Direct-current-output offshore wind-solar new energy collection system and control method thereof

Abstract

The invention discloses a DC-output offshore wind and light new energy collection system and a control method thereof, which are applied to the technical field of power grids, and the system comprises a DC bus, a DC-DC converter, a DC line, an inverter, an offshore converter station, an AC power grid, a plurality of DC transmission units and a plurality of new energy power generation units. The output end of each new energy power generation unit is connected in series with each direct current transmission unit; the direct current transmission units transmit electric energy to the direct current-direct current converter through the direct current bus, and the direct current bus is connected with the direct current transmission units in parallel; the output end of the DC-DC converter transmits electric energy to the receiving end of the inverter through the DC line; the inverter transmits electric energy to the alternating current power grid through the offshore converter station. According to the system and the method provided by the embodiment of the invention, the power of the power grid can be controlled, and the stability of the system is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of power grids, and in particular, to a DC-out type offshore wind and solar new energy aggregation system and a control method thereof. Background Art

[0002] With the transformation of the global energy structure and the continuous progress of renewable energy technologies, offshore wind power, as a clean and renewable energy form, is gradually becoming an important part of the new energy system architecture.

[0003] In the prior art, the cable impedance of the offshore wind and solar new energy platform is complex. When multiple DC power transmission units are connected in parallel directly to the DC bus, due to the differences in line impedance and the inconsistent parameters between lines, the power of the power grid based on offshore wind and solar new energy is unstable.

[0004] Therefore, how to control the power of the wind and solar new energy power grid to ensure the stability of the system has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0005] The present invention provides a DC-out type offshore wind and solar new energy aggregation system and a control method thereof, so as to solve the problem of unstable power of the offshore wind and solar new energy power grid, and achieve the effect of controlling the power of the offshore wind and solar new energy power grid and ensuring the stability of the system.

[0006] To solve the above technical problem, an embodiment of the present invention provides a DC-out type offshore wind and solar new energy aggregation system, including: A DC bus, a DC-DC converter, a DC line, an inverter, an offshore converter station, an AC power grid, a plurality of DC power transmission units, and a plurality of new energy power generation units; The output end of each new energy power generation unit is connected in series with each DC power transmission unit; The DC power transmission unit transports electric energy to the DC-DC converter through the DC bus, wherein the DC bus is connected in parallel with a plurality of the DC power transmission units; The output end of the DC-DC converter transports electric energy to the receiving end of the inverter through the DC line; The inverter transports electric energy to the AC power grid through the offshore converter station.

[0007] Another embodiment of the present invention provides a power control method based on a DC-out type offshore wind and solar new energy aggregation system, which is applied to the DC-out type offshore wind and solar new energy aggregation system as described above. The power control method based on the DC-out type offshore wind and solar new energy aggregation system includes: Obtain the voltage values and current values of the circuits on both sides of each DC power transmission unit in the target offshore wind and solar new energy collection system; Based on the voltage values and the current values of the circuits on both sides of each DC power transmission unit, construct a number of impedance models; Use the recursive least squares method to perform recursive update processing on each of the impedance models to obtain impedance estimation values, where the impedance estimation values at least include a resistance component estimation value and an inductance component estimation value; Based on the resistance component estimation value and the inductance component estimation value, obtain the virtual impedance value of the target offshore wind and solar new energy collection system; Perform smoothing processing on the virtual impedance value to obtain a stable virtual impedance value; Introduce a circulating current suppression coefficient, and input all the circulating current suppression coefficients and all the stable virtual impedance values into the constructed power control model to obtain a power control signal, where each of the circulating current suppression coefficients is obtained by processing the current value of each circuit; Execute the power control strategy generated by the power control signal.

[0008] As one of the preferred solutions, the constructing a number of impedance models based on the voltage values and the current values of the circuits on both sides of each DC power transmission unit includes: Apply a step voltage to the voltage value to obtain a current response; apply a current pulse to the current value to obtain a voltage response; Perform convolution processing on the voltage response and the current response to obtain a time-domain impulse response; Use Fourier transform to process the time-domain impulse response to obtain the impedance model.

[0009] As one of the preferred solutions, the using the recursive least squares method to perform recursive update processing on each of the impedance models to obtain impedance estimation values includes: Obtain a preset impedance estimation value and a preset covariance matrix; Based on the preset impedance estimation value, the preset covariance matrix and the current value obtained by real-time detection, input them into the impedance model to obtain a gain vector; Use the recursive least squares method to perform recursive update on the gain vector to obtain the impedance estimation value.

[0010] As one of the preferred solutions, the obtaining the virtual impedance value of the target offshore wind and solar new energy collection system based on the resistance component estimation value and the inductance component estimation value includes: Based on the resistance component estimation value and the current value, obtain a resistance component voltage; Perform differential processing on the current value to obtain a differential current value; Based on the estimated value of the inductance component and the differential current value, an inductance component voltage is obtained; The resistance component voltage and the inductance component voltage are processed using a Kalman gain function to obtain the virtual impedance value of the target offshore wind and solar new energy collection system.

[0011] As one preferred solution, the smoothing the virtual impedance value to obtain a stable virtual impedance value includes: Determining a step parameter based on the current value of the target offshore wind and solar new energy collection system; Introducing the step parameter, and using the step approximation method to smooth the virtual impedance value to obtain a stable virtual impedance value.

[0012] As one preferred solution, each of the circulating current suppression coefficients is obtained by processing the current value of each circuit, including: Based on the current values of the circuits on both sides of each converter in the target offshore wind and solar new energy collection system, a circulating current value is obtained; Performing harmonic analysis on the circulating current value to obtain a circulating current signal to be suppressed; Performing fuzzy logic control on the circulating current signal to obtain a circulating current suppression coefficient.

[0013] As one preferred solution, the construction process of the power control model includes: Based on the voltage value and the current value, the output power of the converter is obtained; Using a droop control algorithm to process the output power of the converter to obtain a power reference value; Based on the output power of the converter and the power reference value, a power error is obtained; Using the stable virtual impedance value to correct the voltage value, and obtaining a voltage reference value based on the correction result; Using the sequential Monte Carlo algorithm to train the circulating current suppression coefficient, the power reference value, and the voltage reference value to obtain a power control model.

[0014] As one preferred solution, after obtaining the power control model, the power control method for the offshore wind and solar new energy collection system based on DC transmission further includes: Using simulated game to solve the Bayesian Nash equilibrium of the power control model to obtain a voltage-power equilibrium point, and the voltage-power equilibrium point reflects that the network power flow is stable and satisfies the voltage constraint of the target offshore wind and solar new energy collection system.

[0015] As one of the preferred solutions, after implementing the power control strategy generated by the power control signal, the power control method for the offshore wind and solar new energy collection system based on DC transmission further includes: Taking the average power of the target offshore wind and solar new energy collection system within a preset time range as a reference, the stability of the power obtained after implementing the power control strategy is verified by using the Nyquist criterion.

[0016] Compared with the prior art, the beneficial effects of the embodiments of the present invention are at least one of the following: The system of the present invention includes a DC bus, a DC-DC converter, a DC line, an inverter, an offshore converter station, an AC power grid, a plurality of DC power transmission units, and a plurality of new energy power generation units; the output end of each new energy power generation unit is connected in series with each DC power transmission unit; the DC power transmission unit transports electric energy to the DC-DC converter through the DC bus, wherein the DC bus is connected in parallel with a plurality of DC power transmission units; the output end of the DC-DC converter transports electric energy to the receiving end of the inverter through the DC line; the inverter transports electric energy to the AC power grid through the offshore converter station. Compared with the prior art, by adding DC power transmission units in the DC bus and the new energy power generation units, when the electric energy enters the DC bus through the DC power transmission units, the electric energy is processed. The processing process includes: obtaining the voltage value and current value of the circuits on both sides of each DC power transmission unit in the target offshore wind and solar new energy collection system; based on the voltage value and current value of the circuits on both sides of each DC power transmission unit, constructing a plurality of impedance models; using the recursive least squares method to perform recursive update processing on each impedance model to obtain impedance estimation values, where the impedance estimation values at least include a resistance component estimation value and an inductance component estimation value; obtaining the virtual impedance value of the target offshore wind and solar new energy collection system based on the resistance component estimation value and the inductance component estimation value; performing smoothing processing on the virtual impedance value to obtain a stable virtual impedance value; introducing a circulating current suppression coefficient, and inputting all the circulating current suppression coefficients and all the stable virtual impedance values into the constructed power control model to obtain a power control signal, where each circulating current suppression coefficient is obtained by processing the current value of each circuit; implementing the power control strategy generated by the power control signal. In this processing process, the DC power transmission unit constructs a dynamic control basis by performing impedance estimation and virtual impedance generation on the real-time voltage value and real-time current value of the circuit, and then controls the power of the offshore wind and solar new energy power grid through smoothing processing and circulating current suppression, and finally realizes the closed-loop stable control of the power grid. Description of the Drawings

[0017] Figure 1It is a schematic structural diagram of an offshore wind and solar new energy collection system based on DC transmission in one embodiment of the present invention; Figure 2 It is a schematic flowchart of a power control method for an offshore wind and solar new energy collection system based on DC transmission in one embodiment of the present invention.

[0018] Reference numerals: Among them, 11, new energy power generation unit; 12, DC power transmission unit; 13, DC bus; 14, DC-DC converter; 15, DC line; 16, inverter; 17, offshore converter station; 18, AC power grid. Specific embodiments

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0020] In the description of the present invention, the terms "first", "second", "third", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", "third", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0021] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the internal communication of two components. The terms "vertical", "horizontal", "left", "right", "up", "down" and similar expressions used herein are only for the purpose of illustration, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] In the description of the present invention, it should be noted that unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0023] With the transformation of the global energy structure and the rapid development of renewable energy, offshore wind power, as a clean and efficient energy form, is gradually becoming a key area of energy development. In recent years, the development scale of offshore wind power has been continuously expanding, the distance of the wind farm from the shore is getting farther and farther, and the single-unit capacity and the total installed capacity of the wind farm are also increasing continuously. In the context of the large-scale development of offshore wind power, wind farms are usually located in waters dozens or even hundreds of kilometers offshore, and the capacity of a single wind farm is relatively large. It is often necessary to collect the electric energy of multiple wind farms and then use flexible DC transmission technology to send it out.

[0024] In the prior art, the cable impedance of the offshore wind-solar new energy platform is complex. When multiple DC power transmission units are connected in parallel directly to the DC bus, due to the difference in line impedance and the inconsistency of parameters between lines, the power of the power grid based on offshore wind-solar new energy will be unstable.

[0025] Therefore, to control the power of the wind-solar new energy power grid and ensure the stability of the system, an embodiment of the present invention provides an offshore wind-solar new energy collection system for DC transmission. Specifically, please refer to Figure 1 , Figure 1 which shows a schematic structural diagram of the offshore wind-solar new energy collection system for DC transmission in one embodiment of the present invention. The system includes: a DC bus 13, a DC-DC converter 14, a DC line 15, an inverter 16, an offshore converter station 17, an AC power grid 18, a plurality of DC power transmission units 12, and a plurality of new energy power generation units 11.

[0026] The connection relationships of the components in the system include: the output end of each new energy power generation unit 11 is connected in series with each DC power transmission unit 12; the DC power transmission unit transports electric energy to the DC-DC converter 14 through the DC bus 13, wherein the DC bus 13 is connected in parallel with a plurality of the DC power transmission units 12; the output end of the DC-DC converter 14 transports electric energy to the receiving end of the inverter 16 through the DC line 15; the inverter 16 transports electric energy to the AC power grid 18 through the offshore converter station 17.

[0027] Specifically, in the present invention, the current obtained by new energy power generation units 11 such as wind power and photovoltaic is transmitted to the DC bus 13 through the DC power transmission unit 12. In the prior art, due to the differences in the line impedance of each new energy power generation unit 11, unstable direct current is generated, resulting in unstable power input to the DC bus 13. Therefore, in the present invention, the current and voltage of the DC power transmission unit 12 are processed. Specifically, the DC power transmission unit estimates the impedance and generates virtual impedance based on the real-time voltage value and real-time current value of the circuit, constructs a dynamic control basis, and then controls the power of the offshore wind-solar new energy power grid through smoothing processing and circulating current suppression, ultimately achieving the closed-loop stable control of the power grid.

[0028] Among them, the function of the DC-DC converter 14 is to efficiently transmit to the centralized converter station through the DC line by boosting the DC voltage level.

[0029] The function of the inverter 15 is to invert the high-voltage direct current into high-frequency alternating current and input it into the AC power grid.

[0030] Another embodiment of the present invention provides a power control method for an offshore wind-solar new energy collection system based on DC output. Specifically, please refer to Figure 2 , Figure 2 which shows a schematic flow chart of the power control method for the offshore wind-solar new energy collection system based on DC output in one embodiment of the present invention. The method includes: S1: Obtain the voltage values and current values of the circuits on both sides of each DC power transmission unit in the target offshore wind-solar new energy collection system; S2: Based on the voltage values and current values of the circuits on both sides of each DC power transmission unit, construct a number of impedance models; S3: Use the recursive least squares method to perform recursive update processing on each impedance model to obtain impedance estimation values, where the impedance estimation values at least include resistance component estimation values and inductance component estimation values; S4: Obtain the virtual impedance value of the target offshore wind-solar new energy collection system based on the resistance component estimation value and the inductance component estimation value; S5: Perform smoothing processing on the virtual impedance value to obtain a stable virtual impedance value; S6: Introduce a circulating current suppression coefficient, input all the circulating current suppression coefficients and all the stable virtual impedance values into the constructed power control model to obtain a power control signal, where each circulating current suppression coefficient is obtained by processing the current value of each circuit; S7: Execute the power control strategy generated by the power control signal.

[0031] The above method controls the power of the offshore wind and solar new energy collection system for DC transmission based on the DC power transmission unit as the executing entity.

[0032] In step S1, by real-time monitoring the voltage and current values of the circuits on both sides of each DC power transmission unit in the target offshore wind and solar new energy collection system, where the voltage and current values can be used to calculate power and impedance characteristics, analyze circulating current, load changes, and dynamic responses, reflecting the real-time operating state of the power grid.

[0033] In step S2, based on the voltage value and the current value of the circuits on both sides of each DC power transmission unit, several impedance models are constructed, including: Apply a step voltage to the voltage value to obtain a voltage response; apply a current pulse to the current value to obtain a current response; perform convolution processing on the voltage response and the current response to obtain a time-domain impulse response; use Fourier transform to process the time-domain impulse response to obtain the impedance model.

[0034] Normally, by artificially applying a step voltage or a current pulse, the dynamic response of the power grid is excited to facilitate the extraction of the impedance characteristics of the system.

[0035] Specifically, instantaneously change the voltage amplitude at the DC bus or on the AC side and record the current response after the voltage change. The step response reflects the low-frequency impedance characteristics of the system; inject a short high-frequency current pulse (such as a rectangular wave) into the circuit and record the transient response of the voltage. The current pulse response reflects the high-frequency impedance characteristics.

[0036] Establish the time-domain relationship between voltage and current through convolution operation to characterize the dynamic impedance characteristics of the system. In this process, specifically, align the time axes of the step / pulse excitations to eliminate measurement delays.

[0037] The convolution operation fuses the responses under two excitations in the time domain, eliminates the limitations of single tests, and improves the model accuracy. By combining the excitation signal (step or pulse) with the response signal through convolution operation, the time-domain impulse response of the system is derived to characterize the system characteristics: the impulse response represents the dynamic behavior of the system to instantaneous disturbances and directly reflects the time-domain correlation between voltage and current.

[0038] Convert the time-domain impulse response into a frequency-domain impedance model to reveal the impedance behavior of the system at different frequencies, and at the same time locate the resonant frequency or the high-frequency noise sensitive area, providing a basis for stability analysis and control design.

[0039] There are several circuits in the target offshore wind and solar new energy collection system. Based on the voltage value and the current value of each circuit, an impedance model is constructed.

[0040] In step S3, the recursive least squares method is used to perform recursive update processing on each of the impedance models to obtain impedance estimation values, where the impedance estimation values at least include a resistance component estimation value and an inductance component estimation value. Specifically, it includes: obtaining a preset impedance estimation value and a preset covariance matrix; inputting the preset impedance estimation value, the preset covariance matrix, and the current value obtained by real-time detection into the impedance model to obtain a gain vector; using the recursive least squares method to perform recursive update on the gain vector to obtain the impedance estimation value.

[0041] First, initialize the impedance estimation values. For example, both the resistance component estimation value and the inductance component estimation value are zero. The preset covariance matrix represents the credibility of the initial parameter estimation. Generally, the covariance matrix is initialized as a diagonal matrix, and the diagonal elements reflect the confidence level of the initial parameter error.

[0042] Input the current value detected in real time into the impedance model, combine the current impedance estimation value to predict the voltage response, and calculate the gain vector based on the deviation between the predicted voltage and the actual measured voltage, the covariance matrix, and the current data. The larger the gain, the more significant the influence of the current data on the parameter correction.

[0043] Among them, the gain vector is mainly used to balance the weights of "new measurement data" and "historical estimation values", determine the influence degree of the current data on the parameter update, and at the same time reduce the interference of measurement noise on the parameter estimation through the gain vector.

[0044] Use the recursive least squares method to perform recursive update on the gain vector and the prediction error (the difference between the actual voltage and the model-predicted voltage), correct the resistance and inductance components. If the current data indicates an increase in the system inductance (such as a load mutation), the algorithm automatically increases the impedance estimation value, and at the same time reduces the value of the covariance matrix, indicating an improvement in the confidence level of the parameter estimation. If the data noise is large, the covariance matrix retains a higher value to maintain the flexibility of the parameter update.

[0045] Feed the updated resistance and inductance back into the impedance model for virtual impedance generation, circulating current suppression, or power distribution optimization.

[0046] Through this process, the recursive least squares method provides real-time and adaptive impedance parameter estimation capabilities for the offshore wind and solar new energy power grid, which is the core technical support for ensuring system stability and performing power control.

[0047] In step S4, a virtual impedance value of the target offshore wind and solar new energy collection system is obtained based on the estimated resistance component and the estimated inductance component. Specifically, it includes obtaining a resistance component voltage based on the estimated resistance component and the current value; performing a differential process on the current value to obtain a differential current value; obtaining an inductance component voltage based on the estimated inductance component and the differential current value; and using a Kalman gain function to process the resistance component voltage and the inductance component voltage to obtain the virtual impedance value of the target offshore wind and solar new energy collection system.

[0048] In the offshore wind and solar new energy power grid, the process of generating a virtual impedance value based on the estimated resistance and inductance components aims to dynamically simulate the additional impedance characteristics to optimize the system stability and control performance.

[0049] First, the current value detected in real time is multiplied by the resistance estimate updated by the recursive least squares method to obtain a resistance component voltage. The resistance component voltage reflects the ohmic loss generated when the current flows through the line or equipment (such as cable heating), directly correlates the real-time current value with the resistance parameter, and provides a static (low-frequency) voltage component for the construction of the virtual impedance to offset the negative impact of the actual resistance.

[0050] Then, the real-time current signal is digitally differentiated to calculate the rate of change of the difference between the current at the current moment and the previous moment to obtain a differential current value. Preferably, the digital differentiation is the backward difference method. In this process, the current differential value reflects the instantaneous rate of change of the current, such as the current fluctuation caused by load mutation or switch action, and is used to characterize the dynamic characteristics of the system. At the same time, the differential operation amplifies high-frequency noise and fast transient processes and provides an input for the inductance component voltage.

[0051] The differential current value is multiplied by the inductance estimate to obtain an inductance component voltage. Among them, the inductance component voltage reflects the inertial response of the system to the current change, that is, it suppresses the current mutation, and by simulating the inductance voltage drop, it offsets the voltage fluctuation caused by the actual inductance and improves the dynamic stability of the system.

[0052] The resistance component voltage and the inductance component voltage are processed using a Kalman gain function to obtain the virtual impedance value of the target offshore wind and solar new energy collection system. The Kalman gain function dynamically adjusts the contribution weights of the resistance component voltage and the inductance component voltage according to the system noise level and measurement reliability, and then filters out the measurement noise (such as sensor error) and model error through filtering to output a more accurate virtual impedance value.

[0053] However, in this process, it has relatively high requirements for the computing power end. The algorithm needs to complete the calculation within milliseconds to meet the fast response requirements of power electronic control.

[0054] Through this process, the virtual impedance value becomes the core bridge connecting parameter estimation and closed-loop control, significantly enhancing the dynamic performance and robustness of the offshore wind and solar new energy power grid.

[0055] In step S5, the virtual impedance value is smoothed to obtain a stable virtual impedance value, which specifically includes determining a step parameter based on the current value of the target offshore wind and solar new energy collection system; introducing the step parameter, and using the step approximation method to smooth the virtual impedance value to obtain a stable virtual impedance value.

[0056] The absolute value or change rate of the current is calculated in real time, and the current characteristics are mapped to the step parameter according to a preset rule. The rule is: the higher the current change rate, the smaller the step parameter. When the current changes violently, the step parameter is smaller, allowing finer step adjustments to quickly track the virtual impedance change; when the current is stable, the step parameter is larger, reducing the adjustment frequency to avoid interference with the control signal caused by frequent fluctuations.

[0057] According to the magnitude or change rate of the real-time current value, the step size of the step parameter is dynamically adjusted to balance the smoothing effect and the response speed. Based on the difference between the virtual impedance target value to be tracked in the upstream control and the current virtual impedance value, the number of steps to be passed is determined, and the impedance is updated step by step.

[0058] If the current suddenly changes midway, such as the step parameter is dynamically reduced due to current fluctuations, recalculate the remaining number of steps and the step size to ensure smoothness.

[0059] In step S5, the continuous virtual impedance target value is decomposed into multiple discrete step segments, and the impedance value remains constant within each segment, gradually approaching the target value. Through step transitions, direct jumps of the virtual impedance to the target value are avoided, preventing instantaneous impacts on the power controller or modulation signal.

[0060] In step S6, a circulating current suppression coefficient is introduced, and all the circulating current suppression coefficients and all the stable virtual impedance values are input into the constructed power control model to obtain a power control signal, where each circulating current suppression coefficient is obtained by processing the current value of each circuit.

[0061] Among them, each circulating current suppression coefficient is obtained by processing the current value of each circuit, specifically including: Based on the current values of the circuits on both sides of each converter in the target offshore wind and solar new energy collection system, the circulating current value is obtained; harmonic analysis is performed on the circulating current value to obtain the circulating current signal to be suppressed; fuzzy logic control is performed on the circulating current signal to obtain the circulating current suppression coefficient.

[0062] Specifically, the current values on both sides of the converter (such as the upper and lower bridge arms or the outlets of different converter stations) are monitored in real time. By measuring the current difference between the circuits on both sides of the converter, that is, the circulating current value, the circulating current value directly reflects the magnitude of the circulating current. Perform a fast Fourier transform (FFT) or band-pass filtering on the circulating current value to extract specific frequency components, record the amplitude and phase of the target harmonics, and use them as the input of the fuzzy logic control. Convert the input quantity into a fuzzy linguistic variable, define the membership function. If the circulating current amplitude is "large" and the change rate is "fast", then significantly increase the suppression coefficient. If the circulating current amplitude is "small", then maintain the current suppression coefficient.

[0063] Preferably, the fuzzy output is converted into an accurate circulating current suppression coefficient by the centroid method or the maximum membership degree method.

[0064] Harmonic analysis can accurately separate the circulating current components to be suppressed, avoiding "one-size-fits-all" suppression. Moreover, the fuzzy logic automatically adapts to different working conditions (such as sudden changes in wind speed and load fluctuations) without the need for manual parameter readjustment. Through this process, the circulating current suppression coefficient realizes a closed-loop control from "passive detection" to "active suppression", significantly improving the reliability and power quality of the offshore wind and solar new energy power grid.

[0065] Specifically, the construction process of the power control model includes: Obtain the output power of the converter based on the voltage value and the current value; process the output power of the converter using the droop control algorithm to obtain a power reference value; obtain a power error based on the output power of the converter and the power reference value; perform a correction process on the voltage value using the steady virtual impedance value, and obtain a voltage reference value based on the correction result; use the sequential Monte Carlo algorithm to train the circulating current suppression coefficient, the power reference value, and the voltage reference value to obtain a power control model.

[0066] Specifically, obtain the output power of the converter through the voltage value and the current value, then define the droop slope of the voltage varying with the power, and generate a target power reference value according to the current power and the droop curve. In this process, according to the preset droop characteristics, dynamically distribute the power loads of each converter in the power grid to avoid single-point overload.

[0067] Use the sequential Monte Carlo algorithm to train the circulating current suppression coefficient, the power reference value, and the voltage reference value to obtain a power control model. The sequential Monte Carlo (SMC) is a probabilistic algorithm based on random sampling and dynamic update, mainly used to deal with dynamic system modeling state estimation and parameter optimization problems. Its core idea is to gradually approximate the true state or optimal solution of a complex system through the iterative "sampling - evaluation - resampling" process. Therefore, the power control model constructed using the sequential Monte Carlo algorithm can obtain the optimal power control signal.

[0068] After obtaining the power control model, a simulation game is used to solve the Bayesian Nash equilibrium of the power control model to obtain the voltage-power equilibrium point, which reflects that the network power flow is stable and satisfies the voltage constraints of the target offshore wind and solar new energy collection system.

[0069] This process replaces centralized control with game equilibrium to meet the decentralized decision-making requirements of the offshore power grid. Moreover, the Bayesian framework effectively handles environmental interference and incomplete information problems, and the equilibrium point naturally incorporates voltage constraints, avoiding the limitations of artificial weighting of constraints in traditional optimization.

[0070] Among them, the simulation game is a process of simulating the strategic interaction of multiple agents (such as multiple converters in the power grid) through computer modeling and simulation technology. The participants (converters) dynamically adjust their own strategies (such as power output, voltage reference value) according to preset rules and real-time data, and the goal is to achieve the global optimum or equilibrium state.

[0071] The Bayesian Nash equilibrium is an equilibrium concept in game theory, which describes the state where all participants choose optimal strategies based on probabilistic beliefs in a scenario of multiple participants and incomplete information (such as the strategies of other participants or the power grid state being unknown).

[0072] In summary, the simulation game is a tool for strategy verification and multi-agent coordination, revealing complex interaction effects under decentralized control through simulation; the Bayesian Nash equilibrium is the target state in game theory, ensuring that the strategies of each converter are both stable and compliant under incomplete information; the combination of the two provides an intelligent autonomous coordination mechanism for the offshore wind and solar new energy power grid, taking into account efficiency, stability, and security.

[0073] Execute the power control strategy generated by the power control signal.

[0074] After executing the power control strategy generated by the power control signal, based on the average power of the target offshore wind and solar new energy collection system within a preset time range, the Nyquist criterion is used to verify the stability of the power obtained after executing the power control strategy.

[0075] The process of verifying the system stability through the Nyquist criterion after executing the power control strategy aims to ensure the stable operation of the offshore wind and solar new energy power grid during dynamic regulation and avoid power oscillations or voltage collapse.

[0076] Among them, the Nyquist Criterion is a classic frequency-domain method in control engineering for judging the stability of a closed-loop system. It predicts whether unstable phenomena will occur after closing the loop by analyzing the open-loop frequency response of the system (i.e., the characteristics when the feedback is not closed).

[0077] In the new energy power grid of offshore scenery, it helps engineers quickly identify potential oscillation risks of power control strategies and ensure system robustness through parameter tuning.

[0078] Compared with the prior art, the beneficial effects of the embodiments of the present invention are at least one of the following: The system of the present invention includes a DC bus, a DC-DC converter, a DC line, an inverter, an offshore converter station, an AC power grid, a plurality of DC power transmission units, and a plurality of new energy power generation units; the output end of each new energy power generation unit is connected in series with each DC power transmission unit; the DC power transmission unit transports electric energy into the DC-DC converter through the DC bus, wherein the DC bus is connected in parallel with a plurality of the DC power transmission units; the output end of the DC-DC converter transports electric energy to the receiving end of the inverter through the DC line; the inverter transports electric energy into the AC power grid through the offshore converter station. Compared with the prior art, by adding DC power transmission units to the DC bus and new energy power generation units, when electric energy enters the DC bus through the DC power transmission unit, the electric energy is processed. The processing process includes: obtaining the voltage values and current values of the circuits on both sides of each DC power transmission unit in the target offshore scenery new energy collection system; based on the voltage values and current values of the circuits on both sides of each DC power transmission unit, constructing a plurality of impedance models; using the recursive least squares method to perform recursive update processing on each impedance model to obtain impedance estimation values, where the impedance estimation values at least include resistance component estimation values and inductance component estimation values; obtaining the virtual impedance value of the target offshore scenery new energy collection system based on the resistance component estimation values and the inductance component estimation values; performing smoothing processing on the virtual impedance value to obtain a stable virtual impedance value; introducing a circulating current suppression coefficient, and inputting all the circulating current suppression coefficients and all the stable virtual impedance values into the constructed power control model to obtain a power control signal, where each circulating current suppression coefficient is obtained by processing the current value of each circuit; implementing the power control strategy generated by the power control signal. In this processing process, the DC power transmission unit constructs a dynamic control basis by performing impedance estimation and virtual impedance generation on the real-time voltage value and real-time current value of the circuit, and then controls the power of the offshore scenery new energy power grid through smoothing processing and circulating current suppression, and finally realizes the closed-loop stable control of the power grid.

[0079] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent for the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention shall be subject to the appended claims.

Claims

1. A direct current transmission offshore wind and solar energy collection system, characterized in that: include: DC bus, DC-DC converter, DC line, inverter, offshore converter station, AC grid, several DC transmission units and several renewable energy power generation units; The output end of each of the new energy power generation units is connected in series with each of the direct current transmission units; The DC power transmission unit transmits electric energy to the DC-DC converter via the DC bus, wherein the DC bus is connected in parallel with a plurality of the DC power transmission units; The output end of the DC-DC converter transmits electric energy to the receiving end of the inverter through the DC line; The inverter transmits electric energy to the AC power grid through the offshore converter station.

2. A power control method for an offshore wind-solar renewable energy collection system based on direct current transmission, characterized in that: Applied to the offshore wind-solar renewable energy collection system based on direct current transmission as claimed in claim 1, the power control method of the offshore wind-solar renewable energy collection system based on direct current transmission comprises: Obtain the voltage and current values ​​of the circuits on both sides of each DC power transmission unit in the target offshore wind and solar energy collection system; Constructing a plurality of impedance models based on the voltage value and the current value of the circuits at both sides of each DC power transmission unit; Recursively updating each of the impedance models using a recursive least squares method to obtain an impedance estimate, wherein the impedance estimate includes at least a resistance component estimate and an inductance component estimate; Obtaining a virtual impedance value of the target offshore wind-solar new energy collection system based on the estimated value of the resistance component and the estimated value of the inductance component; Smoothing the virtual impedance value to obtain a stable virtual impedance value; Introducing a circulating current suppression coefficient, inputting all the circulating current suppression coefficients and all the stable virtual impedance values ​​into the constructed power control model to obtain a power control signal, wherein each of the circulating current suppression coefficients is obtained by processing the current value of each circuit; A power control strategy generated by the power control signal is executed.

3. The power control method of the offshore wind-solar new energy collection system based on direct current transmission as claimed in claim 2 is characterized in that: The step of constructing a plurality of impedance models based on the voltage value and the current value of the circuits at both sides of each DC power transmission unit includes: Applying a step voltage to the voltage value to obtain a current response; applying a current pulse to the current value to obtain a voltage response; Performing convolution processing on the voltage response and the current response to obtain a time domain impulse response; The time domain impulse response is processed by Fourier transform to obtain the impedance model.

4. The power control method of the offshore wind-solar new energy collection system based on direct current transmission as claimed in claim 2 is characterized in that: The method of recursively updating each impedance model using the recursive least squares method to obtain an impedance estimation value includes: Obtaining a preset impedance estimation value and a preset covariance matrix; Based on the preset impedance estimation value, the preset covariance matrix and the current value obtained by real-time detection, the impedance model is input to obtain a gain vector; The gain vector is recursively updated using a recursive least squares method to obtain the impedance estimation value.

5. The power control method of the offshore wind-solar new energy collection system based on direct current transmission as claimed in claim 2 is characterized in that: The method of obtaining the virtual impedance value of the target offshore wind-solar new energy collection system based on the estimated value of the resistance component and the estimated value of the inductance component includes: obtaining a resistance component voltage based on the resistance component estimated value and the current value; Performing differentiation processing on the current value to obtain a differential current value; Obtaining an inductance component voltage based on the inductance component estimated value and the differential current value; The resistance component voltage and the inductance component voltage are processed by using the Kalman gain function to obtain a virtual impedance value of the target offshore wind-solar new energy collection system.

6. The power control method of the offshore wind-solar new energy collection system based on direct current transmission as claimed in claim 2 is characterized in that: The step of smoothing the virtual impedance value to obtain a stable virtual impedance value includes: Determining step parameters based on the current value of the target offshore wind-solar new energy collection system; The step parameter is introduced, and the virtual impedance value is smoothed by using the step approximation method to obtain a stable virtual impedance value.

7. The power control method of the offshore wind-solar new energy collection system based on direct current transmission as claimed in claim 2 is characterized in that: Each of the circulating current suppression coefficients is obtained by processing the current value of each circuit, including: Obtaining a circulating current value based on the current values ​​of the circuits on both sides of each converter in the target offshore wind-solar new energy collection system; Performing harmonic analysis on the circulating current value to obtain a circulating current signal to be suppressed; The circulation signal is subjected to fuzzy logic control to obtain a circulation suppression coefficient.

8. The power control method of the offshore wind-solar new energy collection system based on direct current transmission as claimed in claim 2 is characterized in that: The construction process of the power control model includes: Obtaining an output power of the converter based on the voltage value and the current value; Processing the output power of the converter by using a droop control algorithm to obtain a power reference value; Obtaining a power error based on the output power of the converter and the power reference value; Using the stable virtual impedance value to correct the voltage value, and obtaining a voltage reference value based on the correction result; The circulating current suppression coefficient, the power reference value and the voltage reference value are trained using a sequential Monte Carlo algorithm to obtain a power control model.

9. The power control method of the offshore wind-solar new energy collection system based on direct current transmission as claimed in claim 8 is characterized in that: After obtaining the power control model, the power control method of the offshore wind-solar new energy collection system based on direct current transmission further includes: The power control model is solved by Bayesian Nash equilibrium using simulated game theory to obtain a voltage-power equilibrium point, which reflects that the network flow is stable and meets the voltage constraints of the target offshore wind-solar new energy collection system.

10. The power control method of the offshore wind-solar new energy collection system based on direct current transmission as claimed in claim 2, characterized in that: After executing the power control strategy generated by the power control signal, the power control method of the offshore wind-solar new energy collection system based on direct current transmission further includes: Taking the average power of the target offshore wind-solar new energy collection system within a preset range of time as a benchmark, the Nyquist criterion is used to verify the stability of the power obtained after executing the power control strategy.

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