Abstract:
The invention relates to an electrochemical composite storage system and to an electrical circuit comprising an electrochemical composite storage system of this type. The circuit and system comprise branches (ST 1 , ST 2 , ST 3 , ST 4 , ST 5 , ST 6 ), which are connected in parallel, of electrochemical storage modules ( 10 ), said storage modules ( 10 ) having first connection terminals and each module having an electrical circuit. The composite storage system is designed to operate the branches (ST 1 , ST 2 , ST 3 , ST 4 , ST 5 , ST 6 ) inside the composite storage system optionally as a current source or a voltage source, by means of the electrical circuits.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to an electrochemical composite storage system comprising a plurality of electrochemical storage modules. The present invention particularly relates to an electrochemical composite storage system which is designed to operate a plurality of strings of storage modules, which strings are connected in parallel, without unequal states of charge or undesired compensation currents occurring. 
         [0002]    Electrochemical storage modules with a simple half- or full-bridge as the coupling unit are known from the prior art. Modules of this kind can be used to set the terminal voltage of a respective module in certain limits. However, current regulation is not possible with units of this kind. A storage module which is called a UniBB (Universal Buck-Boost) module is also known from the prior art, said module comprising one or more rechargeable battery cells together with a coupling unit, wherein the coupling unit also contains an inductance. This module can be used both as a voltage source and as a current source. Since a module of this kind is designed for voltages of below 60 V, it is necessary, in particular for applications which have extremely large power requirements (for example vehicles in the automobile industry), for a plurality of modules to be connected in series in order to reach the available power at a controllable current. In addition, it may be necessary to connect these serial strings in parallel with one another in order to further increase the available current. However, in the normal case according to the prior art, connecting strings in parallel leads to undesired compensation currents between the strings on account of generally unequal states of charge. A possible design of a UniBB module is discussed in greater detail further below in conjunction with  FIG. 4 . 
         [0003]    One object of the present invention is to provide an electrochemical energy store which is of modular construction and remedies the disadvantages of the prior art. 
       SUMMARY OF THE INVENTION 
       [0004]    According to the invention, the abovementioned object is achieved by an electrochemical composite storage system comprising strings of electrochemical storage modules, which strings are connected in parallel. In this case, the electrochemical storage modules can comprise an electrochemical storage cell or a plurality of electrochemical storage cells and a processing unit. The storage module is designed to provide electrical energy which is stored in the electrochemical cell or the electrochemical cells and has the characteristics of a voltage source and/or a current source at output-end terminals of the storage module by means of the processing unit. To this end, the storage module has first connection terminals and in each case one electrical circuit, wherein the electrochemical composite storage system is designed to operate the strings within the electrochemical composite storage system selectively as a current source or as a voltage source (inter alia by means of the electrical circuit). To this end, the electrochemical composite storage system can further have a processing unit (which is superordinate to the storage modules) by means of which control commands can be sent to the individual storage modules and the energy output characteristics of said control commands can therefore be individually set. Selective driving as a current source or as a voltage source can ensure no undesired compensation currents flow between the strings which are connected in parallel. In addition, charge compensation of unequal states of charge between the strings can be controlled in a targeted manner. 
         [0005]    The electrochemical composite storage system is preferably designed to operate a first string of storage modules which are connected in series as a voltage source and a second string of electrochemical storage modules as a current source. Since the second string is operated as a current source, a current flow which is independent of the set current is not possible through the second string. Therefore, undesired compensation currents are avoided. 
         [0006]    As an alternative or in addition, the electrochemical composite storage system can be designed to operate all of the strings of the storage module, with the exception of the first string, as a current source or in a blocking mode. In other words, the first string is further connected as a voltage source, while all of the other strings either have the characteristics of a current source or are blocked (that is to say interrupted). In this way, no undesired compensation currents can flow in the entire electrochemical composite storage system. Moreover, unequal states of charge can be avoided or compensated in a targeted manner. 
         [0007]    The electrochemical composite storage system is further preferably designed to operate a first storage module of a string under consideration as a current source, and to operate a further storage module of the same string as a voltage source or in a bypass mode. In this way, compensation currents between the strings can be prevented since accurate voltage control can be performed. In particular, the storage modules which function as a voltage source can operate as unregulated voltage sources. The number of storage modules which function as a voltage source depends on the level of the required total voltage which is to be supplied by the string or the electrochemical composite storage system. In this case, control is performed in a manner which stabilizes the same voltage level for each possible state of charge of the strings. In this way, all of the storage modules of the same string in any desired combination are operated as a voltage source or in a bypass mode. To this end, both the buck and also the boost mode can be selected for the storage module which is operating in the current source mode. This depends on the states of charge of the cells in the strings. This ensures that no compensation currents flow between the strings which are connected in parallel. Depending on the driving of the modules, operation as a direct or alternating current source of the strings which are connected in parallel is possible, wherein said strings are controlled in a synchronized manner in order to exhibit identical voltages, so that the currents can be added up. 
         [0008]    Each of the strings of the composite storage system preferably has a contactor by means of which the respective string is designed to be incorporated into the composite storage system or electrically disconnected from the composite storage system. The contactors can be driven by the storage modules of the string itself if one of the storage modules identifies a defect and signals switching off of the contactor in the string. As an alternative or in addition, a respective contactor can also be driven by a processing unit which is superordinate to the strings. This allows flexible adaptation to currents which are to be supplied by the electrochemical composite storage system and disconnection of defective strings. 
         [0009]    The storage modules are preferably designed as UniBB modules. UniBB modules allow a large number of different characteristics of the electrical terminal power when using one and the same electrochemical energy store within the UniBB module. The electrical design of said UniBB module is cost-effective, driving is simple and the long service life of said UniBB module leads to a high-quality electrochemical composite storage system. In addition, it is possible to extend the electrochemical composite storage system in a modular manner particularly when all of the storage modules are designed as UniBB modules. 
         [0010]    An electrical circuit comprising an electrical load and a first composite storage system and also a second composite storage system is proposed according to a second aspect of the present invention. The two composite storage systems can be designed as electrochemical composite storage systems, as have been described in detail above. According to the invention, the load is arranged electrically between the first composite storage system and the second composite storage system. In other words, a first connection of the load is connected to a first output of the first composite storage system, and a second connection of the load is connected to a first connection of the second composite storage system. The respective second connections of the first and the second composite storage system can be connected, for example, to electrical ground. In addition, the load can be bridged by a switch. In addition, a second switch and a third switch can be provided between the load and the first connections of the electrochemical composite storage systems in order to disconnect the load from the electrochemical composite storage systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Exemplary embodiments of the invention will be described in detail below with reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  is a schematic illustration of an electrical circuit comprising a single string of storage modules which are connected in series; 
           [0013]      FIG. 2  shows an electrical circuit according to one exemplary embodiment of the present invention; 
           [0014]      FIG. 3  shows an electrical circuit according to a second exemplary embodiment of the present invention; and 
           [0015]      FIG. 4  shows a schematic design of an exemplary embodiment of a storage module in the form of a UniBB module. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  shows a circuit diagram of a schematic design of a series circuit comprising UniBB modules  10  as storage modules. The storage modules are designated M 1 , M 2  and Mn. It goes without saying that more storage modules could be added in order to increase the string voltage. A branch, comprising a charger L and a first switch SL, and a further branch, comprising a load Z and a second contactor S 1 , are provided in parallel with the string ST of UniBB modules  10 . The UniBB modules  10  are oriented electrically in the same direction. In this case, the respective negative pole of a UniBB module  10  is oriented in the direction of the electrical ground of the string ST, while the positive pole points in the direction of the two other strings. A processing unit (not illustrated) is designed to switch the modules M 1 , M 2 , Mn to a bypass, charging or blocking mode selectively as a voltage source in the buck or boost mode or a current source in the buck or boost mode. In this case, the processing unit can be arranged within the illustrated composite storage system or outside said composite storage system. 
         [0017]      FIG. 2  shows a schematic circuit diagram of an electrical circuit according to an exemplary embodiment of the present invention which has three strings ST 1 , ST 2 , ST 3 , which are connected in parallel, of in each case three UniBB modules  10  (identified by M 1 - 1  to M 3 - n ) which are illustrated by way of example. An arrow P 1  indicates that the illustrated strings ST 1 , ST 2 , ST 3  could be extended by the further parallel connection of additional strings and therefore the rated current of the illustrated electrical circuit could be correspondingly increased. The strings ST 1 , ST 2 , ST 3  have respective contactors S 1 , S 2  and S 3  by means of which they are connected to a busbar between a charger L and an electrical load Z. A first contactor SL is arranged between the charger L and the busbar, while a second contactor Sv is arranged between the busbar and the electrical load Z. If all of the contactors S 1 , S 2 , S 3  are closed, the currents of the three strings can be added up given a suitable control method for the modules. The contactors S 1 , S 2 , S 3  are intended to be understood only functionally and can also be realized by a blocking mode within one storage module  10  of the strings ST 1 , ST 2 , ST 3 . In the blocking mode, all of the switches (also called “semiconductor valves”) within the storage module  10  in question are switched off. Therefore, in principle, it is necessary for one string to function as a voltage source and all of the other strings to function as a current source in order to allow parallel connection. If the load is a voltage source or, for example, a capacitive load, all of the strings can also be operated as current sources. In the case of the capacitive load, the currents are then regulated such that the desired voltage is established across the capacitor. All of the strings can be charged in parallel by means of the charger L. To this end, the contactors S 1 , S 2 , S 3 , SL are closed or only the contactors of the strings which are to be charged are closed. The charging method differs on a case-to-case basis. If only one string is charged, the charging method can be dispensed with as would be the case if only one string of UniBB modules  10  which are connected in series were contained in the electrical circuit. If all of the strings are intended to be charged in parallel, the charger L has to function as a voltage source and current control takes place within the strings ST 1 , ST 2 , ST 3 . This takes place under the assumption that no compensation currents are intended to flow between the strings. For the sake of completeness, it should be mentioned that the illustrated arrangement could also be used for parallel connection of strings of a different kind (for example with a capacitor or modules with reversed polarities, as are known in the prior art) and the corresponding operating method could be carried out in a similar way. It is characteristic of the operating method that in each case one module per string is operated as a current source, while the rest of the modules operate in the voltage source mode or—depending on the instantaneous voltage requirement—remain in the bypass mode. 
         [0018]      FIG. 3  shows a further embodiment of an electrical circuit according to the present invention. In said figure, strings ST 1 , ST 2 , ST 3  and, respectively, ST 4 , ST 5 , ST 6  which are connected in parallel are illustrated on each side of an electrical load Z, it being possible to extend said strings with additional strings in any desired manner in accordance with the arrows P 1 , P 2 . The UniBB modules  10  of the strings ST 1 , ST 2 , ST 3  and, respectively, ST 4 , ST 5 , ST 6  are consecutively numbered M 1 - 1  to M 6 - n . The negative poles of said UniBB modules are oriented in the direction of a respective string ground, while the positive poles of said UniBB modules are oriented in the direction of a respective common busbar to which they are connected by means of a respective string contactor S 1 , S 2 , S 3  or S 4 , S 5 , S 6 . A load contactor Sv 1  is connected between the first three strings S 1 , S 2 , S 3  and the electrical load Z. A second load contactor Sv 2  is connected between the electrical load Z and the strings S 4 , S 5 , S 6 . The busbars on either side of the load Z are electrically connected to one another by means of a further contactor SL 2 . A charger L is connected to the busbar in parallel with the first string ST 1  by means of a charger contactor SL 1 . The control method for the illustrated electrical circuit in a discharge mode provides that either the strings ST 1 , ST 2 , ST 3  or the strings ST 4 , ST 5 , ST 6  are in the bypass mode. Therefore, both positive and also negative voltages and currents can be provided for the electrical load Z. Here, it is also characteristic of the operating method for in each case one module per string to operate in the current source mode, while the rest of the modules of the same string operate in the voltage source mode or—depending on the instantaneous voltage requirement—are in the bypass mode. In accordance with the arrangement illustrated in  FIG. 2 , all strings of one side (that is to say the strings ST 1 , ST 2 , ST 3  and, respectively, the strings ST 4 , ST 5 , ST 6 ) can be charged in parallel by the contactors SL 1 , S 1 , S 2 , S 3  and, respectively, S 4 , S 5 , S 6  in conjunction with SL 2  being closed. It goes without saying that the strings ST 1 , ST 2 , ST 3 , ST 4 , ST 5 , ST 6  can also be charged individually by the respective string contactor S 1 , S 2 , S 3 , S 4 , S 5 , S 6  in conjunction with the charging contactor SL 1  or the additional contactor SL 2  being closed. If all of the strings are intended to be charged in parallel, the charger L has to function as a voltage source. In this case, the current control also takes place in the strings ST 1 , ST 2 , ST 3  and, respectively, ST 4 , ST 5 , ST 6 . This also takes place under the assumption that no compensation currents are intended to flow between the strings ST 1 , ST 2 , ST 3  and, respectively, ST 4 , ST 5 , ST 6 . 
         [0019]      FIG. 4  shows the circuit diagram of an exemplary embodiment of a UniBB module  10 . By means of a first connection  11  and a second connection  12 , the UniBB module  10  is designed to be connected up with further UniBB modules  10  to form a string. Four semiconductor switches T 1 , T 2 , T 3 , T 4 , which are preferably designed as MOSFETs or IGBTs, together with associated freewheeling diodes D 1 , D 2 , D 3 , D 4 , are arranged between the first connection  11  and the second connection  12 . The semiconductor switches T 1  to T 4  can be combined with the respective freewheeling diodes D 1  to D 4  as electrical two-pole networks ZP 1  to ZP 4 . In this case, a first connection of the first two-pole network ZP 1  is connected to a positive connection of the energy store  7 . A second connection of the first two-pole network ZP 1  is connected firstly to a first connection of the fourth two-pole network ZP 4  and secondly, via a coil L, to a first connection of the second two-pole network ZP 2  and also to a second connection of the third two-pole network ZP 3 . A first connection of the third two-pole network ZP 3  is connected to the first connection  11  of the UniBB module  10 . A first connection of a capacitor C, of which the second connection is connected to the second connection of the second two-pole network ZP 2  or to the second connection of the fourth two-pole network ZP 4 , is also connected to the first connection  11 . The second connections of the second two-pole network ZP 2  or of the fourth two-pole network ZP 4  are connected firstly to the second connection  12  of the UniBB module  10  and secondly to a second connection of the electrical energy store  7 . The energy store  7  provides a module voltage U M . The illustrated UniBB module  10  has a positive pole at the first connection  11  and a negative pole at the second connection  12 . Control lines for driving the semiconductor switches T 1  to T 4  are not illustrated for reasons of clarity. The same applies for current sensors. The electrical energy store  7  can comprise one or more electrochemical cells or other electrical energy stores which, in this case, jointly provide the module voltage U M . The UniBB module  10  can assume a plurality of different operating states, depending on how the semiconductor switches T 1  to T 4  are operated. In particular, a bypass, a voltage source in the buck or boost mode, a current source in the buck or boost mode, a charging circuit and blocking can be realized. 
         [0020]    Even though the aspects according to the invention and advantageous embodiments have been described in detail with reference to the exemplary embodiments explained in conjunction with the attached figures of the drawing, modifications and combinations of features of the illustrated exemplary embodiments are possible for a person skilled in the art without departing from the scope of the present invention for which the scope of protection is defined by the attached claims.