CN111416366A - Doubly-fed wind power plant sub-synchronous oscillation suppression method through series compensation considering load model - Google Patents

Doubly-fed wind power plant sub-synchronous oscillation suppression method through series compensation considering load model Download PDF

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CN111416366A
CN111416366A CN202010365674.7A CN202010365674A CN111416366A CN 111416366 A CN111416366 A CN 111416366A CN 202010365674 A CN202010365674 A CN 202010365674A CN 111416366 A CN111416366 A CN 111416366A
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series compensation
doubly
load
oscillation
fed
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王黎明
张骞
魏本刚
林清明
边晓燕
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Shanghai Hengnengtai Enterprise Management Co ltd Puneng Power Technology Engineering Branch
Shanghai University of Electric Power
Shanghai Electric Power University
State Grid Shanghai Electric Power Co Ltd
University of Shanghai for Science and Technology
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Shanghai Hengnengtai Enterprise Management Co ltd Puneng Power Technology Engineering Branch
Shanghai Electric Power University
State Grid Shanghai Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
    • H02J3/1807—Arrangements for adjusting, eliminating or compensating reactive power in networks using series compensators
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

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Abstract

The invention relates to a method for restraining sub-synchronous oscillation of doubly-fed wind power plant through series compensation and external transmission by considering a load model, which comprises the following steps of: 1) constructing a sub-synchronous oscillation electromagnetic transient model of a doubly-fed wind power plant with static and dynamic load models and through series compensation external transmission; 2) considering whether a wind power plant grid-connected point contains the influence of load on subsynchronous oscillation or not, and taking a comprehensive load model as a load model; 3) according to the generation mechanism of the induction generator effect IGE, the series compensation degree and the wind speed are used as factors for reducing the induction generator effect; 4) according to the generation mechanism of SSCI (sub-synchronous control interaction), taking the current inner-loop parameters of a frequency converter at the rotor side of the double-fed fan as factors for reducing the sub-synchronous control interaction; 5) and meanwhile, the subsynchronous oscillation of the system is suppressed by controlling the series compensation degree of the circuit, the wind speed and the current inner ring parameter of the frequency converter at the rotor side of the doubly-fed fan. Compared with the prior art, the method has the advantages of considering a comprehensive load model, good inhibition effect, convenience in implementation and the like.

Description

Doubly-fed wind power plant sub-synchronous oscillation suppression method through series compensation considering load model
Technical Field
The invention relates to the technical field of wind power grid-connected subsynchronous oscillation, in particular to a load model double-fed wind power plant series compensation and external transmission subsynchronous oscillation suppression method.
Background
In recent years, wind power is used as renewable clean energy, as the power generation cost is low and the resources are in recent years, China vigorously develops clean and low-carbon renewable energy, particularly the utilization rate of wind power resources is remarkably improved, and China has established seven million kilowatt-level wind power bases in Xinjiang, Hebei, Gansu, Jilin, inner Mongolia and the like, large-scale wind power transmission is inevitable, as the resources and load centers in China are reversely distributed, the problem of wind power absorption can be solved through a large-capacity and long-distance power transmission mode, the series compensation alternating current transmission technology can effectively increase the transmission capacity of a line, the stability limit of the system is improved, the main mode of large-scale wind power transmission is large-scale wind power transmission, but the SSO generated by the series compensation external transmission is usually in three forms, namely, the SSO generated by the series compensation external transmission of the wind power generation system is a Sub-Synchronous Generator set (SSO-Synchronous Resonance, SSR) which means that the mutual Effect between the wind power generation set and a fixed series compensation shafting Generator set is generated by mutual oscillation of a Synchronous Generator (IGparallel-series Resonance Generator), the SSO generated by the mutual Effect of a series compensation electric Generator set is neglected in series Resonance of a Synchronous Resonance Generator, the electric grid oscillation of a Synchronous Generator set, the SSO generated by the electric Generator set, the mutual Resonance of a series compensation transformer, the SSO generated by the SSO, the SSO generated by the mutual Resonance of a series compensation transformer, the electric Generator set is a Synchronous Generator set, and a Synchronous Generator set, the SSO generated by the electric Generator set, the SSC, the SSO generated by the electric Generator set, the SSO generated by the.
According to the existing documents, when a load model is considered at a short-circuit point close to a load center, a measured value and a calculated value of the apparent impedance of the subsynchronous oscillation of the system can be equal, so that the influence of the load model on the stability of the system needs to be concerned in the process of researching the low-frequency oscillation and the subsynchronous oscillation of the thermal power unit.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a series-compensated external-transmission subsynchronous oscillation suppression method for a double-fed wind power plant considering a load model.
The purpose of the invention can be realized by the following technical scheme:
a method for restraining sub-synchronous oscillation of doubly-fed wind power plant through series compensation and external transmission considering a load model comprises the following steps:
1) constructing a sub-synchronous oscillation electromagnetic transient model of a doubly-fed wind power plant with static and dynamic load models and through series compensation external transmission;
2) considering whether a wind power plant grid-connected point contains the influence of load on subsynchronous oscillation or not, and taking a comprehensive load model as a load model;
3) according to the generation mechanism of the induction generator effect IGE, the series compensation degree and the wind speed are used as factors for reducing the induction generator effect;
4) according to the generation mechanism of SSCI (sub-synchronous control interaction), taking the current inner-loop parameters of a frequency converter at the rotor side of the double-fed fan as factors for reducing the sub-synchronous control interaction;
5) and meanwhile, the subsynchronous oscillation of the system is suppressed by controlling the series compensation degree of the circuit, the wind speed and the current inner ring parameter of the frequency converter at the rotor side of the doubly-fed fan.
In the step 2), the comprehensive load is specifically that the wind power plant grid-connected point simultaneously contains a dynamic load and a static load.
The static load comprises constant power, constant current and constant impedance load, and the dynamic load is composed of induction motors with different proportions.
In the step 2), a comprehensive load model formed by 60% of induction motors and 40% of constant impedance models is selected.
In the step 3), under the condition that the wind speed of the doubly-fed wind turbine generator is not changed, the frequency and the amplitude of the subsynchronous oscillation are increased along with the increase of the series compensation degree.
In the step 3), the lower the wind speed is, the higher the possibility of occurrence of the IGE phenomenon is under the condition that the series compensation degree is not changed.
In the step 4), the current inner ring parameters of the frequency converter at the rotor side of the doubly-fed wind turbine comprise a proportionality coefficient KpAnd integral coefficient Ki。
In the step 4), the wind speed, the series compensation degree and the proportionality coefficient K of the doubly-fed wind turbine generator are measuredpProbability of SSCI occurring with integral coefficient K under constant conditionsiIs increased.
In the step 4), the wind speed, the series compensation degree and the integral coefficient K of the doubly-fed wind turbine generator are measurediProbability of SSCI under constant conditions with scaling factor KpIs increased.
In the step 5), the suppression of the subsynchronous oscillation of the system is realized through the control of the line series compensation degree, the wind speed and the current inner ring parameter of the frequency converter at the rotor side of the doubly-fed fan specifically:
the value range of the line series compensation degree is 15% -45%;
the value range of the wind speed is 8m/s-12 m/s;
at a proportionality coefficient KpThe integral coefficient K is constant under the conditions that the wind speed is 10m/s and the line series compensation degree is 10 percentiThe value range of (A) is 5-90;
at integral coefficient KiUnder the conditions of constant wind speed of 10m/s and line series compensation degree of 10 percent, the proportionality coefficient KpThe value range of (A) is 0.20-0.22.
Compared with the prior art, the invention has the following advantages:
aiming at the problem of subsynchronous oscillation of a double-fed wind power plant through series compensation and external transmission at present, the invention provides a load-related subsynchronous oscillation model to solve the problem of subsynchronous oscillation, and different series compensation degrees and wind speeds are set under the conditions of setting and/or not considering the load by setting up a system equivalent model of a double-fed wind power unit connected into an infinite power grid through a series compensation circuit, so that a corresponding electromagnetic torque T is obtainedeThe oscillation curve of the rotor side converter is used for verifying the influence factors of IGE, considering the influence of RSC current inner loop control parameters of the rotor side converter on subsynchronous oscillation, applying small disturbance, and applying a small disturbance when a proportionality coefficient K is obtainedpKeeping the integral coefficient K unchanged and changing the integral coefficientiThen, different K's are obtained by simulationiLower corresponding electromagnetic torque TeThe method provided by the invention considers the influence of the load on the subsynchronous oscillation, is more comprehensive in the exploration of the influence factors, adopts the control of the series compensation degree and the wind speed of the doubly-fed fan and the current inner loop parameter of the rotor side frequency converter to restrain the subsynchronous oscillation of the system, has good restraining effect and is convenient to realize.
Drawings
FIG. 1 is an equivalent model of a double-fed wind power plant access alternating current system.
Fig. 2 is a system equivalent circuit after load is taken into account.
Fig. 3 is a line current spectrum analysis at different series compensation degrees.
Fig. 4 is a line current spectrum analysis at different wind speeds.
Fig. 5 shows the correlation factor between different state quantities and lambda.
FIG. 6 shows the electromagnetic torque T at different series compensation degreeseOscillation curve in which the electromagnetic torque T at the degree of series compensation of 15% is shown in FIG. 6aeThe oscillation curve, FIG. 6b, is the electromagnetic torque T at a series compensation of 30%eThe oscillation curve, FIG. 6c, is that at a series compensation degree of 45%Electromagnetic torque TeAn oscillation curve.
FIG. 7 shows the electromagnetic torque T at different wind speedseAn oscillation curve in which the electromagnetic torque T at a wind speed of 8m/s is shown in FIG. 7aeAn oscillation curve, in which FIG. 7b shows the electromagnetic torque T at a wind speed of 10m/seAn oscillation curve, in which FIG. 7c shows the electromagnetic torque T at a wind speed of 12m/seAn oscillation curve.
FIG. 8 shows a difference KiLower electromagnetic torque TeOscillating curve, where, in graph (8a), kp0.20 and kiElectromagnetic torque T of 5 hourseOscillating curve, fig. (8b) is kp0.20 and kiElectromagnetic torque T at 90 DEG FeOscillating curve, fig. (8c) is kp0.20 and kiElectromagnetic torque T at 100eAn oscillation curve.
FIG. 9 shows a difference KpLower electromagnetic torque TeOscillating curve, where, in graph (9a), k i5 and kpElectromagnetic torque T of 0.20eOscillating curve, fig. (9b) is k i5 and kpElectromagnetic torque T of 0.22eOscillating curve, fig. (9c) is k i5 and kpElectromagnetic torque T of 0.27eAn oscillation curve.
FIG. 10 is a flow chart of a method of the present invention.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Examples
The invention provides a method for restraining sub-synchronous oscillation of a double-fed wind power plant through series compensation and external transmission considering a load model, and provides a sub-synchronous oscillation model of a large-scale double-fed wind turbine generator through series compensation and external transmission considering the load model, wherein the sub-synchronous oscillation model analyzes the influence of static load and dynamic load on the sub-synchronous oscillation, analyzes the mechanism of IGE and SSCI of a system and the influence of a load model on oscillation mode damping by using an impedance analysis method and a characteristic value analysis method, and adopts the series compensation degree and wind speed of a double-fed fan circuit and the control of the wind speed to restrain the IGE phenomenon by aiming at the influence of the line series compensation degree, the wind speed and the current inner ring control parameters of a frequency converter at the rotor side of the double-fed fan before and after the load; the method for suppressing the SSCI phenomenon by adopting the current inner loop control of the doubly-fed wind turbine rotor-side converter specifically comprises the following steps as shown in FIG. 10:
step 1, building a sub-synchronous oscillation electromagnetic transient model of a doubly-fed wind power plant with static and dynamic load models and through series compensation and external transmission.
And 2, analyzing the influence of static load and dynamic load on subsynchronous oscillation on the basis of a load-containing model of a wind power plant grid-connected point.
And 3, establishing a series compensation grid-connected impedance analysis model of the wind power plant with the load, analyzing a mechanism of generating an Induction Generator Effect (IGE), and analyzing the influence of the series compensation degree and the wind speed on the IGE.
And 4, analyzing the mechanism of the system for generating the IGE and the SSCI and the influence of the load model on the oscillation mode damping by means of a characteristic value analysis method, and providing a strong correlation state quantity influencing the oscillation.
And 5, verifying the influences of the series compensation degree and the wind speed of the circuit before and after the load meter by using time domain simulation, and inhibiting the subsynchronous oscillation of the system by adopting the series compensation degree and the wind speed of the doubly-fed fan and the current inner-loop parameter control of the rotor side frequency converter.
Analysis of IGE mechanism
When series compensation capacitor is added to the transmission line, the system has a natural resonant frequency, namely
Figure RE-GDA0002526440040000051
In the formula: f. of0Is the system synchronization frequency; xlΣIs the total reactance value of the system; xcIs the capacitive reactance of the series compensation capacitor. Due to Xc＝kXlΣAnd the degree of cross-compensation k < 1, so that fn＜f0When the line is disturbed, a subsynchronous frequency f is generatednThe rotor slip ratio of the doubly-fed wind turbine generator is as follows:
sr＝(fn-fr)/fr(2)
in the formula: f. ofrTo turn toSub-frequency, which can be considered as f in a shorter oscillation periodrIs constant. General rule fn＜frThus srIs less than 0. In a steady state, influence of frequency converters on two sides of the fan is ignored, and a system equivalent circuit for analyzing the IGE effect is shown in figure 2.
In fig. 2, the dotted line portion represents the increased load portion; due to sr< 0 therefore Rr/srAnd < 0, namely the equivalent resistance of the rotor winding is in a negative resistance characteristic. When the negative equivalent resistance of the rotor is larger than the sum of the resistances of the stator and the transmission line at the frequency, self-excitation is generated in the electric loop, and an IGE effect is caused.
Keeping the wind speed at 11m/s, changing the line series compensation degree, calculating the characteristic roots of the system before and after the load, screening out the subsynchronous electrical resonance mode from the characteristic roots, and obtaining the calculation result shown in table 1.
TABLE 1 results of calculation
Figure RE-GDA0002526440040000052
As can be seen from Table 1: when the degree of series compensation is increased from 15% to 45%, the frequency f of the rotor induced current0-fnGradually decreasing, subsynchronous oscillation frequency fnBecoming progressively larger. And, after accounting for the load model, the system subsynchronous oscillation frequency is increased; it can also be seen from the characteristic root real part σ that as the degree of series compensation increases, the positive damping of the oscillation mode gradually decreases, and the system loses stability. The results of the spectrum analysis of the line currents at three different series compensation degrees are shown in fig. 3. It can be seen that the line currents at the three series compensation degrees correspond to the subsynchronous oscillation frequencies of 26.7Hz, 31.5Hz and 34Hz respectively, and are close to complementary with the induced current frequency of the rotor. And with the increase of the series compensation degree, the oscillation amplitude is gradually increased, the oscillation is intensified, and the oscillation is consistent with the feature root calculation result.
Keeping the line series compensation degree at 10%, changing the wind speed, calculating characteristic roots of the system before and after the load is taken into consideration, screening out subsynchronous electrical resonance modes from the characteristic roots, and obtaining a calculation result shown in a table 2.
TABLE 2 calculation results
Figure RE-GDA0002526440040000061
As can be seen from Table 2: when the wind speed increases from 8m/s to 12m/s, the frequency f of the rotor induced current0-fnGradually increasing, subsynchronous oscillation frequency fnGradually decreases. And, after accounting for the loading model, there is no significant change in the system characteristic root and oscillation damping. The line current at three different wind speeds was subjected to spectral analysis, the results of which are shown in fig. 4. It can be seen that the line currents at the three wind speeds respectively correspond to subsynchronous oscillation frequencies of 29.5Hz, 27.2Hz and 26.8Hz, and are approximately complementary to the induced current frequency of the rotor obtained by the characteristic root analysis.
SSCI mechanistic analysis
After a small disturbance is applied to a grid-connected system, a corresponding subsynchronous current component is induced on a rotor by a line resonant current, namely a DFIG stator current, the output voltage of an inverter is regulated after the RSC acquires the variation of the rotor current, and the variation of the output voltage is reacted with the rotor current, so that a closed loop feedback is formed. If the output voltage has an effect of increasing the rotor current, the oscillation of the resonant current is also intensified, so that the system oscillates in a large range and SSCI occurs.
The model analysis module in DIgSI L ENT/PowerFactory is used for carrying out model analysis on the system to obtain the correlation between different state quantities and the electric resonance model, namely the correlation factor, as shown in FIG. 5, in the graph, the length of an arrow reflects the correlation between a certain state quantity and the characteristic root lambda of the resonance model, and the included angle between the arrow and the positive half shaft of the x axis represents the influence of the state quantity on the phase of the oscillation modelpAnd KiIs relatively large, namely K is consideredpAnd KiIs a "strongly correlated state quantity", i.e. KpAnd KiStrongly correlated with SSCI.
For analyzing current inner ring control parameter K of rotor side frequency converter of doubly-fed wind turbine generatorpAnd KiEffect on SSCI by putting 10% series compensation on the lineAnd calculating the electric resonance mode of the system after the system is subjected to disturbance stabilization before and after the load model is considered, and the result is shown in table 3.
TABLE 3 results of calculation
Figure RE-GDA0002526440040000062
Figure RE-GDA0002526440040000071
As can be seen from table 3: maintenance of KpNot change when KiWhen the value is gradually increased, the positive damping of the system is reduced, and the electric resonance mode gradually tends to be unstable. Maintenance of KiNot change when KpWhen the value is gradually increased, the resonance mode also tends to be unstable gradually. Meanwhile, after the load model is considered, the system characteristic root has no obvious change.
Step 3 the differential ratio SrIt can be determined whether oscillation has occurred.
Subsynchronous oscillation frequency f in step 4nThe degree of oscillation can be judged according to the size of the signal; the positive damping of the oscillation mode can be judged by the characteristic root real part sigma; oscillations can be determined by spectral analysis of the line current.
The electromagnetic torque T can be passed in step 5eThe oscillation curve of (2) determines the influence of the parameter.
According to the invention, a system equivalent model of a doubly-fed wind turbine generator set connected into an infinite power grid through a series compensation circuit is built on a simulation platform DIgSI L ENT/PowerFactory, and different series compensation degrees and wind speeds are set under the conditions of setting and considering/not considering loads, so that a corresponding electromagnetic torque T is obtainedeVerifying the influence factors of the IGE; considering the influence of RSC current inner loop control parameters of the rotor side converter on subsynchronous oscillation, applying a small disturbance when the proportionality coefficient K ispKeeping the integral coefficient K unchanged and changing the integral coefficientiThen, different K's are obtained by simulationiLower corresponding electromagnetic torque TeThe influence of the coefficients on the SSCI was verified.
Example 1: modes of oscillation under different loads
On the basis of the improved IEEE first standard model shown in fig. 1, other parameters are unchanged, and the system electrical oscillation modes under different loads are respectively calculated by adopting a characteristic value method: 1) no load is connected to Bus 3; 2) the Bus3 is respectively connected with Z, I static load and P static load; 3) the Bus3 is respectively connected with dynamic loads consisting of induction motors with different proportions. The calculation results are shown in table 4.
TABLE 4 results of calculation
Type of load σ+jω f0-fn
Without load -10.111±j118.732 18.897
Constant impedance (Z) -9.504±j119.010 18.941
Constant current (I) -9.510±j119.000 18.939
Constant power (P) -9.515±j118.989 18.938
30% induction motor -8.561±j119.021 18.943
50% induction motor -8.546±j119.042 18.946
70% induction motor -8.529±j119.064 18.949
As can be seen from table 4: compared with an electric oscillation mode without load, after the static load is accessed, the system damping only changes slightly; after the dynamic load is connected, the system damping changes strongly, and the positive damping is reduced along with the increase of the proportion of the dynamic load, so that the system stability is weakened. Therefore, a comprehensive load model of 60% induction motor + 40% constant impedance model is selected to represent the situation of considering the load, and the influence factors are analyzed.
Example 2: induction generator effect simulation under different series compensation degrees and different wind speeds
Different series compensation degrees:
the doubly-fed wind turbine generator keeps the wind speed at 11m/s, other conditions are kept unchanged, the size of series compensation capacitance on a circuit is only changed, and when the series compensation degrees of the circuit are respectively 15%, 30% and 45%, corresponding electromagnetic torque T under different series compensation degrees of loads is obtained and accounted and not accounted by simulationeAs shown in fig. 6.
As can be seen from fig. 6: under the condition that a load model is not taken into account, when the series compensation degree is 15%, the electromagnetic torque hardly oscillates; when the series compensation degree is 30%, the electromagnetic torque slightly oscillates; when the degree of cross-talk is 45%, the electromagnetic torque oscillates strongly. After the load model is considered, under the same three kinds of series compensation degrees, the oscillation amplitude of the electromagnetic torque is obviously increased compared with the oscillation amplitude without the load, and the increment of the amplitude is more obvious along with the increase of the series compensation degrees. Simulation results show that the higher the line series compensation degree is, the more likely the IGE phenomenon is to occur, and the consideration of load characteristics under different series compensation degrees has a greater influence on the oscillation of the system electromagnetic torque.
Different wind speeds:
setting the series compensation degree of the line to be 10%, keeping other conditions unchanged, only changing the blowing wind speed of the doubly-fed wind turbine generator, and applying a small disturbance 2s after the system is stabilized when the wind speeds are 8m/s, 10m/s and 12m/s respectively, wherein simulation is used for obtaining corresponding electromagnetic torque T at different wind speeds without considering load different series compensation degreeseAs shown in fig. 7.
As can be seen from fig. 7: under the condition that a load model is not taken into account, when the wind speed is 8m/s, the electromagnetic torque oscillation is diverged; when the wind speed is 10m/s, the electromagnetic torque is approximately oscillated in a constant amplitude; when the wind speed is 12m/s, the electromagnetic torque oscillation converges. After the load model is taken into account, the oscillation of the electromagnetic torque at the same three wind speeds is almost coincident with that at the time when the load is not taken into account. The simulation results show that the lower the wind speed, the more likely the IGE phenomenon occurs. And under the working condition of low series compensation degree, the load characteristic is considered at different wind speeds, and the influence on the system electromagnetic torque oscillation is not large.
Example 3: subsynchronous interaction simulation
Considering the influence of RSC current inner loop control parameters of the rotor-side converter on subsynchronous oscillation, setting the wind speed of the system shown in the figure 1 to be 10m/s and the line series compensation degree to be 10%, applying a small disturbance 2s after the system stably operates, and applying a small disturbance when a proportionality coefficient K is obtainedpKeeping the integral coefficient K unchanged and changing the integral coefficientiThen, different K's are obtained by simulationiLower corresponding electromagnetic torque TeThe oscillation curve of (a); when integral coefficient KiKeeping the proportionality coefficient K unchanged and changingpThen, different K's are obtained by simulationpLower corresponding electromagnetic torque TeFig. 8 and 9 show the oscillation curves of (a).
Coefficient of proportionality KpKeeping the integral coefficient K unchanged and changing the integral coefficienti：
As can be seen from fig. 8: without taking into account the load model whenKpConstant value, KiWhen the value is 5, 90 and 100, the corresponding electromagnetic torque oscillation is more and more severe from convergence to constant amplitude to divergence. When considering the load model, at the same three kinds of KiThe oscillation behavior of the electromagnetic torque is almost coincident with that of the oscillation behavior of the electromagnetic torque when the load is not considered. The simulation result shows that with KiThe subsynchronous oscillations are more and more intense and the probability of SSCI occurring is higher. And under the working condition of lower series compensation degree, the working conditions are different in KiThe load characteristic is considered, and the influence on the system electromagnetic torque oscillation is not large.
When integral coefficient KiKeeping the proportionality coefficient K unchanged and changingp:
As can be seen from fig. 9: when K is not taken into account in the case of a load modeliConstant value, KpWhen the value is 0.20, 0.22 and 0.27, the corresponding electromagnetic torque oscillation is from convergence to constant amplitude to divergence and is increasingly severe. When considering the load model, at the same three kinds of KpThe oscillation behavior of the electromagnetic torque is almost coincident with that of the oscillation behavior of the electromagnetic torque when the load is not considered. The simulation result shows that with KpThe subsynchronous oscillations are more and more intense and the probability of SSCI occurring is higher. And under the working condition of lower series compensation degree, the working conditions are different in KpThe load characteristic is considered, and the influence on the system electromagnetic torque oscillation is not large.

Claims (10)

1. A doubly-fed wind power plant series compensation external supply subsynchronous oscillation suppression method considering a load model is characterized by comprising the following steps of:
1) constructing a sub-synchronous oscillation electromagnetic transient model of a doubly-fed wind power plant with static and dynamic load models and through series compensation external transmission;
2) considering whether a wind power plant grid-connected point contains the influence of load on subsynchronous oscillation or not, and taking a comprehensive load model as a load model;
3) according to the generation mechanism of the induction generator effect IGE, the series compensation degree and the wind speed are used as factors for reducing the induction generator effect;
4) according to the generation mechanism of SSCI (sub-synchronous control interaction), taking the current inner-loop parameters of a frequency converter at the rotor side of the double-fed fan as factors for reducing the sub-synchronous control interaction;
5) and meanwhile, the subsynchronous oscillation of the system is suppressed by controlling the series compensation degree of the circuit, the wind speed and the current inner ring parameter of the frequency converter at the rotor side of the doubly-fed fan.
2. The method for suppressing the sub-synchronous oscillation of the doubly-fed wind farm after series compensation and external transmission considering the load model according to claim 1, wherein in the step 2), the comprehensive load is a dynamic load and a static load at a grid-connected point of the wind farm.
3. The method for restraining the doubly-fed wind power plant from the sub-synchronous oscillation by series compensation and external transmission based on the load model according to claim 2, wherein the static load comprises a constant-power load, a constant-current load and a constant-impedance load, and the dynamic load is a dynamic load comprising induction motors with different proportions.
4. The method for suppressing the series-compensated external-transmission subsynchronous oscillation of the doubly-fed wind farm in consideration of the load model as recited in claim 3, wherein in the step 2), a comprehensive load model consisting of 60% of induction motors and 40% of constant impedance models is selected.
5. The method for suppressing the sub-synchronous oscillation of the doubly-fed wind farm fed by the series compensation according to the load model in claim 1, wherein in the step 3), the frequency and the amplitude of the sub-synchronous oscillation increase with the increase of the series compensation degree under the condition that the wind speed of the doubly-fed wind turbine generator is not changed.
6. The method for suppressing the doubly-fed wind farm subsynchronous oscillation through series compensation and external transmission in consideration of the load model according to claim 1, wherein in the step 3), the lower the wind speed is, the higher the possibility of occurrence of the IGE phenomenon is under the condition of constant series compensation degree.
7. The method of claim 1The method for suppressing the sub-synchronous oscillation of the doubly-fed wind power plant through series compensation and external transmission in consideration of the load model is characterized in that in the step 4), the current inner loop parameters of the rotor-side frequency converter of the doubly-fed wind turbine comprise a proportionality coefficient KpAnd integral coefficient Ki。
8. The method for suppressing the sub-synchronous oscillation of the doubly-fed wind farm fed through the series compensation according to the claim 7, wherein in the step 4), the wind speed, the series compensation degree and the proportionality coefficient K of the doubly-fed wind turbine generator are calculatedpProbability of SSCI occurring with integral coefficient K under constant conditionsiIs increased.
9. The method for suppressing the sub-synchronous oscillation of the doubly-fed wind farm fed through the series compensation according to the claim 7, wherein in the step 4), the wind speed, the series compensation degree and the integral coefficient K of the doubly-fed wind turbine generator are calculated according to the load modeliProbability of SSCI under constant conditions with scaling factor KpIs increased.
10. The method for suppressing the sub-synchronous oscillation of the doubly-fed wind power plant through series compensation and external transmission in consideration of the load model according to claim 7, wherein in the step 5), the suppression of the sub-synchronous oscillation of the system is realized through the control of the line series compensation degree, the wind speed and the current inner loop parameter of the frequency converter at the rotor side of the doubly-fed wind turbine specifically:
the value range of the line series compensation degree is 15% -45%;
the value range of the wind speed is 8m/s-12 m/s;
at a proportionality coefficient KpUnder the conditions of constant wind speed of 10m/s and line series compensation degree of 10 percent, the integral coefficient KiThe value range of (A) is 5-90;
at integral coefficient KiUnder the conditions of constant wind speed of 10m/s and line series compensation degree of 10 percent, the proportionality coefficient KpThe value range of (A) is 0.20-0.22.
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