A method and system for suppressing subsynchronous oscillation based on parallel converters

Abstract

The present invention proposes a subsynchronous oscillation suppression method and system based on a parallel converter, which relates to the technical field of power system stability and control. The method includes: constructing a coupling impedance model based on a series compensation wind farm and a parallel converter, obtaining the desired system total resistance at the resonant frequency, and calculating the system coupling impedance corresponding to the system total resistance; inputting the power generation side impedance, the grid impedance and the coupling impedance satisfying the resistance constraint condition into a coupling coefficient calculator to sequentially obtain the coupling grid impedance and the parallel converter admittance; according to the coupling grid impedance and the parallel converter admittance, obtaining a coupling vector and calculating the standard amplitude and standard phase of the coupling vector, using the standard amplitude and the standard phase as the design parameters of the phase shifter, and obtaining the phase lag and time constant of the phase shifter; based on the phase lag and the time constant, correspondingly adjusting the control parameters of the subsynchronous damping controller to suppress subsynchronous oscillation. The present invention is helpful to improve the responsiveness and stability of the power system to unstable factors.

Description

Technical Field

[0001] The present invention relates to the technical field of power system stabilization and control, and in particular to a subsynchronous oscillation suppression method and system based on parallel converters. Background Art

[0002] As one of the most reliable renewable energy sources, wind power generation is developing rapidly. Since wind farms are usually far away from residential and commercial load centers, series compensation capacitors are widely used to improve the transmission capacity of long-distance transmission lines. However, there is a sub-synchronous control interaction (SSCI) between wind turbine controllers and series compensated transmission lines, which leads to sub-synchronous oscillation (SSO) problems.

[0003] The Chinese patent with the announcement number CN107017646B discloses a method for suppressing subsynchronous oscillation of a doubly fed wind turbine based on virtual impedance control. The dq axis component of the doubly fed wind turbine rotor current is used as the input signal, and the subsynchronous current component is obtained after filtering the low-frequency component and the fundamental frequency component through a bandpass filter; the current component introduces a virtual impedance in the rotor circuit through a proportional amplifier and a differential link, thereby increasing the subsynchronous oscillation damping and suppressing the subsynchronous oscillation. Starting from the rotor controller structure, the present invention studies the relationship between the rotor current and the output voltage of the rotor controller, and obtains the equivalent resistance of the rotor side controller, that is, the virtual resistance value; then the doubly fed wind turbine rotor current transfer function model is used to solve the virtual inductance value required for virtual impedance control. However, the above scheme improves the wind turbine control system or the flexible direct current control system to achieve the suppression effect. The suppression method of changing the wind turbine control strategy proposed on the basis of the rotor controller structure needs to adjust each wind turbine in the wind farm, which has a large amount of engineering and parameter deviation is inevitable. Therefore, it is very necessary to provide a subsynchronous oscillation suppression method and system based on parallel converters to achieve the purpose of reducing parameter deviations and improve the system's responsiveness and stability to unstable factors. Summary of the invention

[0004] In view of this, the present invention proposes a subsynchronous oscillation suppression method and system based on parallel converters. By constructing a coupling impedance model and calculating the system impedance resistance value and resistance constraint conditions to determine whether the signal input to the coupling coefficient calculator needs to be regulated, the coupling grid impedance and the system impedance resistance value are regulated at the same time, and the control parameters of the coupling coefficient calculator are adjusted according to the above parameters, which effectively alleviates the subsynchronous oscillation problem and improves the system's responsiveness and stability to unstable factors.

[0005] The present invention provides a method for suppressing subsynchronous oscillation based on parallel converters, the method comprising:

[0006] Constructing a coupling impedance model based on a series-compensated wind farm and a parallel converter, obtaining a desired total system resistance at a resonant frequency, and calculating a system coupling impedance corresponding to the total system resistance;

[0007] Input the power generation side impedance, the grid impedance and the coupling impedance satisfying the resistance constraint condition into the coupling coefficient calculator to obtain the coupling grid impedance and the parallel converter admittance in turn;

[0008] According to the coupled grid impedance and the parallel converter admittance, respectively calculating the standard amplitude and standard phase of the coupling vector, and using the standard amplitude and the standard phase as design parameters of the phase shifter to obtain the phase lag and time constant of the phase shifter;

[0009] Based on the phase lag and the time constant, control parameters of the subsynchronous damping controller are adjusted accordingly to suppress subsynchronous oscillations.

[0010] On the basis of the above technical solution, preferably, obtaining the expected total system resistance at the resonant frequency and calculating the system coupling impedance corresponding to the total system resistance specifically includes:

[0011] Obtain the resonant frequency when the reactance in the system impedance is zero, and calculate the generation side resistance and grid resistance at the resonant frequency;

[0012] The coupled impedance model obtains the total system resistance at the resonant frequency according to the power system's generation side impedance and the grid impedance at the resonant frequency;

[0013] Based on the total system resistance and the grid-side impedance, a system coupling impedance is calculated.

[0014] On the basis of the above technical solution, preferably, the expression of the system coupling impedance is:

[0015] k=k d cosθ d +jk d sinθ d

[0016]

[0017] Z sys (s)=Z1(s)+Z e (s)

[0018] Among them, Z sys(s) represents the system coupling impedance, Z1(s) represents the power generation side impedance, Z2(s) represents the grid side impedance, Z3(s) represents the shunt impedance, and Z e (s) represents the equivalent coupled grid impedance of the grid side impedance Z2(s) and the shunt impedance Z3(s), s n represents the Laplace operator at the resonant frequency, k represents the coupling vector, k d represents the magnitude of the coupling vector k, θ d represents the phase of the coupling vector k.

[0019] More preferably, the power generation side impedance satisfying the resistance constraint condition, the grid impedance and the system coupling impedance satisfying the resistance constraint condition are input into a coupling coefficient calculator, so that the coupling coefficient calculator outputs the coupled grid impedance and the parallel converter admittance, specifically including:

[0020] Determining whether the total resistance value of the system is less than a preset resistance value;

[0021] If the system impedance resistance value is less than the preset resistance value, the power generation side impedance, the grid impedance and the system coupling impedance satisfying the resistance constraint condition are input into a coupling coefficient calculator;

[0022] The coupling coefficient calculator calculates the coupled grid impedance and the parallel converter admittance in sequence according to the power generation side impedance, the grid impedance and the system coupling impedance satisfying the resistance constraint condition.

[0023] More preferably, the expression of the coupled grid impedance is:

[0024] Z e =R2-(1+k m )ΔR-jX1

[0025] Among them, Z e represents the coupling grid impedance, R2 represents the gate side resistance value, k m represents the resistance margin, ΔR represents the sum of the resistance value on the generator side and the resistance value on the grid side at the resonant frequency, and X1 represents the inductive reactance on the generator side at the resonant frequency.

[0026] More preferably, the amplitude and phase of the coupling vector in the coupling coefficient calculator are respectively expressed as:

[0027]

[0028] Y3=k·Y2

[0029]

[0030]

[0031] Where, Y3 represents the parallel converter admittance, Y e Indicates the equivalent coupled grid impedance Z e (s) is the coupled grid admittance corresponding to the grid impedance, Y2 is the grid admittance corresponding to the grid impedance, R1 is the generator resistance at the resonant frequency, X1 is the generator inductive reactance at the resonant frequency, R2 is the grid resistance, X2 is the grid capacitive reactance, k m represents the resistance margin, ΔR represents the sum of the resistance value of the generator side and the resistance value of the grid side at the resonant frequency, k d represents the magnitude of the coupling vector k, θ d represents the phase of the coupling vector k, and Im represents the imaginary part of a complex number.

[0032] More preferably, the expression of the time constant is:

[0033] θ PS =θ d -θ BSF -θ BPF -θ c

[0034]

[0035] Among them, θ PS represents the phase lag of the phase shifter, θ d represents the phase of the coupling vector k, θ BSF represents the phase difference caused by the band-stop filter, θ BPF represents the phase difference caused by the bandpass filter, θ c represents the current inner loop bandwidth of the parallel converter, and T represents the time constant of the phase shifter.

[0036] In a second aspect of the present application, a subsynchronous oscillation suppression system based on a parallel converter is provided, wherein the subsynchronous oscillation suppression system comprises a coupling impedance construction module, a coupling parameter design module and an oscillation suppression control module connected in sequence, wherein:

[0037] The coupling impedance building module is used to build a coupling impedance model based on the series compensation wind farm and the parallel converter, obtain the expected total system resistance at the resonant frequency, and calculate the system coupling impedance corresponding to the total system resistance;

[0038] The coupling parameter design module is used to input the power generation side impedance, the grid impedance and the system coupling impedance that meets the resistance constraint condition into the coupling coefficient calculator, so that the coupling coefficient calculator outputs the coupled grid impedance and the parallel converter admittance, and calculates the standard amplitude and standard phase of the coupling vector according to the coupled grid impedance and the parallel converter admittance respectively, and uses the standard amplitude and the standard phase as the design parameters of the phase shifter to obtain the phase lag and time constant of the phase shifter;

[0039] The oscillation suppression control module is used to adjust the control parameters of the subsynchronous damping controller accordingly based on the phase lag and the time constant to suppress subsynchronous oscillations.

[0040] In a third aspect of the present application, an electronic device is provided, comprising a processor, a memory, a user interface and a network interface, wherein the memory is used to store instructions, the user interface and the network interface are used to communicate with other devices, and the processor is used to execute the instructions stored in the memory.

[0041] In a fourth aspect of the present application, a computer-readable storage medium is provided, on which a computer program is stored, and the computer program is executed by a processor to implement the steps of a subsynchronous oscillation suppression method based on parallel converters.

[0042] The subsynchronous oscillation suppression method and system based on parallel converters provided by the present invention have the following beneficial effects compared with the prior art:

[0043] (1) By constructing a coupling impedance model and calculating the system impedance resistance value and resistance constraint conditions, it is determined whether the signal input to the coupling coefficient calculator needs to be regulated. At the same time, the power generation side impedance, the grid impedance, and the system coupling impedance that meets the resistance constraint conditions are regulated, and the control parameters of the coupling coefficient calculator are adjusted according to the above parameters, thereby ensuring the accuracy and effectiveness of the control strategy. In addition, through the dynamic adjustment of the standard amplitude and standard phase, the system can better adapt to changes in grid conditions, improve the responsiveness and stability of the power system to unstable factors, effectively alleviate the subsynchronous oscillation problem, and enhance the stability of the power system and the flexibility of operation;

[0044] (2) By calculating the vector relationship between the grid-side impedance Z2 and the shunt impedance Z3, the system impedance can be adjusted more accurately, which helps to more effectively control and suppress subsynchronous oscillations, thereby enhancing the stability of the entire power system. e By analyzing the changes in parameters, it is possible to identify risks that may lead to performance degradation or even system instability, and help avoid adverse effects caused by parameter deviations. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 A flow chart of a subsynchronous oscillation suppression method based on parallel converters provided by the present invention;

[0047] Figure 2 A simplified schematic diagram of a test system and a proportional current coupled parallel converter provided by the present invention;

[0048] Figure 3 An equivalent circuit diagram of the test system and the proportional current coupled parallel converter provided by the present invention;

[0049] Figure 4 A simplified equivalent circuit diagram of the test system and the proportional current coupled parallel converter provided by the present invention;

[0050] Figure 5 A coupling impedance model of the test system and parallel converter provided by the present invention in the Laplace domain;

[0051] Figure 6 The power generation side impedance Z1, the grid side impedance Z2, the shunt impedance Z3 and the admittance vector diagram thereof provided by the present invention;

[0052] Figure 7 The grid side impedance Z2, the shunt impedance Z3 and the corresponding admittance vector diagram under different resistance margins provided by the present invention;

[0053] Figure 8 The coupling vector k deviation to Z when different resistance margins are provided by the present invention e Vector diagram of the impact;

[0054] Fig. 9 A schematic diagram of the structure of the subsynchronous oscillation suppression system provided by the present invention;

[0055] Fig.10 This is a schematic structural diagram of an electronic device provided by the present invention.

[0056] Explanation of the accompanying drawings: 1. Subsynchronous oscillation suppression system; 11. Coupling impedance construction module; 12. Coupling parameter design module; 13. Oscillation suppression control module; 2. Electronic device; 21. Processor; 22. Communication bus; 23. User interface; 24. Network interface; 25. Memory. DETAILED DESCRIPTION

[0057] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0058] The present invention discloses a subsynchronous oscillation suppression method based on parallel converters, referring to Figure 1 The method includes steps S1 to S4.

[0059] Step S1, constructing a coupling impedance model based on a series compensated wind farm and a parallel converter, constructing a coupling impedance model based on a series compensated wind farm and a parallel converter, obtaining a desired system total resistance at a resonant frequency, and calculating a system coupling impedance corresponding to the system total resistance.

[0060] In this step, a series-compensated DFIG-type wind farm with N wind turbines is selected as the experimental system. Assuming that the wind speed and parameters of the wind turbines are the same, the simplified representation of the test system and the shunt converter with proportional current coupling is as follows: Figure 2 As shown in the figure, the DFIG type wind farm is connected to the infinite grid through an equivalent series compensation line, and a parallel converter with proportional current coupling is added to the output port of the wind farm. Symbols i1, i2 and i3 represent the current on the generating side, the current on the grid side and the parallel current respectively.

[0061] like Figure 3 As shown, R r , R s , R T and R g Respectively represent the resistance of the rotor winding, stator winding, transformer and transmission line, R RSC and R GSC are the equivalent resistances of the rotor-side converter (RSC) and grid-side converter (GSC) of the doubly-fed induction generator (DFIG), respectively, and L r , L s , L T and L g Respectively represent the inductance of the rotor winding, stator winding, transformer and transmission line, L GSC Represents the equivalent inductance of the grid-side converter, L m represents the mutual inductance between the rotor winding and the stator winding, C g represents the series compensation capacitance of the transmission line, u r and u g They represent the equivalent voltage of the rotor-side converter and the grid voltage respectively, n represents the number of wind turbines running online, ss Indicates rotor slip s s =(f s -f m ) / f s , where f s and f m represent the stator frequency and rotor frequency respectively.

[0062] Sometimes the equivalent circuit can be simplified with acceptable modeling error. Since the impedance of the grid-side converter is always much larger than that of the rotor-side converter, the impedance branch of the grid-side converter can be omitted. In addition, the impedance of the mutual inductance is usually several dozen times larger than the impedance of the rotor side and the grid side, and has little impact on the system. Therefore, the mutual inductance branch is also omitted. The simplified equivalent circuit diagram of the test system and the parallel converter with proportional current coupling is shown in Figure 4 shown.

[0063] Among them, the parallel current is proportional to the current on the generating side or the current on the grid side.

[0064] i3(ω n )=k·i i (ω n )i∈(1,2)

[0065] Among them, i3(ω n ) represents the reference resonant current output at the resonant frequency. When i=1, i i (ω n ) represents the current on the generating side at the resonant frequency. When i=2, i i (ω n ) represents the grid-side current at the resonant frequency, and k represents the coupling vector.

[0066] It is important to note that if the shunt current is proportional to the generator current, the shunt converter should be analyzed together with the generator system. Similarly, if the shunt current is proportional to the grid current, the shunt converter should be analyzed together with the grid system. Since the shunt converter is considered as a controlled current source rather than an independent system, any attempt to analyze it separately from its coupled input signal may destroy the coupling and compromise the validity of the analysis.

[0067] The coupled impedance model of the test system and the parallel converter in the Laplace domain is as follows: Figure 5 As shown in Figure 1, the model is derived at the target frequency ω (rather than the synchronous frequency). Where s represents the Laplace operator, and s = jω, Z1(s) and Z2(s) are the generator side impedance and grid side impedance respectively, and Z3(s) is the equivalent impedance of the parallel converter, which can be obtained by coupling

[0068] If the parallel current is coupled with the generator current, the parallel impedance should be aggregated with the generator impedance, such as Figure 5 (a). On the contrary, if the shunt current is coupled with the grid-side current, the shunt impedance should be aggregated with the grid-side impedance, as shown in Figure 5 (b) as shown.

[0069] The expression of the equivalent resistance value of the RSC controller in the three-phase coordinate system is:

[0070]

[0071] Among them, s represents the Laplace operator, k p1 represents the proportional coefficient of the outer loop of the RSC controller, k i1 represents the integral coefficient of the outer loop of the RSC controller, k p2 represents the proportional coefficient of the inner loop of the RSC controller, k i2 Represents the integral coefficient of the RSC controller inner loop, e s is the stator voltage amplitude; ω s Indicates the rated angular velocity, L m represents the mutual inductance between the rotor winding and the stator winding, L s Represents the inductance of the stator winding.

[0072] In this embodiment, the resonant frequency when the reactance in the system impedance is zero is obtained, and the generation side resistance and the grid resistance at the resonant frequency are calculated; the coupled impedance model obtains the total system resistance at the resonant frequency based on the generation side impedance and the grid impedance of the power system at the resonant frequency; based on the total system resistance and the grid side impedance at the resonant frequency, the system coupling impedance is calculated.

[0073] The expression of system coupling impedance is:

[0074] k=k d cosθ d +jk d sinθ d

[0075]

[0076] Z sys (s)=Z1(s)+Z e (s)

[0077] Among them, Z sys (s) represents the system coupling impedance, Z1(s) represents the generation side impedance, Z2(s) represents the grid side impedance, Z3(s) represents the shunt impedance, and Z e (s) represents the equivalent coupled grid impedance of the grid side impedance Z2(s) and the shunt impedance Z3(s), s nrepresents the Laplace operator at the resonant frequency, k represents the coupling vector, k d represents the magnitude of the coupling vector k, θ d represents the phase of the coupling vector k.

[0078] Step S2, inputting the power generation side impedance, the grid impedance and the coupling impedance satisfying the resistance constraint condition into the coupling coefficient calculator to obtain the coupling grid impedance and the parallel converter admittance in sequence.

[0079] In this step, step S2 also includes steps S21 to S23.

[0080] Step S21, determining whether the total resistance value of the system is less than a preset resistance value.

[0081] By finding the frequency at which the reactance of the system impedance is zero, the resonant frequency f of the system can be obtained. n . From this, the system impedance resistance value at the resonant frequency is:

[0082] R sys (s n )=Re|Z sys (s n )|

[0083] Among them, s n is the Laplace operator at the resonant frequency, and Re represents the real part of a complex number.

[0084] In this embodiment, when the system impedance resistance value R sys (s n )<0, the system is unstable, otherwise, the system is stable.

[0085] Step S22: if the system impedance resistance value is less than the preset resistance value, the power generation side impedance, the grid impedance, and the coupling impedance that meets the resistance constraint condition are input into the coupling coefficient calculator.

[0086] Furthermore, a subsynchronous damping controller (SSDC) based on a parallel converter is added to the parallel converter to simulate the parallel impedance, wherein the subsynchronous damping controller includes a band stop filter (BSF), a band pass filter (BPF), a gain block and a phase shifter.

[0087] Since the designed shunt impedance only considers the resonant frequency, the stator frequency ω is selected s and the resonant frequency ω n They are used as the center frequencies of the band-stop filter and the band-pass filter respectively, and the fundamental frequency of the input current is removed to extract the resonant component of the input signal.

[0088] The transfer functions of the band-stop filter and the band-pass filter are expressed as:

[0089]

[0090]

[0091] Among them, ζ0 and ζ n Denote the damping ratio of the band-stop filter and the band-pass filter, ω n represents the resonant frequency, s represents the Laplace operator, and in this embodiment, the damping ratios of the band-stop filter and the band-pass filter are set to 0.5 and 2, respectively.

[0092] The amplitude k of the coupling vector is adjusted by the gain block and the phase shifter d and phase θ d , the phase shifter uses two lead-lag modules, which can be expressed as:

[0093]

[0094] Wherein, T1 and T2 are the time constants of the phase shifter, which determine the phase difference between the input signal and the output signal of the phase shifter. The subsynchronous damping controller outputs the reference resonant current i* 3n , as the input signal of the controller in the parallel converter.

[0095] Considering the dynamic characteristics of the parallel converter, there is a phase difference between the reference current and the injected current. The dynamic transfer function of the parallel converter can be expressed as:

[0096]

[0097] Among them, k c represents the steady-state gain of the inner loop of the parallel converter, T c It represents the delay of the inner loop of the parallel converter. The delay of the inner loop of the parallel converter is generally 5ms. s represents the Laplace operator.

[0098] Step S23, calculating the coupled grid impedance and the parallel converter admittance in sequence according to the generator side impedance, the grid impedance and the coupled system impedance that satisfies the resistance constraint condition.

[0099] In this step, since there is only fundamental frequency voltage in the infinite grid, u p The resonant component of can be regarded as proportional to the resonant component of i2, and the proportionality coefficient is the grid side impedance. p As an input signal, the shunt impedance is associated with the grid side impedance Z2(s), which is the same as i2. However, in the actual subsynchronous oscillation problem, the resonant component at u p The percentage content in u is much lower than that in i2. p It shows a lower signal-to-noise ratio. Therefore, i2 is higher than u pMore suitable for sub-synchronous damping controller. Therefore, i2 is the most suitable signal for sub-synchronous damping controller and can be used as a supplementary signal, while i1 is not recommended. Therefore, i2 is selected as the input signal of sub-synchronous damping controller.

[0100] Furthermore, in addition to the type of input signal, the direction of the input signal and the shunt current also need to be carefully considered. If the system current is selected as the input signal, the direction of the current can be considered to be the same only when all currents flow into or out of the PCC. p As the input signal, only when the parallel current flows into the PCC can it be considered that u p The equivalent impedance of the shunt converter is valid only when the input signal direction is the same as the shunt current direction. If the input signal and the shunt current are in opposite directions, the phase of vector k will be θ d +180°, impedance needs to be recalculated.

[0101] In order to facilitate a more direct analysis, the symbol Z i (sn) is simplified to Z i , Z i . i The resistance and inductance of Z2 are denoted as R1 and X1 respectively; the resistance and capacitive reactance of Z2 are R2 and X2 respectively. At the resonant frequency, X1 = X2. First, the aggregate impedance Z of the grid side impedance Z2 and the shunt impedance Z3 is designed. e , then Z2 and the designed Z e Export Z3.

[0102] When the system resistance is greater than zero, the subsynchronous oscillation problem can be eliminated, that is,

[0103] R1+Re|Z e |>0

[0104] In order to ensure the effectiveness of the subsynchronous damping controller, a resistance margin needs to be reserved. Therefore, the above formula can be rewritten as:

[0105] Re|Z e |=R2-(1+k m )·ΔR=R2-(1+k m )·(R1+R2)

[0106] Among them, k m is the resistance margin, ΔR is the sum of the resistance value on the generator side and the resistance value on the grid side at the resonant frequency. When ΔR is negative, the larger the resistance margin is, the more stable the system is. However, the larger the resistance margin is, the worse the reliability of the subsynchronous damping controller is. Here the resistance margin is set to 0.5.

[0107] In addition, it should be noted that due to the coupled grid impedance Ze The resistor is designed at a fixed resonant frequency and may be invalid if the system resonant frequency changes significantly due to the shunt impedance. Therefore, a limit is added to the reactance of the coupled grid impedance Ze.

[0108] Im|Z e |=Im|Z2

[0109] The expression of the coupled grid impedance at the resonant frequency is:

[0110] Z e =R2-(1+k m )ΔR-jX1

[0111] Among them, Z e represents the coupled grid impedance, R2 represents the grid side resistance value, k m represents the resistance margin, ΔR represents the sum of the resistance value on the generator side and the resistance value on the grid side at the resonant frequency, and X1 represents the inductive reactance on the generator side at the resonant frequency.

[0112] like Figure 6 As shown, in order to simplify the analysis of the parallel impedance branch, the impedance is converted into admittance, and the relationship between the power supply side impedance Z1, the grid side impedance Z2 and the shunt impedance Z3 at the resonant frequency is represented by constructing an impedance and admittance vector diagram.

[0113] The amplitude and phase of the coupling vector k in the coupling coefficient calculator are expressed as:

[0114]

[0115] Y3=k·Y2

[0116] When Y2 and Y3 are available, the amplitude and phase of vector k can be derived as:

[0117]

[0118] Where, Y3 represents the admittance of the parallel converter, Y e Indicates the equivalent coupled grid impedance Z e (s) is the coupled grid admittance corresponding to the grid impedance, Y2 is the grid admittance corresponding to the grid impedance, R1 is the generator resistance or grid value at the resonant frequency, X1 is the generator inductive reactance at the resonant frequency, R2 is the grid resistance, X2 is the grid capacitive reactance, k m represents the resistance margin, ΔR represents the sum of the resistance value of the generator side and the resistance value of the grid side at the resonant frequency, k d represents the magnitude of the coupling vector k, θ d represents the phase of the coupling vector k, and Im represents the imaginary part of a complex number.

[0119] Step S3, calculating the standard amplitude and standard phase of the coupling vector according to the coupled grid impedance and the admittance of the parallel converter, and taking the standard amplitude and standard phase as design parameters of the phase shifter to obtain the phase lag and time constant of the phase shifter.

[0120] In this step, ideally, the magnitude k of the coupling vector k is used d and phase θ d As parameters of the gain block and phase shifter, the designed shunt impedance can be achieved. However, the bandpass filter, the bandpass filter and the dynamic characteristics of the parallel converter introduce additional phase lag between the actual resonant component of the grid-side current and the output current of the parallel converter, resulting in a large deviation in the designed parallel impedance. Due to the additional phase lag, the capacitive reactance of the system will be larger than the designed system impedance, resulting in a higher resonant frequency of the system. Therefore, the larger the resonant frequency, the smaller the side resistance R1, which increases the risk of subsynchronous oscillation.

[0121] Actual grid-side resonant current i 2n To the parallel resonant current i 3n The total transfer gain is:

[0122]

[0123] Among them, k g represents the gain of the overall transfer function, G BSF (s n ) represents the transfer function of the band-stop filter at the resonant frequency, G BSF (s n ) represents the transfer function of the bandpass filter at the resonant frequency, G PS (s n ) represents the dynamic characteristic transfer function at the resonant frequency, G c (s n ) represents the phase loss function at the resonant frequency.

[0124] The actual gate side resonant current i 2n With the parallel resonant current i 3n The total phase difference can be derived as:

[0125] θ total =θ BSF +θ BPF +θ PS +θ c

[0126] =arctan(G BSF (s n ))+arctan(G BSF (s n))+arctan(G PS (s n ))+arctan(G c (s n ))

[0127] Among them, θ BSF represents the phase difference caused by the band-stop filter, θ BPF represents the phase difference caused by the bandpass filter, θ PS represents the phase difference caused by the phase shifter, θ c Represents the current inner loop bandwidth of the parallel converter.

[0128] If the total phase lag θ total Equal to the phase θ of the coupling vector k d , the required shunt impedance can be achieved and the phase lag of the phase shifter is calculated as:

[0129] θ PS =θ d -θ BSF -θ BPF -θ c

[0130] The expression for the time constant is:

[0131]

[0132] Among them, θ PS represents the phase lag of the phase shifter, θ d represents the phase of the coupling vector k, θ BSF represents the phase difference caused by the band-stop filter, θ BPF represents the phase difference caused by the bandpass filter, θ c represents the current inner loop bandwidth of the parallel converter, T represents the time constant of the phase shifter. Since the phase shifter outputs a lagging phase, the time constants T1 and T2 of the phase shifter can be designed to be the same value.

[0133] Step S4: Based on the phase lag and the time constant, the control parameters of the subsynchronous damping controller are correspondingly adjusted to suppress the subsynchronous oscillation.

[0134] like Figure 7 As shown, Figure 7 The vector diagram of the grid impedance Z2 and the shunt impedance Z3, and the corresponding admittance under different resistance margins. The larger the system impedance change, the smaller Z2(s)+Z3(s). In order to achieve a large system impedance change, the accuracy of the small impedance Z2(s)+Z3(s) must be guaranteed.

[0135] It is obvious that as the resistance margin increases, the shunt impedance Y3 gets closer and closer to the relative vector of the gate side admittance Y2. At the same time, the parameter k d Approaching 1, θ d approaches 180°. In this case, even a small deviation of the coupling vector k will result in a coefficient Z e The deviation of is large, which greatly affects the reliability of the proposed subsynchronous damping controller. Fig. 9 The deviation of coupling vector k on Z when using different resistance margins e impact.

[0136] Figure 8 (a) The effect of coupling vector k deviation on Z when a smaller resistance margin is used e Obviously, when the amplitude deviation is negative Δk d Or the phase deviation is positive Δθ d When Z e The change of is small and the mitigation effect on subsynchronous oscillation is negligible, which means that the subsynchronous damping controller has high reliability when a small resistance margin is adopted.

[0137] Figure 8 (b) The deviation of the coupling vector k to Z when a larger resistance margin is used e It can be observed that even if the deviation is small, the coupled grid impedance Z e Obviously, when the phase deviation Δθ d When Δk is positive, the capacitive reactance of the coupled grid impedance increases significantly, which may deteriorate the performance of the subsynchronous damping controller. If the positive phase deviation or resistance margin increases further, the resistance of the aggregate impedance may even become negative, which will not only fail to alleviate the subsynchronous oscillation of the system, but will amplify the subsynchronous oscillation of the system. In addition, when a negative amplitude deviation Δk appears d When the resistance of the aggregate impedance is significantly reduced, the capacitive reactance of the system is significantly increased, which is also unfavorable. Therefore, when a larger resistance margin is used, the reliability of the subsynchronous damping controller cannot be guaranteed.

[0138] According to the above analysis, there is a conflict between the stability margin of subsynchronous oscillation and the reliability of subsynchronous damping controller. Considering the stability of subsynchronous oscillation and the reliability of subsynchronous damping controller, it is necessary to design its resistance margin. Figure 7 A potential risk parameter area is defined in , and the radius of the circular area is set to 0.2 times the Y3 modulus. The design parameters should be outside this range, otherwise the reliability of the subsynchronous damping controller cannot be guaranteed.

[0139] By constructing a coupled impedance model and calculating the system impedance resistance value and resistance constraints, it is determined whether the signal input to the subsynchronous damping controller needs to be regulated. At the same time, the generation side impedance, the grid impedance and the system coupled impedance that meets the resistance constraints are regulated, and the control parameters of the subsynchronous damping controller are adjusted according to the above parameters, thereby ensuring the accuracy and effectiveness of the control strategy. Through the dynamic adjustment of the standard amplitude and standard phase, the system can better adapt to changes in grid conditions, improve the responsiveness and stability of the power system to unstable factors, effectively alleviate the subsynchronous oscillation problem, and enhance the stability of the power system and the flexibility of operation.

[0140] Based on the above method, the embodiment of the present application discloses a subsynchronous oscillation suppression system based on parallel converters, referring to Fig. 9 The subsynchronous oscillation suppression system 1 comprises a coupling impedance construction module 11, a coupling parameter design module 12 and an oscillation suppression control module 13 connected in sequence, wherein:

[0141] The coupling impedance building module 11 is used to build a coupling impedance model based on the series compensation wind farm and the parallel converter, obtain the expected total system resistance at the resonant frequency, and calculate the system coupling impedance corresponding to the total system resistance;

[0142] The coupling parameter design module 12 is used to input the power generation side impedance, the grid impedance and the coupling system impedance that meets the resistance constraint condition into the coupling coefficient calculator, and the coupling coefficient calculator is used to obtain the coupling grid impedance and the parallel converter admittance in turn, and obtain the coupling vector and calculate the standard amplitude and standard phase of the coupling vector according to the coupling grid impedance and the parallel converter admittance, and use the standard amplitude and standard phase as the design parameters of the phase shifter to obtain the phase lag and time constant of the phase shifter;

[0143] The oscillation suppression control module 13 is used to adjust the control parameters of the subsynchronous damping controller accordingly based on the phase lag and the time constant to suppress the subsynchronous oscillation.

[0144] In one example, the coupling impedance construction module 11 is used to obtain the resonant frequency when the reactance in the system impedance is zero, and calculate the generation side resistance and the grid resistance at the resonant frequency; the coupling impedance model obtains the total system resistance at the resonant frequency based on the generation side impedance and the grid impedance of the power system at the resonant frequency; based on the total system resistance and the grid side impedance, the system coupling impedance is calculated.

[0145] In one example, the expression for the system coupling impedance is:

[0146] k=k d cosθ d +jk d sinθ d

[0147]

[0148] Z sys (s)=Z1(s)+Z e (s)

[0149] Among them, Z sys (s) represents the system coupling impedance, Z1(s) represents the generation side impedance, Z2(s) represents the grid side impedance, Z3(s) represents the shunt impedance, and Z e (s) represents the equivalent coupled grid impedance of the grid side impedance Z2(s) and the shunt impedance Z3(s), s n represents the Laplace operator at the resonant frequency, k represents the coupling vector, k d represents the magnitude of the coupling vector k, θ d represents the phase of the coupling vector k.

[0150] In one example, the coupling parameter design module 12 is used to determine whether the system impedance resistance value is less than the preset resistance value; if the system impedance resistance value is less than the preset resistance value, the power side impedance, the grid impedance and the coupling system impedance that meets the resistance constraint condition are input into the coupling coefficient calculator; the coupling coefficient calculator calculates the coupled grid impedance and the parallel converter admittance in sequence according to the power side impedance, the grid impedance and the coupling system that meets the resistance constraint condition.

[0151] In one example, the expression for the coupled grid impedance is:

[0152] Z e =R2-(1+k m )ΔR-jX1

[0153] Among them, Z e represents the coupled grid impedance, R2 represents the grid side resistance value, k m represents the resistance margin, ΔR represents the sum of the resistance value on the generator side and the resistance value on the grid side at the resonant frequency, and X1 represents the inductive reactance on the generator side at the resonant frequency.

[0154] In one example, the amplitude and phase of the coupling vector in the coupling coefficient calculator are expressed as:

[0155]

[0156] Y3=k·Y2

[0157]

[0158] Where, Y3 represents the parallel converter admittance, Y e Indicates the equivalent coupled grid impedance Z e(s) is the coupled grid admittance corresponding to the grid impedance, Y2 is the grid admittance corresponding to the grid impedance, R1 is the generator resistance at the resonant frequency, X1 is the generator inductive reactance at the resonant frequency, R2 is the grid resistance, X2 is the grid capacitive reactance, k m represents the resistance margin, ΔR represents the sum of the resistance value of the generator side and the resistance value of the grid side at the resonant frequency, k d represents the magnitude of the coupling vector k, θ d represents the phase of the coupling vector k, and Im represents the imaginary part of a complex number.

[0159] In one example, the expression for the time constant is:

[0160] θ PS =θ d -θ BSF -θ BPF -θ c

[0161]

[0162] Among them, θ PS represents the phase lag of the phase shifter, θ d represents the phase of the coupling vector k, θ BSF represents the phase difference caused by the band-stop filter, θ BPF represents the phase difference caused by the bandpass filter, θ c represents the current inner loop bandwidth of the parallel converter, and T represents the time constant of the phase shifter.

[0163] See also Fig.10 , is a schematic diagram of the structure of an electronic device provided in an embodiment of the present application. Fig.10 As shown, the electronic device 2 may include: at least one processor 21 , at least one network interface 24 , a user interface 23 , a memory 25 , and at least one communication bus 22 .

[0164] The communication bus 22 is used to realize the connection and communication between these components.

[0165] The user interface 23 may include a display screen (Display) and a camera (Camera), and the optional user interface 23 may also include a standard wired interface and a wireless interface.

[0166] The network interface 24 may optionally include a standard wired interface or a wireless interface (such as a WI-FI interface).

[0167] Among them, the processor 21 may include one or more processing cores. The processor 21 uses various interfaces and lines to connect various parts of the entire server, and executes various functions of the server and processes data by running or executing instructions, programs, code sets or instruction sets stored in the memory 25, and calling data stored in the memory 25. Optionally, the processor 21 can be implemented in at least one hardware form of digital signal processing (Digital Signal Processing, DSP), field programmable gate array (Field ~ Programmable Gate Array, FPGA), and programmable logic array (Programmable Logic Array, PLA). The processor 21 can integrate one or a combination of a central processing unit (Central Processing Unit, CPU), a graphics processor (Graphics Processing Unit, GPU) and a modem. Among them, the CPU mainly processes the operating system, user interface and application programs; the GPU is responsible for rendering and drawing the content to be displayed on the display screen; the modem is used to process wireless communications. It can be understood that the above-mentioned modem may not be integrated into the processor 21, and it can be implemented separately through a chip.

[0168] Among them, the memory 25 may include a random access memory (Random Access Memory, RAM) and may also include a read-only memory (Read-Only Memory). Optionally, the memory 25 includes a non-transitory computer-readable storage medium (non-transitory computer-readable storage medium). The memory 25 can be used to store instructions, programs, codes, code sets or instruction sets. The memory 25 may include a program storage area and a data storage area, wherein the program storage area may store instructions for implementing an operating system, instructions for at least one function (such as a touch function, a sound playback function, an image playback function, etc.), instructions for implementing the above-mentioned method embodiments, etc.; the data storage area may store data involved in the above-mentioned method embodiments, etc. The memory 25 may also be optionally at least one storage device located away from the aforementioned processor 21. As Fig.10 As shown, the memory 25 as a computer storage medium may include an operating system, a network communication module, a user interface module, and an application program based on a method for suppressing subsynchronous oscillations of parallel converters.

[0169] exist Fig.10In the electronic device 2 shown, the user interface 23 is mainly used to provide an input interface for the user and obtain data input by the user; and the processor 21 can be used to call the application program stored in the memory 25 for the sub-synchronous oscillation suppression method based on the parallel converter. When executed by one or more processors, the electronic device executes one or more methods in the above-mentioned embodiments.

[0170] A computer-readable storage medium stores instructions, which, when executed by one or more processors, enable the computer to execute one or more methods in the above-mentioned embodiments.

[0171] It should be noted that, for the aforementioned method embodiments, for the sake of simplicity, they are all described as a series of action combinations, but those skilled in the art should be aware that the present application is not limited by the order of the actions described, because according to the present application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required for the present application.

[0172] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0173] In the several embodiments provided in this application, it should be understood that the disclosed devices can be implemented in other ways. For example, the device embodiments described above are only schematic, such as the division of units, which is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some service interfaces, and the indirect coupling or communication connection of devices or units can be electrical or other forms.

[0174] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0175] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0176] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable memory. Based on this understanding, the technical solution of the present application, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, which is stored in a memory and includes several instructions for a computer device (which can be a personal computer, server or network device, etc.) to perform all or part of the steps of the various embodiments of the present application. The aforementioned memory includes: various media that can store program codes, such as USB flash drives, mobile hard drives, magnetic disks or optical disks.

[0177] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for suppressing subsynchronous oscillation based on parallel converters, characterized in that: The method comprises: Constructing a coupled impedance model based on a series-compensated wind farm and a parallel converter, obtaining a desired total system resistance value at a resonant frequency, and calculating a coupled system impedance corresponding to the total system resistance value; Input the power generation side impedance, the grid impedance and the coupling system impedance satisfying the resistance constraint condition into the coupling coefficient calculator to obtain the coupling grid impedance and the parallel converter admittance in turn; The step of inputting the power generation side impedance, the grid impedance and the system coupling impedance satisfying the resistance constraint condition into the coupling coefficient calculator, so that the coupling coefficient calculator outputs the coupled grid impedance and the parallel converter admittance, specifically includes: Determining whether the total resistance value of the system is less than a preset resistance value; If the total system resistance value is less than the preset resistance value, the power generation side impedance, the grid impedance and the system coupling impedance satisfying the resistance constraint condition are input into a coupling coefficient calculator; The coupling coefficient calculator calculates the coupled grid impedance and the parallel converter admittance in sequence according to the power generation side impedance, the grid impedance and the system coupling impedance satisfying the resistance constraint condition; The expression of the coupling grid impedance is: From e =R2-(1+k m )ΔR-jX1 Among them, Z e represents the coupled grid impedance, R2 represents the grid resistance value, k m represents the resistance margin, ΔR represents the sum of the generator side resistance and the grid resistance at the resonant frequency, and X1 represents the generator side inductive reactance or the grid side inductive reactance at the resonant frequency; The amplitude and phase of the coupling vector in the coupling coefficient calculator are expressed as: Y3=k·Y2 Where, Y3 represents the admittance of the parallel converter, Y e Indicates the equivalent coupled grid impedance Z e (s) is the coupled grid admittance corresponding to the grid impedance, Y2 is the grid admittance corresponding to the grid impedance, R1 is the generator resistance at the resonant frequency, X1 is the generator inductive reactance at the resonant frequency, R2 is the grid resistance, X2 is the grid capacitive reactance, k m represents the resistance margin, ΔR represents the sum of the resistance value of the generator side and the resistance value of the grid side at the resonant frequency, k d represents the magnitude of the coupling vector k, θ d represents the phase of the coupling vector k, and Im represents the imaginary part of a complex number; According to the coupled grid impedance and the parallel converter admittance, a coupling vector is obtained and a standard amplitude and a standard phase of the coupling vector are calculated, the standard amplitude and the standard phase are used as design parameters of a phase shifter, and a phase lag and a time constant of the phase shifter are obtained; Based on the phase lag and the time constant, control parameters of the subsynchronous damping controller are adjusted accordingly to suppress subsynchronous oscillations.

2. The method according to claim 1, characterized in that The obtaining of the expected total system resistance and the coupling impedance model at the resonant frequency, and calculating the coupling system impedance corresponding to the total system resistance, specifically includes: Obtain the resonant frequency when the reactance in the system impedance is zero, and calculate the generation side resistance and grid resistance at the resonant frequency; The coupled impedance model obtains the total system resistance at the resonant frequency according to the power system's generation side impedance and the grid impedance at the resonant frequency; Based on the total system resistance and the grid-side impedance, a system coupling impedance is calculated.

3. The method according to claim 2, characterized in that The expression of the system coupling impedance is: k=k d cosθ d +jk d sinθ d Z sys (s)=Z1(s)+Z e (s) Among them, Z sys (s) represents the system coupling impedance, Z1(s) represents the power generation side impedance, Z2(s) represents the grid side impedance, Z3(s) represents the shunt impedance, and Z e (s) represents the equivalent coupled grid impedance of the grid side impedance Z2(s) and the shunt impedance Z3(s), s n represents the Laplace operator at the resonant frequency, k represents the coupling vector, k d represents the magnitude of the coupling vector k, θ d represents the phase of the coupling vector k.

4. The method according to claim 1, characterized in that The expression of the time constant is: i PS =θ d -θ BSF -θ BPF -θ c Among them, θ PS represents the phase lag of the phase shifter, θ d represents the phase of the coupling vector k, θ BSF represents the phase difference caused by the band-stop filter, θ BPF represents the phase difference caused by the bandpass filter, θ c represents the current inner loop bandwidth of the parallel converter, and T represents the time constant of the phase shifter.

5. A subsynchronous oscillation suppression system based on parallel converters, characterized in that: The subsynchronous oscillation suppression system (1) comprises a coupling impedance construction module (11), a coupling parameter design module (12) and an oscillation suppression control module (13) which are connected in sequence, wherein: The coupling impedance construction module (11) is used to construct a coupling impedance model based on a series compensation wind farm and a parallel converter, obtain a desired system total resistance value at a resonant frequency, and calculate a coupling system impedance corresponding to the system total resistance value; The coupling parameter design module (12) is used to input the power generation side impedance that meets the resistance constraint condition, the grid impedance, and the system coupling impedance that meets the resistance constraint condition into a coupling coefficient calculator, so that the coupling coefficient calculator outputs the coupled grid impedance and the parallel converter admittance, and calculates the standard amplitude and standard phase of the coupling vector according to the coupled grid impedance and the parallel converter admittance respectively, and uses the standard amplitude and the standard phase as design parameters of the phase shifter to obtain the phase lag and time constant of the phase shifter; Inputting the power generation side impedance, the grid impedance and the system coupling impedance satisfying the resistance constraint condition into the coupling coefficient calculator, so that the coupling coefficient calculator outputs the coupled grid impedance and the parallel converter admittance, specifically including: Determining whether the total resistance value of the system is less than a preset resistance value; If the total system resistance value is less than the preset resistance value, the power generation side impedance, the grid impedance and the system coupling impedance satisfying the resistance constraint condition are input into a coupling coefficient calculator; The coupling coefficient calculator calculates the coupled grid impedance and the parallel converter admittance in sequence according to the power generation side impedance, the grid impedance and the system coupling impedance satisfying the resistance constraint condition; The expression of the coupling grid impedance is: From e =R2-(1+k m )ΔR-jX1 Among them, Z e represents the coupled grid impedance, R2 represents the grid resistance value, k m represents the resistance margin, ΔR represents the sum of the generator side resistance and the grid resistance at the resonant frequency, and X1 represents the generator side inductive reactance or the grid side inductive reactance at the resonant frequency; The amplitude and phase of the coupling vector in the coupling coefficient calculator are expressed as: Y3=k·Y2 Where, Y3 represents the admittance of the parallel converter, Y e Indicates the equivalent coupled grid impedance Z e (s) is the coupled grid admittance corresponding to the grid impedance, Y2 is the grid admittance corresponding to the grid impedance, R1 is the generator resistance at the resonant frequency, X1 is the generator inductive reactance at the resonant frequency, R2 is the grid resistance, X2 is the grid capacitive reactance, k m represents the resistance margin, ΔR represents the sum of the resistance value of the generator side and the resistance value of the grid side at the resonant frequency, k d represents the magnitude of the coupling vector k, θ d represents the phase of the coupling vector k, and Im represents the imaginary part of a complex number; The oscillation suppression control module (13) is used to adjust the control parameters of the subsynchronous damping controller accordingly based on the phase lag and the time constant, so as to suppress subsynchronous oscillation.

6. An electronic device, characterized in that: The electronic device (2) comprises a processor (21), a memory (25), a user interface (23) and a network interface (24), wherein the memory (25) is used to store instructions, the user interface (23) and the network interface (24) are used to communicate with other devices, and the processor (21) is used to execute the instructions stored in the memory (25) so that the electronic device (2) executes the method according to any one of claims 1 to 4.

7. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

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