Power conversion device and energy storage system

Abstract

The utility model discloses a power conversion device and an energy storage system. The power conversion apparatus includes a first converter group, a second converter group, and a transformer module. And the second converter in the second converter group is a string type converter. The first converter group is connected with the first side of the corresponding transformer through a first node, the second converter group is connected with the first side of the corresponding transformer through a second node, and the second side of each transformer in the transformer module is configured to be connected to a power grid during grid-connected operation. According to the embodiment of the utility model, the low switching frequency of the second converter is utilized to carry out harmonic suppression without additionally adding a passive filter, so that the cost is reduced, and the situation that the stability of grid-connected operation of the energy storage system is influenced by further resonance caused by the passive filter bank is also avoided.

Description

Technical Field

[0001] This utility model relates to the field of converter technology, and more specifically, to a power conversion device and an energy storage system. Background Technology

[0002] As the number of converters increases, the superposition effect of harmonics generated by the converters becomes more pronounced, resulting in higher harmonic amplitudes at the converter-grid connection point (PCC). The voltage and current at the PCC point may exceed the limits specified by the grid standards, affecting the stability of the converter's grid-connected operation.

[0003] In related technologies, harmonics at the PCC point can be improved by adding a passive filter bank at the grid connection point of the converter. However, the solution of adding passive filters is costly, and when the grid strength changes, the passive filter bank is prone to causing further inductor-capacitor (LC) resonance, resulting in harmonic instability and affecting the stability of the converter's grid-connected operation. Utility Model Content

[0004] This utility model provides a power conversion device and an energy storage system.

[0005] The power conversion device provided in this application includes a first converter group, a second converter group, and a transformer module. The first converter group includes N first converters connected to a first node. The second converter group includes M second converters connected to a second node. The second converters are string converters, and N and M are positive integers. The transformer module includes at least one transformer. The first converter group is connected to a first side of a corresponding transformer via the first node, and the second converter group is connected to a first side of a corresponding transformer via the second node. The second side of each transformer in the transformer module is configured to connect to the power grid when the energy storage system is connected to the grid.

[0006] This invention utilizes the lower switching frequency of the second converter for harmonic mitigation, eliminating the need for additional passive filters, thus reducing costs and preventing further inductor-capacitor (LC) resonance caused by passive filter banks, which could affect the stability of the energy storage system's grid-connected operation.

[0007] In some implementations, all N first converters in the first converter group are centralized converters.

[0008] The hybrid converter energy storage system provided in this application combines the advantages of centralized converters and string converters. While reducing the operating cost of large-scale energy storage systems, it can also improve harmonics through string converters and ensure the stability of grid-connected operation of the energy storage system.

[0009] In some implementations, the switching frequency of the first converter is lower than that of the second converter.

[0010] In some implementations, the switching frequency of the first converter is below 5 kHz, and the switching frequency of the second converter is above 10 kHz.

[0011] In some implementations, all N first converters in the first converter group are string converters.

[0012] In some implementations, the transformer module includes a first transformer and a second transformer, the first converter group is connected to a first side of the first transformer through the first node, the second converter group is connected to a first side of the second transformer through the second node, and a second side of the first transformer is connected to a second side of the second transformer and configured to connect to the power grid during grid-connected operation.

[0013] In some implementations, the transformer module includes a third transformer, the first converter group is connected to a first side of the third transformer via the first node, the second converter group is connected to the first side of the third transformer via the second node, and the second side of the third transformer is configured to connect to the power grid during grid-connected operation.

[0014] In some embodiments, the power conversion device includes a current sensor disposed at the first node and configured to detect the current at the first node.

[0015] In some embodiments, the power conversion device includes a voltage sensor disposed at the first node and configured to detect the voltage at the first node.

[0016] The energy storage system provided by this utility model includes the power conversion device described in the above embodiments.

[0017] This invention provides a power conversion device and an energy storage system. The power conversion device includes a first converter group, a second converter group, and a transformer module. The first converter group includes N first converters connected to a first node. The second converter group includes M second converters connected to a second node. The second converters are string converters, and N and M are positive integers. The transformer module includes at least one transformer. The first converter group is connected to a first side of a corresponding transformer through the first node, and the second converter group is connected to a first side of a corresponding transformer through the second node. The second side of each transformer in the transformer module is configured to connect to the power grid during grid-connected operation.

[0018] This invention utilizes the lower switching frequency of the second converter for harmonic mitigation, eliminating the need for additional passive filters, thus reducing costs and preventing further inductor-capacitor (LC) resonance caused by passive filter banks, which could affect the stability of the energy storage system's grid-connected operation.

[0019] Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The above and / or additional aspects and advantages of this invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0021] Figure 1 This is a schematic diagram of the energy storage system of a centralized converter in related technologies;

[0022] Figure 2 This is a schematic diagram of the energy storage system provided in this embodiment of the utility model;

[0023] Figure 3 This is a schematic diagram of the energy storage system of the hybrid converter provided in this embodiment of the utility model;

[0024] Figure 4 This is a schematic diagram of the energy storage system of the string converter provided in this embodiment of the utility model;

[0025] Figure 5 This is the first structural schematic diagram of the transformer module provided in this embodiment of the utility model;

[0026] Figure 6 This is a second structural schematic diagram of the transformer module provided in this embodiment of the utility model;

[0027] Figure 7This is a first structural schematic diagram of the sensor provided in this embodiment of the utility model;

[0028] Figure 8 This is a second structural schematic diagram of the sensor provided in this embodiment of the utility model.

[0029] Reference numerals: power conversion device 100, energy storage system 1000, first converter group 110, first converter 111, second converter group 120, second converter 121, transformer module 130, first transformer 131, second transformer 132, third transformer 133, current sensor 140, voltage sensor 150. Detailed Implementation

[0030] The embodiments of this utility model are described in detail below, and these embodiments are illustrated in the accompanying drawings. Throughout the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model.

[0031] This application provides a power conversion device and an energy storage system, relating to the field of converter technology.

[0032] First, the technical field involved in the embodiments of this application will be explained as follows:

[0033] As the number of converters increases, the superposition effect of harmonics generated by the converters becomes more pronounced, resulting in higher harmonic amplitudes at the converter-grid connection point (PCC). The voltage and current at the PCC point may exceed the limits specified by the grid standards, affecting the stability of the converter's grid-connected operation.

[0034] In related technologies, harmonics at the PCC point can be improved by adding a passive filter bank at the grid connection point of the converter. However, the solution of adding passive filters is costly, and when the grid strength changes, the passive filter bank is prone to causing further inductor-capacitor (LC) resonance, resulting in harmonic instability and affecting the stability of the converter's grid-connected operation.

[0035] Figure 1 This is a schematic diagram of the energy storage system using a centralized converter in related technologies, such as... Figure 1 As shown, in a centralized converter energy storage system, several centralized converters constitute a subsystem, and several subsystems constitute the energy storage system. When the energy storage system is connected to the grid, the connection point (PCC) between the energy storage system and the grid is through the equivalent impedance Z. g Connect to the power grid.

[0036] Because the amplitudes of harmonics in similar photovoltaic-storage PCS systems are superimposed, the characteristics of their current harmonics, to a certain extent, satisfy the characteristics of Equation 1 below, and the characteristics of their voltage harmonics, to a certain extent, satisfy the characteristics of Equation 2 below. As the capacity of the energy storage system increases, the harmonic amplitude at the high-voltage side PCC point also increases, easily exceeding the high-voltage side harmonic amplitude requirements. Energy storage systems with centralized converters are limited by the switching frequency, making it difficult to effectively manage mid-to-high-order harmonics; additional filtering measures are needed for harmonic mitigation.

[0037]

[0038] Among them, I h Injecting current harmonics from the power grid into the subsystem, I N，h The current harmonics injected into the power grid for a centralized converter, V h Injecting voltage harmonics from the power grid into the subsystem, V N，h When injecting voltage harmonics into the power grid for a centralized converter, it is easy to see that the larger the power plant system capacity, the greater the current and voltage harmonics injected into the power grid. Therefore, when the grid-connected capacity reaches a certain size, it is necessary to carry out additional harmonic mitigation. Adding passive filters will significantly increase the system cost, and passive filter banks are prone to causing further inductor-capacitor (LC) resonance, resulting in harmonic instability and affecting the stability of the grid-connected operation of the energy storage system.

[0039] To solve the above-mentioned technical problems, the power conversion device and energy storage system (such as...) provided by the embodiments of this utility model Figures 2-8 (As shown) Harmonics are mitigated by utilizing the higher switching frequency of the string converter system. Ultimately, the harmonics at the PCC point of the entire energy storage system can be significantly improved, and theoretically, the harmonic content injected into the grid will not be affected by the increase in power plant capacity.

[0040] In some embodiments, an energy storage system may include energy storage modules and a power conversion device. The energy storage module is responsible for storing and releasing electrical energy. Common energy storage modules include battery packs, compressed air energy storage modules, pumped hydro storage devices, and new energy power generation equipment such as photovoltaic modules. The power conversion device is used to convert electrical energy into electrical energy.

[0041] In some embodiments, the energy storage system further includes an isolation transformer for converting high-voltage and low-voltage electrical energy and isolating high-voltage equipment and energy storage equipment to ensure the safe operation of the system. When the energy storage system is connected to the grid, the isolation transformer is used to convert the grid voltage (e.g., 10kV or 6kV) to a voltage level suitable for the energy storage module (e.g., 0.4kV).

[0042] Energy storage systems can be energy storage power stations. As the capacity of energy storage power stations increases, the number of converters also increases, and the superposition effect of harmonics generated by the converters becomes more pronounced, resulting in higher harmonic amplitudes at the converter-grid connection point (PCC). The power conversion device provided in this application embodiment can improve the harmonics generated by the converters and is suitable for large-capacity energy storage power stations.

[0043] Power conversion devices may include converters. A converter may include an inverter circuit that converts direct current (DC) from an energy storage module into alternating current (AC), and a converter may also include a rectifier circuit that converts AC to DC.

[0044] In some embodiments, the converter can be a power conversion system (PCS) that enables bidirectional power conversion. The PCS converts the direct current (DC) from the energy storage module into alternating current (AC) to meet the grid's demands. Simultaneously, during charging of the energy storage module, the AC is converted back to DC and stored within the module. The core functions of the PCS include charge / discharge control, grid synchronization, and power regulation.

[0045] Figure 2 This is a structural schematic diagram of the energy storage system 1000 provided in an embodiment of this utility model. (See attached diagram.) Figure 2 As shown, the power conversion device 100 provided in this embodiment includes a first converter group 110, a second converter group 120, and a transformer module 130. The first converter group 110 includes N first converters 111 connected to a first node. The second converter group 120 includes M second converters 121 connected to a second node. The second converters 121 are string converters, and N and M are positive integers. The transformer module 130 includes at least one transformer. The first converter group 110 is connected to the first side of a corresponding transformer via the first node, and the second converter group 120 is connected to the first side of a corresponding transformer via the second node. The second side of each transformer in the transformer module 130 is configured to connect to the power grid during grid-connected operation.

[0046] Specifically, the first node can be node N1, and N first converters 111 are connected to node N1. The second node can be node N2, and N second converters 121 are connected to node N2.

[0047] Transformer module 130 is used to convert high-voltage and low-voltage electrical energy and isolate high-voltage equipment and energy storage equipment to ensure the safe operation of the system. When the energy storage system 1000 is connected to the power grid, the first side of transformer module 130 is connected as the low-voltage side to the first converter group 110 and the second converter group 120, and the second side of transformer module 130 is connected to the power grid as the high-voltage side.

[0048] The second converter 121 is a string converter. When the energy storage system 1000 is connected to the grid, the second converter 121 can perform harmonic control. Its current harmonic characteristics satisfy the characteristics of Equation 3 to a certain extent, and its voltage harmonic characteristics satisfy the characteristics of Equation 4 to a certain extent.

[0049]

[0050] The harmonics emitted by the first converter group 110 can be canceled out by the harmonics emitted by the second converter group 120, which have the same equivalent amplitude but opposite phase. Therefore, the I flowing into the power grid h With V h It can achieve a low level of filtering without the need for additional filtering measures.

[0051] Among them, I h Injecting current harmonics from the power grid into the subsystem, I N，h The current harmonics injected into the power grid by a certain first converter 111, I′ M，h The current harmonics injected into the power grid by a certain second converter 121, V h Injecting voltage harmonics from the power grid into the subsystem, V N，h The voltage harmonics V′ injected into the power grid by a certain first converter 111 M，h Voltage harmonics are injected into the power grid for a certain second converter 121.

[0052] Thus, this utility model embodiment uses the second converter 121 to perform harmonic control without the need to add an additional passive filter, which reduces costs and avoids the passive filter bank causing further inductor-capacitor (LC) resonance that could affect the stability of the grid-connected operation of the energy storage system 1000.

[0053] Figure 3 This is a structural schematic diagram of the energy storage system 1000 of the hybrid converter provided in this embodiment of the utility model. Figure 3 As shown, in some embodiments, the N first converters 111 in the first converter group 110 are all centralized converters.

[0054] Specifically, a centralized converter typically refers to a large PCS (converter system) connecting multiple battery modules, with current centrally managed through a busbar. A string converter, on the other hand, may refer to multiple smaller converters connected in series or parallel, with each converter managing one battery module, which may offer greater flexibility.

[0055] Centralized converters have a simple structure but poor scalability; a failure in a centralized converter can affect the entire system. String converters, on the other hand, can be modularly designed, easily expanded, and a single failure does not affect overall operation. The configuration of the busbar may differ in different architectures; for example, centralized converters require larger busbar capacities, while string converters may have each module with its own busbar path.

[0056] Centralized converters offer advantages such as high cost-effectiveness and high system integration in large-scale energy storage systems. However, centralized converters typically integrate multiple power modules operating in parallel. Differences in the switching frequencies and phases of these modules can lead to the superposition of harmonic components, particularly a significant increase in the amplitude of low-frequency harmonics.

[0057] String converters, on the other hand, adopt a modular design, with a small cabinet size and flexible configuration. Using string converters for harmonic mitigation is more cost-effective and can improve high-frequency harmonics.

[0058] In the energy storage system 1000 with hybrid converters, the N first converters 111 in the first converter group 110 are all centralized converters. The N string converters generate certain harmonic currents and harmonic voltages during normal operation, and the other M string converters operate in harmonic mitigation mode to mitigate the harmonics generated by the N string converters, thus achieving harmonic mitigation within the energy storage system 1000.

[0059] The hybrid converter energy storage system 1000 provided in this application combines the advantages of centralized converters and string converters. While reducing the operating cost of the large energy storage system 1000, it can also improve harmonics through string converters and ensure the stability of the grid-connected operation of the energy storage system 1000.

[0060] In some implementations, the switching frequency of the first converter 111 is lower than the switching frequency of the second converter 121.

[0061] Specifically, compared to string converters, centralized converters need to handle larger power outputs, therefore, the switching losses of centralized converters increase more rapidly with increasing switching frequency. Higher switching frequencies generate more heat, requiring more complex cooling systems, increasing cost and size. Therefore, to maintain efficiency and reliability, the switching frequency of centralized converters must be limited, resulting in a lower switching frequency for centralized converters than for string converters. In other words, the switching frequency of the first converter 111 is lower than that of the second converter 121.

[0062] In addition, the centralized design of centralized converters focuses more on overall efficiency and long-term operating costs. The use of multi-level or complex topologies does not allow operation in high-frequency environments. In contrast, string converters can use simpler topologies and allow high-frequency operation. That is to say, the switching frequency of the first converter 111 is lower than the switching frequency of the second converter 121.

[0063] Understandably, a higher switching frequency reduces the harmonic content per switching cycle, making the output waveform closer to an ideal sine wave. Therefore, using the switching frequency of a string converter for harmonic mitigation is less costly and can improve high-frequency harmonics.

[0064] In some implementations, the switching frequency of the first converter 111 is below 5 kHz, and the switching frequency of the second converter 121 is above 10 kHz.

[0065] The switching frequency of the first converter 111 is below 5 kHz. The low switching frequency and phase difference may lead to the superposition of harmonic components, especially the significant increase in the amplitude of low-frequency harmonics (5th to 7th). Using the switching frequency of a string converter for harmonic mitigation is less costly and can improve high-frequency harmonics (above 30th), which can meet the grid-connected operation requirements of the energy storage system.

[0066] Figure 4 This is a structural schematic diagram of the energy storage system 1000 of the string converter provided in this embodiment of the utility model. Figure 4 As shown, in some embodiments, the N first converters 111 in the first converter group 110 are all string converters.

[0067] Specifically, in the centralized converter energy storage system 1000, the N first converters 111 in the first converter group 110 are all string converters. The N string converters generate certain harmonic currents and harmonic voltages during normal operation. In addition, M string converters operate in harmonic mitigation mode to mitigate the harmonics generated by the N string converters, thus achieving harmonic mitigation within the energy storage system 1000.

[0068] Figure 5 This is the first structural schematic diagram of the transformer module 130 provided in this embodiment of the utility model. (See attached diagram.) Figure 5 As shown, in some embodiments, transformer module 130 includes a first transformer 131 and a second transformer 132. A first converter group 110 is connected to a first side of the first transformer 131 through a first node, and a second converter group 120 is connected to a first side of the second transformer 132 through a second node. The second side of the first transformer 131 is connected to the second side of the second transformer 132 and is configured to connect to the power grid during grid-connected operation.

[0069] Specifically, the first side of the first transformer 131 is connected to the first converter group 110 as the low-voltage side, the first side of the second transformer 132 is connected to the second converter group 120 as the low-voltage side, and the second sides of the first transformer 131 and the second transformer 132 are connected to the power grid as the high-voltage side when the energy storage system 1000 is connected to the grid.

[0070] The first node can be node N1, with N first converters 111 connected to node N1 and connected to the low-voltage side of the first transformer 131 through node N1. The second node can be node N2, with N second converters 121 connected to node N2 and connected to the low-voltage side of the second transformer 132 through node N2.

[0071] Figure 6 This is a second structural schematic diagram of the transformer module 130 provided in this embodiment of the utility model, as shown below. Figure 6 As shown, in some embodiments, transformer module 130 includes a third transformer 133, a first converter group 110 is connected to a first side of the third transformer 133 via a first node, a second converter group 120 is connected to the first side of the third transformer 133 via a second node, and a second side of the third transformer 133 is configured to be connected to the power grid during grid-connected operation.

[0072] Specifically, the first side of the third transformer 133 serves as the low-voltage side, connecting the first converter group 110 and the second converter group 120. The second side of the third transformer 133 serves as the high-voltage side, connecting to the power grid when the energy storage system 1000 is connected to the grid.

[0073] The first node can be node N1, with N first converters 111 connected to node N1 and connected to the low-voltage side of the third transformer 133 through node N1. The second node can be node N2, with N second converters 121 connected to node N2 and connected to the low-voltage side of the third transformer 133 through node N2.

[0074] Figure 7 This is a first structural schematic diagram of the sensor provided in this embodiment of the utility model, as shown below. Figure 7 As shown, in some embodiments, the power conversion device 100 includes a current sensor 140, which is disposed at a first node and configured to detect the current at the first node.

[0075] Specifically, the second converter group 120 can be communicatively connected to the current sensor 140, and determine the current at the first node based on the current detected by the current sensor 140 for harmonic mitigation. Based on Equation 3 above, the harmonics emitted by the first converter group 110 can be canceled by the equivalent amplitude but opposite phase harmonic current emitted by the second converter group 120. Therefore, the I flowing into the power grid... hIt can achieve a low level of filtering without the need for additional filtering measures.

[0076] In some implementations, the current sensor 140 may also be located on the high-voltage side corresponding to the first node, and the second converter group 120 may be communicatively connected to the current sensor 140 and determine the current at the first node based on the high-voltage side corresponding to the first node to perform harmonic mitigation.

[0077] Figure 8 This is a second structural schematic diagram of the sensor provided in this embodiment of the utility model, as shown below. Figure 8 As shown, the power conversion device 100 includes a voltage sensor 150, which is disposed at a first node and configured to detect the voltage at the first node.

[0078] Specifically, the second converter group 120 can be communicatively connected to the voltage sensor 150, and determine the voltage at the first node based on the voltage detected by the voltage sensor 150 for harmonic mitigation. Based on Equation 3 above, the harmonics emitted by the first converter group 110 can be canceled by the equivalent amplitude but opposite phase harmonic voltage emitted by the second converter group 120. Therefore, the V flowing into the power grid... h It can achieve a low level of filtering without the need for additional filtering measures.

[0079] In some implementations, the voltage sensor 150 may also be located on the high-voltage side corresponding to the first node, and the second converter group 120 may be communicatively connected to the voltage sensor 150 and determine the voltage at the first node based on the high-voltage side corresponding to the first node to perform harmonic mitigation.

[0080] In the description of this specification, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with an embodiment or example that are included in at least one embodiment or example of this utility model. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0081] Furthermore, the term "connection" should be interpreted broadly. For example, it can include a fixed connection, a detachable connection, or an integral connection; it can include a direct connection or an indirect connection through an intermediate medium; and it can also include communication between the internal components of two elements. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0082] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this utility model, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0083] Any process or method described in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the present invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order according to the functions involved, as should be understood by those skilled in the art to which embodiments of the present invention pertain.

[0084] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A power conversion device, characterized in that, include: The first converter group includes N first converters, and the N first converters are connected to the first node; The second converter group includes M second converters, the M second converters are connected to the second node, the second converters are string converters, and N and M are positive integers; A transformer module includes at least one transformer, a first converter group is connected to a first side of a corresponding transformer via a first node, a second converter group is connected to a first side of a corresponding transformer via a second node, and the second side of each transformer in the transformer module is configured to connect to the power grid during grid-connected operation.

2. The power conversion device according to claim 1, characterized in that, All N converters in the first converter group are centralized converters.

3. The power conversion device according to claim 2, characterized in that, The switching frequency of the first converter is lower than that of the second converter.

4. The power conversion device according to claim 3, characterized in that, The switching frequency of the first converter is less than 5 kHz, and the switching frequency of the second converter is greater than 10 kHz.

5. The power conversion device according to claim 1, characterized in that, All N first converters in the first converter group are string converters.

6. The power conversion device according to claim 1, characterized in that, The transformer module includes a first transformer and a second transformer. The first converter group is connected to the first side of the first transformer through the first node, and the second converter group is connected to the first side of the second transformer through the second node. The second side of the first transformer is connected to the second side of the second transformer and is configured to connect to the power grid during grid-connected operation.

7. The power conversion device according to claim 1, characterized in that, The transformer module includes a third transformer. The first converter group is connected to the first side of the third transformer through the first node, and the second converter group is connected to the first side of the third transformer through the second node. The second side of the third transformer is configured to be connected to the power grid during grid-connected operation.

8. The power conversion device according to claim 1, characterized in that, The power conversion device includes a current sensor disposed at the first node and configured to detect the current at the first node.

9. The power conversion device according to claim 1, characterized in that, The power conversion device includes a voltage sensor disposed at the first node and configured to detect the voltage at the first node.

10. An energy storage system, characterized in that, The energy storage system includes the power conversion device according to any one of claims 1-9.

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