CN112751346B - Design method of DFIG-PSS controller based on virtual impedance - Google Patents
Design method of DFIG-PSS controller based on virtual impedance Download PDFInfo
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Abstract
The invention provides a design method of a DFIG-PSS controller based on virtual impedance, which comprises the following steps: firstly, constructing a power grid system containing a double-fed induction motor model, combining a power system stabilizer and virtual impedance, connecting the power system stabilizer and the virtual impedance to a rotor side converter, and then obtaining the relation between the output voltage of the rotor side converter and the rotor current by adopting a stator flux linkage directional vector control technology; secondly, obtaining the relation between the stator current and the output power of the stator according to the relation among the stator voltage, the electronic flux linkage and the electronic current; then, obtaining a relation between a parameter of a power system stabilizer-virtual impedance and the output power of the stator according to the relation between the output voltage of the rotor side converter and the rotor current and the relation between the stator current and the output power of the stator; and finally, the output power of the stator is adjusted by changing the parameters of the power system stabilizer-virtual impedance, so that the damping characteristic of the power grid system is influenced. The invention can improve the low-frequency oscillation characteristic of the wind power system.
Description
Technical Field
The invention relates to the technical field of wind power systems, in particular to a design method of a DFIG-PSS controller based on virtual impedance.
Background
The large-scale wind turbine generator system is connected to the grid, new challenges are brought to stable operation of a power system, the wind turbine generator system such as a Doubly Fed Induction Generator (DFIG) affects the original oscillation mode of the system, a new oscillation mode may be introduced, and adverse effects are generated on the dynamic stability of the system, particularly the small-interference stability. Conventional synchronous generators employ Power System Stabilizers (PSS) to provide additional damping during system disturbances, improving the low frequency oscillation characteristics of the system. With the increase of wind power permeability, the power grid requires that the wind turbine generator can also provide damping for the power system, and research through an additional damping control strategy similar to a traditional synchronous generator becomes important.
In recent years, a great deal of research work has been carried out at home and abroad aiming at the problem of low-frequency oscillation caused by large-scale wind power integration, and abundant research results are obtained. Research shows that the influence of a large-capacity wind turbine generator set on an electric power system cannot be ignored, so that the research on the influence of the wind turbine generator set, particularly the doubly-fed wind turbine generator set widely applied at present, on the small interference stability of an interconnection system is particularly important. The document [ Jose Luis doming guez-Garc1, oriol Gomis-Bellmenta, fernando D.Bianchi, andrea Sumpera.Power oscillation supported by wind power, areview [ J ]. Renewable and Sustainable Energy Reviews,2012,16 (7): 4982-4993 ] explains the influence of wind power generation on small signal stability, and introduces a control method for a wind power generation unit to suppress internal and power system oscillation modes. The literature [ Liu Yong, joe R.Gracia, thomas J.King, liu Yilu. Frequency alignment and stabilization constraints of variable-speed wind generators in the U.S.eastern Interconnection (EI) [ J ]. IEEETransactions on stable Energy, 8978 xft 8978 (3): 951-957 ] proposes a fast active power control technique for variable speed wind turbines and discusses how to apply these controls to frequency regulation and oscillation damping in the eastern United states Interconnection system. The document [ Mohit Singh, alicia J.Allen, eduard Muljadi, vahanGevorgian, zhang Yingchen, surya Santoo. Interarea interaction control for wire power plants IEEE Transactions on Stationable Energy,2015,6 (3): 967-975 ] adds a control signal to the active power control loop to improve the glitch stability of the system by adjusting the DFIG active power output. The document [ Liao Kai, he Zhengyou, xu Yan, guo Chen, zhao Yang, kit Po Wong. Assembling mode Based damping control of DFIG for interactive Power regulation. IEEE Transactions on stabilizing Energy,2017,8 (1): 258-267.] proposes a sliding mode second order controller to modulate DFIG Reactive Power output, and document [ Fan linking, YInHaiping, miao Zhixin. On Active/Reactive Power Modulation of DFIG-Based creation for Interactive Oscillation damping. IEEE transaction Conversion,2011,26 (2): 513-521] indicates that Modulation of the axis of function may result in more optimal Reactive Power Modulation. The adoption of the PSS to suppress the low-frequency oscillation is a common means of the traditional power system, and the DFIG can also adopt an additional damping control strategy similar to a synchronous generator to improve the low-frequency oscillation characteristic of the interconnected power system, namely DFIG-PSS. Documents [ f.michael Hughes, olimpo Anaya-Lara, nicholas Jenkins, goran straba. Power system stability for DFIG-based wind generation. Ieee Transactions on Power Systems,2006,21 (2): 763-772 ] demonstrate that the addition of a properly designed Power system stabilizer to a doubly fed wind generator can significantly enhance the contribution of the wind farm to the grid damping and can be achieved without degrading the quality of the voltage control provided. The documents Bian Xiaoyan, geng Yan, yuan Fangqi, li Xuewu, fu Yang discussion of DFIG-PSS input signal selection in multiple modes of operation [ J ] Power systems and their Proc of Automation, 2016,28 (07): 47-50 ] analyzed the effects of DFIG-PSS position and input on its damped oscillation. Documents [ Li Shenghu, sun Qi, dan Xuemei, huang Jiejie ] wind power system weak damping low frequency oscillation mode suppression [ J ] power system protection and control based on regional pole configuration 2017,45 (20): 14-20 ] apply regional pole configuration method to design DFIG-PSS. The literature [ BianXiaoyan, ding Yang, jia Qingyu, shi Lei, zhang Xiaooping, L.LO Kwok.Mitigation of sub-synchronous control interaction of a power system with DFIG-based with a farm surface multi-operating points [ J ]. IET Generation, transmission & Distribution,2018,12 (21): 5834-5842 ] controls interaction probability sensitivity based on sub-synchronizations, selects DFIG-PSS positions and inputs, and optimizes control parameters. Documents [ Li Shenghu, zhang Hao ] sensitivity analysis of a wind power system oscillation mode on a DFIG-PSS transfer function [ J ] power system protection and control, 2020,48 (16): 11-17 ] state equations containing the DFIG-PSS system are established, characteristic value increment is introduced into transfer function increment iterative operation, and parameter sensitivity, transfer function sensitivity error and control effect of the correspondingly designed DFIG-PSS are compared through simulation.
When wind power is connected to the grid, the output voltage of the system has certain requirements on the output impedance characteristic, and the equivalent output impedance can present the expected characteristic of the system by adopting a corresponding Virtual Impedance (VI) control strategy. Documents [ Zhou Peng, zhang Xinyan, mansion, yujiahui, xing Chen ] a virtual synchronous machine control-based double-fed wind turbine generator pre-synchronization grid-connection strategy [ J ] power system automation, 2020,44 (14): 71-84 ] propose a virtual synchronous machine (VSG) controlled double-fed wind turbine generator non-phase-locked loop pre-synchronization control strategy, and propose to introduce virtual impedance in a reactive control loop, so as to replace a reference input quantity with virtual current, thereby realizing quick and effective smooth grid-connection of the double-fed wind turbine generator. The influence mechanism of a virtual synchronous machine on small interference stability based on damping torque analysis is researched by a mechanism of influence of the virtual synchronous machine on the small interference stability in Juzuntao, ma Yarong, ji Zhinan [ J/OL ]. China Motor engineering newspaper, 1-10[2020-11-30] on the small interference stability, and the fact that the small interference stability of a system is facilitated by properly increasing the inductance of a virtual impedance link is found. The document [ Li Hui, wang Kun, hu Yu, wang Xiao, xia Guisen impedance modeling and stability analysis of virtual synchronous control of a double-fed wind power system [ J ]. China Motor engineering newspaper, 2019,39 (12): 3434-3443 ] provides a virtual synchronous control strategy under a d-q rotating coordinate system based on the virtual synchronous control strategy of the double-fed wind power system.
The traditional PSS adopts open loop control, and is easy to generate some oscillation signals which have adverse effects on a system. When the grid-connected inverter operates with a nonlinear load, the output current of the system contains harmonic waves, the output impedance presents non-resistance characteristics, and the output impedance characteristics can be adjusted by adopting virtual impedance self-correction.
Disclosure of Invention
Aiming at the defects in the background art, the invention provides a design method of a DFIG-PSS controller based on virtual impedance, which solves the technical problem of low-frequency oscillation of the existing wind power-containing power system.
The technical scheme of the invention is realized as follows:
a design method of a DFIG-PSS controller based on virtual impedance comprises the following steps:
the method comprises the following steps: constructing a power grid system containing a double-fed induction motor model, wherein the double-fed induction motor model comprises a rotor-side converter and a wind generating set, and the rotor-side converter controls the wind generating set through a stator and a rotor;
step two: combining a power system stabilizer and virtual impedance and then connecting the power system stabilizer and the virtual impedance to a rotor side converter, and obtaining the relation between the output voltage of the rotor side converter and the rotor current by adopting a stator flux linkage directional vector control technology;
step three: obtaining the relation between the stator current and the output power of the stator according to the relation among the stator voltage, the stator flux linkage and the stator current;
step four: obtaining the relation between the parameter of the power system stabilizer-virtual impedance and the output power of the stator according to the relation between the output voltage of the rotor side converter and the rotor current and the relation between the stator current and the output power of the stator;
step five: the output power of the stator is adjusted by changing the parameters of the power system stabilizer-virtual impedance, so that the damping characteristic of the power grid system is influenced.
The relation between the output voltage of the rotor side converter and the rotor current is as follows:
wherein, K p1 、K i1 、K p3 、K i3 、K q1 、K i2 Are all parameters of a rotor-side converter control proportional-integral controller, V rd Representing d-axis rotor voltage, P s * Representing the rotor active power reference value, P s Representing a measured value of active power of the rotor, i rd Representing d-axis rotor current, V rq The q-axis rotor voltage is represented,
representing the reference value of reactive power, Q, of the rotor s Representing measured values of rotor reactive power, i rq Representing the q-axis rotor current, s representing the differential operator, u errs Power system stabilizer-input signal of virtual impedance after automatic voltage regulator device.
The input signal of the power system stabilizer-virtual impedance after passing through the automatic voltage regulator device is as follows:
in the formula, T e 、K f1 、T c 、T b 、T f1 、K a 、T a 、T r K is a control parameter of the automatic voltage regulator, and delta P represents a reference value P of active power of the rotor s * With measured value P of active power of rotor s U represents the stator voltage of the doubly-fed induction motor model, G 1 (s) represents the transfer function of the power system stabilizer-virtual impedance.
The relationship between the stator current and the output power of the stator is as follows:
in the formula: l is m Is the mutual inductance of the coaxial equivalent windings of the stator and the rotor of a d-q coordinate system, L s Is the stator equivalent two-phase winding self-inductance in a d-q coordinate system, omega s For synchronizing the angular velocities of rotation of the magnetic field, P s ' is the active output power of the stator, Q s ' is the reactive output power of the stator, i ds Representing d-axis stator current, i qs Representing the q-axis stator current, u ds Representing d-axis stator voltage, U s Representing the stator voltage.
The stator current is:
the relation between the parameters of the power system stabilizer-virtual impedance and the output power of the stator is as follows:
compared with the prior art, the invention has the following beneficial effects:
1) The invention adds a virtual impedance link on the basis of the traditional PSS, adopts a closed-loop negative feedback control mode to enhance the anti-interference capability of the controller to the outside, and verifies the improvement effect of the virtual impedance link on the controller by carrying out step response test on the controller.
2) The DFIG-PSS-VI model is built in DIgSILENT/PowerFactory simulation software, the built controller is added into a reactive power control loop of a DFIG rotor side controller by taking a 4-machine 2-area system as an example, and the improvement effect of the designed controller on the low-frequency oscillation characteristic of the system is verified through time domain simulation.
3) The overshoot of the controller based on the virtual impedance is lower than that of the traditional controller, the controller has good step response characteristic, and the improvement effect on the system stability is more obvious.
4) The DFIG rotor side reactive power control loop is additionally provided with a virtual impedance PSS, so that the low-frequency oscillation characteristic of a wind power-containing power system can be improved, and a certain effect is achieved when the power of a tie line changes.
5) The DFIG-PSS-VI gain and the virtual impedance inductance have certain influence on the system damping, the improvement effect on the vibration in the area is limited, and a new idea is provided for inhibiting the low-frequency vibration between the areas of the interconnected system containing the wind power area.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the prior art descriptions will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 is a virtual impedance vector diagram.
FIG. 2 is a PSS-VI step response curve.
FIG. 3 is a PSS-VI unit step response curve.
FIG. 4 is a structural diagram of the DFIG-PSS-VI control of the present invention.
FIG. 5 is a block diagram of a 4-machine 2-zone system including a DFIG according to the present invention.
FIG. 6 shows the PSS-VI gain K of the present invention 1 And (3) distributing the influence on inter-area oscillation mode characteristic roots of the 4-machine 2 area system containing the DFIG.
FIG. 7 shows the PSS-VI parameter K of the present invention L And (3) distributing the influence on inter-area oscillation mode characteristic roots of the 4-machine 2 area system containing the DFIG.
FIG. 8 is a load fluctuation response curve of a DFIG-containing 4-machine 2-zone system with PSS-VI added, wherein (a) is a generator G 1 The power angle response curve (b) is the generator G 1 A voltage response curve.
FIG. 9 is a three-phase short-circuit response curve of a DFIG-containing 4-machine 2-region system with PSS-VI, wherein (a) is a generator G 1 The power angle response curve (b) is the generator G 1 Voltage response curves.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
The virtual impedance is a control method for simulating the impedance action of an actual line by introducing a feedback loop in a control link, the realization method of the virtual impedance is flexible, and the virtual impedance can be introduced for compensation when the output impedance of a controller or the impedance of the line is small. By choosing a reasonable virtual impedance Z vi Output impedance Z with PSS oi Forming a new output impedance Z i Further, the system impedance property is changed to achieve the purpose of improving the system stability.
According to the open-loop system stability criterion, if the system stability is improved, the damping of the system can be improved, and the overshoot of the system can be reduced, as can be seen from fig. 1, when Z is vi When changed, Z can be changed i The PSS-VI output impedance is adjusted by changing the virtual impedance, so that good unit step response of the controller is ensured. And the closed loop feedback link is adopted, so that the controller can be ensured to have higher precision, the anti-interference capability of the controller is enhanced, and the small interference stability of the system is ensured.
PSS-VI is shown in FIG. 2, and its transfer function is:
in the formula, K L ，K r A virtual impedance link parameter is obtained; k 1 Is the PSS-VI controller gain, G 1 (s) denotes the PSS-VI transfer function, T W Representing the time constant of the filtering element, T 1 、T 2 、T 3 、T 4 Representing the compensated link time constant.
FIG. 3 shows the unit step response of the PSS-VI, and it can be seen that although the PSS-VI adopts the control mode of closed-loop negative feedback, the common problems of overshoot and oscillation of the closed-loop system do not occur, and the PSS-VI has good step response characteristics, and changes the parameter K of the virtual impedance link L The unit step response of the controller can be adjusted.
The embodiment of the invention provides a design method of a DFIG-PSS controller based on virtual impedance, which comprises the following specific steps:
the method comprises the following steps: constructing a power grid system containing a double-fed induction motor model, wherein the double-fed induction motor model comprises a rotor side converter and a wind generating set, and the rotor side converter controls the wind generating set through a stator and a rotor; the doubly-fed generator adopts a vector control strategy to realize decoupling control of active power and reactive power, and considers maximum wind power and reactive compensation, as shown in fig. 4. The controller adopts a traditional nested ring structure, namely an external rotating speed/active power and reactive power control loop and an internal d-q rotor current control loop, can effectively estimate the rotor d-q reference current from an actual reference value and a reactive reference value, and saves a power ring controller with a nested control structure.
The damping effect of the doubly-fed generator with the basic power and voltage control loop on the electromechanical oscillation mode of the power grid is small, but the damping effect can be obviously enhanced by introducing additional damping control. The additional damping control signal is added to the DFIG active power control loop or the reactive power control loop via an Automatic Voltage Regulator (AVR).
The electromagnetic torque of the generator is more effectively changed through active regulation, but the active regulation deteriorates the dynamic characteristics of a DFIG shaft, reactive regulation possibly deteriorates the dynamic characteristics of stator voltage, the DFIG sometimes needs to sacrifice partial dynamic characteristics of the DFIG shaft to perform damping control, and the damping control and the dynamic performance of a system need to be considered simultaneously when the DFIG is actually realized.
Step two: the method comprises the steps of combining a power system stabilizer and a virtual impedance, connecting the power system stabilizer and the virtual impedance to a rotor side converter, and obtaining the turn-off of the output voltage and the rotor current of the rotor side converter by adopting a stator flux linkage directional vector control technologyIs a step of; the PSS-VI input signal selection has a great influence on the performance of the controller, the input signal can select the rotor speed, voltage, current or frequency, and the signal selection mode based on residual analysis is the most common signal selection mode. The active power reference value P of the DFIG is selectable when the output signal is applied to the quadrature component of the rotor voltage, i.e. the reactive power control loop s * With measured value of active power P s The difference Δ P of (a) as an input signal. The invention outputs a PSS-VI control signal U PSS-VI And adding the voltage into a reactive power control loop, and summing to obtain the quadrature component of the rotor voltage.
The DFIG rotor side converter adopts a stator flux linkage directional vector control technology, and the relationship between rotor current and RSC output voltage is as follows:
after the PSS-VI controller is added, the relation between the rotor current and the RSC output voltage can be obtained according to the formula (2):
wherein, K p1 、K i1 、K p3 、K i3 、K q1 、K i2 Are all parameters of a rotor side converter control PI (proportional integral) controller, V rd Representing d-axis rotor voltage, P s * Representing the rotor active power reference value, P s Representing a measured value of active power of the rotor, i rd Representing d-axis rotor current, V rq Representing the Q-axis rotor voltage, Q s * Representing the reference value of reactive power, Q, of the rotor s Representing measured values of rotor reactive power, i rq Representing the q-axis rotor current, s representing the differential operator, u errs Power system stabilizer-input signal of virtual impedance after automatic voltage regulator device.
u errs The input signal of the power system stabilizer after the virtual impedance passes through the AVR device.
In the formula, T e 、K f1 、T c 、T b 、T f1 、K a 、T a 、T r K are all AVR control parameters, U PSS-VI Representing the PSS-VI output signal and u representing the DFIG stator voltage.
Step three: obtaining the relation between the stator current and the output power of the stator according to the relation among the stator voltage, the stator flux linkage and the stator current;
synchronously rotating the d axis of the coordinate system and the stator voltage vector u under the stator voltage orientation s The directions are overlapped, the stator magnetic flux vector is consistent with the negative direction of the q axis after the stator resistance is ignored, and the stator voltage vector is lagged by 90 degrees. The stator current and power expressions obtained from the relationship of the voltage, flux linkage and current on the stator side are:
in the formula: l is m Is the mutual inductance of the coaxial equivalent windings of the stator and the rotor of a d-q coordinate system, L s Is the stator equivalent two-phase winding self-inductance in a d-q coordinate system, omega s For synchronizing the angular velocities of rotation of the magnetic field, P s ' is the active output power of the stator, Q s ' is the reactive output power of the stator, i ds Representing d-axis stator current, i qs Representing the q-axis stator current, u ds Representing d-axis stator voltage, U s Representing the stator voltage.
Step four: obtaining the relation between the parameter of the power system stabilizer-virtual impedance and the output power of the stator according to the relation between the output voltage of the rotor side converter and the rotor current and the relation between the stator current and the output power of the stator;
the relationship between the stator output power and the PSS-VI controller parameters can be obtained from equations (4) - (6) as follows:
step five: the output power of the stator is adjusted by changing the parameters of the power system stabilizer-virtual impedance, so that the damping characteristic of the power grid system is influenced. According to the formula (7), when the parameter PSS-VI is changed, the output reactive power of the DFIG can follow the change, and the damping characteristic of the system is further influenced.
Simulation experiment
In order to research the effectiveness of the method for improving the low-frequency oscillation characteristic of the wind power-containing power system, a DFIG-PSS-VI model is built on DigSilent/PowerFactory simulation software, and the DFIG-PSS-VI model is analyzed on a 4-machine 2 region interconnection system (the system for short) by adopting characteristic root analysis and time domain simulation. The reference capacity of the system is 100MVA, the frequency is 50Hz, and the transmission power of the tie line is 400MW. Zone 1 and zone 2 of the system communicate through a double-circuit link, G 1 、G 2 、G 3 、G 4 The system is characterized by comprising 4 thermal power generating units with rated capacities of 900MVA and 20kV, wherein a node 3 is a reference node, and the active output of each power generating unit is 700MW. The DFIG access point is a bus 10, and a system diagram of the system is shown in FIG. 5.
The simulation experiment firstly researches the influence of the controller gain, and adjusts the gain K of the PSS-VI controller on the premise of ensuring that other control parameters are not changed 1 From the formulas (7) and (4), it can be seen that K is 1 When the output reactive power of the DFIG is reduced, the DFIG correspondingly reduces, and fig. 6 shows the distribution situation of characteristic roots of the oscillation mode among the system areas, and as can be known from fig. 6, as the gain of the PSS-VI controller is reduced, the characteristic value of the oscillation mode among the system areas is in a left-shift trend, and the damping ratio is in an increasing trend.
PSS-VI controller gain K 1 =0.45, keeping other parameters unchanged, and changing the virtual impedance link parameter K L FIG. 7 shows the distribution of characteristic root of the oscillation mode between the system areas, and it can be seen from FIG. 7 that the virtual impedance link parameters of the controller follow the PSS-VIK L And the characteristic value of the inter-area oscillation mode characteristic root system of the system is in a left-moving trend, and the damping ratio is in an increasing trend.
According to the previous analysis, the PSS-VI parameters were taken: t is W ＝0.01，T 1 ＝0.2，T 2 ＝0.08，T 3 ＝0.06，T 4 ＝0.4，K 1 ＝0.45，K r ＝0.2，K L =0.5. Some characteristic values before and after the system is equipped with the PSS-VI controller are given in Table 1, and mode 1 and mode 4 are inter-region oscillation modes, and mode 2 and mode 3 are intra-region oscillation modes. It can be seen that the damping ratio of the inter-region oscillation mode 1 is significantly improved, and the robustness of the system is improved.
TABLE 1 System Oscillating mode after adding PSS-VI
Suppose system load L 1 Step 5% when active power is 1s, system load is recovered when active power is 1.5s, the transmission power of a tie line is 400MW, simulation time is 20s, and a generator G before and after a PSS-VI controller is added to a system when load fluctuation occurs is shown in FIG. 8 1 Relative power angle delta and bus 6 voltage variation.
Assuming that a three-phase short circuit occurs between the connecting lines 6 and 7 at t =1s, the fault is cleared at t =1.1s, and the simulation time is 20s, fig. 9 shows the frequency variation curve of the generator G1 with respect to the power angle δ and the bus 6.
As can be seen from FIGS. 8 and 9, when different types of disturbances occur in the system, the generator G is added with the PSS-VI controller 1 The relative power angle delta and the voltage oscillation amplitude of the bus 6 are reduced to different degrees, which shows that the PSS-VI controller has a certain inhibition effect on system oscillation and improves the damping characteristic of the wind power system.
The output of the generator or the change of the load power can change the transmission power of the tie line, and even change the power transmission direction of the tie line. To further validate the established model, consider changing the tie-line power by changing the contribution of the synchronous generator, and study its improvement effect at different tie-line powers.
TABLE 2 oscillation modes of the system at different junctor transmission powers
The tie line power is adjusted to 300MW, 450MW and 600MW respectively, the power is transmitted from the area 1 to the area 2, and the system characteristic values when different tie line transmission powers are given in table 2. As can be seen from Table 2, after the PSS-VI controller is added, the damping ratio variation of the oscillation mode 1 between the system areas is improved under the condition of different transmission powers of the tie lines.
Aiming at the problem of low-frequency oscillation in a wind power grid-connected system, the DFIG-PSS controller based on the virtual impedance is constructed, then step response analysis is carried out on the constructed controller, and the lifting effect of the virtual impedance link on the controller is verified. A designed DFIG-PSS-VI model is built in DIgSILENT/PowerFactory simulation software, a 4-machine 2-area system is taken as an example, the built controller is added into a reactive power control loop of a DFIG rotor side controller, and the improvement effect of the designed controller on the low-frequency oscillation characteristic of the system is verified through time domain simulation. The invention has the following advantages:
(1) The overshoot of the controller based on the virtual impedance is lower than that of the traditional controller, the controller has good step response characteristic, and the improvement effect on the system stability is more obvious.
(2) The low-frequency oscillation characteristic of a wind power-containing power system can be improved by additionally arranging the virtual impedance PSS-based reactive power control loop on the rotor side of the DFIG, and a certain effect is achieved when the power of a tie line changes.
(3) The DFIG-PSS-VI gain and the virtual impedance inductance have certain influence on the system damping, the improvement effect on the vibration in the area is limited, and a new idea is provided for inhibiting the low-frequency vibration between the areas of the interconnected system containing the wind power area.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (4)
1. A design method of a DFIG-PSS controller based on virtual impedance is characterized by comprising the following steps:
the method comprises the following steps: constructing a power grid system containing a double-fed induction motor model, wherein the double-fed induction motor model comprises a rotor side converter and a wind generating set, and the rotor side converter controls the wind generating set through a stator and a rotor;
step two: combining a power system stabilizer and virtual impedance and then connecting the power system stabilizer and the virtual impedance to a rotor side converter, and obtaining the relation between the output voltage of the rotor side converter and the rotor current by adopting a stator flux linkage directional vector control technology;
the relation between the output voltage of the rotor side converter and the rotor current is as follows:
wherein, K p1 、K i1 、K p3 、K i3 、K q1 、K i2 Are all parameters of a rotor-side converter control proportional-integral controller, V rd Representing d-axis rotor voltage, P s * Representing the rotor active power reference value, P s Representing a measured value of active power of the rotor, i rd Representing d-axis rotor current, V rq The q-axis rotor voltage is represented,
representing the reference value of reactive power, Q, of the rotor s Representing measured values of rotor reactive power, i rq Representing the q-axis rotor current, s representing the differential operator, u errs The power system stabilizer-the input signal of the virtual impedance after the automatic voltage regulator device;
the input signal of the power system stabilizer-virtual impedance after passing through the automatic voltage regulator device is as follows:
in the formula, T e 、K f1 、T c 、T b 、T f1 、K a 、T a 、T r K are control parameters of the automatic voltage regulator, and delta P represents a reference value P of active power of the rotor s * With measured value P of active power of rotor s U represents the stator voltage of the doubly-fed induction motor model, G 1 (s) a transfer function representing power system stabilizer-virtual impedance;
in the formula, K L ，K r A virtual impedance link parameter is obtained; k 1 For the PSS-VI controller gain, T W Representing the time constant of the filtering element, T 1 、T 2 、T 3 、T 4 Representing a time constant of a compensation link;
step three: obtaining the relation between the stator current and the output power of the stator according to the relation among the stator voltage, the stator flux linkage and the stator current;
step four: obtaining the relation between the parameter of the power system stabilizer-virtual impedance and the output power of the stator according to the relation between the output voltage of the rotor side converter and the rotor current and the relation between the stator current and the output power of the stator;
step five: the output power of the stator is adjusted by changing the parameters of the power system stabilizer-virtual impedance, so that the damping characteristic of the power grid system is influenced.
2. The method of designing a DFIG-PSS controller based on virtual impedance of claim 1, wherein the relation between the stator current and the output power of the stator is:
in the formula: l is m Is the mutual inductance of the coaxial equivalent windings of the stator and the rotor of a d-q coordinate system, L s Is the stator equivalent two-phase winding self-inductance in a d-q coordinate system, omega s For synchronizing the angular velocities of rotation of the magnetic field, P s ' is the active output power of the stator, Q s ' is the reactive output power of the stator, i ds Representing d-axis stator current, i qs Representing the q-axis stator current, u ds Representing d-axis stator voltage, U s Representing the stator voltage.
3. The method of claim 2, wherein the stator currents are:
4. the design method of the DFIG-PSS controller based on the virtual impedance as claimed in claim 2, wherein the relation between the parameters of the power system stabilizer-virtual impedance and the output power of the stator is as follows:
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| CN116167232B (en) * | 2023-03-03 | 2023-12-26 | 国网浙江省电力有限公司电力科学研究院 | DFIG sequence impedance model identification method and system |
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