High-voltage reactance configuration method for improving resonance stability of power system and related equipment

Abstract

The invention belongs to the technical field of resonance stability of a power system, and discloses a high-voltage reactance configuration method for improving resonance stability of the power system, which solves the precision defect caused by neglecting voltage fluctuation in traditional modeling by establishing a fan and static var generator precise admittance model considering DC voltage fluctuation. The dq admittance model of the alternating current system is obtained according to the nodes, connected to the alternating current system, of the fan and the static var generator, general calculation of dq admittance of the multi-node alternating current system is achieved, the limitation that only single-node modeling is supported in a traditional method is broken through, the complex stability problem is quantized into an optimizable amplitude margin index, and the stability of the system is improved. A clear basis is provided for resonance stability analysis, high reactance configuration is expanded from traditional reactive compensation to resonance stability active optimization, and the resonance stability design efficiency of the new energy grid-connected system is remarkably improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power system resonance stability, and particularly relates to a high-resistance configuration method for improving power system resonance stability and related equipment. BACKGROUND

[0002] Under the background of large-scale access of new energy, the resonance stability of the power system is increasingly concerned. In the research on resonance stability, the impedance analysis method is often used, that is, the wideband impedance or admittance model of the converter and the alternating current system is first established, and then the Nyquist stability criterion based on impedance ratio is applied to judge the resonance stability of the system. At present, the research on resonance stability mainly focuses on power electronic devices such as inverters. Among them, the voltage source converter (VSC) has become a very common inverter in the new energy grid-connected system due to its simple and flexible advantages. However, the model is not accurate when the previous research models the VSC, because the DC side power supply is regarded as a rigid power supply, that is, the influence of DC voltage fluctuation is not considered.

[0003] In the current research, a simple RLC network is often used to replace the alternating current system. However, the actual alternating current system is very complex, composed of transformers, lines, high-voltage reactors and other components, and the topological structure is also various. Proper adjustment of the parameters and topological structure of the alternating current system components can also improve the resonance stability of the system. In order to explore the influence of the alternating current system on the resonance stability by using the impedance method, the impedance or admittance of the alternating current system needs to be modeled. In the current research on modeling of the impedance or admittance of the alternating current system, the positive sequence admittance of the alternating current system is often modeled, and a small amount of research on the admittance in the dq coordinate system only calculates the self-admittance from one node, without proposing a general modeling method for the self-admittance and mutual admittance of the alternating current system in the dq coordinate system.

[0004] At present, the research on high-voltage reactor configuration mainly focuses on overvoltage analysis, cable or line current carrying capacity verification and other traditional aspects. In terms of resonance stability, the research on high-voltage reactor configuration is still in a blank state, lacking systematic theoretical and application research. Unreasonable high-resistance configuration can lead to wide-frequency oscillation. SUMMARY

[0005] The application provides a high-resistance configuration method for improving the resonance stability of a power system and related equipment, which solves the problem of wide-frequency oscillation caused by unreasonable high-resistance configuration.

[0006] To achieve the above purpose, the application provides the following technical scheme: A high-resistance configuration method for improving the resonance stability of a power system, comprising: establishing a dq admittance model of a wind turbine and a dq admittance model of a static var generator; An AC system dq admittance model is obtained according to a node where the wind turbine and the static var generator are connected to the AC system; An amplitude margin is obtained as a stability margin evaluation index according to the wind turbine dq admittance model, the static var generator dq admittance model and the AC system dq admittance model; The system is optimized for high-resistance configuration according to the amplitude margin.

[0007] Preferably, the step of establishing the wind turbine dq admittance model comprises obtaining a small signal model of a grid-side inverter of the wind turbine, analyzing a multiple-dq coordinate system coupling effect caused by a phase-locked loop based on the small signal model of the grid-side inverter of the wind turbine, and obtaining the wind turbine dq admittance model according to the multiple-dq coordinate system coupling effect and the small signal model of the grid-side inverter of the wind turbine. The wind turbine dq admittance model is:

[0008] wherein, is an output impedance of a filter circuit, is a DC side voltage, is a transfer function matrix between a voltage and a modulation signal in a dq coordinate system of a power system, is a matrix composed of steady-state values of the modulation signal, is a transfer function matrix between a DC side current and a DC side voltage of an inverter, is a transfer function matrix between the modulation signal and the DC side current of the inverter in the dq coordinate system of the system, is a transfer function matrix between an AC side current and the DC side current of the inverter, is a transfer function matrix between an AC side voltage of the inverter and the modulation signal in the dq coordinate system of the system, and I is an identity matrix.

[0009] Preferably, the static var generator dq admittance model is:

[0010] wherein, is an output impedance of a filter circuit, is a DC side voltage, is a transfer function matrix between a voltage and a modulation signal in a dq coordinate system of a power system, is a matrix composed of steady-state values of the modulation signal, is a transfer function matrix between a DC side current and a DC side voltage of an inverter, is a transfer function matrix between the modulation signal and the DC side current of the inverter in the dq coordinate system of the system, is a transfer function matrix between an AC side current and the DC side current of the inverter, is the transfer function matrix between the AC side voltage of the inverter in the dq coordinate system and the modulation signal, I is a unit matrix, is the transfer function matrix between the reactive power and the AC side voltage in the dq coordinate system, is the transfer function matrix between the AC side voltage in the dq coordinate system of the system and the AC side voltage in the dq coordinate system of the controller, is the transfer function matrix between the reactive power and the AC side current in the dq coordinate system of the system, is the transfer function matrix between the AC side current in the dq coordinate system of the system and the AC side current in the dq coordinate system of the controller.

[0011] Preferably, the step of obtaining the dq admittance model of the AC system according to the node where the wind turbine and the static var generator are connected to the AC system is specifically: establishing positive and negative sequence admittance models of elements of the AC system; calculating positive and negative sequence equivalent admittances of the AC system from the perspective of the node where the wind turbine and the static var generator are connected to the AC system based on the positive and negative sequence admittance models of elements of the AC system; converting the positive and negative sequence equivalent admittances of the AC system into the dq coordinate system to obtain the dq admittance model of the AC system.

[0012] Preferably, the calculation of the positive and negative sequence equivalent admittances of the AC system from the perspective of the node where the wind turbine and the static var generator are connected to the AC system is specifically:

[0013] in the formula, , , , are four block matrices obtained by blocking the admittance matrix of the AC system node, represents the self-admittance matrix of the node in the AC system that is not connected to external equipment, represents the self-admittance matrix of the node connected to external equipment, is the mutual admittance matrix of the two types of nodes, is the mutual admittance matrix of the two types of nodes, Y g represents the matrix composed of admittances in each equivalent circuit after the internal power sources of the AC system are respectively equivalent to Norton circuits.

[0014] Preferably, the step of obtaining the amplitude margin as the stability margin evaluation index according to the dq admittance model of the wind turbine, the dq admittance model of the static var generator, and the dq admittance model of the AC system is specifically: The dq admittance model of the alternating current system is equivalent to a Thevenin equivalent circuit, the dq admittance model of the wind turbine and the dq admittance model of the static var generator are equivalent to a Norton equivalent circuit, the Thevenin equivalent circuit and the Norton equivalent circuit are connected to the system at corresponding positions, and an expression of injected current of the alternating current system is obtained; An open-loop transfer function of the power system is obtained according to the expression of the injected current of the alternating current system; A Nyquist curve of an eigenvalue of the open-loop transfer function of the power system is drawn, and an amplitude margin is calculated according to the Nyquist curve.

[0015] Preferably, the step of optimizing the high-resistance configuration of the system according to the amplitude margin is specifically: The reactive power balance demand of the alternating current system is calculated, and the total capacity of the high-voltage reactor is determined; The ratio of the rated capacity of the high-voltage reactor to the total capacity and the ratio of the distance from the intermediate compensation station to the step-up station to the total length of the cable are obtained based on the total capacity of the high-voltage reactor; The position distribution and capacity distribution scheme of the high-voltage reactor are optimized based on the ratio of the rated capacity of the high-voltage reactor to the total capacity, the ratio of the distance from the intermediate compensation station to the step-up station to the total length of the cable, and the amplitude margin of the system.

[0016] A high-resistance configuration system for improving the resonance stability of a power system, comprising: A modeling module for establishing a dq admittance model of a wind turbine and a dq admittance model of a static var generator; A conversion module for obtaining a dq admittance model of an alternating current system according to a node of the wind turbine and the static var generator connected to the alternating current system; An amplitude margin obtaining module for obtaining an amplitude margin as a stability margin evaluation index according to the dq admittance model of the wind turbine, the dq admittance model of the static var generator, and the dq admittance model of the alternating current system; An optimization module for optimizing the high-resistance configuration of the system according to the amplitude margin.

[0017] Preferably, in the modeling module, the step of establishing the dq admittance model of the wind turbine is that a small-signal model of a grid-side inverter of the wind turbine is obtained, a multi-dq coordinate system coupling effect caused by a phase-locked loop is analyzed based on the small-signal model of the grid-side inverter, and the dq admittance model of the wind turbine is obtained according to the multi-dq coordinate system coupling effect and the small-signal model of the grid-side inverter. The dq admittance model of the wind turbine is:

[0018] wherein, is an output impedance of a filter circuit, is a DC side voltage, a transfer function matrix between the voltage in the dq coordinate system of the power system and the modulation signal, a matrix composed of steady-state values of the modulation signal, a transfer function matrix between the DC side voltage of the inverter and the DC side current, a transfer function matrix between the DC side current of the inverter and the modulation signal in the dq coordinate system of the system, a transfer function matrix between the DC side current of the inverter and the AC side current, a transfer function matrix between the AC side voltage of the inverter in the dq coordinate system of the system and the modulation signal, I being a unit matrix.

[0019] Preferably, in the modeling module, the dq admittance model of the static reactive power generator is:

[0020] wherein, the output impedance of the filter circuit, the DC side voltage, a transfer function matrix between the voltage in the dq coordinate system of the power system and the modulation signal, a matrix composed of steady-state values of the modulation signal, a transfer function matrix between the DC side voltage of the inverter and the DC side current, a transfer function matrix between the DC side current of the inverter and the modulation signal in the dq coordinate system of the system, a transfer function matrix between the DC side current of the inverter and the AC side current, a transfer function matrix between the AC side voltage of the inverter in the dq coordinate system of the system and the modulation signal, I being a unit matrix, a transfer function matrix between the reactive power and the AC side voltage in the dq coordinate system of the system, a transfer function matrix between the AC side voltage in the dq coordinate system of the system and the AC side voltage in the dq coordinate system of the controller, a transfer function matrix between the reactive power and the AC side current in the dq coordinate system of the system, a transfer function matrix between the AC side current in the dq coordinate system of the system and the AC side current in the dq coordinate system of the controller.

[0021] Preferably, in the conversion module, the step of obtaining the dq admittance model of the AC system according to the node where the wind turbine and the static reactive power generator are connected to the AC system is specifically: establishing positive and negative sequence admittance models of elements of the AC system; calculating positive and negative sequence equivalent admittances of the AC system from the perspective of the node where the wind turbine and the static reactive power generator are connected to the AC system based on the positive and negative sequence admittance models of elements of the AC system; The positive sequence and negative sequence equivalent admittance of the alternating current system is converted into the dq coordinate system to obtain a dq admittance model of the alternating current system.

[0022] Preferably, the positive sequence and negative sequence equivalent admittance of the node where the fan and the static var generator are connected to the alternating current system is calculated and is specifically:

[0023] In the formula, , , , After the admittance matrix of the node of the alternating current system is divided into four sub-matrices, represents the self-admittance matrix of the node in the alternating current system which is not connected to the external device, represents the self-admittance matrix of the node connected to the external device, is the mutual admittance matrix of the two types of nodes, is the mutual admittance matrix of the two types of nodes, Y g represents the matrix composed of the admittance of the equivalent circuit after each power source in the alternating current system is respectively equivalent to a Norton circuit.

[0024] Preferably, in the amplitude margin obtaining module, the step of obtaining the amplitude margin as the stability margin evaluation index according to the dq admittance model of the fan, the dq admittance model of the static var generator and the dq admittance model of the alternating current system is specifically: The Thevenin equivalent circuit is obtained by performing Thevenin equivalent on the dq admittance model of the alternating current system, the dq admittance model of the fan and the dq admittance model of the static var generator are equivalent to the form of the Norton equivalent circuit, the Thevenin equivalent circuit and the Norton equivalent circuit are connected to the corresponding position of the system, and the expression of the injected current of the alternating current system is obtained; The open-loop transfer function of the power system is obtained according to the expression of the injected current of the alternating current system; The Nyquist curve of the characteristic value of the open-loop transfer function of the power system is drawn, and the amplitude margin is calculated according to the Nyquist curve.

[0025] Preferably, in the optimization module, the step of optimizing the high resistance configuration of the system according to the amplitude margin is specifically: The reactive power balance demand of the alternating current system is calculated to determine the total capacity of the high voltage reactor; The ratio of the rated capacity of the high voltage reactor to the total capacity and the ratio of the distance from the intermediate compensation station to the booster station to the total length of the cable are obtained based on the total capacity of the high voltage reactor; The position distribution and capacity distribution scheme of the high voltage reactor are optimized based on the ratio of the rated capacity of the high voltage reactor to the total capacity, the ratio of the distance from the intermediate compensation station to the booster station to the total length of the cable and the amplitude margin of the system.

[0026] A computer device comprises a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor implements the steps of a high resistance configuration method for improving the resonance stability of a power system when executing the computer program.

[0027] A computer readable storage medium stores a computer program, and the computer program implements the steps of a high resistance configuration method for improving the resonance stability of a power system when executed by a processor.

[0028] Compared with the prior art, the present application has the following beneficial effects: the present application provides a high resistance configuration method for improving the resonance stability of a power system, which solves the precision defects caused by the traditional modeling ignoring voltage fluctuations by establishing an accurate admittance model of a fan and a static var generator considering DC voltage fluctuations, obtains a dq admittance model of an AC system according to the nodes of the AC system where the fan and the static var generator are connected, realizes general calculation of the dq admittance of a multi-node AC system, breaks through the limitation of traditional methods that only support single-node modeling, quantifies complex stability problems into an amplitude margin index that can be optimized, provides a clear basis for resonance stability analysis, expands high resistance configuration from traditional reactive power compensation to active optimization of resonance stability, and significantly improves the resonance stability design efficiency of a new energy grid-connected system.

[0029] Further, considering that the voltage and current of each inverter connected node are in different dq coordinate systems when multiple inverters are connected to different nodes of an AC system, a calculation method of self-admittance and mutual admittance of an AC system in a dq coordinate system of multiple nodes is proposed, which makes up for the shortcoming of previous calculation methods that can only calculate the impedance or admittance of a single-node AC system in a dq coordinate system with an initial phase of 0. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A high resistance configuration method for improving the resonance stability of a power system according to an embodiment of the present application is shown in the flowchart; Figure 2 A topology structure diagram of a grid-connected system of an offshore wind farm according to an embodiment of the present application is shown in the figure; Figure 3 A topology and control schematic diagram of a fan grid-side inverter according to an embodiment of the present application is shown in the figure; Figure 4 A small-signal model of a fan grid-side inverter according to an embodiment of the present application is shown in the figure; Figure 5 A system DQ coordinate system and a controller DQ coordinate system according to an embodiment of the present application are shown in the figure; Figure 6 A small-signal control block diagram of a fan grid-side inverter according to an embodiment of the present application is shown in the figure; Figure 7DQ admittance verification of the fan in the embodiment of the present application; Figure 8 Small signal control block diagram of the SVG in the embodiment of the present application; Figure 9 DQ admittance verification of the SVG in the embodiment of the present application; Figure 10 Bergeron model of the lossy line in the embodiment of the present application; Figure 11 Transformer schematic diagram in the embodiment of the present application; Figure 12 Double-winding transformer in the embodiment of the present application Equivalent circuit model; Figure 13 Parallel load model in the embodiment of the present application; Figure 14 DQ coordinate system defined by the voltage of the i th node and the dq coordinate system with initial phase of 0 in the embodiment of the present application; Figure 15 Wideband DQ admittance verification of the AC system in the embodiment of the present application; Figure 16 Equivalent admittance model of the wind farm in the embodiment of the present application; Figure 17 Nyquist curve in the steady state in the embodiment of the present application; Figure 18 Q-axis current of the grid-side inverter of the fan in the steady state in the embodiment of the present application; Figure 19 Nyquist curve in the unstable state in the embodiment of the present application; Figure 20 Q-axis current of the grid-side inverter of the fan in the unstable state in the embodiment of the present application; Figure 21 High reactance configuration system block diagram for improving the resonance stability of the power system in the embodiment of the present application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, but not all the embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0032] Therefore, the following detailed description of embodiments of the application provided in the accompanying drawings is not intended to limit the scope of the application claimed, but merely represents selected embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the application.

[0033] It should be noted that similar reference numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0034] In order for those skilled in the art to better understand the technical solutions of the present application, the present application will be further described in detail below in conjunction with the drawings.

[0035] As shown in Figure 1 A high resistance configuration method for improving the resonance stability of a power system, comprising: S1, establishing a dq admittance model of a wind turbine and a dq admittance model of a static var generator; S2, obtaining a dq admittance model of an alternating current system according to a node of the alternating current system where the wind turbine and the static var generator are connected; S3, obtaining an amplitude margin as a stability margin evaluation index according to the dq admittance model of the wind turbine, the dq admittance model of the static var generator and the dq admittance model of the alternating current system; S4, optimizing the high resistance configuration of the system according to the amplitude margin.

[0036] By establishing an accurate admittance model of the wind turbine and the static var generator considering the DC voltage fluctuation, the precision defect caused by the traditional modeling ignoring the voltage fluctuation is solved. According to the node of the alternating current system where the wind turbine and the static var generator are connected, the dq admittance model of the alternating current system is obtained, the general calculation of the dq admittance of the multi-node alternating current system is realized, the limitation of the traditional method supporting only single-node modeling is broken through, the complex stability problem is quantified as an optimizable amplitude margin index, and a clear basis is provided for resonance stability analysis. The high resistance configuration is expanded from traditional reactive power compensation to active optimization of resonance stability, which significantly improves the resonance stability design efficiency of the new energy grid-connected system.

[0037] The detailed steps are: Based on the impedance method for analyzing the resonance stability of the system, the impedance or admittance model of the inverter and the alternating current system in the system needs to be established first. Due to the difference in control strategy and converter devices, there are various inverters in the power system. The present application takes the direct-drive wind turbine and static var compensator (SVG) commonly used in the offshore wind farm grid-connected system as an example. Figure 2

[0038] Figure 2 ​The topology of a certain offshore wind farm is given, which has a total installed capacity of 205 MW and is composed of 41 single units with a rated power of 5 MW. The parameters of the single unit are shown in Table 1. The outlet voltage of the wind turbine is 0.69 KV, which is connected to the 220 KV submarine cable through two-stage voltage boost, and is connected to the land control center through the submarine cable. The transformer connection group is Yg / D11, the short-circuit voltage percentage is 10%, and the length of the submarine cable is 79.1 km. The offshore high resistance station is set at the high voltage side of the offshore booster station and 35.2 km away from the offshore booster station. The high resistance station is set at the landing point of the submarine cable, and the adjustable reactor and the static var generator (SVG) are set. The parameters of the SVG are shown in Table 2.

[0039] Table 1 Parameters of the grid-side inverter of the wind turbine

[0040] Table 2 Parameters of the SVG

[0041] Wide-band DQ admittance modeling of direct-drive wind turbine The wind turbines used in offshore wind farms are mostly direct-drive wind turbines. Since the capacitance between the grid-side inverter and the machine-side inverter is very large, the machine-side inverter can be regarded as a direct current power supply under the condition that the direct current voltage is controlled at a constant value, so that the influence of the machine-side inverter admittance can be ignored, and only the grid-side inverter admittance is modeled. The grid-side inverter of the wind turbine adopts voltage outer loop and current inner loop control, as shown in Figure 3

[0042] In order to consider the influence of direct current voltage fluctuation, the process of establishing the small signal model of the grid-side inverter of the wind turbine is described in this section. For the main circuit shown in Figure 2 , the Kirchhoff voltage law can be obtained as follows: (1) After abc-dq coordinate system transformation of equation (1), the state equation in dq coordinate system can be obtained, as shown below (2) Among them (3) The small signal quantity is added to each voltage and current in dq coordinate system in equation (2) and linearized to obtain equation (4).

[0043] (4) For the main circuit shown in Figure 2 , the Kirchhoff current law can be obtained as follows (5) The abc-dq coordinate system transformation is performed on the two three-dimensional vectors on the right side of equation (5) to obtain the following expression (6).​ (6) Adding small signal quantities to each voltage and current in the dq coordinate system in formula (6) and linearizing, formula (7) is obtained.

[0044] (7) In addition, the relationship of the inverter DC side voltage and current is shown in formula (8), where C is the capacitance value of the DC side capacitor.

[0045] (8) The small signal model of the inverter can be obtained from formula (4), formula (6) and formula (8), as shown in formula (9). Figure 4

[0046] Figure 4 The expressions of each transfer function in formula (9) are as follows, where s is the complex frequency, is the angular frequency at the fundamental frequency. R and L represents the switching loss of the inverter, M d is the steady-state value of the d-axis modulation signal, M q is the steady-state value of the q-axis modulation signal. I d is the steady-state value of the d-axis current, I q is the steady-state value of the q-axis current. V d is the steady-state value of the d-axis voltage, V q is the steady-state value of the q-axis current. V dc is the steady-state value of the DC voltage, C is the capacitance value of the DC side capacitor.

[0047] (9) (10) (11) (12) (13) (14) Due to the existence of the phase-locked loop, the inverter has two dq coordinate systems: one is the system dq coordinate system defined by the grid voltage, and the other is the controller dq coordinate system defined by the phase-locked loop (PLL), as shown in formula (15). Figure 5 ​The two coordinate systems are aligned at steady state, while the position of the system dq coordinate system changes when a small signal disturbance is added to the grid voltage, the angle between the two coordinate systems is Δθ, as shown in Fig. 2. Figure 5 The matrix T Δθ is used to rotate the voltage and current vectors in the system dq coordinate system to the controller dq coordinate system. Δθ The duty cycle command generated by the feedback control is rotated to the system dq coordinate system by the inverse of the matrix T PLL to control the power semiconductors.

[0048] The small signal disturbance of the system voltage propagates to the PLL output angle in the controller dq coordinate system, and then to the current and duty cycle vectors. The transfer function expression of this process is (15) (16) (17) In the above matrix, G PLL is the expression of (18) where (19) where k pPLL is the proportional gain of the phase-locked loop, k iPLL is the integral gain of the phase-locked loop. The fan grid-side inverter uses a current inner loop controller and a voltage outer loop controller in the synchronous coordinate system, as shown in Fig. 3. Figure 6

[0049] where G ci is the current controller, G cout is the voltage outer loop controller, and G dei is the decoupling term, whose expressions are (20) (21) (22) where k pi is the proportional gain of the current loop, k ii is the integral gain of the current loop, k pdc is the proportional gain of the voltage loop. k idc is the integral gain of the voltage loop. The solution is as shown in Fig. 4. Figure 6The equation group is shown, and the output admittance of the fan grid-side inverter is obtained when the current inner loop and the voltage outer loop are included: (23) In formula (23) is the output impedance of the filter circuit, is the DC side voltage, is the matrix composed of the steady-state values of the modulation signal, is the transfer function matrix between the DC side voltage and the DC side current of the inverter, is the transfer function matrix between the DC side current of the inverter and the modulation signal in the dq coordinate system of the system, is the transfer function matrix between the DC side current of the inverter and the AC side current, is the transfer function matrix between the AC side voltage of the inverter and the modulation signal in the dq coordinate system of the system, I is the unit matrix, and G mi represents the relationship between the voltage and the modulation signal in the dq coordinate system of the system, and its expression is shown in formulas (24), (25), and (26).

[0050] (24) (25) (26) Figure 7 The comparison between the theoretical Bode diagram of the fan wide-band impedance and the sweep frequency result is given, verifying the correctness of the fan impedance calculation and proving that the machine-side inverter has little effect on the overall impedance of the fan.

[0051] Since the fan grid-side inverter works at a unit power factor, its DQ axis coupling effect is weak, Y dq and Y qd are much smaller than Y dd and Y qq , and a very small measurement error will be more obvious in the Bode diagram, so the measurement error can be ignored.

[0052] (II) SVG wide-band DQ admittance modeling Compared with the fan grid-side inverter, the SVG control strategy has an additional reactive power outer loop, as shown in Figure 8 .

[0053] As can be seen from Figure 8 , after adding the reactive power outer loop controller, the control block diagram compared with Figure 6 has an additional power calculation module, and the transfer functions G cout and related to the outer loop have changed, and the specific transfer functions are as follows.

[0054] (27) (28) (29) (30) wherein, k pQ is a proportional link coefficient of the outer loop of the reactive power, k iQ is an integral link coefficient of the outer loop of the reactive power. From Figure 8 The SVG admittance in dq coordinate system can be derived as (31) In formula (31) is the output impedance of the filter circuit, is the DC side voltage, is the transfer function matrix between the voltage in dq coordinate system of the power system and the modulation signal, is the matrix composed of the steady-state values of the modulation signal, is the transfer function matrix between the DC side voltage of the inverter and the DC side current, is the transfer function matrix between the DC side current of the inverter and the modulation signal in dq coordinate system of the system, is the transfer function matrix between the DC side current of the inverter and the AC side current, is the transfer function matrix between the AC side voltage of the inverter in dq coordinate system of the system and the modulation signal, and I is the unit matrix, is the transfer function matrix between the reactive power and the AC side voltage in dq coordinate system of the system, is the transfer function matrix between the AC side voltage in dq coordinate system of the system and the AC side voltage in dq coordinate system of the controller, is the transfer function matrix between the reactive power and the AC side current in dq coordinate system of the system, is the transfer function matrix between the AC side current in dq coordinate system of the system and the AC side current in dq coordinate system of the controller, and the transfer functions G mv and G mi have the same meanings as formula (24), but their expressions are changed into the forms of formula (32) and (33).

[0055] (32) (33) Figure 9 The theoretical Bode diagram of the SVG wide-band impedance is compared with the sweep result, and the correctness of the SVG impedance calculation is verified.

[0056] Since SVG outputs almost only reactive power, it does not operate at unity power factor, so its DQ subsystem coupling effect is enhanced, as shown in Figure 9 which is not negligible in terms of measurement error and its impact on system stability.

[0057] (Three) AC system wideband DQ admittance modeling (1) AC system element positive sequence admittance modeling Bergeron model of line This section derives the harmonic admittance expression of the Bergeron model from its time-domain expression. The positive and negative sequence admittance parameters of the line are equal, so the admittance obtained below based on the positive sequence parameter is also applicable to the negative sequence. When considering the Bergeron model of lossy lines, in order to reflect the distribution characteristics of the transmission line, the capacitance and inductance are still distributed parameters, which are equivalent to an infinite number of series of structure models. The resistance is a lumped parameter, with one-fourth on each end of the line and one-half in the middle, as shown in Figure 10 .

[0058] For lossy lines, the following time-domain expressions are obtained (34) (35) where (36) In equation (36) Z c is the wave impedance at harmonic frequency, R is the lumped parameter resistance of the line.

[0059] Take Laplace transform of (35), and then substitute it into the Laplace-transformed (34) to get (37) The matrix in equation (37) is the admittance matrix of the Bergeron model. Among them (38) Transformer The leakage reactance of the primary and secondary windings of the transformer is all calculated to the primary side, and the excitation branch is removed to get Figure 11 : According to Figure 11 , the relationship between voltage and current is obtained in equation (39), where U1 is the primary side voltage, I1 is the primary side current, U2 is the secondary side voltage, and I2 is the secondary side current.

[0060] (39) The transformer admittance is then the matrix in equation (39) and the transformation ratio k is a complex number.

[0061] Thus, we get Figure 12 the π-type equivalent circuit shown.

[0062] The transformer broadband harmonic impedance Z T is given by (40) Load This subsection gives the calculation formula of load admittance at harmonic frequencies. For a three-phase balanced load, its positive and negative sequence admittances are equal.

[0063] A lumped load is suitable to be expressed by a parallel load model.

[0064] At harmonic frequencies, if the active and reactive power absorbed by the load is known, the parallel admittance of the load can be calculated in the following two cases: When , i.e. the load is inductive (41) When , i.e. the load is capacitive (42) A high-voltage reactor is essentially an inductive load with zero active power.

[0065] (2) Harmonic equivalent admittance modeling of AC system Positive and negative sequence admittance modeling On the basis of the mathematical models of transformers, transmission lines, loads, etc., the node admittance matrix at harmonic frequencies is calculated. Each element in the node admittance matrix is not linearly transformed with frequency at different harmonic frequencies, but at each harmonic frequency, the node admittance matrix needs to be recalculated according to the model of each element. It should be noted that, due to the inequality of the positive and negative sequence admittances of the transformer, the positive and negative sequence harmonic node admittance matrices should be formed respectively. Then, based on the formed positive and negative sequence node admittances, the positive and negative sequence equivalent admittances of one or more nodes of the AC system are calculated according to the kron reduction theory.

[0066] (43) Equation (43) is the broadband admittance of the AC system required by the node. In this equation, , , , are the four block matrices obtained by blocking the node admittance matrix of the AC system. Ys represents the self-admittance matrix of the nodes in the AC system which are not connected to the external equipment, Ys represents the self-admittance matrix of the nodes in the AC system which are not connected to the external equipment, Y represents the mutual-admittance matrix of the two types of nodes, Y represents the mutual-admittance matrix of the two types of nodes. g Y represents the matrix of the admittance of the equivalent circuits after each power supply in the AC system is respectively equivalent to a Norton circuit.

[0067] Since the relevant data of the power supply are often provided by the manufacturer, this expression separates the wide-band admittance of the power supply from the admittance matrix formed by other elements in the AC system, and when a power supply is added or a power supply is taken out of operation, only the matrix Y g is modified, and the modified wide-band impedance of the AC system can be calculated. This method has clear physical meaning, and the user can select the equivalent impedance of which nodes to calculate according to needs. The limitation that only the equivalent impedance of one node can be calculated is eliminated, and the cumbersome operation of inverting the entire node admittance matrix is also avoided. DQ admittance modeling The following two steps are mainly used to convert the positive and negative sequence impedance of the AC system into the admittance in the dq coordinate system. First, the sequence admittance is converted to the reference dq coordinate system with the initial phase of 0, and then the admittance of different nodes is transformed to the dq coordinate system defined by the voltage phase of each node.

[0068] (a) Convert the sequence admittance to the reference dq coordinate system with the initial phase of 0 (44) wherein f s is the fundamental frequency, and the transformation matrix C is (45) (b) Transform the admittance of different nodes to the dq coordinate system defined by the voltage phase of each node Since the phase-locked loop of the voltage source type inverter often uses the method of grid voltage orientation, the voltage at the access point of the inverter defines the dq coordinate system in which the voltage and current of the node are located. When multiple inverters are connected to different nodes in the AC system, the voltage and current at the node connected by each inverter are in different dq coordinate systems. Therefore, when calculating the self-admittance and mutual-admittance of the AC system in the dq coordinate system from the perspective of multiple nodes, it is necessary to transform the admittance of different nodes to the dq coordinate system defined by the voltage phase of each node.

[0069] Suppose the voltage at the i-th node is , then the dq coordinate system defined by the voltage at the i-th node and the initial phase of 0 dq coordinate system are as shown in Figure 14 ​For any vector, its projection in two dq coordinate systems is shown as Figure 14 Thus, we have (46) Therefore, the relationship of the projection of the vector in two coordinate systems is (47) From equation (47), when there are N vectors that need to be transformed from the coordinate system with an initial phase of 0 to N different dq coordinate systems, there is the following relationship (48) In equation (48), the superscript number represents the dq coordinate system number, and the subscript number represents the number of N vectors. The matrix therein is denoted as the transformation matrix In the dq coordinate system with an initial phase of 0, for an AC system with N nodes, the voltage , the current , and the admittance have the following relationship (49) where the voltage and the current are both 2N-dimensional vectors, and the admittance is a 2N-dimensional matrix. By transforming the voltage and current of each node in equation (49) to the dq coordinate system defined by the voltage phase of each node using the method shown in equation (48), we have (50) Therefore, the node admittance matrix of the dq coordinate system of the AC system viewed from multiple nodes is (51) It should be noted that the node admittance matrix shown in equation (51) is blocked by dq components. If you want to obtain the node admittance matrix blocked by nodes, you can adjust the position of the elements in the matrix.

[0070] Figure 15 The theoretical Bode plot and the sweep frequency result of the wideband admittance of the self-admittance and mutual admittance of node 1 and node 7 of the AC system are given, verifying the correctness of the calculation of the wideband admittance of the AC system.

[0071] Stability criterion and stability margin index: (I) Stability criterion derivation: The Thevenin equivalent of the AC system is performed, and the wind turbine and SVG are equivalent to the Norton equivalent circuit form, which is connected to the corresponding position of the AC system, as shown in Figure 16 From Figure 1 it can be seen that the wind turbine is connected to node 1, and the SVG is connected to node 7.

[0072] From Figure 16 the following equation can be obtained: (52) (53) where each voltage-current element is a 2-dimensional vector, for example ; each admittance element in the matrix is a 2x2 matrix, for example .

[0073] (52) and (53) can be rearranged to obtain (54) For convenience of subsequent analysis, (54) is written as (55) where the symbols have the same meaning as the corresponding matrix or vector in (54). I is the identity matrix, represents the current injected into the power grid; represents the size of the equivalent circuit current source after Norton equivalence of the wind turbine and SVG; represents the internal harmonic voltage of the power grid. represents the inverter admittance matrix in the dq coordinate system, Y g represents the self-admittance and mutual admittance of node 1 and node 7 in the dq coordinate system. In (55), if the current vector is stable, the system is stable without (right half plane) RHP poles. Next, the conditions under which the system is stable are analyzed.

[0074] After Norton equivalence, the wind turbine and SVG are a current source system. For a current source system, the following assumptions and conclusions are made: When there is no load, i.e., the load is short-circuited, the current source itself is stable, i.e., has no RHP poles; When powered by an ideal current source, the load is stable, so has no RHP poles.

[0075] After Thevenin equivalence, the AC system is a voltage source system. For a voltage source system, the following assumptions and conclusions are made: The voltage source is stable when there is no load, so has no RHP poles; When powered by an ideal voltage source, the load is stable, so has no RHP poles.

[0076] Based on the above assumptions and conclusions, has no RHP poles, so the stability of the system depends on whether there are RHP poles. This expression can be regarded as a closed-loop transfer function, and because and None of them have RHP poles, so their corresponding open-loop transfer functions There are no RHP poles. Therefore, according to the Nyquist stability criterion, when the Nyquist curve encircles (-1,0), the closed-loop transfer function is... The presence of RHP poles indicates system instability; otherwise, the system is stable. Furthermore, subsequent calculations use gain margin as a stability margin indicator. A gain margin greater than 1 indicates system stability; otherwise, the system is unstable. A larger gain margin indicates greater system stability.

[0077] (II) Stability Criterion Verification for Figure 2 The system shown has a proportional element coefficient of 1 / 2000 when the given disturbance is a current loop. k pi =0.68, the coefficient of the integral element is k ii =50, the proportional element coefficient of the phase-locked loop is 50. k pPLL =8, the coefficient of the integral element is k iLPP When the impedance ratio is 60, the Nyquist curve based on the impedance ratio is plotted as follows: Figure 17 As shown, the curve does not enclose (-1,0) at this time, and the magnitude margin is 1.0105. Figure 18 The waveforms of the Q-axis current of the grid-side inverter of the wind turbine before and after the disturbance are shown. It can be seen that the system remains in a stable state after the disturbance.

[0078] When other values ​​of the given disturbance remain unchanged, the current loop proportional element system becomes k pi =0.69, at which point the Nyquist curve is as follows: Figure 19 As shown, the curve encloses (-1,0) at this point, with a gain margin of 0.9977. Figure 20 It can be seen that the system becomes unstable after the disturbance. This verifies the accuracy of the stability criterion. 3. A Highly Resilient Configuration Optimization Method Based on Genetic Algorithms To select a reasonable configuration of high-voltage reactors, a reactive power balance analysis of the system must first be performed to calculate the system's reactive power capacity deficit and determine the total reactor capacity. Then, factors such as system resonant stability, system overvoltage, transmission line current carrying capacity, and economic efficiency must be considered to rationally select the number of reactors and the capacity allocation among them. Currently, research on system overvoltage, line current carrying capacity, and the economic efficiency of reactor configuration is quite comprehensive; therefore, this invention does not consider these factors and focuses solely on optimizing reactor configuration to improve system resonant stability. In practical applications, users can convert other influencing factors into constraints for decision variables during the optimization process and then apply this method to improve system resonant stability.

[0079] (I) High reactive total capacity calculation The total capacity of the high voltage reactor is the line charging power minus the inductive reactive power consumed by the line and the transformer, wherein the formula for calculating the line charging power is (56) wherein, Q C is the charging reactive power of the transmission line, U is the average operating voltage of the transmission line, is the angular frequency of the system, C is the positive sequence capacitance of the transmission line. The reactive power loss of the transmission line is mainly derived from the reactive power loss of the line reactance, which is proportional to the square of the current in the transmission line. The reactive power loss of the transmission line is (57) wherein, Q L is the reactive power loss of the transmission line, P is the active power transmitted at the end of the transmission line, Q is the reactive power transmitted at the end of the transmission line, U is the node voltage at the end of the transmission line, X L is the line reactance. When operating at rated voltage, the reactive power loss of the transformer is (58) Therefore, the total capacity of the high voltage reactor is (59) The voltages used in the above calculation are average voltages or rated voltages, not actual operating voltages, so there will be a certain error between the calculated total capacity of the high voltage reactor and the actual required capacity, and the error power can be compensated by the SVG.

[0080] (II) High reactive optimization configuration method Offshore wind farm grid-connected systems usually have high voltage reactors installed at offshore booster stations and land control centers. When transmitting over long distances, intermediate compensation stations are also installed at certain positions of the submarine cable, as shown in Figure 2 . The present application applies the high reactive configuration optimization method to the system shown in Figure 2 . The system resonance stability is improved by optimizing the high reactive configuration, that is, to find an optimal high reactive configuration method to maximize the amplitude margin calculated based on the impedance method.

[0081] The problem can be converted into a mathematical optimization problem, with the reciprocal of the amplitude margin as the objective function, and the minimum of the reciprocal of the amplitude margin, i.e., the maximum of the amplitude margin. Given the total capacity of high resistance, in order to make the expression universal, the invention uses the ratio of the rated capacity of the high voltage reactor in three positions to the total capacity as three decision variables, represented by x 1、 x 2、 x 3 respectively. In addition to the capacity allocation of the three high resistance, the position of the intermediate compensation station is also a decision variable that needs to be optimized. In order to make the expression more universal, the same ratio is used, i.e., the ratio of the distance from the intermediate compensation station to the offshore booster station to the total length of the submarine cable, represented by x 4. The value range of the four decision variables is (60) and the first three variables have equality constraints: (61) Therefore, this problem is a linear programming problem with a very complex objective function, so it cannot be considered as a linear programming problem. In addition, in the actual calculation process, when the AC system is relatively complex, it is difficult to obtain an analytical expression between the amplitude margin and the four decision variables. Only the numerical value of the amplitude margin and its reciprocal can be obtained when the decision variables take different values, which belongs to the "black box optimization" problem. With the change of the decision variables, the reciprocal of the amplitude margin may have multiple peaks, and the traditional nonlinear programming method can only find a local optimal solution, which is not suitable for solving this problem. Therefore, the invention chooses to use genetic algorithm to find the global optimal solution of the objective function.

[0082] Genetic algorithm (GA) is a global optimization algorithm based on the principles of natural selection and genetic mechanisms, widely used in solving complex nonlinear optimization problems. The core idea is to simulate the selection, crossover and mutation operations in the biological evolution process, gradually optimize the individuals in the population, and approach the optimal solution of the problem. The algorithm first initializes a random population, where each individual represents a potential solution to the problem, and evaluates its quality through the fitness function. In each generation, the algorithm selects individuals based on their fitness values, retaining those with higher fitness. Then, through crossover operation, new offspring individuals are generated to inherit the excellent characteristics of their parents. At the same time, mutation operation is introduced to increase the diversity of the population and avoid falling into local optimum. After multiple iterations, the population gradually evolves, and finally converges to the global optimal solution or an approximate optimal solution.

[0083] MATLAB provides a very mature built-in genetic algorithm function "ga", users can flexibly apply to various optimization problems by defining fitness function, setting variable boundary and constraint condition. Therefore, in this study, the built-in genetic algorithm function of matlab is used, and the reciprocal of amplitude margin is used as fitness function. Because the relationship between fitness function and decision variable is relatively complex, the population size is set to a large value of 300, and the maximum iteration number is also set to 300. Through the above algorithm, the high resistance configuration scheme that makes the system amplitude margin maximum and the resonance stability strongest can be obtained.

[0084] As shown in Figure 21 The application also provides a high resistance configuration system for improving the resonance stability of a power system, comprising: a modeling module for establishing a dq admittance model of a wind turbine and a dq admittance model of a static var generator; a conversion module for obtaining a dq admittance model of an alternating current system according to nodes of the wind turbine and the static var generator connected to the alternating current system; an amplitude margin obtaining module for obtaining an amplitude margin as a stability margin evaluation index according to the dq admittance model of the wind turbine, the dq admittance model of the static var generator and the dq admittance model of the alternating current system; an optimization module for optimizing high resistance configuration of the system according to the amplitude margin.

[0085] In the modeling module, the step of establishing the dq admittance model of the wind turbine is to obtain a small signal model of a grid-side inverter of the wind turbine, analyze a multi-dq coordinate system coupling effect caused by a phase-locked loop, and obtain the dq admittance model of the wind turbine. The dq admittance model of the wind turbine is:

[0086] In the modeling module, the dq admittance model of the static var generator is:

[0087] In the conversion module, the step of obtaining the dq admittance model of the alternating current system according to the nodes of the wind turbine and the static var generator connected to the alternating current system is specifically: establishing a positive and negative sequence admittance model of an element of the alternating current system; calculating positive and negative sequence equivalent admittances of the alternating current system seen from the nodes of the wind turbine and the static var generator connected to the alternating current system, respectively; converting the positive and negative sequence equivalent admittances of the alternating current system into dq coordinate system to obtain the dq admittance model of the alternating current system.

[0088] The calculation of the positive and negative sequence equivalent admittances of the alternating current system seen from the nodes of the wind turbine and the static var generator connected to the alternating current system is specifically: .

[0089] In the amplitude margin obtaining module, the step of obtaining the amplitude margin as the stability margin evaluation index according to the dq admittance model of the fan, the dq admittance model of the static var generator and the dq admittance model of the alternating current system is specifically: The dq admittance model of the alternating current system is subjected to Thevenin equivalent to obtain a Thevenin equivalent circuit, the dq admittance model of the fan and the dq admittance model of the static var generator are equivalent to the form of Norton equivalent circuit, and the Thevenin equivalent circuit and the Norton equivalent circuit are connected to the corresponding position of the system to obtain the expression of the injected alternating current system current; The power system open-loop transfer function is obtained according to the expression of the injected alternating current system current; The Nyquist curve of the power system open-loop transfer function characteristic value is drawn, and the amplitude margin is calculated according to the Nyquist curve.

[0090] In the optimization module, the step of optimizing the high resistance configuration of the system according to the amplitude margin is specifically: The reactive power balance demand of the alternating current system is calculated to determine the total capacity of the high-voltage reactor; Based on the total capacity of the high-voltage reactor, the ratio of the rated capacity of the high-voltage reactor to the total capacity and the ratio of the distance from the intermediate compensation station to the booster station to the total length of the cable are obtained; Based on the total capacity of the high-voltage reactor, the ratio of the rated capacity of the high-voltage reactor to the total capacity, the ratio of the distance from the intermediate compensation station to the booster station to the total length of the cable and the system amplitude margin are used to optimize the position distribution and capacity distribution scheme of the high-voltage reactor.

[0091] An embodiment of the present application provides a terminal device. The terminal device of the embodiment comprises a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps in each of the above method embodiments are implemented. Alternatively, when the processor executes the computer program, the functions of each module / unit in each of the above device embodiments are implemented.

[0092] The computer program can be divided into one or more modules / units, which are stored in the memory and executed by the processor to complete the present application.

[0093] The terminal device can be a desktop computer, a notebook computer, a palm computer, a cloud server and other computing devices. The terminal device can include, but is not limited to, a processor and a memory.

[0094] The processor can be a central processing unit (CPU), and can also be other general-purpose processors, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, etc.

[0095] The memory can be configured to store the computer programs and / or modules, and the processor can realize various functions of the terminal device by running or executing the computer programs and / or modules stored in the memory, and calling data stored in the memory.

[0096] The modules / units integrated in the terminal device, if realized in the form of software function units and sold or used as independent products, can be stored in a computer readable storage medium. Based on such understanding, all or part of the processes in the above-mentioned embodiment methods can also be completed by a computer program instructing related hardware, and the computer program can be stored in a computer readable storage medium. When the computer program is executed by a processor, the steps of the above-mentioned various method embodiments can be realized. The computer program includes computer program code, which can be in the form of source code, object code, executable file or some intermediate form. The computer readable medium can include any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution medium, etc. It should be noted that the computer readable medium can include or exclude contents according to the requirements of legislation and patent practice in the jurisdiction, for example, in some jurisdictions, according to legislation and patent practice, the computer readable medium does not include electrical carrier signals and telecommunication signals.

Claims

1. A method for high resistance configuration to improve the resonance stability of a power system, characterized in that, The method comprises the following steps: a dq admittance model of the wind turbine and a dq admittance model of the static var generator are established; a dq admittance model of the AC system is obtained according to a node where the wind turbine and the static var generator are connected to the AC system; an amplitude margin is obtained as a stability margin evaluation index according to the dq admittance model of the wind turbine, the dq admittance model of the static var generator and the dq admittance model of the AC system; the system is optimized for high-resistance configuration according to the amplitude margin.

2. The high reactance configuration method for improving the resonance stability of a power system according to claim 1, characterized in that, The step of establishing the dq admittance model of the wind turbine is as follows: a small-signal model of a grid-side inverter of the wind turbine is obtained, a multi-dq coordinate system coupling effect caused by a phase-locked loop is analyzed based on the small-signal model of the grid-side inverter of the wind turbine, and the dq admittance model of the wind turbine is obtained according to the multi-dq coordinate system coupling effect and the small-signal model of the grid-side inverter of the wind turbine. The dq admittance model of the wind turbine is as follows: wherein, is the output impedance of the filter circuit, is the DC side voltage, is the transfer function matrix between the voltage in the dq coordinate system of the power system and the modulation signal, is the matrix composed of the steady-state values of the modulation signal, is the transfer function matrix between the DC side voltage and the DC side current of the inverter, is the transfer function matrix between the DC side current of the inverter and the modulation signal in the dq coordinate system of the system, is the transfer function matrix between the DC side current of the inverter and the AC side current, is the transfer function matrix between the AC side voltage of the inverter in the dq coordinate system of the system and the modulation signal, I is the identity matrix.

3. The method of claim 1, wherein the high resistance configuration is used to improve the resonance stability of the power system. The dq admittance model of the static var generator is as follows: wherein, is the output impedance of the filter circuit, is the DC side voltage, is the transfer function matrix between the voltage in the dq coordinate system of the power system and the modulation signal, is the matrix composed of the steady-state values of the modulation signal, is the transfer function matrix between the DC side current of the inverter and the DC side voltage, is the transfer function matrix between the modulation signal in the dq coordinate system of the system and the DC side current of the inverter, is the transfer function matrix between the AC side current and the DC side current of the inverter, is the transfer function matrix between the AC side voltage of the inverter in the dq coordinate system of the system and the modulation signal, I is the unit matrix, is the transfer function matrix between the reactive power and the AC side voltage in the dq coordinate system of the system, is the transfer function matrix between the AC side voltage in the dq coordinate system of the system and the AC side voltage in the dq coordinate system of the controller, is the transfer function matrix between the reactive power and the AC side current in the dq coordinate system of the system, is the transfer function matrix between the AC side current in the dq coordinate system of the system and the AC side current in the dq coordinate system of the controller.

4. The method of claim 1, wherein the high resistance configuration is used to improve the resonance stability of the power system. The step of obtaining the dq admittance model of the AC system according to the node where the wind turbine and the static var generator are connected to the AC system is as follows: a positive and negative sequence admittance model of an element of the AC system is established; positive and negative sequence equivalent admittances of the AC system are calculated according to the positive and negative sequence admittance model of the element of the AC system, and the wind turbine and the static var generator are connected to the node of the AC system; the positive and negative sequence equivalent admittances of the AC system are converted into a dq coordinate system to obtain the dq admittance model of the AC system.

5. The high reactance configuration method for improving the resonance stability of a power system according to claim 4, characterized in that, The positive and negative sequence equivalent admittances of the AC system are calculated according to the node where the wind turbine and the static var generator are connected to the AC system, and the step is as follows: In the formula , , , are four block matrices obtained by blocking the admittance matrix of the AC system node, represents the self-admittance matrix of the node not connected with the external device in the AC system, represents the self-admittance matrix of the node connected with the external device, is the mutual admittance matrix of the two types of nodes, is the mutual admittance matrix of the two types of nodes, Y g represents the matrix composed of the admittance of each equivalent circuit after the internal power supply of the AC system is respectively equivalent to the Norton circuit.

6. The method of claim 1, wherein the high resistance configuration is used to improve the resonance stability of the power system. The step of obtaining the amplitude margin as the stability margin evaluation index according to the dq admittance model of the wind turbine, the dq admittance model of the static var generator and the dq admittance model of the AC system is as follows: a Thevenin equivalent circuit is obtained by performing Thevenin equivalent on the dq admittance model of the AC system, the dq admittance model of the wind turbine and the dq admittance model of the static var generator are equivalent to a Norton equivalent circuit, the Thevenin equivalent circuit and the Norton equivalent circuit are connected to corresponding positions of the system, and an expression of an injected current of the AC system is obtained; an open-loop transfer function of the power system is obtained according to the expression of the injected current of the AC system; a Nyquist curve of characteristic values of the open-loop transfer function of the power system is drawn, and the amplitude margin is calculated according to the Nyquist curve.

7. The method of claim 1, wherein the high resistance configuration is used to improve the resonance stability of the power system. The step of optimizing the system for high-resistance configuration according to the amplitude margin is as follows: a reactive power balance demand of the AC system is calculated, and a total capacity of the high-voltage reactor is determined; a ratio of a rated capacity of the high-voltage reactor to the total capacity and a ratio of a distance from an intermediate compensation station to a step-up station to a total length of a cable are obtained based on the total capacity of the high-voltage reactor, so that the amplitude margin is maximum; the ratio of the rated capacity of the high-voltage reactor to the total capacity, the ratio of the distance from the intermediate compensation station to the step-up station to the total length of the cable and the amplitude margin of the system are used to optimize a position distribution and a capacity distribution scheme of the high-voltage reactor.

8. A high resistance configuration system for improving the resonance stability of a power system, characterized by, The method comprises the following steps: a modeling module is used to establish a dq admittance model of a wind turbine and a dq admittance model of a static var generator; a conversion module is used to obtain a dq admittance model of an AC system according to a node where the wind turbine and the static var generator are connected to the AC system; The amplitude margin obtaining module is configured to obtain an amplitude margin as a stability margin evaluation index according to the dq admittance model of the wind turbine, the dq admittance model of the static var generator and the dq admittance model of the AC system. The optimization module is configured to optimize the high-resistance configuration of the system according to the amplitude margin.

9. The high reactance configuration system for improving the resonance stability of a power system according to claim 8, characterized in that, In the modeling module, the dq admittance model of the wind turbine is obtained by obtaining a small signal model of a grid-side inverter of the wind turbine, analyzing a multi-dq coordinate system coupling effect caused by a phase-locked loop based on the small signal model of the grid-side inverter of the wind turbine, and obtaining the dq admittance model of the wind turbine according to the multi-dq coordinate system coupling effect and the small signal model of the grid-side inverter of the wind turbine. The dq admittance model of the wind turbine is as follows: wherein, is the output impedance of the filter circuit, is the DC side voltage, is the transfer function matrix between the voltage and the modulation signal in the dq coordinate system of the power system, is the matrix of the steady state values of the modulation signal, is the transfer function matrix between the DC side voltage and the DC side current of the inverter, is the transfer function matrix between the DC side current of the inverter and the modulation signal in the dq coordinate system of the system, is the transfer function matrix between the DC side current of the inverter and the AC side current, is the transfer function matrix between the AC side voltage of the inverter and the modulation signal in the dq coordinate system of the system, I is the identity matrix.

10. The high impedance configuration system for improving the resonance stability of a power system according to claim 8, wherein, In the modeling module, the dq admittance model of the static var generator is as follows: wherein, is the output impedance of the filter circuit, is the DC side voltage, is the transfer function matrix between the voltage in the dq coordinate system of the power system and the modulation signal, is the matrix composed of the steady-state values of the modulation signal, is the transfer function matrix between the DC side voltage and the DC side current of the inverter, is the transfer function matrix between the DC side current of the inverter and the modulation signal in the dq coordinate system of the system, is the transfer function matrix between the DC side current of the inverter and the AC side current, is the transfer function matrix between the AC side voltage of the inverter in the dq coordinate system of the system and the modulation signal, I is the unit matrix, is the transfer function matrix between the reactive power and the AC side voltage in the dq coordinate system of the system, is the transfer function matrix between the AC side voltage in the dq coordinate system of the system and the AC side voltage in the dq coordinate system of the controller, is the transfer function matrix between the reactive power and the AC side current in the dq coordinate system of the system, is the transfer function matrix between the AC side current in the dq coordinate system of the system and the AC side current in the dq coordinate system of the controller.

11. The high impedance configuration system for improving the resonance stability of a power system according to claim 8, characterized in that, In the conversion module, the dq admittance model of the AC system is obtained according to a node of the AC system where the wind turbine and the static var generator are connected. The positive and negative sequence admittance models of the elements of the AC system are established. The positive and negative sequence equivalent admittances of the AC system are calculated based on the positive and negative sequence admittance models of the elements of the AC system. The positive and negative sequence equivalent admittances of the AC system are converted into the dq coordinate system to obtain the dq admittance model of the AC system.

12. The high impedance configuration system for improving the resonance stability of a power system according to claim 11, wherein, The positive and negative sequence equivalent admittances of the AC system are calculated based on the positive and negative sequence admittance models of the elements of the AC system. In the formula , , , are four block matrices obtained by blocking the node admittance matrix of the AC system, represents the self-admittance matrix of the node in the AC system not connected with the external device, represents the self-admittance matrix of the node connected with the external device, is the mutual admittance matrix of the two types of nodes, is the mutual admittance matrix of the two types of nodes, Y g represents the matrix composed of the admittance of each equivalent circuit after the internal power sources of the AC system are respectively equivalent to the Norton circuit.

13. The high impedance configuration system for improving the resonance stability of a power system according to claim 8, wherein, In the amplitude margin obtaining module, the amplitude margin as the stability margin evaluation index is obtained according to the dq admittance model of the wind turbine, the dq admittance model of the static var generator and the dq admittance model of the AC system. The open-loop transfer function of the power system is obtained according to the expression of the injected current of the AC system. The Nyquist curve of the characteristic value of the open-loop transfer function of the power system is drawn, and the amplitude margin is calculated according to the Nyquist curve. In the optimization module, the high-resistance configuration of the system is optimized according to the amplitude margin.

14. The high impedance configuration system for improving the resonance stability of a power system according to claim 8, wherein, The total capacity of the high-voltage reactor is calculated according to the reactive power balance demand of the AC system. The ratio of the rated capacity of the high-voltage reactor to the total capacity and the ratio of the distance between the intermediate compensation station and the step-up station to the total length of the cable are obtained based on the total capacity of the high-voltage reactor. The position distribution and capacity distribution scheme of the high-voltage reactor are optimized based on the ratio of the rated capacity of the high-voltage reactor to the total capacity, the ratio of the distance between the intermediate compensation station and the step-up station to the total length of the cable and the amplitude margin of the system. The processor executes the computer program to implement the steps of the high-resistance configuration method for improving the resonance stability of the power system according to any one of claims 1 to 7.

15. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, The computer program is executed by the processor to implement the steps of the high-resistance configuration method for improving the resonance stability of the power system according to any one of claims 1 to 7. 16.A computer readable storage medium, storing a computer program, characterized in that, ​

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