Cooperative suppression method for transient overvoltage of hybrid wind power plant by using network construction type direct-driven fan

Abstract

The invention discloses a cooperative suppression method for transient overvoltage of a hybrid wind power plant by a network-constructing type direct-driven wind turbine, which is suitable for the hybrid wind power plant comprising a network-constructing type permanent magnet direct-driven wind turbine generator and a network-following type permanent magnet direct-driven wind turbine generator. The method comprises the steps of constructing an electrical equivalent model, extracting key parameters, identifying regulation and control factors, formulating a cooperative control strategy, and executing control response and strategy optimization in an abnormal state of a system. Voltage response characteristics are analyzed through indexes such as self-impedance, mutual impedance and short-circuit ratio, and effective suppression of transient overvoltage and improvement of system voltage supporting capability are realized by combining controller parameter setting and reactive power compensation device control.

Description

Technical Field

[0001] The present invention relates to the technical field of voltage stabilization control of wind power systems, and in particular to a method for collaboratively suppressing transient overvoltages in hybrid wind farms using grid-type direct-drive wind turbines. Background Art

[0002] With a high percentage of wind farms connected to the grid, transient voltage stability issues become increasingly prominent due to a decrease in the system's short-circuit ratio. This is especially true after a grid short-circuit fault is cleared, potentially triggering significant transient overvoltages. These transient voltage peaks can exceed safety thresholds, potentially damaging the insulation of connected equipment and leading to risks such as malfunctioning protection and disconnection of turbines. Grid-forming PMSGs (GFM-PMSGs), due to their voltage source characteristics, offer enhanced active support capabilities and have become a key technology focus in recent years for enhancing the grid-forming capabilities of new energy systems.

[0003] Currently, research on grid-connected wind turbine converters primarily focuses on frequency support, inertia support, and voltage regulation. Relatively mature control strategies have emerged, such as virtual synchronous generators (VSGs), droop control, and matching control (MC). Some studies have proposed improving transient voltage stability by optimizing GFM controller parameters or introducing energy storage devices or reactive power compensation devices. However, most existing research focuses on optimizing parameters of a single device or controller, and analytical methods are often based on the effective value of voltage, making it difficult to fully capture the peak voltage characteristics during fault clearing. Furthermore, there is a lack of systematic analysis of the coordinated modeling of wind farm topology configuration, electrical parameters, and control strategies.

[0004] In this context, facing the hybrid wind farm operation scenario where grid-connected and grid-following wind turbines coexist, there is still an urgent need for a technical method that can systematically model the electrical structure and control characteristics of the wind farm, so as to accurately identify the dominant factors affecting the transient overvoltage response, and realize the quantitative evaluation of voltage support capacity and multi-strategy coordinated regulation, so as to solve the problem that transient overvoltages in current wind power systems are difficult to effectively suppress. Summary of the Invention

[0005] In order to solve the problems of the prior art, an embodiment of the present invention provides a method for collaboratively suppressing transient overvoltages in hybrid wind farms using grid-type direct-drive wind turbines. The technical solution is as follows:

[0006] On the one hand, a method for collaboratively suppressing transient overvoltages in hybrid wind farms using grid-type direct-drive wind turbines is provided. The method is applicable to hybrid wind farms that include both grid-type permanent magnet direct-drive wind turbines (GFM-PMSG) and grid-following permanent magnet direct-drive wind turbines (GFL-PMSG). The method comprises the following steps:

[0007] Step 1: Build an equivalent model to describe the electrical characteristics of key wind farm equipment and extract electrical parameters used to quantify the system's transient voltage support capability. These electrical parameters include the wind farm's self-impedance, mutual impedance, and their corresponding short-circuit ratio (SCR).

[0008] Step 2: Based on the electrical parameters extracted from the electrical equivalent model, analyze the impact of different controller parameters and electrical structure configurations on transient voltage response performance, and identify the control factors that are highly correlated with transient overvoltage behavior;

[0009] Step 3: Based on the control factors identified in step 2, jointly configure the wind turbine grid configuration ratio, electrical connection structure and controller parameters to develop a coordinated suppression control strategy for optimizing the system voltage response performance;

[0010] Step 4: When an abnormal system operating state is detected, dynamically execute wind turbine operating mode switching, controller parameter tuning, and control the branch switching state of the reactive power compensation device according to the response conditions set in the coordinated control strategy and real-time monitoring data;

[0011] Step 5: Based on the continuous monitoring results of voltage response performance, evaluate and optimize the controller parameter configuration and implement control strategy updates through state scheduling logic or adaptive mechanism.

[0012] Furthermore, the construction of the electrical equivalent model includes:

[0013] The grid-connected wind turbines, grid-following wind turbines, step-up transformers, and collection lines are equivalently modeled using lumped parameters. The wind farm self-impedance and mutual impedance parameters are extracted, and a quantitative indicator of the system voltage support capability is established based on the following short-circuit ratio calculation formula:

[0014]

[0015] Where: S aci is the grid-connected capacity of new energy station i; P i 、P j Corresponding to the active power injected by stations i and j respectively; Z ii , Z ij are the self-impedance of station i and the mutual impedance between stations i and j respectively.

[0016] The short-circuit ratio is used to quantify the difference in voltage support capacity of a wind farm before and after the grid-type wind turbines are connected. The introduction of grid-type wind turbines can reduce the ratio of self-impedance to mutual impedance, thereby improving the short-circuit ratio and suppressing transient overvoltages.

[0017] Furthermore, the electrical parameters used to quantify the system transient voltage support capability also include a normalized sensitivity coefficient, which is used to evaluate the influence of control parameters and structural configuration on the voltage response index. Its expression is:

[0018] S p =ΔU peak / U base ×100%

[0019] Where: ΔU peak is the peak change, U base is the voltage reference, S p is the normalized sensitivity coefficient, a positive value indicates that an increase in the parameter leads to an increase in overvoltage, while a negative value indicates the opposite.

[0020] Furthermore, the process of identifying the control factors that are highly correlated with transient overvoltage behavior includes:

[0021] Through simulation modeling or fault disturbance simulation based on the electrical equivalent model, the influence of the access ratio of wind turbines with different grid configurations, electrical line parameters and key controller parameters on the short-circuit ratio, sensitivity coefficient and transient voltage peak is evaluated, and the factors whose impact on the system transient response exceeds the preset sensitivity threshold are determined as control factors.

[0022] Furthermore, the formulation of the collaborative inhibition control strategy includes:

[0023] According to the sensitivity ranking results of the control factors, the access ratio of grid-connected wind turbines in the wind farm, the single-circuit length of the 35kV collection line, the proportional gain coefficient of the voltage controller and the proportional gain coefficient of the phase-locked loop are jointly configured to form a control parameter configuration table covering typical fault scenarios for response calls under different transient overvoltage risk levels.

[0024] Furthermore, the response process when the system operating state is detected to be abnormal includes:

[0025] Based on the preset response conditions in the collaborative suppression control strategy, when the bus voltage change rate exceeds the set threshold or the output current of the wind turbine exceeds the rated value, the control mode of the grid-connected wind turbine is triggered to switch to constant voltage control, and the grid-following wind turbine performs low voltage ride-through control. At the same time, the reactive compensation devices such as SVG or SVC are controlled to exit the capacitor branch operation and are delayed to be re-activated after the voltage recovers.

[0026] Furthermore, the control objectives of the response process include:

[0027] The transient overvoltage peak is suppressed to no more than 1.2 times the rated voltage (pu), the voltage recovery time is controlled within 100 milliseconds, the high-frequency disturbance energy does not exceed 20% of the steady-state level before the fault, and the system voltage waveform is stable within 10 power frequency cycles without continuous oscillation.

[0028] Furthermore, the parameter configuration of the wind turbine controller includes:

[0029] The proportional coefficient of the voltage outer loop controller of the grid-type wind turbine generator set is set to no less than 100, and the integral time constant is set to no more than 0.3 seconds; the proportional coefficient of the phase-locked loop of the grid-following wind turbine generator set is set to no less than 200, and the integral coefficient is set to no less than 700 per second; the overall response characteristics of the controller meet the stability requirements of a damping ratio of no less than 0.7 and a bandwidth of no less than 100 Hz.

[0030] Furthermore, the operating state control of the reactive power compensation device includes:

[0031] When it is detected that the bus voltage change rate exceeds the set threshold, the SVG or SVC reactive compensation device suspends its capacitor branch output; when the bus voltage returns to below the set voltage and remains stable for a time that meets the set threshold, the capacitor branch operation is put back into operation.

[0032] Furthermore, the evaluation of the system transient response performance and the optimization of controller parameters include:

[0033] Indicators such as voltage peak, recovery time, and high-frequency disturbance energy are collected and analyzed. When any indicator deviates from the preset target value, the preset control parameter combination in the collaborative control strategy is called for switching and optimization.

[0034] The technical solution provided by the embodiment of the present invention has the following beneficial effects:

[0035] The present invention provides a method for collaboratively suppressing transient overvoltages in hybrid wind farms using grid-type direct-drive wind turbines. By constructing an electrical equivalent model of the wind farm and extracting key electrical parameters, including self-impedance, mutual impedance and short-circuit ratio (SCR), a quantitative assessment of the system's voltage support capability is achieved. Furthermore, based on model parameter analysis, the control factors affecting the voltage response performance are identified, and a collaborative control strategy for jointly configuring the proportion of grid-type units, electrical structure and controller parameters is formulated, enabling the system to have stronger fault adaptability.

[0036] During grid faults and fault clearance, this invention dynamically switches between grid-connected and grid-following wind turbine control modes by setting fault detection criteria and combining them with real-time voltage and current monitoring results. It also coordinates the branch responses of reactive power compensation devices such as SVGs or SVCs, effectively suppressing transient voltage spikes that may occur after fault clearance. Through continuous feedback from closed-loop performance monitoring indicators (such as voltage peaks, recovery times, and spectral disturbances), it automatically optimizes controller parameters and updates response strategies, ensuring stable system operation under various fault scenarios.

[0037] The present invention has technical advantages such as clear response logic, flexible control strategy, and strong scalability. It can significantly improve the dynamic voltage support capability of hybrid wind farms in complex power grid fault environments, suppress transient overvoltage peaks, shorten voltage recovery time, and reduce equipment insulation risks. It provides a practical system-level collaborative control solution for the promotion and application of grid-connected wind turbines in large new energy bases. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0039] Figure 1 This is a flow chart of a method for collaboratively suppressing transient overvoltages in a hybrid wind farm by grid-type direct-drive wind turbines according to an embodiment of the present invention.

[0040] Figure 2 A topology and control block diagram of a hybrid system according to an embodiment of the present invention;

[0041] Figure 3 This is an equivalent diagram of a two-GFL-PMSG grid-connected system according to an embodiment of the present invention;

[0042] Figure 4 This is an equivalent diagram of a system equipped with a GFM-PMSG according to an embodiment of the present invention;

[0043] Figure 5 This is an equivalent diagram of a hybrid wind farm grid-connected system according to an embodiment of the present invention;

[0044] Figure 6 Schematic diagram of the effect of the GFM-PMSG ratio on transient overvoltage according to an embodiment of the present invention;

[0045] Figure 7 Graph showing the relationship between the GFM-PMSG ratio and the transient overvoltage peak value in an embodiment of the present invention;

[0046] Figure 8 Schematic diagram showing the effect of the total number of wind turbines in operation on transient overvoltage according to an embodiment of the present invention;

[0047] Figure 9 A graph showing the relationship between the total number of wind turbines in operation and the transient overvoltage peak value according to an embodiment of the present invention;

[0048] Figure 10 Schematic diagram of the effect of line length on transient overvoltage according to an embodiment of the present invention;

[0049] Figure 11 is a graph showing the relationship between line length and transient overvoltage peak value according to an embodiment of the present invention;

[0050] Figure 12 Schematic diagram of the effect of GFM-PMSG control parameters on transient overvoltage in an embodiment of the present invention Figure 1 ;

[0051] Figure 13 Schematic diagram of the effect of GFL-PMSG control parameters on transient overvoltage in an embodiment of the present invention Figure 2 ;

[0052] Figure 14 Schematic diagram of four-dimensional dominant factors of transient overvoltage according to an embodiment of the present invention;

[0053] Figure 15 Schematic diagram of the coordinated control structure of each unit in a hybrid wind farm according to an embodiment of the present invention;

[0054] Figure 16 A schematic diagram of a coordinated suppression scheme for integrated station layout and unit control according to an embodiment of the present invention;

[0055] Figure 17 1 is a comparison diagram of transient overvoltages under three working conditions of an embodiment of the present invention. DETAILED DESCRIPTION

[0056] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0057] This embodiment provides a method for collaboratively suppressing transient overvoltages in hybrid wind farms using grid-type direct-drive wind turbines. Figure 1 As shown in Figure 1, this method is applicable to a hybrid wind farm that includes both grid-forming permanent magnet direct-drive wind turbines (GFM-PMSG) and grid-following permanent magnet direct-drive wind turbines (GFL-PMSG). It mainly includes the following five steps:

[0058] Step 1: Build an electrical equivalent model and extract key electrical parameters

[0059] Using lumped parameter modeling, we perform equivalent modeling of wind turbines, step-up transformers, and collection lines, extract the self-impedance and mutual impedance of the wind farm, and calculate the short-circuit ratio (SCR), an important indicator for measuring the system's transient voltage support capability. The expression for the short-circuit ratio is as follows:

[0060]

[0061] Where: S aci is the grid-connected capacity of new energy station i; P i 、P j Corresponding to the active power injected by stations i and j respectively; Z ii , Z ij are the self-impedance of station i and the mutual impedance between stations i and j respectively.

[0062] Step 2: Analyze the impact of parameters on voltage response performance

[0063] Based on the parameters extracted from the electrical equivalent model, the influence of different wind turbine configuration ratios, electrical structures and controller parameters on the transient voltage response performance is analyzed. The normalized sensitivity coefficient Sp is introduced and expressed as follows:

[0064] S p =ΔU peak / U base ×100%

[0065] Where: ΔU peak is the peak change, U base is the voltage reference, S p is the normalized sensitivity coefficient, a positive value indicates that an increase in the parameter leads to an increase in overvoltage, while a negative value indicates the opposite.

[0066] The simulation results show that the access ratio of grid-connected wind turbines, line length, voltage controller proportional coefficient and phase-locked loop proportional parameter are the main control factors affecting transient overvoltage.

[0067] Step 3: Develop a collaborative inhibitory control strategy

[0068] Based on the sensitivity ranking results of the above-mentioned control factors, the following control strategy is formulated: the access ratio of grid-connected wind turbines is not less than 50%, the single-circuit length of the 35kV collection line does not exceed 4km, the voltage controller proportional coefficient of the grid-connected wind turbines is set to not less than 100, and the integral time constant is not greater than 0.3 seconds; the phase-locked loop proportional coefficient of the grid-following wind turbines is not less than 200, and the integral coefficient is not less than 700s -1 The above configurations are combined to form a parameter configuration table for response calls under different transient conditions.

[0069] Step 4: Response control when the operating status is abnormal

[0070] During wind farm operation, if the system bus voltage change rate exceeds 5% / ms or the output current exceeds 120% of the rated value, the system is deemed to have entered a transient abnormal state. Based on the control strategy developed in step three, the grid-connected wind turbines switch to constant voltage control mode, while the grid-following wind turbines initiate low voltage ride-through (LVRT) control. Simultaneously, the SVG or SVC reactive power compensation device is controlled to exit the capacitor branch and re-engage the capacitor branch when the system voltage returns to below 1.1 pu and remains stable for 50 ms.

[0071] Step 5: Control parameter optimization and strategy update

[0072] By continuously monitoring the system's voltage peak, recovery time, and spectrum disturbance indicators, the control effectiveness of the current controller parameter configuration is evaluated. If any performance indicator deviates from the set target range, the next set of parameter configurations is called based on the preset parameter configuration table, and the controller is tuned, achieving closed-loop optimization of the control strategy and continuous improvement of system response performance.

[0073] In summary, this embodiment effectively improves the voltage support capability and dynamic response stability of hybrid wind farms during grid faults by constructing an electrical equivalent model of the wind farm, analyzing the key factors affecting transient voltage fluctuations, and formulating and dynamically executing control strategies. This method boasts technical advantages such as strong structural adaptability, precise parameter control, and timely fault response, making it suitable for the engineering deployment and operational optimization of large-scale grid-connected wind power systems.

[0074] Theoretical basis and technical implementation process of the method of the present invention

[0075] To further illustrate the control mechanism, parameter configuration method and its impact on the system response performance of the present invention, the modeling analysis and simulation verification process are shown below:

[0076] The purpose of the present invention is to propose a suppression mechanism and coordination scheme for transient overvoltage of hybrid wind farms by grid-type direct-drive wind turbines.

[0077] Firstly, an equivalent circuit model of a hybrid wind farm is established. Based on the analytical method of impedance and short-circuit ratio, the suppression mechanism of GFM-PMSG on system transient overvoltage is revealed. Secondly, a quantitative parameter sensitivity analysis is conducted to compare and study the influence of layout factors such as GFM-PMSG proportion, line length, and various control parameters of the unit on its transient overvoltage. Then, based on the above influence rules, a coordinated suppression scheme of the comprehensive station layout and unit control of the hybrid wind farm is proposed. Finally, the correctness of the theory of the present invention and the effectiveness of the proposed scheme are verified based on the PSCAD / EMTDC simulation platform.

[0078] The collaborative suppression scheme proposed in this paper fully leverages the site layout and unit control parameters of each hybrid wind farm device. Simply by changing the layout structure and adjusting parameters, it significantly reduces both the peak transient overvoltage at the fault point in the hybrid wind farm and the high-frequency component of the transient overvoltage. This strategy significantly suppresses transient overvoltages in the hybrid wind farm after a three-phase short-circuit fault has been cleared. This collaborative control strategy effectively exploits the transient voltage regulation potential of the GFM-PMSG, providing new insights into addressing transient overvoltage issues in traditional wind farms and offering valuable engineering guidance.

[0079] The purpose of the present invention is to propose a suppression mechanism and coordination scheme for transient overvoltage of hybrid wind farms by grid-type direct-drive wind turbines.

[0080] like Figure 2 As shown in the figure, the hybrid wind farm consists of two parts: GFL-PMSG and MC-controlled GFM-PMSG. The rated capacity of each wind turbine is 5MW. After the wind turbine is stepped up by a 0.69kV / 35kV box transformer, it is connected to the point of common coupling (PCC) at the end of the line through a 35kV line. The connecting bus is equipped with a reactive compensator C Q , and then connected to the grid through a 35kV / 220kV transformer and a 220kV line. The total system capacity is 300MW.

[0081] When the system is in steady-state operation, both GFM-PMSG and GFL-PMSG control are in steady-state control strategy ( Figure 2 Control mode 0). Generator-side control uses a speed outer loop and current inner loop control strategy to achieve maximum power point tracking. On the grid side, the GFL-PMSG uses traditional dual-loop control: a DC capacitor voltage outer loop and a current inner loop (with the same PI parameter settings at the dual positions). The GFM-PMSG, based on a matching control approach, uses a voltage outer loop and a current inner loop that is consistent with the GFL-PMSG, and introduces reactive power droop control to provide system inertia support.

[0082] When a short circuit fault occurs in the system, the control switches to the fault control strategy ( Figure 1 During the fault period, the GFL-PMSG switches to low voltage ride-through control. After the fault is cleared, the GFL-PMSG returns to steady-state control ( Figure 2 Medium control mode 0).

[0083] Figure 2 The system topology parameters are defined as follows: i L 、i Mare the output currents of a single GFL-PMSG and GFM-PMSG respectively; k1 is the transformation ratio of the box transformer, k2 is the transformation ratio of the secondary transformer; N1 is the number of GFM-PMSGs, N2 is the number of GFL-PMSGs; R S1 、X S1 are the 35kV line impedance of a single aggregated wind farm; R S2 、X S2 are the 220kV line impedance after Thevenin equivalent; C Q It is the reactive power compensation capacitor.

[0084] Figure 2 The system control parameters are defined as follows: C DC 、u DC1 , 2 are the DC bus capacitance and voltage respectively; L t1 , 2, C f1 , 2, L g1 , 2, R d1 , 2 are LCL filter parameters, including filter inductance, filter capacitance, and damping resistance, where L is L t1 With L g1 The sum of t1 , 2, U f1 , 2, U g1 , 2 is the voltage of the filter; i t1 、2、i g1 , 2 are the currents output by GSC and filter respectively; u * DC2 for u DC2 The unit of rated value is 1 in steady state; Q f For U f2 Reactive power at measuring point; u n is the phase voltage amplitude at the grid connection point; R V 、X V is the virtual impedance; ω0 is the rated angular velocity; θ pll and θ are the phases at the outlets of the GFL-PMSG and GFM-PMSG filters, respectively. The subscripts “ref” and “dq” are used to indicate reference values ​​and parameters in dq coordinates.

[0085] The program includes the following steps:

[0086] Step 1: By establishing an equivalent circuit model and based on the multi-station short-circuit ratio calculation method, the transient overvoltage suppression mechanism of GFM-PMSG is revealed.

[0087] Adding or retrofitting traditional GFL-PMSG wind farms with GFM-PMSGs can improve the system's voltage support capability and transient overvoltage suppression capabilities. The voltage support capability and transient overvoltage suppression effectiveness of a renewable energy station can be quantified using the short circuit ratio (SCR). The calculation method for the SCR for multi-infeed systems is shown in Equation (2-1).

[0088]

[0089] Where: S aci is the grid-connected capacity of new energy station i; P i 、P j Corresponding to the active power injected by stations i and j respectively; Z ii , Z ij are the self-impedance of station i and the mutual impedance between stations i and j respectively.

[0090] (1) Transient overvoltage suppression mechanism of GFM-PMSG

[0091] To simplify the analysis, we take two units as an example and temporarily ignore the influence of grid-connected capacitors. Figure 3 As shown in the figure, when the wind farm is all GFL-PMSG, the short circuit ratio SCR of station i is i As shown in formula (2-2).

[0092]

[0093] Where: U i is the grid connection point voltage of station i; Z ii =Z Ti +Z i +Z1,Z ij =Z1, where Z Ti is the step-up transformer impedance, Z i is the line impedance of wind farm i, and Z1 is the AC line impedance.

[0094] After GFM-PMSG is connected to 35kV busbar through 0.69kV / 35kV step-up transformer, Figure 4 shown.

[0095] After GFM-PMSG is installed, the self-impedance and mutual impedance of station i change. At this time, the system short-circuit ratio SCR′ i Corrected to:

[0096]

[0097] The self-impedance of the i-th wind turbine is:

[0098]

[0099] The mutual impedance is:

[0100]

[0101] The ratio of mutual impedance to self impedance is:

[0102]

[0103] As shown in equations (2-4) and (2-6), installing a GFM-PMSG can reduce the self-impedance and the ratio of mutual impedance to self-impedance, thereby improving the system short-circuit ratio, i.e., SCR′ i >SCR i , enhance the voltage support capability and thus suppress the transient overvoltage after the fault.

[0104] (2) Transient overvoltage suppression mechanism of GFM-PMSG transformation

[0105] To analyze the impact of GFM-PMSG retrofits on transient overvoltages in wind farms, both GFM-PMSGs and GFL-PMSGs were connected in parallel to a 35kV busbar via a 0.69kV / 35kV step-up transformer. Port impedance models for the GFM-PMSG wind farm, GFL-PMSG wind farm, and equivalent power grid were established, and the equivalent impedance magnitudes of the GFL-PMSG and GFM-PMSG were obtained. The equivalent impedance of the GFL-PMSG was significantly higher than that of the GFM-PMSG.

[0106] When all units are GFL-PMSG, that is, Figure 4 The GFM-PMSG is replaced by GFL-PMSG, and the equivalent impedance of GFL-PMSG is Z′ S3 Greater than the GFM-PMSG equivalent impedance Z S3 , at this time, the self-impedance and mutual impedance of station i both change, and the self-impedance formula (2-4) should be corrected to:

[0107]

[0108] The ratio of mutual impedance to self-impedance (2-6) should be modified to:

[0109]

[0110] At this time, the system short circuit ratio R SC-Si Corrected to:

[0111]

[0112] As shown in Equations (2-7), (2-8), and (2-9), when the GFM-PMSG is replaced by the GFL-PMSG, the self-impedance increases, and the ratio of mutual impedance to self-impedance increases, resulting in a decrease in the short-circuit ratio, i.e., SCR″ i <SCR′ i Similarly, after transforming the GFL-PMSG into a GFM-PMSG, the self-impedance is reduced, the ratio of mutual impedance to self-impedance is reduced, and the system short-circuit ratio is improved, thereby enhancing the voltage support capability and suppressing transient overvoltages.

[0113] (3) Impact mechanism of system transient overvoltage on hybrid wind farms

[0114] In order to study the transient voltage characteristics of the hybrid wind farm grid-connected system, its equivalent value is simplified to Figure 5 The model shown in the figure is used for analysis. Since the line resistance is much smaller than the line inductance, its influence is ignored in the system modeling process.

[0115] Depend on Figure 5 It can be seen that the mathematical relationship between GFM-PMSG, GFL-PMSG and the voltage between the grid and PCC point during system steady-state operation can be expressed as:

[0116] Q ac =Q L +Q M +Q C (2-10)

[0117]

[0118] Among them, the longitudinal component and transverse component of the voltage drop are:

[0119]

[0120] From formula (2-12), we can see that the main factors affecting the change of the bus voltage include: GFL-PMSG active power P L , reactive power Q L 、GFM-PMSG active power P M , reactive power Q M And the line inductance X S Parameters such as transient overvoltage are closely related to factors such as system capacity, transmission line impedance, and GFM-PMSG ratio.

[0121] In addition, the control parameters of the GFM-PMSG and GFL-PMSG also affect the bus voltage level. A quantitative analysis of the parameter sensitivity of each influencing factor is performed, and the calculation formula is shown in Equation (2-13).

[0122] S p =ΔU peak / Ubase ×100% (2-13)

[0123] Where: ΔU peak is the peak change, U base is the voltage reference, S p is the normalized sensitivity coefficient, a positive value indicates that an increase in the parameter leads to an increase in overvoltage, while a negative value indicates the opposite.

[0124] Step 2: Study the influence of factors such as station layout and unit control on transient overvoltage, and determine the dominant factors affecting transient overvoltage.

[0125] The factors affecting the station layout of transient overvoltage are as follows:

[0126] (1) GFM-PMSG ratio

[0127] 1) Ratio of GFM-PMSG installation

[0128] The simulation conditions are set as follows: the output of a single wind turbine is 100% of the rated power, the number of GFL-PMSGs in operation is fixed at 60, and the proportion of GFM-PMSGs installed is 0%, 10%, 20%, 30%, 40%, and 50% respectively. The highest phase transient overvoltage waveform of the 35kV busbar of the wind farm under a three-phase short circuit fault is as follows: Figure 6 (a) shows the relationship between its proportion and transient overvoltage peak value. Figure 7 shown.

[0129] like Figure 6 (a) and Figure 7 As shown in Figure 1, as the proportion of GFM-PMSGs installed increases and the short-circuit ratio improves, the transient overvoltage peak shows a significant downward trend. When the proportion of GFM-PMSGs installed increases from 0% to 50%, the peak value drops from 2.787 pu to 2.427 pu, a decrease of 12.9%. This verifies the theory proposed in Section 1 that GFM-PMSGs suppress transient overvoltages by reducing impedance.

[0130] 2) Proportion of GFM-PMSG transformation

[0131] The simulation conditions are set as follows: the output of a single wind turbine is fixed at 100%, the number of wind turbines in operation is 60, the system capacity remains unchanged, and the proportion of GFM-PMSG transformation is set to 0%, 10%, 20%, 30%, 40%, and 50%. The highest phase transient overvoltage waveform on the wind farm grid-connected bus after a three-phase short circuit fault is as follows: Figure 6 (b) shows that the relationship between its proportion and transient overvoltage peak is as follows: Figure 7 shown.

[0132] like Figure 6 (b) and Figure 7As shown, the transient overvoltage peak value shows a monotonically decreasing trend with increasing grid modification proportion: when the proportion of GFM-PMSG modification increases from 0% to 50%, the overvoltage peak value decreases from 2.787 pu to 2.277 pu, a decrease of 18.3%. Compared with simply installing GFM-PMSG (peak value reduction of 12.9%), the modification solution has a more significant suppression effect. Therefore, the subsequent analysis is based on a 50% GFM-PMSG modification proportion.

[0133] (2) Total number of boot units

[0134] To analyze the impact of the total number of wind turbines on transient overvoltage, the single-unit output was fixed at 100%, the proportion of GFM-PMSG transformation was set at 50%, and the total number of GFM-PMSG and GFL-PMSG units in operation was set to 10, 20, 30, 40, 50, and 60 respectively for simulation. Connecting multiple wind turbines in parallel increases the system capacity, reduces the system equivalent impedance, and improves the system short-circuit ratio, thereby enhancing the ability to suppress transient overvoltage. Figure 8 and Figure 9 As shown in the figure, as the total number of powered-on devices increases, the overvoltage peak value decreases from 2.632 pu to 2.277 pu, a decrease of 13.5%.

[0135] (3) Line length

[0136] 1) 35kV line length

[0137] To explore the impact of 35kV line length, the single-unit output of fixed wind turbines is 100%, the GFM-PMSG transformation accounts for 50%, and the line lengths are set to 1, 2, 4, 6, 8, and 10km for simulation. Figure 10 (a) with Figure 11 Figure (a) shows that the transient overvoltage peak value is significantly positively correlated with line length: the inductive impedance of the line increases linearly with length, exacerbating the LC resonance effect and, consequently, the transient overvoltage. As the line length increases from 1 km to 10 km, the peak value increases from 2.044 pu to 2.434 pu, with a sensitivity coefficient of +16.0%. See Table 5 for details.

[0138] 2) 220kV line length

[0139] In order to compare and analyze the impact of the 220kV line length, the 220kV line lengths are set to 25, 50, 75, 100, 125, and 150km for simulation. Figure 10 (b) with Figure 11Figure (b) shows that the 220 kV line impedance is far from the resonant circuit, making a limited contribution to transient energy accumulation. Therefore, the 220 kV line length has a minimal effect on transient overvoltage. When the 220 kV line length increases from 25 km to 150 km, the overvoltage peak fluctuates between 2.249 and 2.277 pu, with a sensitivity coefficient of only -1.2%. See Table 5 for details.

[0140] A quantitative parameter sensitivity analysis of various influencing factors was conducted based on Equation (2-13). The calculated results are shown in Table 5, with the following key conclusions: 1) The dominant layout factors for transient overvoltage are the proportion of GFM-PMSGs and the length of the 35kV line, with corresponding Sp values ​​of -18.3% and +16.0%. For every 10% increase in the proportion of GFM-PMSGs, the overvoltage peak decreases by approximately 0.1 pu. This is due to the GFM-PMSG suppressing transient overvoltages by reducing the system's equivalent impedance and improving the short-circuit ratio. For every 1 km of 35kV line extension, the peak value increases by approximately 0.04 pu, primarily due to the linear increase in inductive impedance exacerbating the LC resonance effect. 2) Secondary factors primarily include the total number of wind turbines in operation, with a sensitivity coefficient of -13.5%. Other factors include the length of the 220kV line, with a sensitivity coefficient of -1.2%, which is negligible.

[0141] The factors affecting unit control of transient overvoltage are as follows:

[0142] (1)GFM-PMSG virtual impedance parameters

[0143] When the control strategies of GFL-PMSG and GFM-PMSG remain unchanged, analysis: 1) R v =0.001,

[0144] L v =0.000013; 2) R v =0.006, L v =0.000043; 3) R v =0.012, L v =0.000103; three parameters

[0145] Transient overvoltage at the 35kV busbar of the wind turbine.

[0146] like Figure 12 As shown in Figure 1 (a) and Table 1, increasing the virtual impedance will slightly increase the overvoltage peak, which is consistent with the influence of increasing the 35kV line length. The sensitivity coefficient is only +0.27%. The virtual impedance should be appropriately reduced during parameter optimization.

[0147] Table 1 Effect of GFM-PMSG virtual impedance parameters on transient overvoltage

[0148]

[0149] (2)GFM-PMSG voltage loop parameters

[0150] Figure 2 The closed-loop transfer function of the GFM-PMSG voltage loop is obtained as follows:

[0151]

[0152] Where: K p4M K is the GFM-PMSG voltage loop proportional coefficient; i4M K is the integral coefficient of the GFM-PMSG voltage loop, i4M =1 / T i4M ; s is a complex variable.

[0153] The relationship between its control parameters, control bandwidth and damping ratio is:

[0154]

[0155] Where: ω c-vm =2πf c-vm , f c-vm is the GFM-PMSG voltage loop control bandwidth; vm is the GFM-PMSG voltage loop control damping ratio.

[0156] From formula (2-15), we can see that the damping ratio and bandwidth of the GFM-PMSG voltage loop determine the response speed of the GFM-PMSG voltage loop. p4M When it increases, its bandwidth is improved, the response speed is accelerated, it can track the input signal faster, the damping ratio is increased, the system has no overshoot and no oscillation, thereby avoiding the aggravation of transient overvoltage.

[0157] When the control strategies of GFL-PMSG and GFM-PMSG remain unchanged, analysis: 1) K p4M =100, T i4M =0.3; 2)K p4M =10, T i4M =0.3; 3)K p4M =10, T i4M =3; transient overvoltage level at the 35kV busbar of the wind turbine under three parameters.

[0158] GFM-PMSG voltage loop proportional coefficient K p4M It plays a leading role in transient overvoltage suppression and increases K p4M It can significantly improve the dynamic response speed, thereby suppressing transient overvoltage. Figure 12 (b) and Table 2, K p4MIncreasing it from 10 to 100 can reduce the overvoltage peak from 2.244 pu to 1.921 pu, and the sensitivity coefficient reaches -14.4%.

[0159] Table 2 Influence of GFM-PMSG voltage loop parameters on transient overvoltage

[0160]

[0161] (3) GFL-PMSG current loop parameters

[0162] Figure 2 The closed-loop transfer function of the GFL-PMSG current loop is obtained as follows:

[0163]

[0164] Where: K p2L K is the GFL-PMSG current loop proportional coefficient; i2L K is the integral coefficient of the GFL-PMSG current loop, i2L =1 / T i2L .

[0165] The relationship between its control parameters, control bandwidth and damping ratio is:

[0166]

[0167] Where: ω c-il =2πf c-il , f c-il is the GFL-PMSG current loop control bandwidth; il is the GFL-PMSG current loop control damping ratio.

[0168] It can be seen from formula (2-17) that the damping ratio and bandwidth of the current loop determine the response speed and tracking accuracy of the voltage loop, thereby affecting the output voltage of the converter and indirectly affecting the transient overvoltage of the hybrid wind farm.

[0169] When the control strategies of GFL-PMSG and GFM-PMSG remain unchanged, analysis: 1) K p2L =10,

[0170] T i2L =0.0018; 2)K p2L =5, T i2L =0.0018; 3)K p2L =5, T i2L =0.0036; transient overvoltage level at the 35kV busbar of the wind turbine under three parameters.

[0171] like Figure 13 (a) and Table 3, K p2L With Ti2L Directly affects the adjustment accuracy, K p2L Reducing from 10 to 5 can reduce the overvoltage peak by 0.22%, while T i2L Increasing the time from 0.0018 to 0.0036s slightly worsens the overvoltage, with a sensitivity coefficient of +0.75%. The GFL-PMSG current loop parameters have little effect on transient overvoltage.

[0172] Table 3 Effect of GFL-PMSG current loop parameters on transient overvoltage

[0173]

[0174] (4) GFL-PMSG phase-locked loop parameters

[0175] Figure 2 The closed-loop transfer function of the GFM-PMSG voltage loop is obtained as follows:

[0176]

[0177] Where: K ppll is the phase-locked loop proportional coefficient; K ipll is the phase-locked loop integral coefficient, K i4M =1 / T i4M .

[0178] The relationship between its control parameters, control bandwidth and damping ratio is:

[0179]

[0180] Where: ω pll =2πf pll , f pll is the phase-locked loop control bandwidth; pll is the damping ratio of the phase-locked loop control.

[0181] From formula (2-19), we can see that when K ppll When it increases, its damping ratio increases, overshoot decreases, stability increases, and dynamic response speeds up, thereby avoiding the aggravation of transient overvoltage.

[0182] When the control strategies of GFL-PMSG and GFM-PMSG remain unchanged, analysis: 1) K ppll =200,K ipll =700;2)K ppll =120,K ipll =700;3)K ppll =120,K ipll =800; transient overvoltage levels at the 35kV busbar of the wind turbine under three parameters.

[0183] like Figure 12(b) and Table 4, K ppll With K ipll Determines the phase tracking accuracy and dynamic response speed. K ppll Increasing the R from 120 to 200 can reduce the overvoltage peak by 3.6%. Optimizing the phase-locked loop parameters can reduce reactive power fluctuations caused by phase errors and thus reduce transient overvoltages.

[0184] Table 4 Effect of GFL-PMSG phase-locked loop parameters on transient overvoltage

[0185]

[0186] The normalized sensitivity coefficient of formula (2-13) is used to quantitatively evaluate the influencing factors of each control parameter, as shown in Table 5. As shown in Table 5, the dominant control factor of transient overvoltage is the GFM-PMSG voltage outer loop proportional coefficient K p4M and the phase-locked loop ratio parameter K ppll . Increase the voltage outer loop gain K p4M It can significantly speed up the voltage regulation speed, thus suppressing transient overvoltage. p4M When the ratio increases from 10 to 100, the overvoltage peak value is reduced by 14.4%. Optimizing the phase-locked loop tracking accuracy can reduce reactive power fluctuations caused by phase errors, thereby suppressing transient overvoltages. ppll When the value increases from 120 to 200, the peak value decreases by 3.6%.

[0187] Table 5 Parameter sensitivity of transient overvoltage influencing factors

[0188]

[0189]

[0190] Step 3: Using the above influence rules, a coordinated suppression scheme for the comprehensive site layout and unit control of hybrid wind farms is proposed.

[0191] Based on the above research, the four-dimensional influencing factors of transient overvoltage in hybrid wind farms are as follows: Figure 14 As shown in the figure, (1) increasing the capacity of wind farms, by increasing the total number of units in operation (recommended ≥60 units), the overvoltage peak can be reduced by 13.5%; (2) optimizing the configuration of network units, when the proportion of GFM-PMSG transformation is increased to 50%, the system short-circuit ratio is improved, and the overvoltage peak can be reduced by 18.3%; (3) optimizing the line length, controlling the 35kV line length to ≤4km, to avoid voltage accumulation caused by low-frequency oscillation; (4) adjusting the control parameters, increasing the proportional coefficient K of the GFM-PMSG voltage outer loop p4M and the proportional coefficient K of the GFL-PMSG phase-locked loop ppll The peak value can be reduced by 14.4%.

[0192] In order to further suppress transient overvoltage, the present invention proposes the following solutions to the transient overvoltage problem caused by sudden changes in GFM-PMSG voltage amplitude and phase, GFL-PMSG control lag, and the inability of reactive compensation equipment to achieve instantaneous regulation during faults: Figure 15 The hybrid wind farm coordinated control strategy shown mainly includes fault detection, GFL-PMSG low voltage ride-through control, GFM-PMSG constant voltage control and leading reactive power removal control strategy.

[0193] Finally, combined with Figure 15 The four-dimensional dominant influencing factors of station layout and unit control are shown in the figure, and a coordinated suppression scheme integrating station layout and unit control is proposed as follows: Figure 16 As shown in the figure, the specific coordinated suppression scheme is as follows: increase the total number of startups (system expansion), increase the proportion of GFM-PMSG transformation, reduce the length of 35kV line, increase the GFM-PMSG voltage loop proportional coefficient and the GFL-PMSG phase-locked loop proportional coefficient, and adopt a coordinated control strategy of fault detection, GFM-PMSG constant voltage control and leading reactive power removal.

[0194] Application Examples

[0195] To verify the effectiveness of the proposed coordinated suppression scheme for integrated station layout and unit control, an electromagnetic transient model of the wind farm was established based on PSCAD / EMTDC. A three-phase short-circuit fault occurred on the 35kV busbar at 1.2-1.7s. Three typical scenarios were set for comparative analysis: a full GFL-PMSG, a hybrid of traditional GFL-PMSG and GFM-PMSG, and a hybrid wind power grid-connected system using the coordinated suppression scheme of the present invention.

[0196] Operating condition 1 - Full GFL-PMSG grid-connected system: The wind turbine output is fixed at 100% of the rated active power, the GFM-PMSG ratio is 0%, and the system capacity is 300MW.

[0197] Operating Condition 2: Traditional GFL-PMSG and GFM-PMSG hybrid wind power grid-connected system: The wind turbine output is fixed at 100%, the system capacity is 300MW, the GFM-PMSG modification accounts for 50%, and traditional control is adopted.

[0198] Working condition 3 - hybrid wind power grid-connected system using the collaborative suppression scheme of the present invention: the wind turbine output is fixed at 100%, the GFM-PMSG transformation accounts for 50%, and the system capacity is expanded to 500MW and the 35kV line length is reduced. The proportional coefficient of the GFM-PMSG voltage outer loop is increased to 100 and the proportional coefficient of the phase-locked loop is 200. The control adopts Figure 14 The cooperative control strategy shown.

[0199] Figure 17 The figure is a comparison of transient overvoltages under three working conditions, and the data is shown in Table 6. The transient overvoltages under the three working conditions are analyzed as follows: (1) Peak suppression effect: The peak voltage of working condition 1 is 2.787 pu. In working condition 2, the peak value is reduced to 2.277 pu due to the modification of GFM-PMSG, with a reduction of 18.3%. In working condition 3, the peak value is reduced to 1.140 pu by adopting the collaborative suppression scheme of the present invention, with a reduction of 59.1%; (2) Dynamic characteristics: Working condition 1 shows a continuous oscillation characteristic, working condition 2 has less oscillation than working condition 1, working condition 3 has the shortest dynamic adjustment time and almost no oscillation, and the three-phase voltage cycle is basically consistent with the steady state; (3) Harmonic characteristics: The harmonic component of the transient overvoltage in working condition 3 is significantly lower than that in working conditions 1 and 2.

[0200] In summary, the collaborative suppression scheme of the present invention not only greatly reduces the peak value of transient overvoltage, but also significantly reduces the high-frequency component of transient overvoltage, and has a significant effect on suppressing transient overvoltage in the hybrid wind power grid-connected system after the short-circuit fault is cleared.

[0201] Table 6 Quantitative analysis of transient overvoltage suppression effect under three working conditions

[0202]

[0203] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for collaboratively suppressing transient overvoltage in a hybrid wind farm using grid-type direct-drive wind turbines, characterized in that: The following steps are involved: Step 1: Build an equivalent model to describe the electrical characteristics of key wind farm equipment and extract electrical parameters used to quantify the system's transient voltage support capability. These electrical parameters include the wind farm's self-impedance, mutual impedance, and their corresponding short-circuit ratio. Step 2: Based on the electrical parameters extracted from the electrical equivalent model, analyze the impact of different controller parameters and electrical structure configurations on transient voltage response performance, and identify the control factors that are highly correlated with transient overvoltage behavior; Step 3: Based on the control factors identified in step 2, jointly configure the wind turbine grid configuration ratio, electrical connection structure and controller parameters to develop a coordinated suppression control strategy for optimizing the system voltage response performance; Step 4: When an abnormal system operating state is detected, dynamically execute wind turbine operating mode switching, controller parameter tuning, and control the branch switching state of the reactive power compensation device according to the response conditions set in the coordinated control strategy and real-time monitoring data; Step 5: Based on the continuous monitoring results of voltage response performance, evaluate and optimize the controller parameter configuration and implement control strategy updates through state scheduling logic or adaptive mechanism.

2. The method according to claim 1, characterized in that The construction of the electrical equivalent model includes: The grid-connected wind turbines, grid-following wind turbines, step-up transformers, and collection lines are equivalently modeled using lumped parameters. The wind farm self-impedance and mutual impedance parameters are extracted, and a quantitative indicator of the system voltage support capability is established based on the following short-circuit ratio calculation formula: Where: S aci is the grid-connected capacity of new energy station i; P i 、P j Corresponding to the active power injected by stations i and j respectively; Z ii 、Z ij are the self-impedance of station i and the mutual impedance between stations i and j respectively; The short-circuit ratio is used to quantify the difference in voltage support capacity of a wind farm before and after the grid-type wind turbines are connected. The introduction of grid-type wind turbines can reduce the ratio of self-impedance to mutual impedance, thereby improving the short-circuit ratio and suppressing transient overvoltages.

3. The method according to claim 2, characterized in that The electrical parameters used to quantify the system transient voltage support capability also include a normalized sensitivity coefficient, which is used to evaluate the influence of control parameters and structural configuration on voltage response indicators. The normalized sensitivity coefficient is expressed as follows: S p =ΔU peak / U base ×100% Where: ΔU peak is the peak change, U base is the voltage reference, S p is the normalized sensitivity coefficient, a positive value indicates that an increase in the parameter leads to an increase in overvoltage, while a negative value indicates the opposite.

4. The method according to claim 1, wherein The process of identifying the control factors highly correlated with transient overvoltage behavior includes: Through simulation modeling or fault disturbance simulation based on the electrical equivalent model, the influence of the access ratio of wind turbines with different grid configurations, electrical line parameters and key controller parameters on the short-circuit ratio, sensitivity coefficient and transient voltage peak is evaluated, and the factors whose impact on the system transient response exceeds the preset sensitivity threshold are determined as control factors.

5. The method according to claim 1, wherein The formulation of the collaborative inhibitory control strategy includes: According to the sensitivity ranking results of the control factors, the access ratio of grid-connected wind turbines in the wind farm, the single-circuit length of the 35kV collection line, the proportional gain coefficient of the voltage controller and the proportional gain coefficient of the phase-locked loop are jointly configured to form a control parameter configuration table covering typical fault scenarios for response calls under different transient overvoltage risk levels.

6. The method according to claim 1, characterized in that The response process when an abnormal system operation state is detected includes: Based on the preset response conditions in the collaborative suppression control strategy, when the bus voltage change rate exceeds the set threshold or the output current of the wind turbine exceeds the rated value, the control mode of the grid-connected wind turbine is triggered to switch to constant voltage control, and the grid-following wind turbine performs low voltage ride-through control. At the same time, the SVG or SVC reactive compensation device is controlled to exit the capacitor branch operation and is delayed to be re-activated after the voltage recovers.

7. The method according to claim 6, characterized in that The control objectives of the response process include: The transient overvoltage peak is suppressed to no more than 1.2 times the rated voltage (pu), the voltage recovery time is controlled within 100 milliseconds, the high-frequency disturbance energy does not exceed 20% of the steady-state level before the fault, and the system voltage waveform is stable within 10 power frequency cycles without continuous oscillation.

8. The method according to claim 7, characterized in that The parameter configuration of the wind turbine controller includes: The proportional coefficient of the voltage outer loop controller of the grid-type wind turbine generator set is set to no less than 100, and the integral time constant is set to no more than 0.3 seconds; the proportional coefficient of the phase-locked loop of the grid-following wind turbine generator set is set to no less than 200, and the integral coefficient is set to no less than 700 per second; the overall response characteristics of the controller meet the stability requirements of a damping ratio of no less than 0.7 and a bandwidth of no less than 100 Hz.

9. The method according to claim 8, characterized in that The operating state control of the reactive power compensation device includes: When it is detected that the bus voltage change rate exceeds the set threshold, the SVG or SVC reactive compensation device suspends its capacitor branch output; when the bus voltage returns to below the set voltage and remains stable for a time that meets the set threshold, the capacitor branch operation is put back into operation.

10. The method according to claim 9, characterized in that The evaluation of the system transient response performance and the optimization of controller parameters include: The voltage peak, recovery time, and high-frequency disturbance energy indicators are collected and analyzed. When any indicator deviates from the preset target value, the preset control parameter combination in the collaborative control strategy is called for switching and optimization.

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