CN116826779A - Subsynchronous oscillation suppression method of soft direct grid-connected system based on active disturbance rejection control - Google Patents
Subsynchronous oscillation suppression method of soft direct grid-connected system based on active disturbance rejection control Download PDFInfo
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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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- 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
- H02J3/002—Flicker reduction, e.g. compensation of flicker introduced by non-linear load
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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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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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
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
- H02J2003/365—Reducing harmonics or oscillations in HVDC
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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
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/28—The renewable source being wind energy
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Abstract
The application provides a method for suppressing subsynchronous oscillation of a soft direct grid-connected system based on active disturbance rejection control, which comprises the following steps: step 1: establishing a simulation model of the direct-driven wind power plant through a soft direct-connected system by considering multiple control links; step 2: researching the influence of external influence parameters such as wind speed and internal controllable parameters such as the change of controller parameters on the subsynchronous oscillation of the system, and obtaining key influence links of the subsynchronous oscillation of the system; step 3: determining the position of the controller and selecting input and output signals; an additional subsynchronous damping controller of a direct-driven wind power plant through a soft direct grid-connected system is designed based on an active disturbance rejection control theory; step 4: and optimizing and setting parameters of the additional subsynchronous damping controller by adopting a genetic algorithm, and adding the obtained additional subsynchronous damping controller into a direct-drive wind power plant through a soft direct-connected system so as to realize system subsynchronous oscillation suppression. By the technical scheme, the subsynchronous oscillation of the system can be restrained, and the robustness is high.
Description
Technical Field
The application relates to the technical field of power system control, in particular to a soft direct grid-connected system subsynchronous oscillation suppression method based on active disturbance rejection control.
Background
Because the land wind power resources and the photovoltaic are mainly concentrated in northwest, north China and northeast China, renewable energy sources and electric loads are reversely distributed in geographic positions; although the eastern region contains a large amount of offshore wind power resources, the eastern region is far away from the load center, and the offshore wind power is usually required to be transmitted to the load center through a large-capacity long-distance transmission technology.
The flexible direct current transmission mode can better meet the large-scale, large-scale and flexible transmission requirements of clean energy, so that the flexible direct current transmission mode can be applied to the current scene of multi-new energy power generation, and power stations such as multi-wind power stations and photovoltaic power stations for generating power by using renewable energy sources are connected to a power grid. The power transmission mode can well realize the power transmission from renewable resources to the load center of the city, and provides a good solution for the scenes of new energy grid connection, island power supply and the like. However, with the gradual construction of new energy power generation, the large-scale grid connection of the new energy power generation brings new challenges to the safe and stable operation of the power system. Subsynchronous oscillation accidents cause increased frequency of occurrence of fan off-grid, large-scale power failure and power quality problems.
The mechanism that the new energy source generates subsynchronous oscillation through the soft direct-connected system is mainly that the new energy source unit and the MMC control system relate to the coordination cooperation of controllers with different control bandwidths and interaction exists between the controllers, so that the output impedance of the new energy source unit and the MMC impedance have resonance points in subsynchronous frequency bands, the damping of the grid-connected system at the resonance points is insufficient, and even negative damping is presented, and subsynchronous oscillation is generated.
At present, the method for restraining the subsynchronous oscillation of the new energy through the soft direct grid-connected system generally comprises three methods of parameter optimization, subsynchronous electric quantity blocking and system damping improvement. The parameter optimization method directly avoids the resonance point of the system by adjusting the existing electrical parameters or control parameters in the system to proper values, and has simple operation and low cost, but the coupling between the parameters can not be ignored when the parameters are too many, and the adaptability under different working conditions is low. The method for blocking the subsynchronous electric quantity comprises adding a line filter, a static blocking filter, a bypass blocking filter and the like. Methods of improving system damping include additional damping controllers, subsynchronous damping control of parallel flexible ac transmission system (FlexibleAC Transmission Systems, FACTS) devices, etc., with additional damping controllers being the most commonly employed method. However, when the current research of the additional damping controller is performed on the system with large disturbance or the working point is far away from the initial working point due to the change of the system running state, so that a new mode is generated, the controller parameters of the additional damping controller need to be readjusted, and the robustness is poor.
Disclosure of Invention
Therefore, the application aims to provide the soft direct-connected grid-connected system subsynchronous oscillation suppression method based on the active disturbance rejection control, which realizes the system subsynchronous oscillation suppression and has stronger robustness.
In order to achieve the above purpose, the application adopts the following technical scheme: a soft direct grid-connected system subsynchronous oscillation suppression method based on active disturbance rejection control comprises the following steps:
step 1: based on the topological structure of the direct-drive fan and the flexible direct-current transmission system and the principle of a control system, a direct-drive wind power plant simulation model which considers multiple control links is built through a flexible direct-connected system;
step 2: researching the influence of external influence parameters such as wind speed and internal controllable parameters such as the change of controller parameters on the subsynchronous oscillation of the system, and obtaining key influence links of the subsynchronous oscillation of the system;
step 3: determining the position of the controller and the selection of input and output signals based on the analysis conclusion of the key influence links of the system subsynchronous oscillation in the step 2; an additional subsynchronous damping controller of a direct-driven wind power plant through a soft direct grid-connected system is designed based on an active disturbance rejection control theory;
step 4: and optimizing and setting parameters of the additional subsynchronous damping controller by adopting a genetic algorithm, and adding the obtained additional subsynchronous damping controller into a direct-drive wind power plant through a soft direct-connected system so as to realize system subsynchronous oscillation suppression.
In a preferred embodiment, step 3 takes the rotation speed of the fan rotor as the input signal of the additional subsynchronous damping controller based on the analysis of the key influence link in step 2, the output signal of the controller is added into the internal and external ring control of the network-side converter of the key link direct-driven fan which influences the subsynchronous oscillation of the system, and the additional subsynchronous damping controller structure is designed based on the active disturbance rejection control theory.
In a preferred embodiment of the present application,
(1) The direct-drive wind power plant adopts classical vector control through a direct-drive fan side converter MSC and a network side converter GSC in a soft direct-grid system simulation model, and an MMC converter station level control strategy adopts an island control strategy or a non-island control strategy; the direct-drive fan side converter MSC adopts vector control of rotor magnetic field orientation to control electromagnetic torque of the generator, so that the generator can operate at variable speed along with the change of wind speed, thereby capturing maximum wind energy and transmitting generator power to the direct-current side of the converter; the grid-side converter GSC adopts grid voltage directional vector control to control direct current bus capacitor voltage and grid-connected reactive power;
(2) Changing parameters of an inner ring controller of a wind speed, a direct-driven fan side converter and a net side converter in a built simulation model, and obtaining key influence links of system subsynchronous oscillation by comparing amplitude changes and oscillation frequency changes of the system subsynchronous oscillation under parameter changes;
(3) According to the analysis conclusion of the key influence link of the subsynchronous oscillation, the rotating speed of the fan rotor is set as an output signal of the controller, and the output signal is added into the internal and external ring control of the GSC of the fan;
(4) The direct-driven wind power plant designed based on the active disturbance rejection control theory comprises a tracking differentiator, an extended state observer, a nonlinear error feedback and control quantity generation link and a soft direct grid-connected system additional subsynchronous damping controller; the tracking differentiator TD realizes fast tracking of an input signal and synchronous output of a differentiated signal, and the mathematical expression is as follows:
wherein v is 1 Can track the control input v, v quickly without overshoot 2 Is the approximate derivative of v; h is a sampling period; r is (r) 0 Is a tracking speed factor; h is a 0 Is a filtering factor; fhan is the fastest synthesis function;
the extended state observer ESO can estimate the real-time action value of the internal and external disturbance of the system, and expand the total disturbance into a new state variable of the system; the extended state observer ESO compensates the tracking signal through feedback, and eliminates the influence of the total disturbance in the system by using the compensation quantity; the mathematical expression of the nonlinear extended state observer ESO is:
wherein the expression of the nonlinear function fal (x, a, δ) is:
wherein: delta >0; sign (x) is a sign function;
nonlinear error feedback NLSEF obtains error signal e according to tracking signal outputted by TD and signal obtained by ESO observation 1 ＝v 1 －z 1 Error differential signal e 2 ＝v 2 －z 2 By nonlinear combination, the disturbance is compensated for to control the corresponding object. The nonlinear combination is generally of two types (4) and (5):
u 0 ＝β 1 fal(e 1 ,a 3 ,δ)+β 2 fal(e 2 ,a 4 ,δ) (4)
u 0 ＝fhan(e 1 ,ce 2 ,r,h 1 ) (5)
the mathematical expression of the control amount is:
formula (6) comprises two moieties: -z 3 /b 0 To compensate for the disturbance, u 0 /b 0 To control an integral series section with nonlinear feedback, where b 0 Is a compensation factor;
(5) Parameter beta of additional subsynchronous damping controller by adopting genetic algorithm GA 01 、β 02 、β 03 、β 1 、β 2 Optimizing and setting; the fitness function is shown as a formula (1);
wherein: p (P) * 、P 、 Q * Q is the reference value and the actual value of the active power and the reactive power of the wind farm; u (U) dc * 、U dc The reference value and the actual value of the voltage of the direct current bus of the fan are obtained.
Compared with the prior art, the application has the following beneficial effects:
(1) The proposed additional subsynchronous damping controller does not depend on the exact model of the system;
(2) The additional subsynchronous damping controller can effectively improve the subsynchronous frequency band damping of the system and realize the subsynchronous oscillation suppression of the system;
(3) The additional subsynchronous damping controller can estimate disturbance in the system in real time so as to adapt to different disturbance in the system, and has stronger robustness.
Drawings
Fig. 1 is a schematic diagram of a direct-drive wind farm through an MMC-HVDC grid-connected system according to a preferred embodiment of the present application;
FIG. 2 is a schematic diagram of the basic structure of a direct-drive wind turbine system according to a preferred embodiment of the present application;
FIG. 3 is a control block diagram of a direct drive fan side converter in accordance with a preferred embodiment of the present application;
fig. 4 is a control block diagram of a direct-drive fan grid-side converter according to a preferred embodiment of the present application;
FIG. 5 is a schematic diagram of a modular multilevel circulator topology according to a preferred embodiment of the application;
FIG. 6 is a block diagram of MMC control mode selection in accordance with a preferred embodiment of the application;
fig. 7 is a VCO control block diagram of a preferred embodiment of the present application;
FIG. 8 is an island mode control block diagram of a preferred embodiment of the present application;
FIG. 9 is a graph showing the waveform of active power output by a wind farm at different wind speeds in accordance with a preferred embodiment of the present application;
FIG. 10 is a graph showing wind farm output current waveforms at different wind speeds in accordance with a preferred embodiment of the present application;
FIG. 11 is a graph showing the results of Fourier analysis of active power and current at different wind speeds in accordance with a preferred embodiment of the present application;
FIG. 12 is a waveform diagram of fan output active power versus current for different Kp1 in accordance with a preferred embodiment of the present application;
FIG. 13 is a chart showing the Fourier analysis results of current waveforms at different Kp1 in accordance with the preferred embodiment of the present application;
FIG. 14 is a waveform diagram of fan output active power versus current for different Ki 1's in accordance with a preferred embodiment of the present application;
FIG. 15 is a waveform diagram of fan output active power versus current for different Kp2 in accordance with a preferred embodiment of the present application;
FIG. 16 is a chart showing the result of Fourier analysis of current at different Kp2 in a preferred embodiment of the present application;
FIG. 17 is a block diagram of an additional subsynchronous damping controller in accordance with a preferred embodiment of the present application;
fig. 18 is a schematic diagram of a direct drive fan with MMC-HVDC grid-connected subsynchronous oscillation suppression strategy controller according to a preferred embodiment of the present application;
FIG. 19 is a flowchart of the optimization of additional subsynchronous damping controller parameters based on genetic algorithm in accordance with a preferred embodiment of the present application;
FIG. 20 is a waveform diagram of the fan output active power and Fourier analysis results in accordance with a preferred embodiment of the present application;
FIG. 21 is a graph of wind farm output active power waveforms in accordance with a preferred embodiment of the present application.
Detailed Description
The application will be further described with reference to the accompanying drawings and examples.
It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the application. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the present application; as used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
In this embodiment, taking the direct-driven wind farm shown in fig. 1 as an example through a soft direct grid-connected system, the effectiveness of the new energy based on the active disturbance rejection control theory provided by the application is verified through a subsynchronous oscillation suppression method of the soft direct grid-connected system.
The method comprises the following steps:
step 1: based on the topological structure of the direct-drive fan and the flexible direct-current transmission system and the principle of a control system, a direct-drive wind power plant simulation model which considers multiple control links is built through a flexible direct-connected system.
Step 2: based on simulation analysis, the influence of external influence factors and internal controllable parameter changes on the system subsynchronous oscillation is researched, and a key influence link of the system subsynchronous oscillation is obtained. Wherein the external influencing factors and the internal controllable parameters are shown in table 1. Analysis of key impact links of system subsynchronous oscillation can be used for design of subsequent controllers.
TABLE 1summary of influence factors of subsynchronous oscillation Tab 1Summary offactors affecting system subsynchronous oscillation of the System
Step 3: and (3) determining the position of the controller and the selection of input and output signals based on the analysis conclusion of the key influence links of the system subsynchronous oscillation in the step (2). And (3) designing an additional subsynchronous damping controller of the direct-driven wind power plant through the soft direct grid-connected system based on an active disturbance rejection control theory by considering disturbance and change possibly occurring in the system. And 3, based on the analysis of the key influence links in the step 2, taking the rotating speed of the fan rotor as an input signal of an additional subsynchronous damping controller, adding an output signal of the controller into the internal and external ring control of the network-side converter of the key link direct-driven fan which influences the subsynchronous oscillation of the system, and designing an additional subsynchronous damping controller structure based on an active disturbance rejection control theory. The input quantity of the controller adopts the rotating speed of the fan rotor directly related to the wind speed, and the design of the controller considers the disturbance and the change possibly occurring in the system, so that the additional subsynchronous damping controller can adapt to different working conditions and has stronger robustness.
Step 4: and optimizing and setting parameters of the additional subsynchronous damping controller by adopting a genetic algorithm, and adding the obtained additional subsynchronous damping controller into a direct-drive wind power plant through a soft direct-connected system so as to realize system subsynchronous oscillation suppression.
The specific implementation is as follows:
1. establishing simulation model of direct-driven wind power plant through flexible direct grid-connected system
The basic structure schematic diagram of the direct-drive wind turbine generator system is shown in fig. 2, a wind turbine is directly connected to a synchronous generator, and the generator is completely decoupled from a power grid through a converter. The control system of the direct-drive fan comprises an MSC and a GSC. Wherein the control target of the MSC is to control the active power and the alternating current voltage output by the fan, and the control block diagram is shown in figure 3; the GSC controls the direct current bus capacitor voltage and the reactive power of the grid connection, and the control block diagram is shown in figure 4.
The basic structure of the MMC is shown in fig. 5, the converter station level control strategy can adopt a non-island control strategy or an island control strategy, and the control mode selection relation block diagram is shown in fig. 6.
When non-island control is adopted, the MMC converter station control strategy is divided into inner loop current control and outer loop power control, and the control output is the reference value i of the current component sd * And i sq * . When island control is employed, the VCO control block diagram is shown in fig. 7, wherein: d (D) f Is the power droop coefficient; f (f) max 、f min The upper and lower frequency limit values are set. Fig. 8 is an island mode control block diagram, wherein: u (u) ac * Is the reference value of alternating voltage, U rms Is an effective value of alternating voltage, Q is reactive power, H 11 (s) is a PI control link transfer function, D ac Is the control coefficient of the AC sag.
And establishing a simulation model of the direct-driven wind power plant through the soft direct-connected system topological structure and the control system schematic block diagram.
2. System subsynchronous oscillation key influence link analysis
The stability of the direct-drive wind power plant through the flexible direct-connected system is easily influenced by external factors and control parameters of each control link, and the influence factors influencing the subsynchronous oscillation of the system are analyzed by changing the wind speed and the magnitude of the controller parameters of the inner ring of the direct-drive fan.
(1) Wind farm wind speed
Wind farm output power is affected by wind speed and has the characteristics of randomness and uncontrollability, which makes the wind farm output power possible to fluctuate widely. And analyzing the influence of the wind field output on the subsynchronous oscillation by changing the wind speed of the wind field. In order to simplify the analysis, assuming that the wind speeds of the wind fields are equal and the wind speeds of the wind fields are synchronously changed, when SSO exists in the system, the initial wind speed is set to be 7m/s, the wind speed is changed when t=1.0s, the wind speed value is gradually increased, and the output active power and current of the wind fields are observed, and the results are shown in fig. 9 and 10.
From the simulation results, it can be derived that: when the wind speeds are 9m/s, 10m/s and 11m/s, the system generates oscillation conditions, and Fourier analysis is carried out on the wind power field output active power and current data under the conditions, so that the result shown in FIG. 11 can be obtained.
As can be seen from fig. 11, when the wind speed is switched to 9m/s, the active power oscillation frequency of the wind power plant is 24.8Hz, the current oscillation frequency of the wind power plant is 25.2Hz, and the sum of the active power and the current oscillation frequency is 50Hz, which is a complementary relationship, so that the typical subsynchronous oscillation characteristics are satisfied; when the wind speed is switched to 10m/s, the amplitude of the Fourier analysis result shows that the oscillation is aggravated, and at the moment, the active power oscillation frequency of the wind power plant is 22Hz, and the current oscillation frequency of the wind power plant is 28Hz. Meanwhile, when the wind speed is increased to 10m/s, other dominant oscillation frequency trends are shown; when the wind speed is switched to 11m/s, the subsynchronous oscillation of the system is further increased, and a new oscillation frequency is caused. The active power oscillation frequency of the wind power plant is 18.67Hz and 37.33Hz, the current oscillation frequency of the wind power plant is 31.33Hz and 12.67Hz, and at the moment, the two groups of oscillation frequencies of the active power and the current still meet the complementary relation.
The simulation waveform diagram and the result of Fourier analysis can be integrated to obtain: when the wind speed increases, the wind field output increases, at which time the subsynchronous oscillation frequency amplitude increases significantly and a new oscillation frequency occurs. During the gradual increase of wind speed, the subsynchronous oscillation frequency of the system changes and the oscillation frequency gradually becomes smaller.
(2) MSC inner loop controller parameters
Changing fan MSC inner ring controller K p1 Parameters set as: (a) K (K) p1 ＝2；(b)K p1 ＝3；(c)K p1 =5. The waveform diagram of the fan output active power and current is shown in figure 12.
From FIG. 12, it can be seen that K p1 When=2, the system oscillation converges; k (K) p1 When=3, the system oscillates with constant amplitude; k (K) p1 At=5, the oscillation of the system is exacerbated. The current was fourier analyzed and the result is shown in fig. 13.
From fig. 13, the following can be more intuitively concluded: with K p1 The increase in value, the system exhibits oscillations at frequencies other than the fundamental frequency; k (K) p1 At=3, the system exhibits an oscillation frequency of 27.84Hz, K p1 When=5, the system exhibits an oscillation frequency of 17.67 and 23.84Hz, the latter is lower and increases the oscillation frequency point compared to the former; however, from the waveform, it can be seen that by K p1 And the system is not unstable due to the adjustment of the value.
Changing fan MSC inner ring controller K i1 Parameters set as: (a) K (K) i1 ＝30；(b)K i1 ＝100；(c)K i1 =200. The waveform diagram of the fan output active power and current is shown in fig. 14.
As can be seen from fig. 14, changing this parameter has no significant effect on the oscillation situation of the system.
(3) GSC inner loop controller parameters
Change fan GSC inner loop controller K p2 Parameters set as: (a) K (K) p2 ＝1；(b)K p2 ＝2；(c)K p2 =3. The waveform diagram of the fan output active power and current is shown in fig. 15.
From FIG. 15, it can be seen that K p2 ＝1、K p2 When=2, the system oscillations are converged, and the oscillation amplitude follows K p2 Increasing the value by increasingLarge; k (K) p2 At=3, the system experiences a situation where the oscillation diverges and eventually destabilizes. The current was fourier analyzed and the result is shown in fig. 16.
Fig. 16 shows that: k (K) p2 ＝1、K p2 When=2, the system oscillates at no significant frequency other than the fundamental frequency; k (K) p2 At=3, the system exhibits oscillation frequencies of 32.67Hz and 67.18Hz, i.e., subsynchronous and supersynchronous frequency oscillations occur simultaneously. The following can thus be concluded: with K p2 The system oscillation amplitude increases, and when the system oscillation is increased to a certain value, the system oscillation diverges, so that the fan GSC inner loop controller K p2 Is a key influencing factor for influencing the subsynchronous oscillation of the system. Therefore, the oscillation can be suppressed by optimizing the direct drive fan GSC link.
Changing GSC inner loop controller parameter K i2 The simulation results of (2) have substantially no effect on system oscillations and are therefore not analyzed in detail here.
3. Additional subsynchronous damping controllers are designed based on active disturbance rejection control theory and genetic algorithm is adopted to set controller parameters
The additional subsynchronous damping controller based on the active disturbance rejection control theory comprises a tracking differentiator, an extended state observer and a nonlinear error feedback and control quantity generation link, and a control block diagram is shown in figure 17. Based on the analysis result of the influencing factors, the rotating speed of the fan rotor is selected as an input signal of a controller, and the output signal of the controller is superposed into the inner and outer ring control of the grid-side converter, as shown in fig. 18.
Wherein v is 1 Can track the control input v, v quickly without overshoot 2 Is the approximate derivative of v; h is a sampling period; r is (r) 0 Is a tracking speed factor; h is a 0 Is a filtering factor; fhan is the fastest synthesis function.
The extended state observer (extended state observer, ESO) can estimate the real-time contribution of the internal and external disturbances of the system, and extend the total disturbance into a new state variable of the system. The ESO compensates the tracking signal through feedback, and the influence of the total disturbance in the system is eliminated by using the compensation quantity. The mathematical expression for nonlinear ESO is:
wherein the expression of the nonlinear function fal (x, a, δ) is:
nonlinear error feedback (nonlinear state error feedback, NLSEF) can obtain error signal e based on tracking signal outputted by TD and signal obtained by ESO observation 1 ＝v 1 －z 1 Error differential signal e 2 ＝v 2 －z 2 By nonlinear combination, the disturbance is compensated for to control the corresponding object. The nonlinear combination is generally of two types (4) and (5):
u 0 ＝β 1 fal(e 1 ,a 3 ,δ)+β 2 fal(e 2 ,a 4 ,δ) (4)
u 0 ＝fhan(e 1 ,ce 2 ,r,h 1 ) (5)
the mathematical expression of the control amount is:
formula (6) comprises two moieties: -z 3 /b 0 To compensate for the disturbance, u 0 /b 0 To control an integral series section with nonlinear feedback, where b 0 Is a compensation factor.
And (3) optimizing and setting parameters of the controller by adopting a genetic algorithm, wherein the parameters to be set are as follows: r is (r) 0 、h、β 01 、β 02 、β 03 、h 0 、β 1 、β 2 、b 0 、a 3 A4, δ. In the TD partH is required to be consistent with the actual simulation step length in the simulation model; filtering factor h 0 The harmonic wave in the reference differential input can be removed, and when h is fixed, the normal h 0 The value of (2) may be an integer multiple of h, thereby achieving a filtering effect. r is (r) 0 Gradually increasing the value of TD v 1 Will be close to v, but will have a value that, if too large, will cause v 2 Generating fluctuations, typically setting r 0 =1000. In ESO a 1 、a 2 The values of (2) are typically empirically taken as: 0.5 and 0.25; delta=h is generally taken. In addition, to ensure the effect of ESO, it is often necessary to know the actual value of b or close to the actual value. If the accurate value of b cannot be known, the estimated value b is used 0 Instead of b, the equivalent is to convert the unknown part of b into the total disturbance of the system. In NLSEF, typically 0<a 3 <1<a 4 ，δ>0, generally 3 is between 5h and 10 h. Therefore, parameters actually required to be set are: beta 01 、β 02 、β 03 、β 1 、β 2 。
The optimization objective function is defined as follows:
wherein: p (P) * 、P、Q * Q is the reference value and the actual value of the active power and the reactive power of the wind farm; u (U) dc * 、U dc The reference value and the actual value of the voltage of the direct current bus of the fan are obtained.
The optimization flow is as shown in fig. 19:
in the simulation model, the parameter settings of Optimum Run are shown in Table 2.
TABLE 2 parameter settings for Optimum Run
And adding the designed additional subsynchronous damping controller into the simulation model, and adopting the optimized parameters to simulate, so as to respectively verify the wind speed change and the oscillation suppression effect of the controller under the condition of system failure.
(1) Wind speed variation simulation verification
And comparing simulation results of whether the additional damping controller exists or not under the condition of different wind speeds.
And under the three conditions of the wind speed of 9m/s, 10m/s and 11m/s, the waveform diagram of the active power output by the fan and the corresponding Fourier analysis result are shown in figure 20.
As can be seen from fig. 20, the system can quickly reach a stable transmission power state after adding an additional subsynchronous damping controller, and the subsynchronous frequency oscillation component in the active power waveform is obviously reduced. Comparing the simulation results of fig. 20 (c) with those of fig. 20 (a) and 20 (b), it can be found that the waveform of the additional subsynchronous damping control fluctuates by a certain magnitude with increasing wind speed, but still achieves a satisfactory oscillation suppression effect. Therefore, the additional damping controller designed in the section has a good improvement effect on the condition that the original system transmits active power to oscillate with large amplitude and constant amplitude under the condition of different wind speeds, can well inhibit subsynchronous oscillation of the system, and verifies that the additional damping control strategy has certain robustness.
(2) Fault simulation verification
And setting a three-phase short-circuit grounding fault at the grid-connected PCC point of the system, wherein the fault occurrence time t=1.0 s and the fault duration time is 0.05s. The waveform diagram of the active power output by the wind farm is shown in fig. 21. As can be seen from fig. 21, under the three-phase short-circuit ground fault, the additional subsynchronous damping controller still has good control performance, and the control strategy is verified to have the active disturbance rejection capability.
Claims (3)
1. The method for restraining the subsynchronous oscillation of the soft direct grid-connected system based on the active disturbance rejection control is characterized by comprising the following steps of:
step 1: based on the topological structure of the direct-drive fan and the flexible direct-current transmission system and the principle of a control system, a direct-drive wind power plant simulation model which considers multiple control links is built through a flexible direct-connected system;
step 2: researching the influence of external influence parameters such as wind speed and internal controllable parameters such as the change of controller parameters on the subsynchronous oscillation of the system, and obtaining key influence links of the subsynchronous oscillation of the system;
step 3: determining the position of the controller and the selection of input and output signals based on the analysis conclusion of the key influence links of the system subsynchronous oscillation in the step 2; an additional subsynchronous damping controller of a direct-driven wind power plant through a soft direct grid-connected system is designed based on an active disturbance rejection control theory;
step 4: and optimizing and setting parameters of the additional subsynchronous damping controller by adopting a genetic algorithm, and adding the obtained additional subsynchronous damping controller into a direct-drive wind power plant through a soft direct-connected system so as to realize system subsynchronous oscillation suppression.
2. The method for suppressing the subsynchronous oscillation of the soft direct grid-connected system based on the active disturbance rejection control according to claim 1 is characterized in that step 3 takes the rotating speed of a fan rotor as an input signal of an additional subsynchronous damping controller on the basis of analysis of a key influence link in step 2, the output signal of the controller is added into the inner and outer ring control of a key link direct-driven fan grid-side converter which influences the subsynchronous oscillation of the system, and an additional subsynchronous damping controller structure is designed based on an active disturbance rejection control theory.
3. The method for suppressing subsynchronous oscillation of a soft-direct-grid-connected system based on active-disturbance-rejection control according to claim 1,
(1) The direct-drive wind power plant adopts classical vector control through a direct-drive fan side converter MSC and a network side converter GSC in a soft direct-grid system simulation model, and an MMC converter station level control strategy adopts an island control strategy or a non-island control strategy; the direct-drive fan side converter MSC adopts vector control of rotor magnetic field orientation to control electromagnetic torque of the generator, so that the generator can operate at variable speed along with the change of wind speed, thereby capturing maximum wind energy and transmitting generator power to the direct-current side of the converter; the grid-side converter GSC adopts grid voltage directional vector control to control direct current bus capacitor voltage and grid-connected reactive power;
(2) Changing parameters of an inner ring controller of a wind speed, a direct-driven fan side converter and a net side converter in a built simulation model, and obtaining key influence links of system subsynchronous oscillation by comparing amplitude changes and oscillation frequency changes of the system subsynchronous oscillation under parameter changes;
(3) According to the analysis conclusion of the key influence link of the subsynchronous oscillation, the rotating speed of the fan rotor is set as an output signal of the controller, and the output signal is added into the internal and external ring control of the GSC of the fan;
(4) The direct-driven wind power plant designed based on the active disturbance rejection control theory comprises a tracking differentiator, an extended state observer, a nonlinear error feedback and control quantity generation link and a soft direct grid-connected system additional subsynchronous damping controller; the tracking differentiator TD realizes fast tracking of an input signal and synchronous output of a differentiated signal, and the mathematical expression is as follows:
wherein v is 1 Can track the control input v, v quickly without overshoot 2 Is the approximate derivative of v; h is a sampling period; r is (r) 0 Is a tracking speed factor; h is a 0 Is a filtering factor; fhan is the fastest synthesis function;
the extended state observer ESO can estimate the real-time action value of the internal and external disturbance of the system, and expand the total disturbance into a new state variable of the system; the extended state observer ESO compensates the tracking signal through feedback, and eliminates the influence of the total disturbance in the system by using the compensation quantity; the mathematical expression of the nonlinear extended state observer ESO is:
wherein the expression of the nonlinear function fal (x, a, δ) is:
wherein: delta >0; sign (x) is a sign function;
nonlinear error feedback NLSEF obtains error signal e according to tracking signal outputted by TD and signal obtained by ESO observation 1 ＝v 1 －z 1 Error differential signal e 2 ＝v 2 －z 2 Compensating for the disturbance by nonlinear combination to control the corresponding object; the nonlinear combination is generally of two types (4) and (5):
u 0 ＝β 1 fal(e 1 ,a 3 ,δ)+β 2 fal(e 2 ,a 4 ,δ) (4)
u 0 ＝fhan(e 1 ,ce 2 ,r,h 1 ) (5)
the mathematical expression of the control amount is:
formula (6) comprises two moieties: -z 3 /b 0 To compensate for the disturbance, u 0 /b 0 To control an integral series section with nonlinear feedback, where b 0 Is a compensation factor;
(5) Parameter beta of additional subsynchronous damping controller by adopting genetic algorithm GA 01 、β 02 、β 03 、β 1 、β 2 Optimizing and setting; the fitness function is shown as a formula (1);
wherein: p (P) * 、P、Q * Q is the reference value and the actual value of the active power and the reactive power of the wind farm; u (U) dc * 、U dc The reference value and the actual value of the voltage of the direct current bus of the fan are obtained.
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