ENERGY ACCUMULATOR FOR VEHICLE

Description

[0001] The present invention relates to a vehicle energy storage device, in particular a vehicle energy storage device for the electrical supply of an electric drive unit of a motor vehicle.

[0002] A number of battery configurations that function as vehicle energy storage devices for motor vehicles are known in the prior art.

[0003] For example, in the prior art, 96 battery cells are connected in series (topology 1). In this configuration, the battery cells are used together to supply the electrical power to an electric drive unit of a motor vehicle.

[0004] The development of electric vehicles, which has been strongly promoted in recent years due to environmental considerations and the increasing scarcity of fossil fuels, requires ever greater power output and higher energy density. To meet these requirements, battery configurations with multiple parallel-connected battery cells are increasingly being used. Two different types of battery configurations are known in this regard.

[0005] First, four battery cells are connected in parallel to form a group. Then, for example, 96 such groups are connected in series (topology 2).

[0006] Alternatively, for example, 96 individual battery cells are connected in series to form a string. Then, four such strings are connected in parallel (topology 3).

[0007] The resulting increase in power and energy density of the battery configurations also leads to increased short-circuit currents, which can potentially occur, for example, in an accident. At typical voltages used in motor vehicles, on the order of 400V, the short-circuit currents for the battery configuration described first (Topology 1) are approximately 4000A. Commercially available contactors and fuses are subjected to considerable stress in order to reliably interrupt these short-circuit currents.

[0008] If additional battery cells are connected in parallel, as in the two other battery configurations described above (topologies 2 and 3), the short-circuit currents increase to up to 30,000 A. At this magnitude of current, contactors and fuses reach their limits. Firstly, contactors cannot trip quickly enough and therefore must have sufficient current-carrying capacity before the fuse blows. Secondly, even fuses struggle to reliably interrupt currents of this magnitude. Furthermore, wiring harnesses and connectors installed in the vehicle must withstand these high short-circuit currents and therefore be dimensioned accordingly. Connectors, in particular, pose a problem in this context.

[0009] Accordingly, other solutions have been developed in the prior art that do not require contactors and fuses and can handle such short-circuit currents. These solutions are based on pyrotechnic switches that, in the event of a short circuit, disconnect the battery terminals. By their very nature, such pyrotechnic switches can only be triggered once and subsequently require replacement.

[0010] In addition to the aforementioned problems, the described battery configurations, particularly topologies 1 and 2, require the threshold current at which the battery disconnection is triggered to be determined by a safety factor. This safety factor is on the order of 10% and is based on the fact that the current flowing through the battery can be distributed asymmetrically across the parallel battery cells, a distribution which is not precisely known. Consequently, the battery capacity cannot be fully utilized in these configurations.

[0011] Further state of the art can be found in the following documents: DE 10 2011 115550 A1, DE 10 2012 213053 A1, EP2 910 405 A1, EP 2 403 105 A2 and DE 20 2011 011 799 A1.

[0012] These documents describe battery packs with overcurrent protection devices.

[0013] Document XP055933758 describes overcurrent detection using operational amplifiers.

[0014] Against this background, the main objective of the present invention is to create a vehicle energy storage device that allows for reliable and non-destructive disconnection at high currents. Furthermore, the secondary objective of the present invention is to enable efficient utilization of the available battery power.

[0015] The main problem is solved with a vehicle energy storage device according to claim 1. Further preferred embodiments are the subject of the dependent claims.

[0016] According to one aspect of the invention, a vehicle energy storage device for the electrical supply of an electric drive unit of a motor vehicle includes: a positive potential connection and a negative potential connection, which are connected to the drive unit during normal operation of the vehicle energy storage system; a first strand connecting the positive potential terminal and the negative potential terminal, in which at least one electrical energy storage cell is arranged; and at least a second strand, which connects the positive potential terminal and the negative potential terminal in parallel to the first strand and in which at least one electrical energy storage cell is also arranged; wherein In the first strand and the second strand, at least one semiconductor switching element is arranged which can be controlled to interrupt a current flowing in the respective strand.

[0017] The vehicle energy storage device according to the invention can preferably have, in addition to the first and second strands, a third and a fourth strand. Both the third and fourth strands connect the positive potential terminal to the negative potential terminal in parallel with the first and second strands. More generally, the vehicle energy storage device according to the invention can include, in addition to the first and second strands, a plurality of further parallel strands in which at least one electrical energy storage cell is arranged.

[0018] The voltage supplied by the vehicle energy storage device according to the invention is preferably 400V.

[0019] The first and second strands can be identical or different, particularly with regard to the number of energy storage cells. The same applies to the third and / or fourth strand, or any further strands.

[0020] An energy storage cell is understood to be a structural unit that has a housing containing, for example, an electrolyte solution (e.g., of a lithium battery) and on which the corresponding electrodes for connecting the energy storage cells are arranged.

[0021] Particularly preferably, between 80 and 110, and most preferably 96, individual energy storage cells are arranged in each strand of the vehicle energy storage system. Each strand then preferably forms an energy storage module, which together constitute the vehicle energy storage system.

[0022] The vehicle energy storage device according to the invention can be structurally designed, for example, as having a carrier housing with individual compartments, each containing one of the energy storage cells. The carrier housing can be composed of individual module housings, each module housing having the compartment(s) for the energy storage cell(s) of one of the energy storage modules.

[0023] According to the invention, at least one semiconductor switching element is arranged in the first strand and the second strand, or more generally in each strand, which can be controlled to interrupt the current flow in the respective strand. The semiconductor switching element can preferably be one or a plurality of field-effect transistors or bipolar transistors. In particular, field-effect transistors, such as MOSFETs, or bipolar transistors, such as IGBTs, are suitable within the scope of the invention.

[0024] Because a semiconductor switching element is arranged in both the first and second strands, very high currents flowing through each strand remain manageable. Fuses, pyrotechnic switches, or contactors can preferably be completely omitted.

[0025] Furthermore, the use of semiconductor switching elements in each of the strands according to the invention allows the strand-by-strand interruption to be carried out so quickly that short-circuit currents no longer reach their maximum values ​​or can be very significantly limited. This means that cable harnesses and connectors can be dimensioned smaller with regard to their current-carrying capacity (they no longer need to withstand the short-circuit currents of 30 kA that occur in the prior art). This leads, among other things, to weight savings and lower costs.

[0026] Furthermore, valuable installation space can be saved because semiconductor switching elements are generally much smaller in size than, for example, a contactor, fuses or relays.

[0027] The semiconductor switching elements are designed in such a way that they can at least interrupt the current flowing in the discharge direction of the vehicle energy storage system.

[0028] The vehicle energy storage device according to the invention further includes a current measuring element arranged in the first string and another current measuring element arranged in the second string.

[0029] The current measuring elements, i.e., the current measuring element arranged in the first strand and the current measuring element arranged in the second strand, are preferably measuring resistors, for example shunt resistors, via which the respective current flowing in the corresponding strand can be measured. Alternatively, the current measuring element can also be a Hall effect sensor that outputs a corresponding Hall voltage depending on the current flowing in the corresponding strand.

[0030] The current measuring device can vary in number and its assignment to the strings. The current measuring device(s), as described below, can be integrated into the carrier housing or module housing together with the semiconductor switching elements, the current measuring elements, and the energy storage cells (distributed short-circuit interruption). This allows for further savings in valuable installation space.

[0031] Alternatively, the current measuring device(s) can be part of a control unit that performs other functions in addition to current measurement.

[0032] The arrangement of the current measuring element in each of the strands according to the invention makes it possible to measure the current flowing through the respective strand. This allows us to determine whether the current load on the first and second strands, and more generally on the multitude of strands, is distributed symmetrically or asymmetrically. In general terms, there are no unknown balancing currents. Therefore, it is no longer necessary to consider the safety factor used in the prior art. Consequently, in the intended operation of the vehicle energy storage system according to the invention, it is possible to operate at the performance limit of the vehicle energy storage system without the risk of unintentionally overloading the first or second strand. Overall, performance increases of the aforementioned 10% are possible.

[0033] The vehicle energy storage device according to the invention further comprises a current measuring device assigned to the first string, which is connected to the current measuring element arranged in the first string for measuring the current flowing in the first string; and a current measuring device assigned to the second string, which is connected to the current measuring element arranged in the second string for measuring the current flowing in the second string.

[0034] The current measuring device assigned to the first strand is configured to measure the current flowing in the first strand and to control the semiconductor switching element arranged in the first strand to interrupt the flowing current when the current flowing in the first strand exceeds a threshold value.

[0035] Similarly, the current measuring device associated with the second strand is configured to measure the current flowing in the second strand and to control the semiconductor switching element arranged in the second strand to interrupt the flowing current when the current flowing in the second strand exceeds a threshold value.

[0036] The semiconductor switching element arranged in the first and second strands is controlled by the corresponding associated current measuring device to interrupt the flowing current when a short circuit occurs between the positive potential terminal and the negative potential terminal and the resulting short-circuit current flowing in the discharge direction exceeds the corresponding threshold value.

[0037] The threshold against which the current flowing in the first string is compared and the threshold against which the current flowing in the second string is compared can be identical or different.

[0038] The same applies to the current measuring device assigned to the first strand and the current measuring device assigned to the second strand. This means the current measuring devices can be identical or different in design.

[0039] In particular, the vehicle energy storage device according to the invention is designed as explained above, wherein the current measuring device assigned to the first strand and the second strand each includes an operational amplifier forming a comparator circuit, which compares the current measured via the respective current measuring element with the threshold value and whose output signal controls the semiconductor switching element to interrupt the flowing current when the flowing current exceeds the threshold value.

[0040] The comparator circuit is the operational amplifier to which, for example at its non-inverting input, the voltage drop across the current sensing element (or the Hall voltage) is applied, and which compares the applied voltage with a reference voltage (threshold value) applied, for example, to its inverting input. The output signal of the operational amplifier controls the corresponding semiconductor switching element. For this purpose, the output of the operational amplifier is connected, for example, to a driver circuit that is at least bistable (for example, the driver circuit contains at least one flip-flop), which in turn is connected to the gate terminal of a transistor forming the semiconductor switching element.

[0041] Furthermore, the vehicle energy storage device according to the invention is preferably designed as explained above, wherein in the first and / or second strand, a plurality of semiconductor switching elements are arranged, and the plurality of semiconductor switching elements includes a group of parallel-connected semiconductor switching elements which are jointly controlled to interrupt the current flowing in the respective strand by the respective current measuring device when the current flowing in the respective strand exceeds the threshold value.

[0042] By providing a large number of semiconductor switching elements, it is preferentially achieved that the current load on the individual semiconductor switching elements is reduced.

[0043] The vehicle energy storage system according to the invention further features: a switching arrangement which is arranged in series with the parallel strands and has at least one further semiconductor switching element, wherein the switching arrangement is configured to control the further semiconductor switching element to interrupt an entire current flowing through the vehicle energy storage device depending on a control signal.

[0044] The additional semiconductor switching element of the switching arrangement is preferably oriented such that it can interrupt, in particular, a current flowing into the vehicle energy storage device according to the invention. In other words, the additional semiconductor switching element can interrupt the charging current. With this configuration of the vehicle energy storage device according to the invention, the group arranged in the first string and the group arranged in the second string, each of which is provided for interrupting the charging current, could be replaced by the additional semiconductor switching element. Preferably, the switching arrangement can also have a plurality of semiconductor switching elements connected in parallel in order to reduce the current load. The control of the additional semiconductor switching element(s) is explained below.

[0045] The embodiments of the vehicle energy storage device according to the invention, which make it possible to interrupt the charging and discharging currents, simultaneously allow a legally required switch, by means of which the vehicle energy storage device can be galvanically isolated from the drive unit, to be dimensioned smaller with regard to current withstand capability, because by using the semiconductor switch elements described, the short-circuit currents can be switched so quickly that the switch no longer has to meet high requirements.

[0046] Finally, the invention relates to a motor vehicle comprising a vehicle energy storage device as described above.

[0047] As can be understood from the preceding description, short-circuit currents in both directions (charging and discharging current) can be controlled by using semiconductor switching elements. In particular, the semiconductor switching elements can interrupt the corresponding currents so quickly that the short-circuit currents no longer reach the aforementioned values ​​of 30 kA. This applies especially if the vehicle energy storage system according to the invention has at least four identically designed strings, each containing a plurality of energy storage cells (for example, 96 energy storage cells). Consequently, the elements subjected to the short-circuit currents can be dimensioned smaller with regard to their current-carrying capacity.

[0048] Manufacturers of vehicle energy storage systems typically set warranty limits stipulating that the current flowing through the energy storage system may only reach a maximum value for a specific period of time. Because the present invention enables the interruption of the current flow in the event of a short circuit to occur so rapidly that the short-circuit current does not reach extreme values, these warranty limits can be reliably met even in such cases. This significantly reduces warranty costs; furthermore, a visit to the repair shop can potentially be avoided (preventing breakdowns).

[0049] Preferred embodiments of the invention are explained below with reference to the accompanying figures.

[0050] Figure 1Ashows a vehicle energy storage system according to an embodiment comprising a vehicle energy storage device, a switching arrangement for galvanic isolation of the vehicle energy storage device from a motor, and a vehicle storage control device;

[0051] Figure 1B shows a more detailed representation of a current measuring device of the in Figure 1A shown vehicle energy storage system;

[0052] Figure 2 Figure 1 shows a vehicle energy storage system according to the invention in the preferred embodiment, which differs from the first embodiment in the design of the switching arrangement.

[0053] Figure 3 shows the signal curves of a simulation which qualitatively demonstrates that the short-circuit currents remain manageable through the use of at least one semiconductor switching element in each strand of the vehicle energy storage system according to the invention.

[0054] First embodiment to understand the invention: Figure 1A shows an embodiment of a vehicle energy storage system 1, comprising a vehicle energy storage device 2 and a vehicle storage control device 3.

[0055] The vehicle energy storage device 2 includes a positive potential connection 21 and a negative potential connection 22, via which the vehicle energy storage device 2 is connected to a consumer. In this preferred embodiment, the consumer is an electric drive unit M of a motor vehicle and is supplied with electrical energy stored in the vehicle energy storage device 2 for the propulsion of the motor vehicle.

[0056] The vehicle energy storage system 2 includes a first string 23, which electrically connects the positive potential terminal 21 to the negative potential terminal 22. A plurality of electrical energy storage cells EZ are arranged in the first string 23, with the individual energy storage cells EZ connected in series.

[0057] In series with the energy storage cells EZ, a semiconductor switching element 27 and a current measuring element 28 are arranged in the first string 23.

[0058] The vehicle energy storage system 2 comprises, in addition to the first strand 23, a second strand 24, a third strand 25, and a fourth strand 26. The second strand 24, the third strand 25, and the fourth strand 26 are each arranged parallel to the first strand 23 and connect the positive potential terminal 21 with the negative potential terminal 22. The second, third, and fourth strands 24-26 are each identical in construction to the first strand 23 and contain the same elements. Therefore, the following statements apply equally to all strands 23-26.

[0059] The EZ energy storage cells are preferably lithium batteries, each comprising a housing containing a suitable electrolyte solution with the other elements, and on which the corresponding cell terminals (anode and cathode) are arranged. The EZ energy storage cells are preferably inserted into compartments of a carrier housing (not shown).

[0060] The semiconductor switching element 27 arranged in the first strand 23 can be controlled such that it interrupts the current flowing in the first strand 23. This interruption preferably occurs when a short circuit occurs in the electric drive unit M, by connecting the positive potential terminal 21 to the negative potential terminal 22, and the resulting short-circuit current in the first strand 23 exceeds a certain threshold value. For this purpose, the first strand 23 includes an associated current measuring device 29, which is connected on one side to the semiconductor switching element 27 and on the other side to the current measuring element 28 arranged in the first strand 23.

[0061] The further strands 24-26 are identically constructed, that is, they also each contain a semiconductor switching element 27, a current measuring element 28, and a current measuring device 29 assigned to the corresponding strand, wherein the respective current measuring devices 29 are configured to measure the current flowing in the corresponding strand and to control the corresponding semiconductor switching element 27 to interrupt the current flowing in the strand.

[0062] In this embodiment, the semiconductor switching element 27 arranged in each of the strands is designed as a field-effect transistor, wherein a gate terminal of the respective field-effect transistor is connected to the current measuring device 29.

[0063] Preferably, however, a plurality of semiconductor switching elements 27, i.e. transistors, can be arranged in each of the strands 23-26, wherein in this case the semiconductor switching elements 27 are arranged in parallel to each other in each of the strands and can be controlled jointly by the respective current measuring device 29.

[0064] Preferably, the vehicle energy storage device 2 also includes a switching arrangement 210, which has a contactor 211 and a fuse 212.

[0065] In addition to the vehicle energy storage device 2, the vehicle energy storage system 1 also includes a vehicle energy storage control unit 3, which is connected to the current measuring devices 29 and to the switching arrangement 210. The vehicle energy storage control unit 3 can be a separate battery management system or a control unit that performs other functions besides battery management.

[0066] The vehicle memory control unit 3 can preferably control the contactor 211 in such a way that it interrupts the connection to the positive potential terminal 21 and the negative potential terminal 22.

[0067] The vehicle energy storage system 1 is designed to interrupt the entire current flow through the vehicle energy storage device 2 in the event of a short circuit. Such a short circuit can occur, firstly, during the discharge of the vehicle energy storage device 2, i.e., during the intended operation of the drive unit M, and secondly, during the charging of the vehicle energy storage device 2, i.e., when an external power supply is connected to the positive potential terminal 21 and the negative potential terminal 22. (Short circuit during discharge of the vehicle energy storage 2)

[0068] In the intended operation of the vehicle energy storage system 1, the vehicle storage control unit 3 closes the contactor 211, thereby supplying the drive unit M with the energy stored in the vehicle energy storage unit 2 for the propulsion of the motor vehicle.

[0069] If, for example, a short circuit occurs in the drive unit M in this state, a short-circuit current arises, which flows through the entire vehicle energy storage system 2 and must be interrupted. This is done by interrupting the corresponding current flow in each of the strings 23-26 via the semiconductor switching element 27 when the current flowing in the respective string exceeds a certain threshold. This is done with reference to Fig. 1B will be explained.

[0070] As from Figure 1BAs can be seen, the current measuring device 29 of each string includes an operational amplifier 291, which performs the function of a comparator. One of the terminals for the operating voltage of the operational amplifier 291 is at a positive potential (for example, 10V) and the other terminal is at a ground potential, so that the output of the operational amplifier 291 can switch between the positive potential and the ground potential.

[0071] The output of operational amplifier 291 is connected to a driver 292, which can assume at least two stable states. For this purpose, driver 292 includes, for example, a flip-flop. Additionally, driver 292 can contain elements to adjust the gate-source voltage of the corresponding transistor. These elements can include optocouplers.

[0072] The current measuring device 29 is electrically connected to the current measuring element 28 for measuring the respective current flowing in the corresponding strand. The current measuring element 28 is preferably a measuring resistor (for example, a shunt) or a Hall effect sensor, which outputs a specific Hall voltage depending on the magnitude of the current flowing in the strand.

[0073] More precisely, the non-inverting input of the operational amplifier 291 is connected to the measuring resistor or the Hall effect sensor in such a way that the voltage drop across the measuring resistor or the Hall voltage serves as the input signal of the current measuring device 29.

[0074] A reference voltage Uref is applied to the inverting input of the operational amplifier 291, with which the voltage drop across the measuring resistor or the Hall voltage (generally the input signal) is compared. In this respect, the reference voltage Uref forms the threshold for the comparison.

[0075] If the vehicle energy storage device 2 is operating normally, with the intended currents flowing in the respective circuits, then the voltage drop across the measuring resistor or the Hall voltage is below the reference voltage Uref. This causes the operational amplifier 291 to output a positive potential, and the driver 292 to be in a state in which the semiconductor switching element 27, or the transistor, is in its conducting state. In this conducting state, the transistor can ideally be considered a closed switch.

[0076] If a short circuit occurs in the drive unit M, the corresponding current flow in each of the windings immediately increases. Consequently, the voltage of the current measuring element 28 also rises, exceeding the reference voltage Uref or the threshold value once a certain value of the current flowing through the respective winding is reached.

[0077] This causes the output of operational amplifier 291 to switch to ground potential, thereby controlling driver 292, which in turn switches to a state in which the semiconductor switching element 27, or the transistor, interrupts the current flowing in the corresponding string. In other words, the transistor is switched to its non-conducting state. The interruption described above occurs individually in each of the strings 23–26, so that the strings are interrupted in a corresponding sequence depending on the current flowing.

[0078] The semiconductor switching element 27 is controlled by the current measuring device 29 so quickly that the current flowing through the corresponding strand in the event of a short circuit remains well below its maximum value, which is, for example, approximately 30 kA. This allows cable strands and connectors to be dimensioned smaller with regard to current withstand capability.

[0079] As from Fig. 1BAs can be seen, the vehicle memory control unit 3 is connected to each of the current measuring devices 29 at the output of the corresponding operational amplifier 291 and detects the switching of the operational amplifiers 291. Furthermore, the vehicle memory control unit 3 is also connected to the corresponding driver 292 of the current measuring device 29. If the vehicle memory control unit 3 is designed to detect the switching of the operational amplifier 291 sufficiently quickly, the control of the driver 291 could alternatively also be carried out by the vehicle memory control unit 3.

[0080] The control of the semiconductor switch element 27 also causes the vehicle energy storage control unit 3 to galvanically isolate the vehicle energy storage unit from the drive unit by controlling the contactor 211 accordingly.

[0081] Once the cause of the short circuit has been rectified and the vehicle memory control unit 3 receives this information, it controls the drivers 292 accordingly, thereby resetting them to the state in which they put the semiconductor switch element 27 into its conducting state. Furthermore, the vehicle memory control unit 3 closes the contactor 211 again. (Short circuit during charging of the vehicle energy storage system 2)

[0082] If the vehicle energy storage unit 2 needs to be charged after the operation of the drive unit M, an external power supply is connected to the positive potential connection 21 and to the negative potential connection 22.

[0083] If a short circuit occurs in this state, for example, if the energy storage cells of one of the strings numbered 23-26 burn out, the corresponding short-circuit current will occur at least in the string causing the short circuit. This short-circuit current has the opposite sign compared to the case where the short circuit occurs during the discharge process described above; that is, the short-circuit current flows in the opposite direction.

[0084] The current measuring device 29 assigned to the respective string can indeed detect the short-circuit current occurring during charging of the vehicle energy storage device 2; however, the switching of the semiconductor switching element 27 or the transistor does not interrupt the current flow. This is because field-effect transistors possess an intrinsic diode that makes interrupting the current flow in the necessary direction impossible. In order to nevertheless detect the short circuit occurring during charging and interrupt the entire current flow through the vehicle energy storage device 2, the vehicle energy storage control unit 3 is connected to the current measuring devices 29 and thereby detects the switching of the affected operational amplifiers 291.

[0085] When the vehicle energy storage control unit detects a short circuit via the current measuring devices 29, it activates the contactor 211 accordingly to galvanically isolate the vehicle energy storage unit 2 from the drive unit M. If the contactor 211 cannot be opened, the switching arrangement 210 also has a fuse 212 for this purpose.

[0086] First embodiment Figure 2 shows a vehicle energy storage system 1' according to the embodiment of the invention.

[0087] The vehicle energy storage system 1' shown differs from that of the first preferred embodiment in the design of the switching arrangement 210 and the current measuring devices 29'. The remaining elements are identical to those of the first preferred embodiment and therefore bear the same reference numerals. In this respect, reference is made to the description of the first preferred embodiment.

[0088] The switching arrangement 210 of the embodiment of the vehicle energy storage system 1' according to the invention has no contactor and no fuse, but includes a semiconductor controller 213, which is connected to each of the current measuring devices 29' and the vehicle energy storage control unit 3, a further semiconductor switching element 214 which can be controlled by the semiconductor controller 213, and an ordinary mechanical switch 215 for galvanic isolation of the electric drive unit M from the vehicle energy storage device 2. The ordinary mechanical switch is unnecessary and can be omitted, so that the vehicle energy storage device 2 according to the invention no longer has any mechanical switches.

[0089] The vehicle energy storage device 2 of the second preferred embodiment of the invention is identical to that of the first embodiment, i.e. it includes the plurality of strands 23 to 26 in each of which at least one semiconductor switching element 27 is arranged to interrupt the corresponding current flow.

[0090] The operating principle of the vehicle energy storage device 2 in the event of a short circuit during normal discharge is described in the operating principle of the vehicle energy storage device 2. Figure 1A identical, therefore reference is made to the explanations given there.

[0091] However, the operation of the vehicle energy storage system 1' differs in the event of a short circuit / overcurrent during the intended charging of the vehicle energy storage system 2. (Short circuit / overcurrent during charging of the vehicle energy storage system 2)

[0092] During a charging process of the vehicle energy storage unit 2, an external power supply is connected to the positive potential terminal 21 and the negative potential terminal 22. Switch 215 is closed.

[0093] If a short circuit or overcurrent occurs in this state, for example if the energy storage cells EZ of one of the strings 23 - 26 burn out or the external power supply introduces too high a current, the current flowing in the corresponding string (short-circuit current or overcurrent) increases immediately.

[0094] As in the first embodiment, the field-effect transistors 27 are unable to interrupt the short-circuit current / overcurrent, even though the current measuring device 29 connected to the corresponding field-effect transistor detects the short-circuit current via the current measuring element 28 and controls the corresponding field-effect transistor. This is again due to the intrinsic diode of the field-effect transistors.

[0095] To nevertheless control the short circuit that occurs when charging the vehicle energy storage device 2, each of the current measuring devices 29' includes, compared to the configuration of the first preferred embodiment, an additional operational amplifier whose inputs are connected such that its corresponding output switches when the short-circuit current / overcurrent occurs. The outputs of the additional operational amplifiers are connected to the semiconductor controller 213, which—like the current measuring devices 29 of the first preferred embodiment—includes a driver that, when one of the outputs of the additional operational amplifiers switches, is set to a state such that the additional semiconductor switching element 214 is switched to its non-conducting state.Alternatively, the driver of the switching arrangement could also be controlled by the vehicle memory control unit 3, if it can detect the switching of the outputs of the other operational amplifiers quickly enough.

[0096] Similar to the semiconductor switch elements 27, a large number of further semiconductor switch elements 214 connected in parallel can also be provided in the switching arrangement 210.

[0097] The activation of the additional semiconductor switch element 214 can be carried out so quickly that the short-circuit current remains far below its maximum value or the overcurrent remains below a maximum permissible value. The activation speed is of the same order of magnitude as the activation speed of the semiconductor switch elements 27.

[0098] In this embodiment, it is possible to interrupt the entire current flowing through the vehicle energy storage device 2 by means of semiconductor switching elements 27 or 214 if either a short circuit occurs during the intended discharge or a short circuit / overcurrent occurs during the intended charging; generally speaking, both cases are covered by controlling semiconductor switching elements.

[0099] This embodiment therefore makes it possible to dimension the switch 215 installed in the switching arrangement 210 with a smaller current rating. As already mentioned, this switch 215 can also be omitted entirely.

[0100] Modified examples to help understand the invention. Generally speaking, the explanations and descriptions given in the general part before the description of the figures also apply to the embodiment described and to the examples.

[0101] There, the current flowing through the vehicle energy storage device 2 is interrupted by the switching arrangement 210 if the short circuit occurs during a normal charging process.

[0102] Alternatively, another semiconductor switching element, i.e., another field-effect transistor, can be arranged in each of the strands 23-26, but this is arranged such that the intrinsic diode is polarized in the opposite direction to the one shown, and the corresponding field-effect transistor can interrupt the short-circuit current / overcurrent during a normal charging process. As with the ones in Figures 1A and 2In addition to the semiconductor switching elements 27 shown, a large number of further semiconductor switching elements connected in parallel can also be used. The semiconductor switching element(s) are then also connected via their gate terminal to the respective current measuring device 29, which, in the event of a short circuit / overcurrent, activates all semiconductor switching elements, i.e., field-effect transistors, together.

[0103] The transistors in the preferred embodiments are not limited to field-effect transistors. Other types of transistors, such as IGBTs, or entirely different semiconductor switching elements, such as thyristors, can also be used.

[0104] In preferred embodiments, enhancement-type (n-channel) field-effect transistors are shown. The invention is not limited to these. For example, p-channel transistors can also be used. Furthermore, depletion-type transistors can also be employed.

[0105] The threshold values ​​or reference voltages Uref used in the individual strings can be set individually, for example depending on how many individual energy storage cells EZ are arranged in the corresponding string.

[0106] In the embodiment and examples, each strand is assigned its own current measuring device 29. Alternatively, it is conceivable to use only a single current measuring device 29, which is connected to each of the current measuring elements 28. In this case, if the current flow in one of the strands 23-26 exceeds the threshold value set in the current measuring device 29, the current measuring device as a whole controls all semiconductor switching elements 27 simultaneously. Simulation results

[0107] The Figure 3 shows the signal curves of a simulation carried out by the inventor.

[0108] The simulation was performed using a vehicle energy storage system with a single string, specifically for the scenario where the energy storage system is in its intended discharge process and a short circuit occurs with the corresponding current direction. This single string comprised fourteen individual energy storage cells connected in series.

[0109] This resulted in a total voltage of 60V and a nominal current of 200A.

[0110] The string contained six field-effect transistors connected in parallel, which were controlled by a corresponding current measuring device that, as in the embodiments, measured the current flowing in the single string via a measuring resistor.

[0111] The dashed line K1 shows the voltage UDS that drops across the drain-source channels of the field-effect transistors. At the time corresponding to the ON point, the field-effect transistors are switched to their conducting state by switching a gate drive signal (line K2) accordingly.

[0112] Immediately after the field-effect transistors are switched on, the aforementioned short circuit occurs, with the corresponding short-circuit current rising rapidly (dashed line K3), which is practically only limited by the line inductances and resistances. In the simulation, these values ​​were approximately 5 µH and 14 Ω. The individual current flow through each of the field-effect transistors increases accordingly (line K4).

[0113] The threshold value or reference voltage Uref for triggering the interruption of the current flow was set at 480A.

[0114] The drive time of the field-effect transistors by the current measuring device was approximately 70 µs in the worst case; in Figure 3 It is evident that the gate control signal is switched after this time period (see falling edge of line K2).

[0115] In this case, the maximum short-circuit current was approximately 540 A, meaning about 90 A per field-effect transistor, with the voltage UDS, which drops across the drain-source channels of the field-effect transistors, rising to approximately 110 V. After the short-circuit current (line K3) drops, the field-effect transistors remain in their off state, in which the voltage UDS has the same value as before the ON point.

[0116] This maximum short-circuit current, assuming an ambient temperature of 50 °C, led to a heating of the field-effect transistors (MOSFETs) to approximately 150 °C (line K5 in Figure 3), whereby the field-effect transistors used can easily withstand 175 °C.

[0117] This simulation can qualitatively demonstrate that by using semiconductor switching elements, short-circuit currents can be interrupted so quickly that the maximum currents that occur are greatly reduced and remain manageable.

[0118] The one in Figure 3 The trends shown relate to the following measured variables K1: Voltage UDS across the drain-source channels of the field-effect transistors; K2: Gate drive signal; Voltage UGS between the gate-source terminals of the field-effect transistors; K3: Short-circuit current; K4: Individual short-circuit current per transistor; K5: Temperature of the transistors

Claims

1. Vehicle energy storage device (2) for electrical supply of an electric drive unit (M) of a motor vehicle, which comprises: a positive potential connection (21) and a negative potential connection (22), which are connected to the drive unit (M) during intended operation of the vehicle energy storage device; a first string (23), which connects the positive potential connection (21) and the negative potential connection (22) to one another and in which at least one electrical energy storage cell (EZ) is arranged; and a second string (24 - 26), which connects the positive potential connection (21) and the negative potential connection (22) to one another in parallel to the first string (23) and in which at least one electrical energy storage cell (EZ) is likewise arranged; wherein in the first string (23) and the second string (24 - 26) at least one semiconductor switching element (27) is respectively arranged, which is controllable to interrupt a current flowing in the respective string; and the vehicle energy storage device (2) further comprises: a current measuring element (28), which is arranged in the first string (23); a current measuring element (28), which is arranged in the second string (24 - 26); a current measuring device (29) associated with the first string (23), which is connected to the current measuring element (28) arranged in the first string (23) for measuring the current flowing in the first string (23); and a current measuring device (29) associated with the second string (24 - 26), which is connected to the current measuring element (28) arranged in the second string (24 - 26) for measuring the current flowing in the second string (24 - 26); wherein the current measuring device (29) associated with the first string (24 - 26) is configured to measure the current flowing in the first string (23) and to control the semiconductor switching element (27) arranged in the first string (23) to interrupt the flowing current when the current flowing in the first string (23) exceeds a threshold value, the current measuring device (29) associated with the second string (24 - 26) is configured to measure the current flowing in the second string (24 - 26) and to control the semiconductor switching element (27) arranged in the second string (24 - 26) to interrupt the flowing current when the current flowing in the second string (24 - 26) exceeds a threshold value, characterized in that the current measuring device (29) associated with the first string (23) and the current measuring device (29) associated with the second string (24 - 26) each include an operational amplifier forming a comparator circuit, which compares the current measured via the respective current measuring element (28) with the threshold value and whose output signal controls the semiconductor switching element (27) to interrupt the flowing current when the flowing current exceeds the threshold value; and wherein the vehicle energy storage device further comprises: a switching arrangement (210), which is arranged in series with the strings arranged parallel to one another and has a semiconductor controller (213) including a driver as well as at least one further semiconductor switching element (214), wherein the semiconductor controller (213) is configured to control the further semiconductor switching element (214) in dependence on a control signal to interrupt a total current flowing through the vehicle energy storage device (2), wherein each of the current measuring devices includes a further operational amplifier, which is connected at its inputs such that its corresponding output outputting the control signal switches upon occurrence of a short-circuit current / overcurrent and thereby the driver of the semiconductor controller (213) controls the further semiconductor switching element (214) to interrupt the total current.

2. Vehicle energy storage device (2) according to claim 1, wherein in the first and / or second string a plurality of semiconductor switching elements (27) is respectively arranged, and the plurality of semiconductor switching elements (27) includes a group of semiconductor switching elements (27) connected in parallel, which are jointly controlled by the respective current measuring device (29) to interrupt the current flowing in the respective string when the current flowing in the respective string exceeds the threshold value.

3. Motor vehicle comprising a vehicle energy storage device (2) according to one of claims 1 to 2.