Offshore wind power flexible direct current grid-connected system frequency-voltage cooperative support control method, device, equipment and medium

Abstract

The invention relates to the technical field of power system control, in particular to a frequency-voltage cooperative support control method, device and equipment for an offshore wind power flexible direct current grid-connected system and a medium, and the method comprises the steps: detecting the voltage and frequency states of a grid-connected point of a power grid system, and judging whether disturbance occurs or not; determining that the disturbance is single voltage disturbance, single frequency disturbance or frequency and voltage coupling disturbance; when frequency disturbance and voltage disturbance happen to the system at the same time, a frequency-voltage cooperative supporting control strategy is adopted, partition control is carried out according to the grid-connected point voltage situation, three situations are specifically included, on the basis that implementation is easy in engineering, the frequency-voltage cooperative supporting capacity of the offshore wind power flexible direct current grid-connected system is remarkably improved, and the frequency-voltage cooperative supporting capacity of the offshore wind power flexible direct current grid-connected system is improved. The method improves the safe operation level of a power grid, achieves the cooperative control of the frequency and voltage of the offshore wind plant through the flexible direct current grid-connected system, improves the cooperative active supporting capability of the frequency and voltage of the system, and provides support for the operation analysis and planning of the offshore wind plant through the flexible direct current grid-connected system and the power grid.

Description

Technical Field

[0001] The present invention relates to the field of power system control technology, and in particular to a frequency-voltage coordinated support control method, device, equipment and medium for an offshore wind power flexible direct current grid-connected system. Background Art

[0002] Renewable energy has become an important development direction for national energy transformation. Among them, wind energy is one of the most widely used and fastest-growing energy sources in the world. Offshore wind power has become an important direction for wind power development in various countries in recent years due to its advantages such as stable resources, high utilization rate, close distance to load centers, and small land area. Flexible direct current transmission technology has become the preferred solution for offshore wind power grid connection due to its flexible control, power decoupling, and island operation. However, with the continuous increase in the penetration rate of offshore wind power, the power system faces increasing challenges in frequency and voltage support.

[0003] At present, the frequency-voltage coordinated support methods for offshore wind power flexible direct current grid-connected systems are mainly concentrated in the single field of frequency support or voltage support, and lack comprehensive control measures for frequency and voltage coupling disturbances. When dealing with frequency and voltage disturbances, the existing methods fail to fully consider the coupling effect between the two, resulting in the system being unable to provide effective coordinated support when the frequency and voltage fluctuate at the same time; in addition, the existing control strategies are highly complex and difficult to implement in engineering, making it difficult to meet the stability requirements in actual operation; therefore, there is an urgent need for a simple and efficient control strategy that can simultaneously improve the frequency and voltage support capabilities of offshore wind power flexible direct current grid-connected systems to ensure the safety and stability of power grid operation.

[0004] The information disclosed in this background technology section is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to those skilled in the art. Summary of the invention

[0005] The present invention provides a frequency-voltage coordinated support control method, device, equipment and medium for an offshore wind power flexible direct current grid-connected system, thereby effectively solving the problems in the background technology.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a frequency-voltage coordinated support control method for an offshore wind power flexible direct current grid-connected system, comprising the following steps:

[0007] Detecting the voltage and frequency status of the grid connection point, determining whether a disturbance occurs, and determining whether the disturbance is a single voltage disturbance, a single frequency disturbance, or a coupled disturbance of frequency and voltage;

[0008] When only a single voltage disturbance occurs in the system, the reactive power output is adjusted based on the voltage deviation amplitude, and a constant voltage control strategy is adopted for voltage support, while keeping the active power output unchanged;

[0009] When only a single frequency disturbance occurs in the system, the frequency of the grid-connected system is supported through virtual inertia control and droop control based on the frequency deviation, and reactive power output is ensured to maintain system stability.

[0010] When the system experiences frequency and voltage disturbances at the same time, a frequency-voltage coordinated support control strategy is adopted, and zone control is performed according to the voltage situation at the grid connection point. The grid-side modular multi-level converter station adopts active priority or reactive priority mode for voltage support according to the voltage situation deviation, and achieves frequency support for the system through coordinated frequency regulation or remote communication mode.

[0011] Furthermore, when the system experiences frequency and voltage disturbances at the same time, a frequency-voltage coordinated support control strategy is adopted to perform zoning control according to the voltage situation of the grid connection point. The grid-side modular multilevel converter station adopts active priority or reactive priority mode for voltage support according to the voltage situation deviation, and achieves frequency support for the system through coordinated frequency regulation or remote communication mode, specifically including the following scenarios:

[0012] Scenario 1: When the voltage at the grid connection point is in the range of 0.95pu-1.05pu, the voltage is a normal fluctuation and no reactive power compensation is performed. The grid-side modular multilevel converter station adopts the active power priority mode, and the offshore wind farm and MMC-HVDC adopt a coordinated frequency control strategy to support the system frequency.

[0013] Scenario 2: When the grid connection point voltage is in the range of 1.05pu-1.1pu or 0.9pu-0.95pu, the grid-side modular multilevel converter station continues to adopt the active power priority mode and adjusts the reactive power output to actively support the grid connection point voltage. The offshore wind farm and MMC-HVDC adopt the remote communication mode to support the system frequency.

[0014] Scenario 3: When the voltage at the grid connection point is lower than 0.9pu or higher than 1.1pu, the grid-side modular multilevel converter station adopts a reactive power priority mode and reduces active power output according to actual conditions, mainly using reactive power output to provide voltage support for the grid connection point, and the offshore wind farm and MMC-HVDC use a remote communication mode to provide frequency support for the system.

[0015] Further, the voltage and frequency states of the grid connection point are detected to determine whether a disturbance occurs, and the disturbance is determined to be a single voltage disturbance, a single frequency disturbance, or a coupled disturbance of frequency and voltage. The steps include:

[0016] Real-time collection of voltage and frequency data of the grid connection point of the power grid system;

[0017] Compare the voltage and frequency data with historical operation data to analyze fluctuation trends of the data;

[0018] Based on the preset voltage and frequency thresholds, a multi-level alarm mechanism is set to determine whether the voltage or frequency exceeds the set threshold range;

[0019] According to the feedback result of the multi-level alarm mechanism, it is determined whether a disturbance occurs, and it is judged whether the disturbance is a single voltage disturbance, a single frequency disturbance, or a coupled disturbance of frequency and voltage.

[0020] Furthermore, when the system experiences frequency and voltage disturbances simultaneously, a frequency-voltage collaborative support control strategy is adopted. The control strategy is used to deal with simultaneous voltage disturbances and load disturbances, and includes at least the following operating conditions: voltage drop accompanied by a sudden increase in load, voltage drop accompanied by a sudden decrease in load, voltage increase accompanied by a sudden increase in load, and voltage increase accompanied by a sudden decrease in load.

[0021] Furthermore, the offshore wind farm and the MMC-HVDC adopt a coordinated frequency regulation control strategy to support the frequency of the system, and the coordinated frequency regulation control strategy supports the frequency of the system, including:

[0022] By adding virtual inertial control to offshore wind turbines, the inertial response of conventional synchronous generators is simulated. The specific model includes:

[0023]

[0024] Where ΔP in k is the inertial support frequency provided by the wind turbine by releasing the rotor kinetic energy. in is the inertia control coefficient, f is usually the measurement frequency of the land AC system;

[0025] Offshore wind turbines can also simulate the governor response of the generator through droop control. The specific models include:

[0026] △P dr =-k dr (ff 0 );

[0027] Where ΔP dr represents the frequency support power provided by the wind turbine through droop control, k dr represents the droop control coefficient, f 0 and f represent the rated value and measured value of the frequency of the onshore AC system, respectively;

[0028] To ensure power reserve, offshore wind farms use overspeed load reduction control to ensure power reserve. For different load reduction rates d%, the models of wind turbine load reduction power include:

[0029] P del =P MPPT (1-d%);

[0030] Where P MPPT It is the mechanical power output when the fan is running in MPPT state.

[0031] Furthermore, in the scenario 1, the offshore wind farm and MMC-HVDC adopt a coordinated frequency control strategy as follows:

[0032] When the frequency of the grid connection point changes, the DC voltage of the MMC-HVDC is adjusted along with the frequency change. The change of the DC voltage enables the wind farm to receive frequency information from the onshore system. By adjusting the relationship between the DC voltage and the frequency, active support for the system frequency is achieved.

[0033] The relationship model between the DC voltage and the frequency includes:

[0034] f W =K W K DC △f+f W0 ;

[0035] In the formula, K DC Indicates the DC voltage control coefficient, K W represents the WFMMC frequency control coefficient; f W0 It represents the steady-state frequency of WFMMC, and △f represents the frequency deviation of the land system, that is, the difference between the rated value and the actual value of the frequency.

[0036] Furthermore, in the scenario 1 and scenario 2, the grid-side modular multilevel converter station adopts an active power priority mode, i.e., a d-axis current priority mode, which prioritizes active power output, and the maximum reactive power output is the maximum remaining capacity of the system, which is achieved by controlling the PI limit in the current inner loop control;

[0037] The model of the actual values ​​of the d-axis and q-axis currents in the active power priority mode includes:

[0038]

[0039] In the formula, i d Indicates the actual value of the d-axis current, i q Indicates the actual value of the q-axis current, i qref and i dref They represent the q-axis and d-axis current reference values, respectively. max Indicates the maximum current that the inverter can withstand.

[0040] Furthermore, in the scenario 2 and scenario 3, the voltage support control strategy of the grid-side modular multi-level converter station on the grid connection point includes:

[0041] When the system is operating normally, the grid-side modular multilevel converter station adopts U dc / Q control, working in the rated reactive power state; when voltage disturbance occurs, the grid-side modular multilevel converter station switches to the fixed AC voltage mode to provide voltage support for the system;

[0042] The voltage support control model includes:

[0043]

[0044] In the formula, i qref Indicates the q-axis current reference value, k v Represents the reactive power droop coefficient, V acref and V ac Respectively represent the rated value and measured value of the AC voltage at the grid connection point of the onshore AC system, K p and K i They represent the reactive PI control coefficient respectively, and s represents the commonly used expression quantity of the integral link.

[0045] Furthermore, in the scenario 2 and scenario 3, the offshore wind farm and MMC-HVDC provide frequency support for the system through a remote communication mode, and the remote communication mode uses communication technology to directly transmit the GSMMC grid connection point frequency information to the offshore wind farm, so that the offshore wind farm participates in the system active frequency support.

[0046] Furthermore, in the scenario 3, the grid-side modular multilevel converter station adopts a reactive power priority mode, reduces active power output according to actual conditions, and mainly supports the voltage of the grid connection point with reactive power output;

[0047] The reactive power priority mode is the q-axis current priority mode, which gives priority to reactive power output. The maximum active power output is the maximum remaining capacity of the system, which is achieved by controlling the PI limit in the current inner loop control.

[0048] The model of the actual values ​​of the d-axis and q-axis currents in the reactive priority mode includes:

[0049]

[0050] In the formula, i d Indicates the actual value of the d-axis current, i q Indicates the actual value of the q-axis current, i qref and i dref They represent the q-axis and d-axis current reference values, respectively. max Indicates the maximum current that the inverter can withstand.

[0051] The present invention also includes a frequency-voltage coordinated support control device for an offshore wind power flexible direct current grid-connected system, using the above method, including:

[0052] A detection module, used to detect the voltage and frequency status of the grid connection point, determine whether a disturbance occurs, and determine whether the disturbance is a single voltage disturbance, a single frequency disturbance, or a coupled disturbance of frequency and voltage;

[0053] The voltage support module is used to adjust the reactive power output based on the voltage deviation amplitude when only a single voltage disturbance occurs in the system, adopt a constant voltage control strategy for voltage support, and keep the active power output unchanged;

[0054] The frequency regulation support module is used to provide frequency support to the grid-connected system through virtual inertia control and droop control based on the frequency deviation when only a single frequency disturbance occurs in the system, and ensure reactive power output to maintain system stability;

[0055] The collaborative support module is used to adopt a frequency-voltage collaborative support control strategy when the system is simultaneously disturbed by frequency and voltage, and to perform zoning control according to the voltage situation at the grid-connected point. The grid-side modular multi-level converter station adopts active priority or reactive priority mode for voltage support according to the voltage situation deviation, and achieves frequency support for the system through collaborative frequency modulation or remote communication mode.

[0056] The present invention also includes a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method described above is implemented.

[0057] The present invention also includes a storage medium on which a computer program is stored. When the computer program is executed by a processor, the method described above is implemented.

[0058] The beneficial effects of the present invention are:

[0059] Aiming at the frequency-voltage coupling disturbance of offshore wind power flexible direct current grid-connected system, a frequency-voltage coordinated support strategy for offshore wind power flexible direct current grid-connected system based on voltage situation zoning is proposed. The zoning is carried out according to the GSMMC AC voltage per unit value, and then three different control strategies are adopted according to the zoning results. On the basis of being easy to implement in engineering, this strategy significantly improves the frequency-voltage coordinated support capability of offshore wind power flexible direct current grid-connected system and improves the safe operation level of the power grid. At the same time, the coordinated control idea provided by this method has strong versatility and can be applied to multi-terminal offshore flexible direct current grid-connected system and land flexible direct current grid-connected system, and is not limited to new energy sites such as wind farms. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0061] Figure 1 It is a flow chart of the frequency-voltage coordinated support control method of the offshore wind power flexible direct current grid-connected system;

[0062] Figure 2 The flowchart of the frequency-voltage coordinated support control method for the wind power flexible direct current grid-connected system is provided;

[0063] Figure 3 This is the topological structure diagram of the offshore wind power grid-connected system via flexible direct current;

[0064] Figure 4 Additional frequency control schematic for offshore wind farms;

[0065] Figure 5 Schematic diagram of coordinated frequency regulation control of offshore wind farm and MMC-HVDC;

[0066] Figure 6 This is the schematic diagram of GSMMC voltage support control;

[0067] Figure 7 This is a structural diagram of the frequency-voltage coordinated support control device for the offshore wind power flexible direct current grid-connected system;

[0068] Figure 8 A schematic diagram of the structure of a computer device. DETAILED DESCRIPTION

[0069] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0070] like Figures 1 to 6 As shown: A frequency-voltage coordinated support control method for an offshore wind power flexible direct current grid-connected system, comprising the following steps:

[0071] S10: Detecting the voltage and frequency status of the grid connection point, determining whether a disturbance occurs, and determining whether the disturbance is a single voltage disturbance, a single frequency disturbance, or a coupled disturbance of frequency and voltage;

[0072] S20: When only a single voltage disturbance occurs in the system, the reactive output is adjusted based on the voltage deviation amplitude, a constant voltage control strategy is adopted for voltage support, and the active output is kept unchanged;

[0073] S30: When only a single frequency disturbance occurs in the system, the frequency of the grid-connected system is supported through virtual inertia control and droop control based on the frequency deviation, and reactive power output is ensured to maintain system stability;

[0074] S40: When the system experiences frequency and voltage disturbances at the same time, a frequency-voltage coordinated support control strategy is adopted, and zone control is performed according to the voltage situation at the grid connection point. The grid-side modular multi-level converter station adopts active priority or reactive priority mode for voltage support according to the voltage situation deviation, and achieves frequency support for the system through coordinated frequency regulation or remote communication mode.

[0075] As a preferred embodiment of the above embodiment, when the system has frequency and voltage disturbances at the same time, a frequency-voltage coordinated support control strategy is adopted, and zoning control is performed according to the voltage situation of the grid connection point. The grid-side modular multilevel converter station adopts active priority or reactive priority mode for voltage support according to the voltage situation deviation, and realizes frequency support for the system through coordinated frequency modulation or remote communication mode, which specifically includes the following scenarios:

[0076] Scenario 1: When the voltage at the grid connection point is in the range of 0.95pu-1.05pu, the voltage is a normal fluctuation and no reactive power compensation is performed. The grid-side modular multilevel converter station (GSMMC) adopts the active power priority mode, and the offshore wind farm and MMC-HVDC (modular multilevel converter-high voltage direct current transmission system) adopt a coordinated frequency control strategy to support the system frequency.

[0077] Scenario 2: When the grid connection point voltage is in the range of 1.05pu-1.1pu or 0.9pu-0.95pu, the grid-side modular multilevel converter station (GSMMC) continues to adopt the active power priority mode and adjusts the reactive power output to actively support the grid connection point voltage. The offshore wind farm and MMC-HVDC (modular multilevel converter-high voltage direct current transmission system) adopt the remote communication mode to support the system frequency.

[0078] Scenario 3: When the voltage at the grid connection point is lower than 0.9pu or higher than 1.1pu, the grid-side modular multilevel converter station (GSMMC) adopts reactive power priority mode and reduces active power output according to actual conditions, mainly using reactive power output to support the voltage at the grid connection point. The offshore wind farm and MMC-HVDC (modular multilevel converter-high voltage direct current transmission system) use remote communication mode to support the frequency of the system.

[0079] Aiming at the frequency-voltage coupling disturbance of offshore wind power flexible direct current grid-connected system, a frequency-voltage coordinated support strategy for offshore wind power flexible direct current grid-connected system based on voltage situation zoning is proposed. The zoning is carried out according to the GSMMC AC voltage per unit value, and then three different control strategies are adopted according to the zoning results. On the basis of being easy to implement in engineering, this strategy significantly improves the frequency-voltage coordinated support capability of offshore wind power flexible direct current grid-connected system and improves the safe operation level of the power grid. At the same time, the coordinated control idea provided by this method has strong versatility and can be applied to multi-terminal offshore flexible direct current grid-connected system and land flexible direct current grid-connected system, and is not limited to new energy sites such as wind farms.

[0080] The existing technologies mostly focus on the support control of a single frequency or voltage, and lack comprehensive processing of the coupled disturbances between the two. The present invention introduces a frequency-voltage collaborative support control strategy in S40, which can perform zoning control according to the voltage situation when frequency and voltage disturbances occur simultaneously in the system. This control strategy can select different priorities (such as active power priority or reactive power priority) according to different voltage states (such as normal fluctuations, slight deviations, and severe deviations), optimize the collaborative support effect of frequency and voltage under different circumstances, and thus achieve more stable grid operation.

[0081] The present invention is divided into three scenarios (scenario one, scenario two, scenario three) according to the voltage situation of the grid connection point. Different strategies are adopted in each scenario. No reactive power compensation is performed during normal fluctuations. Reactive power is adjusted for support during mild deviations. Reactive power output is prioritized and active power output is reduced during severe deviations. Through this zoning control based on voltage situation, the system can flexibly respond to disturbances of different degrees.

[0082] In the control strategy, the priority of active and reactive power is flexibly adjusted according to different voltage disturbance conditions. When the voltage is in normal fluctuation, active output is prioritized, while in the case of severe voltage deviation, reactive power support is prioritized and active output is reduced when necessary. This dynamic adjustment improves the system's tolerance to grid voltage fluctuations and ensures more efficient frequency-voltage support.

[0083] It should be noted that Figure 3 The topological structure diagram of the offshore wind farm connected to the grid via flexible direct current is only used as an example. In actual application, the corresponding topological structure diagram should be established according to the actual situation of the offshore wind farm connected to the grid via flexible direct current. The DC transmission line between WFMMC and GSMMC realizes the power transmission between the offshore wind farm and the onshore power grid. The system has the ability of frequency-voltage coordinated support control. chop Stable control of DC voltage is carried out to ensure effective voltage support and frequency regulation when voltage or frequency is disturbed.

[0084] As a preferred embodiment of the above embodiment, in step S10, the voltage and frequency states of the grid connection point are detected, whether a disturbance occurs is determined, and the disturbance is determined to be a single voltage disturbance, a single frequency disturbance, or a coupled disturbance of frequency and voltage, and the steps include:

[0085] S11: Install high-precision sensors at the grid connection points to collect voltage and frequency data of the grid system grid connection points in real time;

[0086] S12: Compare the voltage and frequency data with the historical operation data and analyze the fluctuation trend of the data;

[0087] S13: Based on the preset voltage and frequency thresholds, a multi-level alarm mechanism is set to determine whether the voltage or frequency exceeds the set threshold range;

[0088] S14: Determine whether a disturbance occurs based on the feedback result of the multi-level alarm mechanism, and judge whether the disturbance is a single voltage disturbance, a single frequency disturbance, or a coupled disturbance of frequency and voltage.

[0089] The multi-level alarm mechanism can trigger different levels of alarms according to different degrees of voltage or frequency deviation, thereby improving the flexibility of the system. According to the severity of the disturbance, the system can make a graded response, avoiding excessive intervention in small disturbances and ensuring the accuracy of the control strategy. At the same time, it can take quick action when a large disturbance occurs, thereby improving the emergency handling capability of the power grid.

[0090] In this embodiment, in step S40, when the system experiences frequency and voltage disturbances simultaneously, a frequency-voltage collaborative support control strategy is adopted. The control strategy is mainly used to deal with simultaneous voltage disturbances and load disturbances, and includes at least the following operating conditions: voltage drop accompanied by a sudden increase in load, voltage drop accompanied by a sudden decrease in load, voltage increase accompanied by a sudden increase in load, and voltage increase accompanied by a sudden decrease in load.

[0091] By providing corresponding control strategies for simultaneous disturbances of various complex operating conditions (such as voltage drop and sudden increase / decrease in load, etc.), the system can dynamically adjust the frequency and voltage support to ensure that the power grid can maintain stability even under complex disturbances; by considering the combined disturbances of voltage and load, the system can respond more flexibly and quickly to avoid problems such as frequency instability, overvoltage or undervoltage when the load or voltage changes suddenly, thereby improving the operating safety of the entire power grid; considering multiple complex disturbance combination scenarios, it ensures that the system can also quickly adjust when dealing with single voltage, frequency disturbances and load disturbances, thereby improving the system's adaptability and resilience to various operating conditions.

[0092] like Figure 4As shown, the control block diagram displayed is a schematic diagram of the frequency support control strategy of an offshore wind farm, which involves the virtual inertia control (S41), droop control (S42) and overspeed load reduction control (S43) described in claim 9. By combining these control mechanisms, the wind farm can quickly respond to frequency disturbances and provide continuous frequency support, while providing power reserve to ensure that the grid frequency is effectively regulated and restored when it fluctuates. The inertia and droop frequency support control is as follows:

[0093] As a preferred embodiment of the above, in step S40, the offshore wind farm and the MMC-HVDC (modular multilevel converter-high voltage direct current transmission system) adopt a coordinated frequency modulation control strategy to support the frequency of the system, and the coordinated frequency modulation control strategy supports the frequency of the system including:

[0094] S41: By adding virtual inertial control to offshore wind turbines, the inertial response of conventional synchronous generators is simulated. The specific model includes:

[0095]

[0096] Where ΔP in k is the inertial support frequency provided by the wind turbine by releasing the rotor kinetic energy. in is the inertia control coefficient, f is usually the measurement frequency of the land AC system;

[0097] S42: Offshore wind turbines can also simulate the governor response of the generator through droop control. The specific model includes:

[0098] △P dr =-k dr (ff 0 );

[0099] Where ΔP dr represents the frequency support power provided by the wind turbine through droop control, k dr represents the droop control coefficient, f 0 and f represent the rated value and measured value of the frequency of the onshore AC system, respectively;

[0100] S43: To ensure power reserve, the offshore wind farm ensures power reserve through overspeed load reduction control. For different load reduction rates d%, the model of wind turbine load reduction power includes:

[0101] P del =P MPPT (1-d%);

[0102] Where P MPPT It is the mechanical power output when the fan is running in MPPT state.

[0103] By adding virtual inertia control to the wind turbine, the system can respond quickly when frequency disturbances occur. Virtual inertia control uses the rotor kinetic energy of the wind turbine to simulate the inertial response of a conventional synchronous generator to provide short-term frequency support for the system. This rapid response can effectively suppress frequency fluctuations and enhance the frequency stability of the power grid. On the basis of virtual inertia control, the system continuously adjusts the frequency through droop control to simulate the governor response of a conventional generator. Droop control can gradually adjust the power output of the wind turbine according to the frequency deviation to ensure that the frequency returns to the rated value. This gradual recovery mechanism ensures frequency stability and prevents long-term deviations in the system frequency. Through overspeed load reduction control, offshore wind farms can provide power reserve for the system. Through the load reduction model, wind turbines can reserve a certain amount of power reserve to ensure a rapid response when the load suddenly increases or the frequency drops sharply, further improving the stability and emergency handling capabilities of the system.

[0104] Among them, in step S40, if Figure 5 As shown in the figure, a schematic diagram of coordinated frequency regulation control of offshore wind farm and MMC-HVDC (modular multilevel converter-high voltage direct current transmission system) is shown, covering wind farm active power control, WFMMC frequency control and GSMMC DC voltage control; in scenario 1, the coordinated frequency regulation control strategy of offshore wind farm and MMC-HVDC (modular multilevel converter-high voltage direct current transmission system) is as follows:

[0105] When the frequency at the grid connection point changes, the DC voltage of the MMC-HVDC (modular multilevel converter-high voltage direct current transmission system) is adjusted along with the frequency change. The change of DC voltage enables the wind farm to receive frequency information from the onshore system. By adjusting the relationship between DC voltage and frequency, active support for the system frequency is achieved.

[0106] The relationship model between DC voltage and frequency includes:

[0107] f W =K W K DC △f+f W0 ;

[0108] In the formula, K DC Indicates the DC voltage control coefficient, K W represents the WFMMC frequency control coefficient; f W0 It represents the steady-state frequency of WFMMC, and △f represents the frequency deviation of the land system, that is, the difference between the rated value and the actual value of the frequency.

[0109] By adjusting the DC voltage of the MMC-HVDC (Modular Multilevel Converter - High Voltage Direct Current Transmission System) system, the frequency information can be accurately transmitted to the wind farm. In this way, the wind farm can obtain frequency change information from the onshore system in real time and respond quickly based on this information to ensure the accuracy and timeliness of frequency regulation, and realize the coordinated support of frequency and voltage, which is particularly suitable for dealing with situations with large frequency fluctuations; offshore wind farms can actively adjust their output power based on frequency changes, thereby providing support for the grid frequency. This active support capability enhances the frequency regulation role of wind farms in the grid, effectively reduces the frequency regulation burden of the onshore grid, and improves the stability and safety of the system.

[0110] As a preferred embodiment of the above, in step S40, in scenario 1 and scenario 2, the grid-side modular multilevel converter station (GSMMC) adopts an active power priority mode, i.e., a d-axis current priority mode, which prioritizes active power output, and the maximum reactive power output is the maximum remaining capacity of the system, which is achieved by controlling the PI limit in the current inner loop control;

[0111] The model of the actual value of the d-axis and q-axis current in the active power priority mode includes:

[0112]

[0113] In the formula, i d Indicates the actual value of the d-axis current, i q Indicates the actual value of the q-axis current, i qref and i dref They represent the q-axis and d-axis current reference values, respectively. max Indicates the maximum current that the inverter can withstand.

[0114] In the active power priority mode, the system first ensures the output of active power, especially when the voltage at the grid connection point is within the normal fluctuation range (such as Scenario 1 and Scenario 2). By preferentially adjusting the d-axis current, the active power output of the wind farm can be maximized, the power generation efficiency of the wind power system can be improved, and the stable supply of electricity can be ensured. By dynamically adjusting the reactive power output according to the system capacity surplus value, it is ensured that the system can respond quickly when the grid needs additional voltage support. The maximum output of the q-axis current is limited by the system surplus capacity, so that the reactive power compensation can flexibly adapt to different voltage fluctuations and avoid excessive or insufficient reactive power output.

[0115] Among them, in step S40, if Figure 6 As shown in the figure, a schematic diagram of GSMMC voltage support control is shown. In scenario 2 and scenario 3, the voltage support control strategy of the grid-side modular multilevel converter station (GSMMC) for the grid connection point includes:

[0116] When the system is operating normally, the grid-side modular multilevel converter station (GSMMC) adopts U dc / Q control, working in the rated reactive power state; when voltage disturbance occurs, the grid-side modular multilevel converter station (GSMMC) switches to the fixed AC voltage mode to provide voltage support for the system;

[0117] The model of voltage support control includes:

[0118]

[0119] In the formula, i qref Indicates the q-axis current reference value, k v Represents the reactive power droop coefficient, V acref and V ac Respectively represent the rated value and measured value of the AC voltage at the grid connection point of the onshore AC system, K p and K i They represent the reactive PI control coefficient respectively, and s represents the commonly used expression quantity of the integral link.

[0120] When the system is operating normally, GSMMC is in a constant reactive power state to ensure the stability of the system's reactive output. When a voltage disturbance occurs, GSMMC can automatically switch to a constant AC voltage mode to provide voltage support. This dynamic working mode switching improves the system's adaptability and can respond in a timely manner to voltage fluctuations to ensure the stability of the grid voltage. Through the combination of reactive droop control and PI control, the system can flexibly adjust reactive power output, and the reactive droop coefficient k v Ensures fast response to voltage deviation, while the PI controller uses the proportional K p and integral K i The control accurately adjusts the reactive power output to prevent voltage fluctuations from having a long-term impact on the system. This dual control mechanism effectively improves the accuracy and dynamic response capability of voltage support.

[0121] In this embodiment, in step S40, scenario two and scenario three, the offshore wind farm and MMC-HVDC (modular multilevel converter - high voltage direct current transmission system) provide frequency support for the system through a remote communication mode. The remote communication mode uses communication technology to directly transmit the GSMMC grid connection point frequency information to the offshore wind farm, so that the offshore wind farm participates in the active frequency support of the system.

[0122] Through remote communication technology, the frequency information of the GSMMC grid connection point can be transmitted to the offshore wind farm in real time, allowing the wind farm to respond quickly to frequency changes. This method of rapid information transmission greatly reduces information lag and enhances the frequency regulation response capability of the wind farm, thereby improving the frequency stability of the power grid. By receiving the frequency information of the grid connection point, the offshore wind farm can coordinate the frequency regulation with the MMC-HVDC (modular multilevel converter-high voltage direct current transmission system) system. Through this coordination mechanism, a linkage mechanism can be formed between the wind farm and the onshore power grid, which effectively shares the load of frequency regulation when frequency disturbances occur, thereby improving the frequency regulation efficiency of the entire system.

[0123] As a preferred embodiment of the above, in step S40, in scenario three, the grid-side modular multilevel converter station (GSMMC) adopts a reactive power priority mode, reduces active power output according to actual conditions, and mainly supports the voltage of the grid connection point with reactive power output;

[0124] Reactive power priority mode is the q-axis current priority mode, which gives priority to reactive power output. The maximum active power output is the maximum remaining capacity of the system, which is achieved by controlling the PI limit in the current inner loop control.

[0125] The model of the actual value of the d-axis and q-axis current in the reactive power priority mode includes:

[0126]

[0127]

[0128] In the formula, i d Indicates the actual value of the d-axis current, i q Indicates the actual value of the q-axis current, i qref and i dref They represent the q-axis and d-axis current reference values, respectively. max Indicates the maximum current that the inverter can withstand.

[0129] When a serious voltage disturbance occurs in the power grid (such as scenario three), the system can prioritize reactive power output through reactive power priority mode, thereby effectively supporting the grid voltage. Voltage stability is crucial to the safe operation of the power system. By prioritizing reactive power support, the system can quickly respond to voltage fluctuations and restore stability. In reactive power priority mode, the system reduces active power output according to actual conditions to ensure that the power system can provide more capacity for reactive power. In this way, the system can flexibly adjust the balance between active and reactive power in voltage support, avoid the system from operating in an overloaded state, and ensure the stability of equipment and systems.

[0130] The present invention also includes a frequency-voltage coordinated support control device for an offshore wind power flexible direct current grid-connected system, using the above method, such as Figure 7As shown, including:

[0131] A detection module is used to detect the voltage and frequency status of the grid connection point of the power grid system, determine whether a disturbance occurs, and determine whether the disturbance is a single voltage disturbance, a single frequency disturbance, or a coupled disturbance of frequency and voltage;

[0132] The voltage support module is used to adjust the reactive power output based on the voltage deviation amplitude when only a single voltage disturbance occurs in the system, adopt a constant voltage control strategy for voltage support, and keep the active power output unchanged;

[0133] The frequency regulation support module is used to provide frequency support to the grid-connected system through virtual inertia control and droop control based on the frequency deviation when only a single frequency disturbance occurs in the system, and ensure reactive power output to maintain system stability;

[0134] The collaborative support module is used to adopt a frequency-voltage collaborative support control strategy when the system experiences frequency and voltage disturbances at the same time. It performs zoning control according to the voltage situation at the grid connection point. The grid-side modular multi-level converter station adopts active priority or reactive priority mode for voltage support according to the voltage situation deviation, and achieves frequency support for the system through collaborative frequency regulation or remote communication mode.

[0135] See also Figure 8 A computer device 400 provided in an embodiment of the present application includes: a processor 410 and a memory 420, wherein the memory 420 stores a computer program executable by the processor 410, and when the computer program is executed by the processor 410, the above method is executed.

[0136] The embodiment of the present application further provides a storage medium 430 on which a computer program is stored. When the computer program is run by the processor 410, the above method is executed.

[0137] Among them, the storage medium 430 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 red-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, disk or optical disk.

[0138] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0139] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0140] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0141] Any process or method description in a flowchart or otherwise described herein may be understood to represent a module, segment or portion of code that includes one or more executable instructions for implementing the steps of a specific logical function or process, and the scope of the preferred embodiments of the present invention includes alternative implementations in which functions may not be performed in the order shown or discussed, including performing functions in a substantially simultaneous manner or in the reverse order depending on the functions involved, which should be understood by those skilled in the art to which the embodiments of the present invention belong.

[0142] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as an ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, device or apparatus (such as a computer-based system, a system including a processor, or other system that can fetch instructions from an instruction execution system, device or apparatus and execute instructions), or in combination with these instruction execution systems, devices or apparatuses. For the purposes of this specification, a "computer-readable medium" can be any device that can contain, store, communicate, propagate or transmit a program for use by an instruction execution system, device or apparatus, or in combination with these instruction execution systems, devices or apparatuses. More specific examples of computer-readable media (a non-exhaustive list) include the following: an electrical connection with one or more wires (electronic devices), a portable computer disk box (magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable and programmable read-only memory (EPROM or flash memory), a fiber optic device, and a portable compact disk read-only memory (CDROM). In addition, the computer-readable medium may even be paper or other suitable medium on which the program is printed, since the program may be obtained electronically, for example, by optically scanning the paper or other medium and then editing, interpreting or processing in other suitable ways if necessary, and then stored in a computer memory.

[0143] It should be understood that the various parts of the present invention can be implemented by hardware, software, firmware or a combination thereof. In the above-mentioned embodiments, a plurality of steps or methods can be implemented by software or firmware stored in a memory and executed by a suitable instruction execution system. For example, if implemented by hardware, as in another embodiment, it can be implemented by any one of the following technologies known in the art or their combination: a discrete logic circuit having a logic gate circuit for implementing a logic function for a data signal, a dedicated integrated circuit having a suitable combination of logic gate circuits, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0144] A person skilled in the art may understand that all or part of the steps in the method for implementing the above-mentioned embodiment may be completed by instructing related hardware through a program, and the program may be stored in a computer-readable storage medium, which, when executed, includes one or a combination of the steps of the method embodiment.

[0145] The storage medium mentioned above may be a read-only memory, a magnetic disk or an optical disk, etc. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. A person of ordinary skill in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A frequency-voltage coordinated support control method for an offshore wind power flexible direct current grid-connected system, characterized in that: The steps include: Detecting the voltage and frequency status of the grid connection point, determining whether a disturbance occurs, and determining whether the disturbance is a single voltage disturbance, a single frequency disturbance, or a coupled disturbance of frequency and voltage; When only a single voltage disturbance occurs in the system, the reactive power output is adjusted based on the voltage deviation amplitude, and a constant voltage control strategy is adopted for voltage support, while keeping the active power output unchanged; When only a single frequency disturbance occurs in the system, the frequency of the grid-connected system is supported through virtual inertia control and droop control based on the frequency deviation, and reactive power output is ensured to maintain system stability. When the system experiences frequency and voltage disturbances at the same time, a frequency-voltage coordinated support control strategy is adopted, and zone control is performed according to the voltage situation at the grid connection point. The grid-side modular multi-level converter station adopts active priority or reactive priority mode for voltage support according to the voltage situation deviation, and achieves frequency support for the system through coordinated frequency regulation or remote communication mode.

2. The frequency-voltage coordinated support control method for the offshore wind power flexible direct current grid-connected system according to claim 1 is characterized in that: When the system experiences frequency and voltage disturbances at the same time, a frequency-voltage coordinated support control strategy is adopted to perform zoning control according to the voltage situation at the grid connection point. The grid-side modular multilevel converter station adopts active priority or reactive priority mode for voltage support according to the voltage situation deviation, and achieves frequency support for the system through coordinated frequency regulation or remote communication mode, including the following scenarios: Scenario 1: When the voltage at the grid connection point is in the range of 0.95pu-1.05pu, the voltage is a normal fluctuation and no reactive power compensation is performed. The grid-side modular multilevel converter station adopts the active power priority mode, and the offshore wind farm and MMC-HVDC adopt a coordinated frequency control strategy to support the system frequency. Scenario 2: When the grid connection point voltage is in the range of 1.05pu-1.1pu or 0.9pu-0.95pu, the grid-side modular multilevel converter station continues to adopt the active power priority mode and adjusts the reactive power output to actively support the grid connection point voltage. The offshore wind farm and MMC-HVDC adopt the remote communication mode to support the system frequency. Scenario 3: When the voltage at the grid connection point is lower than 0.9pu or higher than 1.1pu, the grid-side modular multilevel converter station adopts a reactive power priority mode and reduces active power output according to actual conditions, mainly using reactive power output to provide voltage support for the grid connection point, and the offshore wind farm and MMC-HVDC use a remote communication mode to provide frequency support for the system.

3. The frequency-voltage coordinated support control method for the offshore wind power flexible direct current grid-connected system according to claim 2 is characterized in that: Detecting the voltage and frequency status of the grid connection point, determining whether a disturbance occurs, and determining whether the disturbance is a single voltage disturbance, a single frequency disturbance, or a coupled disturbance of frequency and voltage, the steps include: Real-time collection of voltage and frequency data of the grid connection point of the power grid system; Compare the voltage and frequency data with historical operation data to analyze fluctuation trends of the data; Based on the preset voltage and frequency thresholds, a multi-level alarm mechanism is set to determine whether the voltage or frequency exceeds the set threshold range; According to the feedback result of the multi-level alarm mechanism, it is determined whether a disturbance occurs, and it is judged whether the disturbance is a single voltage disturbance, a single frequency disturbance, or a coupled disturbance of frequency and voltage.

4. The frequency-voltage coordinated support control method for the offshore wind power flexible direct current grid-connected system according to claim 2 is characterized in that: When the system experiences frequency and voltage disturbances simultaneously, a frequency-voltage collaborative support control strategy is adopted. The control strategy is used to deal with simultaneous voltage disturbances and load disturbances, and includes at least the following operating conditions: voltage drop accompanied by a sudden increase in load, voltage drop accompanied by a sudden decrease in load, voltage increase accompanied by a sudden increase in load, and voltage increase accompanied by a sudden decrease in load.

5. The frequency-voltage coordinated support control method for the offshore wind power flexible direct current grid-connected system according to claim 2 is characterized in that: The offshore wind farm and MMC-HVDC adopt a coordinated frequency regulation control strategy to support the frequency of the system. The coordinated frequency regulation control strategy supports the frequency of the system, including: By adding virtual inertial control to offshore wind turbines, the inertial response of conventional synchronous generators is simulated. The specific model includes: In the formula, ΔP in k is the inertial support frequency provided by the wind turbine by releasing the rotor kinetic energy. in is the inertia control coefficient, f is usually the measurement frequency of the land AC system; Offshore wind turbines can also simulate the governor response of the generator through droop control. The specific models include: △P dr =-k dr (f-f0); In the formula, ΔP dr represents the frequency support power provided by the wind turbine through droop control, k dr represents the droop control coefficient, f0 and f represent the rated value and measured value of the frequency of the onshore AC system, respectively; To ensure power reserve, offshore wind farms use overspeed load reduction control to ensure power reserve. For different load reduction rates d%, the models of wind turbine load reduction power include: P del =P MPPT (1-d%); Where P MPPT It is the mechanical power output when the fan is running in MPPT state.

6. The frequency-voltage coordinated support control method for the offshore wind power flexible direct current grid-connected system according to claim 2 is characterized in that: In the scenario 1, the coordinated frequency control strategy adopted by the offshore wind farm and MMC-HVDC is as follows: When the frequency of the grid connection point changes, the DC voltage of the MMC-HVDC is adjusted along with the frequency change, and the change of the DC voltage enables the wind farm to receive frequency information from the onshore system; Active support for system frequency is achieved by adjusting the relationship between DC voltage and frequency; The relationship model between the DC voltage and the frequency includes: f W =K W K DC △f+f W0 ; In the formula, K DC Indicates the DC voltage control coefficient, K W represents the WFMMC frequency control coefficient; f W0 It represents the steady-state frequency of WFMMC, and △f represents the frequency deviation of the land system, that is, the difference between the rated value and the actual value of the frequency.

7. The frequency-voltage coordinated support control method for the offshore wind power flexible direct current grid-connected system according to claim 2 is characterized in that: In the above scenario 1 and scenario 2, the grid-side modular multilevel converter station adopts the active power priority mode, that is, the d-axis current priority mode, which gives priority to the active power output, and the maximum reactive power output is the maximum value of the remaining system capacity, which is achieved by controlling the PI limit in the current inner loop control; The model of the actual values ​​of the d-axis and q-axis currents in the active power priority mode includes: In the formula, i d Indicates the actual value of the d-axis current, i q Indicates the actual value of the q-axis current, i qref and i dref They represent the q-axis and d-axis current reference values, respectively. max Indicates the maximum current that the inverter can withstand.

8. The frequency-voltage coordinated support control method for the offshore wind power flexible direct current grid-connected system according to claim 2 is characterized in that: In the scenario 2 and scenario 3, the voltage support control strategy of the grid-side modular multilevel converter station for the grid connection point includes: When the system is operating normally, the grid-side modular multilevel converter station adopts U dc / Q control, working in the rated reactive power state; when voltage disturbance occurs, the grid-side modular multilevel converter station switches to the fixed AC voltage mode to provide voltage support for the system; The voltage support control model includes: In the formula, i qref Indicates the q-axis current reference value, k v Represents the reactive power droop coefficient, V acref and V ac Respectively represent the rated value and measured value of the AC voltage at the grid connection point of the onshore AC system, K p and K i They represent the reactive PI control coefficient respectively, and s represents the commonly used expression quantity of the integral link.

9. The frequency-voltage coordinated support control method for the offshore wind power flexible direct current grid-connected system according to claim 2 is characterized in that: In the scenario 2 and scenario 3, the offshore wind farm and MMC-HVDC provide frequency support to the system through a remote communication mode. The remote communication mode uses communication technology to directly transmit the GSMMC grid connection point frequency information to the offshore wind farm, so that the offshore wind farm participates in the active frequency support of the system.

10. The frequency-voltage coordinated support control method for the offshore wind power flexible direct current grid-connected system according to claim 2 is characterized in that: In the scenario 3, the grid-side modular multilevel converter station adopts a reactive power priority mode, reduces active power output according to actual conditions, and mainly supports the voltage of the grid connection point with reactive power output; The reactive power priority mode is the q-axis current priority mode, which gives priority to reactive power output. The maximum active power output is the maximum remaining capacity of the system, which is achieved by controlling the PI limit in the current inner loop control. The model of the actual values ​​of the d-axis and q-axis currents in the reactive priority mode includes: In the formula, i d Indicates the actual value of the d-axis current, i q Indicates the actual value of the q-axis current, i qref and i dref They represent the q-axis and d-axis current reference values, respectively. max Indicates the maximum current that the inverter can withstand.

11. A frequency-voltage coordinated support control device for an offshore wind power flexible direct current grid-connected system, characterized in that: Use of the method according to any one of claims 1 to 10, comprising: A detection module, used to detect the voltage and frequency status of the grid connection point, determine whether a disturbance occurs, and determine whether the disturbance is a single voltage disturbance, a single frequency disturbance, or a coupled disturbance of frequency and voltage; The voltage support module is used to adjust the reactive power output based on the voltage deviation amplitude when only a single voltage disturbance occurs in the system, adopt a constant voltage control strategy for voltage support, and keep the active power output unchanged; The frequency regulation support module is used to provide frequency support to the grid-connected system through virtual inertia control and droop control based on the frequency deviation when only a single frequency disturbance occurs in the system, and ensure reactive power output to maintain system stability; The collaborative support module is used to adopt a frequency-voltage collaborative support control strategy when the system is simultaneously disturbed by frequency and voltage, and to perform zoning control according to the voltage situation at the grid-connected point. The grid-side modular multi-level converter station adopts active priority or reactive priority mode for voltage support according to the voltage situation deviation, and achieves frequency support for the system through collaborative frequency modulation or remote communication mode.

12. A computer device comprising a memory, a processor and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the method according to any one of claims 1 to 10 is implemented.

13. A 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 10 is implemented.

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