Device for stabilizing supply of a consumer

Abstract

Device (30) for the stabilizing supply of a consumer (20) supplied from an energy store (10) during normal operation from a buffer store (40), wherein the device (30) comprises a DC-DC converter (35), a plurality of controllable switching elements (S1, .., S5) and a control unit (34) for controlling the switching state (1; 0) of the plurality of controllable switching elements (S1, .., S5) as a function of an input voltage (U1) of the device (30), wherein the device (30) is designed to a) to supply the consumer (20) directly from the energy store (10) during normal operation, bypassing components with power losses, if the input voltage (U1) is greater than a predetermined first limit voltage (Ugs1), wherein the first limit voltage (Ugs1) is a minimum voltage of the consumer for its supply; b) to supply the load (20) via the DC-DC converter (35) fed from the energy storage device (10) when the input voltage (U1) falls below the first predetermined limit voltage (Ugs1), wherein the DC-DC converter (35) converts the input voltage to an operating voltage of the load; and c) to feed the DC-DC converter (35) from the buffer storage (40) when the input voltage drops below a second predetermined limit voltage (Ugs2) until a voltage (U3) of the buffer storage (40) reaches the second predetermined limit voltage (Ugs2), wherein the second predetermined limit voltage (Ugs2) is a minimum voltage of the DC-DC converter (35) for its operation, wherein the device comprises a controllable first switching element (S1) which is connected between an input (36) of the DC-DC converter (35) and an input (31) of the device, wherein the DC-DC converter (35) can be connected to the energy store (10) via the first switching element (S1), whereby the consumer (20) can be supplied via the DC-DC converter (35) fed from the energy store (10) when the input voltage (U1) falls below the first predetermined limit voltage (Ugs1); wherein the device comprises a controllable second switching element (S2) connected between the input (36) of the DC-DC converter (35) and a terminal (33) for the buffer memory (40), whereby the load (20) can be supplied via the DC-DC converter (35) fed from the buffer memory (40) when the input voltage (U1) falls below the second predetermined limit voltage (Ugs2); and wherein the first and the second switching element (S1, S2) do not have the same switching state (1; 0) in a control operation, wherein the control operation comprises all operating states with the exception of a safety shutdown in which all switching elements (S1, .., S5) of the device are switched to blocking, whereby either only the energy storage device (10) or the buffer storage device (40) is connected to the input of the DC-DC converter (35).

Description

[0001] The invention relates to a device for stabilizing the supply of energy from a buffer storage device to a consumer that is supplied from an energy storage device during normal operation. In particular, the device relates to the stabilizing supply of energy to a consumer connected to a vehicle electrical system.

[0002] The stabilizing supply of consumers, such as measurement technology temporarily installed in a vehicle, is achieved by providing a buffer battery or a buffer capacitor as a buffer storage device. Due to their high capacity and the high currents that can be achieved in the short term, both during energy extraction and for charging, electrochemical capacitors in the form of so-called supercapacitors (also known as ultracaps or supercaps) are usually used as buffer storage devices. The buffer storage device is intended to ensure that the consumer does not unexpectedly fail or exhibit undefined behavior if the voltage provided by the energy storage device falls below a minimum voltage required for the consumer's operation.The buffer storage is generally dimensioned to allow for short-term operation of the consumer, allowing it to reach a defined state or be brought into a defined state. In this example, which is directed at vehicles, the energy storage device can be a vehicle battery, the voltage provided at a supply terminal of which can fluctuate due to dynamic processes in the vehicle. In principle, however, this problem can arise in other applications. For the sake of simplicity, this description refers to an application in a vehicle, although this application should be considered restrictively.

[0003] To prevent other components from being supplied from the buffer storage when the minimum voltage required to operate the consumer is not reached, which would significantly shorten the time required to stabilize the consumer's supply, a diode is provided between a node to which the consumer and the buffer storage are connected and the energy storage device or the other components. The presence of the diode means that the voltage drop causes unwanted power loss (heat), which should always be avoided. Furthermore, the voltage swing that the buffer storage device can provide to the consumer is reduced by the voltage drop across the diode. Due to the minimum voltage required by the consumer, only a small operating range of the buffer storage device can be used.

[0004] In order to provide the consumer with a constant voltage regardless of the energy storage voltage, a DC-DC converter can be installed between the aforementioned node and the energy storage device. This converter (usually) steps up the voltage provided by the energy storage device, thereby increasing the operating range of the buffer storage device. However, during operation, the DC-DC converter also causes constant power loss, which is dissipated as heat.

[0005] US 2009 / 0 261 657 A1 discloses a method and system for hybrid power management that utilizes a fuel cell module and a secondary cell module to optimally supply power to a load. The secondary cell module and the load are connected to a DC-DC converter via controllable switching elements. For hybrid power management, the switching elements are controlled to select from output power modes, such as supplying power only from the fuel cell module, supplying power from both the fuel cell module and the secondary cell module, or interrupting the power supply to the load depending on the power state of the fuel cell module.

[0006] US 2006 / 0 006 850 A1 discloses the bridging of a DC-DC converter of a power supply with the aid of a controllable switching element depending on a measured voltage signal across a load.

[0007] US 5,161,097 A discloses an electrical power supply unit comprising a chopper-controlled non-isolated DC-DC converter for converting a battery output voltage into a required voltage, a bypass switch for bypassing the DC-DC converter, a comparator for comparing the battery output voltage with a reference voltage corresponding to the required voltage of the load circuit, and a controller for controlling the bypass switch based on the comparator output signal. When the battery output voltage is higher than the reference voltage, the battery is connected directly to the load circuit, allowing the battery power to be delivered to the load circuit without losses due to the operation of the DC-DC converter.When the output voltage is lower than the reference voltage, the battery output voltage is converted by the DC-DC converter into a voltage almost equal to the required voltage of the load circuit, so that essentially all the energy stored in the battery can be effectively utilized.

[0008] US 2005 / 088 793 A1 discloses a system for switching to an emergency power supply. Such a system comprises a threshold detector circuit; a first switching circuit for enabling access to a first power source, the first switching circuit comprising at least a first transistor; and a second switching circuit for enabling access to a second power source, the second switching circuit comprising at least a second transistor; the threshold detector being configured to cause the second switching circuit to enable access to the second power supply when a voltage provided by the first power supply falls below a predetermined threshold.

[0009] US 6,153,949 A discloses an electrical power management system comprising a power supply that, when a first switch and a third switch are closed, supplies power to a DC-to-DC boost converter, which in turn supplies power to a load while simultaneously storing energy in a capacitor. If the load momentarily requires more power than can be provided by the power supply, the first switch and the third switch are opened, and a second switch is closed. The energy previously stored in the capacitor is now supplied to the DC-to-DC boost converter, enabling efficient use of the energy stored in the capacitor.

[0010] It is an object of the present invention to provide a structurally and / or functionally improved device for the stabilizing supply from a buffer storage of a consumer supplied from an energy storage device during normal operation.

[0011] This object is achieved by a device according to the features of claim 1. Advantageous embodiments emerge from the dependent claims.

[0012] A device for the stabilizing supply of a consumer supplied from an energy storage device during normal operation from a buffer storage device is proposed, which device comprises a DC-DC converter, a plurality of controllable switching elements and a control unit for controlling the switching state of the plurality of controllable switching elements as a function of an input voltage of the device.

[0013] The device is designed to supply the load directly from the energy storage device during normal operation, bypassing components with power losses, if the input voltage is greater than a predetermined first threshold voltage, wherein the first threshold voltage is a minimum voltage of the load for its supply. This allows the load to be operated with minimized losses of the voltage stabilization device, provided that stabilization of its supply is not necessary.

[0014] The device is further configured to supply the load via the DC-DC converter fed from the energy storage device when the input voltage drops below the first predetermined threshold voltage, whereby the DC-DC converter converts the input voltage to the operating voltage of the load. Only when the minimum voltage of the load can no longer be provided by the energy storage device is the DC-DC converter activated. It is initially fed from the energy storage device, so that the buffer storage device does not yet need to be activated to stabilize the supply to the load. This makes it possible to postpone the activation of the buffer storage device.

[0015] The device is further configured to feed the DC-DC converter from the buffer storage when the input voltage drops below a second predetermined threshold voltage until a voltage in the buffer storage reaches the second predetermined threshold voltage, wherein the second predetermined threshold voltage is a minimum voltage of the DC-DC converter for its operation. The buffer storage is thus connected to the load by the device via the DC-DC converter. This connection is only established when the voltage provided by the energy storage device is no longer high enough to operate the DC-DC converter.

[0016] The device comprises a controllable first switching element which is connected between an input of the DC-DC converter and an input of the device, wherein the DC-DC converter can be connected to the energy storage device via the first switching element, whereby the consumer can be supplied via the DC-DC converter fed from the energy storage device when the input voltage falls below the first predetermined limit voltage.

[0017] The device comprises a controllable second switching element which is connected between the input of the DC-DC converter and a connection for the buffer storage, whereby the consumer can be supplied via the DC-DC converter fed from the buffer storage when the input voltage falls below the second predetermined limit voltage.

[0018] The device is designed such that the first and second switching elements do not have the same switching state in normal operation, with normal operation encompassing all operating states with the exception of a safety shutdown, in which all switching elements of the device are switched off, whereby either only the energy storage device or the buffer storage device is connected to the input of the DC-DC converter. This means that when the first switching element is closed, the second switching element is open, and vice versa. This ensures that either only the energy storage device or the buffer storage device is connected to the input of the DC-DC converter. This can be ensured by appropriate control of the two switching elements or by a circuit provided as hardware, so that the first and second switching elements can be set to the corresponding switching state with just one control signal.

[0019] The proposed device thus allows for a later start of discharge of the buffer storage, which allows for longer supply to the consumer. Furthermore, the buffer storage can be discharged more deeply than with existing solutions, which also allows for longer supply to the consumer. Furthermore, due to the absence of a diode, the buffer storage can be charged to a higher voltage, which also results in a larger voltage swing and allows for longer supply to the consumer. Each measure, individually and in combination, maximizes the buffer storage capacity.

[0020] As a result, the load operated with this device is optimally stabilized, regardless of fluctuations or failures of the energy storage system. During normal operation, no power loss occurs. Furthermore, critical load voltage conditions cannot arise.

[0021] The device may comprise a controllable third switching element, via which the load can be directly connected to the energy storage device, whereby the load can be supplied from the energy storage device during normal operation, bypassing components with power losses. This minimizes the heat generation of the device.

[0022] The device may comprise a controllable fourth switching element connected between an output of the DC-DC converter and an output of the device, wherein the DC-DC converter can be connected to the load via the fourth switching element. If the fourth switching element is closed, the third switching element is open, thus breaking the direct connection between the load and the energy storage device.

[0023] The device may comprise a controllable fifth switching element connected between the output of the DC-DC converter and the connection for the buffer storage, allowing the buffer storage to be charged. The fifth switching element may be closed at given intervals when the load is not being supplied with energy. The fifth switching element may be closed at given intervals when the load is not being supplied with energy via the DC-DC converter, but directly from the energy storage device. The fifth switching element may be closed at given intervals when the load is being supplied with energy via the DC-DC converter.It goes without saying that if the buffer storage is to be charged by closing the fifth switching element, the connection between the input of the DC-DC converter and the input of the device must also be closed in order for the DC-DC converter to be supplied with power. In other words, this means that the first switching element must also be closed.

[0024] The switching elements are controlled by the control unit. This means that it must be supplied with power to perform this task. For this purpose, the control unit is supplied with power from the device's input or from the buffer storage. This ensures that the control unit functions both during initial operation when the buffer storage is still empty, and when the energy storage is empty and the buffer is in operation until the end.

[0025] The control unit can be configured to detect the input voltage. The control unit can be configured to detect the output voltage of the DC-DC converter. The control unit can be configured to measure the voltage of the buffer storage. Depending on at least one of these voltages, the control unit can be configured to determine the switching states (closed or open) of the switching elements, i.e., the first to fifth switching elements.

[0026] The buffer storage can be an electrochemical capacitor, such as a supercapacitor or ultracapacitor. These have a high energy density and the ability to charge and discharge quickly. The buffer storage can be dimensioned so that, once it begins discharging, it can supply the consumer with power for approximately one minute. The size of the buffer storage must generally be adapted to the specific application.

[0027] The buffer storage can be part of the device. The buffer storage can also be a separate component from the device.

[0028] The invention is explained in more detail below using an exemplary embodiment in the drawing. In the drawings: Fig. 1 shows a circuit arrangement showing a device according to the invention for the stabilizing supply of a consumer supplied from an energy storage device during normal operation from a buffer storage device, and Fig. 2 a table illustrating the different operating states of the device.

[0029] Fig. 1 shows a circuit arrangement of an energy storage device 10, a load 20 to be supplied, and a device 30 for stabilizing the supply to the load. The device 30 for stabilizing the supply to the load is referred to below as a voltage stabilization device. The load 20, e.g., a temporarily used measuring device, is supplied during normal operation from the energy storage device 10, e.g., a vehicle battery. Normal operation is characterized in that the voltage applied to a battery terminal 11 of the energy storage device 10 is greater than a minimum voltage required for the operation of the load 20.

[0030] The voltage stabilizing device 30 has an input 31 and an output 32. The energy storage device 10 is connected with its battery terminal to the input 31 (IN). A supply input 21 of the load 20 is connected to the output 32 (OUT). A buffer storage device 40 is connected to an input 33 of the voltage stabilizing device 30. The buffer storage device is connected to a reference potential with its other terminal. The buffer storage device 40 is an electrochemical capacitor, i.e., a so-called supercapacitor (SuperCap) or ultracapacitor (UltraCap). In the Fig. 1, the buffer memory 40 is not a component of the voltage stabilization device 30. In an alternative embodiment, the buffer memory could also be part of the voltage stabilization device 30.

[0031] The voltage stabilization device 30 comprises a control unit 34, a DC-DC converter 35, and five controllable switching elements S1 to S5. The switching elements S1, .., S5 are, for example, semiconductor switching elements, such as MOSFETs. Other switching element types can also be used. The respective switching state (conductive or blocking) of the switching elements S1, ..., S5 is controlled by the control unit 34. In the following description of the Fig. 2, a conductive switching element is marked with "1", and a blocking switching element is marked with "0". The control unit 34 further has means for measuring various voltages U1, U2, U3 inside the voltage stabilization device 30. These means could also be provided in a separate measuring unit, in which case the result of the measurements would then have to be transmitted to the control unit 34. The control unit 34 is optionally also connected to the DC-DC converter 35 for controlling the latter (control signal s4). The control unit 34 is supplied with voltage from the buffer memory 40 via a supply input 38 of the voltage stabilization device 30, to which the buffer memory 40 is connected. A boost converter, for example, can be used as the DC-DC converter (DC / DC converter).

[0032] A first switching element S1 is connected between the input 31 of the voltage stabilizing device 30 and an input 36 of the DC-DC converter 35. The first switching element S1 is thus connected by one connection to the supply terminal 11 of the energy storage device 10. A second switching element S2 is connected between the input 33 of the voltage stabilizing device 30 and the input 36 of the DC-DC converter 35. The second switching element S2 is thus connected by one connection to the buffer memory 40. A third switching element S3 is connected between the input 31 of the voltage stabilizing device 30 and the output 32 of the voltage stabilizing device 30. The third switching element S3 can thus establish a direct connection, i.e. a connection without components having power losses, between the energy storage device 10 and the consumer 20.A fourth switching element S4 is connected between the output 37 of the DC-DC converter 35 and the output 32 of the voltage stabilization device 30, so that the DC-DC converter 35 can be connected to the load 20 via the fourth switching element S4. A fifth switching element S5 is connected between the output 37 of the DC-DC converter 35 and the input 33 of the voltage stabilization device 30, whereby the DC-DC converter 35 can be connected to the buffer storage 40.

[0033] The control device 34 detects the input voltage U1 of the voltage stabilizing device 30, with the signal representing the voltage U1 being designated m1. The voltage U1 corresponds to the voltage at the input 31 of the voltage stabilizing device 30 and thus to the voltage present at the supply terminal 11. Furthermore, the control device 34 detects the output voltage U2 at the output 37 of the DC-DC converter. The signal representing the voltage U2 is designated m2. Finally, the control device 34 detects the voltage U3, with the signal representing the voltage U3 being designated m3. The voltage U3 thus corresponds to the voltage of the buffer memory 40.

[0034] To control the switching elements S1, .., S5, at least the voltage U1 is processed by the control unit 34, for which purpose a comparison is made with predetermined limit voltages (i.e. threshold values stored in the control unit 34). A first limit voltage Ugs1 is defined by a minimum voltage necessary for the operation of the load 20, possibly plus a safety margin. The first limit voltage can be approximately 10 V if it is assumed that the load 20 can be operated with a voltage between 9 and 16 V. A second limit voltage Ugs2 is defined by a minimum voltage necessary for the operation of the DC-DC converter 35, possibly plus a safety margin. The second limit voltage Ugs2 depends on the implementation of the DC-DC converter 35 and can be approximately 5 V.In the illustrated embodiment, it is assumed that the DC-DC converter 35 can be operated with input voltages between 5 and 16 V. On the output side, the DC-DC converter 35 should be able to provide a voltage between 10 and 16 V.

[0035] In a charging operation of the voltage stabilizing device 30 (line no. 1 in the table of Fig. 2) the load 20 is not supplied with a voltage ("output OFF") and the buffer storage 40 is charged via the energy storage device 10 ("buffer storage charging"). For this purpose, the switching elements S1 and S5 are switched on ("1") and the switching elements S2, S3 and S4 are switched off ("0"). The voltage U1 depends on the voltage provided by the energy storage device 10 and can assume voltages between 5 and 16V, which corresponds to the operating range of the DC-DC converter 35 via which the buffer storage 40 is charged. Since the aim is to charge the buffer storage 40 to its maximum possible capacity, the DC-DC converter generates the maximum output voltage U2. U2 and U3 are therefore 16V.

[0036] The normal operation of the voltage stabilizing device 30 is shown in the table of Fig. 2 in line 2. In normal operation, the load 20 is supplied with voltage from the energy storage device 10 ("output ON"), for which the switching element S3 must be switched on. Due to the direct connection of the load 20 to the energy storage device 10, minimal power loss occurs. To supply the load 20, the operation of the DC-DC converter is not necessary ("without operation of the DC-DC converter"). Only for the optional trickle charge of the buffer storage device 40 ("buffer storage trickle charge") does the DC-DC converter 35 have to be operated in conjunction with the switching elements S1 and S5 being switched on ("1") at specified intervals. The switching elements S2 and S4 are always switched off ("0") in normal operation.

[0037] For normal operation, the voltage U1 must be greater than the first threshold voltage Ugs1, i.e., greater than the voltage required to operate the load 20. The voltage U1 can therefore range between 10 and 16 V. For maintenance charging, the buffer storage 40 is supplied with the maximum possible output voltage of the DC-DC converter 35, i.e., U2 and U3 are 16 V.

[0038] In row no. 3 of the table in Fig. 2 shows a "stabilizing normal operation" of the voltage stabilizing device 30. In this stabilizing normal operation, the load 20 is supplied with voltage from the energy storage device 10 ("output ON via DC-DC converter"), even though the voltage U1 has dropped below the voltage required for the operation of the load 20, i.e. U1 is less than the first limit voltage Ugs1. The load is now supplied via the DC-DC converter 35, which is fed from the energy storage device 10, under the condition that the voltage U1 is greater than the second limit voltage Ugs2, i.e. greater than the minimum input voltage of the DC-DC converter 35. U1 must therefore be between 5 and 10V. For this purpose, the switching element S3 is switched to the blocking position ("0") in order to break the direct connection between the load 20 and the energy storage device 10.Likewise, the switching element S2 is switched to the off position ("0"), since no supply is coming from the buffer memory 40. The switching elements S1 and S4 are switched to the on position ("1") to enable the supply via the DC-DC converter 35.

[0039] The voltage U2 provided by the DC-DC converter 35 is between 10 and 16V. Assuming that before the onset of "stabilizing normal operation" the voltage has not dropped suddenly but gradually below 10V, the voltage U2 can be regulated to 10V to avoid voltage jumps. If a voltage jump is tolerable for the consumer, the voltage can also be regulated to 16V. Likewise, the voltage U2 can be continuously increased in a ramp from 10V to 16V. Corresponding control is carried out by the control unit 34 using the signal s1. In this exemplary embodiment, the buffer storage 40 is not trickle charged during stabilizing normal operation, i.e. the switching element S5 is switched to the off position ("0"). The voltage U3 therefore corresponds to the voltage of the buffer storage 40, which was previously charged to 16V.In one variant, a trickle charge as described above could also be carried out during stabilizing normal operation.

[0040] In row no. 4 of the table in Fig. 2 shows a "stabilizing buffer operation" of the voltage stabilizing device 30. In this stabilizing buffer operation, the load 20 is no longer supplied with voltage from the energy storage device 10, but from the buffer storage device 40 ("output ON via buffer storage device"), since the voltage U1 has dropped below the voltage required for the operation of the DC-DC converter 35, i.e. U1 is less than the second limit voltage Ugs2. U1 is therefore less than 5V. The load is supplied via the DC-DC converter 35, which is fed from the buffer storage device 40. For this purpose, the switching elements S1, S3 and S5 are switched to the off state ("0"), while the switching elements S2 and S4 are switched to the on state ("1").

[0041] Stabilizing buffer operation is possible as long as the voltage U3 of the buffer storage 40 is greater than the minimum voltage required for the operation of the DC-DC converter 35, i.e., U3 must be greater than the second limit voltage Ugs2 and thus greater than 5V. The voltage U2 provided by the DC-DC converter 35 can be between 10 and 16V. As in the previous stabilizing normal operation, the voltage U2 can be regulated to 10V to avoid voltage surges. If the consumer 20 was previously operated with 10V and a voltage surge is tolerable for the consumer 20, the voltage can also be regulated to 16V. Likewise, in this case, the voltage U2 can be continuously increased in a ramp from 10V to 16V. Corresponding control is carried out by means of the signal s1 by the control unit 34. A trickle charge of the buffer storage 40 does not take place in the stabilizing emergency operation in this embodiment, i.e.the switching element S5 is switched to blocking (“0”).

[0042] If the voltage U3 of the buffer storage falls below the second limit voltage Ugs2 due to the continuous discharge, a safety shutdown occurs, in which the load 20 can no longer be supplied with voltage ("Output OFF, safety shutdown"). In this case, line no. 5 of the table in Fig. In the state shown in Figure 2, all switching elements S1 to S5 are or will be switched to the off position ("0"). The voltage U2 at the output of the DC-DC converter 35 is 0V. The voltage U1 is still smaller than the second threshold voltage Ugs2 and is between 0 and 5V.

[0043] The proposed device 30 thus enables a later start of discharging of the buffer storage 40, which enables a longer supply to the load 20. Furthermore, the buffer storage 40 can be discharged to a minimum voltage for the operation of the DC-DC converter and thus much more deeply than the known solutions, which also enables a longer supply to the load 20. Furthermore, the buffer storage 40 can be charged to a maximum possible voltage, which additionally results in an increased voltage swing and enables a further longer supply to the load 20. Each measure, individually and in combination, maximizes the buffer capacity of the buffer storage 40.

[0044] As a result, the load operated with this device is optimally stabilized, regardless of fluctuations or failures of the energy storage system. During normal operation, no power loss occurs. Furthermore, critical load voltage conditions cannot arise. List of reference symbols 10 energy storage 11 Supply terminal of the energy storage device 10 20 consumers 21 Supply input of the consumer 20 30 Device for stabilizing the supply of the consumer 20 31 Input of device 30 (IN) 32 Output of device 30 (OUT) 33 Input for buffer storage 40 34 Control unit 35 DC-DC converters 36 Input of the DC-DC converter 37 Output of the DC-DC converter 38 Supply input for control unit 34 40 buffer storage S1 first switching element S2 second switching element S3 third switching element S4 fourth switching element S5 fifth switching element U1 Input voltage of the device at input 31 U2 Output voltage of the DC-DC converter 35 U3 Voltage of the buffer storage 40 Ugs1 first limit voltage Ugs2 second limit voltage m1 measurement signal representing the input voltage U1 of the device at input 31 m2 measurement signal representing the output voltage U2 of the DC-DC converter m3 measurement signal representing the voltage U3 of the buffer storage 40 s1 control signal for the DC-DC converter

Claims

[1] Device (30) for the stabilizing supply of a consumer (20) supplied from an energy store (10) during normal operation from a buffer store (40), wherein the device (30) comprises a DC-DC converter (35), a plurality of controllable switching elements (S1, .., S5) and a control unit (34) for controlling the switching state (1; 0) of the plurality of controllable switching elements (S1, .., S5) as a function of an input voltage (U1) of the device (30), wherein the device (30) is designed to a) to supply the consumer (20) in normal operation directly from the energy store (10), bypassing components with power losses, if the input voltage (U1) is greater than a predetermined first limit voltage (Ugs1), wherein the first limit voltage (Ugs1) is a minimum voltage of the consumer for its supply; b) supplying the load (20) via the DC-DC converter (35) fed from the energy storage device (10) when the input voltage (U1) falls below the first predetermined limit voltage (Ugs1), wherein the DC-DC converter (35) converts the input voltage to an operating voltage of the load; and c) to feed the DC-DC converter (35) from the buffer storage (40) when the input voltage drops below a second predetermined limit voltage (Ugs2) until a voltage (U3) of the buffer storage (40) reaches the second predetermined limit voltage (Ugs2), wherein the second predetermined limit voltage (Ugs2) is a minimum voltage of the DC-DC converter (35) for its operation, wherein the device comprises a controllable first switching element (S1) which is connected between an input (36) of the DC-DC converter (35) and an input (31) of the device, wherein the DC-DC converter (35) can be connected to the energy store (10) via the first switching element (S1), whereby the consumer (20) can be supplied via the DC-DC converter (35) fed from the energy store (10) when the input voltage (U1) falls below the first predetermined limit voltage (Ugs1); wherein the device comprises a controllable second switching element (S2) which is connected between the input (36) of the DC-DC converter (35) and a terminal (33) for the buffer memory (40), whereby the load (20) can be supplied via the DC-DC converter (35) fed from the buffer memory (40) when the input voltage (U1) falls below the second predetermined limit voltage (Ugs2); and wherein the first and the second switching element (S1, S2) do not have the same switching state (1; 0) in a control operation, wherein the control operation comprises all operating states with the exception of a safety shutdown in which all switching elements (S1, .., S5) of the device are switched to blocking, whereby either only the energy storage device (10) or the buffer storage device (40) is connected to the input of the DC-DC converter (35). [2] Device according to claim 1, wherein it comprises a controllable third switching element (S3) via which the consumer (20) can be connected directly to the energy store (10), whereby the consumer (20) can be supplied from the energy store during normal operation, bypassing components having power losses. [3] Device according to claim 1 or 2, wherein it comprises a controllable fourth switching element (S4) which is connected between an output (37) of the DC-DC converter (35) and an output (32) of the device, wherein the DC-DC converter (35) can be connected to the load (20) via the fourth switching element (S4). [4] Device according to one of the preceding claims, in which it comprises a controllable fifth switching element (S5) which is connected between the output (37) of the DC-DC converter (35) and the connection (33) for the buffer memory (40), whereby the buffer memory (40) can be charged. [5] Device according to one of the preceding claims, in which the control unit (34) is supplied with voltage from the buffer memory. [6] Device according to one of the preceding claims, in which the control unit (34) is designed to measure the input voltage (U1), the output voltage of the DC-DC converter (U2) and the voltage of the buffer memory (40) and to determine the switching states (1; 0) of the switching elements (S1, ..., S5) depending on these. [7] Device according to one of the preceding claims, wherein the buffer storage (33) is an electrochemical capacitor (supercapacitor, ultracapacitor). [8] Device according to one of the preceding claims, in which the buffer memory (40) is a component of the device.

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