Patent Publication Number: US-9885759-B2

Title: Test arrangement of an energy storage device

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a test arrangement for an energy storage device having at least one energy storage module with a plurality of energy storage units, having an AC/DC converter which is connected on the input side to a power supply, and the use of such a test arrangement in a test and forming system. 
     The Prior Art 
     Current cell testers mainly work with inefficient linear charging regulators and convert all the charging energy into heat. This results in high costs for powerful cooling systems and high energy costs in the production and testing of batteries, e.g. for forming, quality checking, endurance tests, emulation, etc. 
     Occasionally, switching converters which are capable of feeding back energy are also used for cell testers; these are complex, expensive and have a poor efficiency as they have to provide a very high voltage ratio, e.g. step up from 3V to 400V. A switching converter for testing batteries is shown, for example, in WO 97/07385 A2, in which a number of bidirectional DC/DC converters are connected to an AC/DC converter. 
     It is an object of the present invention to specify an efficient, cost-effective and at the same time flexibly usable or configurable test arrangement. 
     SUMMARY OF THE INVENTION 
     According to the invention, this object is achieved in that the AC/DC converter is connected on the output side to at least one bidirectional isolated module DC/DC converter, wherein the output of the bidirectional isolated module DC/DC converter is connected to a plurality of parallel-connected cell DC/DC converters and the outputs of the cell DC/DC converters are brought out as outputs of the test arrangement. This hierarchical structure of the test arrangement by means of isolated DC/DC converters enables the test arrangement to be configured extremely flexibly; in particular, widely differing expansion stages are possible therewith. Equipment ranging from individual energy storage units to individual energy storage modules and complete energy storage devices can be tested and formed therewith without having to change the internal structure of the test arrangement. In doing so, the configuration can be changed very easily by means of controllable switches. 
     Basically, as is known, the efficiency of a converter improves with higher power level and with higher voltage level. In the present hierarchical structure of the test arrangement, the AC/DC converter has an efficiency of ˜92%, the module DC/DC converters an efficiency of ˜85%, and the cell DC/DC converters an efficiency of ˜75%. Whenever possible, an attempt is therefore made to provide the energy for testing and emulation by the highest converter stage (AC/DC converter), which is possible thanks to the present structure. For many test cases, in particular when used as a test and emulation system for batteries, all energy storage units (e.g. the battery cells) are tested with the same setpoint over a long time. For example, in a charging cycle, all energy storage units can be supplied by the highest converter stage (AC/DC converter) for almost the whole CC (constant current) phase. The module or cell DC/DC converters only have to come into play when transferring to the CV (constant voltage) phase. This results in an efficiency advantage of ˜92−75%=17% for usually more than 50% of the test period. The test arrangement according to the invention therefore also allows work to be carried out with the best possible efficiency. 
     For testing or forming, an energy storage unit of the energy storage module is simply connected to an output of a cell DC/DC converter. This enables the energy storage unit to be subjected to a specifiable charging current at the level of the cell DC/DC converter. 
     When the outputs of a module DC/DC converter are connected to the series-connected outputs of the associated cell DC/DC converters which are connected in series, discharging can take place even when using unidirectional cell DC/DC converters. With this, all energy storage units can be discharged by deactivating all cell DC/DC converters. However, individual energy storage units can also be subjected to any load current by superimposing a current of the cell DC/DC converter on the current of the associated module DC/DC converter. 
     Larger energy storage devices can be tested and formed when a plurality of module DC/DC converters are connected in parallel to the output of the AC/DC converter and each module DC/DC converter is connected to a plurality of parallel-connected cell DC/DC converters. This enables any expansion stages and configurations of an energy storage device to be tested and formed, which increases the flexibility of the test arrangement. 
     If the outputs of the module DC/DC converters can be connected in series by means of switches, energy storage devices which consist of a plurality of interconnected energy storage modules can also be tested or formed as a whole with high efficiency. 
     By bringing out the outputs of the module DC/DC converters via a switch, the test arrangement can also be connected at module level, e.g. as an input for a battery management system or for testing or forming individual energy storage modules as a whole. 
     If the output of the AC/DC converter is brought out via a switch as output of the test arrangement, the test arrangement can also be connected at energy storage device level, e.g. as an input for a battery management system or for testing or forming individual energy storage devices as a whole. 
     The flexibility of the test arrangement can be further increased if the outputs of a plurality of cell DC/DC converters can be connected in series by means of switches and/or the outputs of the series-connected cell DC/DC converters are brought out via a switch as outputs of the test arrangement. 
    
    
     
       The present invention is explained in more detail below with reference to the attached drawings, which show advantageous embodiments of the invention in an exemplary, schematic and non-restricting form. In the drawings: 
         FIG. 1  shows a test arrangement according to an embodiment of the invention, and 
         FIGS. 2 and 3  show the use of the test arrangement for testing or forming battery cells. 
     
    
    
     DETAILED DESCRIPTION 
     The test arrangement  1  according to the invention for electrical energy storage devices consists of a bidirectional AC/DC converter  2  on the input side which can be connected by means of an input connector  4  to a power supply  3 , e.g. a 400 VAC voltage source. A number of (at least one) module DC/DC converters  5   1  . . .  5   n  are connected in parallel to the DC output of the AC/DC converter  2 , e.g. a 400 VDC output. The module DC/DC converters  5   1  . . .  5   n  are designed as commercially available bidirectional isolated DC/DC converters. The module DC/DC converters  5   1  . . .  5   n  convert the high-voltage DC output of the AC/DC converter  2  to a DC voltage which corresponds to the voltage range of an energy storage module, such as a battery module or a fuel cell module for example, consisting of a plurality of energy storage units, such as battery cells or fuel cells for example, e.g. 12V or 48V DC. The outputs of the module DC/DC converters  5   1  . . .  5   n  can also be connected in series by means of switches SM, which is possible as the module DC/DC converters  5   1  . . .  5   n  are designed as isolated DC/DC converters. 
     A number of (at least one) cell DC/DC converters  6   11  . . .  6   nm  are connected in parallel to the output of a module DC/DC converter  5   1  . . .  5   n . The cell DC/DC converters  6   11  . . .  6   nm  are designed as commercially available isolated DC/DC converters. At the same time however, the cell DC/DC converters  6   11  . . .  6   nm  can also be designed as bidirectional DC/DC converters. The cell DC/DC converters  6   11  . . .  6   nm  convert the DC output of the associated module DC/DC converter  5   1  . . .  5   n  to a DC voltage which corresponds to the voltage range of the energy storage unit of an energy storage module, e.g. 0.5V to 5.5V DC for battery cells of a battery module. The outputs of the cell DC/DC converters  6   11  . . .  6   nm  can also be connected in series by means of switches SZ, which is possible as the cell DC/DC converters  6   11  . . .  6   nm  are designed as isolated DC/DC converters. 
     At energy storage device level, the outputs A E+ , A E−  of the AC/DC converter  2 , and, at energy storage module level, the outputs A M1+ , A M1−  . . . A Mn+ , A Mn−  of the module DC/DC converters  5   1  . . .  5   n  and the outputs A 1+ , A 1−  . . . A x+ , A x−  of the cell DC/DC converters  6   11  . . .  6   nm  can be brought out as outputs of the test arrangement  1  and can be connected electrically. Likewise, preferably each of the first and last output A Z1+ , A Z1−  . . . A Zx+ , A Zx−  of the series-connectable cell DC/DC converters  6   11  . . .  6   nm  are brought out as shown in  FIG. 1 . 
     The outputs A E+ , A E−  of the AC/DC converter  2  can be activated by means of switch S 1 . The outputs A M1+ , A M1−  . . . A Mn+ , A Mn−  of the module DC/DC converters  5   1  . . .  5   n  can be activated by means of switch S 2 . The outputs A Z1+ , A Z1−  . . . A Zx+ , A Zx−  of the series-connectable cell DC/DC converters  6   1m  . . .  6   nm , that is to say in essence the first and last output of the series-connected cell DC/DC converters  6   11  . . .  6   nm , can be activated by means of switch S 3 . 
     In the maximum configuration, a test arrangement  1  according to the invention has, for example, an AC/DC converter  2  to which eight module DC/DC converters  5   1  . . .  5   8  are connected, to each of which 12 cell DC/DC converters  6   11  . . .  6   812  are connected. As a result, consequently, up to 96 energy storage units or 8 energy storage modules each comprising 12 energy storage units can be tested or formed. Other expansion stages are of course conceivable. 
     In this case, the AC/DC converter  2 , the module DC/DC converters  5   1  . . .  5   n  and the cell DC/DC converters  6   11  . . .  6   nm  are controlled according to requirements by a control unit  10 , which can also be integrated into the test arrangement  1 . Likewise, the control unit  10  can control the opening/closing of the switches S 1 , S 2 , S 3 , SM, SZ. The control cables  20  from the control unit  10  to the individual components of the test arrangement  1  are not shown or are only indicated in  FIG. 1  for reasons of clarity. 
     The function of the test arrangement  1  according to the invention is described in more detail below based on a specific exemplary embodiment in the form of a test and forming system for an electrical energy storage device. 
     In the example according to  FIG. 2 , the test arrangement  1  according to the invention is connected to a battery pack  7  consisting of n battery modules  8   1  . . .  8   n  each comprising m battery cells  9   11  . . .  9   nm  in order to test or form the battery pack  7 . Each battery cell  9   11  . . .  9   nm  is connected to the output A 1+ , A 1−  . . . A x+ , A x−  of a cell DC/DC converter  6   11  . . .  6   nm  of the test arrangement  1 . Here, the battery modules  8   1  . . .  8   n  are not connected in series but each module DC/DC converter  5   1  . . .  5   n  is in each case connected to a battery module  8   1  . . .  8   n . For this purpose, the switches S 2  are closed and the connection between the module DC/DC converters  5   1  . . .  5   n  is opened by the switch SM. By this means, each battery cell  9   11  . . .  9   nm  can be provided with any (within the voltage and current capacity of the cell DC/DC converters  6   11  . . .  6   nm ) load current (charge/discharge current) and individual battery cells  9   11  . . .  9   nm  can be differently charged or discharged. This enables a battery pack  7 , individual battery modules  8  or even individual battery cells  9  to be tested. Other energy storage modules or energy storage cells can also be tested instead of a battery pack or battery modules. Each battery cell  9  or each battery module  8  can also be connected to a battery management system  11  (BMS) which is sufficiently well known. The battery management system  11  can also be connected to the control unit  10  to enable actual values of the cells or modules to be measured and processed. 
     When using unidirectional cell DC/DC converters  6   11  . . .  6   nm , discharging can only take place at energy storage module level, as is described with reference to the module DC/DC converter  5   n  in  FIG. 2 . In order to discharge the battery cells  9   n1  . . .  9   nm  which are connected to the cell DC/DC converters  6   n1  . . .  6   nm  of the module DC/DC converter  5   n , the switches SZ and the switches S 2 , S 3  are closed, whereby the outputs of the cell DC/DC converters  6   n1  . . .  6   nm  are connected in series and are connected via the outputs A Zx+ , A Zx−  to the outputs A Mn+ , A Mn−  of the module DC/DC converter  5   n . The module DC/DC converter  5   n  now applies a discharge current to the battery cells  9   n1  . . .  9   nm , and the cell DC/DC converters  6   n1  . . .  6   nm  are deactivated. By this means, the battery cells  9   n1  . . .  9   nm  are all discharged with the same discharge current. If an individual battery cell  9   n1  . . .  9   nm  (or a plurality thereof) is not to be discharged, the discharge current of the module DC/DC converter  5   n  can be compensated for by the associated cell DC/DC converter  6   n1  . . .  6   nm  in that the latter generates an equal and opposite charging current which acts on the battery cells  9   n1  . . .  9   nm . 
     As a result of the interaction of cell DC/DC converters  6   11  . . .  6   nm  and the associated module DC/DC converter  5   n , each individual battery cell  9   n1  . . .  9   nm  can be tested or formed with any load current in the manner described above. In particular, the current of a module DC/DC converter  5   1  . . .  5   n  can be overlaid by any current of a cell DC/DC converter  6   11  . . .  6   nm , whereby the current of the module DC/DC converter  5   1  . . .  5   n  at energy storage unit level can also be strengthened. 
     When switches S 1 , S 2 , S 3 , SZ and SM are open, only voltages which lie below the safety extra-low voltage level are present at the outputs A 1+ , A 1−  . . . A x+ , A x−  and A Z1+ , A Z1−  . . . A Zx+ , A Zx−  of the cell DC/DC converters  6   11  . . .  6   nm  and at the outputs A M1+ , A M1−  . . . A Mn+ , A Mn−  of the module DC/DC converters  5   1  . . .  5   n , as a result of which protection against contact can be entirely dispensed with. This is particularly interesting for forming and energy storage. 
     At the same time, the battery cells  9   11  . . .  9   nm  can also be connected or disconnected individually by means of switches SB 11  . . . SB nm  between the series-connected battery cells  9   11  . . .  9   nm . In doing so, the switches SB 11  . . . SB nm  can also be controlled by the control unit  10 . 
     When a cell DC/DC converter is designed as a bidirectional DC/DC converter  6   11  . . .  6   nm , this also enables discharging to be carried out at energy storage unit level (battery cell). 
       FIG. 3  shows the use of the test arrangement  1  in a test system with a battery pack  7  (energy storage device) consisting of four battery modules  8   1  . . .  8   4  (energy storage modules) each comprising four battery cells  9   11  . . .  9   44  (energy storage units) which are in each case connected in series by means of the switches SB 11  . . . SB 44 . The individual battery modules  8   1  . . .  8   4  are connected in series by means of switches SM. For this purpose, the switches S 1  at energy storage device level are closed and the switches S 2  at energy storage module level are open. Here, the AC/DC converter  2  is designed in two stages having an AC/DC converter  21  on the input side and a DC/DC converter  22  connected thereto.