CN111130136A - Subsynchronous oscillation suppression method based on additional virtual impedance control - Google Patents

Subsynchronous oscillation suppression method based on additional virtual impedance control Download PDF

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CN111130136A
CN111130136A CN201911350960.XA CN201911350960A CN111130136A CN 111130136 A CN111130136 A CN 111130136A CN 201911350960 A CN201911350960 A CN 201911350960A CN 111130136 A CN111130136 A CN 111130136A
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边晓燕
张奥运
徐鑫裕
赵健
王小宇
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Shanghai University of Electric Power
Shanghai Electric Power University
University of Shanghai for Science and Technology
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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
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract

The invention relates to a subsynchronous oscillation suppression method based on additional virtual impedance control, which comprises the following steps of: 1) constructing a mixed impedance model of a VSC-HVDC (voltage source converter-high voltage direct current) grid-connected system based on a doubly-fed wind power plant; 2) and inhibiting subsynchronous oscillation in a virtual resistance control mode by reasonably configuring parameters according to a mixed impedance model and a cascade system characteristic stability criterion. Compared with the prior art, the invention solves the cost problem of adding an FACTS device, and the designed additional virtual impedance controller can inhibit the subsynchronous oscillation phenomenon of a multi-AC/DC parallel grid-connected system, improve the subsynchronous stability of the system and ensure the safe and stable operation of new energy power transmission.

Description

Subsynchronous oscillation suppression method based on additional virtual impedance control
Technical Field
The invention relates to the field of grid-connected control of a wind power plant through VSC-HVDC, in particular to a subsynchronous oscillation suppression method based on additional virtual impedance control.
Background
In recent years, wind power is used as a renewable clean energy source, and has the advantages of low power generation cost, rich resource reserves and the like, so that the wind power is developed rapidly, particularly, the proportion of the offshore wind power is increased rapidly, and the market prospect is wide. With the increase of the scale of an offshore wind farm and the distance of grid-connected power transmission, after a high-voltage direct-current power transmission project is put into a power system, considerable influence is brought to the running performance of the whole system, and meanwhile, a lot of problems are brought to the stability of an alternating-current and direct-current parallel power transmission system.
The first point is that when a wind power plant is subjected to VSC-HVDC grid connection, a VSC-HVDC control device and a frequency converter control device of a double-fed wind turbine generator set generate interaction, so that the system presents weak damping or negative damping; and a second point: the AC transmission system can also influence the subsynchronous oscillation stability of the system; and a third point: at present, a more popular measure for suppressing the sub-synchronous oscillation is to add FACTS equipment, but the cost of the FACTS equipment is high, the occupied area is large, the investment cost of a system is increased, and a damping controller is also proposed to be added to suppress the sub-synchronous oscillation in documents. Therefore, it is necessary to further analyze a new problem of sub-synchronous oscillation caused by the parallel connection of alternating current and direct current in the wind power plant, and a virtual resistance control technology is provided for suppressing the sub-synchronous oscillation phenomenon aiming at the equivalent negative resistance effect of the controller.
Disclosure of Invention
The present invention aims to overcome the defects of the prior art and provide a subsynchronous oscillation suppression method based on additional virtual impedance control.
The purpose of the invention can be realized by the following technical scheme:
a subsynchronous oscillation suppression method based on additional virtual impedance control comprises the following steps:
1) constructing a mixed impedance model of a VSC-HVDC (voltage source converter-high voltage direct current) grid-connected system based on a doubly-fed wind power plant;
2) and inhibiting subsynchronous oscillation in a virtual resistance control mode by reasonably configuring parameters according to a mixed impedance model and a cascade system characteristic stability criterion.
The hybrid impedance model based on the double-fed wind power plant and through the VSC-HVDC alternating current and direct current grid-connected system comprises a double-fed fan impedance model, a VSC-HVDC impedance model and an alternating current transmission line impedance model, wherein the alternating current transmission line impedance and the VSC-HVDC impedance are connected in parallel to conduct impedance polymerization, and form a series impedance network with the double-fed fan impedance.
The expression of the impedance model of the doubly-fed wind turbine is as follows:
Figure BDA0002334656070000021
wherein Z isDFIG(s) is the frequency domain impedance of the doubly fed wind turbine, Rs、LsRespectively stator resistance and stator leakage inductance reactance, Rr、LrRotor resistance, rotor leakage inductance reactance, LmBeing the excitation inductance, omega, of induction machinesmAs angular speed of the rotor, Kp2、Ki2Respectively controlling the proportional and integral coefficients, omega, of the RSC inner loop current loopsFor stator angular velocity, j is the unit of imaginary number in the complex domain and s is the complex frequency.
The expression of the VSC-HVDC impedance model is as follows:
Figure BDA0002334656070000022
wherein Z isVSC-HVDC(s) is VSC-HVDCFrequency domain impedance of, Kp8、Ki8Respectively is VSC-HVDC rectification side outer ring active power control proportion and integral coefficient, Kp9、Ki9Respectively control proportion and integral coefficient of inner loop current of VSC-HVDC rectification side, omega is reference angular frequency, ZcIs the filter impedance at the port, j is the imaginary unit in the complex domain, s is the complex frequency
The expression of the impedance model of the alternating-current transmission line is as follows:
Figure BDA0002334656070000023
wherein Z isL(s) is an AC transmission linePath frequency domain impedance, RL、LLThe inductance is respectively corresponding to the resistance and the reactance of the alternating current transmission line, C is a series compensation capacitor of the alternating current transmission line, j is an imaginary number unit in a complex domain, and s is a complex frequency.
In the step 2), the criterion for stabilizing the characteristics of the cascade system is specifically as follows:
when the double-fed wind power plant and the alternating current transmission line form an equivalent resonance loop and the impedance is a negative value at the frequency point, a resonance phenomenon occurs, namely at ZDFIGImaginary part and polymerization impedance Z of alternating current transmission line and VSC-HVDCΣinZ with the sum of imaginary parts being 0DFIGAnd ZΣinWhen the sum of the real parts is less than 0, resonance occurs and the oscillation phenomenon is dispersed.
In the step 2), the control method of the virtual resistor with reasonably configured parameters comprises the following steps:
and the virtual resistor is introduced to increase the equivalent impedance of the double-fed fan, so that the resistance of the system in the sub-synchronous frequency band is improved.
The control of introducing the virtual resistor by the rotor side controller is specifically as follows:
by taking the rotor current iqr、idrAs the input signal of the virtual resistance, introduce the voltage control loop through filtering link and proportion link, then there are:
Figure BDA0002334656070000031
wherein R isviTo introduce a virtual resistance-controlled resistance magnitude, Δ udqrD and q axis voltage variations, K0Control of gain magnitude, i, for virtual resistancedqrAre the d and q axis currents of the rotor.
When the virtual resistance control gain is equal to the equivalent negative resistance of the doubly-fed wind turbine generator, namely K0＝Kp2(1+Kp1UsLm/Ls)+RrThe subsynchronous oscillations of the system are completely eliminated.
Compared with the prior art, the invention has the following advantages:
the control method can effectively inhibit the problem of subsynchronous oscillation caused by AC/DC parallel grid connection under the condition of adopting proper gain parameters, not only improves the subsynchronous stability of the system, but also can ensure the safe operation of new energy power transmission, has small investment, small occupied area and convenient operation and maintenance by adding virtual impedance control, and also solves the problems of increasing the investment cost of the system and the like caused by adopting external FACTS equipment for inhibition at present.
Drawings
FIG. 1 is a DFIG impedance frequency characteristic.
Fig. 2 is a system aggregate impedance frequency characteristic.
Fig. 3 is an oscillation mode distribution diagram.
Fig. 4 is a virtual impedance controller.
FIG. 5 shows that the wind power plant outputs active power when the series compensation degrees are different.
FIG. 6 shows the fan output active power at different gains, where FIG. 6a shows the value at K0When the output power is 0.9, the fan outputs active power, and the graph (6b) shows that the output power is K0When the value is 0.6, the fan outputs active power, and the graph (6c) shows that the value is K0When the power is 0.2, the fan outputs active power.
FIG. 7 is a flow chart of the 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 is described in detail below with reference to the figures and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the scope of the present invention is not limited to the following embodiments.
The invention provides a subsynchronous oscillation suppression method based on additional virtual impedance control, which comprises the following specific steps of:
1. building a mixed impedance model based on a doubly-fed wind power plant through a VSC-HVDC alternating current and direct current grid-connected system, wherein the mixed impedance model comprises a doubly-fed fan impedance model, a VSC-HVDC impedance model and an alternating current transmission line impedance model;
1.1 doubly-fed wind turbine impedance modeling
The double-fed wind turbine generator set comprises a fan, a double-fed asynchronous machine, a rotor side converter, a grid side converter and the like. The outer ring active control and the inner ring current control are used for decoupling the stator output active power and reactive power of the DFIG, so that the DFIG can track the input power of the DFIG and maintain the stability of the terminal voltage.
Figure BDA0002334656070000041
For a doubly-fed wind farm, the following impedance model was employed:
wherein Z isDFIG(s) is the frequency domain impedance of the doubly fed wind turbine, Zs(s)、Zm(s)、Zr(s) a resistance word in the frequency domain of the rotor winding, the stator winding and the mutual inductance winding respectively; rs、LsThe resistance is stator resistance and leakage inductance reactance; rr、LrRotor resistance and leakage inductance reactance; l ismIs the excitation inductance of the induction motor; zRSCIs the equivalent impedance of the rotor-side converter; slip(s) is a slip ratio,
Figure BDA0002334656070000042
ωmis the rotor angular velocity.
When the impedance of the doubly-fed wind turbine is modeled, the control link is simplified to a certain extent: the influence of a network side controller on the research of the subsynchronous problem is small; the rotor side controller RSC inner loop current control response speed is far faster than that of an outer loop active control link, so that the outer loop control is regarded as a fixed value, the frequency domain is not considered, the gain of a rotor current loop cross term is ignored, and the gain is simplified, so that the gain can be obtained:
Figure BDA0002334656070000043
wherein, Kp2、Ki2Respectively controlling the proportional and integral coefficients, omega, of the RSC inner loop current loopsIs the stator angular velocity.
And (3) obtaining equivalent frequency domain impedance of the fan by sorting:
Figure BDA0002334656070000051
1.2VSC-HVDC impedance modeling
The flexible direct current transmission system consists of a rectification side converter station, a network side inverter station and an air system. The grid side inverter station controls the direct voltage stability and the reactive power, the influence on the wind power plant is small, and only the rectifier side control is considered in the impedance modeling.
According to the control principle of the rectification side, the following impedance model is adopted:
Figure BDA0002334656070000052
wherein, Kp8、Ki8Respectively providing VSC-HVDC rectification side outer ring active control proportion and integral coefficient; kp9、Ki9Respectively controlling proportion and integral coefficient for VSC-HVDC rectification side inner loop current; omega is the reference angular frequency, ZcIs the filter impedance at the port.
The rectifying-side impedance of the impedance model consists of two parts, in the actual case, due to the filter impedance ZcSmaller, the latter part of the impedance is not considered when equating the impedance model of the whole system.
1.3 AC Transmission line impedance modeling
Disregarding infinite impedance, the equivalent frequency domain impedance of the external network alternating current transmission line is:
Figure BDA0002334656070000053
wherein Z isL(s) is the frequency domain impedance of the AC transmission line, RL、LLThe inductance is respectively corresponding to the resistance and the reactance of the alternating current transmission line, and C is the series compensation capacitance of the alternating current transmission line.
2. The principle of subsynchronous oscillation generation is analyzed based on the characteristic stability criterion of the cascade system;
the cascade system is the most typical multi-module system in practical application. An important research direction of the cascade system is to research the reasons of reduction of system stability margin and even instability aiming at the stability problem caused by mutual influence among different power electronic converters. The impedance-based stability criteria for cascaded systems were derived from the input filter design of the regulating converter in the middle of 1970. The stability analysis based on impedance is a very intuitive and effective method for analyzing the stability of the cascade system, and the impedance modeling is the basis of the impedance stability analysis.
By adopting an impedance modeling method, a positive sequence impedance model of each element can be established according to the topological structure of a target system, and the impedance topological structure of a certain wind power plant is established according to the impedance network modeling method of the new energy power generation grid-connected system in the existing literature. When the stability is analyzed for the impedance network, impedance aggregation operation is often required, and the circuit is simplified by means of series-parallel connection and the like. The relevant oscillation frequency can be found out according to the frequency characteristic curves of the various elements and the total aggregation impedance, and the stability of the oscillation mode of interest can be analyzed by using an RLC impedance analysis method.
According to an impedance analysis method, the impedance of a certain wind power plant can be divided into a double-fed wind turbine ZDFIGZ of an AC transmission lineLineAnd a flexible DC power transmission system ZVSC-HVDC。The AC transmission line and the flexible DC transmission system run in parallel, and the impedance of the AC transmission line and the flexible DC transmission system is aggregated into Z∑inAnd forming a typical structure diagram together with the equivalent impedance of the doubly-fed fan. Further can be aggregated into a single impedance Z∑Typically a high order complex frequency domain transfer function. The general literature adopts the Nyquist criterion, and compares an impedance frequency characteristic curve formed by the impedance of the current transformer and the impedance of the network to determine the stability of the system.
According to the RLC impedance analysis method, when the doubly-fed wind power plant and the line load module form an equivalent resonant circuit and at the frequency point, the impedance is a negative value, a resonance phenomenon occurs. From FIG. 2, it can be seen that at ZDFIGImaginary part and Z∑inZ with the sum of imaginary parts being 0DFIGAnd Z∑inWhen the sum of the real parts is less than 0, resonance and divergent oscillation phenomena occur, namely:
Figure BDA0002334656070000061
3. a virtual resistance control technology with reasonably configured parameters is designed to inhibit the subsynchronous oscillation phenomenon.
By observing the equivalent impedance formula of the system, the capacity of the system for inhibiting the subsynchronous oscillation can be enhanced by improving the resistance of the system when the subsynchronous oscillation occurs. The equivalent impedance of the double-fed wind turbine generator is increased, so that the resistance of the system in the sub-synchronous frequency band is improved. The equivalent impedance of the doubly-fed wind turbine generator is mainly determined by a machine side, the rotor side controller directly controls the rotor current, and the virtual resistor is introduced into the rotor side controller simply and conveniently.
With the virtual impedance control structure shown in FIG. 4, the rotor current i is takenqr、idrThe input signal of the virtual resistor is introduced into a voltage control loop through a filtering link and a proportion link. The filtering link is used for reducing the influence of virtual resistance control on the PI link of the rotor side converter. After introducing the scaling element, the introduced virtual reactance can be expressed as:
Figure BDA0002334656070000062
wherein R isviTo introduce a virtual resistance-controlled resistance magnitude, Δ udqrThe d-axis voltage variation and the q-axis voltage variation are respectively.
Considering the following three conditions according to the magnitude of the virtual resistance gain, respectively taking different values to compare the influence of the system subsynchronous oscillation stability
1. The virtual resistance controls the gain to obtain the equivalent negative resistance of the doubly-fed wind turbine generator, and the equivalent negative resistance is obtained
K0＝Kp2(1+Kp1UsLm/Ls)+Rr＝0.9 (8)
2. The virtual resistance control gain ignores the influence of the outer ring parameter of the double-fed fan, and the virtual resistance control gain is obtained
K0＝Kp2+Rr＝0.6 (9)
3. Controlling the gain by the virtual resistor while neglecting the influence of the outer ring parameter and the rotor equivalent resistance of the doubly-fed fan, and taking
K0＝Kp2＝0.2 (10)
Example 1: the correctness of equivalent impedance modeling of the AC-DC parallel system is verified
And (3) combining the deduced impedance model of the doubly-fed wind turbine generator, the series compensation power grid impedance model and the VSC-HVDC impedance model, and drawing curves of system equivalent inductive reactance, series compensation capacitance capacitive reactance and system equivalent resistance changing along with frequency in the same graph. The intersection frequency of the equivalent inductive reactance and the capacitive reactance is the subsynchronous resonance frequency of the system, and the positive and negative of the equivalent resistance at the point determine whether the system oscillation is convergent or divergent.
Based on the equivalent impedance calculation formula, characteristic curves of the imaginary part and the real part of the total impedance of the doubly-fed wind power plant near the power frequency are drawn and shown in fig. 1.
From fig. 1, in the doubly-fed wind farm, in the subsynchronous oscillation frequency range, the real part of the equivalent total impedance is smaller than zero, the imaginary part is larger than zero, and the total impedance is in a negative resistance-positive inductance property. The main reason for the negative resistance is because the equivalent resistance of the rotor-side controller RSC is negative at the sub-synchronous frequency, reducing the impedance of the entire system at the sub-synchronous frequency.
Further drawing the impedance-frequency characteristic of the whole system under the subsynchronous frequency, wherein the fan side is ZDFIGThe network side is the parallel impedance of the equivalent impedance of the flexible DC power transmission system and the AC power transmission line, namely ZVSC-HVDC||ZLineThe total system aggregate impedance is Z∑As shown in fig. 2.
According to the system aggregation impedance frequency characteristic curve graph, when the imaginary part of the impedance crosses zero and the corresponding real part of the impedance at the moment is smaller than zero, namely the RLC series resonance condition is met, the system R is smaller than 0, the subsynchronous oscillation of the system is triggered and rapidly diverged at the moment until the amplitude limit is reached and the constant amplitude oscillation is maintained, and the oscillation frequency is 18Hz at the moment.
And then, analyzing the double-fed wind turbine generator set through a flexible direct current grid-connected system by adopting a small signal analysis method and a characteristic root analysis method, and verifying the effectiveness of the short-circuit ratio index.
And analyzing and comparing the oscillation of the VSC system with the wind power accessed to the alternating current power grid. Establishing a characteristic matrix equation of small signal analysis based on the model:
Figure BDA0002334656070000081
in the formula: the state variable delta x mainly comprises a double-fed fan, a VSC-HVDC system and an alternating current transmission system. Solving a system state equation to obtain a relevant oscillation mode as shown in table 1:
TABLE 1 eigenvalue analysis
Mode(s) Eigenvalues σ ± j ω Modal frequency f/Hz Damping ratio ξ
sso-1 0.676±j113.883 18.125 -0.676
sso-2 -2.356±j88.569 14.096 2.356
sso-3 -33.414±j84.131 13.389 33.414
sso-4 -11.044±j57.183 9.101 11.044
Fig. 3 shows 4 main oscillation modes in the sub-synchronous frequency band (2.0-50 Hz), wherein the mode sso-1 is in the first and fourth quadrants, and the system is in an unstable state, as can be seen from table 1, the damping ratio is-0.067, the negative damping state, and the oscillation is divergent. The modes sso-2, sso-3 and sso-4 are in the second quadrant and the third quadrant, the system is in a stable state, the damping ratio is larger than zero, and the damping is positive.
The modal frequency of an unstable oscillation mode obtained by a characteristic root analysis method is 18.125Hz, and is approximately equal to 18Hz obtained by establishing equivalent impedance, and the small signal analysis method is considered to be a method for approximately linearizing a system and then analyzing the synchronization, so that the two are considered to be consistent in an error range, the accuracy of equivalent impedance modeling of an AC-DC parallel system is verified, and the method can reasonably explain the principle of subsynchronous oscillation generation.
Influence of series compensation degree of alternating current transmission system on subsynchronous oscillation
In order to research the influence of an alternating current transmission system on the subsynchronous oscillation stability of the system, when the serial compensation degree of an alternating current line is 20% and 40%, the three-phase short-circuit fault is set at the initial time, and the duration is 0.5 s. Fig. 5 is a variation curve of active power output by the wind farm when the series compensation degrees are different.
When an alternating-current transmission line is added with a series compensation device, the original purpose is to improve the transmission limit, but the introduction of the series compensation device can cause the problem of the subsynchronous oscillation stability of the system. As can be seen from fig. 5, when the crosstalk compensation degree is 20%, the system rapidly stabilizes after a small disturbance. When the series compensation degree is increased to 40%, the wind power plant output active response curve presents a divergent state after small disturbance, and subsynchronous oscillation occurs and gradually diverges. Therefore, in an alternating current-direct current parallel system, the series compensation degree of an alternating current transmission line is determined according to the actual situation, and the subsynchronous oscillation stability of the system is reduced due to the fact that the series compensation degree is too high.
Verifying the effect of virtual resistance control on subsynchronous oscillation
And under the condition that the series compensation degree is 40%, adding an additional virtual resistor controller, respectively setting three virtual resistor gain values, setting three short-circuit faults at the initial time, keeping the short-circuit faults for 0.5s, and analyzing and comparing the response condition of the active power output by the wind power plant.
As shown in fig. 6, comparing the three different gain values, it can be known that: when gain K0When a response value is obtained according to the equivalent negative impedance of the rotor side, the problem of the subsynchronous oscillation of the system can be well solved when the gain is too small, the controller provides insufficient positive resistance, and the subsynchronous oscillation of the system can be completely eliminated; when neglecting the internal control value K of the rotor side0In the process, the virtual resistance controller can provide certain positive damping, but the oscillation phenomenon is not eliminated, and the complex oscillation phenomenon still exists; when the gain is too small, the virtual resistance controller hardly acts.
Therefore, when the problem of the subsynchronous oscillation of the system is analyzed, the virtual resistance controller can well inhibit the subsynchronous oscillation phenomenon. However, according to the actual situation, an appropriate virtual resistance gain value should be obtained to achieve the best suppression effect.

Claims (9)

1. A subsynchronous oscillation suppression method based on additional virtual impedance control is characterized by comprising the following steps:
1) constructing a mixed impedance model of a VSC-HVDC (voltage source converter-high voltage direct current) grid-connected system based on a doubly-fed wind power plant;
2) and inhibiting subsynchronous oscillation in a virtual resistance control mode by reasonably configuring parameters according to a mixed impedance model and a cascade system characteristic stability criterion.
2. The subsynchronous oscillation suppression method based on additional virtual impedance control according to claim 1, wherein the hybrid impedance model based on the doubly-fed wind farm through the VSC-HVDC alternating current/direct current grid-connected system comprises a doubly-fed wind turbine impedance model, a VSC-HVDC impedance model and an alternating current transmission line impedance model, wherein the alternating current transmission line impedance and the VSC-HVDC impedance are connected in parallel to perform impedance aggregation, and form a series impedance network with the doubly-fed wind turbine impedance.
3. The subsynchronous oscillation suppression method based on the additional virtual impedance control according to claim 2, wherein the expression of the impedance model of the doubly-fed wind turbine is as follows:
Figure FDA0002334656060000011
wherein Z isDFIG(s) is the frequency domain impedance of the doubly fed wind turbine, Rs、LsRespectively stator resistance and stator leakage inductance reactance, Rr、LrRotor resistance, rotor leakage inductance reactance, LmBeing the excitation inductance, omega, of induction machinesmAs angular speed of the rotor, Kp2、Ki2Respectively controlling the proportional and integral coefficients, omega, of the RSC inner loop current loopsFor stator angular velocity, j is the unit of imaginary number in the complex domain and s is the complex frequency.
4. The subsynchronous oscillation suppression method based on additional virtual impedance control according to claim 2, characterized in that the expression of the VSC-HVDC impedance model is:
Figure FDA0002334656060000012
wherein Z isVSC-HVDC(s) frequency-domain impedance of VSC-HVDC, Kp8、Ki8Respectively is VSC-HVDC rectification side outer ring active power control proportion and integral coefficient, Kp9、Ki9Respectively control proportion and integral coefficient of inner loop current of VSC-HVDC rectification side, omega is reference angular frequency, ZcIs the filter impedance at the port, j is the imaginary unit in the complex domain, s isA complex frequency.
5. The subsynchronous oscillation suppression method based on additional virtual impedance control according to claim 2, wherein the expression of the impedance model of the alternating current transmission line is as follows:
Figure FDA0002334656060000021
wherein Z isL(s) is the frequency domain impedance of the AC transmission line, RL、LLThe inductance is respectively corresponding to the resistance and the reactance of the alternating current transmission line, C is a series compensation capacitor of the alternating current transmission line, j is an imaginary number unit in a complex domain, and s is a complex frequency.
6. The subsynchronous oscillation suppression method based on additional virtual impedance control according to claim 1, wherein in the step 2), the criterion for stabilizing the characteristics of the cascade system is specifically as follows:
when the double-fed wind power plant and the alternating current transmission line form an equivalent resonance loop and the impedance is a negative value at the frequency point, a resonance phenomenon occurs, namely at ZDFIGImaginary part and polymerization impedance Z of alternating current transmission line and VSC-HVDCΣinZ with the sum of imaginary parts being 0DFIGAnd ZΣinWhen the sum of the real parts is less than 0, resonance occurs and the oscillation phenomenon is dispersed.
7. The subsynchronous oscillation suppression method based on additional virtual impedance control according to claim 1, wherein in the step 2), the virtual resistance control mode for reasonably configuring parameters comprises:
and the virtual resistor is introduced to increase the equivalent impedance of the double-fed fan, so that the resistance of the system in the sub-synchronous frequency band is improved.
8. The subsynchronous oscillation suppression method based on additional virtual impedance control according to claim 7, wherein the control of introducing the virtual resistance by the rotor-side controller is specifically as follows:
by taking the rotor current iqr、idrAs the input signal of the virtual resistance, introduce the voltage control loop through filtering link and proportion link, then there are:
Figure FDA0002334656060000022
wherein R isviTo introduce a virtual resistance-controlled resistance magnitude, Δ udqrD and q axis voltage variations, K0Control of gain magnitude, i, for virtual resistancedqrAre the d and q axis currents of the rotor.
9. The subsynchronous oscillation suppression method based on additional virtual impedance control of claim 8, characterized in that when the virtual resistance control gain is equivalent negative resistance of doubly-fed wind turbine generator, K is0＝Kp2(1+Kp1UsLm/Ls)+RrThe subsynchronous oscillations of the system are completely eliminated.
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CN112350345A (en) * 2020-10-28 2021-02-09 许继集团有限公司 Method for designing impedance correction device of modular multilevel converter and correction device
CN113013898A (en) * 2021-03-17 2021-06-22 江苏国科智能电气有限公司 Grid-connected inverter subsynchronous oscillation suppression method based on far-end power grid phase locking
CN113725910A (en) * 2021-10-08 2021-11-30 南通大学 Stability analysis and quantitative evaluation method for wind power plant grid-connected system
CN113985128A (en) * 2021-10-26 2022-01-28 中国电力科学研究院有限公司 Oscillation early warning method and system based on measurement data, storage medium and server
CN114362150A (en) * 2021-12-16 2022-04-15 广东电网有限责任公司 Method and device for identifying forced subsynchronous oscillation risk of offshore wind farm

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