A control method and system for stability of a sending-end power grid considering wind power access

Abstract

The application provides a control method and system for stability of a sending terminal power grid after wind power is connected, and is based on equivalent external characteristics of a wind turbine at different moments and the equal-area rule, and adopts a wind turbine equivalent capacity replacement synchronous machine mode and a wind turbine direct connection mode to change wind power penetration, so as to study internal influence mechanism of different influencing factors such as different wind turbine connection modes, capacity proportions and connection positions on system power angle stability, summarize relevant influence rules, determine a suitable wind power connection proportion and an optimal wind turbine connection position, effectively promote new energy consumption, reduce waste of abandoned wind power, reduce power grid operation risk, and improve power grid stability margin and safe operation level.

Description

Technical Field

[0001] This invention belongs to the field of power grid control technology and relates to a control method and system that takes into account the impact of wind power integration on the stability of the sending-end power grid. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With the rapid increase in demand for clean energy power generation, various types of clean energy, such as hydropower, wind power, and photovoltaic power, have been developed on a large scale. Among them, wind power is one of the more mature power generation methods in renewable energy development and utilization, with certain large-scale development and commercial prospects. Large-scale wind power grid connection will have significant randomness and intermittency, relatively low controllability, difficulty in regulating active power output, and large fluctuations. At the same time, wind power grid connection increases the number of power electronic interfaces in the power system, which will change the fundamental stability mechanism of the power system and bring huge challenges to the stability of the power system. On the other hand, for traditional power generation and wind turbine cluster joint transmission systems, the difference in power characteristics between wind turbines and synchronous units makes the stability problem of the system more complex. Among them, many factors such as the connection method of wind turbines, the proportion of wind power connected, and the connection location of wind turbines will all have a certain impact on the stability of the sending-end grid.

[0004] Currently, the main technology for analyzing the impact of wind power on system transient stability is time-domain simulation analysis. This method solves the system's differential algebraic equations to obtain the trajectory of changes in system algebraic and state variables over time. Among various evaluation methods, time-domain simulation is often considered reliable and is the most fundamental method for studying power system transient stability. Many studies on the impact of wind turbine grid connection on system transient stability are based on time-domain simulation analysis; however, different conclusions may be drawn for different systems. However, time-domain simulation analysis lacks in-depth analysis of the intrinsic nature of changes in system transient stability characteristics. Therefore, revealing the mechanism of these changes is one of the key challenges and difficulties in this research. Furthermore, previous studies using impedance analysis to simplify wind turbine grid connection only considered the impact of single turbine output changes on system stability, lacking a comparative analysis of the intrinsic mechanism of the impact of changes in permeability at different connection locations and methods during fault periods on system transient stability. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a control method and system that considers the impact of wind power integration on the stability of the sending-end power grid. Based on the equivalent external characteristics and equal area rule of wind turbines at different times, this invention employs two integration methods—wind turbine capacity replacement of synchronous machines and direct wind turbine integration—to change the wind power penetration rate. This study investigates the intrinsic influence mechanism of different factors, such as wind turbine integration methods, capacity ratios, and integration locations, on the system's power angle stability, summarizes the relevant influence laws, and determines the appropriate wind power integration ratio and optimal wind turbine integration location. The aim is to effectively promote the consumption of new energy, reduce wind curtailment waste, lower grid operation risks, and improve grid stability margin and safe operation levels.

[0006] According to some embodiments, the present invention adopts the following technical solution:

[0007] A control method considering the impact of wind power integration on the stability of the sending-end power grid includes the following steps:

[0008] For target systems with wind turbine grid connection, a wind power penetration rate index is introduced, and equivalent models considering wind power penetration rate are constructed under different operating conditions. The equivalent models are then integrated into the power grid.

[0009] For the connection of wind turbines during the fault period, different connection methods of wind turbines to the grid are considered. The wind power penetration rate is changed under the connection method to determine the allocation scheme of the optimal wind power penetration rate under different connection methods.

[0010] Keeping the wind turbine connection method unchanged, gradually change the wind turbine connection location, introduce the wind turbine connection location index, calculate its impact on the synchronous machine power characteristics and the transient stability trend, and determine the optimal wind turbine connection location.

[0011] As an alternative implementation, the following steps are also included:

[0012] Using the limit cut-off time and limit cut-off angle as evaluation indicators to reflect the changing trend of transient power angle stability, the optimal wind power penetration rate and the best wind turbine connection location that can enhance the power angle stability of the system under different conditions are verified.

[0013] As an alternative implementation method, the specific process of constructing equivalent models under different operating conditions and considering wind power penetration rate includes: analyzing the wind turbine using a doubly fed wind turbine model, transmitting new energy to the receiving end single unit infinite power supply via a high-voltage transmission line, with the system wind power penetration rate being k, simplifying and equipping the wind turbine under different operating conditions, and analyzing the impact of wind power access on the power angle stability of the sending end synchronous machine.

[0014] As an alternative implementation, the different operating conditions include before the fault, during the fault, and after the fault is cleared.

[0015] As a further step, during modeling, before the system failure, the wind turbine only outputs active power to the system, at which point the doubly-fed wind turbine is equivalent to a constant negative resistor;

[0016] During system failures, the doubly fed wind turbine is equivalent to a variable negative resistor and a variable negative reactance connected in parallel at the grid connection port, and its value is related to the voltage and active and reactive power output at the grid connection point.

[0017] In the later stages of fault clearing, the active and reactive power outputs of the doubly-fed wind turbine reached constant values, basically consistent with those before the fault.

[0018] As alternative implementation methods, the access methods include the wind turbine equal capacity replacement synchronous machine method and the wind turbine direct access method. In the wind turbine equal capacity replacement synchronous machine method, the total active power output of the sending-end synchronous machine and the wind turbine remains unchanged. Under the condition of ensuring that the system does not become unstable and high voltage ride-through fails, the active power output of the wind turbine gradually increases to replace the synchronous machine. In the wind turbine direct access method, the output of the sending-end synchronous machine remains unchanged, and the active power output of the wind turbine is gradually increased to increase the wind power penetration rate.

[0019] As an alternative implementation method, the specific process of determining the optimal wind power penetration rate allocation scheme under different access methods includes: based on the system equivalent model of wind power penetration rate under different public conditions, calculating the self-impedance and transfer impedance under the corresponding conditions, substituting them into the synchronous machine power characteristic equation, obtaining the offset change of the synchronous machine power angle characteristic curve, determining the acceleration area and deceleration area changes by the equal area rule, and determining the optimal wind power penetration rate that can keep the system stable under different access methods.

[0020] As an alternative implementation method, the specific process for determining the optimal wind turbine connection location includes: keeping the wind turbine connection method unchanged, gradually changing the wind turbine connection location using an equal capacity replacement method, with the connection location gradually moving away from the sending-end synchronizing machine and closer to the receiving-end infinite power source, obtaining the system equivalent model and the sending-end synchronizing machine power characteristic equation after considering the wind turbine connection location index, calculating the self-impedance and mutual impedance of the system model after the doubly-fed wind turbine generator, substituting them into the synchronizing machine power characteristic equation to obtain the shift change of the synchronizing machine power angle characteristic curve, determining the changes in acceleration area and deceleration area using the equal area rule, obtaining the system sending-end transient stability trend, and thus determining the optimal wind turbine connection location under the actual system allowable operating conditions.

[0021] A control system that considers the impact on the stability of the sending-end power grid after wind power integration includes:

[0022] The equivalent model construction module is configured to introduce the wind power penetration rate index for target systems containing wind turbine grid connection, construct equivalent models under different operating conditions and after considering the wind power penetration rate, and integrate the equivalent models into the power grid.

[0023] The optimal wind power penetration rate determination module is configured to consider different grid connection methods for wind turbines during a fault, change the wind power penetration rate under different connection methods, and determine the optimal wind power penetration rate allocation scheme under different connection methods.

[0024] The optimal wind turbine access location determination module is configured to keep the wind turbine access method unchanged, gradually change the wind turbine access location, introduce wind turbine access location index, calculate its impact on the synchronous machine power characteristics and the transient stability trend, and determine the optimal wind turbine access location.

[0025] As an alternative implementation, a verification module is also included, which is configured to use the limit cut-off time and limit cut-off angle as evaluation indicators to reflect the changing trend of transient power angle stability, thereby verifying the optimal wind power penetration rate and the best wind turbine connection location that can enhance the system power angle stability under different conditions.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] This invention proposes a control method that considers the impact of wind power integration on the stability of the sending-end power grid. Based on the transient characteristics of doubly-fed induction generator (DFIG) wind turbines, the method considers the wind power penetration rate parameter k and the turbine grid connection location parameter m, and then simplifies the grid-connected wind turbines under different operating conditions, transforming them into an equivalent impedance model with respect to the penetration rate parameter k and the turbine grid connection location parameter m.

[0028] This invention considers the impact of changes in wind power penetration rate on the transient stability of the system under different wind turbine connection methods, rather than a single wind turbine connection method. In this way, different optimal wind power penetration rates that are beneficial to the transient stability of the system can be selected under different operating conditions, which solves the problem of absorption caused by high proportion of wind power grid connection, reduces wind curtailment waste, and improves the stability margin and safe operation level of the system.

[0029] This invention considers the impact of changes in wind turbine connection location on system transient stability, and comprehensively analyzes the interaction between wind turbine grid connection location, wind power penetration rate and transient stability, to obtain a solution for providing the optimal wind turbine connection location that is conducive to system transient stability. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0031] Figure 1 This is a power system model that includes wind turbines.

[0032] Figure 2 This is the equivalent circuit diagram of the system under stable operating conditions with a wind power ratio of k.

[0033] Figure 3 The equivalent circuit diagram for a fault is given, where the proportion of wind power in the system is k.

[0034] Figure 4 To change the equivalent circuit during a fault in the wind turbine connection location.

[0035] Figure 5 The power angle curve of the fan before the fault.

[0036] Figure 6 The curve shows the capacity replacement access curve for wind turbines during the fault period.

[0037] Figure 7 The power angle curve is directly connected to the fan during the fault period.

[0038] Figure 8 The power angle curve for the wind turbine connection after fault clearance.

[0039] Figure 9 The power angle curve is adjusted to change the fan connection position during a fault.

[0040] Figure 10 This is a power system model that includes wind power transmission.

[0041] Figure 11 The power angle curves of synchronous machines with different permeability under equal capacity replacement.

[0042] Figure 12 The power angle curves of the synchronous machine with different penetration rates under direct access.

[0043] Figure 13 The curves represent the transient stability changes of the busbars at different grid connection locations.

[0044] Figure 14 This is a three-dimensional surface diagram showing the relationship between wind power penetration rate and ultimate cut-off time at the grid connection location of the wind turbine. Detailed Implementation

[0045] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0046] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0047] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0048] Example 1

[0049] Power systems containing doubly fed wind turbines, such as Figure 1 As shown, after the doubly fed wind turbine is connected to the grid, the output power characteristic equation of the synchronous generator is given by formula (1).

[0050]

[0051] In the formula, E is the internal electromotive force of the synchronous generator; U is the voltage at the infinite bus of the single unit; δ is the angle between the internal electromotive force E of the synchronous generator and the voltage U at the infinite bus of the single unit; Z 11 θ 11 Z represents the self-impedance of the synchronous generator in the system and its phase angle; 12 θ 12 Let be the transfer impedance and phase angle of the synchronous generator in the system.

[0052] Step (1): For a system with wind turbines connected to the grid, based on the transient characteristics of the wind turbines, the wind power penetration rate index k is introduced. The system is then evaluated under various operating conditions, including before the fault, during the fault, and after the fault is cleared. The wind turbines are simplified and converted into equivalent models with different impedances and connected to the grid.

[0053] It can be divided into the following steps:

[0054] (1.1) Under stable system operation conditions (including before and after the fault), the wind turbine only outputs active power to the system. At this time, the doubly-fed induction generator can be equivalent to a constant negative resistor r. F Introducing the wind power penetration rate k, the increase in wind power penetration rate is achieved by reducing the capacity of the synchronous generator. At this point, the equivalent circuit of the system is as follows: Figure 2 As shown. Where x d For the internal reactance of the synchronous machine, x T It is the transformer reactance, x L It is the line equivalent reactance, P F For the active power output of the doubly-fed induction generator (DFIG), PCC is the grid-connected bus of the wind turbine, U PCC It is the grid-connected bus voltage of the wind turbine, and the equivalent internal reactance of the sending-end system is jx1 = jx d +jx TAt this point, the self-impedance and mutual impedance of the synchronous generator are obtained as follows:

[0055] Self-impedance:

[0056]

[0057] in:

[0058]

[0059]

[0060] Mutual impedance:

[0061]

[0062] in:

[0063]

[0064] d=(x T +x d ) / (1-k)+x L (5)

[0065] (1.2) During a system failure, the doubly-fed fan is equivalent to a variable negative resistor r. F and a variable negative reactance x F Connected in parallel to the grid bus, with wind power penetration rate k introduced, the system equivalent circuit is as follows: Figure 3 As shown, Q F For the reactive power output of the doubly-fed generator unit, the self-impedance and mutual impedance of the synchronous generator are obtained as follows:

[0066] Self-impedance:

[0067]

[0068] in:

[0069]

[0070]

[0071] Mutual impedance:

[0072]

[0073] in:

[0074]

[0075]

[0076] After obtaining the simplified system model in step (2), the connection of wind turbines during the fault period is considered in terms of different connection methods of wind turbines to the grid, namely, the wind power penetration rate under the two connection methods of wind turbines replacing synchronous machines with equal capacity and wind turbines directly connected. Based on the power characteristic equation of the sending end synchronous machine, the influence of the change of penetration rate on the power characteristics of the synchronous machine under different connection methods is obtained. The power angle curve after the synchronous machine deflection is obtained, and its transient stability change trend is analyzed. The optimal wind power penetration rate allocation scheme that is conducive to the transient stability of the system under different connection methods of wind turbines is obtained.

[0077] In step (2), we consider different grid connection methods for wind turbines, namely, the wind power penetration rate is changed under two connection methods: wind turbines with equal capacity replacing synchronous machines and wind turbines directly connected. That is, based on the above step (1.2), we calculate the wind power penetration rate k by changing the connection method:

[0078] Step (3): Keep the wind turbine access method unchanged, gradually change the wind turbine access position, introduce the wind turbine access position index m, obtain the system equivalent model and the power characteristic equation of the sending end synchronous machine after considering the wind turbine access position index m, calculate its impact on the synchronous machine power characteristics and the transient stability change trend, and obtain the optimal wind turbine access position solution that can guarantee the transient stability of the system.

[0079] In step (3), during a system failure, the doubly-fed fan is equivalent to a variable negative resistor r. F and a variable negative reactance x F Connected in parallel to the grid bus, in Figure 1 By changing the wind turbine connection location on the transmission line and introducing the wind turbine grid connection location parameter m, the equivalent circuit of the system is as follows: Figure 4 As shown, the self-impedance and mutual impedance of the synchronous generator are obtained as follows:

[0080] Self-impedance:

[0081]

[0082] in:

[0083]

[0084]

[0085] Mutual impedance:

[0086]

[0087] in:

[0088]

[0089]

[0090] μ=x1 / (1-k)+mx L (14)

[0091]

[0092] Since 0≤k<1 and 0≤m≤1, the transfer impedance between the synchronous machine and the infinite system decreases as m increases, causing the synchronous machine's power angle curve to shift upward, increasing electromagnetic power and decreasing acceleration area.

[0093] In summary, by obtaining the different self-impedance and mutual impedance of the sending-end synchronous generator under different operating conditions, and substituting them into the synchronous generator power characteristic equation, the power angle characteristic curves and their offsets (changes in acceleration and deceleration area) under different operating conditions can be obtained. By applying the equal area rule, the influence mechanism of different influencing factors on the power angle stability of the sending end can be summarized to control the stability of the sending end of the system.

[0094] The technical solution of the present invention will be further described with reference to specific embodiments.

[0095] Taking a system with centralized access of doubly-fed induction generator (DFIG) wind turbines as the object, this paper uses the electromechanical transient simulation software ADPSS to build a three-turbine, two-zone system model to illustrate the feasibility and effectiveness of the proposed method. Figure 10 As shown: G1 is a synchronous generator, and G3 is a doubly-fed induction generator (DFIG). The power from conventional power generation and wind power at the sending end is transmitted to the receiving end's single-unit infinite bus system via a high-voltage line. The synchronous generator adopts a second-order classical model, and the wind turbine is a DFIG-type wind turbine unit.

[0096] The generator transient reactance is 0.265 pu, the transformer impedance is 0.02 J, and the impedance of each line segment is 0.001 + 0.007 J. Relevant data and voltage levels for each bus node in the system are shown in Table 1. The generator active and reactive power output P under different operating conditions is applied. F Q F The equivalent internal reactance of the sending-end system, the equivalent reactance of the line, and the corresponding self-impedance of the synchronous machine, the self-impedance phase angle, the transfer impedance between the self-impedance phase angle and the system end, and their phase angles are calculated respectively. Substituting these into the synchronous machine output power characteristic equation, the synchronous machine power angle characteristic curves under different operating conditions can be obtained. Figure 5-9 As shown in the figure, the optimal wind power penetration rate and the best access location are obtained under different access methods that enhance the transient stability of the system, based on the changes in the offset or acceleration / deceleration area.

[0097] Figure 5 In the middle: Connect the doubly-fed fan before the fault occurs to ensure the mechanical power P output by the prime mover. TThe doubly-fed induction generator (DFIG) remains unchanged, and the equivalent negative resistance of the grounded turbine is maintained. Before the turbine is connected, the synchronous motor operates at point a with a power angle of δ0. The connection of the wind power causes the synchronous motor's power angle curve to shift to the right and downward to a certain extent, shifting to the right by Δα. 12 Angle shifted downwards Δ|E 2 sinα 11 / Z 11 The amplitude of |. From equation (5), the wind power penetration rate k is positively correlated with both the real and imaginary parts of the mutual impedance, and the phase angle of the mutual impedance is 0° < θ. 12 <90°, therefore the complementary angle of mutual impedance α 12 =90°-θ 12 >0°, positively correlated with wind power penetration rate k. Therefore, as the wind power ratio k increases, the transfer impedance between the synchronous machine and the infinite bus system increases, Δα 12 The greater the increase in the power angle, the greater the downward and rightward shift of the synchronous machine's power angle curve, and the worse the system's static power angle stability becomes.

[0098] Figure 6 In the context of a fault, a doubly-fed induction generator (DFIG) is equivalent to a grounded negative resistance and negative reactance connected in parallel. Figure 6 In this system, the doubly-fed induction generator (DFIG) wind turbines are connected to the grid using an equal-capacity replacement method. Before grid connection, the prime mover outputs mechanical power P. T1 The initial operating point of the synchronous machine is point h, and the power angle is δ. 01 After the fault occurred, the synchronous motor's power angle characteristic curve changed to P. G2 At this point, the mechanical power output of the prime mover is greater than the electromagnetic power of the synchronous machine, thus generating a large excess power. Under the action of the excess torque, the generator rotor accelerates, and the rotor moves to δ c When the fault is cleared, the acceleration area of ​​the synchronous motor's power angle curve is S. bfgh After the fault was cleared, the synchronous motor power angle characteristic curve returned to P. G1 At this time, the mechanical power output of the prime mover is less than the electromagnetic power of the synchronous machine, and the rotor undergoes deceleration motion. The maximum usable deceleration area is S. abc By employing an equal-capacity replacement method, the output mechanical power of the prime mover after the wind turbine is connected becomes P. T2 (k = 30%), at this time the acceleration area is S femn The maximum deceleration area is S ade The deceleration area is significantly increased, which is determined by the equal area rule, thus enhancing transient stability. Furthermore, calculations show that the larger the k value, the higher the wind power penetration rate, and the better the transient stability.

[0099] Figure 7 In the middle: During the fault, the wind turbine is directly connected to the grid, and the mechanical power P output by the prime mover is... T Before wind power is connected, the acceleration area of ​​the synchronous motor's power angle curve remains unchanged at S. abce The deceleration area is S gbfAfter wind power is connected, the area will increase to S. abcd However, the maximum available deceleration area remains unchanged. According to the equal area rule, the transient stability deteriorates. Furthermore, calculations show that the larger the k value, the higher the wind power penetration rate, and the worse the transient stability.

[0100] Figure 8 In the later stages of fault clearing, the connection of wind power caused the synchronous motor power angle curve to shift to the right and downward to a certain extent. When the wind turbine is connected and the wind power ratio k increases from 30% to 50%, the deceleration area of ​​the power angle curve gradually decreases, and the system power angle stability gradually deteriorates.

[0101] Figure 9 In the middle: When k=30%, the wind turbine connection position is changed, and the wind turbine grid connection position changes from the initial position of line L3 (m=0) to the 50% position (m=50%). The acceleration area of ​​the power angle curve changes from S abcd Reduce to S abe Transient stability is enhanced. Calculations show that, for the same k value, the larger the m value, i.e., the closer the wind turbine is to the infinite power source, the better it is for the system's transient stability.

[0102] Meanwhile, on the other hand, this paper designs three schemes: Case 1 considers changing the wind power penetration rate under the method of replacing synchronous machines with wind turbines of equal capacity; Case 2 considers changing the wind power penetration rate under the method of direct wind turbine connection; Case 3 considers the interaction between wind turbine grid connection location, wind power penetration rate and transient stability when the wind turbine connection location is constantly changed.

[0103] In Case 1, considering the replacement of synchronous machines with wind turbines of equal capacity, the wind power penetration rate is changed. That is, the total active power output of the sending-end synchronous machine and the wind turbine remains unchanged, with a total output of 1200MW. Under the premise of ensuring system instability and high-voltage ride-through failure, the active power output of the wind turbine gradually increases to replace the synchronous machine. A three-phase short-circuit fault occurs on the transmission line at 3 seconds. The power angle curves of the synchronous machines with different penetration rates and their corresponding limit cut-off times and limit cut-off angles are shown below. Figure 11 As shown in Table 2, when replacing synchronous machines with wind turbines of the same capacity, as the penetration rate of wind power increases, the first swing angle decreases, the fault limit clearing time increases, the limit clearing angle increases, and the transient stability of the system is enhanced.

[0104] Using Case 2, which considers changing the wind power penetration rate under the direct wind turbine connection method, i.e., keeping the output of the sending-end synchronous machine constant at 600MW, and gradually increasing the active power output of the wind turbine to increase the wind power penetration rate, a three-phase short-circuit fault occurs in the transmission line at 3s. The synchronous machine power angle curves for different penetration rates and their corresponding limit cut-off times and limit cut-off angles are shown below. Figure 12According to Table 3, when wind power is directly connected to the sending-end system, as the wind power penetration rate increases, the first swing angle increases, the fault limit clearing time decreases, the limit clearing angle decreases, and the system transient stability weakens.

[0105] When using Case 3, firstly, under the same wind power penetration rate of 30%, a three-phase short-circuit fault occurs on bus 3 after 3 seconds. The wind turbine connection location is gradually changed on the transmission line, i.e., the value of the wind turbine grid connection location parameter m is changed. The corresponding changes in the transient stability are shown in Table 4. Secondly, when the wind turbine grid connection bus locations are selected as bus G1, bus 1, and bus 2 in sequence, an equal-capacity replacement method is used to change the wind power penetration rate. The corresponding changes in the transient stability are shown in Table 4. Figure 13 and Figure 14 As shown, the larger the value of the wind turbine grid connection location parameter m, the longer the cut-off time and the larger the cut-off angle, which is more conducive to the transient stability of the system. When the wind turbine grid connection location is bus G1, the cut-off time remains basically unchanged with the increase of the wind power ratio. However, when the wind turbine grid connection location is bus 1 or bus 2, the change in wind power penetration rate has a significant impact on the cut-off time, and the cut-off time increases with the increase of penetration rate. Moreover, under the same wind power penetration rate, the cut-off time of the doubly-fed induction generator (DFIG) wind turbine grid connection at bus G1, bus 1, and bus 2 increases sequentially, and the transient stability of the system is enhanced. That is, in studying different operating conditions of changing the wind turbine connection location, the closer the wind turbine grid connection location is to the infinite power source, the more significant the impact of wind power penetration rate on transient stability. Moreover, under the same wind power ratio, the closer the grid connection location is to the infinite power source, the longer the cut-off time, which is more conducive to the transient stability of the system.

[0106] Table 1 contains relevant data for system bus nodes.

[0107]

[0108] Table 2 Transient stability of different permeability rates under equal capacity replacement method

[0109]

[0110] Table 3 Transient stability at different penetration rates under direct access methods

[0111]

[0112] Table 4 Transient stability of parameter m at different wind turbine grid connection locations

[0113]

[0114] In summary, for power systems with wind power integration, the following conclusions can be drawn from the results:

[0115] (1) Under stable operating conditions, the connection of wind power will deteriorate the static power angle stability of the system, and the stability deterioration will be more severe as the wind power penetration rate increases. Therefore, under stable operating conditions, the connection of wind power should be reduced as much as possible while meeting the actual operating conditions.

[0116] (2) When replacing the synchronous machine with a wind turbine of equal capacity during a fault, as the penetration rate of connected wind power increases, the first swing angle decreases, the fault clearance time increases, the clearance angle increases, and the system's transient stability is enhanced. Therefore, when replacing the synchronous machine with a wind turbine of equal capacity during a fault, the wind power penetration rate should be increased as much as possible while meeting actual operating conditions to facilitate system transient stability. The optimal wind power penetration rate for the system is approximately 80%. However, the wind power penetration rate should not be too high; if it exceeds 80%, the system will experience high-voltage ride-through failure.

[0117] (3) When wind turbines are directly connected to the sending-end system during a fault, the first swing angle increases with the increase of wind power penetration, the fault clearance time decreases, the clearance angle decreases, and the system's transient stability weakens. Therefore, when wind turbines are directly connected during a fault, the connection of wind power should be minimized as much as possible while meeting actual operating conditions, which is beneficial to the system's transient stability.

[0118] (4) When considering the location of the wind turbine connection, under the same wind power ratio, the closer the grid connection location is to the infinite power source, the longer the ultimate disconnection time and the larger the ultimate disconnection angle, which is more conducive to the transient stability of the system. Therefore, during a fault, the wind turbine connection location should be as close as possible to the receiving end infinite power source under the actual operating conditions (in the example selected by the method of this invention, the optimal wind turbine connection location is bus 2), and the stronger the transient stability of the system.

[0119] The control analysis method proposed in this invention can provide optimal selection schemes for the stability of the control system and the improvement of the grid's transient stability margin, including the optimal wind power penetration rate and the optimal wind access location under different operating conditions, based on actual operating conditions and conditions.

[0120] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A control method considering the impact of wind power integration on the stability of the sending-end power grid, characterized in that, Includes the following steps: For target systems with wind turbine grid connection, a wind power penetration rate index is introduced, and equivalent models considering wind power penetration rate are constructed under different operating conditions. The equivalent models are then integrated into the power grid. For the connection of wind turbines during the fault period, different connection methods of wind turbines to the grid are considered. The wind power penetration rate is changed under the connection method to determine the allocation scheme of the optimal wind power penetration rate under different connection methods. Keeping the wind turbine connection method unchanged, gradually changing the wind turbine connection location, introducing the wind turbine connection location index, calculating its impact on the synchronous machine power characteristics and the transient stability trend, and determining the optimal wind turbine connection location. The specific process for determining the optimal wind turbine connection location includes: keeping the wind turbine connection method unchanged, gradually changing the wind turbine connection location using the equal capacity replacement method, with the connection location gradually moving away from the sending-end synchronous machine and closer to the receiving-end infinite power source, obtaining the system equivalent model and the power characteristic equation of the sending-end synchronous machine after considering the wind turbine connection location index, calculating the self-impedance and mutual impedance of the system model after the doubly-fed wind turbine, substituting them into the synchronous machine power characteristic equation to obtain the shift change of the synchronous machine power angle characteristic curve, determining the changes in acceleration area and deceleration area using the equal area rule, obtaining the transient stability trend of the system at the sending end, and thus determining the optimal wind turbine connection location under the actual system's allowable operating conditions.

2. The control method for considering the impact of wind power integration on the stability of the sending-end power grid as described in claim 1, characterized in that, It also includes the following steps: The limiting cut-off time and limiting cut-off angle are used as evaluation indicators to reflect the changing trend of transient power angle stability. In this way, the optimal wind power penetration rate and the best wind turbine connection location that can enhance the power angle stability of the system under different conditions are verified.

3. The control method for considering the impact of wind power integration on the stability of the sending-end power grid as described in claim 1, characterized in that, The specific process of constructing equivalent models under different operating conditions and considering wind power penetration includes: analyzing the wind turbine using a doubly fed wind turbine model, transmitting new energy to the receiving end unit's infinite power supply via a high-voltage transmission line, with the system's wind power penetration rate being k, simplifying and equipping the wind turbine under different operating conditions, and analyzing the impact of wind power access on the power angle stability of the sending end synchronous machine.

4. The control method for considering the impact of wind power integration on the stability of the sending-end power grid as described in claim 3, characterized in that, The different operating conditions include before the fault, during the fault, and after the fault is cleared.

5. The control method for considering the impact of wind power integration on the stability of the sending-end power grid as described in claim 4, characterized in that, During modeling, before the system failure, the wind turbine only outputs active power to the system, and at this time the doubly-fed induction generator is equivalent to a constant negative resistor; During system failures, the doubly fed wind turbine is equivalent to a variable negative resistor and a variable negative reactance connected in parallel at the grid connection port, and its value is related to the voltage and active and reactive power output at the grid connection point. In the later stages of fault clearing, the active and reactive power outputs of the doubly-fed wind turbine reached constant values, basically consistent with those before the fault.

6. The control method for considering the impact of wind power integration on the stability of the sending-end power grid as described in claim 1, characterized in that, The access methods include the wind turbine equal capacity replacement synchronous machine method and the wind turbine direct access method. In the wind turbine equal capacity replacement synchronous machine method, the total active power output of the sending end synchronous machine and the wind turbine remains unchanged. Under the condition of ensuring that the system does not become unstable and high voltage ride-through fails, the active power output of the wind turbine gradually increases to replace the synchronous machine. In the wind turbine direct access method, the output of the sending end synchronous machine remains unchanged, and the active power output of the wind turbine is gradually increased to increase the wind power penetration rate.

7. The control method for considering the impact of wind power integration on the stability of the sending-end power grid as described in claim 1, characterized in that, The specific process of determining the optimal wind power penetration rate allocation scheme under different access methods includes: based on the system equivalent model of wind power penetration rate under different public conditions, calculating the self-impedance and transfer impedance under the corresponding conditions, substituting them into the synchronous machine power characteristic equation, obtaining the offset change of the synchronous machine power angle characteristic curve, determining the acceleration area and deceleration area changes by the equal area rule, and determining the optimal wind power penetration rate that can keep the system stable under different access methods.

8. A control system that considers the impact of wind power integration on the stability of the sending-end power grid, characterized in that, A control method for considering the impact of wind power integration on the stability of the sending-end power grid, as described in any one of claims 1-7, includes: The equivalent model construction module is configured to introduce the wind power penetration rate index for target systems containing wind turbine grid connection, construct equivalent models under different operating conditions and after considering the wind power penetration rate, and integrate the equivalent models into the power grid. The optimal wind power penetration rate determination module is configured to consider different grid connection methods for wind turbines during a fault, change the wind power penetration rate under different connection methods, and determine the optimal wind power penetration rate allocation scheme under different connection methods. The optimal wind turbine access location determination module is configured to keep the wind turbine access method unchanged, gradually change the wind turbine access location, introduce wind turbine access location index, calculate its impact on the synchronous machine power characteristics and the transient stability trend, and determine the optimal wind turbine access location.

9. A control system considering the impact on the stability of the sending-end power grid after wind power integration, as described in claim 8, is characterized in that... It also includes a verification module, which is configured to use the limit cut-off time and limit cut-off angle as evaluation indicators to reflect the changing trend of transient power angle stability, thereby verifying the optimal wind power penetration rate and the best wind turbine connection location that can enhance the system power angle stability under different conditions.

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