Energy storage valve submodule and high-voltage boost transformerless energy storage system

Abstract

This invention relates to an energy storage valve submodule and a high-voltage boost transformerless energy storage system. By adding an under-attenuation oscillation suppression circuit to the energy storage valve submodule, the suppression circuit is connected in series with a first capacitor, and the resistor-capacitance branch formed by the suppression circuit being connected in series with the first capacitor is connected in parallel with the power conversion unit and the energy storage unit, respectively. The suppression circuit can suppress the under-attenuation oscillation current that occurs when the energy storage valve submodule switches between conduction and disconnection states by adjusting the resistance value of the impedance in the energy storage valve submodule. This reduces the under-attenuation oscillation current that occurs when the energy storage valve submodule switches between conduction and disconnection states, thereby reducing the damage that the under-attenuation oscillation current inflicts on the energy storage valve submodule and improving the reliability of the energy storage valve submodule.

Description

Technical Field

[0001] (Cross-reference to Related Applications) This application refers to Chinese Patent Application No. 2023106870411, titled "Energy Storage Valve Sub-module and High-Voltage Boost Transformerless Energy Storage System", filed on June 9, 2023, the content of which is hereby incorporated by reference in its entirety into this application.

[0002] This application relates to the field of energy storage technology, particularly to an energy storage valve sub-module and a high-voltage boost transformerless energy storage system.

Background Art

[0003] With the development of large-scale energy storage, high-voltage boost transformerless energy storage systems are gradually being widely used.

[0004] In some cases, a high-voltage boost transformerless energy storage system includes a plurality of energy storage valve sub-modules connected in cascade, and each energy storage valve sub-module includes an energy storage unit. During use, by controlling the conduction and cutoff states of each energy storage valve sub-module, the charging and discharging of the energy storage unit in each energy storage valve sub-module can be realized.

[0005] However, in the above cases, the reliability of the energy storage valve sub-module is relatively low.

Summary of the Invention

[0006] Based on this, to address the above technical problems, there is a need to provide an energy storage valve sub-module and a high-voltage boost transformerless energy storage system that improve the reliability of the energy storage valve sub-module. Here, "boost transformerless" means connecting the energy storage system to the power grid without passing through a boost transformer, and this connection does not exclude the existence of other components.

[0007] According to a first aspect, an embodiment of the present application provides an energy storage valve submodule, which includes a power conversion unit, a first capacitor, a suppression circuit, and an energy storage unit, wherein the suppression circuit is connected in series with the first capacitor to form a resistive-capacitance branch, and the resistive-capacitance branch is connected in parallel with the power conversion unit and the energy storage unit, respectively.

[0008] The energy storage valve submodule according to the embodiment of the present invention adds an under-attenuation oscillation suppression circuit to the energy storage valve submodule. The suppression circuit is connected in series with the first capacitor, and the resistor-capacitance branch formed by the suppression circuit being connected in series with the first capacitor is connected in parallel with the power conversion unit and the energy storage unit, respectively. The suppression circuit can suppress the under-attenuation oscillation current that occurs when the energy storage valve submodule switches between conduction and disconnection states by adjusting the resistance value of the impedance in the energy storage valve submodule. In this way, the under-attenuation oscillation current that occurs when the energy storage valve submodule switches between conduction and disconnection states is significantly reduced, achieving the effect of suppressing the under-attenuation oscillation current, and thereby significantly reducing the damage that the under-attenuation oscillation current inflicts on the energy storage valve submodule, thereby improving the reliability of the energy storage valve submodule.

[0009] In one embodiment, the first capacitor includes a DC link capacitor.

[0010] In one embodiment, the energy storage valve submodule includes a power conversion unit, a DC link capacitor, a suppression circuit, and an energy storage unit, wherein the suppression circuit is connected in series with the DC link capacitor to form a resistive-capacitive branch, and the resistive-capacitive branch is connected in parallel with the power conversion unit and the energy storage unit, respectively.

[0011] The energy storage valve submodule according to the embodiment of the present invention adds an under-attenuation oscillation suppression circuit to the energy storage valve submodule. The suppression circuit is connected in series with a DC link capacitor, and the resistor-capacitance branch formed by the suppression circuit being connected in series with the DC link capacitor is connected in parallel with the power conversion unit and the energy storage unit, respectively. The suppression circuit can suppress the under-attenuation oscillation current that occurs when the energy storage valve submodule switches between conduction and disconnection states by adjusting the resistance value of the impedance in the energy storage valve submodule. This significantly reduces the under-attenuation oscillation current that occurs when the energy storage valve submodule switches between conduction and disconnection states, achieving the effect of suppressing under-attenuation oscillation current and significantly reducing the damage that under-attenuation oscillation current inflicts on the energy storage valve submodule, thereby improving the reliability of the energy storage valve submodule.

[0012] In one embodiment, the suppression circuit includes a resistive element.

[0013] In the embodiments of this invention, a suppression circuit is realized using a resistive element, and the resistive element provides the necessary resistance value to suppress the under-attenuation oscillation current that occurs when the energy storage valve submodule conducts. This is economical, convenient, and simple, and significantly reduces the additional impact on the overall function of the energy storage valve submodule, thereby further improving the reliability of the energy storage valve submodule.

[0014] In one embodiment, the suppression circuit further includes a switch circuit, which is used to control the conduction and disconnection states of a resistive element.

[0015] In the embodiment of the present invention, a switch circuit controls whether the resistive element is connected to or disconnected from the energy storage valve submodule. Only when the resistive element is connected to the energy storage valve submodule and operating does the energy storage unit suppress under-attenuation oscillation that occurs when it is connected in the corresponding state. This improves the accuracy of suppressing under-attenuation oscillation of the energy storage valve submodule.

[0016] In one of these embodiments, the switch circuit is connected in parallel with the resistive element.

[0017] In the embodiment of the present invention, a switch circuit is connected in parallel next to the resistive element, and the resistive element is either connected to or disconnected from the energy storage valve submodule by the on and off of the switch circuit. By suppressing the under-attenuation oscillation that occurs when the energy storage unit is connected to the energy storage valve submodule in the corresponding state only when the resistive element is connected to the energy storage valve submodule and operates, the accuracy of suppressing under-attenuation oscillation of the energy storage valve submodule can be improved.

[0018] In one embodiment, the suppression circuit further includes a switch circuit, which is connected in parallel to a resistive element.

[0019] In the embodiment of the present invention, a switch circuit is connected in parallel next to the resistive element, and the resistive element is made conductive to or disconnected from the energy storage valve submodule by turning the switch circuit on and off. Only when the energy storage valve submodule is made conductive and operates does the energy storage unit suppress under-attenuation oscillation that occurs when conductive in the relevant state, thereby improving the accuracy of suppressing under-attenuation oscillation of the energy storage valve submodule.

[0020] In one embodiment, the resistive element includes a first resistor and a second resistor connected in series with respect to each other, and the switch circuit further includes a first switch and a second switch, the first switch connected in parallel with the first resistor and the second switch connected in parallel with the second resistor.

[0021] In the embodiment of the present invention, two resistors are added to the energy storage valve submodule, and two different switches are added to control the conduction and disconnection states of the two resistors in the energy storage valve submodule, respectively. Only one of the two resistors is conducted when the energy storage unit is in a charging state or when the energy storage unit is in a discharge state. As a result, the resistance values ​​of the two resistors are different, and the degree of under-attenuation oscillation that can be suppressed when the energy storage unit is in a charging state or when the energy storage unit is in a discharge state is also different, thereby more accurately suppressing under-attenuation oscillation of the energy storage unit in the different charging and discharging states.

[0022] In one embodiment, the first switch and / or the second switch are diodes.

[0023] In the embodiment of the present invention, a diode is used to realize the first and second switches. Since the diode does not require control, it switches between two states, on and off, depending on the voltage in the circuit. This has the advantage of a fast switching speed and a particularly short switching time, which allows for rapid and accurate control of the conduction and disconnection states of the resistive element. Furthermore, it is possible to more accurately suppress under-attenuation oscillation of the energy storage unit in different charging and discharging states.

[0024] In one embodiment, the resistance value of the first resistor is greater than the resistance value of the second resistor.

[0025] In an embodiment of the present application, by setting the resistance value of the first resistor to be larger than the resistance value of the second resistor, it is possible to relatively greatly suppress the insufficient attenuation oscillation current generated during conduction when the energy storage unit is in a charged state, and the degree of suppression of the insufficient attenuation oscillation current generated during conduction when the energy storage unit is in a discharged state may be relatively small. In this way, by setting the first resistor and the second resistor to have different resistance values, it is possible to distinguish and suppress the insufficient attenuation oscillation current generated during conduction when the energy storage unit is in a charged state and a discharged state, and improve the suppression accuracy of the insufficient attenuation oscillation of the energy storage valve sub-module.

[0026] In an embodiment of the present application, by setting the resistance value of the first resistor to be larger than the resistance value of the second resistor, it is possible to relatively greatly suppress the insufficient attenuation oscillation current generated during conduction when the energy storage unit is in a charged state, and the degree of suppression of the insufficient attenuation oscillation current generated during conduction when the energy storage unit is in a discharged state may be relatively small. In this way, by setting the first resistor and the second resistor to have different resistance values, it is possible to distinguish and suppress the insufficient attenuation oscillation current generated during conduction when the energy storage unit is in a charged state and a discharged state, and improve the suppression accuracy of the insufficient attenuation oscillation of the energy storage valve sub-module.

[0027] In one embodiment, the resistive element includes a third resistor and a fourth resistor connected in parallel with each other, the switch circuit further includes a third switch and a fourth switch, the third switch is connected in series with the third resistor, and the fourth switch is connected in series with the fourth resistor.

[0028] In an embodiment of the present application, two resistors are added to the energy storage valve sub-module. By adding two different switches, the conduction and cutoff states of these two resistors in the energy storage valve sub-module are controlled respectively. Only one of the two resistors is conducted when the energy storage unit is in a charging state or when the energy storage unit is in a discharging state. Based on this, the resistance values of the two resistors are different, and the degree of insufficient attenuation oscillation that can be suppressed when the energy storage unit is in a charging state or when the energy storage unit is in a discharging state is also different. Thereby, the insufficient attenuation oscillation of the energy storage unit in different charging and discharging states can be more accurately suppressed.

[0029] In one embodiment, the third switch and / or the fourth switch is a diode.

[0030] In an embodiment of the present application, a diode is adopted to realize the third switch and the fourth switch. Since the diode does not require control, by switching between the on and off states depending on the voltage in the circuit, it has the advantages of fast switching speed and particularly short switching time. Thus, the conduction and cutoff states of the resistance element can be controlled quickly and accurately, and further, the effect that the insufficient attenuation oscillation of the energy storage unit in different charging and discharging states can be more accurately suppressed can be realized.

[0031] In one embodiment, the resistance value of the third resistor is larger than the resistance value of the fourth resistor.

[0032] In the embodiment of the present invention, by setting the resistance value of the third resistor to be greater than that of the fourth resistor, the under-attenuation oscillation current generated when the energy storage unit is conducting in a charged state can be suppressed relatively significantly, while the degree of suppression of the under-attenuation oscillation current generated when the energy storage unit is conducting in a discharged state may be relatively small. In this way, by setting the third resistor and the fourth resistor to different resistance values, the under-attenuation oscillation current generated when the energy storage unit is conducting in a charged state and a discharged state can be distinguished and suppressed, thereby improving the accuracy of suppressing under-attenuation oscillation in the energy storage valve submodule.

[0033] In one embodiment, the resistance range of the resistive element is 10 ohms (mΩ) to 500 mΩ.

[0034] In the embodiment of the present invention, by setting the value range of the resistive element to 10 mΩ to 500 mΩ, the resistive element can be made to correspond to the capacitance value of the first capacitor, the inductance value of the equivalent stray inductance in the energy storage unit, and the resistance value of the equivalent internal resistance in the energy storage unit under the configuration conditions of the high-voltage boost transformerless energy storage system. This makes it possible to accurately suppress under-attenuation oscillation of the energy storage submodule under the configuration conditions of the high-voltage boost transformerless energy storage system.

[0035] In one embodiment, the energy storage valve submodule further includes a second capacitor, which is connected in parallel to the resistor-capacitance branch.

[0036] In the embodiment of the present invention, by connecting a second capacitor in parallel with the resistor-capacitance branch, the overvoltage stress during the shutdown of the power device in the power conversion unit can be reduced. This reduces the risk of the power device in the power conversion unit failing due to excessive overvoltage stress, improves the operational reliability of the power device in the power conversion unit, and further improves the operational reliability of the energy storage valve submodule.

[0037] In one embodiment, the second capacitor includes a snubber capacitor.

[0038] In one embodiment, the energy storage valve submodule further includes a snubber capacitor, which is connected in parallel to the resistive-capacitive branch.

[0039] In the embodiment of the present invention, by connecting a snubber capacitor in parallel with the resistor-capacitance branch, the overvoltage stress during the interruption of power devices in the power conversion unit can be reduced. This reduces the risk of power devices in the power conversion unit failing due to excessive overvoltage stress, improves the operational reliability of power devices in the power conversion unit, and further improves the operational reliability of the energy storage valve submodule.

[0040] In one embodiment, the capacitance value of the second capacitor is smaller than the capacitance value of the first capacitor.

[0041] In the embodiment of the present invention, by setting the capacitance value of the second capacitor to be smaller than that of the first capacitor, a certain distinction is made between the high-frequency current passing through the second capacitor and the high-frequency current passing through the first capacitor when the energy storage valve submodule is conducting. Furthermore, because the capacitance value of the second capacitor is much smaller than that of the first capacitor, it is possible to suppress the deterioration of under-attenuation oscillation of the energy storage valve submodule due to an excessive capacitance value of the second capacitor, thereby reducing the overvoltage stress when the power device in the power conversion unit is shut off, reducing the risk of associated effects, and improving the operational reliability of the energy storage valve submodule.

[0042] In one embodiment, the capacitance value of the snubber capacitor is smaller than the capacitance value of the DC link capacitor.

[0043] In the embodiment of the present invention, by setting the capacitance value of the snubber capacitor to be smaller than that of the DC link capacitor, a certain distinction is made between the high-frequency current passing through the snubber capacitor and the high-frequency current passing through the DC link capacitor when the energy storage valve submodule is conducting. Furthermore, because the capacitance value of the snubber capacitor is much smaller than that of the DC link capacitor, it is possible to suppress the deterioration of the degree of under-attenuation oscillation of the energy storage valve submodule due to an excessive capacitance value of the snubber capacitor, thereby reducing the overvoltage stress when the power device in the power conversion unit is shut off, reducing the risk of associated effects, and improving the operational reliability of the energy storage valve submodule.

[0044] In one embodiment, the capacitance range of the second capacitor is 10 microfarads (uF) to 300uF.

[0045] In the embodiment of the present invention, the capacitance range of the second capacitor is set to 10uF to 300uF. This reduces the overvoltage stress when the power device in the power conversion unit is interrupted under the configuration conditions of high-voltage boost transformerless energy storage, while simultaneously reducing the incidental influence on the overall topology of the energy storage valve submodule and improving the operational reliability of the energy storage valve submodule.

[0046] In one embodiment, the capacitance range of the snubber capacitor is 10uF to 300uF.

[0047] In the embodiment of this application, the capacitance range of the snubber capacitor is set to 10uF to 300uF. This reduces the overvoltage stress when the power device in the power conversion unit is interrupted under the configuration conditions of high-voltage boost transformerless energy storage, while simultaneously reducing the incidental influence on the overall topology of the energy storage valve submodule and improving the operational reliability of the energy storage valve submodule.

[0048] In one embodiment, the energy storage valve submodule further includes a bypass circuit, which is connected in parallel to the energy storage valve submodule.

[0049] In the embodiment of the present invention, a bypass circuit is installed between the energy storage valve submodule and the port of the main circuit to which the high-voltage boost transformerless energy storage system is connected. This allows the energy storage valve submodule to be isolated from the high-voltage boost transformerless energy storage system in the event of a failure in the energy storage valve submodule, thereby improving the operational stability and safety of the high-voltage boost transformerless energy storage system.

[0050] In one embodiment, the switching frequency of conduction and disconnection of the energy storage valve submodule has a positive correlation with the energy loss generated by the suppression circuit.

[0051] In the embodiment of the present invention, due to the characteristic that the conduction and disconnection switching frequencies of the energy storage valve submodule have a positive correlation with the energy loss generated by the suppression circuit, by setting the equivalent conduction and disconnection switching frequencies when the energy storage valve submodule is conducted and disconnected once in a high-voltage boost transformerless energy storage system, the energy storage valve submodule can be conducted and disconnected at a relatively low equivalent conduction and disconnection switching frequency, thereby reducing the losses of the energy storage valve submodule and improving the economics and safety of the energy storage valve submodule application.

[0052] In one embodiment, the rate of change of the interruption current of the power device in the power conversion unit has an inverse correlation with the parameter value of the drive device in the power device drive circuit.

[0053] In the embodiment of the present invention, the characteristic that the rate of change of the interruption current of the power device in the power conversion unit has an inverse correlation with the parameter value of the drive device in the drive circuit of the power device reduces the rate of change of the interruption current of the power device in the power conversion unit. This further reduces the interruption overvoltage of the power device in the power conversion unit, and significantly reduces the problem of the power device in the power conversion unit failing due to excessive overvoltage stress, thereby improving the operational reliability of the power conversion unit.

[0054] In one embodiment, the parameter values ​​of the drive device include the resistance value of the gate-off resistor in the drive circuit and / or the capacitance value of the gate capacitor in the drive circuit.

[0055] According to a second aspect, an embodiment of the present application provides a high-voltage boost transformerless energy storage system. This high-voltage boost transformerless energy storage system includes an energy storage valve submodule provided in any one embodiment of the first aspect described above.

[0056] The above description is merely an outline of the proposed technology. In order to better understand the technical means of this application, and to make the above and other objectives, features, and advantages of this application clearer and easier to understand, specific embodiments of this application will be described below, in particular. [Brief explanation of the drawing]

[0057] To more clearly explain the technical concept of the embodiments of this application, the drawings used in the embodiments of this application are briefly introduced below. Obviously, the drawings described below are only a few embodiments of this application, and those skilled in the art can obtain other drawings based on these without expending any creative effort.

[0058] [Figure 1] This is a schematic diagram of the configuration of a high-voltage boost transformerless energy storage system in one embodiment. [Figure 2] This is a schematic topology diagram of an energy storage valve submodule in one embodiment. [Figure 3] This is a schematic diagram of the equivalent stray inductance and equivalent internal resistance of the energy storage unit within the energy storage valve submodule in one embodiment. [Figure 4] This is a schematic topology diagram of an energy storage valve submodule in another embodiment. [Figure 5] This is a schematic topology diagram of an energy storage valve submodule in another embodiment. [Figure 6] This is a schematic diagram of the implementation structure of a power conversion unit within an energy storage valve submodule in one embodiment. [Figure 7] This is a schematic diagram of the implementation structure of the power conversion unit within the energy storage valve submodule in another embodiment. [Figure 8] This is a schematic diagram of the implementation structure of the suppression circuit within the energy storage valve submodule in one embodiment. [Figure 9] This is a schematic diagram of the equivalent network after adding a suppression circuit to the energy storage valve submodule in one embodiment. [Figure 10] This is a schematic diagram of the implementation structure of the suppression circuit within the energy storage valve submodule in another embodiment. [Figure 11] This is a schematic diagram of the implementation structure of the switch circuit in the suppression circuit in one embodiment. [Figure 12] This is a schematic diagram of the implementation structure of the suppression circuit within the energy storage valve submodule in another embodiment. [Figure 13] This is a schematic diagram of the implementation structure of the suppression circuit within the energy storage valve submodule in another embodiment. [Figure 14] This is a schematic diagram of a structure in which a second capacitor is added to an energy storage valve submodule in one embodiment. [Figure 15] This is a schematic diagram of the drive circuit for a power device in a power conversion unit in one embodiment. [Figure 16] This is a schematic diagram of a structure in which a bypass circuit is added to an energy storage valve submodule in one embodiment. [Modes for carrying out the invention]

[0059] The embodiments of the present invention will be described in detail below with reference to the drawings. The following embodiments are provided solely to clarify the present invention and are illustrative only; they do not limit the scope of protection of the present invention.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art of the present application. The terms used herein are solely for the purpose of describing specific embodiments and are not intended to limit the present application. The term “including” and any variations thereof in the description of the present specification, claims, and drawings are intended to intentionally cover non-exclusive “including.” In the descriptions of embodiments of the present application, technical terms such as “first,” “second,” “third,” “fourth,” etc., are solely for the purpose of distinguishing different subjects and should not be understood as indicating or implying relative importance or suggesting the number, specific order, or hierarchical relationship of technical features. In the descriptions of embodiments of the present application, unless otherwise clearly and specifically limited, “multiple” means two or more.

[0061] In this specification, the “Examples” refer to certain features, structures, or characteristics described in conjunction with the Examples may be included in at least one Example of the Application. The appearance of this phrase in each location in the Specification does not necessarily refer to the same Example, nor does it mean that each Example is mutually exclusive or alternative to the others. Those skilled in the art will understand, both explicitly and implicitly, that the Examples described herein can be combined with other Examples.

[0062] In the description of the embodiments of this application, unless otherwise explicitly defined or limited, technical terms such as "connection" should be understood in a broad sense. For example, it may refer to a direct connection, an indirect connection through an intermediate medium, internal communication between two elements, or an interaction relationship between two elements. A person skilled in the art will be able to understand the specific meaning of the above terms in the embodiments of this application depending on the specific circumstances.

[0063] The high-voltage boost transformerless energy storage system is a novel energy storage system that utilizes modularized multi-level cascade connection technology to cascade multiple energy storage valve submodules, enabling simultaneous AC / DC power conversion and energy storage. Its advantages, such as a high degree of modularization and good harmonic characteristics, have led to its increasing use in power grids. Each energy storage valve submodule in the high-voltage boost transformerless energy storage system contains an energy storage unit, which includes a battery pack. In actual use, charging and discharging of the energy storage unit in each energy storage valve submodule can be achieved by controlling each cascaded energy storage valve submodule.

[0064] Figure 1 is a schematic diagram of the configuration of a high-voltage AC step-up transformerless energy storage system, using a step-up transformerless energy storage system for three-phase power grids A, B, and C as an example. As shown in Figure 1, the high-voltage step-up transformerless energy storage system includes three-phase energy storage cascade chains A, B, and C, and each phase energy storage cascade chain includes one bridge arm reactor and m energy storage modules. Here, the energy storage modules on the three-phase energy storage cascade chain are represented as SM1#m, SM2#m, SM3#m, respectively, where m is 1, 2, 3, ..., n. In other embodiments, for example, in a high-voltage DC step-up transformerless energy storage system, the three-phase AC current may be converted to DC current by a converter valve, the energy storage valve may be directly mounted on the DC power grid, and the energy storage valve may include multiple energy storage valve submodules.

[0065] In related technologies, the topology of the energy storage valve submodule in a high-voltage boost transformerless energy storage system includes a power conversion unit 10, a first capacitor 20, and an energy storage unit 30, as shown in Figure 2. In Figure 2, S1 and S2 represent two connection ports, and each energy storage valve submodule needs to be connected to the main circuit of the high-voltage boost transformerless energy storage system via the two connection ports S1 and S2 in order to connect to the high-voltage power grid via the main circuit. Refer to S1 and S2 in Figure 1 for the connection relationships here.

[0066] Generally, a relatively large equivalent internal resistance and equivalent stray inductance exist within the energy storage unit. This equivalent internal resistance and equivalent stray inductance originate not only from the connection bars within the energy storage unit but also from the busbars connecting the energy storage unit and the power conversion unit in the overall topology of the energy storage valve submodule. After the energy storage unit is connected in the manner shown in Figure 2, the equivalent resistance, equivalent stray inductance, and first capacitor within the energy storage unit are equivalent to a single parallel-connected RLC network. The energy storage valve submodule has two operating modes in the overall high-voltage boost transformerless energy storage system: conduction and disconnection. When the energy storage valve submodule switches between conduction and disconnection, current from the main circuit of the high-voltage boost transformerless energy storage system enters the energy storage valve submodule, and this current can be considered as a step current source excitation for the RLC network. Referring to Figure 3, which is a schematic diagram of a parallel RLC network equivalent to the topology of the energy storage valve submodule, where L represents the equivalent stray inductance, Rdc represents the equivalent internal resistance, and I / P represents the step current source excitation. The power conversion unit in the energy storage valve submodule is not shown in Figure 3.

[0067] Because the equivalent stray inductance is relatively large, the inductive reactance of the equivalent stray inductance L in the energy storage valve submodule and the capacitive reactance of the first capacitor become mismatched. In this case, when this step current source excitation I / P occurs, the mismatch between the inductive reactance of the equivalent stray inductance L and the capacitive reactance of the first capacitor causes under-attenuation oscillation to occur throughout the entire RLC network, forming an under-attenuation network that causes under-attenuation oscillation in the first capacitor and the energy storage unit.

[0068] This under-attenuation oscillation can cause certain damage to the energy storage valve submodule, including, but not limited to, overcurrent in the energy storage unit, leading to damage, degradation, and reduced lifespan of the energy storage unit, and increasing the capacitor current in the energy storage valve submodule. For example, it can increase by about 30%. This leads to an increase in the weight, volume, and cost of the capacitor, and if the energy storage valve submodule remains in an overcurrent state for a long period during operation, it can also impose relatively large current stresses on the electrical components in the energy storage valve submodule. This affects the operational reliability of the energy storage valve submodule.

[0069] This can be addressed by at least one of the following means: increasing the capacitance value of the capacitor in the energy storage valve submodule, reducing stray inductance, or increasing resistance. However, considering that the main sources of equivalent stray inductance in the energy storage unit are the connection bars inside the energy storage unit and the busbars connecting the energy storage unit and the power conversion unit, it is difficult to reduce it. Furthermore, the equivalent internal resistance in the energy storage unit mainly originates from the internal resistance of the large number of series-parallel connected battery cores inside, and since the resistance value of this equivalent internal resistance is relatively low and fluctuates relatively large with the charge-discharge frequency, this equivalent internal resistance is not sufficient to suppress under-attenuation oscillation. Adding a resistor to the main circuit of a high-voltage boost transformerless energy storage system results in significant losses even when adding a milliohm-level resistor, because the charge-discharge current of energy storage in a high-voltage boost transformerless energy storage system can reach several thousand amperes. This causes a substantial temperature rise and affects the heat dissipation design and lifespan of the energy storage unit. When suppressing oscillation by increasing the capacitance of the capacitor in an energy storage valve submodule, it is necessary to increase the capacitor's capacitance value to several hundred mF. However, as the capacitance value increases, the volume, weight, and cost of the capacitor also increase accordingly, which will have a certain impact on the applicability and convenience of the energy storage valve submodule.

[0070] Based on the above considerations, it is currently not possible to suppress under-attenuation oscillation by adjusting the parameters in the energy storage valve submodule. Therefore, the embodiment of the present application improves the topology of the energy storage valve submodule and adds an under-attenuation oscillation suppression circuit to the energy storage valve submodule. The suppression circuit suppresses the under-attenuation oscillation current that occurs when the entire energy storage valve submodule switches between conduction and disconnection states, thereby significantly reducing the under-attenuation oscillation current that occurs when the energy storage valve submodule switches between conduction and disconnection states. This achieves the effect of suppressing under-attenuation oscillation current, and by significantly reducing the damage that under-attenuation oscillation current inflicts on the energy storage valve submodule, the reliability of the energy storage valve submodule can be improved.

[0071] The detailed implementation process of the energy storage valve submodule according to the present invention will be described below with reference to specific embodiments. As shown in Figure 4, this is a schematic topology of the energy storage valve submodule provided in the embodiment of the present invention. This energy storage valve submodule includes a power conversion unit 10, a first capacitor 20, a suppression circuit 40, and an energy storage unit 30. The suppression circuit 40 is connected in series with the first capacitor 20 to form a resistor-capacitance branch, and the resistor-capacitance branch is connected in parallel with the power conversion unit 10 and the energy storage unit 30, respectively.

[0072] In the embodiments of this application, an energy storage valve submodule is generally a submodule of an energy storage system, where the energy storage system can adjust the direction or magnitude of the power flow in the power grid system, and is similar in function to a valve, and is also called an energy storage valve. However, it should be emphasized that in the embodiments of this application, a submodule in an energy storage system is called an energy storage valve submodule, and this is merely a representative example of each submodule in the energy storage system, and is not used to limit the nature of each submodule's function, structure, or usage conditions. Therefore, it may be called an energy storage submodule, charge / discharge submodule, submodule, etc., depending on the actual demand at the time of use, and this application does not limit the names of each submodule in the energy storage system.

[0073] In the embodiment of the present invention, a suppression circuit 40 is connected in series to the branch where the first capacitor 20 in the energy storage valve submodule is located, forming a resistive-capacitive branch, which is connected in parallel to both the power conversion unit 10 and the energy storage unit 30. As can be seen, Figure 4 is just one example of a connection configuration, and under some operating conditions, the resistive-capacitive branch may be connected in the configuration shown in Figure 5.

[0074] In one embodiment, the first capacitor 20 includes a DC link capacitor, where the DC link capacitor is located at the DC terminal of the module, has a relatively large capacitance value, and is used to support the module voltage or suppress voltage fluctuations.

[0075] This energy storage valve submodule includes a power conversion unit, a DC link capacitor, a suppression circuit, and an energy storage unit. The suppression circuit is connected in series with the DC link capacitor to form a resistive-capacitive branch, which is connected in parallel with the power conversion unit and the energy storage unit, respectively.

[0076] In the energy storage valve submodule, the power conversion unit 10 primarily realizes two operating modes, conduction and interruption, in the charge and discharge states of the energy storage unit 30 via different passages. The power conversion unit 10 may be a half-bridge circuit composed of power semiconductor devices, a full-bridge circuit composed of power semiconductor devices, or a quasi-full-bridge circuit composed of power semiconductor devices.

[0077] In one embodiment, the implementation method of the power conversion unit 10 is shown as in Figure 6. It should be noted that Figure 6 and the drawings of subsequent embodiments of the embodiment of this application are both shown based on the connection method of Figure 4. Figure 6 shows a half-bridge circuit composed of power semiconductor devices. Here, T1 and T2 are both power devices, and may be implemented, for example, by insulated gate bipolar transistors (IGBTs).

[0078] In another embodiment, as shown in Figure 7, a different implementation method for the power conversion unit 10 is shown. Figure 7 shows a full-bridge circuit. Here, T1, T2, T3, and T4 are all power devices, and may all be implemented by IGBTs.

[0079] Furthermore, taking the power device in the power conversion unit 10 as an IGBT as an example, since the IGBT is a switch tube, a single drive circuit is connected to the gate of the IGBT in both Figures 6 and 7, and is mainly used to drive the IGBT on and off. However, in order to clearly emphasize the point, the drive circuit connected to the gate of the IGBT is not shown in the embodiment of this application.

[0080] When actually operating, the energy storage unit 30 in the energy storage valve submodule is divided into conduction mode and interruption mode in the charged state, and conduction mode and interruption mode in the discharge state. Referring to Figure 6 as an example, the operating principles in conduction mode and interruption mode will be explained with reference to the schematic circuit diagram. Specifically, it is as follows.

[0081] (1) Conduction mode in which the energy storage unit 30 is in a charged state: In this mode, the T2 tube is in an interrupted state, and the D2 and T1 tubes are also not conducting due to the reverse voltage. The current on the main circuit of the high-voltage boost transformerless energy storage system flows in from port S1, flows into the energy storage unit 30 via D1, and then flows out from port S2 to form a circuit. This allows the energy storage unit 30 to be charged.

[0082] (2) Disconnection mode when the energy storage unit 30 is in a charged state: In this mode, the T2 tube is conducting, and when the T2 tube is conducting, the voltage drop is very low, so the current on the main circuit flows in from port S1, passes directly through T2, and then flows out from port S2 to form a circuit, disconnecting the energy storage unit 30 from the main circuit and preventing it from charging. At this time, since there is voltage applied to the energy storage unit 30, D1 is clamped by the reverse voltage and enters a disconnection state.

[0083] (3) Conduction mode in which the energy storage unit 30 is in a discharge state: In this mode, the T2 tube, D2 and D1 are not conducting, but only the T1 tube is conducting, and the current on the main circuit of the high-voltage boost transformerless energy storage system flows directly into the energy storage unit 30 from the S2 port, passes through the T1 tube, and then flows out from the S1 port to form a circuit and put the energy storage unit 30 into a discharge state.

[0084] (4) Disconnection mode in which the energy storage unit 30 is in a discharge state: In this mode, the T2 tube, D2 and T1 are not conducting, and the current on the main circuit of the high-voltage boost transformerless energy storage system flows in from the S2 port, passes through D2 and flows out directly from the S1 port to form a circuit, completely disconnecting the energy storage unit 30 from the main circuit and preventing discharge.

[0085] As can be seen from the explanation of the operating principle of the power conversion unit 10 above, when the aforementioned energy storage valve submodule switches between conduction and disconnection states, current from the main circuit of the high-voltage boost transformerless energy storage system flows into the energy storage valve submodule, and this current can be considered as a single step current source excitation for the entire energy storage valve submodule. This is because the switching of the energy storage valve submodule between conduction and disconnection states must be achieved by turning the IGBT in the power conversion unit 10 on or off, and because the speed of turning the IGBT on or off is extremely fast, the current flowing in from the main circuit after the IGBT is turned on forms a single step current source excitation. Under this step current source excitation, under-attenuation oscillation occurs when the energy storage valve submodule switches between conduction and disconnection states due to a mismatch between the capacitive reactance of the first capacitor 20 and the inductive reactance of the equivalent stray inductance in the energy storage valve submodule. To suppress this under-attenuation oscillation, it is necessary to reduce the mismatch between the capacitive reactance of the first capacitor 20 and the inductive reactance of the equivalent stray inductance as much as possible, which essentially means suppressing the under-attenuation oscillation current generated by the energy storage valve submodule.

[0086] The functions of the first capacitor 20 in the energy storage valve submodule include, but are not limited to, filtering of high-frequency harmonics during IGBT switching and constructing a power device commutation circuit, and are essential parts of the energy storage valve submodule. Since the equivalent stray inductance is also due to the energy storage unit 30, which is essential to the energy storage valve submodule, it is not possible to adjust the capacitive reactance and inductive reactance as described above. On the other hand, the impedance of the RLC network equivalent to the first capacitor 20 and the energy storage unit 30 includes resistance in addition to the reactance composed of capacitive reactance and inductive reactance. Accordingly, the embodiment of the present invention adjusts the resistance in the impedance value of this RLC network by adding a suppression circuit 40, thereby putting this RLC network into an over-attenuated state and suppressing the under-attenuation oscillation phenomenon of the RLC network, thereby suppressing the under-attenuation oscillation current.

[0087] In some embodiments, the suppression circuit 40 may include a resistive element. That is, the suppression circuit 40 in the embodiments of the present application may be implemented by a resistive element. By providing the resistance value necessary to suppress the under-attenuation oscillation current that occurs when the energy storage valve submodule conducts, the resistive element is not only economical, easy to use, and simple, but also significantly reduces the additional impact on the overall function of the energy storage valve submodule.

[0088] In actual applications, the resistive element in the embodiment of the present invention may be implemented by any device having a resistance value in any connection manner, for example, by a resistor, or by several passive devices containing a resistance value.

[0089] The energy storage valve submodule according to the embodiment of the present invention is configured by adding an under-attenuation oscillation suppression circuit to the energy storage valve submodule. This suppression circuit is connected in series with the first capacitor, and the resistor-capacitance branch formed by the suppression circuit being connected in series with the first capacitor is connected in parallel with the power conversion unit and the energy storage unit, respectively. This suppression circuit can suppress the under-attenuation oscillation current that occurs when the energy storage valve submodule switches between conduction and disconnection states by adjusting the resistance value of the impedance in the energy storage valve submodule. As a result, the under-attenuation oscillation current that occurs when the energy storage valve submodule switches between conduction and disconnection states is significantly reduced, achieving the effect of suppressing under-attenuation oscillation current, and significantly reducing the damage that under-attenuation oscillation current inflicts on the energy storage valve submodule, thereby improving the reliability of the energy storage valve submodule.

[0090] Naturally, if the first capacitor is a DC link capacitor, the suppression circuit in this energy storage valve submodule is connected in series with the DC link capacitor, and the resistor-capacitance branch formed by the suppression circuit being connected in series with the DC link capacitor is connected in parallel with the power conversion unit and the energy storage unit, respectively. This suppression circuit can suppress the under-attenuation oscillation current that occurs when the energy storage valve submodule switches between conduction and disconnection states by adjusting the resistance value of the impedance in the energy storage valve submodule. This significantly reduces the under-attenuation oscillation current that occurs when the energy storage valve submodule switches between conduction and disconnection states, achieving the effect of suppressing under-attenuation oscillation current, and greatly reducing the damage that under-attenuation oscillation current inflicts on the energy storage valve submodule, thereby improving the reliability of the energy storage valve submodule.

[0091] As shown in Figure 8, the embodiment of the present invention will describe in detail how to implement the suppression circuit 40 using the above-mentioned resistor element as an example. Here, for the sake of clarity, a resistor element 401 is shown as an example in Figure 8. By adding the resistor element 401 to the branch of the first capacitor 20, the under-attenuation state of the entire energy storage valve submodule is changed, and the under-attenuation oscillation current is suppressed. In actual use, the resistor element 401 may be installed as needed, and may be implemented by a single resistor or a combination of series and parallel connections of multiple resistors.

[0092] Regardless of the implementation method of the suppression circuit 40, the resistance value of the resistor element 401 must be precisely designed in order to suppress the under-attenuation oscillation current generated when the energy storage valve submodule switches between conduction and disconnection states by adjusting the impedance resistance value of the energy storage valve submodule. The resistance value of this resistor element 401 must be such that the current generated throughout the entire network when the energy storage valve submodule switches between conduction and disconnection states does not exceed the allowable current of the energy storage unit 30. If this is not done, the entire network cannot be brought into a critically attenuated or over-attenuated state.

[0093] As shown in Figure 9, Figure 9 is a schematic diagram of the equivalent network after connecting a damping resistor in series to the energy storage valve submodule formed by combining Figures 3 and 8.

[0094] According to Kirchhoff's current law and Kirchhoff's voltage law, establishing a model of the equivalent network in Figure 9 yields the following second-order differential equation.

[0095]

number

[0096] Here, in the above second differential equation, L represents the equivalent stray inductance value in the energy storage unit 30, C represents the capacitance value on the first capacitor 20, Rc represents the resistance value of the resistive element 401 in the suppression circuit 40, and R1 represents the resistance value of the equivalent internal resistance Rdc in the energy storage unit 30. JPEG2026512137000003.jpg32165OCV represents the starting voltage on the first capacitor 20 in the steady state of the energy storage valve submodule, and the energy storage valve submodule is in a steady state when the step current on the main circuit has not yet flowed into the energy storage valve submodule. In such a steady state, the capacitor is not connected to DC and corresponds to a break, so OCV may be understood as the voltage on the energy storage unit 30.

[0097] Solving the above quadratic differential equation yields the following general solution to the characteristic equation.

[0098]

number

[0099] JPEG2026512137000005.jpg14130 Accordingly, according to Equation 2, the resistance value of the resistive element 401 is related to the capacitance value of the first capacitor 20 in the energy storage valve submodule, the inductance value of the equivalent stray inductance L in the energy storage valve submodule, and the resistance value of the equivalent internal resistance Rdc in the energy storage valve submodule.

[0100] In other words, in actual use, the resistance value of the resistive element 401 can be calculated by substituting specific values ​​such as the capacitance value of the first capacitor 20 in the energy storage valve submodule, the inductance value of the equivalent stray inductance L of the energy storage unit 30 in the energy storage valve submodule, and the resistance value of the equivalent internal resistance Rdc of the energy storage unit 30 into the above equation 2.

[0101] For example, in the configuration conditions of a high-voltage boost transformerless energy storage system, if the capacitance value of the first capacitor 20 is at the mF level, the inductance value of the equivalent stray inductance L in the energy storage unit 30 is at the μH level, and the resistance value of the equivalent internal resistance Rdc in the energy storage unit 30 is at the 1mΩ to 10mΩ level. Under these conditions, if the entire network of the energy storage valve submodule is required to be in an over-attenuated state when switching between conduction and disconnection states, combining this with the above equation 2, the resistance value of the resistive element 401 will be in the range of 10mΩ to 500mΩ. For example, the resistance value of the resistive element 401 may be 50mΩ, 100mΩ, 150mΩ, etc., and a detailed list is omitted here, but any value within this range is applicable.

[0102] In the embodiment of the present invention, by setting the value range of the resistive element to 10 mΩ to 500 mΩ, the resistive element can be matched to the capacitance value of the first capacitor, the inductance value of the equivalent stray inductance in the energy storage unit, and the resistance value of the equivalent internal resistance in the energy storage unit, in the configuration conditions of the high-voltage boost transformerless energy storage system. This makes it possible to accurately suppress under-attenuation oscillation of the energy storage valve submodule in the configuration conditions of the high-voltage boost transformerless energy storage system.

[0103] In the embodiment of this application, a second-order differential equation for the topology network model of the energy storage valve submodule is constructed based on Kirchhoff's current law and Kirchhoff's voltage law within the energy storage valve submodule. By solving this second-order differential equation, the equivalent stray inductance of the energy storage unit, the equivalent internal resistance of the energy storage unit, and the functional relationship between the first capacitor and the resistive element are derived. Substituting the capacitance value of the first capacitor, the equivalent stray inductance value of the energy storage unit, and the equivalent internal resistance value of the energy storage unit into this functional relationship and solving it yields the resistance value of the resistive element. Because this second-order differential equation is constructed based on an energy storage valve submodule with added resistive elements, it can accurately reflect the topological characteristics of the entire energy storage valve submodule, allowing for a more accurate calculation of the resistance value of the resistive element, thereby effectively suppressing under-attenuation oscillation current generated in the energy storage valve submodule.

[0104] Furthermore, considering that under-attenuation oscillation current in the energy storage valve submodule may occur not only when the energy storage unit 30 is conducting in the charged state, but also when the energy storage unit 30 is conducting in the discharge state, the embodiment of the present invention provides a method that can accurately suppress under-attenuation oscillation by the energy storage unit 30 when the charged state and the discharge state are different.

[0105] In one embodiment, the suppression circuit 40 further includes a switch circuit 402, which is used to control the conduction and disconnection states of the resistive element.

[0106] Regarding the connection method between the switch circuit 402 and the resistor element 401, the embodiment of this application provides three types of methods. Each of the three methods will be described in detail below.

[0107] As shown in Figure 10, in one embodiment, the switch circuit 402 is connected in parallel with the resistor element 401.

[0108] The switch circuit 402 is used to control the conduction and disconnection states of the resistive element 401 in the energy storage valve submodule. Specifically, by connecting the switch circuit 402 in parallel to the side of the resistive element 401, when the energy storage unit 30 is in a charging state, the switch circuit 402 opens and the resistive element 401 becomes conductive, and when the energy storage unit 30 is in a discharge state, the switch circuit 402 closes and the resistive element 401 becomes disconnected.

[0109] Here, when the resistive element 401 is conducting, the switch circuit 402 is open. In this case, the current on the main circuit passes through the resistive element 401, suppressing the under-attenuation oscillation current that occurs when the energy storage unit 30 is conducting in the charged state. Similarly, when the resistive element 401 is disconnected, the switch circuit 402 is closed. In this case, the current on the main circuit passes through the switch circuit 402, and the resistive element 401 is short-circuited by the switch circuit 402, with almost no current flowing through it. As a result, the under-attenuation oscillation current that occurs when the energy storage unit 30 is conducting in the discharged state is not suppressed.

[0110] As shown in Figure 11, in the suppression circuit 40 in which a diode is used as the switch circuit 402, the diode is in an interrupted state when the energy storage unit 30 is in a charged state due to the switching characteristics of the diode. When conducting, the current of the main circuit passes only through the resistive element 401. When the energy storage unit 30 is in a discharge state, the diode becomes conductive, and the resistive element 401 is short-circuited. When conducting, the current on the main circuit flows directly through the diode. By using a diode to realize the switch circuit, the diode does not require control and switches between on and off states depending on the voltage in the circuit. It also has the advantage of a fast switching speed and a particularly short switching time. Therefore, it is possible to quickly and accurately control the conduction and interruption states of the resistive element, and to more accurately suppress under-attenuation oscillation of the energy storage unit in different charging and discharging states.

[0111] It should be explained that when the switch circuit is a diode, the direction of the positive and negative terminals when connected is not unique, and the position of the diode and the direction of its positive and negative terminal connection may be set according to the circuit in which the resistor that needs to conduct is located. Furthermore, the diode mentioned above is just one example; when a non-directional switch is used in the switch circuit, the on and off states of the switch circuit should be controlled by considering the circuit in which the resistor that needs to conduct is located.

[0112] In the embodiment of the present invention, a switch circuit is connected in parallel to the side of the resistive element, and the switching operation of the switch circuit realizes a state in which the resistive element is conductive to or disconnected from the energy storage valve submodule. Only when the energy storage unit is conductive to the energy storage valve submodule and operating can the under-attenuation oscillation that occurs when conductive in the corresponding state be suppressed, thereby improving the accuracy of suppressing under-attenuation oscillation of the energy storage valve submodule.

[0113] The above is an embodiment in which accurate suppression of under-attenuation oscillations during the different charging and discharging processes of the energy storage unit 30 is achieved by a configuration in which the resistive element 401 includes one resistor and the switch circuit 402 includes one switch. Alternatively, accurate suppression of under-attenuation oscillations during the different charging and discharging processes of the energy storage unit 30 may be achieved by a configuration in which the resistive element 401 includes multiple resistors and the switch circuit 402 includes multiple switches.

[0114] In one embodiment, as shown in Figure 12, the resistor element 401 includes a first resistor R1 and a second resistor R2 connected in series with each other, and the switch circuit 402 further includes a first switch D5 and a second switch D6, the first switch D5 being connected in parallel with the first resistor R1 and the second switch D6 being connected in parallel with the second resistor R2. In some embodiments, the first switch D5 and / or the second switch D6 are diodes.

[0115] For the sake of explanation, Figure 12 illustrates diode D5 as the first switch, diode D6 as the second switch, R1 as the first resistor, and R2 as the second resistor. It should be noted that in actual use, both the first switch D5 and the second switch D6 may be diodes, or one of the first switch D5 and the second switch D6 may be a diode.

[0116] Similarly to the principle described above, in Figure 12, when the energy storage unit 30 is in a charged state, when the energy storage valve submodule conducts, the first switch D5 turns off in the reverse direction and the second switch D6 turns on in the forward direction. As a result, the current on the main circuit passes through the first resistor R1 and then through the second switch D6. In this case, only the first resistor R1 is in a conducting state, and the second resistor R2 is in a closed state. Therefore, the first resistor R1 can suppress the under-attenuation oscillation current that occurs when the energy storage unit 30 is in a charged state and conducts.

[0117] When the energy storage unit 30 is in a discharge state, if the energy storage valve submodule conducts, the first switch D5 turns on in the forward direction and the second switch D6 turns off in the reverse direction. In this case, the current on the main circuit passes through the second resistor R2 and then through the first switch D5. In this case, only the second resistor R2 is in a conduction state, and the first resistor R1 is in a disconnected state. Therefore, the second resistor R2 can suppress the under-attenuation oscillation current that occurs when the energy storage unit 30 conducts while in a discharge state.

[0118] Similarly, in this embodiment, when the first switch D5 and the second switch D6 are configured with diodes, the direction of the positive and negative terminals when connected is not unique, and the position of the diodes and the direction of the positive and negative terminal connections of the diodes may be set according to the circuit in which the resistor that needs to be conductive is located.

[0119] Based on the above operating process, depending on the actual demand, for example, if the degree of under-attenuation oscillation current generated when the energy storage unit 30 is in a charged state is greater than the degree of under-attenuation oscillation current generated when the energy storage unit 30 is in a discharged state, the under-attenuation oscillation current generated when the energy storage unit 30 is in a charged state may be suppressed to a relatively large extent, and the under-attenuation oscillation current generated when the energy storage unit 30 is in a discharged state may be suppressed to a relatively small extent. Based on this, in one embodiment, the resistance value of the first resistor R1 is set to be greater than the resistance value of the second resistor R2. That is, the larger the resistance value, the stronger the suppression of under-attenuation oscillation current. In this way, by setting the first resistor R1 and the second resistor R2 to different resistance values, it is possible to distinguish and suppress the under-attenuation oscillation current generated when the energy storage unit 30 is in a charged state and when it is in a discharged state, and the accuracy of suppressing under-attenuation oscillation of the energy storage valve submodule can be improved.

[0120] In one embodiment, as shown in Figure 13, the resistive element 401 includes a third resistor R3 and a fourth resistor R4 connected in parallel with each other, and the switch circuit 402 further includes a third switch D7 and a fourth switch D8. The third switch D7 is connected in series with the third resistor R3, and the fourth switch D8 is connected in series with the fourth resistor R4. In some embodiments, the third switch D7 and / or the fourth switch D8 are diodes.

[0121] Similarly, for the sake of explanation, Figure 13 illustrates that the third switch is diode D7, the fourth switch is diode D8, the third resistor is R3, and the fourth resistor is R4.

[0122] It should be explained that in Figure 13, the second resistor R4 may be swapped with the fourth switch D8, and the two methods are substantially equivalent. Furthermore, as described above, in actual use, both the third switch D7 and the fourth switch D8 may be diodes, or only one of the third switch D7 and the fourth switch D8 may be a diode. Naturally, if the third switch D7 and the fourth switch D8 are diodes, swapping the positions of the second resistor R4 and the second switch D8 will change the positive and negative terminals of the diodes acting as switches, as well as the connection direction accordingly. That is, in the embodiment of the present application, when the third switch D7 and the fourth switch D8 are diodes, the direction of the positive and negative terminals when connected is not unique, and the position of the diodes and the connection direction of the positive and negative terminals of the diodes may be set according to the circuit in which the resistor that needs to conduct is located.

[0123] Similarly to the principle described above, in Figure 13, when the energy storage unit 30 is in a charged state, when the energy storage valve submodule conducts, the third switch D7 turns on in the forward direction and the fourth switch D8 turns off in the reverse direction, and the current on the main circuit flows through the third resistor R3 and then through the third switch D7. In this case, only the third resistor R3 is in a conducting state, and the fourth resistor R4 is interrupted. Therefore, the third resistor R3 can suppress the under-attenuation oscillation current that occurs when the energy storage unit 30 conducts in a charged state.

[0124] When the energy storage unit 30 is in a discharge state, when the energy storage valve submodule conducts, the third switch D7 turns off in the reverse direction and on in the forward direction, and the current on the main circuit flows through the fourth switch D8 and then through the fourth resistor R4. In this case, only the fourth resistor R4 is in a conduction state, and the third resistor R3 is interrupted. Therefore, the fourth resistor R4 can suppress the under-attenuation oscillation current that occurs when the energy storage unit 30 conducts while in a discharge state.

[0125] Based on the above operating process, depending on the actual demand, for example, if the degree of under-attenuation oscillation current generated when the energy storage unit 30 is in a charged state is greater than the degree of under-attenuation oscillation current generated when the energy storage unit 30 is in a discharged state, the under-attenuation oscillation current generated when the energy storage unit 30 is in a charged state may be suppressed to a relatively large extent, and the under-attenuation oscillation current generated when the energy storage unit 30 is in a discharged state may be suppressed to a relatively small extent. Based on this, in one embodiment, the resistance value of the third resistor R3 is set to be greater than the resistance value of the fourth resistor R4. That is, the larger the resistance value, the stronger the suppression of under-attenuation oscillation current. In this way, by setting the third resistor R3 and the fourth resistor R4 to different resistance values, it is possible to distinguish and suppress the under-attenuation oscillation current generated when the energy storage unit 30 is in a charged state and when it is in a discharged state, and the accuracy of suppressing under-attenuation oscillation of the energy storage valve submodule can be improved.

[0126] In the embodiment of the present invention, the conduction and disconnection states of the two resistors in the energy storage valve submodule are controlled by adding two resistors and two different switches to the energy storage valve submodule. Only one of the two resistors is conducted when the energy storage unit is in a charging state or when the energy storage unit is in a discharge state. As a result, the resistance values ​​of the two resistors are different, and the degree to which under-attenuation oscillation can be suppressed is also different when the energy storage unit is in a charging state or when the energy storage unit is in a discharge state. In this way, the suppression of under-attenuation oscillation of the energy storage unit in the different charging and discharging states can be made more precise.

[0127] When the first capacitor 20 in the energy storage valve submodule is connected in series with the suppression circuit 40, the resistance in the suppression circuit 40 causes a corresponding increase in the overvoltage stress at the time of IGBT interruption in the power conversion unit 10. Here, for similar IGBT switch di / dt (rate of change of interruption current per unit time) values, the overvoltage U at the time of IGBT interruption increases according to U = L * di / dt + i * R. Here, R represents the resistance value present in the resistive element itself, and L represents the stray inductance present in the resistive element itself.

[0128] Based on this, embodiments of the present invention reduce overvoltage stress during IGBT interruption by connecting a second capacitor in parallel with the resistive-capacitive branch overall. As shown in Figure 14, in one embodiment, the energy storage valve submodule further includes a second capacitor 50, which is connected in parallel with the resistive-capacitive branch.

[0129] It should be noted that the connection method of the second capacitor 50 shown in Figure 14 is merely an example. In actual use, the second capacitor 50 may be connected in parallel with the power conversion unit 10 and the resistor-capacitance branch as shown in Figure 14, or it may be connected in parallel with the resistor-capacitance branch and the energy storage unit 30. Of course, if the resistor-capacitance branch is connected in parallel with the energy storage unit 30 according to the method shown in Figure 5, the second capacitor 50 may be connected in parallel with the resistor-capacitance branch, or with the energy storage unit 30 and the resistor-capacitance branch, based on the schematic diagram in Figure 5.

[0130] In one embodiment, the second capacitor 50 includes a snubber capacitor. That is, the energy storage valve submodule of the second capacitor 50 mainly has the function of buffering high-frequency current in the current when the energy storage valve submodule is conducting, and reduces the overvoltage stress when the IGBT is interrupted by reducing the rate of change of the interruption current when the IGBT is interrupted.

[0131] In one embodiment, the capacitance value of the second capacitor 50 is smaller than the capacitance value of the first capacitor 20.

[0132] By setting the capacitance value of the second capacitor 50 to be much smaller than that of the first capacitor 20, a certain distinction is made between the high-frequency current passing through the second capacitor 50 and the high-frequency current passing through the first capacitor 20 when the energy storage valve submodule is conducting. For example, the second capacitor 50 mainly allows the high-frequency components of the current to pass through, while the first capacitor 20 mainly allows the low-frequency components of the current to pass through.

[0133] In actual use, the determination process for the capacitance value of the second capacitor 50 can be implemented through circuit simulation. During the simulation, it is necessary to consider not only the overvoltage capability when the IGBT is interrupted, but also whether the degree of under-attenuation oscillation of the energy storage valve submodule worsens if the capacitance value of the second capacitor 50 is excessive. Therefore, the capacitance value of the second capacitor 50 must be set within a range that does not cause under-attenuation oscillation in relation to other devices in the energy storage valve submodule.

[0134] In some embodiments, the capacitance value of the second capacitor 50 may be at the sub-mF level. For example, the capacitance value range of the second capacitor 50 is 10uF to 300uF. Also, for example, if the second capacitor 50 is a snubber capacitor, the capacitance value range of the snubber capacitor is 10uF to 300uF. This capacitance value range may also be the value range in the case of a high-voltage boost transformerless system. When the second capacitor 50 takes a value within this range, it is possible to reduce the overvoltage stress during IGBT interruption while simultaneously reducing the additional impact on the overall topology of the energy storage valve submodule.

[0135] In the embodiments of this application, the number of second capacitors 50 (taking snubber capacitors as an example) may be one snubber capacitor or a combination of N snubber capacitors connected in parallel. N may be a positive integer of 1 or more, for example, 2, 3, 5, 8, 10, 20, 50, 100, etc. The embodiments of this application do not limit the specific number of snubber capacitors.

[0136] In the embodiments of this application, by connecting a second capacitor in parallel to the side of the resistive-capacitive branch, the overvoltage stress during IGBT interruption is reduced, thereby reducing the risk of IGBT failure due to excessive overvoltage stress, improving the operational reliability of the IGBT and further improving the operational reliability of the energy storage valve submodule.

[0137] For example, if the first capacitor 20 is a DC link capacitor and the second capacitor 50 is a snubber capacitor, the capacitance value of the snubber capacitor is smaller than that of the DC link capacitor. By setting the capacitance value of the snubber capacitor to be smaller than that of the DC link capacitor in this way, a certain distinction is made between the high-frequency current passing through the snubber capacitor and the high-frequency current passing through the DC link capacitor when the energy storage valve submodule is conducting. Furthermore, because the capacitance value of the snubber capacitor is much smaller than that of the DC link capacitor, the deterioration of the degree of under-attenuation oscillation of the energy storage valve submodule caused by an excessive capacitance value of the snubber capacitor is reduced, and the operational reliability of the energy storage valve submodule can be increased by reducing the overvoltage stress when the power device in the power conversion unit is shut off and simultaneously reducing the risk of additional effects occurring.

[0138] The snubber capacitor included in this energy storage valve submodule is connected in parallel to the resistive-capacitive branch. By connecting a single snubber capacitor in parallel to the resistive-capacitive branch in this way, the overvoltage stress during power device interruption in the power conversion unit can be reduced. In this way, the risk of power device failure in the power conversion unit due to excessive overvoltage stress is reduced, thereby improving the operational reliability of the power device in the power conversion unit and further improving the operational reliability of the energy storage valve submodule.

[0139] In the above embodiment, the overvoltage stress at the time of IGBT shutdown is reduced by connecting the second capacitor 50 in parallel. However, in actual use, after connecting the suppression circuit 40 to the energy storage valve submodule, a relatively large shutdown overvoltage exists at the IGBT due to the resistance value of the suppression circuit 40, and it is possible that the second capacitor 50 alone cannot completely cancel out the IGBT shutdown overvoltage stress. Therefore, the embodiment of the present application further provides a method that can reduce the overvoltage at the time of IGBT shutdown by reducing the di / dt at the time of IGBT shutdown, thereby reducing the risk of IGBT failure caused by excessive overvoltage stress.

[0140] Specifically, the power conversion unit 10 of the energy storage valve submodule is implemented by IGBTs, and as can be seen in conjunction with the description of the previous embodiment, a drive circuit is connected to the gate of each IGBT in the power conversion unit 10, and the drive circuit drives the IGBT to turn on and off. In some embodiments, the parameter values ​​of the drive device in the drive circuit have an inverse correlation with the rate of change of the IGBT's interruption current. That is, in the embodiments of the present application, the interruption di / dt (i.e., rate of change of interruption current) of the IGBT can be reduced by increasing the parameter values ​​of the drive device.

[0141] As shown in Figure 15, Figure 15 is a schematic diagram of an IGBT drive circuit. For clarity, only a schematic diagram of a single IGBT connected drive circuit is shown in Figure 15. In Figure 15, Rgon represents the gate-on resistance, Rgoff represents the gate-off resistance, and Cg represents the gate capacitor. Rgon, Rgoff, diodes D1 and D2, and gate capacitor Cg are used to turn the IGBT on and off.

[0142] In light of the need to reduce di / dt during IGBT shutdown, in one embodiment, increasing the parameter values ​​of the drive device may involve increasing the resistance value of the gate off resistor Rgoff and / or increasing the capacitance value of the gate capacitor Cg, i.e., increasing the parameter values ​​of either or both of the gate off resistor Rgoff and the gate capacitor Cg. In either case, a reduction in di / dt during IGBT shutdown can be achieved.

[0143] In actual use, the specific amount to which the gate-off resistor Rgoff and gate capacitor Cg need to be increased can be determined based on the IGBT specifications. Different IGBT specifications result in different voltage and current levels, and therefore the adjustment range for the drive device parameters in the drive circuit also differs. Consequently, adjustments must be made in combination with the actual conditions.

[0144] For example, if the IGBT voltage-current level is 4.5kV / 3kA, in this case, in the flexible DC power transmission process (a flexible DC power transmission process is a DC power transmission technology based on a voltage source converter (VSC)), the parameter values ​​of the drive device may be adjusted so that the di / dt at the time of IGBT tripping reaches 5000A / μs. However, in the configuration of a high-voltage boost transformerless energy storage system, the parameter values ​​of the drive device may be adjusted so that the di / dt at the time of IGBT tripping in this energy storage valve submodule is reduced to 3000A / μs. By reducing the di / dt at the time of IGBT tripping in the energy storage valve submodule to 3000A / μs, the IGBT tripping overvoltage can be effectively reduced.

[0145] In the embodiment of the present invention, the characteristic that the rate of change of the interruption current of the power device in the power conversion unit has an inverse correlation with the parameter value of the drive device in the drive circuit of the power device allows for a reduction in the rate of change of the interruption current of the power device in the power conversion unit, thereby further reducing the interruption overvoltage of the power device in the power conversion unit. As a result, the problem of power device failures in the power conversion unit caused by excessive overvoltage stress can be significantly reduced, and the operational reliability of the power conversion unit can be improved.

[0146] In actual use, adding the suppression circuit 40 to the energy storage valve submodule results in additional ohmic heat loss to the entire energy storage valve submodule due to the resistance characteristics of the suppression circuit 40. Based on this, the heat loss to the energy storage valve submodule due to the suppression circuit 40 can be reduced by adjusting the conduction and disconnection switching frequency of the energy storage valve submodule.

[0147] In one embodiment, the switching frequency of conduction and disconnection of the energy storage valve submodule has a positive correlation with the energy loss generated by the suppression circuit.

[0148] If the energy storage valve submodule is conducted and shut off once in a high-voltage boost transformerless energy storage system, the energy loss due to the resistance of the suppression circuit 40 is E, and the equivalent conduction and shut-off switching frequency of the energy storage valve submodule is f, then the heat generation power P ≈ f * E of the resistance of the suppression circuit 40 is equal to f. In other words, the higher the conduction and shut-off switching frequency f, the greater the energy loss E due to the resistance of the suppression circuit 40, and the conduction and shut-off switching frequency becomes positively correlated with the energy loss generated by the suppression circuit.

[0149] Based on the relationship between the equivalent conduction and interruption switching frequencies of the energy storage valve submodule and the energy loss generated by the suppression circuit, the value of the equivalent conduction and interruption switching frequency can be set based on the energy loss value generated by the resistance of the specific suppression circuit 40 of the energy storage valve submodule. For example, in the actual process of flexible DC, the value of f of the converter valve may be set to around 100Hz to 200Hz, but in the application of a DC boost transformerless energy storage valve, the value of the switching frequency f may be set between 50Hz and 150Hz.

[0150] It should be noted that the values ​​for the equivalent conduction and interruption switch frequencies of the energy storage valve submodule described above are merely examples. In actual use, the equivalent conduction and interruption switch frequencies may be set to relatively low switch frequencies that the system can tolerate, provided that the operational demands of the high-voltage boost transformerless energy storage system are met. In other words, by reducing the system conduction and interruption switch frequencies as much as possible, the losses of the high-voltage boost transformerless energy storage system can be optimized.

[0151] The embodiment of the present invention utilizes the characteristic that the switching frequency of conduction and disconnection of the energy storage valve submodule has a positive correlation with the energy loss generated by the suppression circuit. By setting the equivalent conduction and disconnection switching frequency for one conduction and disconnection in a high-voltage boost transformerless energy storage system, the energy storage valve submodule can be conducted and disconnected at a relatively low equivalent conduction and disconnection switching frequency. This reduces the losses of the energy storage valve submodule and improves the economic efficiency and safety of the energy storage valve submodule during use.

[0152] In one embodiment, as shown in Figure 16, the energy storage valve submodule further includes a bypass circuit 60, which is connected in parallel to the energy storage valve submodule.

[0153] Continuing to refer to Figure 16, a bypass circuit 60 is placed between the two ports S1 and S2 of the energy storage valve submodule and the power conversion unit 10. In the event of a failure in the energy storage valve submodule, or if there is a possibility of a failure in the energy storage valve submodule, the bypass circuit 60 can disconnect the energy storage valve submodule from the high-voltage boost transformerless energy storage system.

[0154] For example, when an overvoltage occurs in a high-voltage boost transformerless energy storage system, the bypass circuit 60 conveniently and promptly disconnects the energy storage valve submodule from the high-voltage boost transformerless energy storage system. This significantly reduces the probability of the energy storage valve submodule failing due to overvoltage generated from the high-voltage boost transformerless energy storage system, thereby improving the operational stability and safety of the high-voltage boost transformerless energy storage system.

[0155] In some embodiments, the bypass circuit 60 may be a bypass switch, and in some embodiments, this bypass switch may be a mechanical bypass switch or a semiconductor device bypass switch, but is not limited to these.

[0156] If a fault occurs in the energy storage valve submodule, current flows into the main circuit through port S1, causing the bypass switch to close. This then causes the current to flow out through port S2 via the bypass switch, completely short-circuiting the entire energy storage valve submodule. This completely isolates the energy storage valve submodule from the high-voltage boost transformerless energy storage system.

[0157] In the embodiment of the present invention, by installing a bypass circuit between the energy storage valve submodule and the port of the main circuit to which the energy storage valve submodule is connected to the high-voltage boost transformerless energy storage system, the energy storage valve submodule can be isolated from the high-voltage boost transformerless energy storage system in the event of a failure in the energy storage valve submodule, thereby improving the operational stability and safety of the high-voltage boost transformerless energy storage system.

[0158] Furthermore, embodiments of the present application provide a high-voltage boost transformerless energy storage system, which includes an energy storage valve submodule provided in any one of the embodiments described above.

[0159] The high-voltage step-up transformerless energy storage system in the embodiment of the present application may include a DC high-voltage step-up transformerless energy storage system or an AC high-voltage step-up transformerless energy storage system. Here, Figure 1 above shows an example of an AC high-voltage step-up transformerless energy storage system.

[0160] The energy storage valve submodule according to the embodiment of the present invention can suppress under-attenuated oscillation power that occurs when switching between conduction and disconnection states, and has relatively high reliability. Therefore, a high-voltage boost transformerless energy storage system employing the energy storage valve submodule construction according to the embodiment of the present invention can also be given relatively high reliability.

[0161] The technical features of the above embodiments can be combined in any way, and for the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no inconsistency in these combinations of technical features, they should all be considered to be within the scope described herein.

[0162] As stated above, the embodiments merely represent multiple embodiments of the present application, and although their descriptions are relatively specific and detailed, this should not be understood as limiting the scope of the patent of the present application. It should be noted that a person skilled in the art can make multiple modifications and improvements without departing from the concept of the present application, and all of these fall within the scope of protection of the present application. Therefore, the scope of protection of the present application should be the same as the scope of the attached claims. [Explanation of Symbols]

[0163] 10: Power Conversion Unit 20: First capacitor 30: Energy storage unit 40: Suppression circuit 401: Resistor element 402: Switch Circuit 50: Second capacitor 60: Bypass Circuit

Claims

1. Energy storage valve submodule, It includes a power conversion unit, a first capacitor, a suppression circuit, and an energy storage unit. The suppression circuit is connected in series with the first capacitor to form a resistor-capacitance branch, and the resistor-capacitance branch is connected in parallel with the power conversion unit and the energy storage unit, respectively, in an energy storage valve submodule.

2. The suppression circuit includes a resistive element, as described in claim 1, for the energy storage valve submodule.

3. The energy storage valve submodule according to claim 2, wherein the suppression circuit further includes a switch circuit, which is used to control the conduction and disconnection states of the resistive element.

4. The switch circuit is connected in parallel to the resistive element, as described in claim 3, for the energy storage valve submodule.

5. The resistive element includes a first resistor and a second resistor connected in series with respect to each other. The energy storage valve submodule according to claim 3, wherein the switch circuit further includes a first switch and a second switch, the first switch being connected in parallel to the first resistor and the second switch being connected in parallel to the second resistor.

6. The energy storage valve submodule according to claim 5, wherein the first switch and / or the second switch is a diode.

7. The energy storage valve submodule according to claim 5, wherein the resistance value of the first resistor is greater than the resistance value of the second resistor.

8. The resistive element includes a third resistor and a fourth resistor connected in parallel with each other. The energy storage valve submodule according to claim 3, wherein the switch circuit further includes a third switch and a fourth switch, the third switch being connected in series with the third resistor and the fourth switch being connected in series with the fourth resistor.

9. The energy storage valve submodule according to claim 8, wherein the third switch and / or the fourth switch is a diode.

10. The energy storage valve submodule according to claim 8, wherein the resistance value of the third resistor is greater than the resistance value of the fourth resistor.

11. The energy storage valve submodule according to any one of claims 2 to 10, wherein the resistance range of the resistive element is 10 mΩ to 500 mΩ.

12. The energy storage valve submodule according to any one of claims 1 to 11, further comprising a second capacitor, the second capacitor connected in parallel to the resistor-capacitance branch.

13. The energy storage valve submodule according to claim 12, wherein the second capacitor includes a snubber capacitor.

14. The energy storage valve submodule according to claim 12, wherein the capacitance value of the second capacitor is smaller than the capacitance value of the first capacitor.

15. The energy storage valve submodule according to claim 12, wherein the capacitance value range of the second capacitor is 10uF to 300uF.

16. The energy storage valve submodule according to any one of claims 1 to 15, wherein the first capacitor includes a DC link capacitor.

17. The energy storage valve submodule according to any one of claims 1 to 16, further comprising a bypass circuit, the bypass circuit being connected in parallel to the energy storage valve submodule.

18. The energy storage valve submodule according to any one of claims 1 to 17, wherein the switching frequency of conduction and disconnection of the energy storage valve submodule has a positive correlation with the energy loss caused by the suppression circuit.

19. The energy storage valve submodule according to any one of claims 1 to 18, wherein the rate of change of the interruption current of the power device in the power conversion unit has an inverse correlation with the parameter value of the drive device in the drive circuit of the power device.

20. The energy storage valve submodule according to claim 19, wherein the parameter values ​​of the drive device include the resistance value of the gate off resistor in the drive circuit and / or the capacitance value of the gate capacitor in the drive circuit.

21. A high-voltage boost transformerless energy storage system comprising an energy storage valve submodule according to any one of claims 1 to 20.

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