Voltage control method for full-direct-current offshore wind power transmission system

Abstract

The invention discloses a voltage control method for a full-direct-current offshore wind power transmission system, and relates to the technical field of power electronic control. The method is applied to a direct-current transformer and comprises the following steps: acquiring an expected collection voltage value and an actual collection voltage value of direct current generated by a wind power generation unit; comparing the expected value of the collected voltage with the actual value of the collected voltage to obtain a voltage error value; inputting the voltage error value into a target nonlinear controller to obtain a target modulation quantity for adjusting working parameters of the direct-current transformer; and on the basis of the target modulation quantity, adjusting the collection voltage of the direct current in the full-direct-current offshore wind power transmission system to obtain a first adjustment voltage, and transmitting the direct current of which the voltage value is the first adjustment voltage to a voltage source converter. According to the invention, the control effect of the collection voltage of the direct current in the full-direct-current offshore wind power transmission system can be improved.

Description

Technical Field

[0001] This application belongs to the field of power electronic control technology, and in particular relates to a voltage control method for a full DC offshore wind power transmission system. Background Technology

[0002] With the booming development of the offshore wind power industry, its scale is continuously expanding. Against this backdrop, all-DC offshore wind power transmission systems, with their significant advantages such as low loss, high capacity, and no synchronization constraints, have gradually become a research hotspot. However, all-DC offshore wind power transmission systems are prone to overvoltage phenomena due to frequent wind speed fluctuations, turbine switching in and out operations, and various disturbances to the controller. Therefore, implementing effective control measures for the DC voltage of all-DC offshore wind power transmission systems is particularly necessary.

[0003] Currently, proportional-integral (PI) controllers are commonly used to control the DC voltage of all-DC offshore wind power transmission systems.

[0004] However, DC voltage is subject to frequent and unpredictable disturbances, making it difficult for traditional PI controllers to effectively filter out high-frequency disturbances, resulting in poor voltage control performance. Summary of the Invention

[0005] This application provides a voltage control method for a full DC offshore wind power transmission system, which can improve the control effect of the collected DC voltage in the full DC offshore wind power transmission system.

[0006] A first aspect of this application provides a voltage control method for a fully DC offshore wind power transmission system. The fully DC offshore wind power transmission system includes a wind turbine generator unit, a DC transformer, and a voltage source converter. The input terminal of the DC transformer is connected to the output terminal of the wind turbine generator unit, and the output terminal of the DC transformer is connected to the input terminal of the voltage source converter. The method is applied to the DC transformer and includes: Obtain the expected value and actual value of the collected voltage of the DC power generated by the wind power generation unit; The expected value of the collected voltage is compared with the actual value of the collected voltage to obtain the voltage error value; The voltage error value is input into the target nonlinear controller to obtain the target modulation amount used to adjust the operating parameters of the DC transformer; Based on the target modulation amount, the collected voltage of DC power in the all-DC offshore wind power transmission system is adjusted to obtain the first regulated voltage, and the DC power with the voltage value of the first regulated voltage is transmitted to the voltage source converter.

[0007] Furthermore, this application also proposes that the target nonlinear controller includes proportional parameters, integral parameters, and a nonlinear error function; The voltage error value is input to the target nonlinear controller to obtain the target modulation amount used to adjust the operating parameters of the DC transformer, including: Based on the proportional and integral parameters, proportional and integral operations are performed on the voltage error value to obtain the initial proportional control component and the initial integral control component. The initial proportional control component is used to characterize the control quantity that is rapidly adjusted based on the voltage error value, and the initial integral control component is used to characterize the control quantity that eliminates the steady-state voltage deviation. The initial proportional control component and the initial integral control component are used as independent variables of the nonlinear error function, and after nonlinear transformation, the enhanced proportional control component and the enhanced integral control component are obtained. Based on the enhanced proportional control component and the enhanced integral control component, the target modulation amount for adjusting the operating parameters of the DC transformer is determined.

[0008] Furthermore, this application proposes to use the initial proportional control component and the initial integral control component as independent variables of the nonlinear error function, respectively, and obtain the enhanced proportional control component and the enhanced integral control component after nonlinear transformation, including: The enhanced proportional control component and the enhanced integral control component are determined using the following formulas: In the formula, The function value used to characterize the nonlinear error function, i.e., the enhanced proportional control component or the enhanced integral control component; 'e' is used to characterize the independent variable of the nonlinear error function, i.e., the initial proportional control component or the initial integral control component; 'a' is used to characterize the coefficients of the first function. The coefficients of the second function are used to characterize the sign function, and sgn is used to characterize the sign function.

[0009] Furthermore, this application also proposes that, after obtaining the expected value and the actual value of the collected voltage of the DC power generated by the wind power generation unit, the method further includes: The desired voltage value is input into the tracking differentiator to obtain the current voltage tracking value of the all-DC offshore wind power transmission system; The expected voltage value is compared with the actual voltage value to obtain the voltage error value, including: The current voltage tracking value is compared with the actual voltage value to obtain the voltage error value.

[0010] Furthermore, this application also proposes inputting the expected value of the collected voltage into a tracking differentiator to obtain the current voltage tracking value of the all-DC offshore wind power transmission system, including: Based on the previous voltage tracking value, the previous voltage derivative value, and the expected value of the collected voltage of the all-DC offshore wind power transmission system, determine the rate of change of the voltage derivative value of the all-DC offshore wind power transmission system; Based on the rate of change of the voltage differential value, the previous voltage differential value is updated to obtain the current voltage differential value of the all-DC offshore wind power transmission system; Based on the current voltage differential value, the previous voltage tracking value is updated to obtain the current voltage tracking value of the all-DC offshore wind power transmission system.

[0011] Furthermore, this application also proposes determining the rate of change of the voltage differential value of the all-DC offshore wind power transmission system based on the previous voltage tracking value, the previous voltage differential value, and the expected value of the collected voltage, including: The rate of change of the voltage differential value of the all-DC offshore wind power transmission system is determined by the following formula: In the formula, Used to characterize the rate of change of the differential value of voltage. Used to characterize voltage tracking values, Used to characterize the voltage derivative. The parameter m is used to characterize the desired voltage value, and the parameter n is used to characterize the first adjustment parameter. Used to characterize saturation functions; The saturation function is calculated using the following formula: In the formula, The saturated function is represented by the function value, and A is represented by the independent variable of the saturated function, i.e., in the formula above. n is used to characterize the second adjustment parameter, sgn is used to characterize the sign function operation, and sin is used to characterize the sine function operation.

[0012] Furthermore, this application also proposes that, after adjusting the collected voltage of the DC power in the all-DC offshore wind power transmission system based on the target modulation amount to obtain a first regulated voltage, the method further includes: The actual value of the collected voltage of the DC power generated by the wind power generation unit is updated to the first regulating voltage; The loop returns to input the expected voltage value into the tracking differentiator to obtain the current voltage tracking value of the all-DC offshore wind power transmission system, until the current voltage tracking value equals the pooled expected voltage value, thus obtaining the second regulated voltage.

[0013] Furthermore, this application also proposes adjusting the collected voltage of the DC power in the all-DC offshore wind power transmission system based on the target modulation amount to obtain a first regulated voltage, including: Based on the target modulation amount, the pulse width of the DC transformer is adjusted until the DC power generated by the wind power generation unit reaches the reference current value, thus obtaining the first regulated voltage.

[0014] A second aspect of the embodiments of this application provides a full DC offshore wind power transmission system, which includes a wind power generation unit, a DC transformer, and a voltage source converter; The output of the wind power generation unit is connected to the input of the DC transformer to convert wind energy into DC power. A DC transformer is used to operate the voltage control method of the above-mentioned all-DC offshore wind power transmission system, so as to convert the actual value of the collected DC voltage into a first regulated voltage. The input terminal of the voltage source converter is connected to a DC transformer to convert DC power with a first regulated voltage into AC power with a first AC voltage.

[0015] Furthermore, this application also proposes that the all-DC offshore wind power transmission system also includes an AC transformer; The input terminal of the AC transformer is connected to the output terminal of the voltage source converter, and the output terminal of the AC transformer is connected to the electrical load. It is used to convert AC power with a first AC voltage into AC power with a second AC voltage to meet the actual power demand of the electrical load.

[0016] The voltage control method for a full DC offshore wind power transmission system provided in this application is applied to a DC transformer. First, the expected value and actual value of the collected DC voltage generated by the wind power generation unit are obtained and compared to obtain a voltage error value. Then, the voltage error value is input to a target nonlinear controller to obtain a target modulation amount. Finally, the collected DC voltage is adjusted based on this target modulation amount. Compared to a traditional proportional-integral controller, the target nonlinear controller can better adapt to the nonlinear and frequent changing characteristics of DC voltage disturbances and can more effectively handle high-frequency disturbances, thereby improving the control effect on the collected DC voltage in the full DC offshore wind power transmission system. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic flowchart of a voltage control method for an all-DC offshore wind power transmission system provided in one embodiment of this application; Figure 2 This is a schematic diagram of the principle of a target nonlinear controller provided in one embodiment of this application; Figure 3 This is a schematic diagram of the structure of an all-DC offshore wind power transmission system provided in one embodiment of this application. Detailed Implementation

[0019] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0020] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0021] In current all-DC offshore wind power transmission systems, stable control of the DC voltage is crucial, and PI controllers are commonly used to achieve this goal. Due to their simple structure and ease of implementation, PI controllers are widely used in numerous industrial control scenarios.

[0022] However, the environment in which all-DC offshore wind power transmission systems operate is complex, and the DC voltage is subject to frequent and unpredictable disturbances. These disturbances may originate from natural factors such as strong winds and waves at sea, or they may be caused by the instability of internal equipment. Traditional PI controllers are designed primarily to regulate relatively regular and stable disturbances. For these high-frequency and unpredictable disturbances, their response speed and regulation capabilities are clearly insufficient, making it difficult to effectively filter out these high-frequency disturbances. This results in significant DC voltage fluctuations during actual operation, leading to unsatisfactory control performance and consequently affecting the stability and reliability of the entire offshore wind power transmission system.

[0023] To address the aforementioned issues, this application first analyzes the root cause of the contradiction between dynamic response and steady-state accuracy in traditional PI controllers, finding that their linear regulation mechanism cannot distinguish between low-frequency fundamental components and high-frequency disturbance components. To resolve this problem, a nonlinear control strategy is considered to replace the linear proportional-integral (PI) structure, dynamically adjusting the control components by introducing a nonlinear function. Further exploration reveals that completely abandoning the PI structure may result in a loss of fast response capability, while simply adding a nonlinear element would lead to a significant increase in algorithm complexity. Therefore, this application chooses to reconstruct the control components through a nonlinear function while retaining the PI framework, thus preserving the fast response characteristics of the proportional element and using nonlinear transformation to suppress the transmission of high-frequency disturbance signals.

[0024] To address this, a voltage control method for a fully DC offshore wind power transmission system is provided. The fully DC offshore wind power transmission system includes a wind power generation unit, a DC transformer, and a voltage source converter. The input terminal of the DC transformer is connected to the output terminal of the wind power generation unit, and the output terminal of the DC transformer is connected to the input terminal of the voltage source converter. like Figure 1 As shown, this method is applied to a DC transformer and may specifically include the following steps S101 to S104: S101, obtain the expected value and actual value of the collected voltage of the DC power generated by the wind power generation unit; S102, compare the expected value of the collected voltage with the actual value of the collected voltage to obtain the voltage error value; S103, input the voltage error value to the target nonlinear controller to obtain the target modulation amount used to adjust the operating parameters of the DC transformer; S104, based on the target modulation amount, adjusts the collected voltage of DC power in the all-DC offshore wind power transmission system to obtain a first regulated voltage, and transmits DC power with the voltage value of the first regulated voltage to the voltage source converter.

[0025] In this embodiment, the wind power generation unit refers to a power generation device that converts wind energy into direct current (DC). Specifically, it can be implemented by combining a wind turbine generator and a rectifier to output DC power. The DC transformer refers to a power electronic device used to change the DC voltage level. Specifically, it can be implemented by a modular multilevel converter to adjust the DC voltage. The voltage source converter refers to a power conversion device that can autonomously adjust the output voltage. Specifically, it can be implemented by a full-bridge insulated-gate bipolar transistor topology to realize the mutual conversion between DC and AC.

[0026] The expected value of the collected voltage refers to the pre-set target value of the DC bus voltage, which can be obtained through system scheduling commands and is used as a voltage control reference. The actual value of the collected voltage refers to the real-time collected DC bus voltage measurement value, which can be obtained using a voltage sensor and is used to reflect the actual operating status of the system.

[0027] The voltage error value refers to the algebraic difference between the expected value of the collected voltage and the actual value of the collected voltage. It can be obtained through subtraction and is used to reflect the degree of voltage deviation.

[0028] A target nonlinear controller refers to a control algorithm with nonlinear characteristics, which can be implemented using sliding mode control or fuzzy control, and is used to handle system nonlinearity and high-frequency disturbances.

[0029] The target modulation quantity refers to the adjustment signal that controls the operation of the DC transformer. It can be implemented by using duty cycle or phase shift angle parameters to adjust the switching state of the converter. The first regulation voltage refers to the DC output voltage after closed-loop control. It can be implemented by pulse width modulation technology to achieve dynamic voltage stability.

[0030] The core innovation of this application lies in the adoption of a collaborative control architecture of nonlinear controller and DC transformer. By calculating the voltage error in real time and generating nonlinear control signals, the power transmission characteristics of the DC transformer are dynamically adjusted, effectively suppressing voltage fluctuations caused by wind speed fluctuations and system disturbances, and improving the voltage control accuracy and dynamic response speed of the all-DC offshore wind power transmission system.

[0031] As an example, firstly, the DC voltage output by the wind power generation unit is measured using a voltage sensor to obtain the actual value of the collected voltage. Simultaneously, the desired value of the collected voltage is set according to the system's operational requirements. These two values ​​reflect the system's current voltage state and target voltage state.

[0032] Then, the measured actual value of the collected voltage is compared with the set expected value of the collected voltage, and the voltage error value is calculated. The voltage error value represents the deviation between the current voltage and the target voltage. For example, if the expected value of the collected voltage is 1000V and the actual value of the collected voltage is 980V, then the voltage error value is 20V.

[0033] Next, the calculated voltage error value is input into a pre-designed nonlinear controller. Based on the input voltage error value, the nonlinear controller uses a nonlinear algorithm to calculate the target modulation amount for adjusting the operating parameters of the DC transformer. Specifically, the nonlinear controller can employ nonlinear algorithms such as saturation functions to calculate the target modulation amount of the DC transformer based on the input voltage error value.

[0034] Finally, the DC transformer adjusts the on-time of its internal switching transistors according to the calculated target modulation amount, thereby changing the output voltage. The adjusted DC voltage is the first regulated voltage. Simultaneously, the regulated DC power is transmitted to the voltage source converter at the value of the first regulated voltage. The voltage source converter receives the regulated DC power and converts it into AC power for output to the power grid. Throughout the process, the DC transformer continuously monitors and adjusts the voltage to maintain system voltage stability.

[0035] In this embodiment, the expected and actual values ​​of the collected DC voltage generated by the wind power generation unit are first obtained and compared to obtain a voltage error value. Then, the voltage error value is input to a target nonlinear controller to obtain a target modulation amount. Finally, the collected DC voltage is adjusted based on this target modulation amount. Compared to traditional proportional-integral controllers, the target nonlinear controller is better able to adapt to the nonlinear and frequent changes in DC voltage disturbances and can more effectively handle high-frequency disturbances, thereby improving the control effect on the collected DC voltage in a full DC offshore wind power transmission system.

[0036] In some of the solutions described above in this application, although the initial proportional control component and the initial integral control component are obtained by processing the voltage error value through proportional and integral parameters, which can achieve rapid adjustment of the control quantity and elimination of steady-state voltage deviation, the traditional linear operation method has the problem of insufficient dynamic response when dealing with frequently changing disturbances, resulting in limited voltage control accuracy.

[0037] In this regard, this application further proposes a target nonlinear controller including proportional parameters, integral parameters, and a nonlinear error function; S103 may specifically include: Based on the proportional and integral parameters, proportional and integral operations are performed on the voltage error value to obtain the initial proportional control component and the initial integral control component. The initial proportional control component is used to characterize the control quantity that is rapidly adjusted based on the voltage error value, and the initial integral control component is used to characterize the control quantity that eliminates the steady-state voltage deviation. The initial proportional control component and the initial integral control component are used as independent variables of the nonlinear error function, and after nonlinear transformation, the enhanced proportional control component and the enhanced integral control component are obtained. Based on the enhanced proportional control component and the enhanced integral control component, the target modulation amount for adjusting the operating parameters of the DC transformer is determined.

[0038] In this embodiment, the proportional operation combines the voltage error value with the fixed gain coefficient through multiplication to generate the initial proportional control component, and the integral operation generates the initial integral control component by multiplying the accumulated historical voltage error value with the time step.

[0039] The nonlinear error function can be processed using a piecewise nonlinear approach. When the independent variable exceeds a set threshold, the gain direction is changed through a sign function; within the threshold range, a smooth transition is achieved through a sine function. The enhanced proportional control component and the enhanced integral control component are weighted and summed to generate the final modulation quantity, with their weighting coefficients dynamically adjusted according to the system operating status.

[0040] Specifically, when the voltage error is large, the sign function dominates the nonlinear transformation process, causing the enhanced proportional control component to increase abruptly and quickly eliminate the voltage deviation. When the voltage error approaches steady state, the sine function dominates the nonlinear transformation process, suppressing high-frequency oscillations through continuous and smooth gain changes. The enhanced integral control component, through a variable integral rate mechanism, automatically reduces the intensity of the integral action when the error is large to prevent integral saturation, while resuming the normal integral action in the steady-state phase to eliminate residual deviation.

[0041] As an example, the nonlinear error function can be a hyperbolic tangent function. Substituting the initial proportional control component and the initial integral control component into the hyperbolic tangent function, respectively, yields the enhanced proportional control component and the enhanced integral control component through a nonlinear transformation. Finally, the enhanced proportional control component and the enhanced integral control component are added together to obtain the final target modulation amount.

[0042] like Figure 2 The diagram illustrates the principle of a target nonlinear controller. Specifically, the expected value of the collected voltage V* is first compared with the actual value of the collected voltage v to obtain the voltage error value e. Then, based on the proportional parameter Kp and integral parameter KI of the target nonlinear controller, proportional and integral operations are performed on the voltage error value e respectively to obtain the initial proportional control component and the initial integral control component. Next, the initial proportional control component and the initial integral control component are nonlinearly transformed using the nonlinear error function fal to obtain the enhanced proportional control component and the enhanced integral control component. Finally, the target modulation amount y is determined based on the enhanced proportional control component and the enhanced integral control component.

[0043] This embodiment achieves nonlinear processing of voltage errors. Therefore, it allows for greater control when voltage errors are small, while preventing excessive control input that could lead to system instability when voltage errors are large. Furthermore, by introducing a nonlinear error function, the system's ability to suppress external disturbances is enhanced, improving the accuracy of voltage control and its dynamic response performance.

[0044] In some of the solutions described above in this application, the initial proportional control component and the initial integral control component generated based on the proportional parameter and the integral parameter still adopt a linear operation method, which makes it difficult to balance the dynamic response speed and steady-state accuracy of the control quantity when the error changes rapidly.

[0045] In this regard, this application further proposes to use the initial proportional control component and the initial integral control component as independent variables of the nonlinear error function, and obtain the enhanced proportional control component and the enhanced integral control component after nonlinear transformation, including: The enhanced proportional control component and the enhanced integral control component are determined using the following formula 1: Formula 1 In formula 1, The function value used to characterize the nonlinear error function, i.e., the enhanced proportional control component or the enhanced integral control component; 'e' is used to characterize the independent variable of the nonlinear error function, i.e., the initial proportional control component or the initial integral control component; 'a' is used to characterize the coefficients of the first function. The coefficients of the second function are used to characterize the sign function, and sgn is used to characterize the sign function.

[0046] In this embodiment, the first function coefficient 'a' ranges from 0 to 1 and is used to adjust the nonlinearity of the proportional control component. The second function coefficient... The value range is from 5T to 10T, where T is the sampling time interval, used to determine the segmentation point of the piecewise function.

[0047] The sign function sgn is used when the absolute value of the error is greater than the set second function coefficient. At that time, and By combining the output value with the voltage error value of the same sign, the control component is enhanced; the sign function sgn is set when the absolute value of the error is less than or equal to the set second function coefficient. When, the function behaves as The form achieves a smooth transition.

[0048] For example, when the absolute value of the error is greater than the coefficient of the second function When the control quantity and voltage error have the same sign and the amplitude increases with the increase of the error; when the absolute value of the error is less than or equal to the coefficient of the second function... At that time, the control quantity changes nonlinearly with the error.

[0049] Specifically, the nonlinear error function optimizes the dynamic characteristics of the control quantity through piecewise processing. When the error is large... The dominant calculation process rapidly increases the amplitude of the control component, shortening the system settling time; when the error is small, The form allows the control quantity to change continuously and gradually, eliminating oscillation phenomena.

[0050] This embodiment achieves nonlinear transformation of the initial proportional control component and the initial integral control component, enhancing the robustness and anti-interference capability of the controller. Consequently, when faced with frequent and irregularly changing disturbances, the controller can better adapt to the dynamic characteristics of the system, improving the accuracy and stability of DC voltage control. Furthermore, this nonlinear control method can effectively filter out high-frequency disturbances, overcoming the limitations of traditional PI controllers in handling complex disturbances, thus significantly improving the voltage control performance of the all-DC offshore wind power transmission system.

[0051] In some of the solutions described above in this application, directly comparing the expected value of the pooled voltage with the actual value of the pooled voltage to obtain the voltage error value may result in a large overshoot, which is not conducive to the rapid stabilization of the system and thus affects the regulation effect of the subsequent nonlinear controller, resulting in a reduction in voltage regulation accuracy.

[0052] In this regard, this application further proposes that, following S101, the voltage control method for the all-DC offshore wind power transmission system may also include: The desired voltage value is input into the tracking differentiator to obtain the current voltage tracking value of the all-DC offshore wind power transmission system; S102 may specifically include: The current voltage tracking value is compared with the actual voltage value to obtain the voltage error value.

[0053] In this embodiment, the tracking differentiator achieves dynamic tracking by continuously updating the voltage differential value and the voltage tracking value. Specifically, it calculates the rate of change of the voltage differential value using the previous voltage tracking value, the previous voltage differential value, and the expected voltage value, and then updates the current voltage differential value. Subsequently, it updates the current voltage tracking value based on the current voltage differential value. The saturation function is used to limit the amplitude of the rate of change of the differential value to prevent excessively large abrupt changes. Its calculation process is implemented by combining the sign function and the sine function. The first adjustment parameter m and the second adjustment parameter n control the tracking capability and the saturation amplitude, respectively, to balance the response speed and stability.

[0054] Specifically, the operation of the tracking differentiator consists of three steps. First, based on the difference between the previous voltage tracking value and the expected voltage value, and combined with the previous voltage derivative value, the rate of change of the voltage derivative value is calculated. A saturation function can be used to limit the amplitude of the rate of change to avoid abrupt changes caused by high-frequency disturbances. Second, the rate of change of the voltage derivative value is used to update the previous voltage derivative value to obtain the current voltage derivative value. Finally, the current voltage derivative value is used to update the previous voltage tracking value to obtain the smoothed current voltage tracking value.

[0055] In this process, the first adjustment parameter m is used to adjust the tracking capability; the larger the first adjustment parameter m, the stronger the tracking capability. The second adjustment parameter n is used to control the amplitude of the saturation function; the larger the second adjustment parameter n, the stronger the suppression capability of high-frequency disturbances. By continuously and iteratively executing the above steps, the current voltage tracking value gradually approaches the desired voltage value, while eliminating high-frequency disturbance components.

[0056] As an example, after obtaining the expected and actual collected voltage values ​​of the DC power generated by the wind turbine generator, the expected collected voltage value is input into a tracking differentiator to obtain the current voltage tracking value of the all-DC offshore wind power transmission system. Specifically, a saturated function can be used to construct the tracking differentiator, with the expected collected voltage value as input and the current voltage tracking value as output. The parameters of the tracking differentiator can be adjusted according to the system characteristics to obtain the best tracking effect.

[0057] Furthermore, the current voltage tracking value is compared with the actual voltage value to obtain the voltage error value. Therefore, by introducing a tracking differentiator, large overshoot can be effectively avoided, improving the accuracy and stability of voltage control.

[0058] For example, suppose the expected value of the collected voltage is 1000V, and the actual value is 980V. Inputting 1000V into the tracking differentiator yields a current voltage tracking value of 985V. Then, comparing 985V with 980V gives a voltage error of 5V.

[0059] In this embodiment, by introducing a tracking differentiator to process the expected value of the collected voltage, large overshoot can be effectively avoided, improving the accuracy and stability of voltage control. As a result, the voltage control performance of the all-DC offshore wind power transmission system is significantly improved, and the system operation becomes more stable and reliable. Furthermore, this scheme can quickly track changes in the expected voltage value, improving the system's dynamic response capability and adapting to complex operating conditions such as frequent wind speed fluctuations.

[0060] In some of the solutions described above in this application, the tracking differentiator needs to determine the current voltage tracking value based on the expected value of the pooled voltage. However, in practical applications, since the expected value of the pooled voltage may fluctuate frequently, it can easily lead to tracking lag or error accumulation, affecting the accuracy of subsequent voltage error calculations.

[0061] In this regard, this application further proposes to input the expected value of the collected voltage into the tracking differentiator to obtain the current voltage tracking value of the all-DC offshore wind power transmission system, including: Based on the previous voltage tracking value, the previous voltage derivative value, and the expected value of the collected voltage of the all-DC offshore wind power transmission system, determine the rate of change of the voltage derivative value of the all-DC offshore wind power transmission system; Based on the rate of change of the voltage differential value, the previous voltage differential value is updated to obtain the current voltage differential value of the all-DC offshore wind power transmission system; Based on the current voltage differential value, the previous voltage tracking value is updated to obtain the current voltage tracking value of the all-DC offshore wind power transmission system.

[0062] In this embodiment, the rate of change of the voltage derivative is determined by a saturation function, which limits the amplitude of the rate of change. The saturation function is implemented using a piecewise function; when the absolute value of the input value is less than or equal to n, the output value is a sine function of the input value. The product of the input value and n; when the absolute value of the input value is greater than n, the output value is the product of the sign function of the input value and n.

[0063] The voltage derivative value is updated through integration; the current voltage derivative value equals the previous voltage derivative value plus the product of the rate of change of the voltage derivative value and the time step. Similarly, the voltage tracking value is updated through integration; the current voltage tracking value equals the previous voltage tracking value plus the product of the current voltage derivative value and the time step.

[0064] Specifically, in the calculation of the voltage differential rate of change, the saturation function limits the amplitude of the input value to prevent sudden changes in the voltage differential value that could lead to instability in the tracking process. For example, when the absolute value of the input value exceeds n, the saturation function outputs the sign function of the input value to prevent the voltage differential rate of change from becoming too large. During the updating of the voltage tracking value, the time step must be consistent with the system sampling period to ensure that the update frequency is synchronized with the actual system operation. By continuously iterating the calculation of the voltage differential rate of change and updating the voltage differential and voltage tracking values, the current voltage tracking value eventually converges quickly to the desired voltage value, eliminating the tracking lag problem and improving the accuracy of subsequent voltage error value calculations.

[0065] As an example, the expected value of the collected voltage is input into the tracking differentiator to obtain the current voltage tracking value of the all-DC offshore wind power transmission system. Specifically, the rate of change of the voltage differential value of the all-DC offshore wind power transmission system is first determined based on the previous voltage tracking value, the previous voltage differential value, and the expected value of the collected voltage. Further, based on the rate of change of the voltage differential value, the previous voltage differential value is updated to obtain the current voltage differential value of the all-DC offshore wind power transmission system. Therefore, by updating the previous voltage tracking value based on the current voltage differential value, the current voltage tracking value of the all-DC offshore wind power transmission system can be obtained.

[0066] This embodiment effectively filters out high-frequency disturbances and improves voltage control performance. By introducing a tracking differentiator, smooth tracking of the desired voltage value is achieved, reducing oscillations during voltage control. Simultaneously, the introduction of a nonlinear saturation function enhances the system's ability to suppress disturbances, improving the stability and robustness of voltage control.

[0067] In some of the above-mentioned schemes in this application, the tracking differentiator needs to determine the current voltage tracking value based on the voltage expectation value. However, in practical applications, since the voltage expectation value may fluctuate frequently, the failure to update the voltage tracking value and voltage differential value of the previous moment in a timely manner can easily lead to tracking lag or error accumulation, affecting the calculation accuracy of subsequent voltage error values.

[0068] In this regard, this application further proposes to determine the voltage differential rate of change of the all-DC offshore wind power transmission system based on the previous voltage tracking value, the previous voltage differential value, and the expected value of the collected voltage, including: The voltage differential rate of change of the all-DC offshore wind power transmission system is determined by the following formula 2: Formula 2 In formula 2, Used to characterize the rate of change of the differential value of voltage. Used to characterize voltage tracking values, Used to characterize the voltage derivative. The parameter m is used to characterize the desired voltage value, and the parameter n is used to characterize the first adjustment parameter. Used to characterize saturation functions; The saturation function is specifically calculated using the following formula 3: Formula 3 In formula 3, The saturated function is represented by the function value, and A is represented by the independent variable of the saturated function, i.e., in the formula above. n is used to characterize the second adjustment parameter, sgn is used to characterize the sign function operation, and sin is used to characterize the sine function operation.

[0069] In this embodiment, the first adjustment parameter m is used to adjust the nonlinear intensity in the calculation process of the voltage differential rate of change, which affects the amplitude and response characteristics of the control component; the second adjustment parameter n is used to determine the segmentation point of the saturation function, that is, to determine under what error conditions different function forms are used for calculation.

[0070] In calculating the saturation function At that time, hour, The output value has the same sign as the error, enhancing the control component; when When, the function behaves as The form achieves a smooth transition.

[0071] This embodiment effectively filters out high-frequency disturbances and improves voltage control performance. By introducing a tracking differentiator, smooth tracking of the desired voltage value is achieved, reducing oscillations during voltage control. Simultaneously, the introduction of a nonlinear saturation function enhances the system's ability to suppress disturbances, improving the stability and robustness of voltage control. Furthermore, by adjusting parameters m and n, the system's response speed and stability can be flexibly adjusted to adapt to different wind power scenarios and control requirements.

[0072] In some of the solutions described above in this application, the current voltage tracking value is obtained by a tracking differentiator and compared with the actual value of the collected voltage to obtain an error value. Then, the target modulation amount is generated by a nonlinear controller to adjust the voltage. However, after a single adjustment, the actual value of the collected voltage may still have a steady-state deviation, which makes it impossible to accurately track the expected value of the collected voltage.

[0073] In response, this application further proposes a method for adjusting the collected voltage of DC power in a full DC offshore wind power transmission system based on a target modulation amount. After obtaining a first regulated voltage, the method further includes: The actual value of the collected voltage of the DC power generated by the wind power generation unit is updated to the first regulating voltage; The loop returns to input the expected voltage value into the tracking differentiator to obtain the current voltage tracking value of the all-DC offshore wind power transmission system, until the current voltage tracking value equals the pooled expected voltage value, thus obtaining the second regulated voltage.

[0074] In this embodiment, by updating the adjusted first adjustment voltage to the actual value of the pooled voltage and re-performing iterative calculations through the tracking differentiator, the system can dynamically adjust the tracking process based on the updated actual value of the pooled voltage, gradually reducing the difference between the actual value of the pooled voltage and the expected value of the pooled voltage.

[0075] As a loop termination condition, when the current voltage tracking value output by the tracking differentiator matches the expected value of the pooled voltage, it indicates that the actual value of the pooled voltage has stabilized and reached the expected value. At this point, the second regulated voltage is output as the final result. For example, in each loop, the tracking differentiator recalculates the rate of change of the voltage derivative based on the updated actual value of the pooled voltage and updates the current voltage tracking value, so that the error value continues to decrease in multiple iterations.

[0076] Specifically, after each adjustment, the initial adjusted voltage is fed back to the system as the new actual value input of the pooled voltage. A tracking differentiator regenerates the corresponding voltage tracking value and compares it with the expected pooled voltage value to generate a new error value. This error value drives the nonlinear controller to adjust again, forming a closed-loop control circuit. This process continues until the voltage tracking value output by the tracking differentiator perfectly matches the expected pooled voltage value. At this point, the actual voltage value has no steady-state deviation, and the system outputs the second adjusted voltage. By cyclically executing adjustment and feedback, the residual error of a single adjustment is gradually eliminated, ensuring that the actual voltage value ultimately converges precisely to the expected value, avoiding the persistent deviation problem caused by high-frequency disturbances or dynamic changes in traditional methods.

[0077] As an example, the actual value of the collected voltage of the DC power generated by the wind power generation unit is first updated to the first regulated voltage. Specifically, after adjusting the collected voltage of the DC power in the all-DC offshore wind power transmission system to obtain the first regulated voltage, this first regulated voltage is used as the new actual value of the collected voltage.

[0078] Furthermore, the loop returns to input the expected voltage value into the tracking differentiator, obtaining the current voltage tracking value of the all-DC offshore wind power transmission system. Thus, the system can continuously track changes in the expected voltage value. Specifically, during the loop execution, the updated actual collected voltage value is continuously compared with the expected collected voltage value to obtain a new voltage error value. This step can reflect the deviation of the system voltage in real time.

[0079] The process continues cyclically until the current voltage tracking value equals the expected pooled voltage value, at which point the second regulated voltage is obtained. For example, when the difference between the current voltage tracking value and the expected pooled voltage value is less than a preset threshold, they are considered equal, and the voltage obtained at this point is the second regulated voltage.

[0080] As a preferred implementation, a maximum number of loops or a maximum execution time can be set to prevent the system from getting stuck in an infinite loop. If the current voltage tracking value is not equal to the expected pooled voltage value even after the maximum number of loops or the maximum execution time has been reached, a warning message can be output and the loop can be terminated.

[0081] This embodiment achieves precise voltage control of a full DC offshore wind power transmission system. By continuously updating and aggregating the actual voltage value and cyclically executing the voltage tracking process, the system can quickly respond to voltage changes and effectively suppress voltage fluctuations. This method improves the system's stability and reliability, helping to protect system equipment from the effects of voltage fluctuations. Simultaneously, precise voltage control can optimize the system's energy transmission efficiency and reduce energy loss. Furthermore, this method is highly adaptive, able to adapt to voltage variations under different wind conditions, improving the system's adaptability and robustness.

[0082] In some of the solutions described above in this application, the control of the DC transformer based on the target modulation amount relies on complex parameter adjustments, which can easily lead to insufficient current tracking accuracy due to response lag or parameter mismatch, thereby affecting the voltage regulation effect.

[0083] In this regard, this application further proposes to adjust the collection voltage of the DC power in the all-DC offshore wind power transmission system based on the target modulation amount to obtain a first regulated voltage, including: Based on the target modulation amount, the pulse width of the DC transformer is adjusted until the DC power generated by the wind power generation unit reaches the reference current value, thus obtaining the first regulated voltage.

[0084] In this embodiment, the pulse width is adjusted by changing the on and off times of the switching devices of the DC transformer; the target modulation amount is generated by a nonlinear controller to determine the amplitude and direction of the pulse width adjustment; the DC current value is continuously monitored during the adjustment process, and the pulse width is adjusted further when the deviation between the actual current value and the reference current value exceeds the threshold.

[0085] Specifically, the target modulation amount is input to the pulse width modulation unit of the DC transformer and converted into the corresponding pulse signal duty cycle. The change in duty cycle directly controls the voltage amplitude on the output side of the DC transformer, thereby adjusting the DC current of the wind power generation unit. In each adjustment cycle, the actual current value is compared with the reference current value. If the actual current value does not reach the reference current value, the duty cycle is recalculated based on the target modulation amount, and an updated pulse signal is generated.

[0086] This process is repeated cyclically until the actual current value stabilizes within the allowable error range of the reference current value. At this point, the first regulated voltage output by the DC transformer meets the input requirements of the subsequent voltage source converter. This method ensures the dynamic response speed of voltage regulation through current closed-loop feedback, while avoiding regulation failure caused by system parameter drift in traditional open-loop control.

[0087] As an example, the reference current value is preset to 1000A in the control unit of the DC transformer. When the target modulation amount is calculated to be 0.85, the pulse width modulation module is triggered to generate a square wave drive signal with a duty cycle of 85%. This square wave drive signal is input to the insulated-gate bipolar transistor of the DC transformer, adjusting its on-time ratio to 85%, thereby gradually increasing the DC-side inductor current from the initial 950A to the reference current value. When the current sampling unit detects that the actual current value has reached 1000A, it locks the current pulse width parameter. At this time, the collected voltage on the DC bus is stably adjusted from the initial 750V to 800V, forming the first regulated voltage.

[0088] This embodiment achieves precise control of the DC transformer switching frequency and effectively suppresses current surges caused by sudden wind speed changes through a current closed-loop regulation mechanism. Specifically, when instantaneous power fluctuations occur on the DC side, dynamic adjustment of the pulse width can quickly match the converter's power transmission requirements, preventing the voltage source converter from triggering protection actions due to input voltage instability, and significantly improving the continuous operation capability of the entire DC system under turbulent wind conditions.

[0089] Based on the voltage control method for the all-DC offshore wind power transmission system provided in this application, specific embodiments of the all-DC offshore wind power transmission system are also provided.

[0090] like Figure 3 As shown, this application provides a schematic diagram of a fully DC offshore wind power transmission system. The fully DC offshore wind power transmission system includes a wind power generation unit 310, a DC transformer 320, and a voltage source converter 330. The output terminal of the wind power generation unit 310 is connected to the input terminal of the DC transformer 320 to convert wind energy into DC power. DC transformer 320 is used to operate the above-mentioned all-DC offshore wind power transmission system voltage control method to convert the actual value of the collected DC voltage into the first regulated voltage; The input terminal of the voltage source converter 330 is connected to the DC transformer 320 to convert DC power with a first regulated voltage into AC power with a first AC voltage.

[0091] In this embodiment, the all-DC offshore wind power transmission system 300 may include three wind power generation units 310. The output of each wind power generation unit 310 is connected in parallel to the input of a DC transformer 320. The DC transformer 320 adopts a dual active bridge structure, and its output is connected to the DC side of a voltage source converter 330. The voltage source converter 330 adopts a three-phase two-level topology.

[0092] When wind speed fluctuations cause the actual value of the collected voltage output by the wind power generation unit 310 to deviate from the expected value of 600kV, the DC transformer 320 collects the voltage difference in real time and inputs it into the nonlinear controller to generate a pulse width modulation signal. This signal is then used to adjust the phase shift angle of the dual active bridge to stabilize the output voltage at the target value. The adjusted DC power is then converted into 50Hz / 220kV AC power by the voltage source converter 330 for connection to the power grid.

[0093] This embodiment effectively solves the problem of poor adjustment performance of traditional PI controllers under frequent disturbances. By using a nonlinear control algorithm to dynamically compensate for voltage errors, the influence of high-frequency disturbances on DC bus voltage is suppressed, thereby improving the voltage control accuracy and operational stability of the entire system under complex operating conditions and ensuring that the power quality output by the wind turbine meets grid connection requirements.

[0094] In some of the schemes described above in this application, the all-DC offshore wind power transmission system converts DC power into AC power with a first AC voltage through a voltage source converter. However, the actual operating requirements of different electrical loads in the power system vary, and a single AC voltage level is difficult to meet the access requirements of diverse loads, which may lead to the equipment failing to work properly or experiencing reduced efficiency due to voltage mismatch.

[0095] In this regard, such as Figure 3 As shown, this application further proposes that the all-DC offshore wind power transmission system also includes an AC transformer 340; The input terminal of AC transformer 340 is connected to the output terminal of voltage source converter 330, and the output terminal of AC transformer 340 is connected to the electrical load. It is used to convert AC power with a first AC voltage into AC power with a second AC voltage to meet the actual power demand of the electrical load.

[0096] In this embodiment, the input terminal of the AC transformer 340 is connected to the output terminal of the voltage source converter 330, and the output terminal of the AC transformer 340 is connected to the electrical load. The AC output of the voltage source converter 330 has a first AC voltage, specifically a 35kV three-phase AC voltage. The AC transformer 340 adopts a three-phase dual-winding structure. Its primary winding adopts a star connection and is connected to the three-phase AC output terminal of the voltage source converter 330, while the secondary winding adopts a delta connection. By adjusting the transformation ratio of the AC transformer to 3.5:1, the first AC voltage is converted into a second AC voltage of 10kV to meet the voltage requirements of the power grid distribution network. The core of the AC transformer 340 is made of laminated silicon steel sheets, and the windings are made of copper wire. A tap changer is configured on the secondary side to adjust the output voltage range. When the load side is connected to the distribution network, the AC transformer 340 is connected to the transmission line through an insulating bushing to ensure electrical isolation and safety protection for power transmission.

[0097] This embodiment achieves a secondary transformation of the AC output voltage of the voltage source converter. By adjusting the turns ratio parameters of the AC transformer, the first AC voltage is converted into a second AC voltage that matches the rated voltage of the electrical equipment. This solves the voltage mismatch problem that exists when electrical loads of different voltage levels are connected, ensuring the compatibility and stability of power transmission, while reducing the risk of system failure through electrical isolation design.

[0098] It should be clarified that this application is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of this application is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of this application.

[0099] The functional blocks shown in the above-described structural diagram can be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, they can be, for example, electronic circuits, application-specific integrated circuits (ASICs), appropriate firmware, plug-ins, function cards, etc. When implemented in software, the elements of this application are programs or code segments used to perform the required tasks. Programs or code segments can be stored on a machine-readable medium or transmitted over a transmission medium or communication link via data signals carried on a carrier wave. "Machine-readable medium" can include any medium capable of storing or transmitting information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROM, flash memory, erasable ROM (EROM), floppy disks, CD-ROMs, optical disks, hard disks, fiber optic media, radio frequency (RF) links, etc. Code segments can be downloaded via computer networks such as the Internet, intranets, etc.

[0100] It should also be noted that the exemplary embodiments mentioned in this application describe methods or systems based on a series of steps or apparatus. However, this application is not limited to the order of the above steps; that is, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0101] The foregoing flowcharts and / or block diagrams of methods, apparatus (systems) according to embodiments of the present disclosure have described various aspects of the present disclosure. It should be understood that each block of the flowcharts and / or block diagrams, and combinations of blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to create a machine such that these instructions, executable via the processor of the computer or other programmable data processing apparatus, enable the implementation of the functions / actions specified in one or more blocks of the flowcharts and / or block diagrams. Such a processor can be, but is not limited to, a general-purpose processor, a special-purpose processor, a special application processor, or a field-programmable logic circuit. It is also understood that each block of the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can also be implemented by special-purpose hardware performing the specified functions or actions, or can be implemented by a combination of special-purpose hardware and computer instructions.

[0102] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A voltage control method for a full DC offshore wind power transmission system, characterized in that, The all-DC offshore wind power transmission system includes a wind power generation unit, a DC transformer, and a voltage source converter; the input terminal of the DC transformer is connected to the output terminal of the wind power generation unit, and the output terminal of the DC transformer is connected to the input terminal of the voltage source converter. The method is applied to the DC transformer, and the method includes: Obtain the expected value and the actual value of the collected voltage of the DC power generated by the wind power generation unit; The expected value of the collected voltage is compared with the actual value of the collected voltage to obtain the voltage error value; The voltage error value is input to the target nonlinear controller to obtain the target modulation amount used to adjust the operating parameters of the DC transformer; Based on the target modulation amount, the collected voltage of the DC power in the all-DC offshore wind power transmission system is adjusted to obtain a first regulated voltage, and the DC power with the voltage value of the first regulated voltage is transmitted to the voltage source converter.

2. The method according to claim 1, characterized in that, The target nonlinear controller includes proportional parameters, integral parameters, and a nonlinear error function; The step of inputting the voltage error value into the target nonlinear controller to obtain the target modulation amount for adjusting the operating parameters of the DC transformer includes: Based on the proportional parameter and the integral parameter, proportional and integral operations are performed on the voltage error value to obtain an initial proportional control component and an initial integral control component. The initial proportional control component is used to characterize the control quantity that is rapidly adjusted based on the voltage error value, and the initial integral control component is used to characterize the control quantity that eliminates steady-state voltage deviation. The initial proportional control component and the initial integral control component are respectively used as the independent variables of the nonlinear error function, and after nonlinear transformation, the enhanced proportional control component and the enhanced integral control component are obtained. Based on the enhanced proportional control component and the enhanced integral control component, the target modulation amount for adjusting the operating parameters of the DC transformer is determined.

3. The method according to claim 2, characterized in that, The step of using the initial proportional control component and the initial integral control component as independent variables of the nonlinear error function, and obtaining the enhanced proportional control component and enhanced integral control component after nonlinear transformation, includes: The enhanced proportional control component and the enhanced integral control component are determined by the following formula: In the formula, The function value used to characterize the nonlinear error function, i.e., the enhanced proportional control component or the enhanced integral control component; e is used to characterize the independent variable of the nonlinear error function, i.e., the initial proportional control component or the initial integral control component; a is used to characterize the first function coefficient. The coefficients of the second function are used to characterize the sign function, and sgn is used to characterize the sign function.

4. The method according to any one of claims 1-3, characterized in that, After obtaining the expected value and the actual value of the collected voltage of the DC power generated by the wind power generation unit, the method further includes: The desired value of the collected voltage is input into the tracking differentiator to obtain the current voltage tracking value of the all-DC offshore wind power transmission system; The step of comparing the expected voltage value with the actual voltage value to obtain the voltage error value includes: The current voltage tracking value is compared with the actual voltage value to obtain the voltage error value.

5. The method according to claim 4, characterized in that, The step of inputting the expected value of the collected voltage into the tracking differentiator to obtain the current voltage tracking value of the all-DC offshore wind power transmission system includes: The rate of change of the voltage differential value of the all-DC offshore wind power transmission system is determined based on the previous voltage tracking value, the previous voltage differential value, and the expected value of the collected voltage of the all-DC offshore wind power transmission system. Based on the rate of change of the voltage differential value, the previous voltage differential value is updated to obtain the current voltage differential value of the all-DC offshore wind power transmission system; Based on the current voltage differential value, the previous voltage tracking value is updated to obtain the current voltage tracking value of the all-DC offshore wind power transmission system.

6. The method according to claim 5, characterized in that, The step of determining the voltage differential rate of change of the all-DC offshore wind power transmission system based on the previous voltage tracking value, the previous voltage differential value, and the expected value of the collected voltage includes: The rate of change of the voltage differential value of the all-DC offshore wind power transmission system is determined by the following formula: In the formula, Used to characterize the rate of change of the differential value of voltage. Used to characterize voltage tracking values, Used to characterize the voltage derivative. The parameter m is used to characterize the desired voltage value, and the parameter n is used to characterize the first adjustment parameter. Used to characterize saturation functions; The saturation function is calculated using the following formula: In the formula, The saturated function is represented by the function value, and A is represented by the independent variable of the saturated function, i.e., in the formula above. n is used to characterize the second adjustment parameter, sgn is used to characterize the sign function operation, and sin is used to characterize the sine function operation.

7. The method according to claim 4, characterized in that, After adjusting the collected voltage of the DC power in the all-DC offshore wind power transmission system based on the target modulation amount to obtain a first regulated voltage, the method further includes: The actual value of the collected voltage of the DC power generated by the wind power generation unit is updated to the first regulating voltage; The loop returns to input the expected voltage value into the tracking differentiator to obtain the current voltage tracking value of the all-DC offshore wind power transmission system until the current voltage tracking value equals the expected voltage value, thus obtaining the second regulated voltage.

8. The method according to any one of claims 1-3, characterized in that, The step of adjusting the collected voltage of the DC power in the all-DC offshore wind power transmission system based on the target modulation amount to obtain a first regulated voltage includes: Based on the target modulation amount, the pulse width of the DC transformer is adjusted until the DC power generated by the wind power generation unit reaches the reference current value, thus obtaining the first regulated voltage.

9. A fully DC offshore wind power transmission system, characterized in that, The all-DC offshore wind power transmission system includes wind power generation units, DC transformers, and voltage source converters; The output end of the wind power generation unit is connected to the input end of the DC transformer to convert wind energy into DC power. The DC transformer is used to execute the voltage control method for the all-DC offshore wind power transmission system according to any one of claims 1-8, so as to convert the actual value of the collected DC voltage into a first regulating voltage. The input terminal of the voltage source converter is connected to the DC transformer to convert DC power with a voltage value of the first regulated voltage into AC power with a first AC voltage.

10. The system according to claim 9, characterized in that, The all-DC offshore wind power transmission system also includes an AC transformer; The input terminal of the AC transformer is connected to the output terminal of the voltage source converter, and the output terminal of the AC transformer is connected to the electrical load. It is used to convert AC power with a first AC voltage into AC power with a second AC voltage to meet the actual power demand of the electrical load.

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