Abstract:
An energy storage subsystem includes a metal casing and an electrical storage system mechanically fastened within the metal casing and including at least one super-capacitor module having a plurality of super-capacitors linked together in series. The subsystem includes at least one electrical protection device configured to open an electrical circuit to link electrical ground to either the metal casing or the super-capacitor module.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is claiming priority based on French Patent Application No. 1251443 filed Feb. 16, 2012, the contents of all of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an energy storage subsystem for vehicles, comprising:
         a metal casing,   an electrical storage system mechanically fastened in the metal casing, and comprising at least one supercapacitor module, the or each module comprising a metal enclosure and a plurality of supercapacitors linked together in series and arranged in the metal enclosure.       

     Such an energy storage subsystem is notably designed to recover and store the braking energy of vehicles, in particular of rail vehicles travelling on a network. It can be installed permanently at a fixed point of the network or onboard one of the rail vehicles, the energy being in both cases stored in supercapacitors of the or each module of the subsystem. 
     It is commonplace for such a storage subsystem to comprise a network of supercapacitor modules connected in series, in order to obtain a significant energy reserve for the rail vehicle. When the storage subsystem is onboard a vehicle, the lowest potential of the network of modules is linked to the mechanical ground of the vehicle. Because of this, there is a significant voltage between the electrical ground of the vehicle and the internal elements of the modules furthest away from the mechanical ground, which exhibit a high electrical potential, for example roughly equal to 400 V. In practice, when the enclosure of the modules is metal, each of the modules being mechanically fixed to the mechanical ground, the voltage between this metal enclosure, exhibiting an electrical potential to the ground, and the internal cells of the module, is high. This high voltage does not however result in any flow of high currents in the modules, likely to damage the latter, because an insulating blanket is arranged between the enclosure of each module and the elements internal to the module. 
     However, in the case of failure of the internal insulation of a supercapacitor module, a short circuit to ground occurs with a very high current which is likely to result in the complete destruction of the module and a release of gas which is hazardous, even toxic, in the environment close to the module. This release of gas is due to the presence of electrolyte inside the supercapacitors, the electrolyte being volatilized when a current passes through the enclosure of the module, in the event of piercing for example. 
     BRIEF SUMMARY OF THE INVENTION 
     One of the aims of the invention is to propose an energy storage subsystem for vehicles that makes it possible, in case of the appearance of an internal insulation defect in one of the supercapacitor modules of the subsystem, to limit the short circuit current and the consequent temperature rise of the subsystem, and thus avoid any release of dangerous gases in the vicinity. 
     To this end, the subject of the invention is an energy storage subsystem for vehicles of the abovementioned type, characterized in that it also comprises at least one electrical protection device. 
     According to other embodiments, the energy storage subsystem for vehicles comprises one or more of the following features, taken in isolation or in all technically possible combinations:
         the electrical storage system comprises at least two supercapacitor modules connected in series;   the or each electrical protection device links a supercapacitor module to an electrical ground;   the or each electrical protection device links the metal casing to an electrical ground;   the or each electrical protection device comprises a fuse;   the energy storage subsystem also comprises at least one electrical circuit opening detection member;   the or each electrical circuit opening detection member comprises a threshold voltage detector, electrically connected in parallel with a fuse;   the or each threshold voltage detector comprises a galvanic isolation switching member;   the or each fuse is a striker fuse and the or each electrical circuit opening detection member comprises a switch, said switch being mechanically linked to a striker fuse.       

     Another subject of the invention is an energy storage system for vehicles comprising a high voltage main isolating member, characterized in that it also comprises an energy storage subsystem as described previously, linked to the high voltage main isolating member. 
     Another subject of the invention is a rail vehicle, characterized in that it comprises an energy storage system as described previously. 
     The invention will be better understood on reading the following description, given solely as an example and with reference to the appended drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an energy storage system according to a first embodiment of the invention, comprising three supercapacitor modules; 
         FIG. 2  is an electrical diagram of one of the supercapacitor modules of the energy storage system of  FIG. 1 ; 
         FIG. 3  is a schematic view of an energy storage system according to a second embodiment of the invention; 
         FIG. 4  is a schematic view of an energy storage system according to a third embodiment of the invention; and 
         FIG. 5  is a schematic view of an energy storage system according to a fourth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1 , an energy storage system  10 , installed onboard a rail vehicle, is linked to a power converter  12 . The power converter  12  is, for example, a voltage chopper installed onboard the rail vehicle and designed to be linked to an overhead line. The voltage chopper is notably designed to lower the voltage of the current circulating in the overhead line to deliver a continuous nominal serviceable voltage Uin, applicable as input for the energy storage system  10 . The voltage Uin has a value which is, for example, roughly equal to 400 V. 
     The energy storage system  10  comprises an energy storage subsystem  14  according to the invention and an electrical connector  15  linking the voltage chopper  12  to the subsystem  14 . It also comprises a high voltage main isolating member  16 , for example a circuit breaker, connected to the chopper  12  and linked to the subsystem  14  via the electrical connector  15 . 
     The energy storage subsystem  14  comprises an input terminal  20  designed to receive the input voltage Uin, an output terminal  22  linked to an electrical ground, a metal casing  24  and an electrical storage system  26  mechanically fastened in the metal casing  24 . A subsystem  14  also comprises three electrical protection devices  28 , and three electrical circuit opening detection members  30 , each linked on the one hand to a device  28  and on the other hand to the circuit breaker  16 . In the exemplary embodiment, each electrical protection device  28  is a fuse and each electrical circuit opening detection member  30  is a threshold voltage detector. 
     The electrical storage system  26  is linked on the one hand to the input terminal  20  and on the other hand to the output terminal  22 . It comprises a first supercapacitor module  32 A, a second supercapacitor module  32 B and a third supercapacitor module  32 C. The three supercapacitor modules  32 A,  32 B,  32 C are linked in series in that order. 
     Each supercapacitor module  32 A,  32 B, respectively  32 C, comprises an input terminal  33 A,  33 B, respectively  33 C, and an output terminal  34 A,  34 B, respectively  34 C. Each supercapacitor module  32 A,  32 B, respectively  32 C, also comprises a metal enclosure  36  and an insulating blanket  38  arranged in the metal enclosure  36 . 
     As illustrated in  FIG. 2 , the first supercapacitor module  32 A also comprises twenty supercapacitors  40  arranged in the metal enclosure  36  and linked together in series between the input terminal  33 A and the output terminal  34 A. 
     The second  32 B and third  34 C supercapacitor modules have a structure that is identical to that of the first module  32 A; the latter is therefore not described in more detail hereinbelow. 
     As a variant, each supercapacitor module  32 A,  32 B,  32 C comprises a number N 1  of supercapacitors  40  linked together in series, N 1  being an integer greater than or equal to two. 
     The input terminal  33 A of the first module  32 A is connected to the input terminal  20 . The output terminal  34 A of the first module  32 A is connected to the input terminal  33 B of the second module  32 B. The output terminal  34 B of the second module  32 B is connected to the input terminal  33 C of the third module  32 C. The output terminal  34 C of the third module  32 C is connected to the output terminal  22 . 
     The metal enclosure  36  of each module  32 A,  32 B,  32 C defines a box inside which the supercapacitors  40  are arranged. The metal enclosure  36  of each module  32 A,  32 B,  32 C is also electrically insulated from the input terminal and from the output terminal of said module, as well as from the metal enclosure  36  of the adjacent modules. For example, a layer of an electrically insulating material is arranged between two adjacent metal enclosures  36 . The metal enclosure  36  of each module  32 A,  32 B,  32 C is thus electrically insulated from the metal casing  24 . 
     The insulating blanket  38  covers the entire internal surface of the metal enclosure  36 . The insulating blanket  38  is designed to electrically insulate the supercapacitors  40  from the metal enclosure  36 , as is known per se. 
     Each supercapacitor  40  is characterized by an electrical capacitance with a value of between 1,000 F and 10,000 F, for example equal to 3,000 F, and by a serviceable voltage with a value for example equal to 2.7 V. 
     Each fuse  28  is connected between, on the one hand, the metal enclosure  36  of a supercapacitor module  32 A,  32 B,  32 C, and, on the other hand, an electrical ground. 
     Each fuse  28  is characterized by a rated value corresponding to a maximum admissible current intensity value. 
     Each threshold voltage detector  30  is connected in parallel with a fuse  28  and takes the form of an electronic circuit board, powered by an external power supply which is not represented. Each threshold voltage detector  30  comprises a member  42  for detecting a voltage at the terminals of the fuse  28 . It also comprises a galvanic isolation switching member  44 , electrically connected to the member  42 . 
     The detection member  42  is designed to measure the voltage at the terminals of the corresponding fuse  28  and generate an electrical signal, for example a constant current, when the voltage that it measures exhibits a non-zero value. 
     The galvanic isolation switching member  44  comprises a switch  45  and an actuator  46 , mechanically linked to the switch  45 . In the exemplary embodiment, the galvanic isolation switching member  44  is an electromechanical relay and the actuator  46  is an electromagnet. 
     The galvanic isolation switching member  44  is designed to electrically isolate the electronics implemented in the measurement member  42  from the control electronics implemented to control the circuit breaker  16 . 
     The switch  45  can move between an open position and a closed position. The switch  45  is designed to switch from its closed position to its open position, and vice versa, under the mechanical control of the electromagnet  46 . 
     The electromagnet  46  is designed to control the opening or the closure of the switch  45 . When a current flows within the electromagnet  46 , a magnetic field is created, thus triggering the displacement of a soft iron core inside the electromagnet  46 , and mechanically opening the switch  45 . Conversely, when no current is flowing within the electromagnet  46 , the soft iron core is displaced to another position, and mechanically closes the switch  45 . 
     As a variant, the galvanic isolation switching member  44  is a solid-state relay. The actuator  46  is then an optocoupler, linked by optical pathway to the switch  45 . The switch  45  is, according to this variant, a semiconductor component whose electrical state is designed to switch from a block state to a passing state, and vice versa. 
     Each supercapacitor module  32 A,  32 B,  32 C is associated with a switch  45 , the three switches  45  being connected together in series between a constant voltage source  48  and the circuit breaker  16 . 
     The constant voltage source  48  has a constant electrical potential V −  with a value for example substantially equal to 0 V. 
     Each threshold voltage detector  30  is advantageously designed to be linked to a restoration interface installed permanently onboard the rail vehicle. Once generated by a member  42 , the electrical signal corresponding to the detection of a voltage is then sent to said interface by the corresponding detector  30 . The interface is then able to visually restore to a user information indicating which supercapacitor module is exhibiting an electrical insulation fault. 
     The circuit breaker  16  is designed to automatically cut the current flowing in the electrical connector  15 , for example in case of short circuit between the input and output terminals of each supercapacitor module  32 A,  32 B,  32 C, as is known per se. 
     The circuit breaker  16  comprises a switch  50  and an actuator  52  mechanically linked to the switch  50  for its actuation, as is known per se. 
     The switch  50  can move between an open position and a closed position of the electrical connector  15 . The switch  50  is designed to switch from its closed position to its open position, and vice versa, under the mechanical control of the actuator  52 . 
     The actuator  52  is electrically connected between the switch  45  corresponding to the first supercapacitor module  32 A and a constant voltage source  54 . 
     The constant voltage source  54  exhibits a constant electrical potential V +  with a value for example substantially equal to 24 V. The electrical potentials V − , respectively V + , presented by the voltage sources  48 , respectively  54 , are different, thus allowing for the flow of a current within the actuator  52  and the switches  45 . 
     The actuator  52  is designed to control the opening or the closure of the switch  50 , according to a principle similar to that explained previously for the electromagnet  46  and the switch  45 . When a current flows within the actuator  52 , the switch  50  is closed. When no current flows within the actuator  52 , the switch  50  opens. 
     As a variant, the electrical storage system  26  comprises a number N 2  of supercapacitor modules linked together in series and/or in parallel, N 2  being an integer greater than or equal to two. 
     The operation of the energy storage system  10  will now be explained. 
     It is assumed for the description that the system  10  is initially in service, in other words that it is powered by the voltage chopper  12 , and that the switch  50  is closed. No current is flowing in the fuses  28 , and the voltages at the terminals of said fuses  28  each exhibit a zero value. The switches  45  are therefore closed and a constant voltage Uc is applied to the actuator  52  of the circuit breaker  16 , thus keeping the switch  50  closed. 
     The voltage Uc is given by the formula: Uc=V + −V − . 
     In case of failure of the internal insulation of a supercapacitor module  32 A,  32 B,  32 C, possibly, for example, caused by a wear defect on an insulating blanket  38 , a short circuit appears between the metal enclosure  36  and the electrical ground. Because of the appearance of this short circuit to the ground, a short circuit current flows within the fuse  28  corresponding to the defective module. This short circuit current increases, until its intensity reaches the rating value of the fuse  28 . As soon as this value is exceeded, the fuse  28  opens, resulting in the cancellation of the intensity of the short circuit current. The voltage at the terminals of the fuse  28 , measured by the corresponding member  42 , then exhibits a non-zero value. The member  42  generates a current flowing within the electromagnet  46  and the corresponding switch  45  opens. The constant voltage signal Uc is then no longer applied to the actuator  52 , which results in the opening of the switch  50 . The system  10  is no longer powered by the voltage step-down chopper  12 , thus allowing for a maintenance intervention on the part of an operator. 
     In the particular exemplary embodiment according to which each threshold voltage detector  30  is linked to a restoration interface installed permanently onboard the rail vehicle, the operator responsible for intervening also knows the identity of the defective supercapacitor module. 
     It will be understood that such an energy storage subsystem  14  makes it possible, in case of the appearance of an internal insulation defect in one of the supercapacitors modules of the subsystem  14 , to limit the short circuit current and therefore the temperature rise of the subsystem. Such an energy storage subsystem  14  thus makes it possible to avoid release of dangerous gas into the immediate environment of the passengers of the rail vehicle. 
     Moreover, the energy storage subsystem  14  according to this first embodiment is easier to construct mechanically, compared to the second embodiment described hereinbelow using  FIG. 3 . 
     A second energy storage subsystem  55  according to the invention is represented in  FIG. 3 . In this figure, the elements that are similar to the first embodiment described previously are identified by identical references. 
     According to this second embodiment, the energy storage subsystem  55  comprises a fuse  28  and a threshold voltage detector  30 , connected in parallel with the fuse  28  and linked to the circuit breaker  16 . 
     Moreover, the fuse  28  is connected between, on the one hand, the metal casing  24 , and, on the other hand, an electrical ground. The metal enclosure  36  of each module  32 A,  32 B,  32 C is also electrically linked to the metal casing  24 . 
     The energy storage subsystem  55  according to this second embodiment corresponds to the association of all the modules  32 A,  32 B,  32 C with one fuse  28  and with one threshold voltage detector  30 . 
     As a variant, the person skilled in the art will understand that it is possible to construct N 3  subgroups of modules in the same way, each subgroup being associated with a fuse  28  and with a threshold voltage detector  30 , N 3  being an integer greater than or equal to two and less than the total number of modules. 
     The advantageous connection of the threshold voltage detector  30  to a restoration interface installed permanently onboard the rail vehicle is not envisaged according to this embodiment, the advantages linked to this connection here being nonexistent. 
     The operation of the energy storage subsystem  55  will now be described. 
     In case of failure of the internal insulation of a supercapacitor module  32 A,  32 B,  32 C, a short circuit appears between the metal enclosure  36  and the metal casing  24 . Because of the appearance of this short circuit, a short circuit current flows within the fuse  28 . The rest of the operation of the energy storage subsystem  55  is identical to that of the energy storage subsystem  14 , and is therefore not described in more detail. 
     By comparison with the energy storage subsystem  14  according to the first embodiment, the energy storage subsystem according to this embodiment occupies a more restricted space within the energy storage system  10 , which makes it possible to substantially reduce the manufacturing costs. 
     The other advantages of this second embodiment, concerning the energy storage subsystem, are identical to those of the first embodiment, and are therefore not described again. 
     A third energy storage subsystem  56  according to the invention is represented in  FIG. 4 . In this figure, the elements similar to the first embodiment described previously are identified by identical references. 
     According to this third embodiment, each fuse  28  is a striker fuse. 
     Furthermore, each threshold voltage detector  30  is replaced by a switch  58 , mechanically linked to a striker fuse  28 . 
     Each supercapacitor module  32 A,  32 B,  32 C is associated with a switch  58 , the three switches  58  being connected together in series between the constant voltage source  48  and the actuator  52 . 
     The actuator  52  is electrically connected between the switch  58  corresponding to the first supercapacitor module  32 A and the constant voltage source  54 . 
     Each striker fuse  28  is designed, when the current passing through it reaches the rating value of the fuse, to open and mechanically strike, during this opening, the switch  58  to which it is linked. 
     Each switch  58  can move between a closed position and an open position and is designed, under the effect of a mechanical strike, to switch from its closed position to its open position. 
     The operation of the energy storage subsystem  56  will now be explained. 
     Initially, the system  10  is in service, the switch  50  and the switches  58  are closed. 
     When a short circuit to ground appears within one of the supercapacitor modules  32 A,  32 B,  32 C, a short circuit current flows within the striker fuse  28  corresponding to the defective module. This short circuit current increases, until its intensity reaches the rating value of the striker fuse  28 . As soon as this value is exceeded, the striker fuse  28  opens, resulting in the cancellation of the intensity of the short circuit current. The striker fuse  28  mechanically strikes the switch  58  to which it is linked, resulting in the opening of said switch. The constant voltage signal Uc is then no longer applied to the actuator  52 , which results in the opening of the switch  50 . 
     Since the detection of an internal insulation defect within one of the supercapacitor modules is performed by entirely mechanical means in this third embodiment of the invention, the latter offers the advantage of enhancing the reliability of the detection, compared to the first embodiment described previously, in which the detection is performed by a combination of electronic and mechanical means. 
     A fourth energy storage subsystem  60  according to the invention is represented in  FIG. 5 . In this figure, the elements similar to the third embodiment described previously are identified by identical references. 
     According to this fourth embodiment, the energy storage subsystem  60  comprises a striker fuse  28  and a switch  58 , mechanically linked to the striker fuse  28 , and electrically connected between the constant voltage source  48  and the actuator  52 . 
     Moreover, the striker fuse  28  is connected between, on the one hand, the metal casing  24 , and, on the other hand, an electrical ground. The metal enclosure  36  of each module  32 A,  32 B,  32 C is also electrically linked to the metal casing  24 . 
     The operation of the energy storage subsystem  60  will now be described. 
     In case of failure of the internal insulation of a supercapacitor module  32 A,  32 B,  32 C, a short circuit appears between the metal enclosure  36  and the metal casing  24 . Because of the appearance of this short circuit, a short circuit current flows within the striker fuse  28 . The rest of the operation of the energy storage subsystem  60  is identical to that of the energy storage subsystem  56 , and is therefore not described in more detail. 
     The advantages of this fourth embodiment, concerning the energy storage subsystem, are identical to those of the second embodiment and of the third embodiment, and are therefore not described again. 
     It will thus be understood that the energy storage subsystem according to the invention makes it possible, in case of appearance of an internal insulation defect in one of the supercapacitor modules of the subsystem, to limit the short circuit current and the consequent temperature rise of the subsystem.