Frequency modulation method, electronic equipment, storage medium and sea wind power generation system thereof

Abstract

The invention discloses a frequency modulation method, electronic equipment, a storage medium and a sea wind power generation system thereof, the method is applied to a sea wind sending-out system, and the sea wind sending-out system comprises a sea wind power generation system, a sending-end converter, a receiving-end converter and a direct-current direct-hanging energy storage system; the sea wind power generation system is electrically connected with the receiving end alternating current system through the sending end current converter and the receiving end current converter, the sending end current converter and the receiving end current converter are electrically connected through a direct current cable, and the direct current direct hanging energy storage system is arranged on the direct current side of the receiving end current converter. The method comprises the following steps: acquiring frequency fluctuation information of a receiving end alternating current system; determining a target frequency modulation strategy of the receiving end alternating current system according to the frequency fluctuation information; wherein different frequency fluctuations correspond to corresponding frequency modulation strategies; and according to the target frequency modulation strategy, the frequency of the receiving-end AC system is adjusted, so that the stability and reliability of the receiving-end power system under the weak power grid working condition are improved.

Description

Technical Field

[0001] The present application relates to the technical field of electric power generation, and in particular to a frequency modulation method, electronic equipment and storage medium, and an offshore wind power generation system thereof. Background Art

[0002] As an emerging form of new energy development, flexible direct current transmission from offshore wind farms can help build new power systems, thereby reducing non-renewable resource consumption and carbon dioxide emissions.

[0003] Most existing offshore wind flexible direct current transmission systems use grid-following (GFL) control based on a phase-locked loop (PLL). As the strength of the power system continues to decrease, weak grid conditions with low inertia and low short-circuit ratio will become the norm in future power systems. In this case, PLL-based grid-following control is prone to instability and poor robustness under weak grid conditions. Summary of the Invention

[0004] In view of the above problems, the present application provides a frequency modulation method, electronic equipment and storage medium and its sea wind power generation system, which can solve the problem that the phase-locked loop and grid-type control adopted by the sea wind flexible direct current transmission system is prone to instability and poor robustness under weak grid conditions of the power system.

[0005] In the first aspect, the present application provides a frequency modulation method, which is applied to an offshore wind transmission system, wherein the offshore wind transmission system includes an offshore wind power generation system, a sending-end converter, a receiving-end converter, and a DC direct-connected energy storage system; the offshore wind power generation system is electrically connected to the receiving-end AC system through the sending-end converter and the receiving-end converter, respectively, the sending-end converter and the receiving-end converter are electrically connected through a DC cable, and the DC direct-connected energy storage system is arranged on the DC side of the receiving-end converter; the method includes: obtaining frequency fluctuation information of the receiving-end AC system; determining a target frequency modulation strategy of the receiving-end AC system based on the frequency fluctuation information; wherein different frequency fluctuations correspond to corresponding frequency modulation strategies; and adjusting the frequency of the receiving-end AC system based on the target frequency modulation strategy.

[0006] The frequency modulation method designed above first obtains the frequency fluctuation information of the receiving system, and then calls the multi-stage frequency modulation control strategy of DC capacitors in the DC cable, DC direct-hung energy storage, and wind farm energy of the offshore wind power generation system based on the frequency fluctuation level. The frequency modulation strategy is different under different levels, thereby providing strong voltage and frequency support for the receiving AC system and improving the stability and reliability of the receiving power system under weak grid conditions.

[0007] In some embodiments, obtaining frequency fluctuation information of the receiving-end AC system includes: controlling the DC direct-hung energy storage system to operate in a constant DC voltage control mode, thereby controlling the DC direct-hung energy storage system to transmit a constant voltage to the DC side of the receiving-end converter; obtaining a measured frequency value of the receiving-end AC system; and calculating the difference between the measured frequency value and the rated frequency value of the receiving-end AC system to obtain a frequency fluctuation value of the receiving-end AC system.

[0008] In the above implementation mode, when the DC direct-mounted energy storage system operates in a constant DC voltage control mode, the frequency fluctuation value of the receiving-end AC system is used to reflect the frequency fluctuation information of the receiving-end AC system, thereby improving the measurement accuracy of the frequency fluctuation information.

[0009] In some embodiments, based on the frequency fluctuation information, a target frequency regulation strategy of the receiving-end AC system is determined, including: when it is determined that the frequency fluctuation value is greater than a first frequency fluctuation threshold and the frequency fluctuation value is less than a second frequency fluctuation threshold, determining that the DC direct-connected energy storage system participates in frequency regulation, wherein the second frequency fluctuation threshold is greater than the first frequency fluctuation threshold.

[0010] In the above implementation mode, when the frequency fluctuation value is greater than the first frequency fluctuation threshold and less than the second frequency fluctuation threshold, that is, the degree of frequency fluctuation is not large, this scheme only calls on the DC direct-connected energy storage system to participate in frequency regulation, thereby providing strong voltage and frequency support for the receiving AC system while saving frequency regulation resources.

[0011] In some embodiments, the frequency of the receiving-end AC system is adjusted according to the target frequency regulation strategy, including: adjusting the frequency of the receiving-end AC system by a virtual synchronous machine through a DC direct-connected energy storage system.

[0012] In some embodiments, a DC direct-hung energy storage system is used to adjust the frequency of the receiving-end AC system by means of a virtual synchronous machine, including: obtaining the set primary frequency modulation coefficient, virtual inertia constant, damping coefficient, virtual synchronous torque and torque reference value, and the measured frequency value and rated frequency value of the receiving-end AC system; using a virtual power angle swing equation to control the voltage phase angle of the receiving-end AC system according to the primary frequency modulation coefficient, virtual inertia constant, damping coefficient, virtual synchronous torque and torque reference value, and the measured frequency value and rated frequency value of the receiving-end AC system; obtaining a preset droop control coefficient, voltage integral coefficient, reactive power reference value, reactive power setting initial value, and the measured voltage value and voltage initial value of the DC side of the receiving-end converter; using a droop control equation to control the voltage amplitude of the receiving-end AC system according to the droop control coefficient, voltage integral coefficient, reactive power reference value, reactive power setting initial value, and the measured voltage value and voltage initial value of the DC side of the receiving-end converter, so as to adjust the frequency of the receiving-end AC system.

[0013] In the above implementation mode, when the DC direct-connected energy storage system operates in a constant DC voltage control mode, the frequency of the receiving-end AC system is adjusted by a virtual synchronous machine, thereby making the receiving-end frequency adjustment more accurate.

[0014] In some embodiments, determining the target frequency regulation strategy of the receiving-end AC system based on the frequency fluctuation information also includes: when it is determined that the frequency fluctuation value is not less than the second frequency fluctuation threshold, determining that the DC direct-connected energy storage system and the offshore wind power generation system participate in frequency regulation.

[0015] In the above implementation mode, when the frequency fluctuation value is not less than the second frequency fluctuation threshold, that is, when the frequency fluctuation degree is large, this scheme calls on the DC direct-connected energy storage system and the offshore wind power generation system to jointly participate in frequency regulation, thereby calling on the fast power modulation capability of the offshore wind power generation system to enhance the support strength of the system frequency.

[0016] In some embodiments, the frequency of the receiving-end AC system is adjusted according to the target frequency regulation strategy, including: adjusting the frequency of the receiving-end AC system by means of a virtual synchronous machine through a DC direct-connected energy storage system; controlling the rotor kinetic energy of the offshore wind power generation system and the wind energy surplus energy of the offshore wind power generation system to adjust the frequency of the receiving-end AC system; wherein, the wind energy surplus energy of the offshore wind power generation system is obtained based on the maximum wind energy and the current wind energy, the maximum wind energy represents the wind energy obtained by the fan blades of the offshore wind power generation system under the maximum wind receiving area, and the current wind energy represents the wind energy obtained by the fan blades of the offshore wind power generation system under the current wind receiving area.

[0017] In some embodiments, after controlling the rotor kinetic energy of the offshore wind power generation system and the wind energy surplus energy of the offshore wind power generation system to adjust the frequency of the receiving-end AC system, the method further includes: obtaining wind turbine recovery parameter information; wherein the wind turbine recovery parameter information includes the frequency value of the receiving-end AC system, the output active power slope of the receiving-end converter, and the wind turbine rotor speed slope; when it is determined that the wind turbine recovery parameter information meets the recovery conditions, the wind turbine power reference value is controlled to decrease from the current power value to the first target power value, and after the wind turbine power reference value reaches the first target power value, according to the first target curve equation, the wind turbine power reference value is controlled to decrease from the first target power value to the second target power value; after the wind turbine power reference value reaches the second target power value, according to the second target curve equation, the wind turbine power reference value is controlled to increase until the wind turbine power reference value is the said current power value.

[0018] In the above implementation mode, this solution can suppress the secondary drop of system frequency during the sea breeze speed recovery stage by designing a wind turbine parameter recovery strategy (MPPT recovery strategy) and DC direct-connected energy storage.

[0019] In some embodiments, obtaining frequency fluctuation information of the receiving-end AC system includes: controlling the DC direct-hook energy storage system to operate in a constant current control mode, thereby controlling the DC direct-hook energy storage system to deliver a constant current to the DC side of the receiving-end converter; obtaining a DC voltage measurement value of the receiving-end converter; and calculating the difference between the DC voltage measurement value of the receiving-end converter and the DC voltage nominal value to obtain a DC voltage fluctuation value.

[0020] In the above implementation mode, when the DC direct-mounted energy storage system operates in constant current control mode, the frequency fluctuation information of the receiving-end AC system is reflected by the DC voltage fluctuation value of the receiving-end converter, thereby making the frequency fluctuation information of the receiving-end AC system more accurately collected.

[0021] In some embodiments, based on the frequency fluctuation information, a target frequency regulation strategy of the receiving-end AC system is determined, including: when it is determined that the DC voltage fluctuation value is greater than a first voltage fluctuation threshold and the DC voltage fluctuation value is less than a second voltage fluctuation threshold, determining that the DC capacitors and the DC direct-connected energy storage system in the DC cable participate in frequency regulation, wherein the second voltage fluctuation threshold is greater than the first voltage fluctuation threshold.

[0022] In the above implementation mode, when the DC voltage fluctuation value is greater than the first DC voltage fluctuation threshold and less than the second DC voltage fluctuation threshold, that is, the degree of frequency fluctuation is not large, this scheme only calls on the DC direct-connected energy storage system and DC capacitors to participate in frequency regulation, thereby providing strong voltage and frequency support for the receiving-end AC system while saving frequency regulation resources.

[0023] In some embodiments, the frequency of the receiving-end AC system is adjusted according to the target frequency regulation strategy, including: adjusting the frequency of the receiving-end AC system by using a DC direct-connect energy storage system and a DC capacitor in a DC voltage synchronous control manner.

[0024] In the above implementation mode, this solution uses a DC voltage synchronous control method to adjust the frequency of the receiving-end AC system, thereby improving the accuracy of frequency regulation when the DC direct-connected energy storage system operates in a constant current control mode.

[0025] In some embodiments, the frequency of the receiving-end AC system is adjusted by using a DC direct-hung energy storage system and a DC capacitor using a DC voltage synchronous control method, including: obtaining a set DC voltage droop coefficient and a DC voltage measurement value, a DC voltage nominal value, and a DC voltage fluctuation value of the receiving-end AC system; determining a DC voltage synchronous control signal of the receiving-end converter based on the DC voltage fluctuation value, the DC voltage nominal value, the DC voltage measurement value, and the DC voltage droop coefficient; obtaining the input power of the DC capacitor; and adjusting the frequency of the receiving-end AC system based on the input power of the DC capacitor and the DC voltage synchronous control signal.

[0026] In some embodiments, determining the target frequency regulation strategy of the receiving-end AC system based on the frequency fluctuation information also includes: when it is determined that the DC voltage fluctuation value is not less than the second voltage fluctuation threshold, determining that the DC direct-connected energy storage system, DC capacitors and offshore wind power generation system participate in frequency regulation.

[0027] In the above implementation mode, when the DC voltage fluctuation value is not less than the second DC voltage fluctuation threshold, that is, when the frequency fluctuation degree is large, this scheme calls on the DC direct-mounted energy storage system, DC capacitors and offshore wind power generation system to jointly participate in frequency regulation, thereby calling on the fast power modulation capability of the offshore wind power generation system to enhance the support strength of the system frequency.

[0028] In some embodiments, the frequency of the receiving-end AC system is adjusted according to the target frequency regulation strategy, including: adjusting the frequency of the receiving-end AC system by means of DC voltage synchronous control through a DC direct-mounted energy storage system and a DC capacitor; and controlling the rotor kinetic energy of the offshore wind power generation system and the wind energy surplus energy of the offshore wind power generation system to adjust the frequency of the receiving-end AC system, wherein the wind energy surplus energy of the offshore wind power generation system is obtained based on the maximum wind energy and the current wind energy, the maximum wind energy represents the wind energy obtained by the fan blades of the offshore wind power generation system under the maximum wind receiving area, and the current wind energy represents the wind energy obtained by the fan blades of the offshore wind power generation system under the current wind receiving area.

[0029] In some embodiments, after controlling the rotor kinetic energy of the offshore wind power generation system and the wind energy surplus energy of the offshore wind power generation system to adjust the frequency of the receiving-end AC system, the method further includes: obtaining wind turbine recovery parameter information; wherein the wind turbine recovery parameter information includes the frequency value of the receiving-end AC system, the output active power slope of the receiving-end converter, and the wind turbine rotor speed slope; when it is determined that the wind turbine recovery parameter information meets the recovery conditions, controlling the wind turbine power reference value to decrease from the current power value to the first target power value; after the wind turbine power reference value reaches the first target power value, according to the first target curve equation, controlling the wind turbine power reference value to decrease from the first target power value to the second target power value; after the wind turbine power reference value reaches the second target power value, according to the second target curve equation, controlling the wind turbine power reference value to increase until the wind turbine power reference value is the current power value.

[0030] In the above implementation mode, this solution can suppress the secondary drop of system frequency during the sea breeze speed recovery stage by designing a wind turbine parameter recovery strategy (MPPT recovery strategy) and DC direct-connected energy storage.

[0031] In the second aspect, the present application provides a frequency regulation device, which is applied to an offshore wind transmission system, wherein the offshore wind transmission system includes an offshore wind power generation system, a sending-end converter, a receiving-end converter and a DC direct-connected energy storage system; the offshore wind power generation system is electrically connected to the receiving-end AC system through the sending-end converter and the receiving-end converter respectively, the sending-end converter and the receiving-end converter are electrically connected through a DC cable, and the DC direct-connected energy storage system is arranged on the DC side of the receiving-end converter; the device includes: an acquisition module, a determination module and an adjustment module; the acquisition module is used to obtain frequency fluctuation information of the receiving-end AC system; the determination module is used to determine the target frequency regulation strategy of the receiving-end AC system based on the frequency fluctuation information; wherein different frequency fluctuations correspond to corresponding frequency regulation strategies; the adjustment module is used to adjust the frequency of the receiving-end AC system according to the target frequency regulation strategy.

[0032] The frequency regulation device designed above first obtains the frequency fluctuation information of the receiving system, and then calls the multi-stage frequency regulation control strategy of DC capacitors in the DC cable, DC direct-hung energy storage, and wind farm energy of the offshore wind power generation system based on the frequency fluctuation level. The frequency regulation strategy is different under different levels, thereby providing strong voltage and frequency support for the receiving AC system and improving the stability and reliability of the receiving power system under weak grid conditions.

[0033] On the third aspect, the present application provides an offshore wind power generation system, including an offshore wind transmission system, a receiving-end AC system and a control system; the offshore wind transmission system includes an offshore wind power generation system, a sending-end converter, a receiving-end converter and a DC direct-connected energy storage system, the offshore wind power generation system is electrically connected to the receiving-end AC system through the sending-end converter and the receiving-end converter respectively, the sending-end converter and the receiving-end converter are electrically connected through a DC cable, and the DC direct-connected energy storage system is arranged on the DC side of the receiving-end converter; the control system is respectively communicated with the offshore wind power generation system, the sending-end converter, the receiving-end converter, the DC direct-connected energy storage system and the receiving-end AC system; the control system is used to obtain frequency fluctuation information of the receiving-end AC system; determine the target frequency modulation strategy of the receiving-end AC system according to the frequency fluctuation information; wherein different frequency fluctuations correspond to corresponding frequency modulation strategies; and adjust the frequency of the receiving-end AC system according to the target frequency modulation strategy.

[0034] The above-mentioned offshore wind power generation system is designed in this scheme. By setting up a DC direct-hook energy storage system on the DC side of the receiving converter, and then communicating with the offshore wind transmission system and the receiving AC system through the control system, a new offshore wind power generation system topology scheme is designed. Among them, the DC direct-hook energy storage provides greater control flexibility for the offshore wind flexible direct transmission system, and significantly improves the overall system's ability to provide primary frequency regulation while smoothing out offshore wind output fluctuations. Specifically, the control system obtains the frequency fluctuation information of the receiving system, and then calls the multi-stage frequency regulation control strategy of the DC capacitors in the DC cable, the DC direct-hook energy storage, and the offshore wind power generation system wind farm energy based on the frequency fluctuation level. The frequency regulation strategy is different under different levels, thereby providing strong voltage and frequency support for the receiving AC system and improving the stability and reliability of the receiving power system under weak grid conditions.

[0035] In a fourth aspect, the present application provides an electronic device comprising a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the method in the first aspect and any optional implementation of the first aspect is executed.

[0036] In a fifth aspect, the present application provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method in the first aspect or any optional implementation of the first aspect is executed.

[0037] In a sixth aspect, the present application provides a computer program product, which, when running on a computer, enables the computer to execute the method in the first aspect or any optional implementation of the first aspect.

[0038] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A topological diagram of the sea wind power generation system provided in an embodiment of the present application;

[0040] Figure 2 A topological diagram of a DC direct-mounted energy storage system provided in an embodiment of the present application;

[0041] Figure 3 A schematic diagram of a first flow chart of a frequency modulation method provided in an embodiment of the present application;

[0042] Figure 4 A second flow chart of the frequency modulation method provided in an embodiment of the present application;

[0043] Figure 5 A diagram of the frequency modulation control framework of a virtual synchronous machine provided in an embodiment of the present application;

[0044] Figure 6 This is a diagram of the sea breeze frequency modulation control framework provided in the embodiment of the present application;

[0045] Figure 7 A third flow chart of the frequency modulation method provided in an embodiment of the present application;

[0046] Figure 8 A fourth flow chart of the frequency modulation method provided in an embodiment of the present application;

[0047] Figure 9 A diagram of the DC voltage synchronization control framework provided in an embodiment of the present application;

[0048] Figure 10 A schematic diagram of the structure of the frequency modulation device provided in an embodiment of the present application;

[0049] Figure 11 A schematic diagram of the structure of an electronic device provided in an embodiment of the present application.

[0050] Icons: 10-offshore wind transmission system; 110-offshore wind power generation system; 120-sending-end converter; 130-receiving-end converter; 140-DC direct-mounted energy storage system; 1410-isolating switch; 1420-starting resistor; 1430-reactor; 1440-submodule; 150-DC cable; 20-receiving-end AC system; 30-control system; 1000-acquisition module; 1100-determination module; 1200-regulation module; 1300-control module; 11-electronic equipment; 1101-processor; 1102-memory; 1103-communication bus. DETAILED DESCRIPTION

[0051] As an emerging form of new energy development, flexible direct current transmission from offshore wind farms can help build new power systems, thereby reducing non-renewable resource consumption and carbon dioxide emissions.

[0052] Most existing offshore wind flexible direct current transmission systems use grid-following (GFL) control based on a phase-locked loop (PLL). As the strength of the power system continues to decrease, weak grid conditions with low inertia and low short-circuit ratio will become the norm in future power systems. In this case, PLL-based grid-following control is prone to instability and poor robustness under weak grid conditions.

[0053] Based on the above problems, this application designs a frequency modulation method, electronic equipment, storage medium, and offshore wind power generation system. This application utilizes a multi-stage frequency modulation control strategy based on the frequency fluctuation level, using DC capacitor energy storage, DC direct-connect energy storage, and offshore wind power generation system wind farm energy. Different frequency modulation strategies are used at different levels, thereby providing strong voltage and frequency support for the receiving AC system. Furthermore, this solution further designs a Maximum Power Point Tracking (MPPT) recovery strategy for offshore wind farms, suppressing secondary frequency drops and addressing the contradiction between the economic requirements of offshore wind power generation system wind farm MPPT and the stability requirements of providing active frequency support.

[0054] Based on the above ideas, this application first provides the topology of the designed sea wind power generation system, such as Figure 1 As shown, the offshore wind power generation system includes an offshore wind transmission system 10, a receiving-end AC system 20, and a control system 30. The offshore wind transmission system 10 includes an offshore wind power generation system 110, a sending-end converter 120, a receiving-end converter 130, and a DC direct-connected energy storage system 140. The offshore wind power generation system 110 is electrically connected to the receiving-end AC system 20 via the sending-end converter 120 and the receiving-end converter 130, respectively. The sending-end converter 120 and the receiving-end converter 130 are electrically connected via a DC cable 150. The DC direct-connected energy storage system 140 is disposed on the DC side of the receiving-end converter 130. A DC capacitor is disposed between the DC positive busbar and the DC negative busbar of the DC cable 150.

[0055] The control system 30 is communicatively connected to the offshore wind power generation system 110 , the sending-end converter 120 , the receiving-end converter 130 , the DC direct-connected energy storage system 140 , and the receiving-end AC system 20 .

[0056] In the above-described offshore wind power generation system, offshore wind power generation system 110 is configured to utilize offshore wind power to generate electricity and transmit the generated electrical energy to a sending-end converter 120. The sending-end converter 120 converts the AC power generated by offshore wind power generation system 110 into DC power, which is then remotely transmitted to a receiving-end converter 130 via a DC cable 150. The receiving-end converter 130 then converts the received DC power into AC power and transmits it to a receiving-end AC system 20. The receiving-end AC system 20 can be a conventional residential power grid system, for example.

[0057] The above-mentioned DC direct-hung energy storage system 140 can control the voltage or current on the DC side of the receiving-end converter 130. Specifically, it can have a constant DC voltage control mode and a constant current control mode. In the constant DC voltage control mode, the DC direct-hung energy storage system 140 controls the DC side voltage of the receiving-end converter 130 to be constant; in the constant current control mode, the output current of the DC direct-hung energy storage system 140 is constant.

[0058] As a specific implementation, the DC direct-mounted energy storage system 140 can be as follows: Figure 2 The topology shown is composed of an isolating knife switch 1410, a starting resistor 1420, an inductor 1430 and a series of sub-modules 1440 connected in series, wherein the sub-module 1440 can use a half-bridge sub-module and a full-bridge sub-module, which is composed of a power module and a battery module. The sub-module 1440 has three states, namely, on, off, and locked. Therefore, the output voltage of each sub-module 1440 is the sum of the sub-module capacitor voltage and 0. By adjusting the real-time on-off state of the sub-module 1440, the DC side voltage of the DC direct-hung energy storage system can be changed. Therefore, the control model of the DC direct-hung energy storage system 140 can be changed by changing the reference value of the number of sub-modules 1440 put into operation. It should be noted here that this application Figure 2 The DC direct-hung energy storage system shown is only a possible example. This solution can adopt a DC direct-hung energy storage system with any existing topology type.

[0059] The above-designed sea wind power generation system, the control system can provide strong voltage and frequency support for the receiving end AC system through the designed frequency modulation method. Specifically, this application designs a frequency modulation method, such as Figure 3 As shown, the method can be implemented by the following methods, including:

[0060] Step S300: Obtain frequency fluctuation information of the receiving-end AC system.

[0061] Step S310: Determine the target frequency modulation strategy of the receiving-end AC system according to the frequency fluctuation information.

[0062] Step S320: adjusting the frequency of the receiving-end AC system according to the target frequency modulation strategy.

[0063] In the above embodiment, the frequency fluctuation information of the receiving-end AC system represents the frequency fluctuation of the receiving-end AC system. Specifically, as a possible embodiment, when the DC direct-connected energy storage system is in a constant DC voltage mode, since the DC side voltage of the receiving-end converter is a constant value, the frequency fluctuation information of the receiving-end AC system is reflected through the frequency fluctuation of the receiving-end AC system.

[0064] Furthermore, in the above situation, this scheme can first control the DC direct-hung energy storage system to operate in a constant DC voltage control mode, thereby controlling the DC direct-hung energy storage system to transmit a constant voltage to the DC side of the receiving-end converter, and then measure the frequency of the receiving-end AC system to obtain the measured frequency value, and then calculate the difference between the measured frequency value of the receiving-end AC system and the rated frequency value, thereby obtaining the frequency fluctuation value of the receiving-end AC system.

[0065] As another possible implementation, when the DC direct-connected energy storage system is in constant current mode, the frequency fluctuation information of the receiving-end AC system can be reflected by the DC voltage fluctuation on the DC side of the receiving-end converter.

[0066] Furthermore, in the above situation, this scheme can first control the DC direct-hung energy storage system to operate in a constant current control mode to control the DC direct-hung energy storage system to deliver a constant current to the DC side of the receiving-end converter, and then collect the DC voltage measurement value of the receiving-end converter, calculate the difference between the DC voltage measurement value of the receiving-end converter and the DC voltage nominal value, and thus obtain the DC voltage fluctuation value.

[0067] Based on the above, it can be seen that both the frequency fluctuation value and the DC voltage fluctuation value can reflect the frequency fluctuation information of the receiving-end AC system, and different degrees of frequency fluctuation information have different effects on the power generation system. Therefore, this solution designs corresponding frequency modulation strategies for different degrees of frequency fluctuation information. Specifically, this solution can store the frequency modulation strategies corresponding to different degrees of frequency fluctuation information in advance in the database, and then search for the corresponding target frequency modulation strategy based on the obtained frequency fluctuation information when executing step S310. Among them, the frequency modulation strategy designed by this solution can be as follows: for example, when the frequency fluctuation information is at a reasonable level, this solution may not perform frequency modulation; when the frequency fluctuation information is at a relatively low level, this solution may only call the DC direct-connected energy storage system for frequency modulation; when the frequency fluctuation information is at a relatively large level, this solution may call the offshore wind power generation system and the DC direct-connected energy storage system to jointly participate in frequency modulation.

[0068] When the target frequency modulation strategy is obtained in the above manner, this solution adjusts the frequency of the receiving-end AC system according to the target frequency modulation strategy, thereby providing strong voltage and frequency support for the receiving-end AC system.

[0069] The frequency modulation method designed above first obtains the frequency fluctuation information of the receiving system, and then calls the multi-stage frequency modulation control strategy of DC capacitors in the DC cable, DC direct-hung energy storage, and wind farm energy of the offshore wind power generation system based on the frequency fluctuation level. The frequency modulation strategy is different under different levels, thereby providing strong voltage and frequency support for the receiving AC system and improving the stability and reliability of the receiving power system under weak grid conditions.

[0070] In the optional implementation of this embodiment, it is described above that the DC direct-hung energy storage system can be in a constant DC voltage mode or a constant current mode, and in different control modes, the way in which the DC direct-hung energy storage system participates in frequency modulation is also different. As a possible implementation method, when the DC direct-hung energy storage system is in a constant DC voltage mode, that is, the frequency fluctuation information is the frequency fluctuation value described above, as follows Figure 4As shown, this solution can be frequency modulated in the following ways, including:

[0071] Step S400: Determine whether the frequency fluctuation value is greater than a first frequency fluctuation threshold. If the frequency fluctuation value is greater than the first frequency fluctuation threshold, go to step S410.

[0072] Step S410: Determine whether the frequency fluctuation value is less than the second frequency fluctuation threshold. If the frequency fluctuation value is less than the second frequency fluctuation threshold, go to step S420; if the frequency fluctuation value is not less than the second frequency fluctuation threshold, go to step S430.

[0073] Step S420: Determine whether the DC direct-connect energy storage system participates in frequency regulation.

[0074] Step S430: Determine whether the DC direct-connect energy storage system and the offshore wind power generation system participate in frequency regulation.

[0075] In the above embodiment, this solution compares the frequency fluctuation value with the first frequency fluctuation threshold. If the frequency fluctuation value is not greater than the first frequency fluctuation threshold, it indicates that the frequency fluctuation of the receiving AC system is within a reasonable range, and frequency regulation is not performed. If the frequency fluctuation value is greater than the first frequency fluctuation threshold, this solution indicates that the frequency fluctuation of the receiving AC system exceeds the reasonable range. On this basis, this solution further determines whether the frequency fluctuation value is less than the second frequency fluctuation threshold. If the frequency fluctuation value is less than the second frequency fluctuation threshold, this solution determines that the DC direct-connected energy storage system participates in frequency regulation. Among them, the first frequency fluctuation threshold is less than the second frequency fluctuation threshold. The values ​​of the first frequency fluctuation threshold and the second frequency fluctuation threshold can be obtained based on experience. For example, the first frequency fluctuation threshold is 1% of the rated frequency and the second frequency fluctuation threshold is 10% of the rated frequency. For another example, the first frequency fluctuation threshold is 2% of the rated frequency and the second frequency fluctuation threshold is 10% of the rated frequency, and so on. The specific adjustment can be adaptive according to the actual application scenario.

[0076] When it is determined that the DC direct-connected energy storage system participates in frequency regulation in the above manner, for step S320, this solution can specifically use the DC direct-connected energy storage system to adjust the frequency of the receiving-end AC system by means of a virtual synchronous machine.

[0077] Specifically, the control block diagram for adjusting the frequency of the receiving AC system using a virtual synchronous machine is as follows: Figure 5 As shown, where ω and ω0 are the measured value and rated value of the system frequency (angular velocity), respectively, k p is the set primary frequency modulation coefficient, p0 is the active reference initial value of the virtual synchronous machine, which is usually equal to the steady-state value of the sea wind output power in the sea wind flexible direct current transmission system. T and Tref are the torque and torque reference values ​​of the virtual synchronous machine respectively, which are constants, and the coefficients J and D pare the virtual inertia constant and damping coefficient of the virtual synchronous machine control, which are constants. c and V C0 are the DC voltage of the receiving end converter and the initial value of the DC voltage respectively. q is the set droop control coefficient, Qref is the reactive power reference value, Q0 is the reactive power setting initial value, and K is the voltage integral coefficient.

[0078] According to the parameter information obtained above, this scheme can adopt a primary frequency modulation circuit, using the measured frequency value ω and rated frequency value ω0 of the receiving end AC system and the primary frequency modulation coefficient to realize the primary frequency modulation support function of the receiving end converter, and then use the virtual power angle swing equation and the primary frequency modulation coefficient k p , virtual inertia constant J, damping coefficient D p , virtual synchronous torque T and torque reference value Tref, the measured frequency value ω of the receiving AC system and the rated frequency value ω0 are used to control the voltage phase angle of the receiving AC system to achieve active inertia support and damping support; and the droop control equation is used to calculate the droop control coefficient D q , voltage integral coefficient K, reactive power reference value Qref, reactive power setting initial value Q0, and the measured voltage value and voltage initial value V on the DC side of the receiving converter c and V C0 The voltage amplitude of the receiving AC system is controlled to complete active voltage / reactive power support, thereby adjusting the frequency of the receiving AC system.

[0079] In an optional implementation of this embodiment, if the frequency fluctuation value is determined to be not less than the second frequency fluctuation threshold, it means that the frequency fluctuation of the receiving-end AC system exceeds the reasonable range to a large extent. In this case, this scheme determines that the DC direct-connected energy storage system and the offshore wind power generation system jointly participate in frequency regulation.

[0080] Specifically, this solution also controls the DC direct-mounted energy storage system to adjust the frequency of the receiving-end AC system using the virtual synchronous machine method described above, and this solution controls the rotor kinetic energy of the offshore wind power generation system and the wind energy surplus energy of the offshore wind power generation system to adjust the frequency of the receiving-end AC system.

[0081] The surplus wind energy is obtained based on the maximum wind energy and the current wind energy. The maximum wind energy represents the wind energy obtained by the offshore wind power generation system's blades at their maximum windward area, while the current wind energy represents the wind energy obtained by the offshore wind power generation system's blades at their current windward area. For example, when the offshore wind power generation system is transmitting power normally, the windward area of ​​its blades is 80% of the total blade area (the current windward area). However, when the offshore wind power generation system is participating in frequency modulation, this solution adjusts the windward area of ​​the blades to 100% of the total blade area, thereby obtaining the surplus wind energy.

[0082] Specifically, if Figure 6 The figure shows the control framework diagram of the offshore wind power generation system, where MSG is the machine-side converter, GSC is the grid-side converter, PW is the wind power captured by the wind turbine, Pr is the power input to the MSC, ωr is the wind turbine speed, kMPPT is the maximum power point tracking (MPPT) coefficient, kwf is the offshore wind primary frequency modulation coefficient, and Prref is the MSC active power reference value.

[0083] Under normal conditions, the wind turbine converts wind energy into electrical energy through the captured wind power PW. Only when the system requires frequency modulation does the system's primary frequency modulation control begin. During primary frequency modulation, the GSC measures the frequency of the sea breeze busbar using a phase-locked loop (PLL) and provides the control system with a synchronized phase angle by following the grid. The GSC uses a vector control strategy based on grid voltage orientation to achieve constant DC voltage control and reactive power / voltage control. The MSC uses a control strategy based on rotor magnetic field orientation to achieve active power / reactive power control. The power reference value for the active power control loop is the power calculated by the MPPT algorithm.

[0084] In an optional implementation of this embodiment, when the offshore wind power generation system participates in frequency regulation, when the frequency of the receiving-end AC system reaches the lowest point or the highest point, the frequency begins to recover and the wind turbine speed also needs to be restored. Therefore, an MPPT recovery strategy needs to be set.

[0085] Specifically, if Figure 7 As shown in the figure, the MPPT recovery strategy designed in this scheme can be implemented in the following ways, including:

[0086] Step S700: Obtain wind turbine recovery parameter information.

[0087] Step S710: When it is determined that the wind recovery parameter information meets the recovery conditions, the wind power reference value is controlled to decrease from the current power value to the first target power value. After the wind power reference value reaches the first target power value, according to the first target curve equation, the wind power reference value is controlled to decrease from the first target power value to the second target power value; after the wind power reference value reaches the second target power value, according to the second target curve equation, the wind power reference value is controlled to increase until the wind power reference value is the current power value.

[0088] In the above embodiment, the wind turbine recovery parameter information is used to determine whether the MPPT recovery strategy is activated. If the wind turbine recovery parameter information meets the recovery conditions, the MPPT recovery strategy is activated. Specifically, the wind turbine recovery parameters include the frequency value of the receiving-end AC system, the output active power slope of the receiving-end converter, and the wind turbine rotor speed slope. The recovery condition can specifically be: when the frequency value of the receiving-end AC system is lower than a first frequency threshold, the output active power slope of the receiving-end converter must be less than 0, and the wind turbine rotor speed slope must be greater than 0; or, when the frequency value of the receiving-end AC system is greater than or equal to the first frequency threshold, the output active power slope of the receiving-end converter must be greater than 0, and the wind turbine rotor speed slope must be less than 0. As a possible example, when the first frequency threshold is 50HZ, assuming that the current frequency value of the receiving-end AC system is lower than 50HZ, if at this time the output active power slope of the receiving-end converter is less than 0, and the wind turbine rotor speed slope is greater than 0, then it means that the wind turbine recovery parameters meet the recovery conditions; if the current frequency value of the receiving-end AC system is lower than 50HZ, but the output active power slope of the receiving-end converter and the wind turbine rotor speed slope are both greater than 0, then it is determined that the wind turbine recovery parameters do not meet the recovery conditions.

[0089] When the wind turbine recovery parameters meet the recovery conditions, this solution controls the wind turbine power reference value to drop suddenly from the current power value to the first target power value, forcing the wind turbine rotor to start accelerating, and then after the wind turbine power reference value reaches the first target power value, according to the first target curve equation, the wind turbine power reference value is controlled to slowly decrease from the first target power value to the second target power value, wherein the first target curve equation can be obtained by linear method, quadratic function method, inverse quadratic function method, etc.; after the wind turbine power reference value reaches the second target power value, according to the second target curve equation, the wind turbine power reference value is controlled to increase until the wind turbine power reference value returns to the current power value, wherein the second target curve equation can be an MPPT curve equation, so that the wind turbine power reference value automatically returns to the current power value from the second target power value through the MPPT curve equation, and then returns to the balance point.

[0090] In the implementation method of the above design, during the MPPT recovery phase, the DC direct-mounted energy storage can provide additional capacity for wind turbine speed recovery through frequency modulation control, thereby further suppressing the secondary drop in system frequency. Therefore, the designed MPPT recovery strategy and DC direct-mounted energy storage work together to suppress the secondary drop in system frequency during the sea breeze speed recovery phase.

[0091] In the optional implementation of this embodiment, it is described above that the DC direct-hung energy storage system can be in a constant DC voltage mode or a constant current mode. In different control modes, the way in which the DC direct-hung energy storage system participates in frequency modulation is also different. As a possible implementation method, when the DC direct-hung energy storage system is in a constant current mode, that is, the frequency fluctuation information is the DC voltage fluctuation value described above, as shown in FIG. Figure 8 As shown, this solution can be frequency modulated in the following ways, including:

[0092] Step S800: Determine whether the DC voltage fluctuation value is greater than a first voltage fluctuation threshold value. If it is determined that the DC voltage fluctuation value is greater than the first voltage fluctuation threshold value, go to step S810.

[0093] Step S810: Determine whether the DC voltage fluctuation value is less than the second voltage fluctuation threshold. If it is determined that the DC voltage fluctuation value is less than the second voltage fluctuation threshold, go to step S820; if it is determined that the DC voltage fluctuation value is not less than the second voltage fluctuation threshold, go to step S830.

[0094] Step S820: Determine whether the DC capacitors and the DC direct-connect energy storage system in the DC cable participate in frequency regulation.

[0095] Step S830: Determine whether the DC energy storage system, DC capacitors, and offshore wind power generation system participate in frequency regulation. In the above embodiment, this solution compares the DC voltage fluctuation value with a first DC voltage fluctuation threshold. If the DC voltage fluctuation value is not greater than the first DC voltage fluctuation threshold, it indicates that the frequency fluctuation of the receiving AC system is within a reasonable range, and frequency regulation is not performed, that is, the DC capacitors are used to provide temporary active inertia support for the system. If the DC voltage fluctuation value is greater than the first DC voltage fluctuation threshold, this solution indicates that the frequency fluctuation of the receiving AC system exceeds a reasonable range. Based on this, this solution further determines whether the DC voltage fluctuation value is less than a second DC voltage fluctuation threshold. If the DC voltage fluctuation value is less than the second DC voltage fluctuation threshold, this solution determines that the DC energy storage system and the DC capacitors in the DC cable participate in frequency regulation. Among them, the first DC voltage fluctuation threshold is less than the second DC voltage fluctuation threshold. The values ​​of the first DC voltage fluctuation threshold and the second DC voltage fluctuation threshold can be obtained based on experience. For example, the first DC voltage fluctuation threshold is 1% of the nominal value of the DC voltage, and the second DC voltage fluctuation threshold is 10% of the nominal value of the DC voltage; for another example, the first DC voltage fluctuation threshold is 2% of the nominal value of the DC voltage, and the second DC voltage fluctuation threshold is 10% of the nominal value of the DC voltage, and so on. It can be adaptively adjusted according to the actual application scenario.

[0096] When it is determined that the DC direct-hung energy storage system and the DC capacitor participate in frequency regulation in the above manner, for step S320, this solution can specifically adjust the frequency of the receiving-end AC system by using the DC direct-hung energy storage system and the DC capacitor in a DC voltage synchronous control manner.

[0097] Furthermore, the control block diagram for adjusting the frequency of the receiving end AC system by adopting the DC voltage synchronous control method can be shown as follows: Figure 9As shown in the figure, Vdr is the DC voltage signal of the receiving converter station, Vdr0 is the nominal value of the DC voltage, kDC is the DC voltage droop coefficient, VC and δC are the amplitude and phase angle of the port voltage of the receiving converter, XC is the converter outlet port impedance, XL is the receiving AC system impedance, VS is the receiving AC system terminal voltage, PS is the input power of the DC capacitor, PR is the output power of the receiving converter station, and kD is the damping coefficient.

[0098] Based on the aforementioned parameter information, this solution determines the DC voltage synchronization control signal PWM for the receiving converter based on the DC voltage fluctuation value ΔVdr, the nominal DC voltage value Vdr0, the measured DC voltage value Vdr, and the DC voltage droop coefficient kDC. This solution uses the DC voltage fluctuation value ΔVdr, the nominal DC voltage value Vdr0, the measured DC voltage value Vdr, and the DC voltage droop coefficient kDC to calculate the synchronous phase angle δC of the receiving converter's port voltage in real time, helping the REVSC complete phase-locked loop (PLL)-free self-synchronization. Simultaneously, the receiving converter can achieve system inertia response based on DC capacitor energy storage. Within the voltage control loop, the outer loop sets the AC voltage setpoint VC, while the inner loop controls the modulation ratio to achieve converter port voltage control. Its auxiliary damping control loop, fed by the DC voltage fluctuation signal ΔVdr and the damping coefficient kD, simulates the function of a synchronous machine power system stabilizer (PSS), thereby providing active damping support for the system.

[0099] In the case of obtaining the DC voltage synchronous control signal PWM, this solution adjusts the frequency of the receiving-end AC system according to the input power PS of the DC capacitor and the DC voltage synchronous control signal PWM.

[0100] In an optional implementation of this embodiment, if it is determined that the DC voltage fluctuation value is not less than the second DC voltage fluctuation threshold, it means that the frequency fluctuation of the receiving-end AC system exceeds the reasonable range to a large extent. In this case, this scheme determines that the DC direct-connected energy storage system, DC capacitors and offshore wind power generation system jointly participate in frequency regulation.

[0101] Specifically, this solution uses a DC direct-connect energy storage system and DC capacitors to adjust the frequency of the receiving AC system using a DC voltage synchronous control method. The specific adjustment method is the same as the previous Figure 9 The adjustment method is the same and will not be described here. In addition, this scheme controls the rotor kinetic energy of the sea wind power generation system and the wind energy surplus energy of the sea wind power generation system to adjust the frequency of the receiving end AC system. The specific adjustment method is the same as the previous Figure 6 In addition, when the offshore wind power generation system participates in frequency regulation, this solution also implements Figure 7The MPPT recovery strategy shown in FIG4 further suppresses the secondary drop of the system frequency.

[0102] In the above implementation mode, this solution designs an MPPT recovery strategy to suppress the secondary drop of system frequency, thereby taking into account the contradiction between the economic requirements of MPPT in offshore wind farms and the stability requirements of providing active frequency support.

[0103] It should be noted here that in the frequency modulation strategy process described above, the sending-end converters designed in this solution are all controlled using the current VF control method.

[0104] Figure 10 The present application provides a schematic structural block diagram of a frequency modulation device. It should be understood that the device is applied to the control system of the sea wind power generation system described above. Figures 3 to 9 The method embodiment executed in the embodiment corresponds to the method, and the steps involved in the aforementioned method can be executed. The specific functions of the device can be found in the description above. To avoid repetition, detailed description is appropriately omitted here. The device includes at least one software function module that can be stored in a memory in the form of software or firmware or solidified in the operating system (OS) of the device. Specifically, the device includes: an acquisition module 1000, a determination module 1100 and an adjustment module 1200; the acquisition module 1000 is used to obtain frequency fluctuation information of the receiving-end AC system; the determination module 1100 is used to determine the target frequency modulation strategy of the receiving-end AC system based on the frequency fluctuation information; wherein different frequency fluctuations correspond to corresponding frequency modulation strategies; the adjustment module 1200 is used to adjust the frequency of the receiving-end AC system according to the target frequency modulation strategy.

[0105] The frequency regulation device designed above first obtains the frequency fluctuation information of the receiving system, and then calls the multi-stage frequency regulation control strategy of DC capacitors in the DC cable, DC direct-hung energy storage, and wind farm energy of the offshore wind power generation system based on the frequency fluctuation level. The frequency regulation strategy is different under different levels, thereby providing strong voltage and frequency support for the receiving AC system and improving the stability and reliability of the receiving power system under weak grid conditions.

[0106] In an optional implementation manner of this embodiment, the acquisition module 1000 is specifically used to control the DC direct-hung energy storage system to operate in a constant DC voltage control mode, thereby controlling the DC direct-hung energy storage system to transmit a constant voltage to the DC side of the receiving-end converter; obtaining the measured frequency value of the receiving-end AC system; calculating the difference between the measured frequency value of the receiving-end AC system and the rated frequency value, and obtaining the frequency fluctuation value of the receiving-end AC system.

[0107] In an optional implementation manner of this embodiment, the determination module 1100 is specifically used to determine that the DC direct-connected energy storage system participates in frequency regulation when it is determined that the frequency fluctuation value is greater than the first frequency fluctuation threshold and the frequency fluctuation value is less than the second frequency fluctuation threshold, wherein the second frequency fluctuation threshold is greater than the first frequency fluctuation threshold.

[0108] In an optional implementation manner of this embodiment, the adjustment module 1200 is further specifically configured to adjust the frequency of the receiving-end AC system by means of a virtual synchronous machine through a DC direct-connected energy storage system.

[0109] In an optional implementation manner of this embodiment, the adjustment module 1200 is further specifically used to obtain the set primary frequency modulation coefficient, virtual inertia constant, damping coefficient, virtual synchronous torque and torque reference value, measured frequency value and rated frequency value of the receiving-end AC system; adopt a virtual power angle swing equation to control the voltage phase angle of the receiving-end AC system according to the primary frequency modulation coefficient, virtual inertia constant, damping coefficient, virtual synchronous torque and torque reference value, measured frequency value and rated frequency value of the receiving-end AC system; obtain a preset droop control coefficient, voltage integral coefficient, reactive power reference value, reactive power setting initial value, and measured voltage value and voltage initial value of the DC side of the receiving-end converter; adopt a droop control equation to control the voltage amplitude of the receiving-end AC system according to the droop control coefficient, voltage integral coefficient, reactive power reference value, reactive power setting initial value, and measured voltage value and voltage initial value of the DC side of the receiving-end converter, so as to adjust the frequency of the receiving-end AC system.

[0110] In an optional implementation manner of this embodiment, the determination module 1100 is further specifically configured to determine whether the DC direct-connected energy storage system and the offshore wind power generation system participate in frequency regulation when it is determined that the frequency fluctuation value is not less than a second frequency fluctuation threshold.

[0111] In an optional implementation manner of this embodiment, the regulation module 1200 is specifically used to regulate the frequency of the receiving-end AC system by means of a virtual synchronous machine through a DC direct-mounted energy storage system; and to regulate the frequency of the receiving-end AC system by controlling the rotor kinetic energy of the offshore wind power generation system and the wind energy surplus energy of the offshore wind power generation system; wherein, the wind energy surplus energy of the offshore wind power generation system is obtained based on the maximum wind energy and the current wind energy, the maximum wind energy represents the wind energy obtained by the fan blades of the offshore wind power generation system under the maximum wind receiving area, and the current wind energy represents the wind energy obtained by the fan blades of the offshore wind power generation system under the current wind receiving area.

[0112] In an optional implementation manner of this embodiment, the acquisition module 1000 is also used to obtain wind turbine recovery parameter information; wherein the wind turbine recovery parameter information includes the frequency value of the receiving-end AC system, the output active power slope of the receiving-end converter, and the wind turbine rotor speed slope; the device also includes a control module 1300, which is used to control the wind turbine power reference value to decrease from the current power value to the first target power value when it is determined that the wind turbine recovery parameter information meets the recovery conditions, and after the wind turbine power reference value reaches the first target power value, according to the first target curve equation, control the wind turbine power reference value to decrease from the first target power value to the second target power value; after the wind turbine power reference value reaches the second target power value, according to the second target curve equation, control the wind turbine power reference value to increase until the wind turbine power reference value is the said current power value.

[0113] In an optional implementation manner of this embodiment, the acquisition module 1000 is further specifically used to control the DC direct-hung energy storage system to operate in a constant current control mode, thereby controlling the DC direct-hung energy storage system to deliver a constant current to the DC side of the receiving-end converter; obtaining the DC voltage measurement value of the receiving-end converter; and calculating the difference between the DC voltage measurement value of the receiving-end converter and the DC voltage nominal value to obtain the DC voltage fluctuation value.

[0114] In an optional implementation manner of this embodiment, the determination module 1100 is further specifically used to determine that the DC capacitors and the DC direct-connected energy storage system in the DC cable participate in frequency regulation when it is determined that the DC voltage fluctuation value is greater than the first voltage fluctuation threshold and the DC voltage fluctuation value is less than the second voltage fluctuation threshold, wherein the second voltage fluctuation threshold is greater than the first voltage fluctuation threshold.

[0115] In an optional implementation manner of this embodiment, the adjustment module 1200 is further specifically configured to adjust the frequency of the receiving-end AC system by adopting a DC voltage synchronous control method through a DC direct-connected energy storage system and a DC capacitor.

[0116] In an optional implementation manner of this embodiment, the adjustment module 1200 is further specifically used to obtain the set DC voltage droop coefficient and the DC voltage measurement value, DC voltage nominal value and DC voltage fluctuation value of the receiving-end AC system; determine the DC voltage synchronization control signal of the receiving-end converter based on the DC voltage fluctuation value, DC voltage nominal value, DC voltage measurement value and DC voltage droop coefficient; obtain the input power of the DC capacitor; and adjust the frequency of the receiving-end AC system based on the input power of the DC capacitor and the DC voltage synchronization control signal.

[0117] In an optional implementation manner of this embodiment, the determination module 1100 is further specifically used to determine whether the DC direct-connected energy storage system, the DC capacitor and the offshore wind power generation system participate in frequency regulation when it is determined that the DC voltage fluctuation value is not less than the second voltage fluctuation threshold.

[0118] In an optional implementation manner of this embodiment, the regulation module 1200 is further specifically used to regulate the frequency of the receiving-end AC system by means of DC voltage synchronous control through a DC direct-mounted energy storage system and a DC capacitor; and to regulate the frequency of the receiving-end AC system by controlling the rotor kinetic energy of the offshore wind power generation system and the wind energy surplus energy of the offshore wind power generation system, wherein the wind energy surplus energy of the offshore wind power generation system is obtained based on the maximum wind energy and the current wind energy, the maximum wind energy represents the wind energy obtained by the fan blades of the offshore wind power generation system under the maximum wind receiving area, and the current wind energy represents the wind energy obtained by the fan blades of the offshore wind power generation system under the current wind receiving area.

[0119] According to some embodiments of the present application, Figure 11 As shown, the present application provides an electronic device 11, including: a processor 1101 and a memory 1102, the processor 1101 and the memory 1102 are interconnected and communicate with each other through a communication bus 1103 and / or other forms of connection mechanisms (not marked), and the memory 1102 stores a computer program executable by the processor 1101. When the computing device is running, the processor 1101 executes the computer program to execute any optional implementation method, such as step S300 and step S320: obtaining frequency fluctuation information of the receiving AC system; determining the target frequency modulation strategy of the receiving AC system based on the frequency fluctuation information; and adjusting the frequency of the receiving AC system according to the target frequency modulation strategy.

[0120] The present application provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method in any of the aforementioned optional implementations is executed.

[0121] Among them, the storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic disk or optical disk.

[0122] The present application provides a computer program product. When the computer program product is run on a computer, the computer is enabled to execute the method in any optional implementation manner.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A frequency modulation method, characterized in that: The method is applied to a sea breeze transmission system, which includes a sea breeze power generation system, a sending-end converter, a receiving-end converter, and a direct current (DC) energy storage system. The sea breeze power generation system is electrically connected to a receiving-end AC system via the sending-end converter and the receiving-end converter, respectively. The sending-end converter and the receiving-end converter are electrically connected via a DC cable. The DC energy storage system is arranged on the DC side of the receiving-end converter. The method includes: Acquiring frequency fluctuation information of the receiving-end AC system; Determining a target frequency modulation strategy of the receiving-end AC system according to the frequency fluctuation information; wherein different frequency fluctuations correspond to corresponding frequency modulation strategies; The frequency of the receiving-end AC system is adjusted according to the target frequency modulation strategy.

2. The method according to claim 1, characterized in that The obtaining of frequency fluctuation information of the receiving-end AC system includes: By controlling the DC direct-hook energy storage system to operate in a constant DC voltage control mode, the DC direct-hook energy storage system is controlled to transmit a constant voltage to the DC side of the receiving-end converter; Obtain the measured frequency value of the receiving end AC system; The difference between the measured frequency value and the rated frequency value of the receiving-end AC system is calculated to obtain the frequency fluctuation value of the receiving-end AC system.

3. The method according to claim 2, characterized in that Determining a target frequency modulation strategy of the receiving-end AC system according to the frequency fluctuation information includes: When it is determined that the frequency fluctuation value is greater than a first frequency fluctuation threshold and the frequency fluctuation value is less than a second frequency fluctuation threshold, it is determined that the DC direct-connected energy storage system participates in frequency regulation, wherein the second frequency fluctuation threshold is greater than the first frequency fluctuation threshold.

4. The method according to claim 3, characterized in that The adjusting the frequency of the receiving-end AC system according to the target frequency modulation strategy includes: The frequency of the receiving-end AC system is adjusted by a virtual synchronous machine through a DC direct-connected energy storage system.

5. The method according to claim 4, characterized in that The frequency of the receiving-end AC system is adjusted by a virtual synchronous machine through a DC direct-connected energy storage system, including: Obtain the set primary frequency modulation coefficient, virtual inertia constant, damping coefficient, virtual synchronous torque and torque reference value, and the measured frequency value and rated frequency value of the receiving end AC system; The voltage phase angle of the receiving-end AC system is controlled by using a virtual power angle swing equation according to a primary frequency modulation coefficient, a virtual inertia constant, a damping coefficient, a virtual synchronous torque and a torque reference value, and a measured frequency value and a rated frequency value of the receiving-end AC system; Obtaining the preset droop control coefficient, voltage integral coefficient, reactive power reference value, reactive power setting initial value, and the measured voltage value and voltage initial value of the DC side of the receiving-end converter; A droop control equation is adopted to control the voltage amplitude of the receiving-end AC system according to the droop control coefficient, the voltage integral coefficient, the reactive power reference value, the reactive power setting initial value, and the measured voltage value and the voltage initial value on the DC side of the receiving-end converter, so as to adjust the frequency of the receiving-end AC system.

6. The method according to claim 3, characterized in that The determining, based on the frequency fluctuation information, a target frequency modulation strategy of the receiving-end AC system further includes: When it is determined that the frequency fluctuation value is not less than the second frequency fluctuation threshold, it is determined that the DC direct-connected energy storage system and the offshore wind power generation system participate in frequency regulation.

7. The method according to claim 6, characterized in that The adjusting the frequency of the receiving-end AC system according to the target frequency modulation strategy includes: The frequency of the receiving-end AC system is adjusted by a virtual synchronous machine through a DC direct-connected energy storage system; The frequency of the receiving-end AC system is adjusted by controlling the rotor kinetic energy of the sea wind power generation system and the wind energy surplus energy of the sea wind power generation system; wherein, the wind energy surplus energy of the sea wind power generation system is obtained based on the maximum wind energy and the current wind energy, the maximum wind energy represents the wind energy obtained by the fan blades of the sea wind power generation system under the maximum wind receiving area, and the current wind energy represents the wind energy obtained by the fan blades of the sea wind power generation system under the current wind receiving area.

8. The method according to claim 7, characterized in that After controlling the rotor kinetic energy of the sea wind power generation system and the wind energy surplus energy of the sea wind power generation system to adjust the frequency of the receiving-end AC system, the method further includes: Obtaining wind turbine recovery parameter information; wherein the wind turbine recovery parameter information includes the frequency value of the receiving end AC system, the output active power slope of the receiving end converter, and the wind turbine rotor speed slope; When it is determined that the wind turbine recovery parameter information meets the recovery condition, controlling the wind turbine power reference value to decrease from the current power value to the first target power value; After the wind turbine power reference value reaches the first target power value, controlling the wind turbine power reference value to decrease from the first target power value to a second target power value according to the first target curve equation; After the wind turbine power reference value reaches the second target power value, the wind turbine power reference value is controlled to increase according to the second target curve equation until the wind turbine power reference value reaches the current power value.

9. The method according to claim 1, characterized in that The obtaining of frequency fluctuation information of the receiving-end AC system includes: By controlling the DC direct-hook energy storage system to operate in a constant current control mode, the DC direct-hook energy storage system is controlled to deliver a constant current to the DC side of the receiving-end converter; Obtaining a DC voltage measurement value of a receiving-end converter; The difference between the DC voltage measurement value of the receiving-end converter and the DC voltage nominal value is calculated to obtain the DC voltage fluctuation value.

10. The method according to claim 9, characterized in that Determining a target frequency modulation strategy of the receiving-end AC system according to the frequency fluctuation information includes: When it is determined that the DC voltage fluctuation value is greater than a first voltage fluctuation threshold and the DC voltage fluctuation value is less than a second voltage fluctuation threshold, it is determined that the DC capacitors and the DC direct-connected energy storage system in the DC cable participate in frequency regulation, wherein the second voltage fluctuation threshold is greater than the first voltage fluctuation threshold.

11. The method according to claim 10, characterized in that The adjusting the frequency of the receiving-end AC system according to the target frequency modulation strategy includes: The frequency of the receiving-end AC system is adjusted by using a DC voltage synchronous control method through a DC direct-hook energy storage system and a DC capacitor.

12. The method according to claim 11, characterized in that The frequency of the receiving-end AC system is adjusted by using a DC voltage synchronous control method through a DC direct-connected energy storage system and a DC capacitor, including: Obtain the set DC voltage droop coefficient and the DC voltage measurement value, DC voltage nominal value, and DC voltage fluctuation value of the receiving-end AC system; Determining a DC voltage synchronization control signal of a receiving-end converter according to the DC voltage fluctuation value, the DC voltage nominal value, the DC voltage measured value, and the DC voltage droop coefficient; Get the input power of the DC capacitor; The frequency of the receiving-end AC system is adjusted according to the input power of the DC capacitor and the DC voltage synchronization control signal.

13. The method according to claim 10, characterized in that The determining, based on the frequency fluctuation information, a target frequency modulation strategy of the receiving-end AC system further includes: When it is determined that the DC voltage fluctuation value is not less than the second voltage fluctuation threshold, the DC direct-connected energy storage system, the DC capacitor and the sea wind power generation system are determined to participate in frequency regulation.

14. The method according to claim 13, characterized in that The adjusting the frequency of the receiving-end AC system according to the target frequency modulation strategy includes: The frequency of the receiving-end AC system is adjusted by using a DC voltage synchronous control method through a DC direct-hook energy storage system and a DC capacitor; The frequency of the receiving-end AC system is adjusted by controlling the rotor kinetic energy of the sea wind power generation system and the wind energy surplus energy of the sea wind power generation system, wherein the wind energy surplus energy of the sea wind power generation system is obtained based on the maximum wind energy and the current wind energy, the maximum wind energy represents the wind energy obtained by the fan blades of the sea wind power generation system under the maximum wind receiving area, and the current wind energy represents the wind energy obtained by the fan blades of the sea wind power generation system under the current wind receiving area.

15. The method according to claim 14, characterized in that After controlling the rotor kinetic energy of the sea wind power generation system and the wind energy surplus energy of the sea wind power generation system to adjust the frequency of the receiving-end AC system, the method further includes: Obtaining wind turbine recovery parameter information; wherein the wind turbine recovery parameter information includes the frequency value of the receiving end AC system, the output active power slope of the receiving end converter, and the wind turbine rotor speed slope; When it is determined that the wind turbine recovery parameter information meets the recovery condition, the wind turbine power reference value is controlled to decrease from the current power value to the first target power value; After the wind turbine power reference value reaches the first target power value, controlling the wind turbine power reference value to decrease from the first target power value to a second target power value according to the first target curve equation; After the wind turbine power reference value reaches the second target power value, the wind turbine power reference value is controlled to increase according to the second target curve equation until the wind turbine power reference value reaches the current power value.

16. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the method according to any one of claims 1 to 15 is implemented.

17. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method according to any one of claims 1 to 15 is implemented.

18. A sea wind power generation system, characterized in that: The sea wind power generation system includes a sea wind transmission system, a receiving end AC system and a control system; The sea breeze transmission system includes a sea breeze power generation system, a sending-end converter, a receiving-end converter and a direct current energy storage system. The sea breeze power generation system is electrically connected to the receiving-end AC system through the sending-end converter and the receiving-end converter respectively. The sending-end converter and the receiving-end converter are electrically connected through a DC cable. The direct current energy storage system is arranged on the DC side of the receiving-end converter. The control system is respectively connected to the sea wind power generation system, the sending-end converter, the receiving-end converter, the DC direct-connected energy storage system and the receiving-end AC system; The control system is used to obtain frequency fluctuation information of the receiving AC system; determine a target frequency modulation strategy of the receiving AC system based on the frequency fluctuation information; wherein different frequency fluctuations correspond to corresponding frequency modulation strategies; and adjust the frequency of the receiving AC system according to the target frequency modulation strategy.

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