CN111725837A - Low voltage ride through method and device for DFIG virtual synchronous machine, electronic equipment and medium - Google Patents

Low voltage ride through method and device for DFIG virtual synchronous machine, electronic equipment and medium Download PDF

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CN111725837A
CN111725837A CN202010564040.4A CN202010564040A CN111725837A CN 111725837 A CN111725837 A CN 111725837A CN 202010564040 A CN202010564040 A CN 202010564040A CN 111725837 A CN111725837 A CN 111725837A
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rotor
dfig
voltage
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phase
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CN111725837B (en
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孙丹
王仰铭
赵琛
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Zhejiang University ZJU
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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
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • 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

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Abstract

The invention discloses a DFIG virtual synchronous machine low voltage ride through control method, a DFIG virtual synchronous machine low voltage ride through control device, an electronic device and a medium. The method combines the DFIG virtual synchronous machine control method with the model prediction control to realize the direct control of the rotor current of the DFIG, and utilizes the multivariable control characteristic of the model prediction control cost function to realize the control of the transient flux linkage of the DFIG. The invention is suitable for the faults of symmetrical and asymmetrical drop of the power grid voltage. When the voltage of the power grid symmetrically drops, the invention can prevent the rotor from overcurrent, accelerate the attenuation of the transient magnetic linkage of the rotor and provide reactive power support by changing the power reference value. The invention can also prevent rotor overcurrent when the power grid voltage falls asymmetrically, and can keep the rotor current balanced and sinusoidal by eliminating transient and negative sequence components in the rotor current reference value. The control system is very simple to realize, does not need a phase-locked loop to monitor the frequency of the power grid voltage in real time, and does not need to add an additional control loop.

Description

Low voltage ride through method and device for DFIG virtual synchronous machine, electronic equipment and medium
Technical Field
The invention belongs to the technical field of motor control, and particularly relates to a DFIG virtual synchronous machine low voltage ride through control method, a DFIG virtual synchronous machine low voltage ride through control device, an electronic device and a medium based on model predictive control.
Background
With the rapid development of the renewable energy power generation field, the proportion of the renewable energy power generation system mainly based on wind power and photovoltaic in the power system is also increasing. In modern wind power generation systems, doubly-fed induction generators (DFIGs) are most applied, the technology is the most mature, and the DFIGs are the current mainstream models. The DFIG control system is configured as shown in fig. 1, and the variable speed constant frequency control of the DFIG can be realized by controlling the machine side converter and the grid side converter. The traditional synchronous generator has huge rotational inertia and has the advantage of being natural and friendly to a power grid. For the DFIG, the traditional vector current control mode based on the synchronous phase-locked loop enables the wind power generation system to have almost no inertia due to the fact that the phase-locked loop passively follows the frequency of the power grid, so that frequency and inertia support cannot be provided for the power grid, and the stability of the power grid is reduced. As the permeability of the renewable energy power generation system in the power system increases, the installed proportion of the conventional synchronous generator gradually decreases, and the rotational inertia in the power system relatively decreases, which brings a serious challenge to the stability of the power grid. To this end, some researchers have proposed a Virtual Synchronous Generator (VSG) control technique, which enables a grid-connected inverter to simulate the operation mechanism of a synchronous generator, thereby obtaining the operation characteristics like the synchronous generator and providing inertial support for the grid. Therefore, the trainees apply the virtual synchronous machine control technology to the control of the DFIG, so that the DFIG also has the same inertia characteristics as the synchronous generator, and provides frequency support for the power grid.
However, in addition to frequency disturbances, grid voltage sag faults occur in weak grids, which require low voltage ride through capability in DFIG systems. When the voltage of a power grid symmetrically drops, a large induction voltage is induced on the rotor side by the transient component of the DFIG stator flux linkage, so that the rotor is subjected to overcurrent, and a machine-side converter is damaged. However, the DFIG based on the virtual synchronous machine control has a very slow dynamic response speed, and cannot respond quickly to suppress the transient inrush current and accelerate the decay of the transient flux linkage when the grid voltage drops. When the grid voltage drops asymmetrically, in addition to rotor inrush currents, stator and rotor currents can also be unbalanced or distorted. Therefore, the virtual synchronous machine control technology of the DFIG is required to be improved, so that the DFIG has better low-voltage ride through capability, and can effectively restrain the rotor impact current when the voltage of a power grid drops in a transient state. In addition, when the voltage of the power grid symmetrically drops, the attenuation of transient magnetic linkage needs to be accelerated, and reactive power support needs to be provided for the power grid. In the event of voltage asymmetric drop, an improved control method is also provided to keep the DFIG rotor current as balanced and sinusoidal as possible and improve the current quality.
Nian et al in a document [ Improved virtual synchronous generator control of DFIG to three-through synchronous voltage fault, IEEE Transactions on Energy Conversion ] proposes a fault ride-through control method of a DFIG virtual synchronous machine under a grid voltage symmetric fault, and the idea of the method is to suppress rotor impact current during the fault through a virtual resistor and to add an air gap flux PI control inner ring in a control structure to accelerate attenuation of transient flux. However, the disadvantage of this strategy is that the accuracy and effect of using the virtual resistor to suppress the current depends on the resistance of the virtual resistor, the fault location of the power grid, the voltage drop degree, and other factors, and the parameter adjustment of the virtual resistor is very difficult in practical application, and the complexity of the control structure is increased by adding the air gap flux linkage PI control inner loop. In addition, the strategy is only suitable for the power grid voltage symmetric fault and is not suitable for the power grid voltage asymmetric drop fault.
Chengkun et al propose a DFIG virtual synchronous machine control method applicable to power grid asymmetric faults in a document [ doubly-fed wind generator virtual synchronous control method applicable to power grid asymmetric faults [ J ]. power system automation, 2018,42(09): 120-plus 126], and the idea of the method is to offset or weaken transient state and negative sequence components of rotor back electromotive force generated when the power grid voltage is dropped asymmetrically by adding a rotor voltage compensation component. However, the strategy has the defects that the strategy is only suitable for the power grid voltage asymmetric drop fault and cannot meet the operation requirement of a power grid guide rule on the DFIG under the power grid voltage symmetric drop fault.
Therefore, the research of the DFIG virtual synchronous low-voltage ride-through control method which is simple in control structure and can be simultaneously suitable for the grid voltage symmetrical and asymmetrical faults is of great significance.
Disclosure of Invention
The embodiment of the invention aims to provide a method, a device, electronic equipment and a medium for controlling low voltage ride through of a DFIG virtual synchronous machine based on model prediction control, so as to solve the problems of insufficient application range of power grid faults and complex control structure of the existing DFIG virtual synchronous machine control method.
In order to achieve the above purpose, the technical solution adopted by the embodiment of the present invention is as follows:
in a first aspect, an embodiment of the present invention provides a low voltage ride through method for a DFIG virtual synchronous machine, including:
collecting three-phase stator voltage, three-phase stator current, three-phase rotor current and rotor position angle of the DFIG, and calculating active power and reactive power output by the DFIG stator according to the three-phase stator voltage and the three-phase stator current;
according to the active power and the reactive power, obtaining the amplitude and the phase of the DFIG rotor current vector reference value through a DFIG virtual synchronous machine algorithm;
carrying out rotation coordinate transformation on the three-phase stator voltage, the three-phase stator current and the three-phase rotor current to correspondingly obtain a stator voltage vector, a stator current vector and a rotor current vector under a forward rotation d-q coordinate system, and calculating a rotor flux linkage vector under the forward rotation d-q coordinate system;
respectively eliminating transient components and negative sequence components in the DFIG rotor current vector reference value and the rotor flux linkage vector by utilizing a notch filter with the resonant frequency of 50Hz and 100Hz to obtain a positive sequence component of the DFIG rotor current vector reference value and a positive sequence component of the rotor flux linkage vector;
according to rotor voltage vectors corresponding to eight switching states of the DFIG rotor-side converter and rotor current and rotor flux linkage prediction models, obtaining rotor current vector prediction values and rotor flux linkage vector prediction values of the next control period corresponding to the action of different rotor voltage vectors;
and establishing a cost function, calculating function values corresponding to different rotor voltage vectors, and selecting a machine side converter switching state corresponding to the rotor voltage vector with the minimum function value to control the DFIG machine side converter.
Further, the method for calculating the active power and the reactive power output by the DFIG stator according to the three-phase stator voltage and the three-phase stator current comprises the following steps:
P＝-(UsaIsa+UsbIsb+UscIsc)
Figure BDA0002545769230000031
wherein: u shapesa、Usb、UscRespectively three-phase stator voltage UsabcCorresponding to the phase voltages of three phases a, b and c, Isa、Isb、IscRespectively three-phase stator current IsabcCorresponding to phase currents of three phases a, b and c, P and Q are respectively active power and reactive power output by the DFIG stator.
Further, the amplitude and the phase of the DFIG rotor current vector reference value are obtained through a DFIG virtual synchronous machine algorithm, and the method comprises the following steps:
Figure BDA0002545769230000032
θ＝∫ωvdt
Figure BDA0002545769230000033
wherein: prefAnd QrefCorresponding to a reference value for active power and a reference value for reactive power, DpAs damping coefficient, ωvElectrical angular frequency, omega, generated for a virtual synchronous machine1Rated electrical angular frequency of the power grid, J virtual moment of inertia, K reactive ring inertia coefficient, t time, Ir,refAnd theta are rotor current vector reference values, respectively
Figure BDA0002545769230000034
Amplitude and phase.
Further, calculating a reference value of active power and a reference value of reactive power, comprising:
when the power grid voltage is normal or the power grid voltage drops asymmetrically:
Pref＝P0
Qref＝Q0
when the voltage of the power grid symmetrically drops:
Figure BDA0002545769230000041
Figure BDA0002545769230000042
Figure BDA0002545769230000043
wherein: p0And Q0Corresponding to a set value of active power and a set value of reactive power when the voltage of the power grid is normal, UsBeing the amplitude of the stator voltage, ω1For rating the electrical angular frequency, L, of the networkmFor DFIG stator-rotor mutual inductance, LsIn order to be the DFIG stator inductance,
Figure BDA0002545769230000044
is a reference value of the reactive support current, INFor DFIG rotor rated current, PrefAnd QrefRespectively a reference value of active power and a reference value of reactive power.
Further, performing rotation coordinate transformation on the three-phase stator voltage, the three-phase stator current and the three-phase rotor current to correspondingly obtain a stator voltage vector, a stator current vector and a rotor current vector under a forward rotation d-q coordinate system, and calculating a rotor flux linkage vector under the forward rotation d-q coordinate system, wherein the method comprises the following steps:
Figure BDA0002545769230000045
Figure BDA0002545769230000046
Figure BDA0002545769230000047
Figure BDA0002545769230000048
wherein:
Figure BDA0002545769230000049
and
Figure BDA00025457692300000410
corresponding to stator voltage vector
Figure BDA00025457692300000411
The d-axis component and the q-axis component in the forward rotation d-q coordinate system,
Figure BDA00025457692300000412
and
Figure BDA00025457692300000413
corresponding to stator current vector
Figure BDA00025457692300000414
The d-axis component and the q-axis component in the forward rotation d-q coordinate system,
Figure BDA00025457692300000415
and
Figure BDA00025457692300000416
corresponding to rotor current vector
Figure BDA00025457692300000417
The d-axis component and the q-axis component in the forward rotation d-q coordinate system,
Figure BDA00025457692300000418
as rotor flux linkage vector, Usa、Usb、UscRespectively three-phase statorPress UsabcCorresponding to the phase voltages of three phases a, b and c, Isa、Isb、IscRespectively three-phase stator current IsabcPhase currents corresponding to three phases a, b, c, Ira、Irb、IrcRespectively three-phase rotor current IrabcPhase currents corresponding to three phases a, b, c, thetarFor the rotor position angle, L, of DFIGrIs DFIG rotor inductance, LmThe DFIG stator and rotor mutual inductance is obtained.
Further, according to a rotor voltage vector and a rotor current and rotor flux linkage prediction model corresponding to eight switching states of the DFIG rotor-side converter, a rotor current vector prediction value and a rotor flux linkage vector prediction value of a next control period corresponding to the action of different rotor voltage vectors are obtained, and the method comprises the following steps:
Figure BDA0002545769230000051
Figure BDA0002545769230000052
wherein: k period represents the control period, k +1 period represents the next control period, and σ is the leakage coefficient, ωslipIs the angular frequency of the slip, s is the slip, LrIs DFIG rotor inductance, LmFor DFIG stator-rotor mutual inductance, LsIs the stator inductance, T, of DFIGsOften, for one control period, j is an imaginary unit,
Figure BDA0002545769230000053
to be the rotor voltage vector,
Figure BDA0002545769230000054
in order to predict the value of the rotor current vector,
Figure BDA0002545769230000055
Figure BDA0002545769230000056
and predicting the rotor flux linkage vector value.
Further, establishing a cost function, comprising:
Figure BDA0002545769230000057
Figure BDA0002545769230000058
wherein: f is the value of the cost function, kfIs a variable coefficient, kf1In order to obtain the coefficient of field suppression,
Figure BDA0002545769230000059
is the amplitude of the rotor current, I, of the DFIGlimThe maximum value of the rotor current allowed when the DFIG is operated.
In a second aspect, an embodiment of the present invention further provides a DFIG virtual synchronous machine low voltage ride through control apparatus, including:
the collecting module is used for collecting three-phase stator voltage, three-phase stator current, three-phase rotor current and rotor position angle of the DFIG and calculating active power and reactive power output by the DFIG stator according to the three-phase stator voltage and the three-phase stator current;
the virtual synchronization and algorithm module is used for obtaining the amplitude and the phase of the DFIG rotor current vector reference value through a DFIG virtual synchronous machine algorithm according to the active power and the reactive power;
the vector calculation module is used for performing rotation coordinate transformation on the three-phase stator voltage, the three-phase stator current and the three-phase rotor current to correspondingly obtain a stator voltage vector, a stator current vector and a rotor current vector under a forward rotation d-q coordinate system and calculating a rotor flux linkage vector under the forward rotation d-q coordinate system;
the wave trap module is used for eliminating transient components and negative sequence components in the DFIG rotor current vector reference value and the rotor flux linkage vector respectively by utilizing a wave trap filter with the resonant frequency of 50Hz and 100Hz to obtain a positive sequence component of the DFIG rotor current vector reference value and a positive sequence component of the rotor flux linkage vector;
the model prediction module is used for obtaining a rotor current vector prediction value and a rotor flux linkage vector prediction value of a next control period corresponding to the action of different rotor voltage vectors according to rotor voltage vectors corresponding to eight switching states of the DFIG rotor-side converter and rotor current and rotor flux linkage prediction models;
and the cost function calculation and drive signal generation module is used for establishing a cost function, calculating function values corresponding to different rotor voltage vectors, and selecting the machine side converter switch state corresponding to the rotor voltage vector with the minimum function value to control the DFIG machine side converter.
In a third aspect, an embodiment of the present invention further provides an electronic device, including:
one or more processors;
a memory for storing one or more programs;
when executed by the one or more processors, cause the one or more processors to implement a method as described in the first aspect.
In a fourth aspect, an embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program is configured to, when executed by a processor, implement the method according to the first aspect.
According to the technical scheme, the virtual synchronous machine control method of the DFIG is combined with the model predictive control technology, so that the improved control method can realize direct control on the rotor current of the DFIG, and the characteristic that multivariable control can be easily realized by utilizing the model predictive control cost function, and the control method can also realize control on the transient flux linkage of the DFIG. The invention can be simultaneously suitable for the faults of symmetrical and asymmetrical drop of the power grid voltage. When the voltage of the power grid symmetrically drops, the invention can prevent the rotor from overcurrent, accelerate the attenuation of the transient flux linkage of the rotor and provide reactive power support by changing the power reference value. The invention can also prevent rotor overcurrent when the power grid voltage falls asymmetrically, and eliminate transient and negative sequence components in the rotor current reference value by utilizing a notch filter to keep the rotor current balanced and sinusoidal. The control system is very simple to realize, does not need a phase-locked loop to monitor the frequency of the power grid voltage in real time, and does not need to add an additional control loop.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:
FIG. 1 is a schematic diagram of a typical DFIG system used in accordance with an embodiment of the present invention;
FIG. 2 is a flowchart illustrating a DFIG virtual synchronous machine LVRT control method according to an embodiment of the present invention;
FIG. 3 is a control block diagram of a DFIG virtual synchronous machine low voltage ride through control method according to an embodiment of the invention;
FIG. 4 is a waveform diagram of the DFIG virtual synchronous machine low voltage ride through control system of the present invention when the grid voltage drops by 60% symmetrically; the drop fault starts from 1.0s and lasts 625ms, the reference values of the active power and the reactive power output by the stator of the DFIG are 1p.u. and 0p.u. respectively when the grid voltage is normal, and the maximum value I of the rotor current allowed when the DFIG operateslimSet to 1.8 p.u.;
FIG. 5 is a waveform diagram of the DFIG virtual synchronous machine low voltage ride through control system of the present invention when the voltage recovers after the grid voltage symmetrically drops by 60%; the grid voltage is recovered at 1.625s, the reference values of the active power and the reactive power output by the stator of the DFIG are 1p.u. and 0p.u. respectively when the grid voltage is normal, and the maximum value I of the rotor current allowed when the DFIG operateslimSet to 1.8 p.u.;
FIG. 6 is a waveform diagram of the DFIG virtual synchronous machine low voltage ride through control system of the present invention when the grid voltage drops asymmetrically; the grid single-phase voltage drops by 80% at 1.0s and recovers after lasting 625ms, the reference values of the stator output active power and reactive power of the DFIG are 1p.u. and 0p.u. respectively when the grid voltage is normal, and the maximum value I of the rotor current allowed when the DFIG operateslimSet to 1.8 p.u.;
fig. 7 is a schematic structural diagram of a low voltage ride through device of a DFIG virtual synchronous machine based on model predictive control according to an embodiment of the present invention.
Detailed Description
In order to make the technical solutions of the present invention better understood, 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 derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the terms "comprises" and "comprising," and any variations thereof, in the description and claims of the present invention and the above-described drawings, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
FIG. 1 is a schematic diagram of a typical DFIG system used in accordance with an embodiment of the present invention; the system mainly comprises a DFIG body, a machine side converter and a network side converter; the DFIG rotor is driven by a wind turbine, a DFIG stator winding is directly connected with a power grid, the DFIG rotor winding is connected with the power grid through a back-to-back converter, the back-to-back converter comprises a machine side converter and a grid side converter, the grid side converter is responsible for maintaining the voltage of a direct-current bus to be constant, and the machine side converter is responsible for controlling the DFIG.
FIG. 2 is a flowchart illustrating a DFIG virtual synchronous machine LVRT control method according to an embodiment of the present invention; FIG. 3 is a control block diagram of a DFIG virtual synchronous machine low voltage ride through control method according to an embodiment of the invention; the control system comprises a main circuit and a control loop; the main circuit comprises a 1.5MW DFIG1, a machine side converter 2 connected with a DFIG rotor winding, a voltage sensor 3 used for detecting the three-phase voltage of a DFIG stator, a current Hall sensor 4 used for detecting the three-phase current of the DFIG stator, a current Hall sensor 5 used for detecting the three-phase current of the DFIG stator, and an encoder 6 used for detecting the position angle of the DFIG rotor. The control loop comprises a coordinate rotation calculation module 7, a rotor flux linkage vector calculation module 8, a power calculation module 9, a power reference value calculation module 10, a DFIG virtual synchronous machine algorithm module 11, a notch filter module 12 with the resonant frequency of 50Hz and 100Hz, a rotor current and rotor flux linkage prediction module 13 and a cost function calculation and switch state selection module 14. As shown in fig. 2, the method comprises the steps of:
step S101, collecting three-phase stator voltage, three-phase stator current, three-phase rotor current and rotor position angle of the DFIG, and calculating active power and reactive power output by the DFIG stator according to the three-phase stator voltage and the three-phase stator current;
step S102, obtaining the amplitude and the phase of a DFIG rotor current vector reference value through a DFIG virtual synchronous machine algorithm according to the active power and the reactive power;
step S103, performing rotation coordinate transformation on the three-phase stator voltage, the three-phase stator current and the three-phase rotor current to correspondingly obtain a stator voltage vector, a stator current vector and a rotor current vector under a forward rotation d-q coordinate system, and calculating a rotor flux linkage vector under the forward rotation d-q coordinate system;
step S104, respectively eliminating transient components and negative sequence components in the DFIG rotor current vector reference value and the rotor flux linkage vector by utilizing a notch filter with the resonant frequency of 50Hz and 100Hz to obtain a positive sequence component of the DFIG rotor current vector reference value and a positive sequence component of the rotor flux linkage vector;
step S105, according to rotor voltage vectors corresponding to eight switching states of the DFIG rotor-side converter and rotor current and rotor flux prediction models, obtaining rotor current vector prediction values and rotor flux vector prediction values of a next control period corresponding to the action of different rotor voltage vectors;
and step S106, establishing a cost function, calculating function values corresponding to different rotor voltage vectors, and selecting a machine side converter switch state corresponding to the rotor voltage vector with the minimum function value to control the DFIG machine side converter.
By the embodiment of the invention, the virtual synchronous machine control method of the DFIG is combined with the model predictive control technology, so that the improved control method can realize the direct control of the rotor current of the DFIG, and the characteristic of multivariable control can be easily realized by utilizing the model predictive control cost function, so that the control method can also realize the control of the transient flux linkage of the DFIG. The invention can be simultaneously suitable for the faults of symmetrical and asymmetrical drop of the power grid voltage. When the voltage of the power grid symmetrically drops, the invention can prevent the rotor from overcurrent, accelerate the attenuation of the transient flux linkage of the rotor and provide reactive power support by changing the power reference value. The invention can also prevent rotor overcurrent when the power grid voltage falls asymmetrically, and eliminate transient and negative sequence components in the rotor current reference value by utilizing a notch filter to keep the rotor current balanced and sinusoidal. The control system is very simple to realize, does not need a phase-locked loop to monitor the frequency of the power grid voltage in real time, and does not need to add an additional control loop.
According to the embodiment of the invention, the three-phase stator voltage, the three-phase stator current, the three-phase rotor current and the rotor position angle of the DFIG are collected, and the active power and the reactive power output by the DFIG stator are calculated according to the three-phase stator voltage and the three-phase stator current, which are specifically as follows:
DFIG stator three-phase voltage signal U acquired by using three-phase voltage Hall sensor 3sabcThe three-phase current Hall sensor 4 is used for collecting stator three-phase current signals IsabcThe three-phase current Hall sensor 5 is used for collecting the three-phase current signal I of the rotorrabc(ii) a The collected three-phase voltage signal U of the statorsabcAnd stator three-phase current signal IsabcThe active power P and the reactive power Q output by the DFIG stator are obtained through a power calculation module 9; the calculation expressions of the active power and the reactive power are as follows:
P＝-(UsaIsa+UsbIsb+UscIsc)
Figure BDA0002545769230000091
wherein: u shapesa、Usb、UscRespectively three-phase stator voltage UsabcCorresponding to the phase voltages of three phases a, b and c, Isa、Isb、IscRespectively three-phase stator current IsabcCorresponding to phase currents of three phases a, b and c, P and Q are respectively active power and reactive power output by the DFIG stator.
According to the embodiment of the invention, according to the working power and the reactive power, the amplitude and the phase of the DFIG rotor current vector reference value are obtained through a DFIG virtual synchronous machine algorithm, which specifically comprises the following steps:
the power reference value calculation module 10 is used for obtaining reference values of active power and reactive power, and the reference values, the active power P and the reactive power Q are calculated through the DFIG virtual synchronous machine algorithm module 11 to obtain a DFIG rotor current vector reference value
Figure BDA0002545769230000092
Amplitude of (I)r,refAnd a phase θ; the algorithm formula of the DFIG virtual synchronous machine is as follows:
Figure BDA0002545769230000093
θ＝∫ωvdt
Figure BDA0002545769230000094
wherein: prefAnd QrefCorresponding to a reference value for active power and a reference value for reactive power, DpAs damping coefficient, ωvElectrical angular frequency, omega, generated for a virtual synchronous machine1Rated electrical angular frequency of the power grid, J virtual moment of inertia, K reactive ring inertia coefficient, t time, Ir,refAnd theta are rotor current vector reference values, respectively
Figure BDA0002545769230000095
Amplitude and phase.
The power reference value calculation method comprises the following steps:
a. when the power grid voltage is normal or the power grid voltage drops asymmetrically:
Pref＝P0
Qref＝Q0
b. when the voltage of the power grid symmetrically drops:
Figure BDA0002545769230000096
Figure BDA0002545769230000097
Figure BDA0002545769230000098
wherein: p0And Q0Corresponding to a set value of active power and a set value of reactive power when the voltage of the power grid is normal, UsBeing the amplitude of the stator voltage, ω1For rating the electrical angular frequency, L, of the networkmFor DFIG stator-rotor mutual inductance, LsIn order to be the DFIG stator inductance,
Figure BDA0002545769230000099
is a reference value of the reactive support current, INFor DFIG rotor rated current, PrefAnd QrefRespectively a reference value of active power and a reference value of reactive power.
According to the above embodiment of the present invention, the three-phase stator voltage, the three-phase stator current, and the three-phase rotor current are subjected to rotation coordinate transformation, so as to obtain the stator voltage vector, the stator current vector, and the rotor current vector in the forward rotation d-q coordinate system, and calculate the rotor flux linkage vector in the forward rotation d-q coordinate system, which is specifically as follows:
DFIG rotor position angle theta acquisition using encoder 6rIs connected to three-phase stator voltage UsabcThree-phase stator current IsabcThree-phase rotor current IrabcAnd rotor current vector reference value
Figure BDA0002545769230000101
The phase theta of the stator voltage vector under the forward rotation d-q coordinate system is obtained by the coordinate rotation calculation module 7
Figure BDA0002545769230000102
Stator current vector
Figure BDA0002545769230000103
And rotor current vector
Figure BDA0002545769230000104
Then the stator current vector is converted into
Figure BDA0002545769230000105
And rotor current vector
Figure BDA0002545769230000106
The rotor flux linkage vector under the forward rotation d-q coordinate system is obtained through a rotor flux linkage vector calculation module 8
Figure BDA0002545769230000107
Stator voltage vector under forward rotation d-q coordinate system
Figure BDA0002545769230000108
Stator current vector
Figure BDA0002545769230000109
Rotor current vector
Figure BDA00025457692300001010
And rotor flux linkage vector
Figure BDA00025457692300001011
The calculation methods are respectively as follows:
Figure BDA00025457692300001012
Figure BDA00025457692300001013
Figure BDA00025457692300001014
Figure BDA00025457692300001015
wherein:
Figure BDA00025457692300001016
and
Figure BDA00025457692300001017
corresponding to stator voltage vector
Figure BDA00025457692300001018
The d-axis component and the q-axis component in the forward rotation d-q coordinate system,
Figure BDA00025457692300001019
and
Figure BDA00025457692300001020
corresponding to stator current vector
Figure BDA00025457692300001021
The d-axis component and the q-axis component in the forward rotation d-q coordinate system,
Figure BDA00025457692300001022
and
Figure BDA00025457692300001023
corresponding to rotor current vector
Figure BDA00025457692300001024
The d-axis component and the q-axis component in the forward rotation d-q coordinate system,
Figure BDA00025457692300001025
as rotor flux linkage vector, Usa、Usb、UscRespectively three-phase stator voltage UsabcCorresponding to the phase voltages of three phases a, b and c, Isa、Isb、IscRespectively three-phase stator current IsabcPhase currents corresponding to three phases a, b, c, Ira、Irb、IrcRespectively three-phase rotor current IrabcPhase currents corresponding to three phases a, b, c, thetarFor the rotor position angle, L, of DFIGrIs DFIG rotor inductance, LmThe DFIG stator and rotor mutual inductance is obtained.
According to the above embodiment of the present invention, the notch filters with resonant frequencies of 50Hz and 100Hz are used to respectively eliminate the transient component and the negative sequence component in the DFIG rotor current vector reference value and the rotor flux linkage vector, so as to obtain the positive sequence component of the DFIG rotor current vector reference value and the positive sequence component of the rotor flux linkage vector, which are specifically as follows:
reference value of DFIG rotor current vector
Figure BDA0002545769230000111
And rotor flux linkage vector
Figure BDA0002545769230000112
Respectively eliminating transient components and negative sequence components in the notch filter module 12 with the resonant frequencies of 50Hz and 100Hz to obtain a positive sequence component of the DFIG rotor current vector reference value
Figure BDA0002545769230000113
And the positive sequence component of the rotor flux linkage vector
Figure BDA0002545769230000114
According to the embodiment of the invention, the predicted values of the rotor current vector and the rotor flux linkage vector of the next control period corresponding to the action of different rotor voltage vectors are obtained according to the rotor voltage vectors and the rotor current and rotor flux linkage prediction models corresponding to eight switching states of the DFIG rotor-side converter, which is specifically as follows:
positive sequence component of DFIG rotor current vector reference value
Figure BDA0002545769230000115
Positive sequence component of rotor flux linkage vector
Figure BDA0002545769230000116
Stator voltage vector
Figure BDA0002545769230000117
Stator current vector
Figure BDA0002545769230000118
Rotor current vector
Figure BDA0002545769230000119
Different rotor voltage vectors corresponding to eight switching states of rotor current and DFIG rotor-side converter
Figure BDA00025457692300001110
The rotor current vector predicted value of the next control period corresponding to the action of different rotor voltage vectors is obtained through the rotor current vector and rotor flux linkage vector prediction module 13
Figure BDA00025457692300001111
And rotor flux linkage vector predictor
Figure BDA00025457692300001112
Figure BDA00025457692300001113
The prediction model formula is as follows:
Figure BDA00025457692300001114
Figure BDA00025457692300001115
wherein: k period represents the control period, k +1 period represents the next control period, and σ is the leakage coefficient, ωslipIs the angular frequency of the slip, s is the slip, LrIs DFIG rotor inductance, LmFor DFIG stator-rotor mutual inductance, LsIs the stator inductance, T, of DFIGsOften, for one control period, j is an imaginary unit,
Figure BDA00025457692300001116
to be the rotor voltage vector,
Figure BDA00025457692300001117
in order to predict the value of the rotor current vector,
Figure BDA00025457692300001118
and predicting the rotor flux linkage vector value.
According to the embodiment of the invention, a cost function is established, function values corresponding to different rotor voltage vectors are calculated, and the switching state of the machine-side converter corresponding to the rotor voltage vector with the minimum function value is selected to control the DFIG machine-side converter, which specifically comprises the following steps:
predicting the corresponding rotor current vector values when different rotor voltage vectors act
Figure BDA00025457692300001119
And rotor flux linkage vector predictor
Figure BDA00025457692300001120
Figure BDA00025457692300001121
Selecting the switching state of the machine side converter corresponding to the rotor voltage vector with the minimum function value through a cost function calculation and switching state selection module 14, and outputting a switching signal SaSbScApplying control to the DFIG machine side converter; the cost function is formulated as:
Figure BDA00025457692300001122
Figure BDA00025457692300001123
wherein: f is the value of the cost function, kfIs a variable coefficient, kf1In order to obtain the coefficient of field suppression,
Figure BDA00025457692300001124
is the amplitude of the rotor current, I, of the DFIGlimThe maximum value of the rotor current allowed when the DFIG is operated.
In order to verify the effectiveness of the control method of the embodiment of the invention, simulation verification research is carried out on a DFIG system with 1.5MW capacity.
Referring to fig. 4, under the low-voltage crossing control method of the DFIG virtual synchronous machine based on model prediction control, when the transient symmetry of the grid voltage drops by 60%, the impact current of the rotor is effectively suppressed, and the maximum value is controlled to be about 1.8p.u. set. The stator transient flux linkage also decays very quickly from the power and electromagnetic torque oscillating waveforms. Furthermore, during a fault the DFIG may output reactive power to the grid as required by grid codes to assist in grid voltage recovery.
Referring to fig. 5, under the low-voltage crossing control method of the DFIG virtual synchronous machine based on model prediction control, when the grid voltage is recovered from 60% drop to a normal value, the rotor inrush current is still effectively suppressed to be about 1.8p.u. set. Therefore, the DFIG can keep grid-connected safe operation during the whole grid voltage symmetrical drop fault period.
Referring to fig. 6, under the low-voltage crossing control method of the DFIG virtual synchronous machine based on model prediction control, when the single-phase voltage of the power grid drops by 80% (namely, the voltage asymmetric drop fault), the rotor current of the DFIG does not exceed the limit value during the whole fault period, and the rotor current can keep balance and sine during the asymmetric period of the power grid voltage.
The present invention further provides an embodiment of a model predictive control-based low voltage ride through control device for a DFIG virtual synchronous machine, which is used for executing a model predictive control-based low voltage ride through method for the DFIG virtual synchronous machine, and fig. 7 is a schematic structural diagram of the model predictive control-based low voltage ride through control device for the DFIG virtual synchronous machine according to the embodiment of the present invention, and the device includes:
the collecting module 91 is used for collecting three-phase stator voltage, three-phase stator current, three-phase rotor current and rotor position angle of the DFIG, and calculating active power and reactive power output by the DFIG stator according to the three-phase stator voltage and the three-phase stator current;
the virtual synchronization and algorithm module 92 is used for obtaining the amplitude and the phase of the DFIG rotor current vector reference value through a DFIG virtual synchronous machine algorithm according to the active power and the reactive power;
the vector calculation module 93 is configured to perform rotation coordinate transformation on the three-phase stator voltage, the three-phase stator current and the three-phase rotor current, to correspondingly obtain a stator voltage vector, a stator current vector and a rotor current vector in the forward rotation d-q coordinate system, and to calculate a rotor flux linkage vector in the forward rotation d-q coordinate system;
a wave trap module 94, configured to respectively eliminate a transient component and a negative sequence component in the DFIG rotor current vector reference value and the rotor flux linkage vector by using a wave trap filter with a resonant frequency of 50Hz and 100Hz, so as to obtain a positive sequence component of the DFIG rotor current vector reference value and a positive sequence component of the rotor flux linkage vector;
the model prediction module 95 is configured to obtain a rotor current vector prediction value and a rotor flux linkage vector prediction value of a next control period corresponding to the action of different rotor voltage vectors according to rotor voltage vectors corresponding to eight switching states of the DFIG rotor-side converter and a rotor current and rotor flux linkage prediction model;
and the cost function calculation and drive signal generation module 96 is used for establishing a cost function, calculating function values corresponding to different rotor voltage vectors, and selecting the machine side converter switching state corresponding to the rotor voltage vector with the minimum function value to control the DFIG machine side converter.
An embodiment of the present invention further provides an electronic device, including:
one or more processors;
a memory for storing one or more programs;
when executed by the one or more processors, cause the one or more processors to implement the method as described above.
An embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program is executed by a processor to implement the method as described above.
The above-mentioned serial numbers of the embodiments of the present invention are merely for description and do not represent the merits of the embodiments.
In the above embodiments of the present invention, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.
In the embodiments provided in the present application, it should be understood that the disclosed technology can be implemented in other ways. The above-described embodiments of the apparatus are merely illustrative, and for example, the division of the units may be a logical division, and in actual implementation, there may be another division, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, units or modules, and may be in an electrical or other form.
The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.
In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.
The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a removable hard disk, a magnetic or optical disk, and other various media capable of storing program codes.
The embodiments described above are presented to enable a person having ordinary skill in the art to make and use the invention. It will be readily apparent to those skilled in the art that various modifications to the above-described embodiments may be made, and the generic principles defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications to the present invention based on the disclosure of the present invention within the protection scope of the present invention.

Claims (10)

1. A low voltage ride through method of a DFIG virtual synchronous machine is characterized by comprising the following steps:
collecting three-phase stator voltage, three-phase stator current, three-phase rotor current and rotor position angle of the DFIG, and calculating active power and reactive power output by the DFIG stator according to the three-phase stator voltage and the three-phase stator current;
according to the active power and the reactive power, obtaining the amplitude and the phase of the DFIG rotor current vector reference value through a DFIG virtual synchronous machine algorithm;
carrying out rotation coordinate transformation on the three-phase stator voltage, the three-phase stator current and the three-phase rotor current to correspondingly obtain a stator voltage vector, a stator current vector and a rotor current vector under a forward rotation d-q coordinate system, and calculating a rotor flux linkage vector under the forward rotation d-q coordinate system;
respectively eliminating transient components and negative sequence components in the DFIG rotor current vector reference value and the rotor flux linkage vector by utilizing a notch filter with the resonant frequency of 50Hz and 100Hz to obtain a positive sequence component of the DFIG rotor current vector reference value and a positive sequence component of the rotor flux linkage vector;
according to rotor voltage vectors corresponding to eight switching states of the DFIG rotor-side converter and rotor current and rotor flux linkage prediction models, obtaining rotor current vector prediction values and rotor flux linkage vector prediction values of the next control period corresponding to the action of different rotor voltage vectors;
and establishing a cost function, calculating function values corresponding to different rotor voltage vectors, and selecting a machine side converter switching state corresponding to the rotor voltage vector with the minimum function value to control the DFIG machine side converter.
2. The DFIG virtual synchronous machine low voltage ride through control method according to claim 1, wherein calculating the active power and reactive power output by the DFIG stator according to the three-phase stator voltage and the three-phase stator current comprises:
P＝-(UsaIsa+UsbIsb+UscIsc)
Figure FDA0002545769220000011
wherein: u shapesa、Usb、UscRespectively three-phase stator voltage UsabcCorresponding to the phase voltages of three phases a, b and c, Isa、Isb、IscRespectively three-phase stator current IsabcCorresponding to phase currents of three phases a, b and c, P and Q are respectively active power and reactive power output by the DFIG stator.
3. The DFIG virtual synchronous machine low voltage ride through control method of claim 1, wherein obtaining the amplitude and phase of the DFIG rotor current vector reference value by the DFIG virtual synchronous machine algorithm comprises:
Figure FDA0002545769220000021
θ＝∫ωvdt
Figure FDA0002545769220000022
wherein: prefAnd QrefCorresponding to a reference value for active power and a reference value for reactive power, DpAs damping coefficient, ωvElectrical angular frequency, omega, generated for a virtual synchronous machine1Rated electrical angular frequency of the power grid, J virtual moment of inertia, K reactive ring inertia coefficient, t time, Ir,refAnd theta are rotor current vector reference values, respectively
Figure FDA0002545769220000023
Amplitude and phase.
4. The DFIG virtual synchronous machine low voltage ride through control method according to claim 3, wherein calculating the reference value of active power and the reference value of reactive power comprises:
when the power grid voltage is normal or the power grid voltage drops asymmetrically:
Pref＝P0
Qref＝Q0
when the voltage of the power grid symmetrically drops:
Figure FDA0002545769220000024
Figure FDA0002545769220000025
Figure FDA0002545769220000026
wherein: p0And Q0Corresponding to a set value of active power and a set value of reactive power when the voltage of the power grid is normal, UsBeing the amplitude of the stator voltage, ω1For rating the electrical angular frequency, L, of the networkmFor DFIG stator-rotor mutual inductance, LsIn order to be the DFIG stator inductance,
Figure FDA0002545769220000027
is a reference value of the reactive support current, INFor DFIG rotor rated current, PrefAnd QrefRespectively a reference value of active power and a reference value of reactive power.
5. The DFIG virtual synchronous machine low voltage ride through control method according to claim 1, wherein performing rotation coordinate transformation on three-phase stator voltage, three-phase stator current and three-phase rotor current to obtain a stator voltage vector, a stator current vector and a rotor current vector in a forward rotation d-q coordinate system correspondingly, and calculating a rotor flux linkage vector in the forward rotation d-q coordinate system, comprises:
Figure FDA0002545769220000031
Figure FDA0002545769220000032
Figure FDA0002545769220000033
Figure FDA0002545769220000034
wherein:
Figure FDA0002545769220000035
and
Figure FDA0002545769220000036
corresponding to stator voltage vector
Figure FDA0002545769220000037
The d-axis component and the q-axis component in the forward rotation d-q coordinate system,
Figure FDA0002545769220000038
and
Figure FDA0002545769220000039
corresponding to stator current vector
Figure FDA00025457692200000310
The d-axis component and the q-axis component in the forward rotation d-q coordinate system,
Figure FDA00025457692200000311
and
Figure FDA00025457692200000312
corresponding to rotor current vector
Figure FDA00025457692200000313
The d-axis component and the q-axis component in the forward rotation d-q coordinate system,
Figure FDA00025457692200000314
as rotor flux linkage vector, Usa、Usb、UscRespectively three-phase stator voltage UsabcCorresponding to the phase voltages of three phases a, b and c, Isa、Isb、IscRespectively three-phase stator current IsabcPhase currents corresponding to three phases a, b, c, Ira、Irb、IrcRespectively three-phase rotor current IrabcPhase currents corresponding to three phases a, b, c, thetarFor the rotor position angle, L, of DFIGrFor DFIG to changeSub-inductor, LmThe DFIG stator and rotor mutual inductance is obtained.
6. The DFIG virtual synchronous machine low voltage ride through control method according to claim 1, wherein obtaining the predicted values of the rotor current vector and the rotor flux linkage vector of the next control period corresponding to the action of different rotor voltage vectors according to the rotor voltage vectors and the rotor current and rotor flux linkage prediction models corresponding to eight switching states of the DFIG rotor-side converter comprises:
Figure FDA00025457692200000315
Figure FDA00025457692200000316
wherein: k period represents the control period, k +1 period represents the next control period, and σ is the leakage coefficient, ωslipIs the angular frequency of the slip, s is the slip, LrIs DFIG rotor inductance, LmFor DFIG stator-rotor mutual inductance, LsIs the stator inductance, T, of DFIGsOften, for one control period, j is an imaginary unit,
Figure FDA00025457692200000317
to be the rotor voltage vector,
Figure FDA00025457692200000318
in order to predict the value of the rotor current vector,
Figure FDA00025457692200000319
Figure FDA00025457692200000320
and predicting the rotor flux linkage vector value.
7. The DFIG virtual synchronous machine low voltage ride through control method according to claim 1, wherein establishing a cost function comprises:
Figure FDA0002545769220000041
Figure FDA0002545769220000042
wherein: f is the value of the cost function, kfIs a variable coefficient, kf1In order to obtain the coefficient of field suppression,
Figure FDA0002545769220000043
is the amplitude of the rotor current, I, of the DFIGlimThe maximum value of the rotor current allowed when the DFIG is operated.
8. A DFIG virtual synchronous machine low voltage ride through control device is characterized by comprising:
the collecting module is used for collecting three-phase stator voltage, three-phase stator current, three-phase rotor current and rotor position angle of the DFIG and calculating active power and reactive power output by the DFIG stator according to the three-phase stator voltage and the three-phase stator current;
the virtual synchronization and algorithm module is used for obtaining the amplitude and the phase of the DFIG rotor current vector reference value through a DFIG virtual synchronous machine algorithm according to the active power and the reactive power;
the vector calculation module is used for performing rotation coordinate transformation on the three-phase stator voltage, the three-phase stator current and the three-phase rotor current to correspondingly obtain a stator voltage vector, a stator current vector and a rotor current vector under a forward rotation d-q coordinate system and calculating a rotor flux linkage vector under the forward rotation d-q coordinate system;
the wave trap module is used for eliminating transient components and negative sequence components in the DFIG rotor current vector reference value and the rotor flux linkage vector respectively by utilizing a wave trap filter with the resonant frequency of 50Hz and 100Hz to obtain a positive sequence component of the DFIG rotor current vector reference value and a positive sequence component of the rotor flux linkage vector;
the model prediction module is used for obtaining a rotor current vector prediction value and a rotor flux linkage vector prediction value of a next control period corresponding to the action of different rotor voltage vectors according to rotor voltage vectors corresponding to eight switching states of the DFIG rotor-side converter and rotor current and rotor flux linkage prediction models;
and the cost function calculation and drive signal generation module is used for establishing a cost function, calculating function values corresponding to different rotor voltage vectors, and selecting the machine side converter switch state corresponding to the rotor voltage vector with the minimum function value to control the DFIG machine side converter.
9. An electronic device, comprising:
one or more processors;
a memory for storing one or more programs;
when executed by the one or more processors, cause the one or more processors to implement the method of any one of claims 1-7.
10. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the method according to any one of claims 1-7.
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