CN112821825A - Reactive power control method for improving high voltage ride through capability of double-fed wind power plant - Google Patents

Reactive power control method for improving high voltage ride through capability of double-fed wind power plant Download PDF

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CN112821825A
CN112821825A CN202011628033.2A CN202011628033A CN112821825A CN 112821825 A CN112821825 A CN 112821825A CN 202011628033 A CN202011628033 A CN 202011628033A CN 112821825 A CN112821825 A CN 112821825A
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flux linkage
rotor
stator
doubly
voltage
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CN112821825B (en
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刘新宇
刘雪梅
王亚辉
樊要玲
李勇
顾波
张红涛
王继东
师永彪
刘延华
林政国
岳伟宝
吕灵灵
常瑞
徐燕
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North China University of Water Resources and Electric Power
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
    • 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
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
    • H02P9/007—Control circuits for doubly fed generators
    • 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]
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/70—Wind energy
    • Y02E10/76—Power conversion electric or electronic aspects
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/30—Reactive power compensation

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  • Power Engineering (AREA)
  • Control Of Eletrric Generators (AREA)

Abstract

The invention discloses a reactive power control method for improving the high voltage ride through capability of a doubly-fed wind power plant, which comprises the following steps: the method comprises the following steps: writing a mathematical model of the induction generator under a dq coordinate system of the doubly-fed wind generator; step two: finding out a relational expression between an external voltage applied to a rotor by a frequency converter when a power grid operates and a rotor flux linkage and a relational expression between the rotor flux linkage and active power and reactive power according to a mathematical model of the doubly-fed induction generator under a dq coordinate system; step three: establishing a rotor flux linkage control model of the doubly-fed induction generator according to a relational expression of the rotor flux linkage, an external control voltage and active power and reactive power output by the doubly-fed induction generator; step four: on the basis of a rotor flux linkage control model of the doubly-fed induction generator, the self-adaptive control rate of the rotor flux linkage sliding mode variable structure of the doubly-fed wind driven generator is established based on the sliding mode variable structure control principle, and the optimal control of the output active power and the output reactive power of the doubly-fed wind driven generator in the wind power plant is realized.

Description

Reactive power control method for improving high voltage ride through capability of double-fed wind power plant
Technical Field
The invention belongs to the field of intelligent power grids, can be applied to the fields of new energy power generation, new energy grid connection and the like, and particularly relates to a reactive power control method for improving the high voltage ride through capability of a double-fed wind power plant.
Background
Most of large wind power plants in China are located in remote areas, are far away from a load center of a power system, and have typical weak grid characteristics. The high-proportion wind power plant is switched into the weak grid-connected operation, so that the contradiction between the wind power grid-connection and the safe and stable operation of the power system is more and more prominent. Therefore, strict wind power grid-connection related specifications are developed in the major wind power countries such as the United states and China in succession, and the wind power plants are required to have low voltage ride through capability and also to absorb certain dynamic reactive power rapidly so as to enhance the high voltage ride through capability during the period of grid fault and voltage fluctuation.
Disclosure of Invention
In order to solve the problems, a reactive power control method for improving the high voltage ride through capability of the doubly-fed wind power plant is provided.
The object of the invention is achieved in the following way:
a reactive power control method for improving the high voltage ride through capability of a doubly-fed wind power plant is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: writing a mathematical model of the induction generator under a dq coordinate system of the doubly-fed wind generator;
step two: finding out a relational expression between an external voltage applied to a rotor by a frequency converter when a power grid operates and a rotor flux linkage and a relational expression between the rotor flux linkage and active power and reactive power according to a mathematical model of the doubly-fed induction generator under a dq coordinate system;
step three: establishing a rotor flux linkage control model of the doubly-fed induction generator according to a relational expression of the rotor flux linkage, an external control voltage and active power and reactive power output by the doubly-fed induction generator;
step four: on the basis of a rotor flux linkage control model of the doubly-fed induction generator, the self-adaptive control rate of the rotor flux linkage sliding mode variable structure of the doubly-fed wind driven generator is established based on the sliding mode variable structure control principle, and the optimal control of the output active power and the output reactive power of the doubly-fed wind driven generator in the wind power plant is realized.
The mathematical model of the induction generator under the dq coordinate system of the doubly-fed wind generator is as follows:
stator and rotor voltage equations:
Figure BDA0002877915040000021
stator and rotor flux linkage equations:
Figure BDA0002877915040000022
power output of stator terminal:
Figure BDA0002877915040000023
in the formula, Ls、LrAnd LmThe self inductance and mutual inductance of the stator and the rotor are respectively; rs、RrRespectively a stator resistor and a rotor resistor; omega1And ω2Synchronous speed and slip, respectively; u. ofdsStator voltage d-axis component uqsStator voltage q-axis component, udrRepresenting the d-axis component, u, of the rotor voltageqrRepresenting a rotor voltage q-axis component; i.e. idsRepresenting the d-axis component, i, of the stator currentqsRepresenting stator current q-axis component, idrRepresenting the d-axis component, i, of the rotor currentqrRepresenting a rotor current q-axis component;
Figure BDA0002877915040000024
d-axis component of stator flux linkage,
Figure BDA0002877915040000025
Stator flux q-axis component
Figure BDA0002877915040000026
D-axis component of rotor flux linkage,
Figure BDA0002877915040000027
A rotor flux linkage q-axis component; psRepresenting active power, Q, of the statorsAnd the sub-expression represents the stator reactive power.
When the power grid voltage operates symmetrically, the stator is linked with the magnetic flux
Figure BDA0002877915040000028
Oriented on the d-axis of the synchronously rotating d-and q-coordinate systems, the flux linkages on the d-and q-axes are respectively:
Figure BDA0002877915040000029
the induced electromotive force of the DFIG is approximately equal to the stator voltage, i.e. uds＝0，uqs＝us；usIs the amplitude of the vector of the stator voltage, u after the stator is incorporated into the ideal gridsThe amplitude is equal to the amplitude of the grid voltage; the resistance of the stator winding is far less than the reactance of the stator winding, and the stator flux linkage and the current equation are obtained at the moment:
Figure BDA00028779150400000210
Figure BDA00028779150400000211
when a high-voltage fault occurs to a power grid, the DFIG is in an unstable operation state, the stator voltage and the stator flux linkage of the DFIG are not constant, so that the change of the flux linkage cannot be ignored during the analysis of transient operation of the DFIG, the flux linkage change cannot be mutated, and the stator flux linkage change enables the stator exciting current to change along with the change of the stator flux linkage; in this case, in formula (4)
Figure BDA0002877915040000031
Substituting equation (5) for the rotor flux linkage equation of equation (2) and the rotor voltage equation of equation (1) to obtain:
Figure BDA0002877915040000032
the formula (5) is substituted into the rotor flux linkage equations of the formula (3) and the formula (2) to obtain an active power equation and a reactive power equation:
Figure BDA0002877915040000033
during voltage sudden rise caused by grid failure, according to the equations (6) and (7), the reactive power generated by the doubly-fed wind farm depends on the q-axis component of the rotor flux linkage, and the q-axis component of the rotor flux linkage is controlled by the q-axis excitation voltage with the time constant of
Figure BDA00028779150400000311
Figure BDA00028779150400000312
The derivative of the d-axis component of the rotor flux linkage is represented,
Figure BDA00028779150400000313
the derivative of the q-axis component of the rotor flux linkage is represented.
The third step specifically comprises: writing the applied voltage and flux linkage of the DFIG rotor into the following state space equation form
Figure BDA00028779150400000314
In the formula (I), the compound is shown in the specification,
Figure BDA0002877915040000035
in order to be a state variable, the state variable,
Figure BDA0002877915040000036
for control input, F represents a disturbance caused by a grid fault and has
Figure BDA0002877915040000037
Figure BDA0002877915040000038
Where F represents the disturbance caused by the grid fault,
Figure BDA0002877915040000039
in order to be a state variable, the state variable,
Figure BDA00028779150400000310
for control input, Z11Representing d-axis flux linkage psi of rotordr，Z21Representing rotor q-axis flux linkage psiqr；Z10Representing rotor d-axis flux linkage control signal udr，Z20Representing rotor q-axis flux linkage control signal uqr；f1A component one representing a disturbance caused by a grid fault; f. of2A second component representing a disturbance caused by a grid fault;
rank[B F]＝rank[B]＝2 (9)
according to the formula (9), the sliding mode of the double-fed wind power generation system meets the requirement of no external interference;
order to
Figure BDA0002877915040000041
The q-axis flux linkage error state equation for DFIG is shown below:
Figure BDA0002877915040000042
in the formula (I), the compound is shown in the specification,
Figure BDA0002877915040000043
representing a generalized disturbance of the power system.
The fourth step specifically comprises: integrating sliding mode surfaces:
Figure BDA0002877915040000044
in the formula kpd、kidAre respectively proportional, integral coefficient, and kpd、kidAre all larger than zero; the proportional term is used for accelerating the dynamic tracking response of the system, and the integral term is used for eliminating the steady-state error of the system; therefore, k is changed on the PI integral sliding mode hypersurfacepd、kidThe value of (a) can change the dynamic characteristics of the sliding mode surface; e.g. of the typedRepresenting d-axis flux linkage error;
Figure BDA0002877915040000045
represents the p/q power of the d-axis flux linkage error;
if the generalized perturbation term | Fd|<kd，kdIs constant and greater than zero, resulting in a double feed as followsThe reactive power control law of the wind driven generator is
Figure BDA0002877915040000046
The q-axis flux linkage error e of the DFIG can be converged to zero within a limited time, and the system is robust and stable;
wherein, the gain is switched eta'qThe expression is as follows:
Figure BDA0002877915040000047
in the formula etaqIndicating the switching gain, Q, of the system during normal operation0Representing a given value of reactive power, Q representing the actual reactive power, lambdaqIs a set constant and 0 < lambdaq＜1；
Figure BDA0002877915040000048
A given value representing a rotor q-axis flux linkage; k is a radical ofiqRepresents a scaling factor;
Figure BDA0002877915040000049
represents the p/q power of the q-axis flux linkage error; eta 'of'qRepresents the fast switching gain; sqA q-axis mode surface representing a rotor flux linkage;
when the system has instantaneous high voltage, the control gain is switched to
Figure BDA0002877915040000051
The double-fed wind power plant can quickly absorb redundant reactive power by rapid increase, so that the system voltage can be quickly recovered to a given value; when the system works normally, the switching control gain is recovered to the conventional set value etaq。
Compared with the prior art, the method for improving the voltage ride through control is superior to the traditional PI control method, and the optimization control of the grid-connected high voltage ride through capability of the double-fed wind power plant is realized.
Drawings
FIG. 1 is a diagram of the relationship between the applied voltage and the flux linkage of a DFIG rotor.
Fig. 2 is a system control flow chart.
Fig. 3 is a conventional PI control common bus voltage response curve.
FIG. 4 is a common bus voltage response curve for an improved control strategy.
Fig. 5 is a conventional PI control rotor current response curve.
FIG. 6 is a robust sliding-mode controlled rotor current response curve that accounts for wake effects.
Fig. 7 is a conventional PI control reactive power response curve.
FIG. 8 is a joint additive control reactive power response curve that accounts for wake effects.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same technical 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 example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise, and it should be further understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of the stated features, steps, operations, devices, components, and/or combinations thereof.
In the present invention, terms such as "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "side", "bottom", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only terms of relationships determined for convenience of describing structural relationships of the parts or elements of the present invention, and are not intended to refer to any parts or elements of the present invention, and are not to be construed as limiting the present invention.
In the present invention, terms such as "fixedly connected", "connected", and the like are to be understood in a broad sense, and mean either a fixed connection or an integrally connected or detachable connection; may be directly connected or indirectly connected through an intermediate. The specific meanings of the above terms in the present invention can be determined according to specific situations by persons skilled in the relevant scientific or technical field, and are not to be construed as limiting the present invention.
A reactive power control method for improving the high voltage ride through capability of a doubly-fed wind power plant comprises the following steps:
the method comprises the following steps: writing a mathematical model of the induction generator under a dq coordinate system of the doubly-fed wind generator;
step two: finding out a relational expression between an external voltage applied to a rotor by a frequency converter when a power grid operates and a rotor flux linkage and a relational expression between the rotor flux linkage and active power and reactive power according to a mathematical model of the doubly-fed induction generator under a dq coordinate system;
step three: establishing a rotor flux linkage control model of the doubly-fed induction generator according to a relational expression of the rotor flux linkage, an external control voltage and active power and reactive power output by the doubly-fed induction generator;
step four: on the basis of a rotor flux linkage control model of the doubly-fed induction generator, the self-adaptive control rate of the rotor flux linkage sliding mode variable structure of the doubly-fed wind driven generator is established based on the sliding mode variable structure control principle, and the optimal control of the output active power and the output reactive power of the doubly-fed wind driven generator in the wind power plant is realized.
Equivalent mathematical model of DFIG in accordance with motor convention under synchronous rotation d, q coordinate system:
stator and rotor voltage equations:
Figure BDA0002877915040000061
stator and rotor flux linkage equations:
Figure BDA0002877915040000062
power output of stator terminal:
Figure BDA0002877915040000063
in the formula, Ls、LrAnd LmThe self inductance and mutual inductance of the stator and the rotor are respectively; rs、RrRespectively a stator resistor and a rotor resistor; omega1And ω2Synchronous speed and slip, respectively; u. ofds、uqsudr、uqrStator and rotor excitation voltages respectively; i.e. ids、iqs、idr、iqrStator and rotor exciting currents respectively;
Figure BDA0002877915040000071
respectively carrying out stator and rotor excitation; ps、QsThe active power and the reactive power of the stator are respectively.
When the power grid voltage operates symmetrically, the stator is linked with the magnetic flux
Figure BDA0002877915040000072
Oriented on the d-axis of the synchronously rotating d-and q-coordinate systems, the flux linkages on the d-and q-axes are respectively:
Figure BDA0002877915040000073
the induced electromotive force of the DFIG is approximately equal to the stator voltage, i.e. uds＝0，uqs＝us(ii) a Is the amplitude of the vector of the stator voltage, u after the stator is incorporated into the ideal gridsAnd the amplitude is equal to the amplitude of the power grid voltage. The resistance of the stator winding is much smaller than the reactance of the stator winding, and the influence of the stator resistance can be ignored. The stator flux linkage and current equations are now obtained:
Figure BDA0002877915040000074
Figure BDA0002877915040000075
when a high-voltage fault occurs to a power grid, the DFIG is in an unstable operation state, the stator voltage and the stator flux linkage of the DFIG are not constant, therefore, the change of the flux linkage cannot be ignored during the analysis of transient operation of the DFIG, the flux linkage change cannot be mutated, and the stator excitation current is changed along with the stator flux linkage change. In this case, in formula (4)
Figure BDA0002877915040000076
In consideration of the above, equation (5) is substituted for the rotor flux linkage equation of equation (2) and the rotor voltage equation of equation (1) to obtain:
Figure BDA0002877915040000077
in order to highlight the main problems of research, the equation (5) is substituted into the rotor flux linkage equations (3) and (2) to obtain an active power equation and a reactive power equation:
Figure BDA0002877915040000078
during voltage sudden rise caused by grid failure, according to the equations (6) and (7), the reactive power generated by the doubly-fed wind farm depends on the q-axis component of the rotor flux linkage, and the q-axis component of the rotor flux linkage is controlled by the q-axis excitation voltage with the time constant of
Figure BDA0002877915040000079
The time is generally 8-15 ms; therefore, the speed of reactive power regulation of the doubly-fed wind power plant belongs to millisecond-level rapid control and is almost equal to the reactive power compensation speed of the static reactive power compensator.
According to the equation (6), the structure diagram of the relationship between the applied voltage of the inverter to the rotor and the rotor flux linkage in the power generation operation is shown in fig. 1.
For this purpose, equation (6) is written in the form of the following state space equation
Figure BDA00028779150400000810
In the formula (I), the compound is shown in the specification,
Figure BDA0002877915040000081
in order to be a state variable, the state variable,
Figure BDA0002877915040000082
for control input, F represents a disturbance caused by a grid fault and has
Figure BDA0002877915040000083
Figure BDA0002877915040000084
Where F represents the disturbance caused by the grid fault,
Figure BDA0002877915040000085
in order to be a state variable, the state variable,
Figure BDA0002877915040000086
for control input, Z11Representing d-axis flux linkage psi of rotordr，Z21Representing rotor q-axis flux linkage psiqr。Z10Representing rotor d-axis flux linkage control signal udr，Z20Representing rotor q-axis flux linkage control signal uqr。
Easy certificate
rank[B F]＝rank[B]＝2 (9)
According to the formula (9), the sliding mode of the double-fed wind power generation system meets the requirement of being free from external interference. Therefore, a proper sliding mode controller is designed, so that the doubly-fed wind power generator set has complete robustness to disturbance caused by grid faults, and the sliding mode of the doubly-fed wind power generator set is not influenced by the grid faults.
Based on the above analysis, the DFIG rotor q-axis flux linkage controller is first designed herein. Order to
Figure BDA0002877915040000087
The q-axis flux linkage error state equation for DFIG is shown below:
Figure BDA0002877915040000088
in the formula (I), the compound is shown in the specification,
Figure BDA0002877915040000089
representing a generalized disturbance of the power system.
In view of the above, the following integral slip form surfaces are proposed herein:
Figure BDA0002877915040000091
in the formula kpd、kidAre respectively proportional, integral coefficient, and kpd、kidAre all greater than zero. The proportional term is used for accelerating the dynamic tracking response of the system, and the integral term is used for eliminating the steady-state error of the system. Therefore, k is changed on the PI integral sliding mode hypersurfacepd、kidThe value of (a) may change the dynamic characteristics of the slip-form surfaces.
According to the integral terminal sliding mode surface provided by the invention, if the generalized disturbance term | Fd|<kd，kdIs constant and is larger than zero, and the following reactive power control law of the doubly-fed wind driven generator is obtained
Figure BDA0002877915040000092
The q-axis flux linkage error e of the DFIG can be converged to zero in a limited time, and the system is robust and stable.
Wherein, the gain is switched eta'qThe expression is as follows:
Figure BDA0002877915040000093
in the formula etaqIndicating the switching gain, Q, of the system during normal operation0Representing a given value of reactive power, Q representing the actual reactive power, lambdaqIs a set constant and 0 < lambdaq＜1。
When the system has instantaneous high voltage, the control gain is switched to
Figure BDA0002877915040000094
And the double-fed wind power plant can quickly absorb redundant reactive power by rapid increase, so that the system voltage can be quickly recovered to a given value. When the system works normally, the switching control gain is recovered to the conventional set value etaq。
The simulation results are shown in fig. 3-8.
Fig. 3 and 4 are dynamic response curves of the common bus voltage when the conventional PI control strategy and the joint additional control strategy are adopted, respectively. As can be seen from fig. 3, when the conventional PI control strategy is adopted, during a system fault, the burst increment of the common bus voltage is 0.47pu, the high voltage duration is 500ms, and after the fault disappears, the bus voltage returns to normal again. Fig. 4 shows that when a high-voltage fault is triggered by using the joint additional control strategy considering the wake effect, the sudden increment of the common bus voltage is 0.25pu, and the bus voltage returns to normal again after the fault disappears.
Fig. 5 and 6 are rotor excitation current dynamic response curves when a conventional PI control strategy and a joint additional control strategy considering wake effect are adopted, respectively. As can be seen, under the conventional control strategy, after a high-voltage fault is triggered, the DFIG rotor current hardly changes greatly. After the combined additional control strategy is adopted, the rotor current of the DFIG is rapidly increased to 1.5 times of the original rotor current during the fault occurrence period, so that the DFIG can rapidly generate reactive power, and sudden rise of the voltage of the common bus is effectively inhibited.
Fig. 7 and 8 are dynamic response curves of the reactive power of the DFIG when the conventional PI control strategy and the joint additional control strategy considering the wake effect are adopted, respectively. As can be seen from the figure, by adopting a conventional PI control strategy, the reactive power output by the double-fed fan is in violent oscillation during the fault period, and the reactive power tends to be stable after the fault is eliminated. And a combined additional control strategy is adopted, the double-fed fan can rapidly output reactive power reaching-2.41 pu during the fault period, and the high voltage is subjected to inhibition regulation.
The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.
Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.

Claims (5)

1. A reactive power control method for improving the high voltage ride through capability of a doubly-fed wind power plant is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: writing a mathematical model of the induction generator under a dq coordinate system of the doubly-fed wind generator;
step two: finding out a relational expression between an external voltage applied to a rotor by a frequency converter when a power grid operates and a rotor flux linkage and a relational expression between the rotor flux linkage and active power and reactive power according to a mathematical model of the doubly-fed induction generator under a dq coordinate system;
step three: establishing a rotor flux linkage control model of the doubly-fed induction generator according to a relational expression of the rotor flux linkage, an external control voltage and active power and reactive power output by the doubly-fed induction generator;
step four: on the basis of a rotor flux linkage control model of the doubly-fed induction generator, the self-adaptive control rate of the rotor flux linkage sliding mode variable structure of the doubly-fed wind driven generator is established based on the sliding mode variable structure control principle, and the optimal control of the output active power and the output reactive power of the doubly-fed wind driven generator in the wind power plant is realized.
2. The reactive power control method for improving the high voltage ride through capability of the doubly-fed wind farm according to claim 1, characterized by comprising the following steps: the mathematical model of the induction generator under the dq coordinate system of the doubly-fed wind generator is as follows:
stator and rotor voltage equations:
Figure FDA0002877915030000011
stator and rotor flux linkage equations:
Figure FDA0002877915030000012
power output of stator terminal:
Figure FDA0002877915030000013
in the formula, Ls、LrAnd LmThe self inductance and mutual inductance of the stator and the rotor are respectively; rs、RrRespectively a stator resistor and a rotor resistor; omega1And ω2Synchronous speed and slip, respectively; u. ofdsStator voltage d-axis component uqsStator voltage q-axis component, udrRepresenting the d-axis component, u, of the rotor voltageqrRepresenting a rotor voltage q-axis component; i.e. idsRepresenting the d-axis component, i, of the stator currentqsRepresenting stator current q-axis component, idrRepresenting the d-axis component, i, of the rotor currentqrRepresenting a rotor current q-axis component;
Figure FDA0002877915030000021
d-axis component of stator flux linkage,
Figure FDA0002877915030000022
Stator flux q-axis component
Figure FDA0002877915030000023
D-axis component of rotor flux linkage,
Figure FDA0002877915030000024
A rotor flux linkage q-axis component; psRepresenting active power, Q, of the statorsAnd the sub-expression represents the stator reactive power.
3. The reactive power control method for improving the high voltage ride through capability of the doubly-fed wind farm according to claim 1, characterized by comprising the following steps: when the power grid voltage operates symmetrically, the stator is linked with the magnetic flux
Figure FDA0002877915030000025
Oriented on the d-axis of the synchronously rotating d-and q-coordinate systems, the flux linkages on the d-and q-axes are respectively:
Figure FDA0002877915030000026
the induced electromotive force of the DFIG is approximately equal to the stator voltage, i.e. uds＝0，uqs＝us；usIs the amplitude of the vector of the stator voltage, u after the stator is incorporated into the ideal gridsThe amplitude is equal to the amplitude of the grid voltage; the resistance of the stator winding is far less than the reactance of the stator winding, and the stator flux linkage and the current equation are obtained at the moment:
Figure FDA0002877915030000027
Figure FDA0002877915030000028
when a high-voltage fault occurs to a power grid, the DFIG is in an unstable operation state, the stator voltage and the stator flux linkage of the DFIG are not constant, so that the change of the flux linkage cannot be ignored during the analysis of transient operation of the DFIG, the flux linkage change cannot be mutated, and the stator flux linkage change enables the stator exciting current to change along with the change of the stator flux linkage; in this case, in formula (4)
Figure FDA0002877915030000029
Substituting equation (5) for the rotor flux linkage equation of equation (2) and the rotor voltage equation of equation (1) to obtain:
Figure FDA00028779150300000210
the formula (5) is substituted into the rotor flux linkage equations of the formula (3) and the formula (2) to obtain an active power equation and a reactive power equation:
Figure FDA00028779150300000211
during voltage sudden rise caused by grid failure, according to the equations (6) and (7), the reactive power generated by the doubly-fed wind farm depends on the q-axis component of the rotor flux linkage, and the q-axis component of the rotor flux linkage is controlled by the q-axis excitation voltage with the time constant of
Figure FDA00028779150300000212
Figure FDA00028779150300000213
The derivative of the d-axis component of the rotor flux linkage is represented,
Figure FDA00028779150300000214
the derivative of the q-axis component of the rotor flux linkage is represented.
4. The reactive power control method for improving the high voltage ride through capability of the doubly-fed wind farm according to claim 1, characterized by comprising the following steps: the third step specifically comprises: writing the applied voltage and flux linkage of the DFIG rotor into the following state space equation form
Figure FDA0002877915030000031
In the formula (I), the compound is shown in the specification,
Figure FDA0002877915030000032
in order to be a state variable, the state variable,
Figure FDA0002877915030000033
for control input, F represents a disturbance caused by a grid fault and has
Figure FDA0002877915030000034
Figure FDA0002877915030000035
Where F represents the disturbance caused by the grid fault,
Figure FDA0002877915030000036
in order to be a state variable, the state variable,
Figure FDA0002877915030000037
for control input, Z11Representing d-axis flux linkage psi of rotordr，Z21Representing rotor q-axis flux linkage psiqr；Z10Representing rotor d-axis flux linkage control signal udr，Z20Representing rotor q-axis flux linkage control signal uqr；f1A component one representing a disturbance caused by a grid fault; f. of2A second component representing a disturbance caused by a grid fault;
rank[B F]＝rank[B]＝2 (9)
according to the formula (9), the sliding mode of the double-fed wind power generation system meets the requirement of no external interference;
order to
Figure FDA0002877915030000038
The q-axis flux linkage error state equation for DFIG is shown below:
Figure FDA0002877915030000039
in the formula (I), the compound is shown in the specification,
Figure FDA00028779150300000310
representing a generalized disturbance of the power system.
5. The reactive power control method for improving the high voltage ride through capability of the doubly-fed wind farm according to claim 1, characterized by comprising the following steps: the fourth step specifically comprises: integrating sliding mode surfaces:
Figure FDA00028779150300000311
in the formula kpd、kidAre respectively proportional, integral coefficient, and kpd、kidAre all larger than zero; the proportional term is used for accelerating the dynamic tracking response of the system, and the integral term is used for eliminating the steady-state error of the system; therefore, k is changed on the PI integral sliding mode hypersurfacepd、kidThe value of (a) can change the dynamic characteristics of the sliding mode surface; e.g. of the typedRepresenting d-axis flux linkage error;
Figure FDA0002877915030000041
represents the p/q power of the d-axis flux linkage error;
if the generalized perturbation term | Fd|<kd，kdIs constant and is larger than zero, and the following reactive power control law of the doubly-fed wind driven generator is obtained
Figure FDA0002877915030000042
The q-axis flux linkage error e of the DFIG can be converged to zero within a limited time, and the system is robust and stable;
wherein, the gain is switched eta'qThe expression is as follows:
Figure FDA0002877915030000046
in the formula etaqIndicating the switching gain, Q, of the system during normal operation0Representing a given value of reactive power, Q representing the actual reactive power, lambdaqIs a set constant and 0 < lambdaq＜1；
Figure FDA0002877915030000043
A given value representing a rotor q-axis flux linkage; k is a radical ofiqRepresents a scaling factor;
Figure FDA0002877915030000044
represents the p/q power of the q-axis flux linkage error; eta 'of'qRepresents the fast switching gain; sqA q-axis mode surface representing a rotor flux linkage;
when the system has instantaneous high voltage, the control gain is switched to
Figure FDA0002877915030000045
The double-fed wind power plant can quickly absorb redundant reactive power by rapid increase, so that the system voltage can be quickly recovered to a given value; when the system works normally, the switching control gain is recovered to the conventional set value etaq。
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