Energy storage control method and device, energy storage system and computer program product

Abstract

This application provides an energy storage control method, device, energy storage system, and computer program product; relating to the field of energy storage technology. Given the current problem that frequent inertia release of energy storage batteries shortens their lifespan, this application proposes an energy storage control method, including obtaining the frequency difference between the current grid frequency and the rated grid frequency, a first state of the energy storage battery, and a second state of the supercapacitor; determining a first power reference value for a DC-connected energy storage valve and a second power reference value for a voltage source converter based on the frequency difference, the first state, and the second state; controlling the DC-connected energy storage valve to operate a first number of first sub-modules based on the first power reference value; and / or controlling the voltage source converter to operate a second number of second sub-modules based on the first and second power reference values. This application can reduce the requirements for the charge / discharge rate of the energy storage battery, reduce the rated capacity of the energy storage battery, extend its lifespan, and stabilize the grid balance.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to an energy storage control method, device, energy storage system and computer program product. Background Technology

[0002] Due to the increasing scarcity of fossil fuels and the growing environmental pollution they cause, people are paying more and more attention to the development and utilization of new energy sources. Many renewable energy power generation systems are subject to environmental constraints, and their output power exhibits randomness and fluctuations. When connected to the grid, this affects the power balance, power supply reliability, and power quality on the AC side, thus impacting grid stability.

[0003] Currently, energy storage systems can provide necessary compensation for fluctuations in the output power of renewable energy generation systems by storing and releasing electrical energy, thereby suppressing power fluctuations in the power grid and improving grid stability. However, since the lifespan of energy storage batteries is related to the charge / discharge rate and the number of cycles, controlling the charging and discharging of batteries according to inertia is not conducive to extending battery lifespan. Summary of the Invention

[0004] According to various embodiments of this application, an energy storage control method, apparatus, energy storage system, and computer program product are provided; when the energy storage system provides power compensation, the requirements for the charge / discharge rate of the energy storage battery can be reduced, the rated capacity of the energy storage battery can be reduced, and its lifespan can be extended.

[0005] In a first aspect, this application provides an energy storage control method applied to an energy storage system, the energy storage system including a DC-connected energy storage valve and a voltage source converter; the DC-connected energy storage valve includes a first submodule connected in series, the first submodule integrating an energy storage battery; the voltage source converter includes a second submodule connected in a bridge configuration, the second submodule integrating a supercapacitor; the DC-connected energy storage valve is connected in parallel to the DC side of the voltage source converter, and the DC-connected energy storage valve is connected to the power grid through the voltage source converter; the method includes:

[0006] The system acquires the frequency difference between the current grid frequency and the rated grid frequency, the first state of the energy storage battery, and the second state of the supercapacitor; based on the frequency difference, the first state, and the second state, it determines the first power reference value of the DC-connected energy storage valve and the second power reference value of the voltage source converter; based on the first power reference value, it controls the DC-connected energy storage valve to operate a first number of first sub-modules; and / or based on the first power reference value and the second power reference value, it controls the voltage source converter to operate a second number of second sub-modules.

[0007] By employing the above method, in the event of grid frequency fluctuations, the energy storage system based on a hybrid of energy storage batteries and supercapacitors allocates power reference values ​​to the DC-connected energy storage valve and the voltage source converter, respectively. Power compensation is performed using supercapacitors, which have high power density, high efficiency, long lifespan, and are suitable for high-power, frequent charge-discharge applications, and energy storage batteries, which have high energy density. This reduces the requirements for the charge-discharge rate of the energy storage batteries, decreases their rated capacity, extends their lifespan, and ensures grid stability. The system also exhibits strong ease of use and practicality.

[0008] In one possible implementation of the first aspect, determining a first power reference value for the DC-connected energy storage valve and a second power reference value for the voltage source converter based on the frequency difference, a first state, and a second state includes:

[0009] Based on the frequency difference, the first state, and the second state, the first power to be compensated for the DC-connected energy storage valve and the second power to be compensated for the voltage source converter are determined; based on the actual value of the first power of the DC-connected energy storage valve and the first power to be compensated, a first power reference value is obtained; based on the actual value of the second power of the voltage source converter and the second power to be compensated, a second power reference value is obtained.

[0010] By using the above methods, based on the frequency difference in the power grid and the status of energy storage batteries and supercapacitors, the power variation values ​​that DC direct-connected energy storage valves and voltage source converters can respectively be determined. In this way, the power reference values ​​that need to be output during actual operation can be reasonably allocated, the resources of the energy storage system can be effectively utilized, and the flexible scheduling of the energy storage system can be achieved to cope with the power grid frequency fluctuations caused by different load levels.

[0011] In one possible implementation of the first aspect, determining the first power to be compensated for the DC-connected energy storage valve and the second power to be compensated for the voltage source converter based on the frequency difference, the first state, and the second state includes:

[0012] Based on the preset total virtual inertia and the first and second states, the first virtual inertia corresponding to the DC direct-connected energy storage valve and the second virtual inertia corresponding to the voltage source converter are determined; the frequency difference is filtered and differentiated, and the first power to be compensated is obtained based on the processed frequency difference and the first virtual inertia; and the second power to be compensated is obtained based on the processed frequency difference and the second virtual inertia.

[0013] The above method, by processing the frequency difference, more accurately determines the trend of grid frequency changes; based on the processed frequency difference and virtual inertia, the corresponding power change values ​​of DC direct-connected energy storage valve and voltage source converter are determined respectively, and power compensation is performed through the collaboration of the two; since supercapacitors have high power density and energy storage batteries have high energy density, the utilization efficiency of energy storage batteries and supercapacitors in the energy storage system can be optimized, and the frequency fluctuations of the grid can be responded to quickly, thus improving the response speed.

[0014] In one possible implementation of the first aspect, the first state includes the first energy of the energy storage battery, and the second state includes the second energy of the supercapacitor; based on the preset total virtual inertia and the first and second states, the first virtual inertia corresponding to the DC-connected energy storage valve and the second virtual inertia corresponding to the voltage source converter are determined, including:

[0015] Based on the first energy and the second energy, determine the first virtual inertia ratio corresponding to the DC direct-connected energy storage valve and the second virtual inertia ratio corresponding to the voltage source converter; based on the total virtual inertia and the first virtual inertia ratio, determine the first virtual inertia; based on the total virtual inertia and the second virtual inertia ratio, determine the second virtual inertia.

[0016] The above method allocates the energy state of the energy storage battery and the supercapacitor to the virtual inertia ratio corresponding to the DC-connected energy storage valve and the voltage source converter, respectively, to determine the inertial support corresponding to each of them. This allows both to provide inertial support while ensuring their own operating state, thus extending the service life of the energy storage battery and the supercapacitor.

[0017] In one possible implementation of the first aspect, the first state includes a first state of charge and a first health state of the energy storage battery; before determining the first virtual inertia, the method further includes:

[0018] Based on the first state of charge and the first state of health, the overall battery state of the energy storage battery is determined; if the overall battery state is lower than the first threshold and the energy storage system is in a discharging state, the first virtual inertia ratio is set to zero; or, if the overall battery state is higher than the second threshold and the energy storage system is in a charging state, the first virtual inertia ratio is set to zero; the first threshold is less than the second threshold.

[0019] The above method sets the virtual inertia ratio of the DC-connected energy storage valve to zero when the state of the energy storage battery does not meet the threshold conditions. This reduces the burden of providing virtual inertia, improves the performance and lifespan of the DC-connected energy storage valve, avoids damage caused by over-discharge, and avoids overheating, expansion, or damage to the energy storage battery caused by overcharging. This ensures the reliability and safety of the DC-connected energy storage valve operation.

[0020] In one possible implementation of the first aspect, the second state includes a second state of charge of the supercapacitor; the method further includes, prior to determining the second virtual inertia:

[0021] When the second state of charge is lower than the first threshold and the energy storage system is in a discharging state, the proportion of the second virtual inertia is set to zero; or, when the second state of charge is higher than the second threshold and the energy storage system is in a charging state, the proportion of the second virtual inertia is set to zero; wherein, the first threshold is less than the second threshold.

[0022] The above method sets the virtual inertia ratio of the voltage source converter to zero when the state of the supercapacitor does not meet the threshold condition, thereby reducing the burden of providing virtual inertia, avoiding continued charging and discharging within an unsuitable state of charge range, preventing damage to the supercapacitor caused by overcharging or over-discharging, reducing the number of cycles of the supercapacitor, and extending its service life.

[0023] In one possible implementation of the first aspect, after determining the first virtual inertia percentage corresponding to the DC-connected energy storage valve and the second virtual inertia percentage corresponding to the voltage source converter based on the first energy and the second energy, the method further includes:

[0024] The proportion of the first virtual inertia is adjusted based on a first proportional coefficient, and the proportion of the second virtual inertia is adjusted based on a second proportional coefficient; the first proportional coefficient is less than the second proportional coefficient; the first virtual inertia is obtained based on the adjusted proportion of the first virtual inertia and the total virtual inertia; and the second virtual inertia is obtained based on the adjusted proportion of the second virtual inertia and the total virtual inertia.

[0025] In the above-mentioned method, due to the high power efficiency of supercapacitors, when the energy state of the voltage source converter is sufficient to meet the inertial support, the proportion of virtual inertia can be further adjusted by the proportional coefficient, so that the voltage source converter can give priority to providing inertial support, thereby responding quickly to frequency fluctuations, improving power compensation efficiency, and quickly maintaining the stability of the power grid.

[0026] In one possible implementation of the first aspect, controlling the DC-connected energy storage valve to operate a first number of first sub-modules according to a first power reference value includes:

[0027] Based on the first power reference value and the rated DC voltage value on the DC side of the energy storage system, calculate the DC current reference value; based on the DC current reference value and the current DC current value, calculate the DC current error value; perform proportional and integral processing on the DC current error value to obtain the first quantity; control the DC direct-connected energy storage valve to operate the first quantity of the first sub-module.

[0028] The above method, by calculating the DC current reference value, the DC current error value, and performing proportional-integral processing on the DC current error value, can quickly calculate the number of the first sub-modules that need to be adjusted, efficiently respond to changes in the power grid or load, and can be flexibly applied to various operating scenarios.

[0029] In one possible implementation of the first aspect, controlling the voltage source converter to operate a second number of second sub-modules based on a first power reference value and a second power reference value includes:

[0030] Based on the rated DC voltage of the DC side of the energy storage system and the capacitor voltage of the second submodule, calculate the second number of the second submodules on each phase arm of the voltage source converter; calculate the active power reference value on the grid side based on the first power reference value and the second power reference value; determine the reference wave signal corresponding to each phase arm based on the active power reference value and the reactive power reference value on the grid side; determine the first number of the second submodules of the upper arm and the second number of the second submodules of the lower arm of each phase arm based on the reference wave signal; the second number is the sum of the first number of the second number of the second submodules; control the voltage source converter to operate the second submodules of the first number of the upper arm and the second submodules of the second arm of each phase arm.

[0031] The above method, by determining the reference wave signal corresponding to each phase arm based on the active power reference value and reactive power reference value on the grid side, can precisely adjust the output power of the voltage source converter to match the actual needs of the grid. This helps to reduce power fluctuations and imbalances in the grid, and improve the stability and reliability of the grid. By precisely controlling the number and operating status of the second sub-modules of the upper and lower arms of each phase arm, the transmission and conversion process of energy between the grid and the energy storage system can be optimized. This helps to reduce energy losses during transmission and conversion, and improve energy utilization efficiency.

[0032] In one possible implementation of the first aspect, the reference wave signal corresponding to each phase arm is determined based on the active power reference value and reactive power reference value on the grid side, including:

[0033] The active power reference value and reactive power reference value on the grid side are adjusted by the power control outer loop to obtain the first voltage reference value; the first voltage reference value is adjusted by the voltage and current double closed loop to obtain the second voltage reference value in the rotating coordinate system; the second voltage reference value is processed by coordinate system transformation to obtain the reference wave signal in the ABC three-phase coordinate system.

[0034] The above method obtains a reference wave signal and uses a level approximation modulation strategy based on this reference wave signal to control the number of second modules in the upper and lower arms of the voltage source converter, thereby accurately adjusting the output power of the voltage source converter to match the actual needs of the power grid.

[0035] Secondly, this application provides an energy storage control device for use in an energy storage system, including a DC-connected energy storage valve and a voltage source converter; the DC-connected energy storage valve includes a first submodule connected in series, the first submodule integrating an energy storage battery; the voltage source converter includes a second submodule connected in a bridge configuration, the second submodule integrating a supercapacitor; the DC-connected energy storage valve is connected in parallel to the DC side of the voltage source converter, and the DC-connected energy storage valve is connected to the power grid through the voltage source converter; the device includes:

[0036] The sampling unit is used to acquire the frequency difference between the current grid frequency and the rated grid frequency, the first state of the energy storage battery, and the second state of the supercapacitor.

[0037] The processing unit is used to determine the first power reference value of the DC-connected energy storage valve and the second power reference value of the voltage source converter based on the frequency difference, the first state, and the second state.

[0038] The control unit is configured to control the DC-DC direct-connected energy storage valve to operate a first number of first sub-modules based on a first power reference value; and / or control the voltage source converter to operate a second number of second sub-modules based on a first power reference value and a second power reference value.

[0039] Thirdly, this application provides an energy storage system, including a DC direct-connected energy storage valve, a voltage source converter, a memory, and a processor. The memory stores a computer program, and the processor executes the computer program to implement the method described in any of the first aspects.

[0040] In one possible implementation of the third aspect, the energy storage system also includes a power conversion device for connecting to the power generation system.

[0041] Fourthly, this application provides an energy storage system, including a DC-connected energy storage valve, a voltage source converter, and a controller; the DC-connected energy storage valve integrates multiple first sub-modules connected in series, each first sub-module including an energy storage battery; the voltage source converter integrates a three-phase bridge-connected second sub-module, with multiple second sub-modules connected in series on each phase arm, each second sub-module including a supercapacitor; the DC-connected energy storage valve is connected in parallel to the DC side of the voltage source converter, and the DC-connected energy storage valve is connected to the power grid through the voltage source converter; the controller is communicatively connected to the DC-connected energy storage valve, the voltage source converter, and the power grid; the controller is used to acquire the frequency of the power grid and, based on the frequency of the power grid, control the output power of the DC-connected energy storage valve and / or the voltage source converter.

[0042] Fifthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method described in any one of the first aspects.

[0043] Sixthly, this application provides a computer program product that, when run on a device, causes the device to perform the method described in any one of the first aspects above.

[0044] It is understood that the beneficial effects of the second to sixth aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 A schematic diagram of the energy storage system architecture provided in the embodiments of this application;

[0047] Figure 2 A schematic diagram illustrating the implementation process of the energy storage control method provided in this application embodiment;

[0048] Figure 3 A schematic diagram of the topology of the energy storage system architecture provided in the embodiments of this application;

[0049] Figure 4 This is a schematic diagram illustrating the implementation process for determining the power reference value provided in an embodiment of this application;

[0050] Figure 5 A schematic diagram illustrating the process for determining the power change provided in an embodiment of this application;

[0051] Figure 6 A schematic diagram illustrating the implementation process of the first sub-module for determining the first quantity provided in an embodiment of this application;

[0052] Figure 7 A schematic diagram illustrating the implementation process of the second sub-module for determining the second quantity, provided in an embodiment of this application;

[0053] Figure 8 A schematic diagram illustrating the implementation process of the control strategy provided in the embodiments of this application;

[0054] Figure 9 This is a schematic diagram of the structure of the energy storage control device provided in the embodiments of this application;

[0055] Figure 10 A schematic diagram of the energy storage system is provided for the embodiments of this application. Detailed Implementation

[0056] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0057] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0058] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0059] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0060] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0061] Due to environmental constraints, the power output of renewable energy generation systems exhibits randomness and volatility. When connected to the grid, this unstable output affects the power balance, power supply reliability, and power quality on the AC side. To address this issue, energy storage systems store and release electrical energy to provide necessary compensation during power fluctuations in renewable energy generation systems, thereby suppressing grid power fluctuations and improving grid stability.

[0062] Furthermore, significant changes in power demand from loads on the grid side, or frequent starts, stops, or sudden changes in the operating status of large electrical equipment, can cause power surges in the grid, leading to drastic voltage fluctuations. This can affect the normal operation of other equipment within the same grid, impacting grid stability and reducing power quality. Energy storage systems, through rapid charging and discharging, provide additional power support during power surges, thereby stabilizing grid voltage.

[0063] Currently, energy storage systems only integrate lithium batteries as the energy storage element. Since lithium battery-based energy storage systems have low power density, if they need to provide a large power, the capacity of the lithium batteries needs to be very large, resulting in a waste of lithium battery capacity. Therefore, due to factors such as the charging rate and cycle life of lithium batteries, frequent high-power charging and discharging will shorten the battery's lifespan.

[0064] To address the above technical issues, this application provides an energy storage control method and energy storage system. When power fluctuations occur in the power grid, the system controls the output power based on a hybrid energy storage system to provide power compensation and stabilize the power grid.

[0065] The following section introduces the specific implementation of the energy storage system and energy storage control methods.

[0066] like Figure 1 As shown in the schematic diagram of the energy storage system provided in this application embodiment, the energy storage system may include a DC-connected energy storage valve 10 and a voltage source converter 20. The topology of the energy storage system is as follows: the DC side of the DC-connected energy storage valve 10 is connected in parallel with the DC side of the voltage source converter 20, and the DC-connected energy storage valve 10 is connected to the power grid 30 through the voltage source converter 20. Figure 1 As shown, the DC direct-connected energy storage valve 10 is connected in parallel with the voltage source converter 20 and is connected to the DC bus respectively; the voltage source converter 20 converts the DC voltage into a three-phase AC voltage and connects it to the AC bus on the grid side through the converter transformer.

[0067] like Figure 2 As shown in Figure (a), the DC direct-connected energy storage valve 10 includes a first sub-module (SM) connected in series, such as SM1 to SM2. n The voltage source converter 20 includes a bridge-connected second submodule, which can be a supercapacitor submodule (SC-SM), such as SC-SM1 to SC-SM. n The voltage source converter 20 integrates a supercapacitor on the basis of a modular multilevel converter (MMC), which improves the energy storage and dynamic response capabilities of the energy storage system.

[0068] Among them, U dc U is a DC voltage. va U vb U vc For a voltage source converter, these are the three independent phase voltages (e.g., the voltages of phase A, phase B, and phase C); i va i vb i vc These are the three phase currents of the voltage source converter. The phase voltage is the sum of the output voltages of the second submodule operating in each phase. The output phase voltage is achieved by controlling the switching state of the second submodule on the upper and lower arms of that phase. pa Let i be the current in the upper arm of phase A. na i is the current in the lower bridge arm of phase A; pb Let i be the current in the upper arm of phase B. nb i is the current in the lower bridge arm of phase B; pc For the current in the upper arm of phase C, i nc This represents the current in the lower arm of phase C. Each phase's upper and lower arms also include a resistor R and an inductor L connected in series with the second submodule; the series resistor R and inductor L constitute the arm reactor, also known as a phase reactor or valve reactor. One arm reactor is connected in series in each arm. The phase reactor, together with the leakage reactance of the converter transformer, forms the link between the voltage source converter and the AC system for power transmission. In conjunction with the valve-side voltage of the converter transformer, it determines the power transmission capacity of the voltage source converter, enabling regulation and control of active and reactive power on the grid side and suppressing short-circuit current.

[0069] like Figure 2 As shown in Figure (b), the first submodule includes a half-bridge circuit, a buffer circuit, and an energy storage battery, which can be a lithium battery. The half-bridge circuit includes two power switching devices (such as insulated-gate bipolar transistors (IGBTs) VT5 and VT6), two diodes (VD5 and VD6), and a capacitor C; the buffer circuit is a protection circuit for the half-bridge circuit; and the energy storage battery provides power compensation through charging or discharging.

[0070] like Figure 2 As shown in Figure (c), the second submodule includes a half-bridge circuit structure SM, a DC / DC converter, and a supercapacitor C. SCThe half-bridge circuit structure SM includes diodes VD1 and VD2, insulated-gate bipolar transistors (IGBTs) VT1 and VT2, and capacitor C. SM The DC / DC converter includes diodes VD3 and VD4, insulated-gate bipolar transistors (IGBTs) VT3 and VT4, and inductor L. SC Supercapacitor C SC Power compensation is achieved through charging or discharging.

[0071] Understandably, the supercapacitor integrated in the voltage source converter 20 possesses characteristics such as high power density, high efficiency, and long lifespan, making it suitable for high-power, frequent charge-discharge scenarios. Meanwhile, the energy storage battery integrated in the DC-connected energy storage valve 10 possesses high energy density, making it suitable for large-scale power storage scenarios. Thus, combining the DC-connected energy storage valve 10 with the voltage source converter 20 constitutes a hybrid energy storage system. In the event of power fluctuations, by separately controlling the output power of the DC-connected energy storage valve 10 and the voltage source converter 20, corresponding power compensation is provided. This satisfies both high power density and high energy density requirements, improving response efficiency while reducing the rated capacity of the energy storage battery and extending its lifespan.

[0072] Based on the above architecture, the specific implementation process of the energy storage control method will be described below through examples.

[0073] like Figure 3 The diagram shown illustrates the implementation flow of the energy storage control method provided in this application embodiment. The executing entity of this method can be... Figure 1 The energy storage system shown in the figure may include the following steps:

[0074] S301, obtain the frequency difference between the current grid frequency and the rated grid frequency, the first state of the energy storage battery, and the second state of the supercapacitor.

[0075] In this embodiment, the energy storage system can detect parameters such as the frequency, voltage, and current of the power grid using sensing elements, for example, by measuring the period of the power grid signal using a frequency meter, thereby calculating the current power grid frequency. The rated power grid frequency is the standard frequency specified by the power grid, such as 50 Hz or 60 Hz. When the power grid frequency fluctuates, such as when the current power grid frequency is lower or higher than the rated power grid frequency, the frequency difference between the current power grid frequency and the rated power grid frequency will trigger the energy storage system to perform a power compensation process.

[0076] For example, the first state of the energy storage battery integrated in a DC-DC direct-connected energy storage valve can be the state of energy, such as remaining charge or charge level; the second state of the supercapacitor integrated in a voltage source converter can also be the state of energy. The energy storage system can use a battery management system (BMS) to detect parameters such as voltage, current, and temperature of the energy storage battery, and combine this with the charge / discharge characteristics and capacity information of the energy storage battery to calculate the first state of the energy storage battery.

[0077] The DC-connected energy storage valve includes multiple first sub-modules connected in series. The first states of the energy storage batteries integrated in each first sub-module can be the same or different. The energy storage system can control the operating state of the first sub-module by combining the first states of the energy storage batteries in each first sub-module, so as to provide power compensation when the grid frequency fluctuates.

[0078] For example, the second state of the supercapacitor integrated in the voltage source converter can be the energy state; the energy storage system uses a capacitor monitoring system to detect parameters such as the supercapacitor's voltage and internal resistance, and calculates the second state of the supercapacitor by combining the capacitor's charging and discharging characteristics and capacity information. The voltage source converter includes a bridge-connected second submodule, such as... Figure 2 The half-bridge connection shown includes multiple second sub-modules in both the upper and lower arms, such as SC-SM1 to SC-SM in the upper arm. n and the lower arm SC-SM1 to SC-SM n The second states of the supercapacitors integrated in each second submodule can be the same or different; the energy storage system can control the operating state of the second submodule by combining the second states of the supercapacitors in each second submodule, so as to provide power compensation when the grid frequency fluctuates.

[0079] S302, based on the frequency difference, the first state, and the second state, determine the first power reference value of the DC-connected energy storage valve and the second power reference value of the voltage source converter.

[0080] In this embodiment, the first power reference value is the output power achieved by the DC-connected energy storage valve to provide power compensation, and the second power reference value is the output power achieved by the voltage source converter to provide power compensation. By detecting the first state of the energy storage battery and the second state of the supercapacitor, power reference values ​​corresponding to the DC-connected energy storage valve and the voltage source converter are assigned to address the resulting frequency difference, thereby performing power compensation, suppressing grid frequency fluctuations, and improving grid stability.

[0081] For example, the first power reference value and the second power reference value can be reference values ​​for power compensation by the energy storage system during charging operations, or reference values ​​for power compensation by the energy storage system during discharging operations. For instance, when the current grid frequency is higher than the rated grid frequency, the first power reference value and the second power reference value are reference values ​​for the energy storage system during charging operations; when the current grid frequency is lower than the rated grid frequency, the first power reference value and the second power reference value are reference values ​​for the energy storage system during discharging operations.

[0082] For example, the energy storage system can allocate the power to be compensated based on the first state of the energy storage battery of the DC-connected energy storage valve and the second state of the supercapacitor of the voltage source converter. For instance, the power to be compensated can be allocated proportionally based on the ratio of the first and second states, thus determining the first power reference value corresponding to the DC-connected energy storage valve and the second power reference value corresponding to the voltage source converter. The power to be compensated can be determined based on the frequency difference and a preset virtual inertia of the energy storage system.

[0083] In some embodiments, determining a first power reference value for the DC-connected energy storage valve and a second power reference value for the voltage source converter based on the frequency difference, a first state, and a second state includes:

[0084] S401, based on the frequency difference, the first state and the second state, determine the first power to be compensated for the DC-connected energy storage valve and the second power to be compensated for the voltage source converter.

[0085] For example, based on the first state and the second state, the power compensation that the DC direct-connected energy storage valve and the voltage source converter can provide can be initially evaluated, and then the first power to be compensated and the second power to be compensated can be determined based on the frequency difference.

[0086] For example, based on the ratio between the first state and the second state, the energy storage system allocates the preset total virtual inertia to obtain the virtual inertia corresponding to the DC-connected energy storage valve and the voltage source converter, respectively. Then, based on the virtual inertia allocated to the two and the frequency difference, the first power to be compensated corresponding to the DC-connected energy storage valve and the second power to be compensated corresponding to the voltage source converter are determined.

[0087] Virtual inertia is a quantity that simulates the inertial characteristics of a generator through an energy storage system, providing power compensation to offset grid frequency variations caused by a lack of inertia. Energy storage systems pre-set their total virtual inertia based on their performance characteristics; different energy storage systems can have different total virtual inertia settings.

[0088] In some embodiments, determining the first power to be compensated for the DC-connected energy storage valve and the second power to be compensated for the voltage source converter based on the frequency difference, a first state, and a second state includes:

[0089] A1. Based on the preset total virtual inertia and the first and second states, determine the first virtual inertia corresponding to the DC direct-connected energy storage valve and the second virtual inertia corresponding to the voltage source converter.

[0090] For example, the total virtual inertia can be divided proportionally to obtain the first virtual inertia and the second virtual inertia based on the ratio between the first state and the second state; for example, when the value of the first state is less than that of the second state, the first virtual inertia is less than the second virtual inertia.

[0091] A2 filters and differentiates the frequency difference, and obtains the first power to be compensated based on the processed frequency difference and the first virtual inertia; and obtains the second power to be compensated based on the processed frequency difference and the second virtual inertia.

[0092] For example, such as Figure 5 As shown, f is the current power grid frequency, and f0 is the rated power grid frequency. The frequency difference between the two is obtained by subtraction. Here, s is the first-order filter and differential transfer function, s is the differential operator, and T is the time constant. The frequency difference signal is processed by first-order filtering and differentiation to remove high-frequency noise and retain the low-frequency components, resulting in a smooth frequency variation curve. This curve indicates the trend of power grid frequency fluctuations. The first-order filtered frequency difference signal is then input into the differential transfer function to obtain an output signal indicating the frequency variation trend. The first-order filtering and differentiation process makes the output of the frequency difference signal more accurate and reliable.

[0093] Accordingly, the frequency difference signal after first-order filtering and differentiation is compared with the first virtual inertia H. bat The first power to be compensated, ΔP, is obtained. bat The frequency difference signal after first-order filtering and differentiation is compared with the second virtual inertia H. SC Multiplying them together yields the second power to be compensated, ΔP. SC .

[0094] In some embodiments, the first state includes the first energy of the energy storage battery, and the second state includes the second energy of the supercapacitor; determining the first virtual inertia corresponding to the DC-connected energy storage valve and the second virtual inertia corresponding to the voltage source converter based on the preset total virtual inertia and the first and second states includes:

[0095] A11. Based on the first energy and the second energy, determine the proportion of the first virtual inertia corresponding to the DC direct-connected energy storage valve and the proportion of the second virtual inertia corresponding to the voltage source converter.

[0096] A12. Determine the first virtual inertia based on the proportion of the total virtual inertia and the first virtual inertia; determine the second virtual inertia based on the proportion of the total virtual inertia and the second virtual inertia.

[0097] For example, the first energy can be the electrical energy stored by the DC-connected energy storage valve, and the second energy can be the electrical energy stored by the voltage source converter. The proportions of the first and second virtual inertia, as well as the first and second virtual inertia, are calculated using the following formulas:

[0098]

[0099] Among them, W bat As the primary energy source, W SC Let H be the second energy, H be the total virtual inertia, α be the proportion of the first virtual inertia, and β be the proportion of the second virtual inertia. bat H is the first virtual inertia. SC This is the second virtual inertia.

[0100] In some embodiments, the first state includes a first state of charge and a first state of health of the energy storage battery; the method further includes:

[0101] Based on the first state of charge and the first state of health, the overall state of the energy storage battery is determined; if the overall state of the battery is below a first threshold and the energy storage system is in a discharging state, the first virtual inertia ratio is set to zero; or, if the overall state of the battery is above a second threshold and the energy storage system is in a charging state, the first virtual inertia ratio is set to zero; wherein, the first threshold is less than the second threshold.

[0102] For example, the energy storage system sets a first virtual inertia percentage by detecting the state of charge (SOC) (also known as remaining charge) and state of health (SOH) of the energy storage battery.

[0103] The first state of charge (SOC) indicates the ratio of the remaining dischargeable capacity of the energy storage battery to its fully charged state, usually expressed as a percentage, such as 0 to 100%, where 0 represents a fully discharged battery and 100% represents a fully charged battery. The first state of health indicates the degree of aging of the energy storage battery. For example, it can be the ratio of the current capacity to the standard capacity of the energy storage battery. As the energy storage battery ages, its usable capacity gradually decreases. Alternatively, it can be defined as an internal resistance ratio, or based on the number of cycles, such as subtracting the current number of cycles from the standard number of cycles and then dividing by the standard number of cycles to obtain the state of health.

[0104] For example, for an energy storage battery with a DC-connected energy storage valve, its first state of charge and first state of health can be considered comprehensively. Different weighting systems can be set for the first state of charge and the first state of health to calculate the battery's overall state of X (SOX). For example, the battery's overall state of X (SOX) can be calculated using the following formula:

[0105] SOX=xSOH+(1-x)SOC

[0106] Where x is a weighting coefficient, with a value ranging from 0 to 1. For example, if the SOH of the energy storage battery is less than the SOC, then x is set to 0.5; otherwise, x is set to be less than or equal to 0.5.

[0107] Correspondingly, if the overall state threshold of the energy storage battery is less than the first threshold (e.g., 10%), it indicates that the energy storage battery is no longer suitable for discharge operation. In scenarios where the energy storage system needs to perform power compensation through discharge operation, the first virtual inertia corresponding to the DC direct-connected energy storage valve is set to 0, that is, power compensation is not performed through the energy storage battery.

[0108] Correspondingly, if the overall state of the energy storage battery is higher than the second threshold (e.g., 90%), it means that the energy storage battery is no longer suitable for charging. In scenarios where the energy storage system needs to perform power compensation through charging, the first virtual inertia corresponding to the DC-connected energy storage valve is set to 0, that is, power compensation is not performed through the energy storage battery.

[0109] In some embodiments, the second state includes the second state of charge of the supercapacitor; the method further includes:

[0110] When the second state of charge is lower than the first threshold and the energy storage system is in a discharging state, the proportion of the second virtual inertia is set to zero; or, when the second state of charge is higher than the second threshold and the energy storage system is in a charging state, the proportion of the second virtual inertia is set to zero; wherein, the first threshold is less than the second threshold.

[0111] For example, the second state of charge is the ratio of the remaining capacity of the supercapacitor to its total capacity at the current moment, which can be represented by a value from 0 to 1; for example, when the second state of charge is 0, it means that the supercapacitor is completely discharged, and when the current second state of charge is 1, it means that the supercapacitor is completely charged.

[0112] Accordingly, if the second state of charge of the supercapacitor is lower than the first threshold (e.g., 10%), it means that the supercapacitor is no longer suitable for discharge operation. In scenarios where the energy storage system needs to perform power compensation through discharge operation, the second virtual inertia corresponding to the voltage source converter is set to 0, that is, power compensation is not performed through the supercapacitor.

[0113] Correspondingly, if the second state of charge of the supercapacitor is higher than the second threshold (e.g., 90%), it means that the supercapacitor is no longer suitable for charging. In scenarios where the energy storage system needs to perform power compensation through charging, the second virtual inertia of the voltage source converter is set to 0, that is, power compensation is not performed through the supercapacitor.

[0114] In some embodiments, after determining the first virtual inertia percentage corresponding to the DC-connected energy storage valve and the second virtual inertia percentage corresponding to the voltage source converter based on the first energy and the second energy, the method further includes:

[0115] The first virtual inertia ratio is adjusted based on a first proportional coefficient, and the second virtual inertia ratio is adjusted based on a second proportional coefficient; the first virtual inertia is obtained based on the adjusted first virtual inertia ratio and the total virtual inertia; and the second virtual inertia is obtained based on the adjusted second virtual inertia ratio and the total virtual inertia.

[0116] For example, based on the high power density characteristics of supercapacitors, voltage source converters can handle the demands of rapid charging and discharging and multiple charge-discharge cycles, making them more suitable for small and frequent frequency fluctuations. During energy storage control, the energy storage system can utilize the energy stored in the supercapacitor as the primary energy source for virtual inertia. Based on the high energy density of energy storage batteries, DC-connected energy storage valves can handle large frequency fluctuations. During energy storage control, the energy storage system can use the energy storage batteries of the DC-connected energy storage valve as compensation energy for the supercapacitor, providing sufficient and reliable energy reserves for virtual inertia.

[0117] Accordingly, based on the virtual inertia allocation according to the proportional relationship between the first and second states, the first and second virtual inertia are further dynamically adjusted using a proportional coefficient, so that the energy storage system prioritizes the supply of energy from the virtual inertia through the voltage source converter. For example, the first and second virtual inertia are adjusted using the following formula:

[0118] Hbat =k bat α*H

[0119] H SC =k SC β*H

[0120] Where, k bat k is the first proportionality coefficient. SC The first and second proportional coefficients can be flexibly adjusted based on the actual application scenario. For example, in some cases, if the supercapacitor of the voltage source converter is sufficient to provide inertia support, the first proportional coefficient can be set to 0.

[0121] S402, based on the first actual power value and the first power to be compensated of the DC direct-connected energy storage valve, obtain the first power reference value.

[0122] For example, the first actual power value is the power of the DC-connected energy storage valve in its current operating state; the energy storage system obtains the first actual power value by monitoring the voltage and current on the DC side and calculating the product of the voltage and current. In the event of grid frequency fluctuations, the first power to be compensated is calculated; the first actual power value is added to the first power to be compensated to obtain the first power reference value corresponding to the DC-connected energy storage valve.

[0123] S403, based on the second actual power value and the second power to be compensated of the voltage source converter, obtains the second power reference value.

[0124] For example, the second actual power value is the power of the voltage source converter in its current operating state; the energy storage system obtains this second actual power value by monitoring the three-phase AC voltage and three-phase AC current at the AC grid connection point of the voltage source converter and multiplying them. In the event of grid frequency fluctuations, the second power to be compensated is calculated; the second actual power value is added to the second power to be compensated to obtain the second power reference value corresponding to the AC power source converter.

[0125] S303, based on a first power reference value, controls the DC-connected energy storage valve to operate a first number of first sub-modules; and / or controls the voltage source converter to operate a second number of second sub-modules based on a first power reference value and a second power reference value.

[0126] In the embodiments of this application, after determining the power reference value, the energy storage system adjusts the power by adjusting the current or voltage of the DC-connected energy storage valve, or by adjusting the current or voltage of the voltage source converter, thereby providing inertia support for the power grid.

[0127] For example, when the current grid frequency is higher than the rated grid frequency, it indicates that there is excess active power in the grid. In this case, the first power reference value and the second power reference value can be the power reference values ​​for charging the DC direct-connected energy storage valve and the voltage source converter of the energy storage system, respectively. The energy storage system absorbs the excess active power in the grid through charging to perform power compensation. Correspondingly, when the output power of the power generation system is greater than the planned output power, the energy storage system can also store energy through charging to balance the stability of grid connection, thereby balancing the power supply and demand relationship on the grid side and improving the stability and reliability of the grid.

[0128] For example, if the current grid frequency is lower than the rated grid frequency, it indicates that the active power in the grid is insufficient. At this time, the first power reference value and the second power reference value can be the power reference values ​​for the DC direct-connected energy storage valve and the voltage source converter of the energy storage system to discharge. The energy storage system releases the stored energy through discharge to provide additional active power to the grid for power compensation.

[0129] For example, the output voltage of the first submodule in the DC direct-connected energy storage valve and the second submodule in the voltage source converter can be adjusted by controlling the switching devices inside the first and second submodules respectively, so as to control the operation of a first number of first submodules and / or control the operation of a second number of second submodules, thereby achieving power compensation for the power grid and improving the stability of the power grid.

[0130] The implementation process of determining the first sub-module of the first quantity and the second sub-module of the second quantity is further described below through examples.

[0131] In some embodiments, controlling the DC-connected energy storage valve to operate a first number of first sub-modules according to a first power reference value includes:

[0132] S601, calculate the DC current reference value based on the first power reference value and the rated DC voltage value on the DC side of the energy storage system.

[0133] For example, such as Figure 8 As shown, the first power reference value P corresponding to the DC direct-connected energy storage valve is obtained. batref Then, divide the first power reference value by the rated DC voltage value U on the DC side. dc The DC current reference value i is calculated. DCref .

[0134] 602. Calculate the DC current error value based on the DC current reference value and the current DC current value.

[0135] For example, such as Figure 8 As shown, the DC current reference value i is calculated. DCrefThen, compare the DC current reference value with the current DC current value i. DC The difference is calculated to obtain the DC current error value. This DC current error value represents the difference between the current DC current and the expected current (i.e., the DC current reference value).

[0136] The current DC current value can be obtained through monitoring by the energy storage system, and the rated DC voltage value is the preset rated voltage value.

[0137] S603 performs proportional and integral processing on the DC current error value to obtain the first quantity.

[0138] For example, such as Figure 8 As shown, the DC current error value is input to the proportional-integral controller (PIC) for proportional (P) and integral (I) processing to calculate the control quantity, thus obtaining the first quantity N of the first submodule that needs to be put into operation. ref .

[0139] S604 is the first submodule that controls the operation of the first number of DC-connected energy storage valves.

[0140] For example, the energy storage system controls the current output of the energy storage system by controlling the number of first sub-modules connected to the DC direct-connected energy storage valve, thereby regulating the output power, providing power compensation, and providing inertia support for the power grid.

[0141] Accordingly, after determining the first quantity, the energy storage system can also selectively control the switching devices inside the first submodule based on the state of the energy storage battery integrated in the first submodule, and control the operation of the first quantity of the first submodule; thereby, by controlling the number of first submodules put into operation, the magnitude of the DC current flowing through the DC direct-connected energy storage valve is adjusted, thereby regulating the power of the DC direct-connected energy storage valve and providing inertial support for the power grid.

[0142] In some embodiments, controlling the voltage source converter to operate a second number of second sub-modules based on a first power reference value and a second power reference value includes:

[0143] S701, based on the rated DC voltage on the DC side of the energy storage system and the capacitor voltage of the second submodule, calculate the second number of the second submodule on each phase arm of the voltage source converter.

[0144] For example, such as Figure 2 As shown, the energy storage system will convert the rated DC voltage U dc Divide by the capacitor voltage U of the second submodule SM This yields the second number of second sub-modules on each phase arm, such as the number of second sub-modules to be deployed on phase A, phase B, and phase C.

[0145] The second quantity refers to the total number of second submodules deployed on each phase arm, specifically the sum of the number of second submodules deployed on the upper and lower arms. The energy storage system obtains the capacitance C of the second submodule through voltage detection. SM The voltage U across the capacitor SM .

[0146] S702, calculate the active power reference value on the grid side based on the first power reference value and the second power reference value.

[0147] For example, based on such Figure 1 The system architecture shown shows that the input power of the grid-side energy storage system, the output power of the DC-connected energy storage valve, and the output power of the voltage source converter all satisfy the power conservation law, i.e., P bat +P SC +P g =0.

[0148] like Figure 8 As shown, based on the law of power conservation, the active power reference value P on the grid side can be calculated using the first power reference value and the second power reference value. gref The active power reference value refers to the expected value of active power that the grid-side converter should output. By controlling the active power reference value, the load demand on the grid side is met, and grid stability is maintained.

[0149] S703 determines the reference wave signal corresponding to each phase arm based on the active power reference value and reactive power reference value on the grid side.

[0150] For example, the reactive power reference value is the expected value of the reactive power output by the grid-side converter. By processing the active power reference value and the reactive power reference value, the reference wave signal corresponding to each phase arm is obtained; this reference wave signal can be a voltage or current reference signal in the ABC three-phase stationary coordinate system, representing the expected voltage or current waveform; the waveform of the actual output voltage or current of the grid-side converter is adjusted based on the reference wave signal to ensure the stability of the power grid.

[0151] S704, based on the reference wave signal, determines the first number of sub-modules of the upper arm second sub-module and the second number of sub-modules of the lower arm second sub-module of each phase bridge arm; the second number is the sum of the first number of sub-modules and the second number of sub-modules.

[0152] For example, each phase arm of a voltage source converter can include multiple series-connected second sub-modules in its upper and lower arms. A reference wave signal is used to adjust the output three-phase voltage waveform of the voltage source converter. For the capacitor voltage of each second sub-module, a sorting algorithm and bubble sort are used to determine the capacitor voltage of the target second sub-module in the upper arm that is closest to the currently required output voltage, thereby determining the first number of second sub-modules to be deployed in the upper arm. Since the sum of the number of second sub-modules deployed in the upper arm and the number of second sub-modules deployed in the lower arm equals the total number n of second sub-modules on the arm, after determining the first number of sub-modules corresponding to the upper arm, the number of second sub-modules corresponding to the lower arm is obtained by subtracting the first number of sub-modules from n, thus determining the number of second sub-modules deployed in the upper and lower arms respectively.

[0153] S705 controls the voltage source converter, and operates the second sub-module of the first number of sub-modules of the upper arm of each phase bridge arm and the second sub-module of the second number of sub-modules of the lower arm of each phase bridge arm.

[0154] For example, the energy storage system adjusts the output current of the voltage source converter by controlling the number of second sub-modules connected to the upper and lower arms of the voltage source converter, thereby achieving power compensation for the power grid and providing inertia support for the power grid.

[0155] In some embodiments, the step of determining the reference wave signal corresponding to each phase arm based on the active power reference value and reactive power reference value on the grid side includes:

[0156] The active and reactive power reference values ​​from the grid side are adjusted through the power control outer loop to obtain the first voltage reference value. This first voltage reference value is then adjusted through a voltage-current dual closed loop to obtain the second voltage reference value in a rotating coordinate system. Finally, the second voltage reference value undergoes coordinate system transformation to obtain the reference wave signal in the ABC three-phase coordinate system.

[0157] For example, such as Figure 8 As shown, the active power reference value P gref and reactive power reference value Q gref After adjustment by the power control outer loop, the first voltage reference value E is obtained. ref Using the first voltage reference value as input, the second voltage reference value E in the rotating coordinate system dq is obtained through voltage and current dual closed-loop regulation. dqref The second voltage reference value is transformed by coordinate system transformation to obtain the reference wave signal e in the ABC three-phase stationary coordinate system. iref .

[0158] Through the embodiments of this application, in the event of grid frequency fluctuations, based on the hybrid energy storage system of energy storage batteries and supercapacitors, power reference values ​​are allocated to the DC-connected energy storage valve and the voltage source converter, respectively. Power compensation is performed using supercapacitors (high power density, high efficiency, long lifespan, suitable for high-power, frequent charge-discharge applications) and energy storage batteries (high energy density), respectively. This reduces the requirements for the charge-discharge rate of the energy storage batteries, decreases their rated capacity, and extends their lifespan, ensuring grid stability. The supercapacitor SC integrated in each second submodule is connected in parallel to the DC terminal of each second submodule SM via a bidirectional DC / DC converter. The second submodules adopt a half-H-bridge structure. Each second submodule can function as a distributed energy storage unit, capable of absorbing or releasing active power. The bidirectional DC / DC converter is a bidirectional Buck / Boost converter, which has advantages such as compact structure and high efficiency. When the load experiences active power surges, the voltage source converter responds to the energy storage system's needs, controlling the rapid charging / discharging of the supercapacitor to maintain the voltage stability of the second submodule capacitors and provide active power compensation during transient processes. By monitoring frequency changes and the state of charge (SOC) and state of health (SOH) of the energy storage system, dynamic allocation of the two types of static energy—the energy storage battery and the supercapacitor—is achieved. This prevents the energy storage system from overcharging and over-discharging, not only enabling full utilization of the mixed energy but also effectively avoiding frequent charging and discharging of the battery, thus extending the lifespan of the energy storage system.

[0159] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0160] Corresponding to the energy storage control method provided in the above embodiments, Figure 9 A schematic diagram of the energy storage control device provided in the embodiments of this application is shown. For ease of explanation, only the parts related to the embodiments of this application are shown.

[0161] Reference Figure 9 The energy storage control device includes:

[0162] The sampling unit 91 is used to acquire the frequency difference between the current grid frequency and the rated grid frequency, the first state of the energy storage battery, and the second state of the supercapacitor.

[0163] Processing unit 92 is used to determine the first power reference value of the DC direct-connected energy storage valve and the second power reference value of the voltage source converter based on the frequency difference, the first state and the second state;

[0164] Control unit 93 is configured to control the DC-connected energy storage valve to operate a first number of first sub-modules based on a first power reference value; and / or control the voltage source converter to operate a second number of second sub-modules based on a first power reference value and a second power reference value.

[0165] In one possible implementation, the processing unit 92 is further configured to determine the first power to be compensated for the DC-connected energy storage valve and the second power to be compensated for the voltage source converter based on the frequency difference, the first state, and the second state; obtain a first power reference value based on the first actual power value of the DC-connected energy storage valve and the first power to be compensated; and obtain a second power reference value based on the second actual power value and the second power to be compensated for the voltage source converter.

[0166] In one possible implementation, the processing unit 92 is further configured to determine the first virtual inertia corresponding to the DC-connected energy storage valve and the second virtual inertia corresponding to the voltage source converter based on the preset total virtual inertia and the first and second states; to filter and differentiate the frequency difference, and to obtain the first power to be compensated based on the processed frequency difference and the first virtual inertia; and to obtain the second power to be compensated based on the processed frequency difference and the second virtual inertia.

[0167] In one possible implementation, the first state includes the first energy of the energy storage battery, and the second state includes the second energy of the supercapacitor; the processing unit 92 is further configured to determine the first virtual inertia ratio corresponding to the DC-connected energy storage valve and the second virtual inertia ratio corresponding to the voltage source converter based on the first energy and the second energy; determine the first virtual inertia based on the total virtual inertia and the first virtual inertia ratio; and determine the second virtual inertia based on the total virtual inertia and the second virtual inertia ratio.

[0168] In one possible implementation, the first state includes a first state of charge and a first state of health of the energy storage battery; the processing unit 92 is further configured to determine the overall battery state of the energy storage battery based on the first state of charge and the first state of health; if the overall battery state is lower than a first threshold and the energy storage system is in a discharging state, then the first virtual inertia percentage is set to zero; or, if the overall battery state is higher than a second threshold and the energy storage system is in a charging state, then the first virtual inertia percentage is set to zero; wherein the first threshold is less than the second threshold.

[0169] In one possible implementation, the second state includes the second state of charge of the supercapacitor; the processing unit 92 is further configured to set the second virtual inertia percentage to zero when the second state of charge is below the first threshold and the energy storage system is in a discharging state; or, when the second state of charge is above the second threshold and the energy storage system is in a charging state, set the first virtual inertia percentage to zero.

[0170] In one possible implementation, the processing unit 92 is further configured to adjust the first virtual inertia ratio based on a first proportional coefficient, and adjust the second virtual inertia ratio based on a second proportional coefficient; the first proportional coefficient is less than the second proportional coefficient; obtain the first virtual inertia based on the adjusted first virtual inertia ratio and the total virtual inertia; and obtain the second virtual inertia based on the adjusted second virtual inertia ratio and the total virtual inertia.

[0171] In one possible implementation, the control unit 93 is further configured to calculate a DC current reference value based on a first power reference value and a rated DC voltage value on the DC side of the energy storage system; calculate a DC current error value based on the DC current reference value and the current DC current value; perform proportional and integral processing on the DC current error value to obtain a first quantity; and control the DC direct-connected energy storage valve to operate a first quantity of the first sub-module.

[0172] In one possible implementation, the control unit 93 is further configured to: calculate the second number of second submodules on each phase arm of the voltage source converter based on the rated DC voltage on the DC side of the energy storage system and the capacitor voltage of the second submodule; calculate the active power reference value on the grid side based on the first power reference value and the second power reference value; determine the reference wave signal corresponding to each phase arm based on the active power reference value and the reactive power reference value on the grid side; determine the first number of second submodules on the upper arm and the second number of second submodules on the lower arm of each phase arm based on the reference wave signal; the second number is the sum of the first number of second submodules and the second number of second submodules; and control the voltage source converter to operate the second submodules of the first number of second submodules on the upper arm and the second submodules of the second number of second submodules on the lower arm of each phase arm.

[0173] In one possible implementation, the control unit 93 obtains a first voltage reference value by adjusting the active power reference value and reactive power reference value on the grid side through the power control outer loop; obtains a second voltage reference value in the rotating coordinate system by adjusting the first voltage reference value through the voltage and current double closed loop; and obtains a reference wave signal in the ABC three-phase coordinate system by performing coordinate system transformation on the second voltage reference value.

[0174] Through the embodiments of this application, when grid frequency fluctuates, based on the energy storage system that combines energy storage batteries and supercapacitors, the power reference values ​​corresponding to the DC-connected energy storage valve and the voltage source converter are allocated respectively. Based on the supercapacitor, which has high power density, high efficiency, long life and is suitable for high-power, frequent charge and discharge application scenarios, and the energy storage battery, which has high energy density, power compensation is performed respectively. This can reduce the requirements for the charge and discharge rate of the energy storage battery, reduce the rated capacity of the energy storage battery and extend its life, thus ensuring grid stability.

[0175] Figure 10A schematic diagram of the hardware structure of the energy storage system 100 is shown.

[0176] like Figure 10 As shown, the energy storage system 100 of this embodiment includes: a DC-connected energy storage valve 10, a voltage source converter 20, and at least one processor 1001. Figure 10 (Only one is shown in the image) A memory 1002 stores a computer program 1003 that can run on the processor 1001. When the processor 1001 executes the computer program 1003, it implements the steps in the above method embodiments, for example... Figure 3 S301 to S303 are shown. Alternatively, when the processor 1001 executes the computer program 1003, it implements the functions of each module / unit in the above-described device embodiments.

[0177] It is understood that the structures illustrated in the embodiments of this application do not constitute a specific limitation on the energy storage system 100. In other embodiments of this application, the energy storage system 100 may include more or fewer components than illustrated, or combine some components, or split some components, or have different component arrangements. The illustrated components may be implemented in hardware, software, or a combination of software and hardware.

[0178] The energy storage system 100 may include, but is not limited to, a processor 1001 and a memory 1002. Those skilled in the art will understand that... Figure 10 This is merely an example of the energy storage system 100 and does not constitute a limitation on the energy storage system 100. It may include more or fewer components than shown, or combine certain components, or different components. For example, the server may also include input transmission devices, network access devices, buses, etc.

[0179] The processor 1001 mentioned above can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or any conventional processor.

[0180] The processor 1001 may also include a memory for storing instructions and data. In some embodiments, the memory in the processor 1001 is a cache memory. This memory can store instructions or data that the processor 1001 has just used or that are used repeatedly. If the processor 1001 needs to use the instruction or data again, it can directly retrieve it from the memory. This avoids repeated accesses, reduces the waiting time of the processor 1001, and thus improves the efficiency of the system.

[0181] In some embodiments, the aforementioned memory 1002 may be an internal storage unit of the energy storage system 100, such as a hard disk or memory of the energy storage system 100. The memory 1002 may also be an external storage device of the energy storage system 100, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc., equipped on the energy storage system 100. Furthermore, the memory 1002 may include both internal storage units and external storage devices of the energy storage system 100. The memory 1002 is used to store operating systems, applications, bootloaders, data, and other programs, such as program code for computer programs. The memory 1002 can also be used to temporarily store data that has been sent or will be sent.

[0182] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0183] It should be noted that the structure of the above-mentioned electronic device is only illustrative and may include other physical structures depending on the application scenario. The physical structure of the electronic device is not limited here.

[0184] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0185] This application also provides an energy storage system, including a DC-connected energy storage valve, a voltage source converter, and a controller. The DC-connected energy storage valve integrates multiple first sub-modules connected in series, each first sub-module including an energy storage battery. The voltage source converter integrates a three-phase bridge-connected second sub-module, with multiple second sub-modules connected in series on each phase arm, each second sub-module including a supercapacitor. The DC-connected energy storage valve is connected in parallel to the DC side of the voltage source converter, and the DC-connected energy storage valve is connected to the power grid through the voltage source converter. The controller is communicatively connected to the DC-connected energy storage valve, the voltage source converter, and the power grid. The controller is used to acquire the frequency of the power grid and, based on the frequency of the power grid, control the output power of the DC-connected energy storage valve and / or the voltage source converter.

[0186] This application also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps described in the various method embodiments above.

[0187] This application provides a computer program product that, when run on a server, enables the server to execute the steps described in the above-described method embodiments.

[0188] If the integrated modules / units are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying computer program code, recording media, USB flash drives, portable hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.

[0189] The electronic devices, computer storage media, and computer program products provided in the embodiments of this application are all used to execute the methods provided above. Therefore, the beneficial effects they can achieve can be referred to the beneficial effects corresponding to the methods provided above, and will not be repeated here.

[0190] The technical features of the above embodiments can be combined in any way. 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 contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0191] It should be understood that the above description is merely to help those skilled in the art better understand the embodiments of this application, and is not intended to limit the scope of the embodiments of this application. Based on the examples given above, those skilled in the art can obviously make various equivalent modifications or changes. For example, some steps in the various embodiments of the above detection method may be unnecessary, or new steps may be added. Alternatively, any combination of two or more of the above embodiments may be used. Such modifications, changes, or combinations also fall within the scope of the embodiments of this application.

[0192] It should also be understood that the methods, situations, categories, and classifications of embodiments in this application are for the convenience of description only and should not constitute a special limitation. Various methods, categories, situations, and features in embodiments can be combined without contradiction.

[0193] It should also be understood that, in the various embodiments of this application, unless otherwise specified or in case of logical conflict, the terms and / or descriptions between different embodiments are consistent and can be referenced by each other, and the technical features in different embodiments can be combined to form new embodiments according to their inherent logical relationships.

[0194] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0195] In the embodiments provided in this application, it should be understood that the disclosed apparatus / network devices and methods can be implemented in other ways. For example, the apparatus / network device embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0196] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0197] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

[0198] Finally, it should be noted that the above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An energy storage control method, characterized in that, The method is applied to an energy storage system, which includes a DC-connected energy storage valve and a voltage source converter. The DC-connected energy storage valve includes a first submodule connected in series, which integrates an energy storage battery. The voltage source converter includes a second submodule connected in a bridge configuration, which integrates a supercapacitor. The DC-connected energy storage valve is connected in parallel to the DC side of the voltage source converter, and the DC-connected energy storage valve is connected to the power grid through the voltage source converter. The frequency difference between the current grid frequency and the rated grid frequency, the first state of the energy storage battery, and the second state of the supercapacitor are obtained. Based on the frequency difference, the first state, and the second state, determine the first power reference value of the DC direct-connected energy storage valve and the second power reference value of the voltage source converter; Based on the first power reference value, control the DC direct-connected energy storage valve to operate a first number of the first sub-modules; and / or based on the first power reference value and the second power reference value, control the voltage source converter to operate a second number of the second sub-modules.

2. The method according to claim 1, characterized in that, The step of determining the first power reference value of the DC-connected energy storage valve and the second power reference value of the voltage source converter based on the frequency difference, the first state, and the second state includes: Based on the frequency difference, the first state, and the second state, determine the first power to be compensated for the DC direct-connected energy storage valve and the second power to be compensated for the voltage source converter; Based on the first actual power value of the DC direct-connected energy storage valve and the first power to be compensated, the first power reference value is obtained; The second power reference value is obtained based on the second actual power value of the voltage source converter and the second power to be compensated.

3. The method according to claim 2, characterized in that, The step of determining the first power to be compensated for the DC-connected energy storage valve and the second power to be compensated for the voltage source converter based on the frequency difference, the first state, and the second state includes: Based on the preset total virtual inertia and the first and second states, the first virtual inertia corresponding to the DC direct-connected energy storage valve and the second virtual inertia corresponding to the voltage source converter are determined. The frequency difference is filtered and differentiated, and the first power to be compensated is obtained based on the processed frequency difference and the first virtual inertia; and the second power to be compensated is obtained based on the processed frequency difference and the second virtual inertia.

4. The method according to claim 3, characterized in that, The first state includes the first energy of the energy storage battery, and the second state includes the second energy of the supercapacitor; determining the first virtual inertia corresponding to the DC-connected energy storage valve and the second virtual inertia corresponding to the voltage source converter based on the preset total virtual inertia, the first state, and the second state includes: Based on the first energy and the second energy, determine the first virtual inertia ratio corresponding to the DC direct-connected energy storage valve and the second virtual inertia ratio corresponding to the voltage source converter; The first virtual inertia is determined based on the total virtual inertia and the proportion of the first virtual inertia. The second virtual inertia is determined based on the total virtual inertia and the proportion of the second virtual inertia.

5. The method according to claim 4, characterized in that, The first state includes the first state of charge and the first state of health of the energy storage battery; Before determining the first virtual inertia, the method further includes: Based on the first state of charge and the first health state, the overall battery status of the energy storage battery is determined; If the overall battery condition is below a first threshold and the energy storage system is in a discharged state, then the first virtual inertia percentage is set to zero; or, If the overall battery condition is higher than the second threshold and the energy storage system is in a charging state, then the first virtual inertia percentage is set to zero. Wherein, the first threshold is less than the second threshold.

6. The method according to claim 4, characterized in that, The second state includes the second state of charge of the supercapacitor; Before determining the second virtual inertia, the method further includes: When the second state of charge is below the first threshold and the energy storage system is in a discharging state, the proportion of the second virtual inertia is set to zero; or, When the second state of charge is higher than the second threshold and the energy storage system is in a charging state, the proportion of the second virtual inertia is set to zero. Wherein, the first threshold is less than the second threshold.

7. The method according to claim 4, characterized in that, After determining the first virtual inertia ratio corresponding to the DC-connected energy storage valve and the second virtual inertia ratio corresponding to the voltage source converter based on the first energy and the second energy, the method further includes: The proportion of the first virtual inertia is adjusted based on a first proportionality coefficient, and the proportion of the second virtual inertia is adjusted based on a second proportionality coefficient; The first virtual inertia is obtained based on the adjusted first virtual inertia ratio and the total virtual inertia; and the second virtual inertia is obtained based on the adjusted second virtual inertia ratio and the total virtual inertia.

8. The method according to any one of claims 1 to 7, characterized in that, Based on the first power reference value, controlling the DC-connected energy storage valve to operate a first number of the first sub-modules includes: Calculate the DC current reference value based on the first power reference value and the rated DC voltage value on the DC side of the energy storage system; Calculate the DC current error value based on the DC current reference value and the current DC current value; The DC current error value is proportionally and integrally processed to obtain the first quantity; Control the DC direct-connected energy storage valve to operate the first number of the first sub-modules.

9. The method according to any one of claims 1 to 7, characterized in that, The step of controlling the voltage source converter to operate a second number of the second sub-modules based on the first power reference value and the second power reference value includes: Based on the rated DC voltage on the DC side of the energy storage system and the capacitor voltage of the second submodule, calculate the second quantity of the second submodule on each phase bridge arm of the voltage source converter; Based on the first power reference value and the second power reference value, calculate the active power reference value on the grid side; Based on the active power reference value and reactive power reference value on the grid side, determine the reference wave signal corresponding to each phase bridge arm; Based on the reference wave signal, the first number of sub-modules of the upper bridge arm and the second number of sub-modules of the lower bridge arm of each phase bridge arm are determined; the second number is the sum of the first number of sub-modules and the second number of sub-modules. Control the voltage source converter to operate the second sub-module of the first number of upper bridge arms and the second sub-module of the second number of lower bridge arms of each phase bridge arm.

10. The method according to claim 9, characterized in that, The step of determining the reference wave signal corresponding to each phase arm based on the active power reference value and reactive power reference value on the grid side includes: The active power reference value and reactive power reference value on the grid side are adjusted by the power control outer loop to obtain the first voltage reference value; The first voltage reference value is adjusted by a dual closed-loop voltage and current system to obtain a second voltage reference value in a rotating coordinate system. The second voltage reference value is transformed by coordinate system transformation to obtain the reference wave signal in the ABC three-phase coordinate system.

11. An energy storage control device, characterized in that, An application is made in an energy storage system, the energy storage system comprising a DC-connected energy storage valve and a voltage source converter; the DC-connected energy storage valve integrates a first submodule connected in series, the first submodule comprising an energy storage battery; the voltage source converter integrates a second submodule connected in a bridge configuration, the second submodule comprising a supercapacitor; the DC-connected energy storage valve is connected in parallel to the DC side of the voltage source converter, and the DC-connected energy storage valve is connected to the power grid through the voltage source converter; the device includes: The sampling unit is used to acquire the frequency difference between the current grid frequency and the rated grid frequency, the first state of the energy storage battery, and the second state of the supercapacitor. The processing unit is configured to determine the first power reference value of the DC-connected energy storage valve and the second power reference value of the voltage source converter based on the frequency difference, the first state, and the second state. The control unit is configured to control the DC-connected energy storage valve to operate a first number of the first sub-modules based on the first power reference value; and / or control the voltage source converter to operate a second number of the second sub-modules based on the first power reference value and the second power reference value.

12. An energy storage system, characterized in that, The device includes a DC-connected energy storage valve, a voltage source converter, a memory, and a processor. The memory stores a computer program, and the processor executes the computer program to implement the method of any one of claims 1 to 10.

13. The energy storage system according to claim 12, characterized in that, The energy storage system also includes a power conversion device for connecting to the power generation system.

14. An energy storage system, characterized in that, This includes DC direct-connected energy storage valves, voltage source converters, and controllers; The DC direct-connected energy storage valve integrates multiple first sub-modules connected in series, and the first sub-module includes an energy storage battery; The voltage source converter integrates a three-phase bridge-connected second sub-module, with multiple second sub-modules connected in series on each phase bridge arm. The second sub-module includes a supercapacitor. The DC direct-connect energy storage valve is connected in parallel with the DC side of the voltage source converter, and the DC direct-connect energy storage valve is connected to the power grid through the voltage source converter; The controller is communicatively connected to the DC direct-connected energy storage valve, the voltage source converter, and the power grid, respectively. The controller is used to obtain the frequency of the power grid and, based on the frequency of the power grid, control the output power of the DC direct-connected energy storage valve and / or the voltage source converter.

15. A computer program product, characterized in that, When the computer program product is run on the device, it causes the device to perform the method described in any one of claims 1 to 10.

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