Damping circuit for an energy storage device and method for damping oscillations of the output current of an energy storage device

Abstract

Damping circuit for an energy storage device (10), comprising one or more energy storage modules (3) connected in series in one or more energy supply strings, each with at least one energy storage cell (5a, ..., 5k) and a coupling device (7) with a plurality of coupling elements designed to selectively connect or bridge the energy storage cell (5a, ..., 5k) in the respective energy supply string, comprising: a current sensing device (8) designed to detect an output current of the power supply strings or the energy storage device (10) and to generate an output current signal dependent on the output current; a control circuit (6) which is coupled to the current sensing device (8) and which is designed to regulate the output current signal to a target current signal and to output a corresponding current control signal; a transformer (2) which has a first winding (2a) coupled to an output terminal (1a) of the energy storage device (10) and a second winding (2b) galvanically isolated from the first winding (2a); and a balancing current generating device (4) which is coupled to the control circuit (6) and which is designed to feed a balancing current, which compensates for fluctuations in the output current of the energy storage device (10), into the second winding (2b) of the transformer (2) depending on the current control signal; and a bandpass filter (11) which is coupled between the current sensing device (8) and the control circuit (6), and which is designed to filter frequency components of the output current signal outside a predefinable frequency range; wherein the current sensing device (8) is designed to detect a difference between the output current of the energy storage device (10) and the output current of a DC intermediate circuit (9a) connected to the energy storage device (10).

Description

[0001] The invention relates to a damping circuit for an energy storage device and a method for damping vibrations of the output current of an energy storage device, in particular for battery converter circuits for supplying voltage to loads acting as variable current sources, such as electric machines in drive systems of electrically operated water or land vehicles. State of the art

[0002] It is becoming clear that in the future, both in stationary applications, such as wind turbines or solar power plants, and in vehicles, such as hybrid or electric vehicles, electronic systems will increasingly be used that combine new energy storage technologies with electric drive technology.

[0003] To feed three-phase alternating current into an electric machine, a conventional inverter, specifically a pulse-width modulated inverter, converts the direct current (DC) supplied by a DC link into a three-phase alternating current (AC). The DC link is powered by a string of series-connected battery modules. To meet the power and energy requirements of a given application, several battery modules are often connected in series to form a traction battery. Such an energy storage system is frequently used, for example, in electric vehicles.

[0004] Connecting multiple battery modules in series presents the problem that if a single battery module fails, the entire string fails. Such a failure of the power supply string can lead to a failure of the entire system. Furthermore, temporary or permanent reductions in the performance of a single battery module can lead to performance reductions in the entire power supply string.

[0005] Documents DE 10 2010 027 857 A1 and DE 10 2010 027 861 A1 disclose modularly connected battery cells in energy storage devices that can be selectively connected to or disconnected from the string of serially connected battery cells via suitable control of coupling units. Systems of this type are known as Battery Direct Converters (BDCs). Such systems comprise DC sources in an energy storage module string that can be connected to a DC link for the electrical power supply of an electric machine or an electrical network via a pulse inverter.

[0006] Document DE 10 2010 041 046 A1 discloses a method for charging a DC intermediate circuit of a battery system, which uses a battery with switchable battery modules and thus eliminates the need for a separate charging contactor and series resistor.

[0007] Document US 6,026,126 A discloses a method and a device for reducing the ripple signal at the output of a DC power supply. Instead of using conventional LC filters, an active method is employed that compensates for the ripple by selectively injecting an out-of-phase signal.

[0008] Document JP 2002-272 113 A discloses a circuit arrangement for reducing peak currents and harmonic currents in a rectifier smoothing circuit connecting an AC power source to a load.

[0009] Document EP 1 903 674 A1 discloses a multi-stage low-pass filter for a splitter.

[0010] Document US 4 667 279 A discloses a transformer-coupled interference suppression circuit for DC power supplies.

[0011] Document DE 10 2010 041 040 A1 discloses an energy supply network and a method for charging energy storage cells that serve as an intermediate circuit capacitor for a DC intermediate circuit.

[0012] Battery converters (BDCs) typically exhibit higher efficiency and greater reliability compared to conventional systems. Reliability is ensured, among other things, by the ability to disconnect defective, failed, or underperforming battery cells from the power supply lines through appropriate bypass control of the coupling units.

[0013] The energy storage module strings comprise a plurality of energy storage modules connected in series, each energy storage module having at least one battery cell and an associated controllable coupling unit. This coupling unit allows, depending on control signals, the associated battery cell to be bridged or connected to the respective energy storage module string. Optionally, the coupling unit can be designed to additionally allow the associated battery cell to be connected to the respective energy storage module string with reverse polarity or to interrupt the respective energy storage module string.

[0014] The total output voltage of BDCs is determined by the drive state of the coupling units and can be adjusted in steps, with the steps of the total output voltage depending on the individual voltages of the energy storage modules. Due to the intrinsic complex resistances of the energy storage modules and their components, the energy storage device, together with a downstream DC link capacitor, acts as a resonant circuit. The resonant frequency of this circuit can vary depending on the number and switching rate of the connected energy storage modules, which differ depending on the voltage requirements. This means that undesirable resonances can occur when the energy storage device is coupled to a load acting as a variable current source, such as an inverter and an electric machine connected downstream of the inverter.

[0015] Therefore, there is a need for measures to reduce or suppress the occurrence of such resonances or current fluctuations when coupling a BDC to an intermediate circuit capacitor to supply a load acting as a variable current source. Disclosure of the invention

[0016] According to one embodiment of the present invention, a damping circuit for an energy storage device comprises one or more energy storage modules connected in series in one or more power supply lines, each module having at least one energy storage cell, and a coupling device with a plurality of coupling elements designed to selectively connect or bypass the energy storage cell in the respective power supply line. The damping circuit includes a current sensing device designed to detect an output current of the power supply lines or the energy storage device and to generate an output current signal dependent on the output current, a control circuit coupled to the current sensing device designed to regulate the output current signal to a target current signal and to output a corresponding current control signal, and a transformer.which has a first winding coupled to an output terminal of the energy storage device and a second winding galvanically isolated from the first winding, and a balancing current generating device coupled to the control circuit, and which is designed to feed a balancing current into the second winding of the transformer, depending on the current control signal, which compensates for fluctuations in the output current of the energy storage device.

[0017] According to a further embodiment, the present invention provides a system comprising an energy storage device which has one or more energy storage modules connected in series in one or more energy supply strings, each with at least one energy storage cell and a coupling device with a plurality of coupling elements designed to selectively switch or bridge the energy storage cell in the respective energy supply string, and a damping circuit according to the invention.

[0018] According to a further embodiment, the present invention provides a method for damping oscillations of the output current of an energy storage device, which has one or more energy storage modules connected in series in one or more energy supply strings, each with at least one energy storage cell and a coupling device with a plurality of coupling elements designed to selectively switch or bridge the energy storage cell in the respective energy supply string.The method comprises the steps of detecting an output current from the power supply lines or the energy storage device, generating an output current signal dependent on the detected output current, regulating the output current signal to a target current signal, outputting a current control signal corresponding to the regulation, generating a compensating current which compensates for fluctuations in the output current of the energy storage device, and feeding the compensating current into the second winding of a transformer which has a first winding coupled to an output terminal of the energy storage device and a second winding galvanically isolated from the first winding. Advantages of the invention

[0019] One aspect of the present invention is to superimpose a balancing current on the output current of an energy storage device with modularly constructed power supply strings consisting of a series connection of energy storage modules, thereby dampening resonances caused by current fluctuations in a variable power source supplied by the energy storage device. The output currents of the energy storage device are detected, and balancing currents are actively generated based on these detected output currents and their fluctuations. These balancing currents, along with the actual output currents of the energy storage device, can be fed into the variable power source via galvanic coupling. The balancing currents, whose amplitude is flexibly adjusted, serve to actively dampen potential resonances.

[0020] This damping allows on-board network resonances to be attenuated without additional losses in the power path. Thanks to self-regulation via the current feedback loop, it is advantageously possible to adapt the damping to the position of the resonant frequency and the quality factor of the resonant circuit, regardless of the current operating state of the energy storage device. In particular, measuring the resonant frequency of the energy storage device is no longer necessary. Changes that may occur during the operating life of the energy storage device, for example due to aging or changes in the system topology (such as longer high-voltage lines), are also compensated for flexibly and automatically by the damping circuit.

[0021] Active control allows for the advantageous selection of a damping level across an adjustable frequency range. The energy storage device can then be operated as usual, without the need for lossy variable switching of load-carrying components.

[0022] The damping circuit can advantageously be implemented entirely in the low-voltage domain through galvanic decoupling, thus enabling smooth switching and simple power supply from a 12-volt network. The design and control parameters of the damping circuit are independent of the instantaneous value of a DC link capacitor connected to the energy storage device.

[0023] The damping circuit can advantageously be used in a conventional vehicle electrical system. Furthermore, existing components, such as a current-limiting choke, can be used in the design of the damping circuit, resulting in reduced costs, reduced effort, and reduced installation space requirements.

[0024] According to one embodiment of the damping circuit according to the invention, the damping circuit can further comprise a bandpass filter, which is coupled between the current sensing device and the control circuit, and which is designed to filter frequency components of the output current signal outside a predefinable frequency range. This advantageously enables demand-based damping in the critical resonant frequency range, so that no damping occurs in non-critical ranges and thus no unnecessary resource consumption. In particular, in frequency ranges where otherwise large amounts of power would have to be supplied for active damping, but damping of the current ripple is not necessarily required, this can lead to an increase in the efficiency of the damping circuit.

[0025] According to a further embodiment of the damping circuit according to the invention, the current sensing device can be designed to detect a difference between the output current of the energy storage device and the output current of a DC link connected to the energy storage device. This offers the advantage that a particularly low-inductance connection of a current sensing device to the DC link capacitor can be dispensed with.

[0026] According to a further embodiment of the damping circuit according to the invention, the control circuit can include a summing element which subtracts the output current signal from the target current signal, and a current controller which generates the current control signal depending on the output signal of the summing element.

[0027] According to a further embodiment of the damping circuit according to the invention, the first winding of the transformer can include an output-side current-limiting choke of the energy storage device. This offers the advantage that the existing current-limiting choke can be used for a dual purpose, thus saving installation space and components.

[0028] According to a further embodiment of the damping circuit according to the invention, the compensating current generation device can have an H-bridge circuit with two switching devices in each of the bridge branches. This offers the advantage that low-resistance, low-voltage switches can be used for the switching device, which, as a soft-switching full bridge, can implement a very low-loss active damping control.

[0029] According to a further embodiment of the damping circuit according to the invention, the balancing current generation device can be coupled to a supply connection of one of the energy storage modules and designed to be supplied with a supply voltage from the energy storage module to generate the balancing current. This eliminates the need for an external power supply, and the damping circuit can be powered from the energy storage device itself.

[0030] According to one embodiment of the system according to the invention, the system can further comprise a DC link which is coupled to the output terminals of the energy storage device. Advantageously, the system can also include an inverter coupled to the DC link and an electric machine coupled to the inverter. The inverter can be designed to convert the voltage of the DC link into an input voltage for the electric machine. This is particularly advantageous because the system consisting of the inverter and the electric machine can feed currents with frequency-dependent fluctuations back into the energy storage device via the DC link as a variable current source. These frequency-dependent fluctuations can be particularly well damped by the damping circuit.

[0031] Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings. Brief description of the drawings

[0032] They show: Fig. 1 a schematic representation of a system with an energy storage device and a damping circuit according to an embodiment of the present invention; Fig. 2 a schematic representation of an embodiment of an energy storage module of an energy storage device according to a further embodiment of the present invention; Fig. 3 a schematic representation of a further embodiment of an energy storage module of an energy storage device according to a further embodiment of the present invention; Fig. 4 a schematic representation of a system with an energy storage device and a damping circuit according to a further embodiment of the present invention; and Fig. 5 a schematic representation of a method for damping vibrations of the output current of an energy storage device according to a further embodiment of the present invention.

[0033] Fig. Figure 1 shows a system comprising an energy storage device 10 for providing a supply voltage by means of energy storage modules 3 connected in series in a power supply line between two output terminals 1a, 1b of the energy storage device 10. The energy storage device 10 can alternatively also have several power supply lines connected in parallel. Due to the control of the energy storage modules 3, the energy storage device 10 acts as a current source with a variable output current.

[0034] The energy storage device 10 can be coupled to an input terminal of a DC link 9a via a storage inductance 2a at its output terminal 1a. The storage inductance 2a can be implemented, for example, as a single component such as a current-limiting choke or as multiple distributed components. Alternatively, parasitic inductances of the energy storage device 10 can also be used as the storage inductance 2a. The current flow into the DC link 9a can be controlled by appropriately controlling the energy storage device 10.If the average voltage before the storage inductor 2a is higher than the instantaneous DC link voltage, a current flows into the DC link 9a; if, on the other hand, the average voltage before the storage inductor 2a is lower than the instantaneous DC link voltage, a current flows into the energy storage device 10. The maximum current is limited by the storage inductor 2a in conjunction with the DC link 9a.

[0035] The energy storage device 10 has at least two energy storage modules 3 connected in series in an energy supply line. For example, the number of energy storage modules 3 in Fig. 1. Two energy storage modules 3, but any other number is also possible. The energy storage modules 3 each have two output terminals 3a and 3b, via which a module output voltage of the energy storage modules 3 can be provided. The module output voltages of the energy storage modules 3 can selectively add up to the total output voltage of the energy storage device 10.

[0036] Exemplary configurations of the energy storage modules 3 are shown in the Fig. 2 and Fig. Figure 3 is shown in greater detail. The energy storage modules 3 each comprise a coupling device 7 with several coupling elements 7a and 7c, and optionally 7b and 7d. The energy storage modules 3 also each comprise an energy storage cell module 5 with one or more energy storage cells 5a, 5k connected in series.

[0037] The energy storage cell module 5 can, for example, comprise batteries 5a to 5k connected in series, such as lithium-ion batteries or accumulators. The number of energy storage cells 5a to 5k in the module is... Fig. The energy storage module 3 shown is an example of two, but any other number of energy storage cells 5a to 5k is also possible.

[0038] The energy storage cell modules 5 are connected via connecting cables to input terminals of the associated coupling device 7. The coupling device 7 is in Fig. Figure 2 shows an example of a full bridge circuit with two coupling elements 7a, 7c and two coupling elements 7b, 7d. Each coupling element 7a, 7b, 7c, 7d can have an active switching element, for example a semiconductor switch, and a freewheeling diode connected in parallel. The semiconductor switches can, for example, be field-effect transistors (FETs). In this case, the freewheeling diodes can also be integrated into the semiconductor switches.

[0039] The coupling elements 7a, 7b, 7c, 7d in Fig. The two coupling devices 7 can be controlled such that the energy storage cell module 5 is selectively connected between the output terminals 3a and 3b, or that the energy storage cell module 5 is bypassed. By appropriately controlling the coupling devices 7, individual energy storage cell modules 5 of the energy storage modules 3 can therefore be selectively integrated into the series connection of a power supply line.

[0040] With reference to Fig. 2. The energy storage cell module 5 can, for example, be connected in the forward direction between the output terminals 3a and 3b by setting the active switching element of the coupling element 7d and the active switching element of the coupling element 7a to a closed state, while setting the two remaining active switching elements of the coupling elements 7b and 7c to an open state. In this case, the voltage U is present between the output terminals 3a and 3b of the coupling device 7. MA bridging state can be set, for example, by placing the two active switching elements of coupling elements 7a and 7b in the closed state, while keeping the two active switching elements of coupling elements 7c and 7d in the open state. A second bridging state can be set, for example, by placing the two active switches of coupling elements 7c and 7d in the closed state, while keeping the active switching elements of coupling elements 7a and 7b in the open state. In both bridging states, the voltage between the two output terminals 3a and 3b of coupling device 7 is zero.Similarly, the energy storage cell module 5 can be connected in reverse between the output terminals 3a and 3b of the coupling device 7 by setting the active switching elements of coupling elements 7b and 7c to the closed state, while setting the active switching elements of coupling elements 7a and 7d to the open state. In this case, the voltage -U is present between the two output terminals 3a and 3b of the coupling device 7. M to.

[0041] The total output voltage of the power supply line can be adjusted in steps, with the number of steps scaling with the number of energy storage modules. With n first and second energy storage modules, the total output voltage of the power supply line can be adjusted in 2n+1 steps between -n·U M ,..,0,...,+n·U M be hired.

[0042] Fig. Figure 3 shows another exemplary embodiment of an energy storage module 3. The one in Fig. The energy storage module shown in Figure 3 differs from the one in Figure 3. Fig. The energy storage module 3 shown in Figure 2 differs only in that the coupling device 7 has two coupling elements instead of four, which are connected in a half-bridge circuit instead of a full-bridge circuit.

[0043] In the illustrated implementation variants, the active switching elements can be designed as power semiconductor switches, for example in the form of IGBTs (Insulated Gate Bipolar Transistors), JFETs (Junction Field-Effect Transistors) or MOSFETs (Metal Oxide Semiconductor Field-Effect Transistors).

[0044] The coupling elements 7a, 7b, 7c, 7d allow the output voltage of the power supply string to be varied in steps from a negative maximum value to a positive maximum value via suitable control. The gradation of the voltage levels depends on the gradation of the individual energy storage cell modules 5. For example, to obtain an average voltage value between two voltage levels defined by the gradation of the energy storage cell modules 5, the coupling elements 7a, 7b, 7c, 7d of an energy storage module 3 can be controlled by pulsed modulation (PWM), such that the respective energy storage module 3 delivers an average module voltage that can have a value between zero and the maximum possible module voltage determined by the energy storage cells 5a to 5k.The control of the coupling elements 7a, 7b, 7c, 7d can, for example, be a control device designed to perform, for example, current control with a subordinate voltage control, so that individual energy storage modules 3 can be switched on or off in stages.

[0045] The system in Fig. In addition to the energy storage device 10, 1 also includes an inverter 12 and an electric machine 13. The system serves as an example in Fig. 1 for supplying a three-phase electric machine 13. However, it can also be provided that the energy storage device 1 is used to generate electricity for a power supply network. Alternatively, the electric machine 13 can also be a synchronous or asynchronous machine, a reluctance machine, or a brushless DC motor (BLDC). It may also be possible to use the energy storage device 10 in stationary systems, for example, in power plants, in electrical energy generation plants such as wind turbines, photovoltaic systems, or combined heat and power plants, in energy storage systems such as compressed air energy storage plants, battery storage plants, flywheel energy storage systems, pumped storage plants, or similar systems. Another possible application of the system in Fig. 1 are vehicles designed to transport persons or goods on or under water, for example ships, motorboats or the like.

[0046] In the exemplary embodiment, the DC intermediate circuit 9a feeds into Fig. 1. A pulse inverter 12, which provides a three-phase AC voltage for the electric machine 13 from the DC voltage of the DC link 9a. However, any other type of converter can also be used for the inverter 12, depending on the required voltage supply for the electric machine 13, for example, a DC-DC converter. The inverter 12 can, for example, be operated in space vector pulse width modulation (SVPWM).

[0047] By controlling the inverter 12 and the varying power consumption of the electric machine 13, the inverter-machine combination acts as a variable current source relative to the DC link 9a, which can excite the resonant circuit consisting of the energy storage device 10, storage inductor 2a, and DC link 9a to resonances. The resonant frequency of this circuit depends, among other things, on the number of connected energy storage modules 3, the instantaneous values ​​of the DC link voltage, and the energy content of the storage inductor. Furthermore, the resonant frequency can be subject to long-term fluctuations, which may depend, for example, on component tolerances, component aging, temperature, and other influences. To reduce these oscillations and thus the current ripple to and from the DC link 9a, it is necessary to take measures that suppress these resonances.can dampen the current ripple.

[0048] This is included in the system in Fig. A current sensing device 8 is provided as part of a damping circuit, which is designed to detect an output current of the energy storage device 10 and to generate an output current signal that depends on the output current. The current sensing device 8 can, for example, have a first current sensor 8a, which detects a current flowing from the DC link 9a into the energy storage device 10 or a current flowing from the energy storage device 10 into the DC link 9a. The current sensing device 8 can, for example, further have a second current sensor 8b, which detects a current flowing from the DC link 9a into the variable current source 14 or a current flowing from the variable current source 14 into the DC link 9a.The detected currents can be determined, for example, as the difference between the output current of the energy storage device 10 and the output current of a DC link 9a connected to the energy storage device 10. For this purpose, a summing element 8c can be provided in the current detection device 8, which subtracts the currents detected by the first and second current sensors 8a and 8b from each other.

[0049] It may also be possible to design the current sensing device 8 such that, within the energy storage device 10 with multiple power supply strings, an output current signal is detected at each of the power supply strings. This makes it possible to regulate each of the power supply strings separately, especially since each of the power supply strings forms its own resonant circuit with the DC link 9a.

[0050] The system further includes, as part of the damping circuit, a control circuit 6, which is coupled to the current sensing device 8 and is designed to regulate the output current signal to a target current signal 6c and output a corresponding current control signal. The control circuit 6 can include a summing element 6b, which subtracts the output current signal from the target current signal 6c. Using a current controller 6a, the current control signal can be generated as a function of the output signal of the summing element 6b. The target current signal 6c can, for example, be zero. Alternatively, any other value can be specified for the target current signal 6c.

[0051] The current control signal can be fed into a balancing current generator 4, which is coupled to the control circuit 6 and is designed to generate a balancing current, depending on the current control signal, which compensates for fluctuations in the output current of the energy storage device 10. This balancing current can, for example, supply a transformer 2 formed from the storage inductor 2a as the first winding and a second winding 2b. The first winding 2a can be galvanically isolated from the second winding 2b.

[0052] The balancing power generation unit 4 can be found in the example in Fig. 1. A voltage source 4a is provided, which can be controlled by the current regulator 6a. The voltage source 4a feeds the second winding 2b of the transformer 2. It may, for example, be possible to integrate the storage inductance 2a as the magnetizing inductance of the transformer 2.

[0053] Optionally, a bandpass filter 11 can be provided, which is coupled between the current sensing device 8 and the control circuit 6, and which is designed to filter frequency components of the output current signal outside a predefinable frequency range. This prevents, for example, active damping interventions in frequency ranges where high power would be required to regulate the current ripple, but where a reduction of the current ripple is not required or not required to a significant extent.

[0054] Fig. Figure 4 shows a schematic representation of another system with an energy storage device 10 and a damping circuit. The system in Fig. 4 differs from the system in Fig. 1 essentially by the fact that the balancing current generating device 4 comprises an H-bridge circuit with two switching devices 4b, 4c, 4d, 4e in each of the bridge branches. The switching devices 4b, 4c, 4d, 4e can, for example, comprise low-voltage switches. The switching devices 4b, 4c, 4d, 4e can, for example, be implemented as power semiconductor switches, for example in the form of IGBTs (Insulated Gate Bipolar Transistors), JFETs (Junction Field-Effect Transistors), or MOSFETs (Metal Oxide Semiconductor Field-Effect Transistors).

[0055] Furthermore, the balancing current generator 4 can be coupled to a supply connection 3c of one of the energy storage modules 3. A supply voltage from the energy storage cell module 5 can be provided via the supply connection 3c of the energy storage module 3, which can be used to power the balancing current generator 4. By designing the balancing current generator 4 as a full bridge with soft-switching devices 4b, 4c, 4d, 4e, low-loss generation of the balancing current for injection into the second winding 2b of the transformer can be achieved.

[0056] Fig. Figure 5 shows a schematic representation of an exemplary method 20 for damping oscillations of the output current of an energy storage device, in particular an energy storage device 10, as described in connection with the Fig. 1 to 4 explained. Method 20 can, for example, use a damping circuit as described in the Fig. 1 and Fig. 4 shown.

[0057] The method 20 for damping oscillations of the output current of an energy storage device 10 comprises, in a first step 21, the detection of an output current of the energy storage device. In a second step 22, an output current signal dependent on the detected output current is generated. In a third step 23, the output current signal is regulated to a target current signal. Subsequently, in a fourth step 24, a current control signal corresponding to the regulation can be output, based on which, in a step 25, a compensating current can be generated, which compensates for fluctuations in the output current of the energy storage device 10.Finally, in step 26, the compensating current is fed into the second winding 2b of a transformer 2, which has a first winding 2a coupled to an output terminal 1a of the energy storage device 10, and a second winding 2b galvanically separated from the first winding 2a.

Claims

[1] Damping circuit for an energy storage device (10) comprising one or more energy storage modules (3) connected in series in one or more energy supply strings, each with at least one energy storage cell (5a, ..., 5k) and a coupling device (7) with a plurality of coupling elements designed to selectively connect or bridge the energy storage cell (5a, ..., 5k) in the respective energy supply string, comprising: a current sensing device (8) designed to detect an output current of the power supply strings or the energy storage device (10) and to generate an output current signal dependent on the output current; a control circuit (6) which is coupled to the current sensing device (8) and which is designed to regulate the output current signal to a target current signal and to output a corresponding current control signal; a transformer (2) which has a first winding (2a) coupled to an output terminal (1a) of the energy storage device (10) and a second winding (2b) galvanically isolated from the first winding (2a); and a balancing current generating device (4) which is coupled to the control circuit (6) and which is designed to feed a balancing current, which compensates for fluctuations in the output current of the energy storage device (10), into the second winding (2b) of the transformer (2) depending on the current control signal; and a bandpass filter (11) which is coupled between the current sensing device (8) and the control circuit (6), and which is designed to filter frequency components of the output current signal outside a predefinable frequency range; wherein the current sensing device (8) is designed to detect a difference between the output current of the energy storage device (10) and the output current of a DC intermediate circuit (9a) connected to the energy storage device (10). [2] Damping circuit according to claim 1, wherein the control circuit (6) comprises a summing element (6b) which subtracts the output current signal from the target current signal, and a current controller (6a) which generates the current control signal as a function of the output signal of the summing element (6b). [3] Damping circuit according to one of claims 1 or 2, wherein the first winding (2a) of the transformer (2) comprises an output-side current limiting choke (2a) of the energy storage device (10). [4] Damping circuit according to one of claims 1 to 3, wherein the compensating current generating device (4) has an H-bridge circuit with two switching devices (4b, 4c, 4d, 4e) in each of the bridge branches. [5] Damping circuit according to claim 4, wherein the compensating current generating device (4) is coupled to a supply connection (3c) of one of the energy storage modules (3) and is designed to be supplied with a supply voltage from the energy storage module (3) to generate the compensating current. [6] System, with: an energy storage device (10) comprising one or more energy storage modules (3) connected in series in one or more energy supply strings, each with at least one energy storage cell (5a, ..., 5k) and a coupling device (7) with a plurality of coupling elements designed to selectively connect or bridge the energy storage cell (5a, ..., 5k) in the respective energy supply string; and a damping circuit according to one of claims 1 to 5. [7] System according to claim 6, further comprising: a DC intermediate circuit (9a) which is coupled to output terminals (1a, 1b) of the energy storage device (10). [8] System according to claim 7, further comprising: an inverter (12) which is coupled to the DC link (9a); and an electric machine (13) which is coupled to the inverter (12), wherein the inverter (12) is designed to convert the voltage of the DC intermediate circuit (9a) into an input voltage for the electric machine (13). [9] Method (20) for operating a damping circuit according to one of claims 1 to 5 for damping oscillations of the output current of an energy storage device (10), which has one or more energy storage modules (3) connected in series in an energy supply line, each with at least one energy storage cell (5a, ..., 5k) and a coupling device (7) with a plurality of coupling elements designed to selectively switch or bypass the energy storage cell (5a, ..., 5k) in the respective energy supply line, comprising the steps: Capturing (21) an output current from the power supply strings or the energy storage device (10); Generating (22) an output current signal dependent on the detected output current; Rules (23) of the output current signal to a target current signal; Output (24) a current control signal corresponding to the control; Generating (25) a balancing current which compensates for fluctuations in the output current of the energy storage device (10); and Feeding (26) the balancing current into the second winding (2b) of a transformer (2) which has a first winding (2a) coupled to an output terminal (1a) of the energy storage device (10) and a second winding (2b) galvanically isolated from the first winding (2a).

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