A method and system for frequency-voltage transfer-based offshore wind power frequency support control of a land power grid and a storage medium

Abstract

The present application relates to a kind of offshore wind power based on frequency-voltage transfer frequency support control method, system and storage medium of land grid, the present application is mapped by receiving end converter, and the voltage regulation amount of DC side is mapped by sending end converter, and the voltage amplitude variation of offshore AC grid is mapped by receiving end converter, and the frequency of offshore grid is kept constant;Fan net side converter detects the voltage amplitude of offshore grid, generates additional power of primary frequency modulation, and generates inertia support additional power in combination with inertia coefficient dynamic adjustment, and the total power instruction is formed after the superposition of basic power and additional power, and the output power of fan is controlled.Its effect: realize the frequency support of offshore wind power to land grid under the condition of no communication, avoid the loss of phase-locked loop of fan caused by frequency disturbance of offshore grid, can be adapted to adjust inertia support intensity according to the frequency variation rate of power grid and the standby power of fan, system stability is high, control is flexible, and no new hardware is needed.

Description

Technical Field

[0001] This invention relates to the field of offshore wind power grid connection control technology, and in particular to a method, system and storage medium for offshore wind power frequency support control of onshore power grid based on frequency-voltage transfer. Background Technology

[0002] With the large-scale development of offshore wind power and the transformation of power systems towards high penetration of power electronics, how to achieve frequency support for the onshore power grid from offshore wind power has become a key technical issue. Traditional solutions without communication frequency support typically map frequency disturbances in the onshore power grid to frequency changes in the offshore AC power grid. The sending-end converter uses V / F control, and the grid-side converter of the wind turbine achieves power regulation by detecting the frequency of the offshore power grid.

[0003] This type of method has significant drawbacks: the frequency of the offshore power grid fluctuates with the onshore power grid, and the phase-locked loop (PLL) of the wind turbine grid-side converter is highly sensitive to frequency disturbances, which can easily lead to inaccurate voltage vector locking, power output distortion, and in severe cases, PLL unlocking and system instability. At the same time, the inertia support coefficient of the traditional solution is fixed and cannot be adaptively adjusted according to the wind turbine reserve power and the rate of change of the grid frequency, thus limiting the frequency support effect.

[0004] Therefore, there is an urgent need for a communication-free frequency support technology that can avoid frequency disturbances in offshore power grids, achieve stable phase locking, and have dynamic inertia adjustment capabilities. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems in the prior art by providing a frequency support control method, system and storage medium for offshore wind power to support the frequency of the onshore power grid based on frequency-voltage transfer. It does not require communication between the sending and receiving ends, and uses DC voltage as the information carrier to realize fast, stable and adaptive frequency support of offshore wind power to the onshore power grid, while ensuring the constant frequency of the offshore power grid and reliable wind turbine control, thereby improving the frequency stability and operational safety of the offshore wind power grid connection system.

[0006] The above-mentioned technical objectives of this invention are mainly achieved through the following technical solutions: The technical solution of the first technical subject of this invention is as follows: A frequency-support control method for onshore power grids based on frequency-voltage transfer in offshore wind power: The receiving-end converter collects the frequency of the onshore AC power grid, obtains the frequency deviation, and maps the frequency deviation to the adjustment amount of the DC side voltage through droop control, and adjusts the DC side voltage based on the adjustment amount; The sending-end converter detects changes in DC-side voltage and maps these changes to changes in the voltage amplitude of the offshore AC power grid through droop control, while maintaining a constant frequency for the offshore AC power grid. The wind turbine grid-side converter detects the voltage amplitude of the offshore AC grid, obtains the voltage amplitude deviation and voltage amplitude change rate, generates primary frequency regulation additional power based on the voltage amplitude deviation, and generates inertia support additional power based on the voltage amplitude change rate and inertia coefficient through dynamic adjustment. The base power of the wind turbine under reduced load, the additional power of primary frequency regulation, and the additional power of inertia support are added together to obtain a reference value for the total output power of the wind turbine, and a power command is generated. The grid-side converter of the wind turbine controls the output power of the wind turbine based on power commands, so as to realize the frequency support of the offshore wind power to the onshore power grid under the condition of no communication.

[0007] The difference from existing technologies lies in the fact that by mapping the frequency deviation of the onshore power grid to the DC-side voltage change, and then converting the DC-side voltage change into the voltage amplitude adjustment of the offshore AC power grid, the wind turbine can output power according to the voltage amplitude response of the offshore power grid. This achieves frequency support for the onshore power grid by offshore wind power without the need for a remote communication link, thereby improving the response speed and operational reliability of the offshore wind power grid connection system.

[0008] As a preferred embodiment, when the frequency of the onshore power grid decreases, the receiving-end converter reduces the DC-side voltage through droop control, and the sending-end converter correspondingly increases the voltage amplitude of the offshore AC power grid. When the frequency of the onshore power grid increases, the receiving-end converter increases the DC-side voltage through droop control, while the sending-end converter correspondingly reduces the voltage amplitude of the offshore AC power grid.

[0009] This technical solution establishes a corresponding adjustment relationship between the frequency of the onshore power grid and the DC-side voltage and the voltage amplitude of the offshore power grid, so that the frequency fluctuations of the onshore power grid can be reflected in the voltage amplitude of the offshore power grid intuitively and quickly, providing a clear and reliable basis for frequency regulation of wind turbines, and ensuring accurate frequency regulation direction and timely response.

[0010] Preferably, the sending-end converter adopts a V / F control method, which keeps the frequency of the output voltage constant and adjusts the voltage amplitude according to the fluctuation of the DC side voltage. Using V / F constant frequency control can independently maintain a constant frequency of the offshore AC power grid, avoiding interference from frequency fluctuations to the wind turbine control, while allowing the voltage amplitude to be flexibly adjusted according to the DC side voltage, ensuring a stable and reliable frequency-voltage transfer mechanism.

[0011] Preferably, the sending-end converter employs dual closed-loop control of voltage and current, achieving d / q axis current loop decoupling through equivalent reactance. This allows the sending-end converter to only regulate the voltage amplitude of the offshore AC power grid and output AC power at a constant frequency, thus maintaining the constant frequency of the offshore AC power grid. The use of dual closed-loop control of voltage and current, along with d / q axis decoupling control, enables precise regulation of the offshore power grid voltage amplitude by the sending-end converter, while strictly ensuring a constant output frequency, improving control dynamic performance and avoiding mutual coupling interference between amplitude regulation and frequency output.

[0012] Preferably, the voltage amplitude deviation is obtained by comparing the voltage amplitude of the offshore AC grid with its rated static operating point amplitude. After low-pass filtering, the voltage amplitude deviation is multiplied by the primary frequency regulation droop coefficient and the maximum output power of the wind turbine to obtain the primary frequency regulation additional power. Generating the primary frequency regulation additional power through filtering and coefficient calculation of the voltage amplitude deviation enables the wind turbine to smoothly respond to primary frequency regulation requirements according to changes in the offshore grid voltage amplitude, suppressing noise interference and improving the stability and accuracy of the frequency regulation process.

[0013] Preferably, the voltage amplitude change rate is obtained by differentiating the voltage amplitude of the offshore AC power grid after low-pass filtering, and the voltage amplitude change rate is multiplied by the dynamically adjusted inertia coefficient to obtain the inertia-supported additional power. The inertia coefficient is adaptively adjusted according to the rate of change of the voltage amplitude and the standby power of the fan. The inertia coefficient remains stable when the rate of change of voltage amplitude approaches zero. As the rate of change of voltage amplitude increases, the inertia coefficient gradually increases and tends to the set maximum value; When the standby power of the wind turbine decreases, the inertia coefficient decreases synchronously.

[0014] Based on the voltage amplitude change rate and combined with the adaptive inertia coefficient, the additional power of inertia support is generated, enabling the wind turbine to simulate the inertia response of a synchronous machine and quickly suppress grid frequency changes. At the same time, the inertia coefficient is adaptively adjusted according to the grid disturbance intensity and the wind turbine's reserve power, which not only ensures the support strength but also avoids wind turbine overload, thus improving the system's safe and stable operation capability.

[0015] Preferably, the base power for the wind turbine's unloaded operation is obtained by multiplying the maximum power obtained from the wind turbine's maximum power point tracking by the unload factor, and is used to reserve backup power for primary frequency regulation and inertial response. By adopting unloaded operation and reserving backup power, the wind turbine has the ability to quickly increase / decrease its power, providing sufficient power margin for primary frequency regulation and inertial response, and ensuring that offshore wind power can effectively participate in grid frequency regulation.

[0016] Preferably, the wind turbine grid-side converter adopts PQ control, which locks the voltage vector of the offshore AC grid through a phase-locked loop and keeps the frequency of the offshore AC grid constant. This allows the phase-locked loop to work reliably in a stable frequency environment, making it less prone to loss of lock, ensuring accurate and reliable wind turbine power control, and improving the robustness of the overall frequency regulation control system.

[0017] The technical solution of the second technical subject matter involved in this invention is as follows: A frequency support system for offshore wind power to onshore power grid based on frequency-voltage transfer, used to implement the aforementioned frequency support control method for offshore wind power to onshore power grid based on frequency-voltage transfer, includes: The receiving-end converter is used to acquire the frequency of the onshore AC power grid and generate a frequency deviation. The frequency deviation is mapped to the DC-side voltage regulation amount through droop control to regulate the DC-side voltage. The sending-end converter is used to detect changes in DC-side voltage, and maps these changes to changes in the voltage amplitude of the offshore AC grid through droop control, while maintaining a constant frequency for the offshore AC grid. The wind turbine grid-side converter is used to detect the voltage amplitude and rate of change of the offshore AC grid, generate primary frequency regulation additional power based on the voltage amplitude deviation, and generate inertia support additional power based on the voltage amplitude change rate. The control module is used to superimpose the base power of the wind turbine under reduced load, the additional power of primary frequency regulation, and the additional power of inertia support to obtain a reference value for the total output power, and to generate a power command. The wind turbine grid-side converter executes the power command to regulate the wind turbine output power, so as to achieve frequency support of offshore wind power to the onshore AC grid in the absence of a communication link.

[0018] This technical solution constructs a hardware system that is completely corresponding to the frequency support control method of offshore wind power for onshore power grid based on frequency-voltage transfer. It realizes a communication-free, fast-response, and highly reliable offshore wind power frequency support architecture. The system structure is clear and easy to implement in engineering, and it is suitable for large-scale offshore wind power grid connection scenarios with flexible DC transmission.

[0019] The technical solution of the third technical subject matter involved in this invention is as follows: A computer-readable storage medium stores a computer program that, when executed by a processor, implements the aforementioned frequency support control method for offshore wind power to support onshore power grids based on frequency-voltage transfer. Implementing the frequency support control method through a computer program facilitates direct deployment and upgrades to existing converter controllers and wind turbine main control systems, offering strong versatility, low cost, and promoting the engineering application of this frequency regulation technology.

[0020] The beneficial effects of this invention are as follows: 1. No communication link is required between the sending and receiving ends; frequency support is achieved solely through control strategies, without increasing hardware costs. The system structure is simple and highly reliable.

[0021] 2. By combining the reserved backup power during load reduction operation, the primary frequency regulation and inertia support are coordinated for control. The inertia support is used to quickly suppress frequency mutations and the primary frequency regulation is used to eliminate steady-state frequency deviations, thereby achieving fast, stable, and all-time grid frequency support with better frequency regulation accuracy and dynamic response.

[0022] 3. By adopting the transmission path of "land-based frequency, DC voltage, and offshore voltage amplitude", the frequency of the offshore power grid is not changed and the frequency of the offshore power grid is kept constant. This helps to ensure the stability of the phase-locked loop (PLL) without loss of lock-in and avoids PLL failure or control failure due to frequency disturbance.

[0023] 4. The inertia coefficient is adaptively adjusted according to the voltage amplitude change rate and the standby power of the wind turbine, providing appropriate inertia support when the grid frequency fluctuates, and automatically reducing the inertia output when the standby power is insufficient. This ensures the inertia response effect and avoids wind turbine overload operation, making the control strategy more flexible and the system operation safer. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the control block of the sending-end converter involved in the present invention.

[0025] Figure 2 This is a schematic diagram of the control block of the wind turbine grid-side converter involved in the present invention.

[0026] Figure 3 This is a three-dimensional schematic diagram of the inertia coefficient adjustment equation involved in this invention.

[0027] Figure 4 The present invention relates to the DC voltage of the sending-end converter. A schematic diagram of the simulation waveform.

[0028] Figure 5 The present invention relates to the AC voltage of the sending-end converter. A schematic diagram of the simulation waveform.

[0029] Figure 6 The frequency of the sending-end converter involved in this invention is... A schematic diagram of the simulation waveform.

[0030] Figure 7 This is a waveform diagram of the backup power of the wind turbine involved in the present invention.

[0031] Figure 8 This is a waveform diagram of the additional power for inertia support involved in this invention.

[0032] Figure 9 This is a waveform diagram of the primary frequency modulation additional power involved in the present invention.

[0033] Figure 10 This is a waveform diagram of the inertia coefficient involved in the present invention.

[0034] Figure 11 This is a waveform diagram of the output power of the fan involved in the present invention.

[0035] Figure 12This is a waveform diagram of the AC side voltage of the wind turbine grid-side converter involved in this invention. Detailed Implementation

[0036] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0037] Example 1: The first technical subject of this invention is a frequency support control method for offshore wind power to onshore power grid based on frequency-voltage transfer. Its core control idea is: to obtain the DC side voltage based on the onshore power grid frequency, to obtain the voltage amplitude of the offshore AC power grid based on the DC side voltage, to obtain the wind turbine output power based on the voltage amplitude of the offshore AC power grid, and to use the voltage amplitude as the carrier of frequency information to achieve frequency support under conditions without communication.

[0038] The frequency support control method for onshore power grids based on frequency-voltage transfer in offshore wind power is as follows: The receiving-end converter acquires the frequency of the onshore AC power grid, obtains the frequency deviation, and maps the frequency deviation to a DC-side voltage adjustment amount through droop control. Based on the adjustment amount, the DC-side voltage is adjusted. When the onshore power grid frequency decreases, the receiving-end converter decreases the DC-side voltage through droop control, and the sending-end converter correspondingly increases the voltage amplitude of the offshore AC power grid. When the onshore power grid frequency increases, the receiving-end converter increases the DC-side voltage through droop control, and the sending-end converter correspondingly decreases the voltage amplitude of the offshore AC power grid. The sending-end converter detects changes in DC-side voltage in real time and maps these changes to changes in the voltage amplitude of the offshore AC grid through droop control, while maintaining a constant frequency for the offshore AC grid. When the DC-side voltage decreases, the sending-end converter correspondingly increases the voltage amplitude of the offshore AC grid; when the DC-side voltage increases, the sending-end converter correspondingly decreases the voltage amplitude of the offshore AC grid. The wind turbine grid-side converter detects the voltage amplitude of the offshore AC grid, obtains the voltage amplitude deviation and voltage amplitude change rate, generates primary frequency regulation additional power based on the voltage amplitude deviation, and generates inertia support additional power based on the voltage amplitude change rate and inertia coefficient through dynamic adjustment. The base power of the wind turbine under reduced load, the additional power of primary frequency regulation, and the additional power of inertia support are added together to obtain a reference value for the total output power of the wind turbine, and a power command is generated. The grid-side converter of the wind turbine controls the output power of the wind turbine based on power commands, so as to realize the frequency support of the offshore wind power to the onshore power grid under the condition of no communication.

[0039] The difference from existing technologies lies in the fact that by mapping the frequency deviation of the onshore power grid to the DC-side voltage change, and then converting the DC-side voltage change into the voltage amplitude adjustment of the offshore AC power grid, the wind turbine can output power according to the voltage amplitude response of the offshore power grid. This achieves frequency support for the onshore power grid by offshore wind power without the need for a remote communication link, thereby improving the response speed and operational reliability of the offshore wind power grid connection system.

[0040] This technical solution establishes a corresponding adjustment relationship between the frequency of the onshore power grid and the DC-side voltage and the voltage amplitude of the offshore power grid, so that the frequency fluctuations of the onshore power grid can be reflected in the voltage amplitude of the offshore power grid intuitively and quickly, providing a clear and reliable basis for frequency regulation of wind turbines, and ensuring accurate frequency regulation direction and timely response.

[0041] The sending-end converter employs V / F control or dual closed-loop voltage and current control: When the sending-end converter adopts the V / F control mode, the frequency of the output voltage is kept constant and the voltage amplitude is adjusted according to the fluctuation of the DC side voltage.

[0042] When the sending-end converter adopts voltage and current dual closed-loop control, the d / q axis current loop is decoupled through equivalent reactance, so that the sending-end converter only adjusts the voltage amplitude of the offshore AC power grid and outputs AC power with constant frequency, so as to maintain the constant frequency of the offshore AC power grid, avoid mutual interference between amplitude and frequency control, and improve control accuracy and dynamic response speed.

[0043] Additional power generation from primary frequency regulation of the fan: The voltage amplitude deviation is obtained by comparing the voltage amplitude of the offshore AC grid with its rated static operating point amplitude. After low-pass filtering, the voltage amplitude deviation is multiplied by the primary frequency regulation droop coefficient and the maximum output power of the wind turbine to obtain the primary frequency regulation additional power, enabling the wind turbine to respond smoothly and accurately to the primary frequency regulation demand.

[0044] Wind turbine inertia supports additional power generation: The voltage amplitude change rate is obtained by differentiating the voltage amplitude of the offshore AC power grid after low-pass filtering. The voltage amplitude change rate is multiplied by the dynamically adjusted inertia coefficient to obtain the inertia support additional power, which enables the wind turbine to simulate the inertia characteristics of a synchronous motor and quickly suppress grid frequency changes.

[0045] The inertia coefficient is adaptively adjusted according to the rate of change of the voltage amplitude and the standby power of the wind turbine.

[0046] The inertia coefficient remains stable when the rate of change of voltage amplitude is close to zero.

[0047] As the rate of change of voltage amplitude increases, the inertia coefficient gradually increases and tends to the set maximum value.

[0048] When the standby power of the wind turbine decreases, the inertia coefficient decreases synchronously.

[0049] Based on the voltage amplitude change rate and combined with the adaptive inertia coefficient, the additional power of inertia support is generated, enabling the wind turbine to simulate the inertia response of a synchronous machine and quickly suppress grid frequency changes. At the same time, the inertia coefficient is adaptively adjusted according to the grid disturbance intensity and the wind turbine's reserve power, which not only ensures the support strength but also avoids wind turbine overload, thus improving the system's safe and stable operation capability.

[0050] Total power control of the fan: The wind turbine adopts a reduced load operation mode. The base power of the wind turbine under reduced load operation is obtained by multiplying the maximum power obtained by tracking the maximum power point of the wind turbine by the reduced load coefficient. This power is used to reserve backup power for primary frequency regulation and inertial response.

[0051] The control module superimposes the wind turbine's load reduction base power, primary frequency regulation additional power, and inertia support additional power to obtain a reference value for the wind turbine's total output power and generate a power command.

[0052] The wind turbine grid-side converter adopts PQ control, which locks the voltage vector of the offshore AC grid through a phase-locked loop (PLL) and keeps the frequency of the offshore AC grid constant. This allows the PLL to work reliably in a stable frequency environment, is not prone to loss of lock, can accurately execute power commands, and quickly adjust the output power of the wind turbine, ultimately achieving communication-free frequency support for the onshore AC grid by offshore wind power.

[0053] Next, as Figures 1-12 As shown, the frequency support control method for offshore wind power on onshore power grids based on frequency-voltage transfer is further improved: like Figure 1 As shown, in the steps of real-time detection of DC-side voltage changes in the sending-end converter: Sending-end converter detects DC bus voltage The reference value of the AC side voltage amplitude of the sending-end converter is obtained through the following droop control equation. :

[0054] in, It is the static operating point of the DC voltage of the sending-end converter; It is the static operating point of the AC side voltage amplitude of the sending-end converter; It is the droop control coefficient between the DC voltage and AC voltage amplitudes. When the frequency of the onshore power grid decreases (the DC voltage at the receiving end of the onshore converter decreases), this equation will increase the AC voltage amplitude of the offshore AC grid, resulting in a smaller output current for the wind turbine when it increases its output power to support the grid frequency.

[0055] When the sending-end converter uses V / F control mode: like Figure 1 As shown, the reference value of the AC side voltage amplitude of the sending-end converter. The signal is sent to the voltage and current dual closed-loop control circuit, where... The set frequency for the offshore power grid; , These are the d-axis and q-axis components of the voltage and current at the grid connection point on the AC side of the sending-end converter, respectively. The equivalent reactance of the sending-end converter is used for decoupling the dq channel of the current loop; (Right now and ( ) represents the d-axis and q-axis components of the internal electromotive force of the sending-end converter. Furthermore, for ease of control, the target output voltage vector of the sending-end converter is set. Aligned with the d-axis of the dq rotating coordinate system, at this point, , .at the same time, Rotate the phase through the dq coordinate system The system transforms from the dq coordinate system to the abc coordinate system, and then obtains the control trigger pulses for each bridge arm switch of the sending-end converter through the modulation system.

[0056] During this process, the frequency of the sending-end converter remains at a set value (generally, the set value is...). This ensures that the AC output voltage of the sending-end converter changes only in amplitude with fluctuations in DC voltage, while the frequency remains constant.

[0057] like Figure 4 As shown, the voltage vector amplitude of the offshore AC grid is detected by the wind turbine grid-side converter. The calculation method is as follows:

[0058] in, (Right now and () represents the d-axis and q-axis components of the offshore AC grid voltage. Based on this, the wind turbine grid-side converter calculates the additional power corresponding to the wind turbine's participation in the primary frequency regulation of the onshore power grid according to the following equation. :

[0059] in, It is the amplitude of AC voltage in the offshore AC grid and the additional power of primary frequency regulation. The droop coefficient between; It is the transfer function of a low-pass filter (LPF), used to avoid the high-frequency fluctuations in voltage amplitude. Disturbance; The wind turbine output power command is obtained after processing by the MPPT module and the load reduction factor.

[0060] in, It is the wind turbine load reduction factor, used to generate backup power for primary frequency regulation and inertia response; The Maximum Power Point Tracking (MPPT) module controls the fan speed. The maximum output power obtained.

[0061] The inertial support power of the wind turbine grid-side converter is calculated according to the following equation for the inertial response portion. :

[0062] in, It is the rate of change of AC voltage amplitude and The ratio coefficient between them. The inertia coefficient was calculated using the following adjustment equation:

[0063] in, The rate of change of AC voltage amplitude after passing through the low-pass filter (LPF); and These are the maximum and minimum inertia coefficients, respectively; It is the inertia adjustment coefficient; This is the proportional adjustment factor between the wind turbine's standby power and its inertia coefficient. The three-dimensional graph of this equation is shown below. Figure 3 As shown. It can be seen that when When fixed, It presents a valley-like shape. On the one hand, when Near zero (when the frequency of the land power grid is nearly stable). tending to And there is a smooth area at the bottom of the valley. Almost not following And this variation ensures that the frequency of the onshore power grid fluctuates slowly. Maintain stability. When Increase (when the frequency change rate of the onshore power grid is large). It also gradually increases and tends to And the maximum will not exceed the set value. Furthermore, change The parameter will affect the shape of the inertia surface, a property that influences the inertia coefficient. It can be flexibly adjusted, and changes with the rate of change of AC voltage amplitude. The frequency of the onshore power grid changes dynamically, providing greater inertia when the frequency variation rate is high. On the other hand, when... When fixed, with the maximum output power of the fan The reduction, This also decreases accordingly, which makes the inertia coefficient less sensitive to changes in the available power of the wind turbine. It also has the ability to dynamically adjust; when the wind turbine's output power and standby power are low, it can reduce... This reduces the additional power required for the inertial response.

[0064] like Figure 2 As shown, by summing the power components of the three parts of the wind turbine's MPPT control, primary frequency regulation control, and inertia control (that is, superimposing the basic power of the wind turbine under reduced load, the additional power of primary frequency regulation, and the additional power of inertia support), the desired total output power of the wind turbine can be obtained. After passing through the limiting module, the reference value of the wind turbine's active power output (i.e., the reference value of the total output power of the wind turbine) is obtained. :

[0065] Subsequently, the grid-side converter of the wind turbine utilizes the active power reference value. and reactive power reference value And the actual values ​​of active and reactive power measured from the output port of the grid-side converter of the wind turbine. and Power regulation of the wind turbine grid-side converter is achieved using PQ control. The wind turbine grid-side converter employs a PQ control strategy, with a dual-closed-loop structure. The outer loop controls active and reactive power, and uses PI control (proportional-integral control) to obtain reference values ​​for the current loop. and Then, the internal electromotive force of the wind turbine grid-side converter is obtained using the same inner current control method as in the sending-end converter control. Furthermore, the wind turbine grid-side converter uses a PLL to lock the offshore AC grid voltage vector, providing a rotating phase for the transformation between the dq coordinate system and the abc coordinate system. Furthermore, the frequency of the output voltage of the sending-end converter remains constant.

[0066] Therefore, the frequency support control method for offshore wind power based on frequency-voltage transfer of the present invention can solve the frequency disturbance problem of PLL caused by the "onshore power grid frequency - offshore power grid frequency" transfer process of conventional offshore wind systems.

[0067] Application effect Figure 4 and Figure 5The DC and AC voltage waveforms of the sending-end converter are shown. When the onshore grid frequency fluctuation causes a decrease in DC voltage after 3 seconds, it is clear that the frequency-voltage transfer-based offshore wind power frequency support control method for the onshore grid can increase the voltage amplitude of the offshore AC grid, thus constituting a transfer of "onshore AC grid frequency - offshore AC grid voltage amplitude". Furthermore, the frequency of the offshore AC grid remains constant (e.g., ...). Figure 6 (As shown).

[0068] Figures 7-10 The proposed method is illustrated with reference values ​​for the additional power in the wind turbine backup power and inertia response components. Additional power reference value for primary frequency modulation section and inertia coefficient The waveform. Figures 11-12 The waveforms of the wind turbine's output power and AC side voltage are displayed. In the simulation, at 2 seconds, the frequency of the onshore power grid increases, causing the voltage amplitude of the offshore AC grid to rise. Reduced; at 2.5s, the fan's maximum power... Gradually increase the voltage from 0.4 pu to 0.8 pu; set the quiescent operating point of the AC voltage amplitude. It is 0.95 pu. It is not difficult to observe that... At 2 s according to The rate of change was dynamically adjusted, and an inertial response was instantaneously induced. Dynamically, this is used to absorb excess power from the onshore power grid. Simultaneously, the first primary frequency regulation response gradually began to occur at 2 seconds. At 2.5 seconds, due to... It remains unchanged, therefore it will only produce a second primary frequency modulation response (the droop factor remains unchanged, but...). It automatically increases with the increase of the wind turbine backup power, without causing an inertial response (due to the proposed method). Calculation methods and and The magnitude relationship indicates that after 2.5 seconds... (The value is zero). The above experiments readily demonstrate the effectiveness of the wind turbine grid-side converter control method proposed in this invention. That is, this method can dynamically adjust the frequency information of the onshore AC grid based on the voltage amplitude of the offshore AC grid. It enables flexible inertia support and dynamic adjustment of the primary frequency regulation power based on the wind turbine backup power.

[0069] Example 2: The technical solution of the second technical subject matter involved in this invention is as follows: A frequency support system for offshore wind power to onshore power grid based on frequency-voltage transfer, used to implement the frequency support control method for offshore wind power to onshore power grid based on frequency-voltage transfer described in Example 1, includes: The receiving-end converter is used to acquire the frequency of the onshore AC power grid and generate a frequency deviation. The frequency deviation is mapped to the DC-side voltage regulation amount through droop control to regulate the DC-side voltage. The sending-end converter is used to detect changes in DC-side voltage, and maps these changes to changes in the voltage amplitude of the offshore AC grid through droop control, while maintaining a constant frequency for the offshore AC grid. The wind turbine grid-side converter is used to detect the voltage amplitude and rate of change of the offshore AC grid, generate primary frequency regulation additional power based on the voltage amplitude deviation, and generate inertia support additional power based on the voltage amplitude change rate. The control module is used to superimpose the base power of the wind turbine under reduced load, the additional power of primary frequency regulation, and the additional power of inertia support to obtain a reference value for the total output power, and to generate a power command. The wind turbine grid-side converter executes the power command to regulate the wind turbine output power, so as to achieve frequency support of offshore wind power to the onshore AC grid in the absence of a communication link.

[0070] This technical solution constructs a hardware system that is completely corresponding to the frequency support control method of offshore wind power for onshore power grid based on frequency-voltage transfer. It realizes a communication-free, fast-response, and highly reliable offshore wind power frequency support architecture. The system structure is clear and easy to implement in engineering, and it is suitable for large-scale offshore wind power grid connection scenarios with flexible DC transmission.

[0071] Example 3: The technical solution of the third technical subject matter involved in this invention is as follows: A computer-readable storage medium stores a computer program that, when executed by a processor, implements the frequency support control method for offshore wind power to onshore power grids based on frequency-voltage transfer, as described in Embodiment 1. Implementing the frequency support control method through a computer program facilitates direct deployment and upgrades to existing converter controllers and wind turbine main control systems, offering strong versatility, low cost, and promoting the engineering application of this frequency regulation technology.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations can be made to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A frequency-support control method for offshore wind power on onshore power grids based on frequency-voltage transfer, characterized in that, The receiving-end converter collects the frequency of the onshore AC power grid, obtains the frequency deviation, and maps the frequency deviation to the adjustment amount of the DC side voltage through droop control, and adjusts the DC side voltage based on the adjustment amount; The sending-end converter detects changes in DC-side voltage and maps these changes to changes in the voltage amplitude of the offshore AC power grid through droop control, while maintaining a constant frequency for the offshore AC power grid. The wind turbine grid-side converter detects the voltage amplitude of the offshore AC grid, obtains the voltage amplitude deviation and voltage amplitude change rate, generates primary frequency regulation additional power based on the voltage amplitude deviation, and generates inertia support additional power based on the voltage amplitude change rate and inertia coefficient through dynamic adjustment. The base power of the wind turbine under reduced load, the additional power of primary frequency regulation, and the additional power of inertia support are added together to obtain a reference value for the total output power of the wind turbine, and a power command is generated. The grid-side converter of the wind turbine controls the output power of the wind turbine based on power commands, so as to realize the frequency support of the offshore wind power to the onshore power grid under the condition of no communication.

2. The method for frequency support control of offshore wind power on onshore power grid based on frequency-voltage transfer according to claim 1, characterized in that, When the frequency of the onshore power grid decreases, the receiving-end converter reduces the DC-side voltage through droop control, and the sending-end converter correspondingly increases the voltage amplitude of the offshore AC power grid. When the frequency of the onshore power grid increases, the receiving-end converter increases the DC-side voltage through droop control, while the sending-end converter correspondingly reduces the voltage amplitude of the offshore AC power grid.

3. The method for frequency support control of offshore wind power on onshore power grid based on frequency-voltage transfer according to claim 1 or 2, characterized in that, The sending-end converter adopts a V / F control method to keep the frequency of the output voltage constant and adjust the voltage amplitude according to the fluctuation of the DC side voltage.

4. The method for frequency support control of offshore wind power on onshore power grid based on frequency-voltage transfer according to claim 1 or 2, characterized in that, The sending-end converter adopts voltage and current dual closed-loop control, and achieves d / q axis current loop decoupling through equivalent reactance, so that the sending-end converter only adjusts the voltage amplitude of the offshore AC power grid and outputs AC power with constant frequency to maintain the constant frequency of the offshore AC power grid.

5. The method for frequency support control of offshore wind power on onshore power grid based on frequency-voltage transfer according to claim 1 or 2, characterized in that, The voltage amplitude deviation is obtained by comparing the voltage amplitude of the offshore AC power grid with its rated static operating point amplitude. After low-pass filtering, the voltage amplitude deviation is multiplied by the primary frequency regulation droop coefficient and the maximum output power of the wind turbine to obtain the primary frequency regulation additional power.

6. The method for frequency support control of offshore wind power on onshore power grid based on frequency-voltage transfer according to claim 1 or 2, characterized in that, The voltage amplitude change rate is obtained by differentiating the voltage amplitude of the offshore AC power grid after low-pass filtering. The voltage amplitude change rate is multiplied by the dynamically adjusted inertia coefficient to obtain the inertia-supported additional power. The inertia coefficient is adaptively adjusted according to the rate of change of the voltage amplitude and the standby power of the fan. The inertia coefficient remains stable when the rate of change of voltage amplitude approaches zero. As the rate of change of voltage amplitude increases, the inertia coefficient gradually increases and tends to the set maximum value; When the standby power of the wind turbine decreases, the inertia coefficient decreases synchronously.

7. The method for frequency support control of offshore wind power on onshore power grid based on frequency-voltage transfer according to claim 1 or 2, characterized in that, The base power for wind turbine unloaded operation is obtained by multiplying the maximum power obtained from wind turbine maximum power point tracking by the unload factor, and is used to reserve backup power for primary frequency regulation and inertia response.

8. The method for frequency support control of offshore wind power on onshore power grid based on frequency-voltage transfer according to claim 1 or 2, characterized in that, The wind turbine grid-side converter adopts PQ control, which locks the voltage vector of the offshore AC grid through a phase-locked loop and keeps the frequency of the offshore AC grid constant, so that the phase-locked loop can work reliably in a stable frequency environment.

9. A frequency support system for offshore wind power to onshore power grid based on frequency-voltage transfer, characterized in that, The method for implementing the frequency support control of offshore wind power for onshore power grid based on frequency-voltage transfer as described in any one of claims 1-8 includes: The receiving-end converter is used to acquire the frequency of the onshore AC power grid and generate a frequency deviation. The frequency deviation is mapped to the DC-side voltage regulation amount through droop control to regulate the DC-side voltage. The sending-end converter is used to detect changes in DC-side voltage, and maps these changes to changes in the voltage amplitude of the offshore AC grid through droop control, while maintaining a constant frequency for the offshore AC grid. The wind turbine grid-side converter is used to detect the voltage amplitude and rate of change of the offshore AC grid, generate primary frequency regulation additional power based on the voltage amplitude deviation, and generate inertia support additional power based on the voltage amplitude change rate. The control module is used to superimpose the base power of the wind turbine under reduced load, the additional power of primary frequency regulation, and the additional power of inertia support to obtain a reference value for the total output power, and to generate a power command. The wind turbine grid-side converter executes the power command to regulate the wind turbine output power, so as to achieve frequency support of offshore wind power to the onshore AC grid in the absence of a communication link.

10. A computer-readable storage medium, characterized in that, The system contains a computer program that, when executed by a processor, implements the frequency support control method for offshore wind power to onshore power grid based on frequency-voltage transfer as described in any one of claims 1-8.

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