Active balancing of energy storage preferably at module level and rack level

Abstract

The present invention provides an energy storage unit comprising: a plurality of energy storage sub-units connected in series; and one or more transformers, wherein each of the plurality of energy storage sub-units is also connected together in parallel via the one or more transformers; wherein the one or more transformers comprise a core having a plurality of windings wound therearound.

Description

Technical Field

[0001] This disclosure relates to an energy storage unit, a system comprising two such energy storage units, and a method for providing the energy storage unit. Background Technology

[0002] For grid-connected energy storage (ES) units, the effective capacity is lower than the actual installed capacity due to imbalances between battery / supercapacitor modules (energy storage sub-units). Ideally, all energy storage sub-units should have identical characteristics, and the installed capacity should match the effective capacity. However, due to parameter tolerances and varying load current distributions, perfect load distribution is impossible without additional balancing circuitry. Therefore, oversized designs are required, significantly increasing system (energy storage unit) costs. A good balancing circuit is crucial for reducing oversized design and system cost, as well as increasing effective system capacity.

[0003] For certain energy storage units, energy storage sub-units can be sourced from external suppliers. These sub-units should also be integrated into the energy storage unit using some form of balancing circuitry and / or balancing method. As a system integrator, the energy storage unit should possess module-level balancing capabilities to reduce system costs, while remaining independent of the supplier to ensure secure supply change management and lower procurement prices.

[0004] By means of the features of the independent claims, the aforementioned disadvantages are at least partially overcome and / or the aforementioned advantages are at least partially achieved. The dependent claims define the preferred embodiments of the invention. Summary of the Invention

[0005] This disclosure relates to an energy storage unit comprising: a plurality of energy storage sub-units connected in series; and one or more transformers, wherein each of the plurality of energy storage sub-units is further connected in parallel via one or more transformers; wherein the one or more transformers include a core having a plurality of windings wound around it.

[0006] There are two pairs of connections from each of the multiple energy storage sub-units. First, a series connection for the multiple energy storage sub-units. Second, each of the multiple energy storage sub-units is connected to one or more transformers. This second connection can also be a connection to the same coupling point. This coupling point can be a transformer (such as a transformer with more than two windings, for example...). Figure 2 (as shown) and / or the coupling point can be a bus (such as, for example) Figure 1 (As shown in the diagram). Preferably, each energy storage sub-unit has two poles (connections). Both pairs of connections are connected to these two poles. This means that these two different connections are also coupled to each other.

[0007] The second connection—a parallel connection—can be made via one or more transformers (one or more transformers) at the bus, or it can be to a single transformer (such as a transformer with more than two windings, for example...). Figure 2 The connection shown in the diagram can be made in a different way.

[0008] The transformer including the core can be a single transformer including the core, or it can be more than one transformer, each transformer having a core (one of the transformers includes the aforementioned core). The multiple windings wound around the core can be two or more windings. The multiple windings wound around the core can be two or more windings connected to multiple energy storage sub-units.

[0009] Different energy storage sub-units can be similar to or different from each other. This may involve each of the criteria such as capacity, voltage, and conditions. Similarity is preferably within ±10%, ±5%, or ±1%.

[0010] The bus can be a multiphase bus. It can be configured for DC and / or AC. For example, a multiphase AC bus implementation is superior to a single-phase AC bus. Ripple will differ.

[0011] This disclosure allows for balancing the electrical load of different energy storage sub-units (via one or more transformers). This can increase effective system capacity and extend the lifespan of the energy storage sub-units. The system can be made smaller, simpler, and less expensive. Manufacturing a system or energy storage unit from multiple energy storage sub-units is also easier, especially when these components (such as energy storage sub-units) are purchased as a whole (e.g., for system integrators). Modifications to these components may not be necessary. Balancing using active balancing circuits is particularly robust and efficient. The power of the converter (transformer) can be determined based on the required balancing speed. One or more transformers can provide current isolation.

[0012] Various embodiments may preferably achieve the following features.

[0013] Preferably, one or more transformers are a single transformer, and each of the multiple energy storage sub-units is connected to one of the multiple windings.

[0014] A transformer (as one or more transformers) may have more than two windings. Preferably, the number of windings is equal to the number of energy storage sub-units connected to the transformer plus one. Each connected energy storage sub-unit may be connected to a different winding, while the remaining windings may be connected to a bus.

[0015] Using this embodiment, the total number of transformers can be reduced, thereby reducing costs and space requirements.

[0016] Preferably, the transformer is connected to the bus via another winding wound around the core.

[0017] There may be one or more other windings wound around the core and connected to different phases of the bus (if the bus has different phases). Preferably, there is current isolation between the multiple energy storage sub-units and the bus.

[0018] Balancing can occur via the bus.

[0019] Preferably, the transformer is a multiphase transformer.

[0020] It is also possible to have more than one phase connected from each (or some) of multiple energy storage sub-cells (which can provide more than one phase). In this case, there can be more windings wrapped around the core than the number of energy storage sub-cells plus one (or the number of phases of the bus). Conversely, the number of windings can be the sum of the number of all phases of the multiple energy storage sub-cells plus the number of phases of the bus.

[0021] Preferably, the one or more transformers are multiple multiphase transformers having three or more phases, wherein each transformer is connected to one of a plurality of energy storage sub-units on a first side.

[0022] In this case, the same coupling point to which multiple energy storage sub-units are connected (see “Connection to the same coupling point” above) and the places where multiple energy storage sub-units are connected in parallel can be a bus.

[0023] By using multiple multiphase transformers, multiphase energy can be provided and / or balanced (e.g., via a bus).

[0024] Preferably, the number of energy storage sub-units is equal to the number of multiphase transformers. In this case, each transformer can be connected to a different one of the multiple energy storage sub-units. Multiphase connections can exist between each pair of transformers and energy storage sub-units (which can provide multiple phases connected to different windings of the transformers).

[0025] Preferably, each of the multiple multiphase transformers is connected to the bus via another winding wound around the core of the corresponding transformer. Each of the multiple multiphase transformers may be connected to the bus in a multiphase manner via multiple (preferably phase-wise) windings wound around the core of the corresponding transformer. Preferably, these multiple windings are connected only to the bus and not to any of the multiple energy storage sub-units. Preferably, there is current isolation between the multiple energy storage sub-units and the bus.

[0026] The number of transformers may be less than the number of energy storage sub-units. There may be a mixture of transformers connected to several energy storage sub-units (as described above) and transformers connected to only one energy storage sub-unit (which may be single-phase or multi-phase). In cases where energy storage sub-units have different voltages, it is preferable to connect different transformers (and / or converters) to provide similar voltages at the bus.

[0027] Preferably, one or more transformers are connected to the bus using an AC-DC converter.

[0028] An AC-DC converter can be connected between the corresponding transformer and the bus (an indirect connection between the corresponding transformer and the bus, because there is something connecting them). Alternatively, it can be a direct connection (because there is nothing connected between the corresponding transformer and the bus except for this connection). Alternatively, an AC-DC converter can be connected between the converter and the bus, and then a DC-AC converter can be connected thereafter.

[0029] Preferably, the bus is configured for alternating current (AC). In this case, it is preferable that there is no converter between each strainer and the bus, or that there is an AC-DC converter followed by a DC-AC converter connection.

[0030] Preferably, the bus is configured for direct current (DC). In this case, it is preferable to connect an AC-DC converter between each strain gauge and the bus.

[0031] Preferably, the energy storage unit further includes power electronic circuitry connected between one of the energy storage sub-units and one of one or more transformers.

[0032] Preferably, the energy storage unit further includes multiple power electronic circuits, each of which is connected between a corresponding circuit in the energy storage subunit and a transformer. The power electronic circuits may be converters.

[0033] Preferably, the power electronic circuit includes a DC-AC converter.

[0034] Power electronic circuits may include AC-DC converters, DC-AC converters, full-bridge converters, three-phase (or more phase) converters, single-phase converters, isolated DC-DC converters, and / or rectifiers with diodes or thyristors. Several power electronic circuits may exist, each located between a different pair (or group) of energy storage sub-units and transformers. In the case where several energy storage sub-units are connected to a transformer, it is preferable to have a power electronic circuit (preferably a similar circuit) between each energy storage sub-unit and the transformer.

[0035] Preferably, each of the plurality of energy storage sub-units is a direct current (DC) energy storage unit.

[0036] Preferably, the energy storage unit is an energy storage module, and multiple energy storage sub-units are multiple energy storage cells. The energy storage cells can be batteries, accumulators, etc.

[0037] Preferably, the energy storage unit is an energy storage rack, and the multiple energy storage sub-units are multiple energy storage modules.

[0038] Multiple energy storage modules can be configured as energy storage units as described above—thus creating the structure of this disclosure at two levels (rack-to-module level and module-to-cell level). An energy storage module may include multiple energy storage cells.

[0039] This disclosure also relates to a system comprising two energy storage units as described above.

[0040] The two energy storage units can be similar or identical to each other (in setup and components), or they can be different: for example, one transformer is connected to several energy storage sub-units, while the other transformer is connected to only one energy storage sub-unit.

[0041] Preferably, the two energy storage units in the system are connected to a bus. The two energy storage units are connected to each other in parallel via the bus.

[0042] This can make setup easier, for example, by building the system in a modular way. It can reduce costs.

[0043] This disclosure also relates to a method for providing an energy storage unit, comprising: providing a plurality of energy storage sub-units connected in series; providing one or more transformers; and connecting each of the plurality of energy storage sub-units in parallel via the one or more transformers; wherein the one or more transformers include a core having a plurality of windings wound around it.

[0044] Preferably, the method further includes connecting each of the plurality of energy storage sub-units in parallel via one or more transformers by connecting a power electronic circuit between one of the transformers and one of the plurality of energy storage sub-units.

[0045] The advantages described are neither limited to nor exclusive to these aspects. One aspect may have additional advantages that are not explicitly mentioned. Attached Figure Description

[0046] The exemplary embodiments disclosed herein are intended to provide features that will become apparent from the following description and in conjunction with the accompanying drawings. Exemplary systems, methods, apparatuses, and computer program products are disclosed herein according to various embodiments. However, it should be understood that these embodiments are provided as examples and not as limitations, and that various modifications can be made to the disclosed embodiments without departing from the scope of this disclosure, as will be apparent to those skilled in the art upon reading this disclosure.

[0047] The foregoing and other aspects, as well as their implementations, are described in more detail in the accompanying drawings, specification, and claims.

[0048] Figure 1 An exemplary energy storage unit having a three-phase AC bus and multiple multiphase transformers according to an embodiment of the present disclosure is shown.

[0049] Figure 2 An exemplary energy storage unit having a multi-winding transformer is shown according to an embodiment of the present disclosure.

[0050] Figure 3 An exemplary energy storage unit having a multi-winding transformer is shown according to an embodiment of the present disclosure.

[0051] Figure 4 An exemplary energy storage unit having a multi-winding transformer is shown according to an embodiment of the present disclosure.

[0052] Figure 5a and Figure 5b The converter is shown; Figure 5c A three-phase diode rectifier according to an embodiment of the present disclosure is shown.

[0053] Figure 6 A system of two connected energy storage units according to an embodiment of the present disclosure is shown.

[0054] Figure 7 This describes a method for providing an energy storage unit according to an embodiment of the present disclosure. Detailed Implementation

[0055] Figure 1 An exemplary energy storage unit 10 is shown, comprising a three-phase AC bus 12 and multiple multiphase transformers 14 (14a, 14b, and 14c) (as one or more transformers 14). The energy storage unit 10 also includes multiple energy storage sub-units 16 (16a, 16b, and 16c) and optional converters 18 (18a, 18b, and 18c). The energy storage sub-units 16 are connected in series at connection point 20. The energy storage sub-units 16 are also connected in parallel via the multiple transformers 14 and the bus 12.

[0056] In this figure, three energy storage sub-units 16 and three transformers 14 are shown as a plurality. Alternatively, there may be two or more energy storage sub-units 16 and two or more transformers 14 connected in this manner (as a plurality). The load of the energy storage sub-units 16 can be balanced via transformers 14 and may also potentially via bus 12. In this figure, transformers 14 and bus 12 are used for multiphase (three-phase in this case). More (four or more) or fewer (single or two) phases are also possible. Converter 18 is preferably a DC-AC converter.

[0057] Energy storage subunit 16 is preferably a DC energy storage subunit. Each of the converters 18 may also include several components (such as one or more of a DC-AC converter, AC-DC converter, full-bridge converter, three-phase (or more phase) converter, single-phase converter, isolated DC-DC converter, power electronic circuitry, and / or rectifier with diodes or thyristors). Transformers 14a to 14c preferably have two sets of windings (one set connected to the respective energy storage subunit 16 and the other set connected to the bus 12). Each set is shown as having three windings (according to three phases). More or fewer windings are possible (preferably according to the number of phases). Preferably, the two sets of windings have the same number of windings.

[0058] An additional converter may be present between transformer 14 and bus 12. These additional converters may include one or more of the following: DC-AC converter, AC-DC converter, full-bridge converter, three-phase (or more) converter, single-phase converter, isolated DC-DC converter, power electronic circuit and / or rectifier with diodes or thyristors.

[0059] Bus 12 can be an electrical conductor, such as a cable. Bus 12 can have one or more phases. Bus 12 can be a high-frequency (HV) AC bus. Bus 12 can be connected to other energy storage sub-cell strings. Transformer 14 can be selected to provide voltage on the bus side, thus allowing thin cables to be used as bus 12. Bus 12 can also be connected to an auxiliary power supply.

[0060] This setup can be easily and cost-effectively assembled from its components (energy storage sub-unit 16, transformer 14, etc.). These components can be supplied (purchased) as a whole. These components can then be assembled together in the disclosed manner.

[0061] Figure 2 An exemplary energy storage unit 10 with a multi-winding transformer 14 (as one or more transformers 14) is shown. Because... Figure 2 Many components in Figure 1 The same or similar components are not described here, therefore they are referenced here. Figure 1 Described Figure 1 and Figure 2 The difference between them.

[0062] Figure 2 The transformer 14 is a multiphase transformer with more than two windings. The transformer 14 shown has six windings—three corresponding three phases connected to the bus 12, and each of the other three windings connected to a different energy storage sub-unit 16. Alternatively, different numbers of windings are possible. Preferably, the number of windings connected to the bus is equal to the number of phases of the bus (or it can be twice or another multiple of the number of windings connected to the energy storage sub-units 16). More than one phase can be connected to the transformer 14 from each energy storage sub-unit 16 (possibly via a countercurrent transformer 18). In this case, each phase can be connected to a different winding of the transformer 14. The total number of windings connected to the energy storage sub-units 16 can be the total number of phases on the multiple energy storage sub-units 16. When the number of phases from each energy storage sub-unit 16 is the same, the number of windings connected to the energy storage sub-units 16 can be the number of energy storage sub-units 16 multiplied by the number of phases from each energy storage sub-unit 16. The transformer 14 can be selected to provide voltage on the bus side, thus allowing thin cables as the bus 12.

[0063] Figure 3 An exemplary energy storage unit 10 with a multi-winding transformer 14 (as one or more transformers 14) is shown. The energy storage unit 10 may include the same / similar components as described in other figures. Figure 3 The exemplary energy storage unit 10 illustrates multiple energy storage sub-units 16, multiple converters 18, and multiple primary-side windings 22 (22a, 22b, and 22c), wherein the multiple comprises three or more of each (two are also possible). The converters 18 are DC-AC converters. The transformer 14 includes a primary-side winding 22 and a secondary-side winding 24. The secondary-side winding 24 can be connected to a bus 12. The energy storage unit 10 is also capable of balancing (redistributing) energy among the energy storage sub-units 16 without requiring a secondary-side winding 24 (and without the potential bus 12).

[0064] Figure 4 An exemplary energy storage unit 10 with a multi-winding transformer 14 (as one or more transformers 14) is shown. Because... Figure 4 Many components in Figure 3 China (also with) Figure 1 and Figure 2 The same or similar components (as described in the text) that are not further described here are therefore referenced here. Figure 3 (as well as Figure 1 and Figure 2 ). Described Figure 3 and Figure 4 The difference between them.

[0065] Figure 4 The energy storage unit 10 also includes an AC-DC converter 26 connected to the secondary winding 24. The AC-DC converter 26 can be connected to a bus 12 (preferably a DC bus in this case) on the other side. The AC-DC converter 26 may alternatively be or include a DC-AC converter, an AC-DC converter, a full-bridge converter, a three-phase (or more phases) converter, a single-phase converter, an isolated DC-DC converter, power electronic circuitry, and / or a rectifier with diodes or thyristors. The converter 26 may be an additional converter as mentioned above.

[0066] Figure 5a and Figure 5b The converter is shown; and Figure 5c A three-phase diode rectifier is shown.

[0067] Figure 5a An energy source (likely energy storage sub-unit 16) and a MOSFET-based full-bridge single-phase inverter are shown (as an example for converter 18). Figure 5a The system shown can be an example of an energy storage sub-unit 16 with a converter 18 (or for each of these components) as shown in the previous figures. The fundamental frequency of the AC bus can be selected to minimize the size and cost of the transformer. Due to the nature of single-phase voltage and current, second harmonics may be present on the DC side, and filter capacitors can be further included to reduce the impact of harmonics on the lifespan of the energy storage sub-unit.

[0068] Figure 5b An energy source (likely energy storage sub-unit 16) and a MOSFET-based full-bridge three-phase inverter are shown (as an example for converter 18). Figure 5b The system shown can be an example of an energy storage subunit 16 with a converter 18 (or for each of these components) as shown in the previous figures. Figure 5b and Figure 5a Similarly. However, to reduce the capacitance of the filter capacitor, the AC frequency can be increased or a different method can be used. Figure 5b A three-phase converter. The rated voltage of the MOSFET is determined by the energy storage sub-cell.

[0069] Both single-phase and three-phase inverters are widely available and inexpensive. R&D costs can be minimized, and multiple suppliers ensure a secure supply chain.

[0070] Figure 5c An exemplary three-phase diode rectifier is shown. This could be an example of converter 18 (a portion thereof) or an additional converter (26) between transformer 14 and bus 12.

[0071] When using a rectifier with diodes or thyristors, balancing can work in such a way that the minimum voltage of the module is limited by the AC bus.

[0072] Figure 6 A system with two connected energy storage units 10 is shown. Each of the two energy storage units 10 can be any energy storage unit 10 as described in this disclosure. The system also includes a link 28 (which may be connected in parallel). Link 28 may be an electrical connection. Link 28 may be made of the same components ( / materials) as bus 12. Link 28 enables energy exchange between the two energy storage units 10. Transformer 14 may also include a converter (such as converter 18).

[0073] exist Figure 6 In this case, the energy storage sub-unit 16 can be an energy storage cell, the two energy storage systems 10 are energy storage modules, and the system is an energy storage rack. Alternatively, the energy storage sub-unit 16 can be an energy storage module, the energy storage unit 10 can be an energy storage rack, and the entire system is a combination of racks. Two or more energy storage units 10 can be connected using links 28 or multiple links 28.

[0074] Figure 7 This describes a method 70 for providing energy storage unit 10. Method 70 includes several steps. In step 72, a plurality of energy storage sub-units 16 are provided in series. In step 74, one or more transformers 14 are provided. In step 76, each of the plurality of energy storage sub-units 16 is connected in parallel via the one or more transformers 14. The one or more transformers 14 include a core having a plurality of windings 22, 24 wound around it.

[0075] Method 70 may include step 76: connecting each of the plurality of energy storage sub-units 16 in parallel via one or more transformers 14, which can be accomplished by connecting a power electronic circuit between one of the one or more transformers 14 and one of the plurality of energy storage sub-units 16.

[0076] The described energy storage unit 10 (and Figure 6 The system (can be an AC or DC microgrid) can be controlled based on the SoC and / or SoH of the energy storage sub-unit 16.

[0077] The energy storage unit 10 described herein (described throughout the disclosure) may include a single-phase inverter of 200W to 1000W. These inverters may be compact enough to undertake balancing tasks.

[0078] In an alternative, the energy storage unit 10 described (as described throughout the disclosure) may include an inverter having one or more of the following requirements: • Rated power: 200W - 1kW (depending on the application).

[0079] • Insulation class: <1.5kV DC.

[0080] • AC frequency: 50Hz - 10kHz (depending on the detailed design of the PD stage).

[0081] • AC voltage: 110V - 1000V AC peak (depending on the detailed design of the PD stage).

[0082] • DC voltage: Module voltage 50V - 200V DC (depending on the application).

[0083] • Cooling: Forced air cooling or natural cooling.

[0084] • Transformer primary-to-secondary isolation: 1.5kV DC or 1kV AC rms.

[0085] • Transformer frequency: Same as AC frequency.

[0086] The topologies disclosed herein encompass many cost-effective and practical solutions. This differs from conventional solutions, which teach different system topologies for a specific converter. For example, diode rectifiers are a low-cost and reliable technology. Using diode rectifiers simplifies cost and mechanical integration.

[0087] The transformer configuration provides system flexibility, allowing the use of multi-winding transformers. From a practical perspective, this reduces the number of components and allows for a more compact design.

[0088] The benefit of this disclosure is that it reveals system architectures employing different topologies. In effect, this architecture allows manufacturers to use any off-the-shelf component without needing to know the internal topology of that component. The topology in this application can be a common topology found in off-the-shelf components, but having these topologies is not mandatory.

[0089] While various embodiments of this disclosure have been described above, it should be understood that they are presented by way of example only and not as limitations. Similarly, the various figures may depict exemplary architectures or configurations provided to enable those skilled in the art to understand the exemplary features and functionality of this disclosure. However, those skilled in the art will understand that this disclosure is not limited to the illustrated exemplary architectures or configurations, but can be implemented using various alternative architectures and configurations. Furthermore, as those skilled in the art will understand, one or more features of one embodiment may be combined with one or more features of another embodiment described herein. Therefore, the breadth and scope of this disclosure should not be limited to any of the exemplary embodiments described above.

[0090] It should also be understood that any reference to elements in this document using names such as “first”, “second”, etc., generally does not restrict the number or order of these elements. Rather, these names may be used herein as a convenient way to distinguish two or more elements or instances of elements. Therefore, references to the first element and the second element do not imply that only two elements can be used, or that the first element must somehow precede the second element.

[0091] Furthermore, those skilled in the art will understand that information and signals can be represented using any of a variety of different techniques and methods. For example, data, instructions, commands, information, signals, bits, and symbols that may be referenced in the above description can be represented by voltage, current, electromagnetic waves, magnetic fields or particles, light fields or particles, or any combination thereof.

[0092] Various modifications to the embodiments described in this disclosure will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments without departing from the scope of this disclosure. Therefore, this disclosure is not intended to be limited to the embodiments shown herein, but should be given the widest scope consistent with the novel features and principles disclosed herein, as described in the claims.

Claims

1. An energy storage unit (10), the energy storage unit comprising: Multiple energy storage sub-units connected in series (16); as well as One or more transformers, wherein each of the plurality of energy storage sub-units (16) is also connected together in parallel via the one or more transformers; The one or more transformers include a core having a plurality of windings (22, 24) wound around it. Wherein, the one or more transformers are one or more multiphase transformers.

2. The energy storage unit according to claim 1, wherein, The one or more transformers are a single transformer, and each of the plurality of energy storage sub-units (16) is connected to one of the plurality of windings (22, 24).

3. The energy storage unit according to claim 2, wherein, The transformer is connected to the bus (12) via another winding wound around the core.

4. The energy storage unit according to claim 1, wherein, The one or more transformers are multiple multiphase transformers (14) having three or more phases, wherein each transformer is connected on a first side to one of the multiple energy storage sub-units (16).

5. The energy storage unit according to claim 4, wherein, Each of the plurality of multiphase transformers (14) is connected to the bus (12) via another winding wound around the core of the corresponding transformer.

6. The energy storage unit according to claim 3 or claim 5, wherein, The one or more transformers are connected to the bus (12) using an AC-DC converter.

7. The energy storage unit according to claim 3 or claim 5, wherein, The bus (12) is configured for AC; or The bus (12) is configured for DC.

8. The energy storage unit according to any one of claims 1 to 6, the energy storage unit further comprising a power electronic circuit connected between one of the energy storage sub-units (16) and one of the one or more transformers.

9. The energy storage unit according to claim 8, wherein, The power electronic circuit is a rectifier with diodes or thyristors.

10. The energy storage unit according to claim 2 or 3 or claim 6 when dependent on claim 2, the energy storage unit further comprising a plurality of power electronic circuits, each of the plurality of power electronic circuits being connected between a corresponding one of the energy storage subunit (16) and the transformer.

11. The energy storage unit according to claim 8, wherein, The power electronic circuit includes a DC-AC converter (18).

12. The energy storage unit according to any one of claims 1 to 8 or claims 10 or 11, wherein, Each of the plurality of energy storage sub-units (16) is a DC energy storage device.

13. The energy storage unit according to any one of claims 1 to 8 or claim 10 or 11, wherein, The energy storage unit (10) is an energy storage module, and the plurality of energy storage sub-units (16) are plurality of energy storage cells; or The energy storage unit (10) is an energy storage rack, and the plurality of energy storage sub-units are plurality of energy storage modules.

14. The energy storage unit according to any one of claims 3 to 11, wherein, when subordinate to claim 3, The bus (12) is a multiphase AC bus.

15. The energy storage unit according to any one of claims 1 to 11, wherein, The one or more transformers are a multiphase transformer having two or more windings; wherein the transformer has six windings, wherein three of the six windings are connected to the corresponding three phases of the bus (12), and wherein each of the other three of the six windings is connected to a different energy storage subunit (16).

16. The energy storage unit (10) according to any one of claims 4 to 9 and 11 to 14, wherein, The number of the one or more transformers is less than the number of the plurality of energy storage sub-units, wherein at least one of the one or more transformers is connected to two or more of the plurality of energy storage sub-units, and at least another of the one or more transformers is connected to only one of the plurality of energy storage sub-units.

17. A system comprising two energy storage units (10) according to claim 3 or claim 5, or according to any one of claims 6 to 8 when dependent on claim 3 or claim 5, or any one of claims 10 to 13, wherein, The two energy storage units (10) are connected to the bus (12).

18. A method (70) for providing an energy storage unit (10), the method comprising: Provides (72) multiple energy storage sub-units (16) connected in series; Provide (74) one or more transformers; as well as Each of the plurality of energy storage sub-units (16) is connected in parallel (76) via the one or more transformers. The one or more transformers include a core having a plurality of windings (22, 24) wound around it. Wherein, the one or more transformers are one or more multiphase transformers.

19. The method of claim 17, further comprising: Each of the plurality of energy storage sub-units (16) is connected in parallel (76) via the one or more transformers by connecting power electronic circuitry between one of the one or more transformers and one of the plurality of energy storage sub-units (16).

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