Energy storage systems

Abstract

An energy storage system according to one embodiment disclosed herein may include a plurality of battery units, a plurality of DC-DC converters, each connected to each of the plurality of battery units, which convert input voltages from the connected battery units into output voltages, and a control unit that controls the plurality of DC-DC converters such that the sum of the output voltages of the plurality of DC-DC converters becomes an AC voltage.

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This invention claims the benefit of priority based on Korean Patent Application No. 10 - 2023 - 0045550, filed on April 6, 2023, and includes all the contents disclosed in the literature of the Korean patent application as part of this specification.

[0002] The embodiments disclosed in this document relate to an energy storage system.

Background Art

[0003] An energy storage system (ESS) is a system that combines renewable energy, a battery for storing electricity, and existing grid power. Recently, with the spread of smart grids and renewable energy, and the emphasis on the efficiency and stability of the power grid, the demand for energy storage systems for power supply and demand regulation and power quality improvement has been increasing. Depending on the purpose of use, the output and capacity of the energy storage system are different. To constitute a large - capacity energy storage system, a plurality of battery systems may be connected to each other.

[0004] Such an energy storage system is evolving from an AC - coupled to a DC - coupled energy storage system. In a DC - coupled ESS system, the battery system and the grid have different voltage levels, and the voltage forms are also different, with the battery system being a DC voltage and the grid being an AC voltage. Thus, a DC - DC converter and a DC - AC inverter, which are power conversion devices, are essentially required between the battery system and the grid.

[0005] Of these, DC-DC converters are installed for each battery cell or battery module, functioning as the DC-DC converter for the entire system. Structures have been developed that offer various advantages, such as cell balancing and blocking of faulty cells. While this can reduce the power consumption of the DC-DC converter within the energy storage system, the power consumption generated by the DC-AC inverter remains a problem that needs to be overcome. [Overview of the project] [Problems that the invention aims to solve]

[0006] The embodiments disclosed herein can provide an energy storage system capable of generating an AC voltage using a DC-DC converter at the end of a battery cell, battery module, or battery pack.

[0007] The technical problems of the embodiments disclosed herein are not limited to those mentioned above, and other technical problems not mentioned can be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0008] An energy storage system according to one embodiment disclosed herein may include a plurality of battery units, a plurality of DC-DC converters, each connected to each of the plurality of battery units, which convert input voltages from the connected battery units into output voltages, and a control unit that controls the plurality of DC-DC converters such that the sum of the output voltages of the plurality of DC-DC converters becomes an AC voltage.

[0009] In an energy storage system according to one embodiment disclosed herein, each of the plurality of DC-DC converters may be connected to the positive and negative terminals of each of the plurality of battery units, and the combined voltage may be applied to a grid system connected to the energy storage system.

[0010] In an energy storage system according to one embodiment disclosed in this document, the plurality of DC-DC converters are configured to perform a bypass function that causes the magnitude of the output voltage to be 0V, and the control unit can control the plurality of DC-DC converters using the bypass function so that the sum of the voltages becomes an AC voltage.

[0011] In an energy storage system according to one embodiment disclosed herein, the control unit can control the plurality of DC-DC converters to perform the bypass function according to a specified period.

[0012] In an energy storage system according to one embodiment disclosed herein, the plurality of DC-DC converters are configured to perform an upward control function that causes the output voltage to rise based on a specified gradient and a downward control function that causes the output voltage to fall based on a specified gradient, and the control unit can control the plurality of DC-DC converters using the upward control function and the downward control function so that the sum of the voltages becomes an AC voltage.

[0013] In an energy storage system according to one embodiment disclosed herein, the control unit can control the plurality of DC-DC converters such that the combined voltage has a magnitude, phase, and / or frequency corresponding to the required AC voltage of the grid system.

[0014] In an energy storage system according to one embodiment disclosed herein, the control unit can control the plurality of DC-DC converters based on the state of the plurality of battery units.

[0015] An energy storage system according to one embodiment disclosed herein further includes at least one Battery Management System (BMS) for managing the state of the plurality of battery units, the control unit can acquire state data of the plurality of battery units from the at least one BMS and determine the state of the plurality of battery units based on the state data.

[0016] In an energy storage system according to one embodiment disclosed herein, the state data may be data relating to at least one of the voltage, current, temperature, SOC (State of Charge), or SOH (State of Health) of the plurality of battery units.

[0017] In an energy storage system according to one embodiment disclosed herein, each of the plurality of battery units may be a battery cell, a battery module, a battery pack, or a battery rack. [Effects of the Invention]

[0018] According to the embodiments disclosed herein, a DC-DC converter alone can generate the AC voltage required by the grid system, thus eliminating the need for a DC-AC inverter in the energy storage system, thereby providing advantages in terms of power efficiency, power density, and temperature compared to existing energy storage systems.

[0019] Furthermore, a variety of other effects may be perceived directly or indirectly through this document. [Brief explanation of the drawing]

[0020] [Figure 1] This is a block diagram showing a conventional energy storage system and grid system. [Figure 2] This is a block diagram showing an energy storage system and a grid system according to one embodiment. [Figure 3] This is a drawing for explaining the connection structure of a battery unit and a DC-DC converter in an energy storage system according to an embodiment. [Figure 4a] This is a drawing for explaining an example in which a plurality of DC-DC converters in an energy storage system according to an embodiment sequentially execute specified functions. [Figure 4b] This is a drawing for explaining an example in which a plurality of DC-DC converters in an energy storage system according to an embodiment sequentially execute specified functions. [Figure 4c] This is a drawing for explaining an example in which a plurality of DC-DC converters in an energy storage system according to an embodiment sequentially execute specified functions. [Figure 5] This is a drawing for explaining the connection structure of a battery unit, a DC-DC converter, and a switch in an energy storage system according to an embodiment.

Embodiments for Carrying Out the Invention

[0021] Hereinafter, various embodiments of the present invention are described with reference to the attached drawings. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include various modifications, equivalents, and / or alternatives of the embodiments of the present invention.

[0022] Various embodiments of this document and the terms used therein are not intended to limit the technical features described in this document to specific embodiments, and should be understood to include various modifications, equivalents, or alternatives of the embodiments. Similar reference numerals may be used for similar or related components in connection with the description of the drawings. The singular form of a noun corresponding to an item may include one or more of the said items unless clearly indicated otherwise in the relevant context.

[0023] In this document, each of the phrases such as “A or B,” “at least one of A and B,” “at least one of A or B,” “A, B, or C,” “at least one of A, B, and C,” and “at least one of A, B, or C” may include any one of the items listed together with the phrase in question, or any possible combination thereof. Terms such as “first,” “second,” “first,” “second,” “A,” “B,” “(a),” or “(b)” may be used merely to distinguish one component from other components and, unless otherwise stated, do not limit the component in any other way (e.g., importance or order).

[0024] Wherever a component (e.g., component 1) is referred to as being "connected," "coupled," or "connected" to another component (e.g., component 2), with or without such terms, it means that the component may be connected to the other component directly (e.g., by wire), wirelessly, or via a third component.

[0025] According to various embodiments, each of the components described above (e.g., a module or a program) may include one or more individuals, some of which may be separated and arranged in other components. According to various embodiments, one or more of the components or operations described above may be omitted, or one or more other components or operations may be added. Generally or additionally, multiple components (e.g., a module or a program) may be integrated into a single component. In this case, the integrated component may perform one or more functions of each of the multiple components in the same or similar manner as those performed by the components before the integration. According to various embodiments, operations performed by a module, program or other component may be performed sequentially, in parallel, iteratively, or heuristically, or one or more of the operations may be performed in a different order, omitted, or one or more other operations may be added.

[0026] Figure 1 is a block diagram showing a conventional energy storage system and grid system.

[0027] Referring to Figure 1, a conventional energy storage system 110 is connected to a grid system 120 and includes a battery unit 111, a DC-DC converter 112, and a DC-AC inverter 113.

[0028] The smallest unit of a battery that performs the role of storing power in an energy storage system (ESS) is typically a battery cell. A series / parallel combination of battery cells forms a battery module, and a number of battery modules can constitute a battery pack or battery rack. The battery unit 111 shown in Figure 1 may be a battery pack or a battery rack.

[0029] A conventional energy storage system 110 either transmits power to the grid system 120 (during discharge) or receives power from the grid system 120 (during charging). Here, since the grid system 120 requires AC power, the power transmitted between the energy storage system 110 and the grid system 120 is AC power.

[0030] More specifically, in the case of discharge, the conventional energy storage system 110 converts the DC output power of the battery unit 111 into AC power via the DC-DC converter 112 and the DC-AC inverter 113 and transmits it to the grid system 120. In the case of charging, the conventional energy storage system 110 converts the AC power transmitted from the grid system 120 into DC power via the DC-AC inverter 113 and the DC-DC converter 112 and transmits it to the battery unit 111.

[0031] In other words, conventional energy storage systems 110 essentially require a DC-AC inverter 113 for power transmission and reception as described above. However, this structure results in power consumption while the power passes through the DC-AC inverter 113, reducing power efficiency, and excessive heat generation due to the conversion function of the DC-AC inverter 113 causes the overall system temperature to rise excessively.

[0032] Figure 2 is a block diagram showing an energy storage system and a grid system according to one embodiment.

[0033] Referring to Figure 2, the energy storage system 200 may be connected to the grid system 260. According to one embodiment, the energy storage system 200 and the grid system 260 can transmit and receive AC power. For example, during discharge, the energy storage system 200 can transmit AC power to the grid system 260. As another example, during charging, the energy storage system 200 can receive AC power from the grid system 260.

[0034] According to one embodiment, the energy storage system 200 may include a plurality of battery units 210, 220, 230, 240, a plurality of DC-DC converters 212, 222, 232, 242, and a control unit 250. In some embodiments, the energy storage system 200 shown in Figure 2 may further include at least one component other than those shown in Figure 2 (e.g., a BSC (Battery System Controller), an EMS (Energy Management System), or a PMS (Power Management System)).

[0035] The batteries that perform the role of storing power in the energy storage system 200 may typically be embodied in the form of multiple battery modules, each consisting of multiple battery cells connected in series or parallel, forming a battery pack or battery rack, and multiple battery packs or battery racks forming a battery bank. Each of the multiple battery units 210, 220, 230, and 240 shown in Figure 2 may be a battery cell, a battery module, a battery pack, or a battery rack.

[0036] According to one embodiment, the multiple battery units 210, 220, 230, and 240 may be connected to each other in series or in parallel.

[0037] According to one embodiment, each of the multiple battery units 210, 220, 230, and 240 may be equipped with a Battery Management System (BMS) 211, 221, 231, or 241. The BMS 211, 221, 231, or 241 can manage the status of the battery units 210, 220, 230, or 240 under its control. According to one embodiment, the BMS 211, 221, 231, or 241 can monitor the voltage, current, and / or temperature of the battery units 210, 220, 230, or 240 and calculate the State of Charge (SOC) and / or State of Health (SOH) based on the monitoring results. Furthermore, the BMS 211, 221, 231, or 241 can control charging and discharging based on the status of the battery units 210, 220, 230, or 240.

[0038] According to one embodiment, the BMS 211, 221, 231, or 241 can transmit state data relating to at least one of the voltage, current, temperature, SOC, or SOH of the battery unit 210, 220, 230, or 240 to the control unit 250.

[0039] According to one embodiment, each of the multiple DC-DC converters 212, 222, 232, and 242 may be connected to each of the multiple battery units 210, 220, 230, and 240. For example, the first DC-DC converter 212 may be connected to the first battery unit 210, the second DC-DC converter 222 may be connected to the second battery unit 220, the third DC-DC converter 232 may be connected to the third battery unit 230, and the Nth DC-DC converter 242 may be connected to the Nth battery unit 240 (wherein N is a natural number of 4 or more).

[0040] In one embodiment, a plurality of DC-DC converters 212, 222, 232, 242 may be directly or indirectly connected to a grid system 260. In this case, the sum of the output voltages of the plurality of DC-DC converters 212, 222, 232, 242 may be applied to the grid system 260 via the connection. In one embodiment, a predetermined filter may be connected between the plurality of DC-DC converters 212, 222, 232, 242 and the grid system 260. In this case, the predetermined filter may be embodied in an AC transformer that performs the role of converting the sum of the output voltages of the plurality of DC-DC converters 212, 222, 232, 242 to match the required voltage of the grid system 260. For example, the predetermined filter can perform the role of converting the sum of the AC voltages so that the intermediate voltage value of the sum of the AC voltages is 0V.

[0041] According to one embodiment, multiple DC-DC converters 212, 222, 232, and 242 can convert an input voltage into an output voltage of a specified magnitude. For example, the DC-DC converters 212, 222, 232, or 242 may be embodied in various types of converters, such as full-bridge converters, half-bridge converters, and flyback converters. The DC-DC converters 212, 222, 232, or 242 may include a separate control unit, an input switching set, a primary coil, a secondary coil, an output switching set, and a capacitor.

[0042] Depending on the embodiment, the multiple DC-DC converters 212, 222, 232, 242 may be bidirectional converters. For example, when conversion is performed from multiple battery units 210, 220, 230, 240 to the grid system 260, the inputs of the multiple DC-DC converters 212, 222, 232, 242 may be connected to the multiple battery units 210, 220, 230, 240, and the outputs of the multiple DC-DC converters 212, 222, 232, 242 may be connected to the grid system 260. As another example, when conversion is performed from the grid system 260 to multiple battery units 210, 220, 230, and 240, the inputs of the multiple DC-DC converters 212, 222, 232, and 242 may be connected to the grid system 260, and the outputs of the multiple DC-DC converters 212, 222, 232, and 242 may be connected to the multiple battery units 210, 220, 230, and 240.

[0043] According to one embodiment, the multiple DC-DC converters 212, 222, 232, and 242 may be configured to perform specific functions.

[0044] According to one embodiment, a specific function may include a bypass function that causes the magnitude of the output voltage to be 0V. The DC-DC converters 212, 222, 232, or 242 can interrupt the power output from the connected battery units 210, 220, 230, or 240 by performing the bypass function.

[0045] According to one embodiment, a particular function may include an upward control function that causes the output voltage to become a voltage that rises based on a specified gradient, and / or a downward control function that causes the output voltage to become a voltage that falls based on a specified gradient.

[0046] According to one embodiment, the control unit 250 may include a central processing unit, an application processor, a graphics processing unit, a neural network processing unit (NPU), an image signal processor, a sensor hub processor, or a communication processor.

[0047] According to one embodiment, the control unit 250 can run software to control at least one other component of the energy storage system 200 connected to the control unit 250 (e.g., BMS 211, 221, 231, or 241, DC-DC converters 212, 222, 232, or 242), and can perform various data processing or calculations.

[0048] According to one embodiment, the control unit 250 can control the DC-DC converters 212, 222, 232, 242 such that the sum of the output voltages of the DC-DC converters 212, 222, 232, 242 becomes an AC voltage. According to one embodiment, the control unit 250 can control the DC-DC converters 212, 222, 232, 242 such that the sum of the output voltages has a magnitude, phase, and / or frequency that corresponds to the required AC voltage of the grid system 260.

[0049] According to one embodiment, the control unit 250 can control a plurality of DC-DC converters 212, 222, 232, and 242 using a bypass function so that the sum of the voltages becomes an AC voltage. The control unit 250 can control the number of the DC-DC converters 212, 222, 232, or 242 that output voltage via the bypass function. The control unit 250 can also control the magnitude of the output voltage of the DC-DC converters 212, 222, 232, or 242 that output voltage.

[0050] According to one embodiment, the control unit 250 can control a plurality of DC-DC converters 212, 222, 232, and 242 to perform a bypass function for a specified time.

[0051] According to one embodiment, the control unit 250 can control a plurality of DC-DC converters 212, 222, 232, 242 to perform a bypass function according to a specified period. Here, the specified period may be set to the same period for all of the DC-DC converters 212, 222, 232, 242, or to different periods for each of them. The specified period may also be set based on the magnitude, phase, and / or frequency corresponding to the required AC voltage of the grid system 260. For example, the specified period may be set to a period earlier than the period of the required AC voltage of the grid system 260 so that the sum of the voltages equals the required AC voltage.

[0052] According to one embodiment, the control unit 250 can also control the multiple DC-DC converters 212, 222, 232, and 242 to sequentially execute the bypass function in a specified order.

[0053] In this way, the control unit 250 can control the DC-DC converters 212, 222, 232, and 242 so that their combined voltage becomes an AC voltage (specifically, the AC voltage required by the grid system 260) by controlling the magnitude of the DC output voltages of the DC-DC converters 212, 222, 232, and 242.

[0054] According to one embodiment, the control unit 250 can control a plurality of DC-DC converters 212, 222, 232, and 242 using rise control and fall control functions so that the sum voltage becomes an AC voltage. For example, the control unit 250 can control the DC-DC converters 212, 222, 232, or 242 to output a voltage that rises or falls based on a specified gradient, where the specified gradient may be set based on the magnitude, phase, and / or frequency corresponding to the required AC voltage of the grid system 260. The control unit 250 can transmit a softer form of AC voltage to the grid system 260 via the rise control and fall control functions.

[0055] According to one embodiment, the control unit 250 can control the multiple DC-DC converters 212, 222, 232, and 242 using all of the bypass function, rise control function, and fall control function so that the sum voltage becomes an AC voltage. For example, the control unit 250 can control at least some of the multiple DC-DC converters 212, 222, 232, and 242 to perform the bypass function, and control the rest to perform the rise control function and / or fall control function.

[0056] According to one embodiment, the control unit 250 can control multiple DC-DC converters 212, 222, 232, and 242 based on the status of multiple battery units 210, 220, 230, and 240.

[0057] According to one embodiment, the control unit 250 can acquire status data of multiple battery units 210, 220, 230, and 240 from at least one BMS 211, 221, 231, and / or 241. Based on the acquired status data, the control unit 250 can determine the status of the multiple battery units 210, 220, 230, and 240. For example, the control unit 250 can determine the status of the multiple battery units 210, 220, 230, and 240 as abnormal or normal.

[0058] According to one embodiment, the control unit 250 can control a plurality of DC-DC converters 212, 222, 232, and 242 based on a determined state. For example, the control unit 250 can control a DC-DC converter 212, 222, 232, or 242 connected to a battery unit 212, 222, 232, or 242 that has been determined to be in an abnormal state to perform a bypass function.

[0059] For example, the control unit 250 may determine that a battery unit 210, 220, 230, or 240 is in an abnormal state if its output voltage, SOC, or SOH is below a specified level. As another example, the control unit 250 may determine that a battery unit 210, 220, 230, or 240 is in an abnormal state if its temperature is above a specified temperature.

[0060] Figure 3 is a diagram illustrating the connection structure between a battery unit and a DC-DC converter in an energy storage system according to one embodiment.

[0061] The energy storage system 300 and grid system 360 shown in Figure 3 may have the same configuration as the energy storage system 200 and grid system 260 shown in Figure 2.

[0062] Referring to Figure 3, each of the DC-DC converters 312, 322, 332, and 342 may be connected to the positive and negative terminals of each of the battery units 310, 320, 330, and 340. That is, each of the DC-DC converters 312, 322, 332, and 342 may be connected to convert the output voltages of each of the battery units 310, 320, 330, and 340. This allows the control unit of the energy storage system 300 (e.g., the control unit 250 in Figure 2) to individually control the output voltages of each of the battery units 310, 320, 330, and 340.

[0063] In one embodiment, each of the connection units of the multiple battery units 310, 320, 330, and 340 and each of the multiple DC-DC converters 312, 322, 332, and 342 may be connected in series with each other. In this embodiment, the positive output terminal of the first DC-DC converter 312 and the negative output terminal of the second DC-DC converter 342 may be connected to each other via an energy storage element C1 that performs the role of energy storage. In addition, the positive output terminal of the first DC-DC converter 312 may be connected to the positive input terminal of the grid system 360, and the negative output terminal of the second DC-DC converter 342 may be connected to the negative input terminal of the grid system 360. With such a connection structure, the sum of the output voltages of the multiple DC-DC converters 312, 322, 332, and 342 may be stored in the energy storage element C1 or applied to the grid system 360.

[0064] Figures 4a to 4c are diagrams illustrating an example in which multiple DC-DC converters in an energy storage system according to one embodiment sequentially perform specific functions. Here, the specific functions may include bypass functions, rise control functions, and / or fall control functions.

[0065] Each of the energy storage system 400 and grid system 460 shown in Figures 4a to 4c may have the same configuration as each of the energy storage system 200 and grid system 260 shown in Figure 2.

[0066] Referring to Figure 4a, of the multiple DC-DC converters 412, 422, 432, and 442, the first DC-DC converter 412 may perform a specific function, while the remaining DC-DC converters 422, 432, and 442 do not necessarily perform a specific function. In this case, if the specific function is a bypass function, the sum of voltages applied to the grid system 460 may be the sum of the voltages output from the remaining battery units 420, 430, and 440 (excluding the first battery unit 410) converted by the remaining DC-DC converters 422, 432, and 442.

[0067] Referring to Figure 4b, of the multiple DC-DC converters 412, 422, 432, and 442, the first DC-DC converter 412 and the third DC-DC converter 432 perform specific functions, while the remaining DC-DC converters 422 and 442 do not necessarily perform specific functions. In this case, if the specific function is a bypass function, the total voltage applied to the grid system 460 may be the sum of the voltages output from the remaining battery units 420 and 440 (excluding the first battery unit 410 and the third battery unit 430) and converted by the remaining DC-DC converters 422 and 442.

[0068] Referring to Figure 4c, of the multiple DC-DC converters 412, 422, 432, and 442, the first DC-DC converter 412, the third DC-DC converter 432, and the NDC-DC converter 442 perform specific functions, while the remaining DC-DC converter 422 does not necessarily perform specific functions. In this case, if the specific function is a bypass function, the total voltage applied to the grid system 460 may be the voltage obtained by the remaining DC-DC converter 422 from the voltage output from the remaining battery units 420, excluding the first battery unit 410, the third battery unit 430, and the N battery unit 440.

[0069] In this way, the energy storage system 400 can control whether or not specific functions of the multiple DC-DC converters 400 can be performed so that the sum of the output voltages of the multiple DC-DC converters 400 becomes an AC voltage. More specifically, a control unit within the energy storage system 400 (e.g., the control unit 250 in Figure 2) can control whether or not specific functions of the multiple DC-DC converters 400 can be performed.

[0070] In one embodiment, the energy storage system 400 can control a plurality of DC-DC converters 412, 422, 432, and 442 to sequentially perform specific functions in a specified order. For example, the energy storage system 400 can control the first DC-DC converter 412, the third DC-DC converter 432, and the NDC-DC converter 442 to perform specific functions in that order (i.e., in the order of Figures 4a, 4b, and 4C). This control may be for generating a portion of the AC voltage waveform, which is the sum voltage, where the voltage value drops. However, the specified order is not limited thereto and can be set in various ways so that the sum voltage becomes the required AC voltage.

[0071] Figure 5 is a diagram illustrating the connection structure of a battery unit, DC-DC converter, and switch within an energy storage system according to one embodiment.

[0072] The energy storage system 500 and grid system 590 shown in Figure 5 may have the same configuration as the energy storage system 200 and grid system 260 shown in Figure 2.

[0073] Referring to Figure 5, the energy storage system 500 may include multiple battery units 510, 520, 530, 540, 550, 560, 570, 580, multiple DC-DC converters 512, 522, 532, 542, 552, 562, 572, 582, a switch SW, and an energy storage element C2.

[0074] Each of the multiple DC-DC converters 512, 522, 532, 542, 552, 562, 572, and 582 may be connected to the positive and negative terminals of each of the multiple battery units 510, 520, 530, 540, 550, 560, 570, and 580. That is, each of the multiple DC-DC converters 512, 522, 532, 542, 552, 562, 572, and 582 may be connected to convert the output voltages of each of the multiple battery units 510, 520, 530, 540, 550, 560, 570, and 580. With such a connection structure, the control unit of the energy storage system 500 (e.g., the control unit 250 in Figure 2) can individually control the output voltages of each of the multiple battery units 510, 520, 530, 540, 550, 560, 570, and 580.

[0075] In one embodiment, the connection units of the first battery unit 510, the second battery unit 520, the third battery unit 530, and the Nth battery unit 540, respectively, and the first DC-DC converter 512, the second DC-DC converter 522, the third DC-DC converter 532, and the Nth DC-DC converter 542, respectively, may be connected in series with each other. Also, the connection units of the N+1st battery unit 550, the second N-2nd battery unit 560, the second N-1st battery unit 270, and the second Nth battery unit 580, respectively, and the N+1st DC-DC converter 552, the second N-2nd DC-DC converter 562, the second N-1st DC-DC converter 572, and the second Nth DC-DC converter 582, respectively, may be connected in series with each other. Here, the negative output terminal of the Nth DC-DC converter 542 and the positive output terminal of the N+1st DC-DC converter may be connected with each other.

[0076] According to one embodiment, one end of the energy storage element C2, which performs the role of energy storage, is connected to a switch SW, and the other end is connected to the negative output terminal of the second NDC-DC converter 542 and the positive output terminal of the N+1 DC-DC converter. The switch SW may be configured to connect one end of the energy storage element C2 to the positive output terminal of the first DC-DC converter 512 or the negative output terminal of the second NDC-DC converter 582 based on a predetermined period.

[0077] With this connection structure, while the switch SW is connected to the positive output terminal of the first DC-DC converter 512, the first sum of the output voltages of the first DC-DC converter 512, the second DC-DC converter 522, the third DC-DC converter 532, ... and the NDC-DC converter 542 may be stored in the energy storage element C1 or applied to the grid system 590. Also, while the switch SW is connected to the negative output terminal of the second NDC-DC converter 582, the second sum of the output voltages of the N+1 DC-DC converter 552, ..., the second N-2 DC-DC converter 562, the second N-1 DC-DC converter 572 and the second NDC-DC converter 582 may be stored in the energy storage element C1 or applied to the grid system 590.

[0078] Here, the first and second combined voltages stored in the energy storage element C1 or applied to the grid system 590 can have opposite directions. For example, the first combined voltage can have a positive value and the second combined voltage can have a negative value. This allows the energy storage system 500 to control the intermediate voltage value of the AC voltage applied to the grid system 590 to be 0V without the need for a separate filter. For this reason, the predetermined period during which the switch SW changes can be set to half the required AC voltage period of the grid system 590.

[0079] The terms "contains," "constitutes," or "possesses," as used above, mean that the component in question may be inherent, unless otherwise stated, and should be interpreted as meaning that other components may be included, rather than excluding them. All terms, including technical or scientific terms, have the same meaning as that generally understood by a person of ordinary skill in the art to which the embodiments disclosed herein belong, unless otherwise defined. Commonly used terms, such as those previously defined, should be interpreted in accordance with their meaning in the context of the relevant technology and should not be interpreted in an ideal or overly formal sense unless explicitly defined herein.

Claims

1. Multiple battery units; Multiple DC-DC converters, each connected to one of the aforementioned battery units, which convert the input voltage from the connected battery units into an output voltage; and An energy storage system including a control unit that controls the plurality of DC-DC converters so that the sum of the output voltages of the plurality of DC-DC converters becomes an AC voltage.

2. Each of the aforementioned DC-DC converters is connected to the positive and negative terminals of the respective battery units. The energy storage system according to claim 1, wherein the combined voltage is applied to a grid system connected to the energy storage system.

3. The plurality of DC-DC converters are configured to perform a bypass function that causes the magnitude of the output voltage to be 0V. The energy storage system according to claim 1, wherein the control unit controls the plurality of DC-DC converters using the bypass function so that the sum voltage becomes an AC voltage.

4. The energy storage system according to claim 3, wherein the control unit controls the plurality of DC-DC converters to perform the bypass function according to a specified period.

5. The plurality of DC-DC converters are configured to perform a rise control function that causes the output voltage to rise based on a specified slope and a fall control function that causes the output voltage to fall based on a specified slope. The energy storage system according to claim 1, wherein the control unit controls the plurality of DC-DC converters using the rise control function and the fall control function so that the sum voltage becomes an AC voltage.

6. The energy storage system according to claim 1, wherein the control unit controls the plurality of DC-DC converters such that the combined voltage has a magnitude, phase, and / or frequency corresponding to the AC voltage required by the grid system.

7. The energy storage system according to claim 1, wherein the control unit controls the plurality of DC-DC converters based on the state of the plurality of battery units.

8. It further includes at least one BMS (Battery Management System) that manages the status of the plurality of battery units, The control unit, The status data of the plurality of battery units is obtained from the at least one BMS, The energy storage system according to claim 7, wherein the state of the plurality of battery units is determined based on the state data.

9. The energy storage system according to claim 8, wherein the state data is data relating to at least one of the voltage, current, temperature, SOC (State of Charge), or SOH (State of Health) of the plurality of battery units.

10. The energy storage system according to claim 1, wherein each of the plurality of battery units is a battery cell, a battery module, a battery pack, or a battery rack.

11. Multiple battery units; Each input terminal is electrically connected to the positive and negative terminals of the respective battery units, and the system includes multiple DC-DC converters that convert the input voltage from the connected battery units into an output voltage. Each of the aforementioned battery units and each of the aforementioned DC-DC converters have a connection unit connected in series with the others. An energy storage system in which the plurality of DC-DC converters and the grid system are electrically connected such that at least a portion of the sum of the output voltages of the plurality of DC-DC converters is applied to the grid system.

12. The positive output terminal of the first DC-DC converter among the plurality of DC-DC converters is electrically connected to the positive input terminal of the grid system. The negative output terminal of the second DC-DC converter among the plurality of DC-DC converters is electrically connected to the negative input terminal of the grid system. The energy storage system according to claim 11, wherein the positive output terminals of the remaining DC-DC converters, excluding the first DC-DC converter and the second DC-DC converter from the plurality of DC-DC converters, are electrically connected to the negative output terminals of adjacent DC-DC converters.

13. The energy storage system according to claim 12, further comprising an energy storage element electrically connected to the positive output terminal of the first DC-DC converter and the negative output terminal of the second DC-DC converter.

14. The system further includes a switch configured to selectively connect the positive output terminal of a first DC-DC converter or the negative output terminal of a second NDC-DC converter to the positive input terminal of the grid system, among the 2N (where N is a natural number) DC-DC converters. Of the plurality of DC-DC converters, excluding the first DC-DC converter and the second NDC-DC converter, the positive output terminals of the remaining DC-DC converters are electrically connected to the negative output terminals of the adjacent DC-DC converters. The energy storage system according to claim 11, wherein the negative output terminal of the Nth DC-DC converter among the plurality of DC-DC converters is electrically connected to the positive output terminal of the N+1th DC-DC converter among the plurality of DC-DC converters and to the negative input terminal of the grid system.

15. The energy storage system according to claim 14, further comprising a first stage of the switch electrically connected to the grid system and a storage element electrically connected to the negative output terminal of the NDC-DC converter.

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