An impedance amplitude-phase unified regulation oscillation suppression method and product applied to a wind power flexible direct transmission system

Abstract

The application discloses an impedance amplitude-phase unified regulation oscillation suppression method and product applied to a wind power flexible direct sending system, relates to the field of oscillation suppression, and obtains an impedance curve of a current oscillation working condition. According to the impedance curve of the current oscillation working condition, phase angle regulation parameters and amplitude regulation parameters of the wind power flexible direct sending system are determined. According to the phase angle regulation parameters and the amplitude regulation parameters, a virtual impedance oscillation suppression controller is incorporated in a current loop, the phase angle and the amplitude of the current oscillation working condition of the wind power flexible direct sending system are regulated, the impedance of the wind power flexible direct sending system after oscillation suppression is determined, and the oscillation suppression of the wind power flexible direct sending 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 MMC. The application realizes unified and coordinated control of the amplitude and the phase of the MMC output impedance curve.

Description

TECHNICAL FIELD

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

[0002] With the continuous growth of power demand and large-scale access of renewable energy, power transmission systems are facing more and more challenges. High voltage direct current (HVDC) technology is widely used in modern power systems due to its long transmission distance, low loss, and strong controllability. Flexible direct transmission mode has flexible control and no capacitance effect, which can realize efficient transmission of power 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 high modularization, strong expansion, and good output harmonic characteristics, and becomes the main topology of the converter station. However, the wind power flexible direct transmission system often encounters system oscillation problems during operation, which is a serious challenge to system stability and reliability. Oscillation suppression is a hot and difficult problem in the application of MMC.

[0003] The existing system oscillation suppression method based on impedance method mainly optimizes the device impedance by weakening or eliminating the negative resistance characteristics of the equipment port. At present, three ways of optimizing control parameters, optimizing control loop structure and connecting series / parallel compensators in the control loop can realize impedance optimization, oscillation suppression and system stability. The third way is more flexible, and many existing oscillation suppression methods are based on this. By analyzing the oscillation mechanism, a series / parallel compensator is designed to affect the oscillation generation loop, but these additional dampings are mostly compensated for impedance phase angle, and the unified regulation of impedance amplitude and phase cannot be realized, and there is also a lack of clear physical meaning. SUMMARY

[0004] The purpose of the present application is to provide an impedance amplitude and phase unified regulation oscillation suppression method and product applied to a wind power flexible direct transmission system, to realize the unified and coordinated control of the amplitude and phase of the MMC output impedance curve.

[0005] To achieve the above purpose, the present application provides the following solutions:

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

[0007] obtaining an impedance curve of a current oscillation working condition;

[0008] According to the impedance curve of the current oscillation condition, a phase angle regulation parameter and an amplitude regulation parameter of the wind power flexible direct transmission system are determined; the phase angle regulation parameter comprises a zero point compensation frequency and a pole point compensation frequency;

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

[0010] Optionally, the construction method of the virtual impedance oscillation suppression controller specifically comprises:

[0011] A seventh-order positive sequence impedance model of the wind power flexible direct transmission system is established by using the harmonic linearization method;

[0012] The seventh-order positive sequence impedance model is reduced and simplified to obtain a first-order positive sequence impedance model;

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

[0014] Based on the modular multilevel converter impedance expression form after oscillation suppression, in combination with the impedance curve of the current oscillation condition, the regulation direction of the amplitude and the phase angle is 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 regulation parameter and the amplitude regulation parameter;

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

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

[0017] wherein s is a complex domain frequency; ω d1 is a zero point compensation frequency; ω d2 is a pole point compensation frequency; and k is an amplitude regulation parameter.

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

[0019]

[0020] wherein H xn is a virtual impedance oscillation suppression controller; G(s) is an equivalent oscillation suppression effect; s is a complex domain frequency; V0 is a center element of a 7th order Toeplitz expansion matrix of a small-signal harmonic vector of a sub-module capacitor voltage; Y l is a center element of a diagonal matrix of a bridge arm inductance.

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

[0022] An oscillation frequency of the current oscillation working condition is obtained;

[0023] An extreme point and an extreme value of the equivalent oscillation suppression effect expression are determined;

[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 a phase angle adjustment amount; the phase angle adjustment amount is a set value;

[0025] According to the oscillation frequency and the phase angle adjustment amount, the phase angle regulation parameter of the wind power flexible transmission system is determined;

[0026] According to the phase angle regulation parameter, the oscillation of the wind power flexible transmission system is preliminarily suppressed, and a preliminarily suppressed impedance curve is determined;

[0027] According to the preliminarily suppressed impedance curve, the amplitude regulation parameter is determined.

[0028] Optionally, according to the oscillation frequency and the phase angle adjustment amount, the phase angle regulation parameter of the wind power flexible transmission system is determined, and specifically comprising:

[0029] The phase angle regulation parameter of the wind power flexible transmission system is determined by using a formula ; wherein ω m is an extreme point of the equivalent oscillation suppression effect expression, and the extreme point is set as an oscillation frequency of a current oscillation working condition; is an extreme value of the equivalent oscillation suppression effect expression, and the extreme value is set as a phase angle adjustment amount; ω d1 is a zero point compensation frequency; ω d2 is a pole point compensation frequency.

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

[0031]

[0032] wherein, Z MMC1 is the impedance of the MMC after oscillation suppression; M0 is the center element of the 7th Toeplitz expansion matrix of the small-signal harmonic vector of the modulation signal; I0 is the center element of the 7th Toeplitz expansion matrix of the small-signal harmonic vector of the bridge arm current; V0 is the center element of the 7th Toeplitz expansion matrix of the small-signal harmonic vector of the sub-module capacitor voltage; Y l is the center element of the diagonal matrix of the bridge arm inductance; Z c is the center element of the diagonal matrix of the module capacitor; H i is the current loop PI controller; H xn is the virtual impedance oscillation suppression controller; H v is the voltage loop PI controller; G d_mmc is the transfer function of the time delay element, ω1 is the fundamental frequency; s is the complex frequency domain; j is the imaginary unit.

[0033] In a second aspect, the application provides a computer program product, comprising a computer program which, when executed by a processor, implements the impedance amplitude and phase unified regulation oscillation suppression method applied to the wind power flexible DC transmission system according to any one of the above.

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

[0035] The application provides an impedance amplitude and phase unified regulation oscillation suppression method and product applied to a wind power flexible DC transmission system. The 7th positive sequence impedance model of the wind power flexible DC transmission system established by simplifying the harmonic linearization method is obtained to obtain an equivalent 1st positive sequence impedance model. The oscillation suppression strategy of adding a virtual impedance is adopted to add a virtual impedance oscillation suppression controller in 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 impedance curve of oscillation, the virtual impedance oscillation suppression controller is designed from the perspective of phase angle and amplitude to realize oscillation suppression. The virtual impedance oscillation suppression controller can uniformly regulate the amplitude and phase of the MMC impedance curve, effectively improve the capacitive negative damping in the MMC oscillation frequency band, increase the stability margin, and realize oscillation suppression. BRIEF DESCRIPTION OF DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description only constitute some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0037] Figure 1 A flowchart of an impedance amplitude-phase unified regulation oscillation suppression method applied to a wind power flexible direct transmission system provided by an embodiment of the present application is shown in the figure.

[0038] Figure 2 A structure schematic diagram of a Ruhao offshore wind power flexible direct transmission system is shown in the figure.

[0039] Figure 3 A wind turbine topology structure and control block diagram is shown in the figure.

[0040] Figure 4 A sending end MMC control block diagram is shown in the figure.

[0041] Figure 5 An oscillation condition MMC output voltage and current waveform schematic diagram is shown in the figure.

[0042] Figure 6 An oscillation condition MMC PCC point FFT analysis result schematic diagram is shown in the figure.

[0043] Figure 7 An oscillation condition impedance curve diagram is shown in the figure.

[0044] Figure 8 An amplitude-phase unified regulation step schematic diagram is shown in the figure.

[0045] Figure 9 An impedance curve diagram of the system after adding phase regulation is shown in the figure.

[0046] Figure 10 An MMC impedance curve comparison diagram after adding different amplitude regulation coefficients is shown in the figure.

[0047] Figure 11 An MMC output voltage and current waveform diagram after oscillation suppression is shown in the figure.

[0048] Figure 12 An oscillation suppression MMC PCC point FFT analysis result schematic diagram is shown in the figure.

[0049] Figure 13 An oscillation suppression system impedance curve and MMC impedance sweep verification schematic diagram is shown in the figure.

[0050] Figure 14 A structure schematic diagram of a computer device provided by an embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0051] 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 only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0052] The above purposes, features and advantages of the present application will be more apparent and understandable. The present application will be further described in detail below with reference to the drawings and specific embodiments.

[0053] In an exemplary embodiment, as shown in Figure 1 An impedance amplitude-phase unification regulation oscillation suppression method applied to a wind power flexible direct current transmission system is provided, including the following steps:

[0054] S1: Obtain an impedance curve of a current oscillation working condition.

[0055] S2: Determine a phase angle regulation parameter and an amplitude regulation parameter of the wind power flexible direct current transmission system according to the impedance curve of the current oscillation working condition; the phase angle regulation parameter includes a zero point compensation frequency and a pole point compensation frequency.

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

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

[0058] S22: Determine an extreme point and an extreme value of an equivalent oscillation suppression effect expression.

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

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

[0061] determining the phase angle regulation parameter of the wind power flexible direct current transmission system by using a formula ; wherein ω m is the extreme point of the equivalent oscillation suppression effect expression, the extreme point is set as the oscillation frequency of the current oscillation working condition; is the extreme value of the equivalent oscillation suppression effect expression, the extreme value is set as the phase angle adjustment amount; ω d1 is the zero point compensation frequency; ω d2 is the pole point compensation frequency.

[0062] S25: According to the phase angle regulation parameter, the oscillation of the wind power flexible DC transmission system is preliminarily suppressed, and a preliminary suppression impedance curve is determined.

[0063] S26: According to the preliminary suppression impedance curve, the amplitude regulation parameter is determined.

[0064] S3: According to the phase angle regulation parameter and the amplitude regulation parameter, a virtual impedance oscillation suppression controller is used to regulate the phase angle and amplitude of the current oscillation condition of the wind power flexible DC transmission system, so as to determine the impedance of the wind power flexible DC transmission system after oscillation suppression, and complete the oscillation suppression of the wind power flexible DC transmission system; wherein the virtual impedance oscillation suppression controller is determined by using zero-pole compensation method and based on the 1st order positive sequence impedance model of MMC; the 1st order positive sequence impedance model is obtained by reducing and simplifying the 7th order positive sequence impedance model of MMC; the 7th order positive sequence impedance model is established by using harmonic linearization method; the impedance after oscillation suppression is determined by using the MMC impedance model after oscillation suppression; the MMC impedance model after oscillation suppression is obtained by incorporating the virtual impedance oscillation suppression controller in the current loop of the 1st order positive sequence impedance model.

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

[0066] A 7th order positive sequence impedance model of MMC is established by using harmonic linearization method.

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

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

[0069]

[0070] Wherein, M0 is the center element of the 7th order Toeplitz expansion matrix of the small signal harmonic vector of the modulation signal; I0 is the center element of the 7th order Toeplitz expansion matrix of the small signal harmonic vector of the bridge arm current; V0 is the center element of the 7th order Toeplitz expansion matrix of the small signal harmonic vector of the sub-module capacitor voltage; Y l is the center element of the diagonal matrix of the bridge arm inductance; Z c is the center element of the diagonal matrix of the module capacitor; H i is the current loop PI controller; H v is the voltage loop PI controller; G d_MMCω1 is the fundamental frequency; s is the complex frequency, s = j*ω, where ω = 2*Π*f, f is the frequency; j is the imaginary unit.

[0071] The virtual impedance oscillation suppression controller with unknown expression is incorporated into the current loop of the MMC, and based on the 1st order positive sequence impedance model, the expression form of the MMC impedance model after oscillation suppression is obtained.

[0072] Based on the MMC impedance expression after oscillation suppression, the amplitude and phase angle control direction are determined by combining the impedance curve of the current oscillation condition, and the 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.

[0073] In actual application, the virtual impedance method is used to suppress the intermediate frequency oscillation of the wind power flexible transmission and delivery system, the virtual impedance oscillation suppression controller is incorporated into the MMC current loop, and the 1st order positive sequence impedance model of the MMC after oscillation suppression is obtained.

[0074]

[0075] wherein H xn is the virtual impedance oscillation suppression controller.

[0076] The impedance expression with the virtual impedance oscillation suppression controller is decomposed and common factor extraction is performed, and the specific expression of the virtual impedance with clear physical meaning is obtained in the process:

[0077]

[0078] wherein Z xn is the virtual impedance.

[0079] The common factor of Z MMC1 is extracted, and the common factor is Z MMC , and finally it is transformed into the form of two complex numbers multiplied by the original MMC impedance and the equivalent suppression effect expression:

[0080]

[0081] wherein (1+Z XN / Z MMC ) is the equivalent suppression effect expression.

[0082] The equivalent suppression effect expression is simplified and the expression form H xn of the virtual impedance oscillation suppression controller is solved, small items are ignored, frequency offset is ignored, the reciprocal of the time delay link appears after simplification, which is difficult to realize physically, and according to experience, the amplitude "1" of the link is replaced, and the following is obtained:

[0083]

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

[0085] To realize phase regulation, first, zero-pole compensation is added to the Z MMC , the MMC phase angle curve in the oscillation frequency band is adjusted, and capacitive negative damping is eliminated; then, the amplitude is further adjusted to obtain more stability margin, so that the amplitude-phase unified regulation can be realized, and therefore the equivalent suppression effect expression G(s) is designed as:

[0086]

[0087] wherein ω d1 > ω d2 is the phase lag effect, ω d1 is the zero point compensation frequency, ω d2 is the pole compensation frequency, the phase angle curve can be depressed, and vice versa, the phase angle curve is lifted, and k is the amplitude regulation coefficient.

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

[0089] In actual application, according to the impedance curve of the oscillation condition, the phase angle and amplitude of G(s) are designed in two steps, more stability margin is obtained by using the amplitude-phase unified regulation, and oscillation suppression is realized.

[0090] Firstly, the frequency ω d1 , ω d2 in the equivalent suppression effect expression is designed to realize phase regulation and obtain stability margin. The phase angle expression of G(s) has an extreme value, and the extreme point and the extreme value expression are:

[0091]

[0092] When the parameters are designed, the extreme point is set as the oscillation frequency of the current oscillation condition, and the maximum compensation phase angle is designed, and the ω d1 , ω d2 in the equivalent suppression effect expression can be obtained by solving the equation. When the virtual impedance oscillation suppression controller is designed, the frequency offset is ignored, and the compensation should be performed when the parameters are designed:

[0093] ω m = ω real - ω1.

[0094] wherein ω real is the frequency corresponding to the actual maximum compensation phase angle, and ω1 is the frequency offset.

[0095] Secondly, the amplitude regulation parameter k in the equivalent damping effect expression is designed to achieve effective amplitude adjustment and obtain more stable margin.

[0096] The amplitude regulation parameter k of G(s) is designed according to the actual impedance curve of the oscillation condition after oscillation suppression. If the amplitude curve of the working condition can obtain more stable margin, the value of k is less than 1, otherwise the value of k is greater than 1. According to the actual oscillation suppression effect, a suitable value can be selected to realize the oscillation suppression of the wind power flexible HVDC transmission system.

[0097] Through the above design, the amplitude and phase of the output impedance of the wind power flexible HVDC transmission system can be uniformly and coordinately controlled, the phase margin and amplitude margin of the wind power flexible HVDC transmission system can be effectively and synchronously improved, and the oscillation suppression capability of the wind power flexible HVDC transmission system can be improved.

[0098] The impedance amplitude-phase unified regulation oscillation suppression method applied to the wind power flexible HVDC transmission system of the present application is described by taking the Rudong project as an example.

[0099] The oscillation condition in the present embodiment is the 320Hz medium frequency oscillation phenomenon that occurred after the commissioning of the Rudong project, which is the first offshore wind power flexible HVDC transmission project in China. Figure 2 is a structural schematic diagram of the Rudong offshore wind power flexible HVDC transmission system in China. The offshore wind farm adopts full-power wind turbines, which are composed of two 400MW and one 300MW wind farms. The latter is connected to the sending-end offshore converter station adopting the modular multilevel converter (MMC) topology through the 35 / 220kV offshore booster transformer, converts the alternating current into ±400V direct current voltage, and outputs to the receiving-end offshore converter station on the flexible HVDC line, and finally sends the electric energy to the alternating current power grid.

[0100] The 320Hz medium frequency oscillation occurred in the Rudong project is mainly generated by the interaction between the wind farm and the sending-end flexible HVDC, as shown in Tables 1-3, Figure 3 and Figure 4 Tables 1, 2 and 3 are respectively the oscillation condition simulation parameters of the wind farm, the sending-end flexible HVDC and the transformer parameters between them, Figure 3 、 Figure 4 the wind turbine topology structure and control block diagram and the sending-end MMC control block diagram, Figure 3 L F is the filter inductance, C F is the filter capacitance, C dc is the DC capacitance, H pll is the phase-locked loop PI regulator, H i is the current loop PI regulator, H vdc is the DC voltage loop PI regulator. Figure 4 The parameters are mainly the PI regulators of the loops and the added virtual impedance oscillation suppression controller.

[0101] Table 1 Statistics of wind farm parameters

[0102] Parameter Value Parameter Value Filter inductance 3.03 uH Filter capacitance 73.5 mF DC link capacitance 0.89F DC link voltage 1500V AC link voltage 690V Current loop bandwidth 938 Hz Voltage loop bandwidth 25 Hz Phase locked loop bandwidth 25 Hz

[0103] Table 2 Statistics of sending-end HVDC parameters

[0104] Parameter Value Parameter Value Number of submodules 432 Bridge leg inductance 0.1H Submodule capacitance 8.7 mF Bridge leg resistance 0.05 Ω Control delay 285 us Current loop bandwidth 100 Hz Voltage loop bandwidth 30 Hz Circulating current suppression bandwidth 40 Hz

[0105] Table 3 Statistics of transformer parameters

[0106]

[0107]

[0108] The impedance amplitude-phase unified regulation and control oscillation suppression method applied to the wind power HVDC sending-out system 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 intermediate frequency oscillation occurring in the Dongdong project is the interaction of multiple factors such as sending-end MMC current inner loop, wind turbine current inner loop, and control delay. In order to simplify the impedance expression and facilitate subsequent analysis and derivation, the parts that have little effect on the MMC intermediate frequency impedance curve such as loop current suppression and the coupling between the wind turbine and the sending-end MMC are ignored, the matrix of the impedance is reduced to 1 order, and the obtained MMC impedance expression is Z MMC . The oscillation condition MMC output voltage and current waveform is shown in Figure 5 , and the FFT analysis is shown in Figure 6 . From the oscillation condition impedance curve Figure 7 , it can be seen that the MMC has capacitive negative damping near 320Hz, and the stability margin is insufficient with the wind turbine, and oscillation occurs.

[0111] (2) The virtual impedance method is used to suppress oscillation, and the virtual impedance oscillation suppression controller is incorporated into the MMC current loop (such as Figure 4 H xn ), and the first-order impedance expression after oscillation suppression is Z MMC1 . Mathematical transformation is performed on Z MMC1 to express it as the product of two complex numbers of the original impedance Z MMC and the equivalent suppression effect expression G(s). According to the complex multiplication rule, two complex numbers are multiplied, the product amplitude is the product of the amplitudes of the two items, and the product phase is the sum of the phases of the two items.

[0112] (3) According to the oscillation condition impedance curve as shown in Figure 7 , from the perspective of amplitude and phase unified regulation and control, the amplitude uses the constructed two complex multiplication, and G(s) is designed as a zero-pole compensation form with coefficients:

[0113]

[0114] Where, ω d1 >ω d2 To achieve a phase lag effect, the phase curve can be lowered. In oscillation conditions, the phase curve at 320Hz needs to be lowered to eliminate capacitive negative damping; therefore, ω is designed here. d1 >ω d2 k is the amplitude control parameter, which is selected according to the actual situation.

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

[0116]

[0117] Oscillation suppression controller parameter design:

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

[0119]

[0120] Since the frequency shift caused by the dq transformation was ignored in the previous design, the following should be made at this point:

[0121] ω m =ω real -ω1.

[0122] The frequency corresponding to the maximum compensated phase angle is designed as the oscillation frequency, i.e., ω. real =320 × 2π, Solve for ω d1 =651.838×2π, ω d2 =111.838×2π, and the impedance curve with phase adjustment at this time is as follows. Figure 9 As shown.

[0123] (2) The second step is to add a coefficient k before the transfer function of the zero-pole compensation and adjust the amplitude so that the MMC amplitude curve is in the range of zero-pole compensation. Figure 9 Based on this, the intersection point with the wind turbine impedance curve is shifted backward, thereby utilizing the wind turbine impedance curve to generate more stability margin. To reduce the amplitude, the value of k should be less than 1. The following compares several cases. Figure 10The comparison of the MMC impedance curves with different amplitude regulation coefficients after phase regulation shows that the stability margin is the largest when k = 0.8.

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

[0125] The impedance amplitude and phase unified regulation oscillation suppression method applied to the wind power flexible transmission and delivery system provided in the application includes an oscillation suppression controller transfer function design and parameter design. The method can be used to suppress the oscillation in the wind power flexible transmission and delivery system to improve the stability of the interaction between the fan side and the delivery end flexible. The oscillation suppression method effectively synchronously improves the phase margin and amplitude margin of the wind power flexible transmission and delivery system, realizes the amplitude and phase unified coordinated control of the system output impedance, effectively improves the capacitive negative damping in the MMC oscillation frequency band, increases the stability margin, realizes the suppression of the oscillation, and has the advantages of clear physical meaning of the added virtual impedance.

[0126] In an exemplary embodiment, a computer device, which can be a server or a terminal, is provided, and an internal structure diagram of the computer device can be as shown in Figure 14 . The computer device includes a processor, a memory, an input / output interface (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 external devices. The communication interface of the computer device is used to communicate with external terminals through network connection. The computer program is executed by the processor to implement an impedance amplitude and phase unified regulation oscillation suppression method applied to a wind power flexible transmission and delivery system.

[0127] Those skilled in the art can understand, Figure 14The structure shown in the figure is only a block diagram of 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 can 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 storing a computer program, and the processor executing the computer program to implement the above-mentioned impedance amplitude-phase unified regulation oscillation suppression method applied to a wind power flexible HVDC transmission system.

[0128] In an exemplary embodiment, a computer readable storage medium is provided, storing a computer program, the computer program being executed by a processor to implement the above-mentioned impedance amplitude-phase unified regulation oscillation suppression method applied to a wind power flexible HVDC transmission system.

[0129] In an exemplary embodiment, a computer program product is provided, including a computer program, the computer program being executed by a processor to implement the above-mentioned impedance amplitude-phase unified regulation oscillation suppression method applied to a wind power flexible HVDC transmission system.

[0130] It should be noted that the user information (including but not limited to user equipment information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in the present application are all information and data authorized by the user or authorized by all parties, and the collection, use and processing of related data need to 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. The computer program can be stored in a non-volatile computer readable storage medium, and when the computer program is executed, the processes of the above-mentioned embodiments of the methods can be included. Any reference to 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 storage, high-density embedded non-volatile memory, resistive memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration but not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0132] The database involved in the embodiments provided in the present application can include at least one of a relational database and a non-relational database. The non-relational database can include a distributed database based on a blockchain, etc., without being limited thereto. The processor involved in the embodiments provided in the present application can be a general-purpose processor, a central processing unit, a graphics processing unit, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., without being limited thereto.

[0133] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described, but as long as the combinations of the technical features do not exist, they should be considered as the scope of the present application.

[0134] The principles and implementation modes of the present application are described by applying specific examples herein. The above description of the embodiments is only used to help understand the method and its core idea of the present application; meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range can be changed. In conclusion, the content of the present application should not be understood as a limitation.

Claims

1. An impedance amplitude-phase unified regulation oscillation suppression method applied to a wind power flexible direct transmission system, characterized in that, The method comprises the following steps: obtaining an impedance curve of a current oscillation condition; determining a phase angle regulation parameter and an amplitude regulation parameter of a wind power flexible DC transmission system according to the impedance curve of the current oscillation condition; the phase angle regulation parameter comprises a zero point compensation frequency and a pole point compensation frequency; controlling the phase angle and the amplitude of the current oscillation condition of the wind power flexible DC transmission system by using a virtual impedance oscillation suppression controller according to the phase angle regulation parameter and the amplitude regulation parameter, so as to determine the impedance of the wind power flexible DC transmission system after oscillation suppression, and complete the oscillation suppression of the wind power flexible DC transmission system; wherein 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 a modular multilevel converter; the first-order positive sequence impedance model is obtained by reducing and simplifying a seventh-order positive sequence impedance model of the modular multilevel converter; the seventh-order positive sequence impedance model is established by using a harmonic linearization method; the impedance after oscillation suppression is determined by using a modular multilevel converter impedance model after oscillation suppression; and the modular multilevel converter impedance model after oscillation suppression is obtained by incorporating the virtual impedance oscillation suppression controller in a current loop of the first-order positive sequence impedance model.

2. The impedance amplitude-phase unified regulation oscillation suppression method applied to the wind power flexible direct transmission system according to claim 1, characterized in that, The construction method of the virtual impedance oscillation suppression controller comprises the following steps: establishing a seventh-order positive sequence impedance model of a modular multilevel converter by using a harmonic linearization method; reducing and simplifying the seventh-order positive sequence impedance model to obtain a first-order positive sequence impedance model; incorporating a virtual impedance oscillation suppression controller with an unknown expression into a current loop of the modular multilevel converter, obtaining a modular multilevel converter impedance expression after oscillation suppression based on the first-order positive sequence impedance model; judging the regulation direction of the amplitude and the phase angle based on the modular multilevel converter impedance expression after oscillation suppression and combining the impedance curve of the current oscillation condition, and determining an equivalent oscillation suppression effect expression; the equivalent oscillation suppression effect expression is a zero-pole compensation expression about the phase angle regulation parameter and the amplitude regulation parameter; determining the virtual impedance oscillation suppression controller based on the equivalent oscillation suppression effect expression.

3. The impedance amplitude-phase unified regulation oscillation suppression method applied to the wind power flexible direct transmission system according to claim 2, characterized in that, The equivalent oscillation suppression effect expression is: where s is a complex domain frequency; ω d1 is a zero compensation frequency; ω d2 is a pole compensation frequency; k is an amplitude control parameter.

4. The impedance amplitude-phase unified regulation oscillation suppression method applied to the wind power flexible direct transmission system according to claim 3, characterized in that, the virtual impedance oscillation suppression controller is: wherein H xn is a virtual impedance oscillation suppression controller; G(s) is an equivalent oscillation suppression effect; s is a complex frequency; V0 is a center element of a 7th order Toeplitz expansion matrix of a small-signal harmonic vector of a capacitor voltage of a sub-module; Y l is a center element of a diagonal matrix of a bridge arm inductance.

5. The impedance amplitude-phase unified regulation oscillation suppression method applied to the wind power flexible direct transmission system according to claim 3, characterized in that, determining the phase angle regulation parameter and the amplitude regulation parameter of the wind power flexible DC transmission system according to the impedance curve of the current oscillation condition, specifically comprising: obtaining an oscillation frequency of the current oscillation condition; determining a pole point and a pole value of the equivalent oscillation suppression effect expression; setting the pole point of the equivalent oscillation suppression effect expression as the oscillation frequency, and setting the pole value of the equivalent oscillation suppression effect expression as a phase angle adjustment amount; the phase angle adjustment amount is a set value; determining the phase angle regulation parameter of the wind power flexible DC transmission system according to the oscillation frequency and the phase angle adjustment amount; preliminarily suppressing the oscillation of the wind power flexible DC transmission system according to the phase angle regulation parameter, and determining an impedance curve after preliminary suppression; determining the amplitude regulation parameter according to the impedance curve after preliminary suppression.

6. The impedance amplitude-phase unified regulation oscillation suppression method applied to the wind power flexible direct transmission system according to claim 5, characterized in that, determining the phase angle regulation parameter of the wind power flexible DC transmission system according to the oscillation frequency and the phase angle adjustment amount, specifically comprising: Determine the phase angle regulation parameter of the wind power flexible HVDC transmission system by using the formula Determine the phase angle regulation parameter of the wind power flexible HVDC transmission system by using the formula m Set the extreme point of the equivalent oscillation suppression effect expression as the oscillation frequency of the current oscillation condition; Set the extreme point of the equivalent oscillation suppression effect expression as the oscillation frequency of the current oscillation condition; d1 ω d2 ω 7. The impedance amplitude-phase unified regulation oscillation suppression method applied to the wind power flexible direct transmission system according to claim 1, characterized in that, The impedance model of the modular multilevel converter after oscillation suppression is: wherein Z MMC1 is the impedance of the modular multilevel converter after oscillation suppression; M0 is the center element of the 7th Toeplitz expansion matrix of the small-signal harmonic vector of the modulation signal; I0 is the center element of the 7th Toeplitz expansion matrix of the small-signal harmonic vector of the bridge arm current; V0 is the center element of the 7th Toeplitz expansion matrix of the small-signal harmonic vector of the submodule capacitor voltage; Y l is the center element of the diagonal matrix of the bridge arm inductance; Z c is the center element of the diagonal matrix of the module capacitor; H i is the current loop PI controller; H xn is the virtual impedance oscillation suppression controller; H v is the voltage loop PI controller; G d_mmc is the transfer function of the time delay element, ω1 is the fundamental frequency; s is the complex frequency; j is the imaginary unit.

8. A computer program product comprising a computer program, characterized in that, The computer program is executed by the processor to realize the impedance amplitude-phase unified regulation oscillation suppression method applied to the wind power flexible direct sending system in any one of claims 1-7.

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