Impedance amplitude-phase unified regulation and control oscillation suppression method applied to wind power flexible direct output system and product

Abstract

The invention discloses an impedance amplitude-phase unified regulation and control oscillation suppression method and product applied to a wind power flexible direct output system, relates to the field of oscillation suppression, and aims to obtain an impedance curve of a current oscillation working condition. According to the impedance curve of the current oscillation working condition, phase angle regulation and control parameters and amplitude regulation and control parameters of the wind power flexible direct output system are determined; and according to the phase angle regulation and control parameters and the amplitude regulation and control parameters, a virtual impedance oscillation suppression controller is merged into a current loop, and the phase angle and the amplitude of the current oscillation working condition of the wind power flexible direct current sending-out system are regulated and controlled, so that the impedance of the wind power flexible direct current sending-out system after oscillation suppression is determined, and oscillation suppression of the wind power flexible direct current sending-out system is completed. The virtual impedance oscillation suppression controller is determined by using a zero pole compensation method and based on a first-order positive sequence impedance model of the MMC. According to the invention, unified coordination control of the amplitude and the phase of the output impedance curve of the MMC is realized.

Description

Technical Field

[0001] The present application relates to the field of oscillation suppression, and in particular to an impedance amplitude unified regulation oscillation suppression method and product applied to a wind power flexible direct current transmission system. Background Art

[0002] With the continuous growth of electricity demand and the large-scale access of renewable energy, the power transmission system is facing more and more challenges. High Voltage Direct Current (HVDC) technology is widely used in modern power systems due to its advantages such as long transmission distance, low loss and strong controllability. Flexible direct current transmission mode is flexible to control and does not have capacitor effect. It can achieve efficient transmission of electricity and is one of the main technical approaches for large-scale and long-distance offshore wind power transmission. Modular multilevel converter (MMC), as a new type of converter, has become the main topology of converter stations because of its advantages such as high modularity, strong scalability and good output harmonic characteristics. However, during the operation of wind power flexible direct current transmission system, system oscillation problems are often encountered, which is a severe challenge to the stability and reliability of the system. Oscillation suppression is a hot and difficult problem that needs to be solved in the current MMC application process.

[0003] The existing system oscillation suppression methods based on the impedance method mainly optimize the equipment impedance by weakening or eliminating the negative resistance characteristics of the equipment port. At present, the three ways of optimizing control parameters, optimizing the control loop structure, and connecting series / parallel compensators in the control loop can achieve impedance optimization, suppress oscillation, and achieve system stability. Among them, the third method is more flexible. Many existing oscillation suppression methods are based on this. By analyzing the oscillation mechanism, series / parallel compensators are designed for the loops that affect the oscillation. However, most of these additional dampings are for compensation of the impedance phase angle, which fails to achieve unified regulation of the impedance amplitude and phase, and lacks clear physical meaning. Summary of the invention

[0004] The purpose of this application is to provide an impedance amplitude-phase unified regulation oscillation suppression method and product for use in a wind power flexible direct current transmission system, so as to achieve unified and coordinated control of the amplitude and phase of the MMC output impedance curve.

[0005] To achieve the above objectives, this application provides the following solutions:

[0006] In a first aspect, the present application provides an impedance amplitude unified regulation oscillation suppression method applied to a wind power flexible direct current transmission system, comprising:

[0007] Obtain the impedance curve of the current oscillation condition;

[0008] According to the impedance curve of the current oscillation condition, the phase angle control parameters and amplitude control parameters of the wind power flexible direct current transmission system are determined; the phase angle control parameters include the zero compensation frequency and the pole compensation frequency;

[0009] According to the phase angle control parameter and the amplitude control parameter, a virtual impedance oscillation suppression controller is used to control the phase angle and amplitude of the current oscillation condition of the wind power flexible direct current transmission system, so as to determine the impedance of the wind power flexible direct current transmission system after oscillation suppression, and complete the oscillation suppression of the wind power flexible direct current transmission system; wherein, the virtual impedance oscillation suppression controller is determined by using the zero-pole compensation method and based on the first-order positive-sequence impedance model of the modular multilevel converter; the first-order positive-sequence impedance model is obtained by reducing the order and simplifying the seventh-order positive-sequence impedance model of the modular multilevel converter; the seventh-order positive-sequence impedance model is established by using the harmonic linearization method; the impedance after oscillation suppression is determined by using the impedance model of the modular multilevel converter after oscillation suppression; the impedance model of the modular multilevel converter after oscillation suppression is obtained by incorporating the virtual impedance oscillation suppression controller into the current loop of the first-order positive-sequence impedance model.

[0010] Optionally, the method for constructing the virtual impedance oscillation suppression controller specifically includes:

[0011] The 7th-order positive-sequence impedance model of the wind power flexible direct current transmission system is established by using the harmonic linearization method.

[0012] The 7th-order positive-sequence impedance model is reduced in order and simplified to obtain a 1st-order positive-sequence impedance model;

[0013] Incorporating a virtual impedance oscillation suppression controller whose expression form is unknown into the current loop of the modular multilevel converter, and obtaining an impedance expression form of the modular multilevel converter after oscillation suppression based on the first-order positive sequence impedance model;

[0014] Based on the impedance expression of the modular multilevel converter after oscillation suppression, combined with the impedance curve of the current oscillation working condition, the amplitude and phase angle control direction are judged, and an equivalent oscillation suppression effect expression is determined; the equivalent oscillation suppression effect expression is a zero-pole compensation expression about the phase angle control parameter and the amplitude control parameter;

[0015] Based on the equivalent oscillation suppression effect expression, a virtual impedance oscillation suppression controller is determined.

[0016] Optionally, the equivalent oscillation suppression effect expression is:

[0017] Where s is the complex domain frequency; ω d1 is the zero point compensation frequency; ω d2 is the pole compensation frequency; k is the amplitude control parameter.

[0018] Optionally, the virtual impedance oscillation suppression controller is:

[0019]

[0020] Among them, H xn is a virtual impedance oscillation suppression controller; G(s) is the equivalent oscillation suppression effect; s is the complex domain frequency; V 0 is the central element of the 7th-order Toeplitz expansion matrix of the small signal harmonic vector of the submodule capacitor voltage; Y l is the central element of the diagonal matrix of the bridge arm inductance.

[0021] Optionally, according to the impedance curve of the current oscillation condition, the phase angle control parameter and the amplitude control parameter of the wind power flexible direct current transmission system are determined, specifically including:

[0022] Obtaining the oscillation frequency of the current oscillation working condition;

[0023] Determine the extreme points and extreme values ​​of the expression of equivalent oscillation suppression effect;

[0024] The extreme point of the equivalent oscillation suppression effect expression is set as the oscillation frequency, and the extreme value of the equivalent oscillation suppression effect expression is set as the phase angle adjustment amount; the phase angle adjustment amount is the set value;

[0025] Determining the phase angle control parameters of the wind power flexible direct current transmission system according to the oscillation frequency and the phase angle adjustment amount;

[0026] Preliminarily suppressing the oscillation of the wind power flexible direct current transmission system according to the phase angle control parameter, and determining an impedance curve after the preliminary suppression;

[0027] The amplitude control parameter is determined according to the impedance curve after the preliminary suppression.

[0028] Optionally, determining the phase angle control parameter of the wind power flexible direct current transmission system according to the oscillation frequency and the phase angle adjustment amount specifically includes:

[0029] Using the formula Determine the phase angle control parameters of the wind power flexible direct current transmission system; where ω m is the extreme point of the equivalent oscillation suppression effect expression, and the extreme point is set to the oscillation frequency of the current oscillation condition; is the extreme value of the expression of equivalent oscillation suppression effect, and the extreme value is set to the phase angle adjustment amount; ω d1 is the zero point compensation frequency; ω d2 is the pole compensation frequency.

[0030] Optionally, the impedance model of the modular multilevel converter after oscillation suppression is:

[0031]

[0032] Among them, Z MMC1 M is the impedance of the modular multilevel converter after oscillation suppression; 0 is the central element of the 7th-order Toeplitz expansion matrix of the small signal harmonic vector of the modulation signal; I 0 is the central element of the 7th-order Toeplitz expansion matrix of the small-signal harmonic vector of the bridge arm current; V 0 is the central element of the 7th-order Toeplitz expansion matrix of the small signal harmonic vector of the submodule capacitor voltage; Y l is the central element of the diagonal matrix of the bridge arm inductance; Z c is the central element of the diagonal matrix of the module capacitance; H i is the current loop PI controller; H xn is a virtual impedance oscillation suppression controller; H v is the voltage loop PI controller; G d_mmc is the transfer function of the delay link, ω 1 is the fundamental frequency; s is the complex domain frequency; j is the imaginary unit.

[0033] In a second aspect, the present application provides a computer program product, including a computer program, which, when executed by a processor, implements any of the above-mentioned impedance amplitude unified control oscillation suppression methods applied to a wind power flexible direct current transmission system.

[0034] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0035] The present application provides an impedance amplitude-phase unified regulation oscillation suppression method and product for wind power flexible direct current transmission system. By simplifying the 7th-order positive-sequence impedance model of the wind power flexible direct current transmission system established by the harmonic linearization method, an equivalent 1st-order positive-sequence impedance model is obtained; an oscillation suppression strategy of adding virtual impedance is adopted, and a virtual impedance oscillation suppression controller is added to the current loop of the simplified model to obtain a virtual impedance expression and a specific form of the virtual impedance oscillation suppression controller; based on the oscillating impedance curve, from the perspective of phase angle and amplitude, the phase angle regulation parameters and amplitude regulation parameters of the virtual impedance oscillation suppression controller are designed to achieve oscillation suppression. The virtual impedance oscillation suppression controller of the present application can uniformly regulate the amplitude and phase of the MMC impedance curve, effectively improve the capacitive negative damping that appears in the MMC oscillation frequency band, increase the stability margin, and achieve oscillation suppression. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 A schematic flow chart of an impedance amplitude unified control oscillation suppression method applied to a wind power flexible direct current transmission system provided in one embodiment of the present application;

[0038] Figure 2 This is a structural diagram of the Rudong offshore wind power flexible direct current transmission system;

[0039] Figure 3 It is the topology structure and control block diagram of the fan;

[0040] Figure 4 This is the control block diagram of the MMC at the sending end;

[0041] Figure 5 This is a schematic diagram of the MMC output voltage and current waveforms under oscillation conditions;

[0042] Figure 6 This is a schematic diagram of the FFT analysis results of the MMC PCC point under oscillation conditions;

[0043] Figure 7 It is the impedance curve diagram of oscillation condition;

[0044] Figure 8 Schematic diagram of the steps for unified amplitude and phase regulation;

[0045] Fig. 9 This is the system impedance curve after adding phase regulation;

[0046] Fig.10 This is a comparison of the MMC impedance curves after adding different amplitude control coefficients;

[0047] Fig.11 This is the waveform of the MMC output voltage and current after oscillation suppression;

[0048] Fig.12 This is a schematic diagram of the FFT analysis results of the MMC PCC point after oscillation suppression;

[0049] Fig.13 It is the system impedance curve after oscillation suppression and the schematic diagram of MMC impedance sweep verification;

[0050] Fig.14 A schematic diagram of the structure of a computer device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0051] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0052] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0053] In an exemplary embodiment, Figure 1 As shown, a method for suppressing oscillation by unified impedance amplitude control applied to a wind power flexible direct current transmission system is provided, comprising the following steps:

[0054] S1: Get the impedance curve of the current oscillation condition.

[0055] S2: Determine the phase angle control parameters and amplitude control parameters of the wind power flexible direct current transmission system according to the impedance curve of the current oscillation condition; the phase angle control parameters include the zero compensation frequency and the pole compensation frequency.

[0056] As an optional implementation, S2 specifically includes:

[0057] S21: Obtain the oscillation frequency of the current oscillation working condition.

[0058] S22: Determine the extreme points and extreme values ​​of the expression of equivalent oscillation suppression effect.

[0059] S23: setting the extreme point of the equivalent oscillation suppression effect expression as the oscillation frequency, and setting the extreme value of the equivalent oscillation suppression effect expression as the phase angle adjustment amount; the phase angle adjustment amount is a set value, which is set according to the oscillation suppression requirements.

[0060] S24: Determine the phase angle control parameters of the wind power flexible direct current transmission system according to the oscillation frequency and the phase angle adjustment amount, specifically including:

[0061] Using the formula Determine the phase angle control parameters of the wind power flexible direct current transmission system; where ω m is the extreme point of the equivalent oscillation suppression effect expression, and the extreme point is set to the oscillation frequency of the current oscillation condition; is the extreme value of the expression of equivalent oscillation suppression effect, and the extreme value is set to the phase angle adjustment amount; ω d1 is the zero point compensation frequency; ω d2 is the pole compensation frequency.

[0062] S25: Preliminarily suppressing the oscillation of the wind power flexible direct current transmission system according to the phase angle control parameter, and determining an impedance curve after the preliminary suppression.

[0063] S26: Determine the amplitude control parameter according to the impedance curve after the preliminary suppression.

[0064] S3: According to the phase angle control parameter and the amplitude control parameter, a virtual impedance oscillation suppression controller is used to control the phase angle and amplitude of the current oscillation condition of the wind power flexible direct current transmission system, so as to determine the impedance of the wind power flexible direct current transmission system after oscillation suppression, and complete the oscillation suppression of the wind power flexible direct current transmission system; wherein, the virtual impedance oscillation suppression controller is determined by the zero-pole compensation method and based on the first-order positive-sequence impedance model of MMC; the first-order positive-sequence impedance model is obtained by reducing the order and simplifying the seventh-order positive-sequence impedance model of MMC; the seventh-order positive-sequence impedance model is established by the harmonic linearization method; the impedance after oscillation suppression is determined by the modular multi-level converter impedance model after oscillation suppression; the modular multi-level converter impedance model after oscillation suppression is obtained by incorporating the virtual impedance oscillation suppression controller into the current loop of the first-order positive-sequence impedance model.

[0065] As an optional implementation manner, the method for constructing the virtual impedance oscillation suppression controller specifically includes:

[0066] The seventh-order positive-sequence impedance model of modular multilevel converter is established using the harmonic linearization method.

[0067] The 7th-order positive-sequence impedance model is reduced in order and simplified to obtain a 1st-order positive-sequence impedance model.

[0068] In practical applications, the 7th-order positive-sequence impedance model of MMC established by the harmonic linearization method is reduced and simplified to obtain a simplified 1st-order MMC positive-sequence impedance model:

[0069]

[0070] Among them, M 0 is the central element of the 7th-order Toeplitz expansion matrix of the small signal harmonic vector of the modulation signal; I 0 is the central element of the 7th-order Toeplitz expansion matrix of the small-signal harmonic vector of the bridge arm current; V 0 is the central element of the 7th-order Toeplitz expansion matrix of the small signal harmonic vector of the submodule capacitor voltage; Y l is the central element of the diagonal matrix of the bridge arm inductance; Z c is the central element of the diagonal matrix of the module capacitance; H i is the current loop PI controller; H vis the voltage loop PI controller; G d_MMC is the transfer function of the delay link, ω 1 is the fundamental frequency; s is the complex domain frequency, s=j*ω, where ω=2*Π*f, f is the frequency; j is the imaginary unit.

[0071] A virtual impedance oscillation suppression controller with an unknown expression form is incorporated into the current loop of the MMC, and based on the first-order positive sequence impedance model, an expression form of the impedance model of the modular multilevel converter after oscillation suppression is obtained.

[0072] Based on the impedance expression of the modular multilevel converter after oscillation suppression, combined with the impedance curve of the current oscillation working condition, the amplitude and phase angle control directions are judged to determine the equivalent oscillation suppression effect expression; the equivalent oscillation suppression effect expression is a zero-pole compensation expression about the phase angle control parameter and the amplitude control parameter.

[0073] In practical applications, the virtual impedance method is used to suppress the medium-frequency oscillation in the wind power flexible direct current transmission system. A virtual impedance oscillation suppression controller is incorporated into the MMC current loop to obtain the first-order positive-sequence impedance model of the MMC after oscillation suppression.

[0074]

[0075] Among them, H xn It is a virtual impedance oscillation suppression controller.

[0076] The impedance expression with virtual impedance oscillation suppression controller added is decomposed and common factors are extracted, and the specific expression of virtual impedance with clear physical meaning is obtained in the process:

[0077]

[0078] Among them, Z xn is the virtual impedance.

[0079] Z MMC1 Perform common factor extraction, the common factor is Z MMC , and finally transformed into the two complex product forms of the original MMC impedance and the equivalent suppression effect expression:

[0080]

[0081] Among them, (1+Z XN / Z MMC ) is the equivalent inhibition effect expression.

[0082] The equivalent suppression effect expression is simplified and the expression form of the virtual impedance oscillation suppression controller is solved. xn, ignoring smaller items and frequency offset, the inverse of the delay link appears after simplification, which is difficult to achieve physically. Based on experience, the amplitude "1" of this link is used to replace this link, and we get:

[0083]

[0084] According to the impedance curve of the oscillation condition of the wind power flexible direct current transmission system, the amplitude and phase unified regulation direction is determined, and the equivalent suppression effect expression is designed.

[0085] To achieve phase control, first MMC On the basis of , zero-pole compensation is added to adjust the MMC phase angle curve of the oscillation frequency band to eliminate capacitive negative damping; the amplitude is further adjusted to obtain more stability margin, so that the amplitude and phase can be uniformly controlled. Therefore, the equivalent suppression effect expression G(s) is designed as:

[0086]

[0087] Among them, ω d1 >ω d2 is the phase lag effect, ω d1 is the zero compensation frequency, ω d2 is the pole compensation frequency, which can realize the downward pressure of the phase angle curve. On the contrary, it is the leading effect, and the phase angle curve is raised. k is the amplitude control coefficient.

[0088] Based on the equivalent oscillation suppression effect expression, a virtual impedance oscillation suppression controller is determined.

[0089] In practical applications, according to the impedance curve of the oscillation condition, the phase angle and amplitude of G(s) are designed in two steps, and unified amplitude and phase control is used to obtain more stability margin and achieve oscillation suppression.

[0090] The first step is to calculate the frequency ω in the equivalent inhibition effect expression d1 ,ω d2 Design to achieve phase angle control and obtain stability margin. The phase angle expression of G(s) has extreme values, and the extreme point and extreme expression are:

[0091]

[0092] When designing parameters, the extreme point is set to the oscillation frequency of the current oscillation condition, and the maximum compensation phase angle is designed. The equation can be solved to obtain the ω in the expression of the equivalent suppression effect. d1 ,ω d2 The frequency offset is ignored when designing the virtual impedance oscillation suppression controller, and compensation should be made when designing the parameters:

[0093] ω m =ω real -ω 1 .

[0094] where ω real is the frequency corresponding to the actual maximum compensation phase angle, ω 1 is the frequency offset.

[0095] The second step is to design the amplitude control parameter k in the equivalent suppression effect expression to achieve effective amplitude regulation and obtain more stability margin.

[0096] The amplitude control parameter k of G(s) is designed according to the actual impedance curve of the oscillation condition after oscillation suppression. If the amplitude curve can obtain more stability margin under the condition, the k value is less than 1, otherwise the k value is greater than 1. The oscillation suppression of the wind power flexible direct current transmission system can be achieved by selecting a suitable value according to the actual oscillation suppression effect.

[0097] Through the above design, the amplitude and phase of the output impedance of the wind power flexible direct current transmission system can be uniformly and coordinatedly controlled, effectively and synchronously improving the phase margin and amplitude margin of the wind power flexible direct current transmission system, thereby improving the oscillation suppression capability of the wind power flexible direct current transmission system.

[0098] Taking the Rudong project as an example, the impedance amplitude unified control oscillation suppression method applied to the wind power flexible direct current transmission system of the present application is explained.

[0099] The oscillation condition in this embodiment is the recurrence of the 320Hz medium frequency oscillation phenomenon that occurred in the Rudong Project, China's first offshore wind power flexible direct current transmission project, after it was put into operation. Figure 2 This is a schematic diagram of the structure of the Rudong offshore wind power flexible direct current transmission system in China. The offshore wind farms all use full-power wind turbines, consisting of two 400MW and one 300MW wind farms. They are then connected to the sending-end flexible direct current offshore converter station using a modular multilevel converter (MMC) topology via a 35 / 220kV offshore step-up transformer, which converts the AC power into a ±400V DC voltage and outputs it to the receiving-end flexible direct current converter station, and finally sends the power to the AC grid.

[0100] The 320Hz medium frequency oscillation in the Rudong project is mainly caused by the interaction between the wind farm and the sending end flexible direct current, as shown in Tables 1-3. Figure 3 and Figure 4 As shown in Table 1, Table 2 and Table 3, respectively, are the simulation parameters of the oscillation condition of the wind farm and the sending end flexible direct current and the transformer parameters between them. Figure 3 , Figure 4 It is the fan topology and control block diagram and the sending end MMC control block diagram. Figure 3 L F is the filter inductor, C F is the filter capacitor, C dc is the DC capacitance, H pll is the phase-locked loop PI regulator, H iis the current loop PI regulator, H vdc It is a DC voltage loop PI regulator. Figure 4 The main parameters are the PI regulator of each loop and the added virtual impedance oscillation suppression controller.

[0101] Table 1 Wind farm parameter statistics

[0102] parameter Numeric parameter Numeric Filter Inductor 3.03uH Filter capacitor 73.5mF DC Capacitor 0.89F DC voltage 1500V AC Voltage 690V Current loop bandwidth 938Hz Voltage loop bandwidth 25Hz Phase-locked loop bandwidth 25Hz

[0103] Table 2 Statistics of flexible direct current parameters at the sending end

[0104] parameter Numeric parameter Numeric Number of submodules 432 Bridge arm inductance 0.1H Submodule capacitance 8.7mF Bridge arm resistance 0.05Ω Control delay 285us Current loop bandwidth 100Hz Voltage loop bandwidth 30Hz Circulation suppression bandwidth 40Hz

[0105] Table 3 Transformer parameter statistics

[0106]

[0107]

[0108] The impedance amplitude unified control oscillation suppression method for wind power flexible direct current transmission system of the present application is applied to the above case to suppress system oscillation.

[0109] Virtual impedance oscillation suppression controller transfer function design:

[0110] (1) The main reason for the medium-frequency oscillation in the Rudong project is the interaction of multiple factors such as the inner loop of the MMC current at the sending end, the inner loop of the wind turbine current, and the control delay. In order to simplify the impedance expression and facilitate subsequent analysis and derivation, the parts that have little effect on the MMC medium-frequency impedance curve, such as the circulation suppression and the coupling between the wind turbine and the sending end MMC, are ignored. The matrix of the derived impedance is reduced to the first order, and the MMC impedance expression obtained is Z MMC The waveforms of the MMC output voltage and current under oscillation conditions are as follows: Figure 5 As shown, FFT analysis is as follows Figure 6 As shown. From the oscillation impedance curve Figure 7 It can be seen that the MMC has capacitive negative damping near 320Hz, and the interaction stability margin with the wind turbine is insufficient, resulting in oscillation.

[0111] (2) The virtual impedance method is used to suppress oscillations. The virtual impedance oscillation suppression controller is incorporated into the MMC current loop (e.g. Figure 4 Medium H xn ), the first-order impedance expression after oscillation suppression is obtained as Z MMC1 , for Z MMC1 Mathematically transform it into the original impedance Z MMC The equivalent suppression effect expression G(s) is in the form of a product of two complex numbers. According to the complex number multiplication rule, when two complex numbers are multiplied, the amplitude of the product is the product of the two amplitudes, and the phase of the product is the sum of the two phases.

[0112] (3) According to Figure 7 The impedance curve of the oscillating working condition is shown. From the perspective of unified control of amplitude and phase, the amplitude uses the constructed two complex number multiplication to design G(s) as a zero-pole compensation form with coefficients:

[0113]

[0114] Among them, ω d1 >ω d2 For the phase angle lag effect, the phase angle curve can be pressed down. In the oscillation condition, the phase angle curve at 320Hz needs to be pressed down to eliminate the capacitive negative damping. Therefore, ω is designed here. d1 >ω d2 , k is the amplitude control parameter, which should be selected according to the actual situation.

[0115] (4) According to the above derivation, after the equivalent suppression effect expression is designed, the virtual impedance oscillation suppression controller H can be inversely solved. xn The expression is as follows:

[0116]

[0117] Oscillation suppression controller parameter design:

[0118] (1) According to the impedance curve of the oscillation condition, qualitative analysis is performed and oscillation suppression is achieved by unified regulation of impedance amplitude and phase angle in two steps. The process is as follows: Figure 8 As shown. The first step is to suppress the amplitude near 320Hz by zero-pole compensation to obtain a certain stability margin. The maximum value of the phase angle compensation of the transfer function G(s) and the frequency corresponding to the maximum value are as follows:

[0119]

[0120] Since the frequency offset caused by dq conversion was ignored in the previous design, the following should be used at this time:

[0121] ω m =ω real -ω 1 .

[0122] The frequency corresponding to the maximum compensation phase angle is designed as the oscillation frequency, that is, ω real =320×2π, Solve ω d1 =651.838×2π,ω d2 =111.838×2π, the impedance curve after adding phase control is as follows Fig. 9 shown.

[0123] (2) The second step is to add the coefficient k before the transfer function of zero-pole compensation and adjust the amplitude so that the MMC amplitude curve is Fig. 9 The base is pressed down and the intersection with the wind turbine impedance curve is moved back, so that more stability margin is generated by using the wind turbine impedance curve. If the amplitude is to be reduced, the value of k should be less than 1. The following compares several cases. Fig.10 The MMC impedance curves with different amplitude control coefficients added after phase control is completed are compared. It can be seen that the stability margin is the largest when k=0.8.

[0124] (3) Select k = 0.8, ω d1 =651.838×2π,ω d2 =111.838×2π for simulation, the MMC output voltage and current waveforms are as follows Fig.11 As shown, the FFT analysis of the PCC point is as follows Fig.12 As shown, it can be seen that the system output is stable. From the impedance curve after oscillation suppression Fig.13 It can be seen that there is no negative damping in both the MMC and the fan, and the stability margin at the intersection of the two impedance curves is sufficient, and the 320Hz intermediate frequency oscillation in the original system is successfully suppressed.

[0125] The impedance amplitude-phase unified control oscillation suppression method applied to the wind power flexible direct current transmission system of the present application includes the transfer function design and parameter design of the oscillation suppression controller. It can be used to suppress oscillations occurring in the wind power flexible direct current transmission system to improve the stability of the interaction between the wind turbine side and the flexible direct current at the sending end. The oscillation suppression method described in the present invention effectively and simultaneously improves the phase margin and amplitude margin of the wind power flexible direct current transmission system, realizes the unified coordinated control of the amplitude and phase of the system output impedance, effectively improves the capacitive negative damping occurring in the MMC oscillation frequency band, increases the stability margin, realizes oscillation suppression, and has the advantage of clear physical meaning of the added virtual impedance.

[0126] In an exemplary embodiment, a computer device is provided. The computer device may be a server or a terminal. The internal structure diagram thereof may be as follows: Fig.14As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, referred to as I / O) and a communication interface. The processor, the memory and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a method for suppressing oscillations with unified impedance amplitude regulation applied to a wind power flexible direct current transmission system is implemented.

[0127] Those skilled in the art will understand that Fig.14 The structure shown in the figure is only a block diagram of a part of the structure related to the scheme of the present application, and does not constitute a limitation on the computer device to which the scheme of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components. In an exemplary embodiment, a computer device is provided, including a memory and a processor, the memory stores a computer program, and the processor implements the above-mentioned impedance amplitude unified control oscillation suppression method applied to the wind power flexible direct current transmission system when executing the computer program.

[0128] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program, which, when executed by a processor, implements the impedance amplitude unified regulation oscillation suppression method applied to a wind power flexible direct current transmission system.

[0129] In an exemplary embodiment, a computer program product is provided, including a computer program, which, when executed by a processor, implements the impedance amplitude unified regulation oscillation suppression method applied to a wind power flexible direct current transmission system.

[0130] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0131] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0132] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

[0133] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0134] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. An impedance amplitude unified control oscillation suppression method applied to a wind power flexible direct current transmission system, characterized in that: include: Obtain the impedance curve of the current oscillation condition; Determine the phase angle control parameters and amplitude control parameters of the wind power flexible direct current transmission system according to the impedance curve of the current oscillation condition; The phase angle control parameters include zero compensation frequency and pole compensation frequency; According to the phase angle control parameter and the amplitude control parameter, a virtual impedance oscillation suppression controller is used to control the phase angle and amplitude of the current oscillation condition of the wind power flexible direct current transmission system, so as to determine the impedance of the wind power flexible direct current transmission system after oscillation suppression, and complete the oscillation suppression of the wind power flexible direct current transmission system; wherein, the virtual impedance oscillation suppression controller is determined by using the zero-pole compensation method and based on the first-order positive-sequence impedance model of the modular multilevel converter; the first-order positive-sequence impedance model is obtained by reducing the order and simplifying the seventh-order positive-sequence impedance model of the modular multilevel converter; the seventh-order positive-sequence impedance model is established by using the harmonic linearization method; the impedance after oscillation suppression is determined by using the impedance model of the modular multilevel converter after oscillation suppression; the impedance model of the modular multilevel converter after oscillation suppression is obtained by incorporating the virtual impedance oscillation suppression controller into the current loop of the first-order positive-sequence impedance model.

2. The impedance amplitude unified control oscillation suppression method for wind power flexible direct current transmission system according to claim 1 is characterized in that: The method for constructing the virtual impedance oscillation suppression controller specifically includes: The seventh-order positive-sequence impedance model of modular multilevel converter is established using harmonic linearization method; The 7th-order positive-sequence impedance model is reduced in order and simplified to obtain a 1st-order positive-sequence impedance model; Incorporating a virtual impedance oscillation suppression controller whose expression form is unknown into the current loop of the modular multilevel converter, and obtaining an impedance expression of the modular multilevel converter after oscillation suppression based on the first-order positive sequence impedance model; Based on the impedance expression of the modular multilevel converter after oscillation suppression, combined with the impedance curve of the current oscillation working condition, the amplitude and phase angle control direction are judged, and an equivalent oscillation suppression effect expression is determined; the equivalent oscillation suppression effect expression is a zero-pole compensation expression about the phase angle control parameter and the amplitude control parameter; Based on the equivalent oscillation suppression effect expression, a virtual impedance oscillation suppression controller is determined.

3. The impedance amplitude unified control oscillation suppression method for wind power flexible direct current transmission system according to claim 2 is characterized in that: The equivalent oscillation suppression effect expression is: Where s is the complex domain frequency; ω d1 is the zero point compensation frequency; ω d2 is the pole compensation frequency; k is the amplitude control parameter.

4. The impedance amplitude unified control oscillation suppression method for wind power flexible direct current transmission system according to claim 3 is characterized in that: The virtual impedance oscillation suppression controller is: Among them, H xn is a virtual impedance oscillation suppression controller; G(s) is the equivalent oscillation suppression effect; s is the complex domain frequency; V0 is the central element of the 7th-order Toeplitz expansion matrix of the small signal harmonic vector of the submodule capacitor voltage; Y l is the central element of the diagonal matrix of the bridge arm inductance.

5. The impedance amplitude unified control oscillation suppression method for wind power flexible direct current transmission system according to claim 3 is characterized in that: According to the impedance curve of the current oscillation condition, the phase angle control parameters and amplitude control parameters of the wind power flexible direct current transmission system are determined, specifically including: Obtaining the oscillation frequency of the current oscillation working condition; Determine the extreme points and extreme values ​​of the expression of equivalent oscillation suppression effect; The extreme point of the equivalent oscillation suppression effect expression is set as the oscillation frequency, and the extreme value of the equivalent oscillation suppression effect expression is set as the phase angle adjustment amount; the phase angle adjustment amount is the set value; Determining the phase angle control parameters of the wind power flexible direct current transmission system according to the oscillation frequency and the phase angle adjustment amount; Preliminarily suppressing the oscillation of the wind power flexible direct current transmission system according to the phase angle control parameter, and determining an impedance curve after the preliminary suppression; The amplitude control parameter is determined according to the impedance curve after the preliminary suppression.

6. The impedance amplitude unified control oscillation suppression method for wind power flexible direct current transmission system according to claim 5 is characterized in that: Determining the phase angle control parameters of the wind power flexible direct current transmission system according to the oscillation frequency and the phase angle adjustment amount specifically includes: Using the formula Determine the phase angle control parameters of the wind power flexible direct current transmission system; where ω m is the extreme point of the equivalent oscillation suppression effect expression, and the extreme point is set to the oscillation frequency of the current oscillation condition; is the extreme value of the expression of equivalent oscillation suppression effect, and the extreme value is set to the phase angle adjustment amount; ω d1 is the zero point compensation frequency; ω d2 is the pole compensation frequency.

7. The impedance amplitude unified control oscillation suppression method for wind power flexible direct current transmission system according to claim 1 is characterized in that: The impedance model of the modular multilevel converter after oscillation suppression is: Among them, Z MMC1 is the impedance of the modular multilevel converter after oscillation suppression; M0 is the central element of the 7th order Toeplitz expansion matrix of the small signal harmonic vector of the modulation signal; I0 is the central element of the 7th order Toeplitz expansion matrix of the small signal harmonic vector of the bridge arm current; V0 is the central element of the 7th order Toeplitz expansion matrix of the small signal harmonic vector of the submodule capacitor voltage; Y l is the central element of the diagonal matrix of the bridge arm inductance; Z c is the central element of the diagonal matrix of the module capacitance; H i is the current loop PI controller; H xn is a virtual impedance oscillation suppression controller; H v is the voltage loop PI controller; G d_mmc is the transfer function of the delay link, ω1 is the base frequency; s is the complex domain frequency; j is the imaginary unit.

8. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the impedance amplitude unified regulation oscillation suppression method applied to a wind power flexible direct current transmission system as described in any one of claims 1 to 7 is implemented.

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