIG. 1  is a circuit diagram of a battery system including cell balance devices according to an embodiment of the present invention.  FIG. 2  is a circuit diagram of the cell balance devices according to this embodiment.  FIG. 4  is a circuit diagram of an overcurrent detecting circuit of the cell balance device according to this embodiment. 
         [0024]    A battery system  10  of this embodiment includes a clock generation circuit  102 , n+1 secondary batteries A 1  to An+1 connected in series, n cell balance devices B 1  to Bn, n−1 voltage hold devices (capacitors) C 1  to Cn−1, and external terminals to which a charger  101  or a load is to be connected (n is an integer of 2 or more). 
         [0025]    The first cell balance device B 1  includes switch circuits S 11 , S 21 , and S 31 , a control circuit  201 , overcurrent detecting circuits  211 ,  221 , and  231 , and terminals T 11 , T 21 , T 31 , T 41 , T 51 , and T 61 . The other cell balance devices B 2  to Bn have the same configuration. The overcurrent detection circuit  231  includes a comparator  503 , a constant current circuit  502 , and a switch circuit  501 . The other overcurrent detection circuits have the same configuration. 
         [0026]    In the cell balance device B 1 , the terminal T 11  is connected to a negative terminal of the secondary battery A 1 , the terminal T 21  is connected to a positive terminal of the secondary battery A 1  and a terminal T 12  of the cell balance device B 2 , the terminal T 31  is connected to a positive terminal of the secondary battery A 2  and a terminal T 22  of the cell balance device B 2 , the terminal T 41  is connected to any one terminal of the voltage hold device C 1 , the terminal T 51  is connected to an output of the clock generation circuit  102 , and the terminal T 61  is connected to a terminal T 52  of the cell balance device B 2 . In the cell balance device B 2 , the terminal T 22  is connected to a terminal T 13  of the cell balance device B 3 , a terminal T 32  is connected to a positive terminal of the secondary battery A 3  and a terminal T 23  of the cell balance device B 3 , a terminal T 42  is connected to any one terminal of the voltage hold device C 2  and the other terminal of the voltage hold device C 1 , and a terminal T 62  is connected to a terminal T 53  of the cell balance device B 3 . The same connection as in the cell balance device B 2  is made up to the (n−1)th cell balance device Bn−1. In the cell balance device Bn, a terminal T 1   n  is connected to a negative terminal of the secondary battery An, a terminal T 2   n  is connected to a positive terminal of the secondary battery An and a terminal T 3   n −1 of the cell balance device Bn−1, a terminal T 3   n  is connected to a positive terminal of the secondary battery An+1, and a terminal T 4   n  is connected to the voltage hold device Cn−1. 
         [0027]    In the cell balance device B 1 , the switch circuit S 11  is connected to the terminal T 11  and the terminal T 41 , the switch circuit S 21  is connected to the terminal T 21  and the terminal T 41 , and the switch circuit S 31  is connected to the terminal T 31  and the terminal T 41 . An input of the overcurrent detection circuit  211  is connected to both terminals of the switch circuit S  11 , and an output thereof is connected to the control circuit  201 . An input of the overcurrent detection circuit  221  is connected to both terminals of the switch circuit S 21 , and an output thereof is connected to the control circuit  201 . An input of the overcurrent detection circuit  231  is connected to both terminals of the switch circuit S 31 , and an output thereof is connected to the control circuit  201 . The switch circuits S 11 , S 21 , and S 31  are ON/OFF controlled by signals from the control circuit  201 . The other cell balance devices B 2  to Bn have the same connection. 
         [0028]    In the overcurrent detection circuit  231 , the comparator  503  has a non-inverting input terminal connected to the terminal T 41 , an inverting input terminal connected to any one terminal of the switch circuit  501  and any one terminal of the constant current circuit  502 , and an output terminal connected to the constant circuit  201 . The other terminal of the switch circuit  501  is connected to the terminal T 31 . The other terminal of the constant current circuit  502  is connected to the negative terminal of the secondary battery A 1 . The switch circuits S 31  and  501  are controlled to be turned ON/OFF simultaneously in response to an input signal from the control circuit  201 . The other overcurrent detection circuits have the same connection. 
         [0029]    Next, an operation of the battery system  10  of this embodiment is described.  FIG. 3  is a timing chart of signals in the cell balance devices of this embodiment. 
         [0030]    At a time t 0 , the charger  101  is connected to the external terminals of the battery system  10 , and then the clock generation circuit  102  outputs a clock signal CLK. In the cell balance device B 1 , when the terminal T 51  receives the clock signal CLK, the control circuit  201  generates signals for turning ON the switch circuits S 11  to S 31  in synchronization with the clock signal CLK, and outputs the signals sequentially. The control circuit  201  further outputs the clock signal CLK to the terminal T 61 . In the next cell balance device B 2 , the terminal T 52  receives the clock signal CLK from the cell balance device B 1 . The clock signal CLK is transmitted to the cell balance device Bn in this way, and all the cell balance devices B 1  to Bn can be synchronized with one another. The switch circuits S 11  to S 1   n , the switch circuits S 21  to S 2   n,  and the switch circuits S 31  to S 3   n  are therefore respectively controlled to be turned ON sequentially in synchronization with one another. 
         [0031]    At a time t 1 , the switch circuits S 11  to S 1   n  are all turned ON and the switch circuits S 21  to S 2   n  and the switch circuits S 31  to S 3   n  are all turned OFF, and then the secondary batteries A 1  to A n −1 are connected in parallel to the voltage hold devices C 1  to Cn−1, respectively. Then, the secondary batteries A 1  to An−1 and the voltage hold devices C 1  to Cn−1 perform charging or discharging, respectively. 
         [0032]    At a time t 2 , the switch circuits S 21  to S 2   n  are all turned ON and the switch circuits S 11  to S 1   n  and the switch circuits S 31  to S 3   n  are all turned OFF, and then the secondary batteries A 2  to An are connected in parallel to the voltage hold devices C 1  to Cn−1, respectively. Then, the secondary batteries A 2  to An and the voltage hold devices C 1  to Cn−1 perform charging or discharging, respectively. 
         [0033]    At a time t 3 , the switch circuits S 31  to S 3   n  are all turned ON and the switch circuits S 11  to S 1   n  and the switch circuits S 21  to S 2   n  are all turned OFF, and then the secondary batteries A 3  to An+1are connected in parallel to the voltage hold devices C 1  to Cn−1, respectively. Then, the secondary batteries A 3  to An+1 and the voltage hold devices C 1  to Cn−1 perform charging or discharging, respectively. 
         [0034]    Then, all the cell balance devices B 1  to Bn repeat the same operation, with three clocks as one cycle. 
         [0035]    Then, if the charger  101  is disconnected from the external terminals of the battery system  10 , the clock generation circuit  102  stops outputting the clock signal CLK, thereby finishing the cell balance operation. 
         [0036]    By repeating charging/discharging between the secondary batteries A 1  to An+1 and the voltage hold devices C 1  to Cn−1 in this way, the voltages of the secondary batteries A 1  to An+1 can be averaged to reduce voltage fluctuations. With this configuration including the plurality of voltage hold devices corresponding to the number of secondary batteries to be balanced, the cell balance device can be enhanced in balance performance (can be increased in speed for balance). 
         [0037]    When the terminal T 21  and the terminal T 41  are short-circuited under the state in which all the switch circuits S 31  to S 3   n  are turned ON, a current flows from the secondary battery A 2  via the switch circuit S 31 . At this time, the switch circuit  501  is also turned ON simultaneously, and a current flows from the constant current circuit  502 . Then, a voltage of the inverting input terminal of the comparator  503  is reduced by an ON-state resistance of the switch circuit  501 , and the inverting input terminal maintains a constant voltage. When the current continuously flows through the switch circuit S 31 , and a voltage of the non-inverting input terminal of the comparator  503  falls below the voltage of the inverting input terminal, the comparator  503  outputs a signal of Lo. In response to the signal, the control circuit  201  turns OFF the switch circuit S 31 . In this way, an overcurrent can be prevented from flowing from the secondary battery A 2  via the switch circuit S 31 , to thereby prevent the switch circuit S 31  from being broken down. 
         [0038]    An ON-state resistance RonS 31  of the switch circuit S 31  and an ON-state resistance Ron 501  of the switch circuit  501  are set so as to satisfy RonS 31 /Ron 501 =N (N is a constant). When an overcurrent detection current is represented by Ioc and the current of the constant current circuit  502  is represented by Iref, the ON-state resistance RonS 31  and the ON-state resistance Ron 501  are set so as to satisfy Iref=Ioc×RonS 31 /Ron 501 . The overcurrent detection current Ioc can be set through adjustment of a current value of the constant current Iref and temperature characteristics thereof and the ON-state resistance of the switch circuit  501  and temperature characteristics thereof. For example, when the ON-state resistance Ron 501  is set so that the constant N becomes 0.001, the constant current Iref only needs to be 1/1,000 of the overcurrent detection current Ioc. Thus, in the case where the switch circuit  501  is formed of a MOS transistor, the switch circuit  501  can be smaller than the switch circuit S 31 . 
         [0039]    When the terminal T 11  and the terminal T 41  are short-circuited under the state in which all the switch circuits S 31  to S 3   n  are turned ON, a current flows from the secondary batteries A 1  and A 2  via the switch circuit S 31 . At this time, the switch circuit  501  is also turned ON simultaneously, and a current flows from the constant current circuit  502 . Then, a voltage of the inverting input terminal of the comparator  503  is reduced by an ON-state resistance of the switch circuit  501 , and the inverting input terminal maintains a constant voltage. When the current continuously flows through the switch circuit S 31 , and a voltage of the non-inverting input terminal of the comparator  503  falls below the voltage of the inverting input terminal, the comparator  503  outputs a signal of Lo. In response to the signal, the control circuit  201  turns OFF the switch circuit S 31 . In this way, an overcurrent can be prevented from flowing from the secondary batteries A 1  and A 2  via the switch circuit S 31 , to thereby prevent the switch circuit S 31  from being broken down. Such overcurrent protection can also be provided to the switch circuits S 11  to S 1   n  and S 21  to S 2   n  by the same operation. The methods of setting the ON-state resistance of the switch circuit and the current value of the constant current circuit are the same as described above. 
         [0040]    When the terminal T 21  and the terminal T 41  are short-circuited under the state in which all the switch circuits S 11  to S 1   n  are turned ON, a current flows from the secondary battery A 1  via the switch circuit S 11 . At this time, a voltage is generated across the switch circuit S 11  by its ON-state resistance. The overcurrent detection circuit  211  detects this voltage, and outputs a signal to the control circuit  201  from the output terminal of the overcurrent detection circuit  211 . In response to the signal, the control circuit  201  turns OFF the switch circuit S 11 . In this way, an overcurrent can be prevented from flowing from the secondary battery A 1  via the switch circuit S 11 , to thereby prevent the switch circuit S 11  from being broken down. 
         [0041]    When the terminal T 31  and the terminal T 41  are short-circuited under the state in which all the switch circuits S 11  to S 1   n  are turned ON, a current flows from the secondary batteries A 1  and A 2  via the switch circuit S 11 . At this time, a voltage is generated across the switch circuit S 11  by its ON-state resistance. The overcurrent detection circuit  211  detects this voltage, and outputs a signal to the control circuit  201  from the output terminal of the overcurrent detection circuit  211 . In response to the signal, the control circuit  201  turns OFF the switch circuit S 11 . In this way, an overcurrent can be prevented from flowing from the secondary batteries A 1  and A 2  via the switch circuit S 11 , to thereby prevent the switch circuit S 11  from being broken down. Also in the case where the terminal T 41  is short-circuited with another terminal, a current is similarly detected so that the switch circuit S 11  can be prevented from being broken down. Further, also in the case where the switch circuits S 21  to S 2   n  are turned ON and also in the case of the cell balance devices B 2  to Bn, a current that flows when terminals are short-circuited is detected so that the switch circuit can be prevented from being broken down. 
         [0042]    Note that, the circuit for detecting a current flowing through the switch circuit is not limited to the above-mentioned configuration. 
         [0043]    Further, the cell balance device of this embodiment described above is adapted to achieve a cell balance of the secondary batteries A 1  to An+1 connected in series, but the present invention is not limited to the secondary batteries, and the same effect can be obtained as long as the battery is an electric accumulator having the function of accumulating electricity. 
         [0044]    As described above, according to the battery system including the cell balance devices of this embodiment, an overcurrent flowing through the switch circuit can be detected and the switch circuit can be turned OFF, to thereby prevent the switch circuit from being broken down.