Wind turbine with integrated battery storage

Abstract

The present invention relates to a battery storage and a wind turbine including a generator for generating electric current. A current path is configured to conduct current to a grid via a power converter. The power converter. A battery storage electrically connected to the current path, the battery storage comprising a plurality of battery cells, each battery cell comprising at least one battery element and at least two semiconductor switches. A controller is configured to selectively control the voltage on the battery storage by controlling the state of at least two semiconductor switches of the plurality of battery cells and thereby whether the current path through the battery storage bypasses the at least one battery element, or passes through at least one battery element of one or more of the plurality of battery cells.

Description

Technical Field

[0001] The invention relates to a battery storage and a wind turbine comprising a battery storage, and a method of controlling a current path through a battery cell, the battery storage comprising a plurality of individually controllable battery cells. Background Art

[0002] The amount of electricity generated by a wind turbine varies over time with wind speed. This variation is independent of the power consumption of the grid connected to the wind turbine. Therefore, various energy storage systems have been described that can be connected to individual wind turbines or wind farms. One of the purposes of these systems is to store energy when the wind turbine is generating electricity and when the consumption from the grid is low, and in addition, it can also deliver electricity to the grid when the wind turbine is not generating electricity but the consumption from the grid is high.

[0003] WO2015102398 is one of many prior art documents that disclose battery storage for wind turbines. The battery storage here is connected to the DC link between the machine-side and grid-side converters.

[0004] CN202011766 is one of many prior art documents that disclose a plurality of wind turbines connected to an energy storage via a bidirectional inverter.

[0005] Based on the above mentioned prior art documents representing the prior art related to energy storage from one or more wind turbines, the prior art discloses the use of conventional rechargeable batteries connected directly to the DC link in a back-to-back converter or via an inverter to the output of the wind turbine. Summary of the invention

[0006] The present invention proposes to integrate a new type of intelligent controllable energy storage into a wind turbine, which new type of intelligent controllable energy storage can be connected to the DC link of the converter or to the output of the converter of the wind turbine.

[0007] The method relates to a wind turbine comprising: a rotor that helps rotate a rotor of a generator, thereby generating an electric current; a current path that is configured to conduct the electric current to a grid via a power converter; and a battery storage electrically connected to the current path, the battery storage comprising a plurality of battery cells, each battery cell comprising at least one battery element and at least two semiconductor switches. Wherein a controller is configured to control a voltage on the battery storage by controlling a state of the at least two semiconductor switches of the plurality of battery cells and thereby whether a current path through the battery storage bypasses at least one battery element of one or more of the plurality of battery cells, or passes through at least one battery element of one or more of the plurality of battery cells.

[0008] An advantage of connecting a battery storage to the current path is that it enables the battery storage to store at least a portion of the current flowing in the current path or to deliver current to the current path depending on the voltage across the battery.

[0009] A current path through a battery reservoir is understood to be an electrical path that allows current to flow. The current path starts at the connection point between the battery reservoir and the current path or at the first battery cell in the series of battery cells and ends at the last battery cell in the series of battery cells before returning to the current path again. It should be mentioned that a plurality of battery cells connected in series may be electrically connected, so that in such embodiments the current path can also be said to return and return upward through the battery cells in the parallel column of battery cells connected in series.

[0010] Depending on the state of the switch, the current path may include or exclude battery elements of individual cells of the battery reservoir, and thereby include or exclude the voltage on the battery reservoir. The controller selectively controls whether a particular battery cell is included or bypassed from the current path. Thus, at one point in time, the battery cell may be included in the current path, and at a second point in time, the battery cell may be bypassed instead of being part of the current, and at a third point in time, the battery cell may be included in the current path again, over time, and so on. The controller may control the state of the switch based on the voltage or current requirements from the current path to which the battery reservoir is connected, the load distribution between the battery cells, the state of charge, the state of health, the temperature, and the like. The voltage also determines whether the current flows from the current path to the battery reservoir or from the battery reservoir to the current path.

[0011] An advantage of controlling the voltage across the battery storage is that this has the effect that the current to and from the battery storage can be controlled, and thus whether the battery storage is charging (storing energy) or discharging (delivering energy).

[0012] An advantage of a battery storage is that it has the effect of both an AC voltage or a DC voltage which can be connected to the current path.

[0013] The state of a semiconductor switch is to be understood as either a conducting mode in which the switch is closed to allow current to flow through the switch, or a non-conducting mode in which the switch is open to prevent current from flowing through the switch.

[0014] Preferably, the controller is controlling the state of the semiconductor switches of a plurality of battery cells. This is advantageous because it has the effect that the current path through the battery reservoir can be changed depending on the voltage on the battery (determined based on the reference current), the state of the switches, the state of the battery cells, the required voltage of the battery (DC or AC and its voltage level, such as 24V, 230V, 400V, etc.), etc. Thus, the control state comprises selectively controlling a series of activated (through the current path) and deactivated (bypassing the battery cells) battery cells. It is thereby possible to establish the voltage required at a given time (such as real-time demand), not just a predetermined voltage, and this from a non-predetermined configuration of the battery cells of the battery reservoir.

[0015] According to an embodiment of the present invention, the controller selectively controls the switch and thereby controls the current path. This is advantageous because after bypassing a battery cell, it can be passed through the current path again when needed.

[0016] According to an embodiment of the present invention, at least two semiconductor switches of each battery cell among a plurality of battery cells are mounted on a printed circuit board, wherein the printed circuit board is part of a control signal path between a controller and the at least two semiconductor switches, and wherein the printed circuit board is part of a current path through the battery cell.

[0017] Mounting the semiconductor switch on a PCB (PCB; printed circuit board) has the advantage of reducing the complexity of mass production and facilitating easy scaling of the size of the battery storage.

[0018] The disadvantage of building a battery storage of multiple battery cells including PCB mounted switches is that the size of the switch is reduced (in terms of the possible load current through a single switch). This will result in an increase in the number of battery cells compared to an embodiment using a larger sized switch without PCB mounting. On the other hand, the smaller sized switches are cheaper, which together with the reduced battery cell mass production costs and the increased flexibility in the battery storage design, compensates for the increase in the number of battery cells.

[0019] As an alternative to mounting on a PCB, the switch can be mounted on a busbar or laminated busbars.

[0020] According to an embodiment of the present invention, the control signal path and the current path are electrically isolated. It is advantageous to be able to separate the high voltage changes (e.g., ±1000V) on the switch that occur depending on the switch state from the control signal that controls the switch state. This has the effect that the high voltage does not interfere with the control signal.

[0021] Preferably, electrical isolation is facilitated by means of optical data communication, transformers etc. somewhere at the control signal path between the switch and the controller. Preferably, at the controller end or at the interface of the control signal path and the PCB.

[0022] According to an embodiment of the invention, the converter comprises a generator side converter and a grid side converter connected via a DC link.If the converter is not a back-to-back converter, the battery storage will be connected to the current path between the converter and the grid.

[0023] According to an embodiment of the invention, the battery storage is connected to the current path between the grid side converter and the grid. This is particularly advantageous if the converter is a full scale converter as it is easy to retrofit and helps reduce harmonic currents flowing to the grid.

[0024] The positive results of connecting the battery storage to AC voltage without an AC / DC converter surprised the inventors, since it turned out that due to the varying AC voltage pulses at least once per second and typically once per millisecond, no degradation of the battery elements of the battery cells occurred.

[0025] According to an embodiment of the invention, the battery storage is connected to the current path at the DC link between the generator side converter and the grid side converter. This is advantageous if the converter is full scale and in particular if the converter is for a wind turbine comprising a DFIG generator, as this solution is cheaper than a solution installed after the converter.

[0026] According to an embodiment of the invention, the battery storage is connected to the positive and negative rails of the DC link via a DC / DC converter. This is advantageous because the DC link voltage can be kept more stable and controlled, which is advantageous if an existing converter should be retrofitted with a battery storage.

[0027] According to an embodiment of the present invention, a controller is configured to control the state of at least two semiconductor switches in a plurality of battery cells, thereby regulating a voltage across a battery storage device, wherein the voltage is regulated based on a difference between a reference current established by the controller and a measured current provided to the controller, wherein the measured current represents a current conducted in a current path between the current path and a first battery cell of a column of battery cells connected in series in the battery storage device.

[0028] This is advantageous because it has the effect that the current to and from the battery reservoir can be controlled. Thus, if the reference voltage of the battery reservoir and thus the voltage across the battery reservoir is lower than the voltage of the current path, current will flow to the battery reservoir and charge the battery element. If the reference voltage of the battery reservoir (and thus the voltage across the battery reservoir) is higher than the reference voltage, current will flow, for example, from the battery reservoir to the grid of the wind turbine or to power consuming activities such as the start-up of the wind turbine (the battery element is discharged). If the reference voltage of the battery reservoir (and thus the voltage across the battery reservoir) is equal to the voltage of the current path, no current is established in the system and the state queue (que) in the battery reservoir is maintained. It should be mentioned that the voltage of the current path is the voltage at the current path to which the battery reservoir is connected.

[0029] The reference current is preferably derived by the controller from a power reference received from an external controller. However, the reference current may also be received by the controller from an external controller.

[0030] In a three-phase system, preferably one column of series-connected battery cells is connected to each phase. Therefore, the measured current can be found by a simple measurement between the current path and the first battery cell in any of the three columns. The real-time measured current reflects the real-time status of the current path, i.e. whether the battery storage is being discharged or charged.

[0031] Preferably, the current is measured between the battery reservoir and a location attached to the current path. The current sensor may be a conventional current sensor useful for measuring DC and / or AC current. The measured current may be derived from knowledge of the voltage and power that may be measured at the current path.

[0032] According to an embodiment of the invention, an external controller facilitates establishing a reference current depending on the state of the utility grid or the requirement for delivery from the wind turbine to the utility grid.

[0033] Preferably, the external controller provides the reference current to the controller. This is advantageous as it has the effect that the operation of the wind turbine can be operated more flexibly and in accordance with a wider range of requirements from the utility grid. Such requirements may include delivering a determined amount of power, holding a certain amount of power on standby, storing generated power during a grid blackout / failure.

[0034] According to an embodiment of the present invention, a battery storage comprises a plurality of columns of battery cells, wherein semiconductor switches of each column of battery cells are controlled by a separate controller, and wherein a master controller facilitates control of each of the separate controllers.

[0035] Therefore, preferably, each column of battery cells is controlled by a controller, and accordingly, in the case of, for example, three columns of battery cells, three controllers may be used, one for each column. A master controller may then be used to coordinate the control between each of these controllers. This is advantageous because it has the effect that more controllers may be used if the controller does not have sufficient legs to be able to connect and thereby control the switches. Furthermore, it has the effect that if the controller controlling the first column (i.e. phase) fails, the remaining columns may continue to operate. Furthermore, it has the effect that if each phase (i.e. column) is mounted in a separate panel, one controller may be used in each panel, whereby long wire connections may be avoided.

[0036] According to an embodiment of the invention, the battery unit comprises between 1 and 20 battery elements, preferably between 5 and 18 battery elements, most preferably 7 or 17 battery elements. The number of battery elements is determined based on the required capacity of the battery storage, the operating parameters of the system, etc. Preferably, the battery elements of the battery unit are connected in series.

[0037] According to an embodiment of the invention, the battery storage comprises one column of battery cells connected in series for each phase connected to the battery storage, wherein at least one battery cell in each column is connected to at least one battery cell in an adjacent column. The advantage of having only one column of battery cells connected in series is that it has the effect that the battery storage is cheaper.

[0038] According to an embodiment of the present invention, each battery cell in the battery cell includes four semiconductor switches and at least one battery element. The advantage of this configuration of the battery cell is that it has the following effect, one switch pair including switches 10a and 10b controls the current to and from the battery element in the first half of the AC voltage signal cycle, and the second switch pair including switches 10c and 10d controls the current to and from the battery element in the second half of the AC voltage signal cycle.

[0039] The four switches are preferably arranged in an H-bridge with the battery element in the middle. This arrangement of the battery cells has the advantage that the polarity of the current in the connection point of the battery reservoir to the current path can be changed. Therefore, the H-bridge arrangement is particularly advantageous when the battery reservoir is connected to the AC part of the current path.

[0040] According to an embodiment of the invention, the battery storage is connected to the wind turbine via a first UPS switch and a second UPS switch.

[0041] According to an embodiment of the present invention, a UPS controller is configured to control a first UPS switch and a second UPS switch to provide an AC voltage to a load in the event of a grid fault, wherein the AC voltage is generated by a battery cell string of a battery storage, wherein each of the battery cell strings is controlled by a controller.

[0042] According to an embodiment of the present invention, the controller or the battery storage controller is configured to bypass the switch controlling the battery cell by controlling the PCB bypass switch.

[0043] According to an embodiment of the present invention, a PCB bypass switch is implemented on a PCB.

[0044] According to an embodiment of the present invention, the controller is configured to control a switch of the battery storage so as to allow charging of only one battery cell at a time.

[0045] Furthermore, the present invention relates to a method for controlling current to and from a battery storage device electrically connected to a converter of an energy generator. The energy generator is generating current, which is conducted to a power grid via a current path through a power converter. The battery storage device is electrically connected to the current path. The battery storage device comprises a plurality of battery cells, each of which comprises at least one battery element and at least two semiconductor switches. Wherein, a controller controls the voltage on the battery storage device by controlling the state of each of the at least two semiconductor switches, and thereby controls the current path through the plurality of battery cells.

[0046] This is advantageous because it has the effect that a desired voltage can be generated across the series-connected battery elements of the battery storage, and control of the current to and from the battery storage can thereby be obtained.

[0047] According to an embodiment, the controller establishes a current error between a current reference of a desired current in the current path and a measured current in the current path, wherein the controller establishes a reference voltage based on the current error, and wherein the controller establishes a voltage across the battery reservoir by establishing a plurality of gate signals for controlling the state of a semiconductor switch and thereby a current path through one or more battery elements.

[0048] The above-described wind turbine and method of controlling the current to and from the battery storage of the energy generator is advantageous over conventional topologies / techniques because it is cheaper and thereby results in a reduction in capital expenditures for the wind turbine owner / operator / manufacturer. Furthermore, since the current battery storage is easy to replace and install (e.g., refurbish), operating expenses (operating expenses) are reduced. Furthermore, the operational reliability of the wind turbine is improved compared to conventional technologies because damaged battery elements can be bypassed, which does not affect the operation of the wind turbine.

[0049] The current reference may be established in an external controller and provided to the controller, or established in the actual controller, for example based on a power reference.Preferably, the reference current is a required current in the current path determined by the grid operator.

[0050] Preferably, the reference voltage is established by means of a closed loop controller such as a proportional resonant or a proportional integral derivative controller.

[0051] According to an embodiment of the present invention, a voltage reference is established based at least in part on a state of charge of a battery element.

[0052] This has the advantage that the state of charge of each of the battery elements can be kept substantially the same. In addition, the reference voltage and thus the state of the switch can be at least partially controlled at least partially depending on the state of health of the switch or the battery element. This is advantageous because it has the effect that the remaining life of the switch and the battery element can be more or less the same and in particular the load of the battery element can be distributed according to a desired pattern. Preferably, the switch is mounted on a printed circuit board.

[0053] According to an embodiment of the invention, the energy generator is a wind turbine or a solar energy system.

[0054] In addition, the present invention relates to a battery storage device electrically connected to a current path of an energy system including an energy generator and a load, the battery storage device including a plurality of battery cells, each battery cell including at least one battery element and at least two semiconductor switches, wherein a controller is configured to control the voltage on the battery storage device by controlling the states of the at least two semiconductor switches of the plurality of battery cells and thereby whether the current path through the battery storage device selectively bypasses at least one battery element of one or more battery cells of the plurality of battery cells, or passes through at least one battery element of one or more battery cells of the plurality of battery cells.

[0055] The energy generator is preferably a wind turbine or a solar system, but can also be a so-called black energy generator connected to the utility grid, and the current path preferably starts the generator and ends at the load. Thus, the battery storage of the invention can be connected anywhere between generating energy and using it.

[0056] According to an embodiment of the invention, the battery storage comprises the features of one or more of claims 2 to 19 .

[0057] According to an embodiment of the invention, the battery storage is connected to the current path via a first UPS switch and a second UPS switch.

[0058] According to an embodiment of the present invention, a UPS controller is configured to control a first UPS switch and a second UPS switch to provide an AC voltage to a load in case of a grid failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] For a more complete understanding of the present disclosure, reference is now made to the following brief description taken in conjunction with the accompanying drawings and detailed description, wherein like reference numerals represent like parts:

[0060] Figure 1 shows two positions of the battery reservoir relative to the converter,

[0061] Figure 2 FIG. 1 shows a portion of a battery storage device according to an embodiment of the present invention.

[0062] Figure 3 The control principle of the battery storage according to the embodiment of the present invention is shown.

[0063] Figures 4a to 4c shows a battery storage installed in the DC link in a back-to-back converter,

[0064] Figure 5a to Figure 5c shows a battery storage installed between a converter and a grid according to an embodiment of the present invention,

[0065] Figures 6a to 6c A battery storage device is shown for use as a UPS in a string, and

[0066] Figure 7 A fault tolerant switchboard is shown. DETAILED DESCRIPTION

[0067] Figure 1 Elements of a wind turbine 1 relevant to the present invention are shown. The wind turbine 1 comprises a rotor 2 connected to a rotor of a generator 3 via a shaft. Thus, when the rotor of the generator rotates, the generator generates a current at its output. The output of the generator 3 is connected to a first end of a current path 5, a second end of which is connected to a utility grid 4. Between the generator 3 and the utility grid 4, a converter is located in the current path 5. The converter 6 comprises a generator-side converter 6a connected to a grid-side converter 6b via a direct current (DC) link.

[0068] The battery storage 7 can be used in all types of energy systems, including wind turbine converters, including DFIG (DFIG: Doubly Fed Induction Generator) converters, full power 2-level back-to-back, full power 3-level back-to-back, MMC (MMC; M Modular Multilevel Converter), etc. The battery storage 7 can be located between the converter 6 and the grid 4 (in fact, it can be connected in the DC link), or can be located between the converter and the transformer including the stator path of the DFIG configuration (in fact, it can be placed on any AC or DC power line). In addition, the battery storage 7 can be used for all types of wind generators including induction generators, permanent magnet synchronous generators, doubly fed induction generators, synchronous generators, etc. In addition, the battery storage 7 can be used outside the wind turbine or other renewable energy generation system.

[0069] also, Figure 1 Two battery storages 7 are shown connected to the current path 5. It should be mentioned that usually only one battery storage 7 will be connected to the current path 5, so Figure 1 The illustrations above are only used to illustrate where preferably a battery storage 7 can be connected at the current path 5. In this way, two or more battery storages can be connected in parallel to facilitate simultaneous charging and discharging.

[0070] Figure 2 The design principle of a battery storage 7 including the smallest element of the battery storage 7 is shown. The battery storage 7 is composed of a plurality of battery cells 8. Each of the battery cells 8 comprises at least two semiconductor switches 10a, 10b and at least one battery element 9. The state of the semiconductor switch 10 is controlled by a controller 12, and thereby the controller 12 controls a current path 13 through each of the battery cells 8 of (preferably) the battery storage 7. It should be noted that the current path 13 is considered to pass through the battery cell 8 even if the battery element 9 is bypassed.

[0071] The manner in which the current path 13 passes through the battery reservoir 7 is determined by the state of the semiconductor switch 10 and is therefore controlled by the controller 12. The state of the semiconductor switch 10 is determined based on the availability of the battery elements / cells 8, 9, the state of health of the battery elements / cells 8, 9, the state of charge of the battery elements / cells 8, 9, the available charging voltage, the required / demanded voltage across / from the battery reservoir 7, the health / wear of the switch, etc. The dead time between changes from one state of the switch to another is preferably adjustable between 10 nanoseconds and 1 microsecond, typically this value is several hundred nanoseconds.

[0072] The availability of a battery element 9 may refer to a defective battery element, in which case the battery cell 8 would be unusable. The health of a battery element 9 may refer to the number of times a particular battery element 9 has been charged / discharged. The higher the number, the closer the end of the useful life of the battery element 9 is, and therefore the controller 12 may track this number and activate battery cells 8, attempting to keep this number roughly the same for all battery elements 9 of the battery reservoir 7. Likewise, the health of a switch may also be estimated based on the number of times it has been switched. The most important parameter for determining the state of the switch 10 is the voltage across the battery reservoir 7 as described above, which may be determined relative to the following: Figure 3 to describe.

[0073] Figure 2 The battery storage 7 shown in the figure comprises a first battery cell 8a and a second battery cell 8b, each of which comprises a plurality of battery elements 9a, ..., 9n. Due to the non-conducting state of the switch 10a and the conducting state of the switch 10b, the battery elements 9a-9n of the first battery cell 8a are bypassed. Due to the conducting state of the switch 10a and the non-conducting mode of the switch 10b, the battery elements 9a-9n of the second battery cell 8b are included in the current path 13.

[0074] As described above, the state of the switch 10 is controlled by the controller 12 communicating with the switch 10 via the control signal path 14. The controller 12 is preferably also connected to an external controller 16, which may be implemented as a wind turbine controller or a wind farm controller. Figure 3 The controller 12 is described in more detail. In addition, the controller 12 also preferably receives input from a current sensor 17 implemented in the current path 13 as shown.

[0075] The current path 13 needs to be electrically isolated from the control signal path 14 so as not to interfere with the state control of the switch 10. Figure 2 In the figure, electrical isolation 15 is shown at the controller 12, but this is only an example and it can also be at the battery storage 7, at the battery cell 8 or at the printed circuit board 11 (if any) on which the switch 10 is mounted. Electrical isolation can be established by optical data communication, optoelectronic data communication, with the help of a transformer. It should be mentioned that Figure 2 An example of battery cells 8 connected in series is shown, which will be referred to as a string. The battery storage 7 may include more strings, and in this case, preferably each string has its own controller 12. In this case, these string controllers 12 may communicate with a battery storage controller (not shown), which may again communicate with an external controller 16.

[0076] The number of battery cells 8 of the battery storage 7 can vary between 1 and 25 or even more, typically the battery cells 8 are connected in series in columns in the battery storage 7, wherein each column typically comprises between 5 and 20 battery cells 8. The number of battery cells 8 and thus the number of battery elements 9 is determined by the required voltage on the battery storage 7, which is preferably higher than the peak voltage of the grid 4. The storage capacity of the battery storage 7 is determined by the application in which the battery storage is used. Furthermore, the number of battery elements of a battery cell can vary, since the battery cells 8 do not have to be identical within the battery storage 7, and not even within a string. It is sufficient to update the string controller 12 / battery storage controller with the information behind the individual PCB switch boards 11.

[0077] Preferably, the switch is a semiconductor switch 10 of the IGBT (IGBT; Insulated Gate Bipolar Transistor), MOSFET (MOSFET; Metal Oxide Semiconductor Field Effect Transistor) type, GaN transistor (Gan; Gallium Nitride) or SiC transistor (SiC; Silicon Carbide), but other types of switches may also be used.

[0078] Preferably, commercial switches 10 are selected because they are well tested and inexpensive. Commercial switches are generally not designed to operate at high voltages (e.g., greater than 1000V) and high currents (e.g., greater than 500A), so there are more switches of this type than designs using switches designed for higher voltages and currents. However, the increased number is offset by the lower price of commercial switches. The preferred type of switch 10 used in the present invention is designed for a current of 100A and a voltage of 50V. At the higher voltages of the preferred type of switch, the on-resistance of the semiconductor switch 10 increases, and thereby the power consumption in the switch 10 increases.

[0079] Preferably, the reference to a battery element 9 is a reference to a plurality of battery elements connected in series. The number of battery elements may vary between 2 and 25 or even more in a column of battery elements 9 connected in series. Typically columns are between 10 and 20 battery elements 9 connected in series. The number of battery elements 9 in a column depends on the requirements of the battery storage 7 and on the compromise between a few cells 9, resulting in reduced price and reduced power consumption, and many cells 9, resulting in reduced harmonic current contribution and a more reliable system due to increased redundancy / flexibility of the control.

[0080] The battery element 9 is preferably of the lithium-ion type, since the characteristics of this battery type meet the requirements of the battery storage 7 and the environment of the wind turbine. Having said that, other battery types may also be used. For example, one battery element 9 may be a 3.2V element, which, when connected with, for example, 14 similar elements 9, results in a 48V battery pack within one battery cell 8. Thus, in this example, the battery cell 8 comprises a 48V battery, which may be controlled by the switch 10 of the battery cell 8. The capacity of the battery element 9 is preferably between 10Ah and 200Ah or even higher, but as mentioned above, this is a design choice based on the requirements for the battery storage 7 and the price of the system. In particular, in the preferred embodiment where the switch 10 is mounted on the PCB, the maximum current is determined to be the lower of the maximum current allowed by the current path through the PCB and the maximum battery current. In the case where the semiconductor 10 is not mounted on the PCB, the current limiting factor is the current limitation of the converter.

[0081] Figure 3 An embodiment of the present invention is shown, in which a battery storage 7 is used as an energy storage in an AC system. This embodiment shows a controller 12 according to an embodiment of the present invention and how to control the voltage on the battery storage 7. In a preferred embodiment, the controller 12 includes a control module 12a, a modulator module 12b and a subtraction node 12c. In addition, the controller 12 may also include a current reference generator 12d, which is only meaningful if the controller 12 itself needs to establish a reference current Iref (i.e., the current required in the current path 13 between the current path 5 and the battery storage 7).

[0082] Preferably, an external controller 16, such as a wind turbine controller, provides a power reference, such as an active and / or reactive power reference, or alternatively, a reference current Iref, to the controller 12. In this case, a current reference generator 12d establishes the reference current Iref therefrom based on information received from the external controller 16. If there are multiple strings, as mentioned, the external controller 16 communicates with a not shown battery storage controller, which again communicates with the string controller 12.

[0083] As mentioned, the reference current Iref is the required current in the current path 13 between the current path 5 and the battery storage 7. The reference current Iref is therefore a determining parameter for the current to and from the battery storage 7. The reference current Iref may therefore be determined based on a variety of different scenarios, preferably established by a requirement from the operator of the utility grid 4. A very simple example is that the wind turbine 1 is producing 1.5 MW, and the utility requires 2 MW, in which case the missing 0.5 MW must come from the battery storage 7. Therefore, according to the method described below, it is determined that the reference current Iref is at a level that causes a current to flow from the battery storage 7 to the current path.

[0084] Preferably, the actual current Imeas in the current path 13 between the current path 5 and the battery storage 7 is established by means of a simple current measurement by means of the current sensor 17. The polarity of the reference current Iref is determined for the current direction to the battery storage 7 (charging) or from the battery storage 7 (discharging). The difference between the reference current Iref and the measured current Imeas is used in the controller 12 to determine the series voltage across the battery cell 8 and thus to determine which (or more) of the battery elements 9 must be part of the current path 13 and which (or more) of the battery elements 9 must be bypassed.

[0085] Thus, if Iref is greater than Imeas, current should flow into the battery reservoir 7, if Iref is less than Imeas, current should flow out of the battery reservoir 7, and if Iref is equal to Imeas, no current should flow.

[0086] The required current is determined by the error Ierror found between Iref and Imeas at the subtraction node 12c. Ierror is used by the control module 12a to generate a reference voltage Vref, i.e. the voltage across the battery reservoir 7, which will initiate the required current. Based on the control loop feedback, the control module 12a can be implemented as a PR controller (PR; Proportional Resonance), a PID controller (PID; Proportional Integral Derivative) or other suitable controller.

[0087] The reference voltage Vref is then converted into a plurality of gate signals by the modulator module 12b to control the states of the switches 10 of the individual battery cells 8. Thus, a state pattern of the switches 10 in the individual battery cells 8 required to establish the reference voltage Vref across the battery reservoir 7 is created. Figure 5a An example of measuring this voltage reference Vref on the battery storage 7 is found on the grid side filter 21 and the output inductor 22 .

[0088] The current in the current path 13 is determined by the voltage on the battery storage 7 and the voltage of the current path 5. The voltage of the current path 5 can be determined by knowledge of the power, current or a simple voltage measurement by a voltage sensor. The voltage of the current path 5 can be found, for example, from measurements of the DC voltage in the DC link, the voltage between phases or zero potential, etc. Therefore, in order to be able to control the current to and from the battery storage 7, the battery storage voltage must be higher than the voltage of the current path to which the battery storage is connected. The current control is performed by the switch 10. If the switch does not have an embedded diode, such a diode should be implemented separately.

[0089] Due to the current measurement input to the feedback control loop of the controller 12, the current error Ierror and hence the voltage reference Vref and ultimately the state pattern of the switches are continuously updated.

[0090] As mentioned, if not all cells 8 are needed to establish the required voltage reference Vref / voltage on the battery reservoir 7, the controller 12 may not use the most used cell 8. The controller 12 is thereby able to distribute a load equal to all cells 8.

[0091] Figure 4a An example is shown how a battery storage may be integrated into a converter 6 of a wind turbine 1. As shown, a battery storage 7 is connected to a current path 5 in a DC link between a generator side converter 6a and a grid side converter 6b. Figure 4a The embodiment of shows two columns / strings of battery cells 8 connected in series that together form a battery storage 7. The switches 10 of the string are controlled by a separate string controller 12 that communicates with a battery storage controller 27, which in turn communicates with an external storage controller 16. This configuration shows one way of implementing a battery storage, so other configurations and other connection points of the battery storage 7 to the current path 5, the grid 4, the load 24, etc. are also possible. As indicated by the dotted line between two battery cells 8, the battery storage 7 may include further columns of battery cells 8 connected in series.

[0092] One controller 12 for controlling all battery cells 8 is possible, but as mentioned, one per string is preferred and is therefore not the only possibility for controlling the battery storage 7. Furthermore, a current sensor 17 is shown for measuring the current (Imeas) in the current path 13 between the battery storage 7 and the current path 5, but this is not the only possibility for measuring this current. Furthermore, one voltage sensor 18 is shown for measuring the voltage (Vref) across the battery storage 7, but this is not the only possibility for measuring this voltage.

[0093] like Figure 1 and Figure 4aAs shown above, the battery storage 7 can be integrated in the converter between the positive and negative DC rails of the DC link. Figure 4a An advantage of the implementation of the battery storage 7 shown above is that it may be cheaper and facilitate UPS functionality when, for example, a grid failure occurs.

[0094] Figure 4b is a preferred illustration of an electrical diagram of a battery cell 8 used in a battery storage 7 for connection to the DC portion of a current path 5. The battery cell shown comprises only two semiconductor switches 10. As shown, the semiconductor switches 10 comprise diodes, however, this is due to the fact that the semiconductor switches 10 shown are of the MOSFET type comprising internal diodes. Preferably, as shown, the two semiconductor switches 10 are mounted on a PCB 11.

[0095] The reason for having only two semiconductor switches 10 is that the battery storage 7 is connected to the DC link and is therefore only charged with current having one polarity and delivers current with the same polarity. This is consistent with the Figure 5a , Figure 5b The embodiment shown above is the opposite.

[0096] Figure 4c An alternative method of connecting a battery storage 7 to the DC link of the current path 5 is shown. Here, the connection is made via a DC / DC converter 19. The advantage of connecting via a DC / DC converter is that the DC link voltage can be kept more stable and controlled, which is advantageous in retrofitting an existing converter with a battery storage 7 as described in the prior art documents. It should be mentioned that, as an alternative to a DC / DC converter, a change in the control strategy of retrofitting a converter with a battery storage 7 can be made.

[0097] The design of the battery storage 7 and its control are not affected by the DC / DC converter, ie the design and control as described above.

[0098] Figure 5a An example is shown how a battery storage 7 may be integrated into a converter 6 of a wind turbine 1. As shown, the battery storage 7 is connected to a current path 5 between a grid-side converter 6b and the grid 4. Figure 5a The embodiment of the invention shows three columns (also called strings) of battery cells 8 connected in series, which together form a battery storage 7. Each of the three columns is connected to one of the three phases of the current path 5. Thus, each of the three phases can be regulated individually (at least with a phase shift of 120 degrees). Furthermore, in the case of support from the battery storage 7 to an asymmetric or unbalanced grid, the control of the phases in the battery storage 7 will be different from each other.

[0099] One controller 12 for controlling all battery cells 8 may be used, but this is not the only possibility for controlling the battery storage 7. Each column / phase / string may be controlled by its own controller 12, and then the master controller or battery storage controller 27 may coordinate the control of the controllers 12 of the individual columns / phases / strings as shown. In addition, each of the battery cells 8 may be controlled by a controller (not shown) based on control signals from the controller 12.

[0100] Furthermore, one current sensor 17 is shown for measuring the current (Imeas) in the current path 13 between the battery reservoir 7 and the current path 5, but this is not the only possibility for measuring this current. Furthermore, one voltage sensor 18 is shown for measuring the voltage (Vref) across the battery reservoir 7 (only one voltage sensor 18 is shown, but preferably one voltage sensor 18 per column of the battery reservoir 7), but this is not the only possibility for measuring this voltage.

[0101] As mentioned, the battery storage 7 may be integrated between the grid-side converter 6b and the utility grid 4, i.e. at the AC part of the current path 5. Figure 5a The implementation of the battery storage 7 shown above is particularly advantageous because it is easier to implement (retrofit) into existing systems. In addition, this location can help reduce grid harmonics and thereby reduce filter requirements.

[0102] exist Figure 5b 1 shows an electrical diagram of a battery cell 8 in a battery storage 7 preferably for connection to the AC part of the current path. Figure 4b In the electrical diagram shown above, the diode of the semiconductor switch 10 is the body diode of the MOSFET. Figure 5b The battery cell 8 shown above includes four semiconductor switches 10 as it must comply with the AC current and voltage, both negative and positive polarity, and still be able to bypass the battery cell 8 as described above. Figure 5b Only one battery element 9 in the battery cell 8 is shown, but it can be understood from the above description that there may be a plurality of battery elements 9 in the battery cell 8 .

[0103] Figure 5c Schematically shows Figure 5b The battery cell 8 and the switches 10 implemented on the PCB 11. The PCB is shown to include all four switches 10 and the gate drivers 20 that control the switches 10. Figure 5c The electrical isolation of the embodiment shown above is implemented as a part of the gate driver 20 .

[0104] From the above description, it is now clear that the present invention discloses a battery storage 7 for use in an electrical system such as a power grid 4 in connection with a wind turbine or the like. The battery storage 7 may be connected to a DC part or an AC part of an electrical system, such as a current path 5 of a utility grid 4 from a generator 3 to a wind turbine. The voltage Vref across the battery storage 7 is controlled based on the difference between a reference current Iref (a desired current flowing in a current path 13 between the current path 5 and the battery storage 7) and a measured current Imeas (measured in the current path 13 between the current path 13 and the battery storage 7).

[0105] If the reference voltage Vref is lower than the voltage of the current path 5 to which the battery storage 7 is connected, the battery storage 7 is charged. If the reference voltage Vref is higher than the voltage of the current path 5 to which the battery storage 7 is connected, the battery storage 7 is discharged.

[0106] In addition to the above features of the present invention, the present invention also helps to bypass defective battery cells to continue operation, monitor the state of health (SOH) on each battery element 9 to better plan battery replacement, and thereby reduce operating costs and active filtering, which can reduce the need for grid filter components.

[0107] Thus, the advantages of the present invention are that it facilitates energy storage and power converters in one solution. It reduces CAPEX through highly automated production and modular design. It facilitates high flexibility and scalability in terms of power and energy ratings. It reduces CAPEX due to extended battery life and the ability for predictive maintenance. It promotes higher reliability through modular design, thereby allowing continued operation during failures.

[0108] Through the integrated energy storage solution of the present invention, a cost-effective solution combining energy storage and power conversion in one solution is obtained. This new storage solution will significantly reduce CAPEX and OPEX while maintaining the scalability and flexibility of modular design and solving limitations such as high acquisition and maintenance costs, which hinder the widespread implementation associated with traditional solutions.

[0109] It should be mentioned that the battery storage 7 can also be used in a solar energy system that generates energy from one or more solar panels. In such an embodiment, the battery storage 7 will be controlled as described above and preferably connected between the solar energy system and the grid connected thereto.

[0110] Finally, it should be mentioned that, although described in different embodiments, the above features of the specification and the drawings of the present application can be combined together, since they all relate to the same invention. Therefore, an element shown in one figure may also be present in other figures even if it is not shown therein.

[0111] In an embodiment, the battery storage 7 (also referred to as energy storage) is understood as a so-called uninterruptible power supply (also referred to as UPS). When the battery storage is operated as a UPS, it can be operated as a UPS sometimes referred to as a string UPS and an offline UPS. Regardless of whether the battery storage 7 is operated as a string UPS or an offline UPS, it can be connected to the power system (such as the grid) as part of or connected to the wind turbine or as a separate device independent of the wind turbine, such as Figure 6a Such a UPS 22 is shown above. If connected to the grid as a standalone device, it can be used to support the grid voltage, frequency and power. In addition, it can be used as a buffer for energy storage to store energy until it is needed or at a point in time when the price is better than when it is produced.

[0112] A UPS 22 used outside a wind turbine typically requires a separate UPS controller 23. Figure 6a In the embodiment shown above, the UPS controller 23 receives information from the grid 4 and the controller 12 of the battery storage 7. In an embodiment, the UPS controller 23 also receives information from a load 24, which may be an electricity consumer or it may be another part of the grid 4. This information is used to control a first UPS switch 25 and a second UPS switch 26, the positions of which are used to connect or disconnect the battery storage 7 to the connection between the grid 4 and the load 24.

[0113] exist Figure 6a The embodiment shown above is superior to the classic string UPS solution. In the classic string UPS solution, the AC voltage on the grid 4 must be rectified to a DC voltage to be stored in the UPS solution, and then an inverter is required to subsequently generate the AC voltage for the load / grid. Therefore, the voltage needs to be processed by two converters, which results in low overall efficiency.

[0114] In this embodiment, Figure 6a The battery storage 7 shown above is a DC storage comprising at least one string of battery cells 8 generating an AC voltage corresponding to the relevant grid code requirements. The UPS switches 25, 26 are controlled by a UPS controller 23 which ensures that power for the load 26 is taken from the grid 4 during normal operation.

[0115] When the grid 4 is absent (or faulty), i.e. when operating abnormally, power is delivered by the battery storage 7. Figure 6aThe configuration of the UPS 22 shown above does not require a fast grid fault detection means. This is because the UPS switches 25, 26 are configured and controlled so that the power flow to the load is not disturbed. This is advantageous because for Figure 6a The UPS shown above can be used as energy storage to smooth power fluctuations on or to the grid, and can also be used as a DC UPS, etc.

[0116] Figure 6b Schematically shows how UPS switches 25, 26 are constructed. In this embodiment, UPS switches 25, 26 are bidirectional devices, i.e. two semiconductor switches 10, preferably IGBTs, where the input of switches 25, 26 is connected to the collector leg of a first IGBT 10a, and the output of switches 25, 26 is connected to the collector leg of a second IGBT 10b. The emitter legs of both IGBTs are connected together, and the gate legs of both IGBTs are connected to the UPS controller 23. Figure 6c It is shown that during two grid faults Figure 6b The switches 25 and 26 shown above are Figure 6a Examples of voltages and currents associated with the UPS configuration shown above. Grid faults occur at 0.42 and 0.65 (ending at 0.55 and 0.78 respectively) and as shown, these grid faults are barely noticeable on the "Load Voltage" and "Load Current" graphs. This is due to the coupling of the battery storage shown in the "Battery Storage Current" graph, which is performed by the UPS controller. Figure 7 A PCB 11 according to an embodiment of the present invention is shown. The PBC comprises cascaded coupled H-bridge switches 10, the state of which determines whether a current path 13 is passing through or bypassing a battery cell 8. As shown, an additional PCB bypass switch 28 is shown. This PCB bypass switch 28 is used in order to ensure that the current path 13 through the battery reservoir 7 is intact no matter what happens on the PCB. Thus, in the event of a faulty PCB or component thereof, the controller 12 (string controller or battery reservoir controller) is able to bypass the PCB 11 by closing the bypass switch 28. This is advantageous because it has the effect of making the battery reservoir 7 fault tolerant in terms of PCB faults such as converter faults (gate driver, switch faults), and thereby eliminating single point failures that may occur due to converter faults.

[0117] The bypass switch 28 can be implemented on the PCB, or as shown, external to the PCB. The advantage of implementing the bypass switch 28 on the PCB is that the switch system is easier to design and produce. Implementing the bypass switch 28 external to the PCB is advantageous because if the PCB fails, the bypass switch does not have to be replaced. In addition, the advantage of the implementation external to the PCB is that if the battery cell 8 or the PCB 11 is to be replaced, the bypass function that completely bypasses the battery cell 8 can be used.

[0118] therefore, Figure 7 One of the plurality of battery cells 8 of a battery storage 7 is shown, the current path 13 through the battery storage 7 being controlled by a semiconductor switch arrangement 10 implemented between two terminals of a PCB 11, wherein the semiconductor switch arrangement 10 comprises a controllable current connection, such as a bypass switch 28 between the two AC terminals, which in the event of a fault on the PCB helps to bypass the semiconductor switch arrangement 10. Here, the semiconductor switch arrangement is also referred to as a switch 10 in a so-called cascaded H-bridge.

[0119] Preferably, the bypass switch 28 is controlled by the controller 12 or the battery storage controller 27 .

[0120] An advantageous feature of the battery storage 7 of the present invention is that, due to the possibility of including only one battery cell 8 in the current path through the battery storage 7, it can be charged with a relatively low charging voltage. In order to be able to control the current flowing into the battery storage, the sum of the battery cell voltages must be higher than the absolute value of the charging voltage. Therefore, if the battery cells of the series connection of the battery cells reach, for example, 50V, and only one battery cell is to be charged, the voltage at the input / output of the H-bridge must be between up to 50V AC (peak) or 50V DC. The charging voltage must be lower than the battery voltage in order to be able to control the current of the MOSFET switch (when using a MOSFET switch), otherwise the anti-parallel diode will be turned on and the charging current cannot be controlled by the MOSFET control switch 10. This is particularly advantageous because in a wind turbine or solar energy system, the battery cell 8 can be charged if the voltage established only (according to the above example) is lower than 50V. In this way, when the rotor of the wind turbine is rotating but the wind speed is below the cut-in speed, the generated energy can be used to charge the battery cells 8 of the battery storage 7 one by one. Similarly, if the sun is not shining, the small amount of energy generated by the solar panel energy production plant can be stored in the battery storage 7.

[0121] The controller 12 is therefore provided with information of the voltage in the current path 5, i.e. knowledge of the available charging voltage is provided, which is then used to control the number of active battery cells 8 through the current path 13 of the battery storage 7 and thereby the number of individual battery cells 8 to be charged.

[0122] The type of energy storage device (different types of batteries (lithium ion, etc.), different types of capacitors (lithium capacitors, etc.)) used for the battery storage 7 of the present invention is preferably a lithium ion battery, but other types may also be used. The type is determined by the application in which the battery storage 7 is to be used. If, for example, the main purpose of the battery storage is to deliver a high peak current for a short period of time, a lithium ion battery that facilitates this current may be used in the same manner, and if the main purpose is to deliver a lower current for a long period of time, a lithium ion battery type that supports this current is selected.

[0123] As has become clear from the above, the invention describes a battery storage 7 comprising a plurality of controllable battery cells 8. The battery cells are selectively controllable, which means that by means of switches 10 they can be active or inactive in establishing the total voltage across the battery storage 7. The voltage across the battery storage 7 can be established by a plurality of different combinations of active battery cells 8. If one battery cell 8 is deactivated, another battery cell can be activated and if, for example, the state of charge of the first battery is again higher than the state of charge of the second battery, the battery storage voltage can continue to be established by activating the first battery while the second battery cell 8 is not activated.

[0124] The activation and deactivation of the battery cells are controlled by a switch 10, which is preferably located on a PCB 11. The switch configuration of the PCB 11 is preferably a cascaded H-bridge, and the switch is preferably controlled by a controller 12. In the case where the battery storage 7 comprises more than one string of battery cells 7 connected in series, preferably one string controller is used for each string in the string. Preferably, in such embodiments, the string controller communicates with the main battery storage controller. In this way, in principle any desired voltage can be established from the battery storage, because higher voltages only require more battery cells in series, and higher capacities only require more battery cells in parallel. Furthermore, it should be mentioned that it is possible to connect multiple strings in one large series battery cell by means of switches.

[0125] The battery storage 7 can be directly connected (e.g. without a DC / DC converter) to the electrical system in many different locations inside or outside the wind turbine. Internally on both sides of the converter or in its DC link. External to a wind turbine as part of a wind farm, as energy storage and / or grid support. In any case, during a grid failure, the battery storage 7 can be used for starting or powering one or more wind turbines as an auxiliary power source for yaw and pitch drives, etc.

[0126] Theoretically, there is no high voltage limit for the battery storage 7, and the main current limiter is the availability of the semiconductor switch 10. In a preferred embodiment of the invention, the voltage is about +-1000V, and about 100Arms.

[0127] Finally, it should be mentioned that even though the above description is only of battery cells 8 as described, capacitors can also be used to replace or support battery cells 8. For capacitors, the battery storage 7 is able to deliver or absorb high power in a short period of time, which may be relevant for grid support (if the frequency / voltage drops, the grid can be enhanced by the battery storage 7, if the frequency / voltage rises, the grid can absorb (by charging) power from the grid). Capacitors can be added as a separate string of battery storage 7, as one or more battery cells 8 connected when relevant. The battery storage 7 is able to provide reactive power for grid support. For batteries, the battery storage 7 is able to deliver lower power for longer periods of time, while for capacitors, the battery storage 7 is able to deliver higher power for short periods of time. Therefore, in the battery module 7 of the present invention, the combination of capacitors and batteries has advantages.

[0128] List

[0129] 1. Wind Turbines

[0130] 2. Rotor

[0131] 3. Generator

[0132] 4. Public Grid

[0133] 5. Current path (from generator to utility grid through wind turbine)

[0134] 6. Converter

[0135] a. Generator side converter

[0136] b. Grid-side converter

[0137] 7. Battery storage

[0138] 8. Battery Cell

[0139] 9. Battery components

[0140] 10. Semiconductor switches (10a, 10b, 10c and 10d for distinguishing switches of the same battery cell)

[0141] 11. Printed Circuit Board

[0142] 12. Controller

[0143] a.Control module

[0144] b. Modulator module

[0145] C. Subtraction Node

[0146] d. Current reference generator

[0147] 13. Current path (from the current path and through the battery storage)

[0148] 14. Control signal path

[0149] 15. Electrical isolation

[0150] 16. External Controller

[0151] 17. Current sensor

[0152] 18. Voltage sensor

[0153] 19.DC / DC Converter

[0154] 20. Gate driver

[0155] 21. Grid side filter

[0156] 22. UPS

[0157] 23.UPS controller

[0158] 24. Load

[0159] 25. First UPS switch

[0160] 26. Second UPS switch

[0161] 27.Battery storage controller

[0162] 28.PCB bypass switch

[0163] Iref. Reference current

[0164] Imeas measures current

[0165] Ierroe Error between reference current and measured current

[0166] Vref reference voltage.

Claims

1. A wind turbine (1), comprising: a rotor (2) which helps to rotate the rotor of a generator (3) and thereby generate electric current, a current path (5) configured to conduct the current to the grid (4) via a power converter (6), The battery storage (7) comprises a plurality of battery cells (8), each battery cell (8) comprising at least one battery element (9) and four semiconductor switches (10a-10d) in an H-bridge configuration, The plurality of battery cells (8) are connected in series via the H bridge, thereby forming a battery string. The controller (12) is configured to control the state of the four semiconductor switches (10a-10d) in the H-bridge of each individual battery cell in the plurality of battery cells (8), and thereby whether the current path (13) through the battery string and thus through the battery storage (7) is: - bypassing the at least one battery element (9) of one or more battery cells of the plurality of battery cells (8), or - the at least one battery element (9) passing through one or more battery cells of the plurality of battery cells (8), to control the voltage on the battery string and thus on the battery storage (7), The controller (12) is configured to control the H-bridge of at least one battery cell among the plurality of battery cells (8) of the battery string, and when the absolute value of the voltage of the current path (5) is lower than the voltage of one battery cell (8), the controller (12) is configured to connect the one battery cell (8) to the current path (5), thereby facilitating charging of one battery cell (8) of the battery string at this time.

2. The wind turbine according to claim 1, wherein: The controller (12) selectively controls the switches (10a-10d) and thereby controls the current path (13).

3. A wind turbine according to any one of claims 1 to 2, wherein: At least four semiconductor switches (10a-10d) of each battery cell in the plurality of battery cells (8) are mounted on a printed circuit board (11), wherein the printed circuit board (11) is part of a control signal path (14) between the controller (12) and the at least four semiconductor switches (10a-10d); and The printed circuit board (11) is part of the current path (13) through the battery cell (8).

4. A wind turbine according to claim 1, wherein: The converter (6) comprises a generator-side converter (6a) and a grid-side converter (6b) connected via a DC link.

5. The wind turbine according to claim 4, wherein: The battery storage (7) is connected to the current path (5) between the grid-side converter (6b) and the grid (4).

6. The wind turbine according to claim 4, wherein: The battery storage (7) is connected to the current path (5) at a DC link between the generator side converter (6a) and the grid side converter (6b).

7. The wind turbine according to claim 6, wherein: The battery storage (7) is connected to the positive and negative rails of the DC link via a DC / DC converter.

8. A wind turbine according to claim 1, wherein: The controller (12) is configured to control the states of the at least four semiconductor switches (10a-10d) of a plurality of battery cells (8), thereby regulating the voltage across the battery storage (7). wherein the voltage is adjusted based on a difference between a reference current (Iref) established by the controller (12) and a measured current (Imeas) provided to the controller (12), Therein, the measured current (Imeas) represents the current conducted in the current path (13) between the current path (5) and a first battery cell (8) of a column of battery cells (8) connected in series of the battery storage device (7).

9. A wind turbine according to claim 1, wherein: An external controller (16) facilitates establishing a reference current (iref) depending on the state of a utility grid or a requirement for delivery from the wind turbine to the utility grid.

10. A wind turbine according to claim 1, wherein: The battery storage (7) comprises a plurality of columns of battery cells (8), wherein the semiconductor switches (10a-10d) of the battery cells (8) of each column are controlled by individual controllers (12), and wherein a master controller facilitates control of each of the individual controllers (12).

11. A wind turbine according to claim 1, wherein: The battery unit (8) comprises between 1 and 20 battery elements (9).

12. A wind turbine according to claim 1, wherein: The battery cell (8) comprises between 5 and 18 battery elements.

13. A wind turbine according to claim 1, wherein: The battery unit (8) comprises 7 or 17 battery elements (9).

14. A wind turbine according to claim 1, wherein: The battery storage (7) comprises a column of serially connected battery cells (8) for each phase connected to the battery storage (7), wherein at least one battery cell (8) in each column is connected to at least one battery cell (8) in an adjacent column.

15. A wind turbine according to claim 1, wherein: The battery storage (7) is connected to the wind turbine via a first UPS switch (25) and a second UPS switch (26).

16. The wind turbine of claim 15, wherein: The UPS controller (23) is configured to control the first UPS switch (25) and the second UPS switch (26) in case of a grid failure so as to provide an AC voltage to the load (24). The AC voltage is generated by a string of battery cells (8) of the battery storage (7), wherein each of the strings of battery cells (8) is controlled by a controller (12).

17. A wind turbine according to claim 1, wherein: The controller (12) or the battery storage controller (27) is configured to bypass the switches (10a-10d) controlling the battery cells (8) by controlling the PCB bypass switches (28).

18. The wind turbine of claim 17, wherein: The PCB bypass switch is implemented on the PCB (11).

19. A method of controlling the current to and from a battery storage (7) of a power converter (6) electrically connected to an energy generator, in, The energy generator is generating an electric current which is conducted to the grid (4) via a current path (5) through the power converter (6), The battery storage (7) is electrically connected to the current path (5), The battery storage (7) comprises a plurality of battery cells (8), each battery cell (8) comprising at least one battery element (9) and at least four semiconductor switches (10a-10d) in an H-bridge configuration, The plurality of battery cells (8) are connected in series via the H bridge, thereby forming a battery string. wherein the controller (12) controls the voltage on the battery string and thereby the battery storage (7) by controlling the state of each of the at least four semiconductor switches (10a-10d) in the H-bridge of each individual battery cell in the plurality of battery cells (8) and thereby controlling the current path (13) through the plurality of battery cells (8), The controller (12) is configured to control the H-bridge of at least one battery cell among the plurality of battery cells (8) of the battery string, and when the absolute value of the voltage of the current path (5) is lower than the voltage of one battery cell (8), the controller (12) is configured to connect the one battery cell (8) to the current path (5), thereby facilitating charging of one battery cell (8) of the battery string at this time.

20. The method according to claim 19, wherein: The controller (12) establishes a current error (Ierror) between a current reference (Iref) of a desired current in the current path (13) and a measured current (Imeas) in the current path (13), The controller (12) establishes a voltage reference (Vref) based on the current error (Ierror), and Therein, the controller (12) establishes the voltage across the battery storage (7) by establishing a plurality of gate signals for controlling the states of the semiconductor switches (10a-10d) and thereby the current path (13) through one or more battery elements (9).

21. The method according to claim 20, wherein: The voltage reference (Vref) is established at least in part based on the state of charge of the battery element (9).

22. The method according to any one of claims 19 to 21, wherein: The energy generator is a wind turbine or a solar energy system.

23. A battery storage (7) electrically connected to a current path of an energy system comprising an energy generator and a load, the battery storage (7) comprising a plurality of battery cells (8), each battery cell (8) comprising at least one battery element (9) and at least four semiconductor switches (10a-10d) in an H-bridge configuration, in, The plurality of battery cells (8) are connected in series via the H bridge, thereby forming a battery string. The controller (12) is configured to selectively: - bypassing the at least one battery element (9) of one or more battery cells of the plurality of battery cells (8), or - the at least one battery element (9) passing through one or more battery cells of the plurality of battery cells (8), to control the voltage on the battery string and thus on the battery storage (7), The controller (12) is configured to control the H-bridge of at least one battery cell among the plurality of battery cells (8) of the battery string, and when the absolute value of the voltage of the current path (5) is lower than the voltage of one battery cell (8), the controller (12) is configured to connect the one battery cell (8) to the current path (5), thereby facilitating charging of one battery cell (8) of the battery string at this time.

24. A battery storage according to claim 23, comprising the features according to one or more of claims 2 to 18.

25. The battery storage (7) according to any one of the preceding claims 23 to 24, wherein: The battery storage (7) is connected to the current path (5) via a first UPS switch (25) and a second UPS switch (26).

26. The battery storage (7) according to claim 25, wherein: A UPS controller (23) is configured to control the first UPS switch (25) and the second UPS switch (26) to provide an AC voltage to a load (24) in the event of a grid failure.

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