CN107658911B - Control method for enhancing low voltage ride through of permanent magnet direct-drive wind turbine generator under asymmetric power grid fault - Google Patents

Control method for enhancing low voltage ride through of permanent magnet direct-drive wind turbine generator under asymmetric power grid fault Download PDF

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CN107658911B
CN107658911B CN201711012383.4A CN201711012383A CN107658911B CN 107658911 B CN107658911 B CN 107658911B CN 201711012383 A CN201711012383 A CN 201711012383A CN 107658911 B CN107658911 B CN 107658911B
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grid
side converter
wind turbine
permanent magnet
turbine generator
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CN107658911A (en
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姚骏
李琰
裴金鑫
刘超
迟永宁
汤海雁
田新首
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Chongqing University
China Electric Power Research Institute Co Ltd CEPRI
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China Electric Power Research Institute Co Ltd CEPRI
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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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H02J3/48—Controlling the sharing of the in-phase component
    • 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
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase networks
    • H02J3/386—
    • 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]
    • 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
    • Y02E40/50—Arrangements for eliminating or reducing asymmetry in polyphase networks

Abstract

The invention discloses a control method for enhancing low voltage ride through of a permanent magnet direct-drive wind turbine generator under an asymmetric fault of a power grid, and relates to control over a grid-side converter and a machine-side converter of the permanent magnet direct-drive wind turbine generator. According to the method, on the basis of fully considering the capacity of the converter and the operation condition of the generator set, the given instructions of the positive and negative sequence dq axis currents of the grid-side converter of the permanent-magnet direct-drive wind turbine generator set are obtained, and the obtained positive and negative sequence control voltages of the grid-side converter are further used
Figure 1
And DC bus voltage UdcThe PWM driving signal of the grid-side converter is generated through space vector modulation, so that the permanent magnet direct-drive wind turbine generator can inhibit the voltage unbalance degree of a grid-connected point, and provide active current to a power grid to the maximum extent, and the low voltage ride through capability of the permanent magnet direct-drive wind turbine generator under the asymmetric fault of the power grid and the power quality of the power grid connected with the permanent magnet direct-drive wind turbine generator are obviously enhanced.

Description

Control method for enhancing low voltage ride through of permanent magnet direct-drive wind turbine generator under asymmetric power grid fault
Technical Field
The invention relates to a wind power generation technology, in particular to a method for controlling enhanced fault ride-through of a permanent magnet direct-drive wind turbine generator under the condition of asymmetric faults of a power grid, and belongs to the technical field of new energy power generation.
Background
At present, because the permanent magnet direct-drive wind turbine generator adopts permanent magnet excitation, parts with high failure rate such as a gear box, an electric brush and a slip ring are omitted, and the permanent magnet direct-drive wind turbine generator has the advantages of salt spray corrosion resistance, simple structure, low operation noise and the like, and becomes one of mainstream models in a wind power generation system. Because the permanent magnet direct-drive wind turbine generator realizes grid isolation through the full-power converter, the capacity of the full-power converter is fully utilized to compensate the voltage of the common point of the wind power plant, and the method is a main means for improving the fault ride-through capability of the permanent magnet direct-drive wind turbine generator. And in view of that wind power resources in China are mostly concentrated in remote areas and are weakly connected with a power main grid, compared with a power grid symmetric short-circuit fault, the probability of the power grid asymmetric short-circuit fault occurring in an actual system is higher. When the power grid has an asymmetric drop fault, the power generation system outputs a large amount of negative sequence current, so that the grid-connected converter generates unbalanced heating and increases loss, and the running performance of the grid-connected converter and the grid-connected power quality of the power generation system are seriously threatened; secondly, the unbalance of the voltage of the power grid can cause the oscillation of the power fed into the power grid by the power generation system, so that the voltage fluctuation of a direct current link of the power generation system is caused, and the safe and stable operation of the power generation system and the power grid is seriously influenced. Therefore, in order to improve the low voltage ride through capability of the permanent magnet direct-drive wind turbine generator under the condition of the asymmetric fault of the power grid and the power quality of the power grid connected with the wind turbine generator, further deep research needs to be carried out on the low voltage ride through control method of the permanent magnet direct-drive wind turbine generator under the condition of the asymmetric fault of the power grid. At present, for the asymmetric fault ride-through technology of the permanent magnet direct-drive wind turbine generator, relevant researches have been carried out by scholars at home and abroad, such as the following published documents:
(1) zhang Ying, Cheng Zhi, Li Gem, Ding, Jian direct drive permanent magnet wind power generation system voltage stabilization control [ J ] under asymmetric grid fault power system protection and control 2013,41(18):17-24.
(2) Zhu Xiaojun, Yaojun, Jiangquan, XianXifeng, Wenyiyiyuyu, Longhong Yu, the permanent magnet direct-drive wind power system with the flywheel energy storage unit enhances the operation control strategy under the asymmetric fault of the power grid [ J ] the power grid technology, 2013,37(5):1454 + 1463.
Document (1) adopts a double current loop control strategy under a double synchronous rotating coordinate shafting, or realizes that no negative sequence current is output to a power grid, or realizes that output active power and frequency multiplication fluctuation of a direct-current side bus voltage 2 are effectively inhibited, or realizes that output reactive power has no fluctuation, so that the fault ride-through capability of a permanent magnet direct-drive wind power system is improved to a certain extent, but a plurality of operation targets cannot be realized simultaneously. In the document (2), an energy storage device is additionally arranged on a direct current bus of a converter to absorb frequency multiplication fluctuation of a direct current capacitor 2 and active power output by a generator so as to maintain the voltage of the direct current bus stable and free from fluctuation, and a negative sequence component of output current or 2 frequency multiplication fluctuation of the output power is eliminated by a grid-side converter, so that the fault ride-through capability of a wind power system and the electric energy quality of a grid-connected system are enhanced, but the capacity of the grid-side converter is not fully exerted, and the use of hardware equipment inevitably increases the cost of the whole system.
During the asymmetric fault of the power grid, the running performance of the permanent magnet direct-drive wind turbine generator is inevitably seriously influenced due to the negative sequence voltage of the power grid and the negative sequence current of the system. Therefore, on the basis of not increasing additional hardware equipment, the capacity and the controllability of a converter in the permanent magnet direct-drive wind turbine generator are fully utilized, and the enhanced low voltage ride through control method of the permanent magnet direct-drive wind turbine generator under the asymmetric fault of the power grid is researched, so that the permanent magnet direct-drive wind turbine generator is guaranteed to be in non-grid-disconnected safe and stable operation, the unbalance degree of the grid-connected point voltage is restrained, the transient voltage level of the power grid is further improved, and the method has important practical significance for enhancing the fault ride through capability of the permanent magnet direct-drive wind turbine generator and the power quality of the power grid connected with.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a method for controlling the enhanced low voltage ride through of the permanent magnet direct-drive wind turbine generator under the asymmetric fault of a power grid.
The technical scheme of the invention is realized as follows:
a control method for enhancing low voltage ride through of a permanent magnet direct-drive wind turbine generator under the asymmetric fault of a power grid relates to the control of a grid side converter and a machine side converter of the permanent magnet direct-drive wind turbine generator;
(A) the control steps of the permanent magnet direct-drive wind turbine generator system grid-side converter are as follows:
A1) collecting grid-connected point three-phase voltage signal u of permanent magnet direct-drive wind turbine generatorgabcThree-phase current signal i output by grid-side convertergabcAnd a DC bus voltage signal Udc；
A2) Collected permanent magnet direct-drive wind turbine generator grid-connected point three-phase voltage signal ugabcObtaining the electrical angle theta of the positive sequence voltage vector of the grid-connected point of the permanent magnet direct-drive wind turbine generator after passing through the digital phase-locked loop P LLgAnd synchronous electrical angular velocity omegae；
A3) Direct-drive permanent magnet wind turbine generator grid-connected point three-phase voltage signal ugabcThrough constant power coordinate transformation from a static three-phase abc coordinate system to a static two-phase αβ coordinate system, the constant power coordinate transformation is converted into a voltage signal under a static two-phase αβ coordinate system, namely ugα、ugβ；
A4) Respectively carrying out the voltage signal u under the stationary two-phase αβ coordinate axis system obtained in the step A3) in a positive sequence voltage d-axis orientation mode of a grid-connected point of a permanent-magnet direct-drive wind turbine generatorgα、ugβConstant power conversion from static two-phase αβ coordinate axis system to forward and reverse synchronous angular speed rotating coordinate axis system, and 2 omega conversioneFiltering by a wave trap to obtain dq axis components of three-phase voltages of grid-connected points of the permanent-magnet direct-drive wind turbine generator in the operation period under the condition of asymmetric faults of a power grid, namely, the dq axis components under a forward and reverse synchronous angular speed rotating coordinate axis system
Figure BDA0001445755580000021
A5) Collected three-phase current signals i of the grid-side convertergabcObtaining output current i under a stationary two-phase αβ coordinate axis system through constant power coordinate transformation from the stationary three-phase abc coordinate axis system to the stationary two-phase αβ coordinate axis systemgα、igβ；
A6) Outputting current i of the grid-down side converter of the stationary two-phase αβ coordinate axis system obtained in the step A5)gα、igβConstant power conversion from static two-phase αβ coordinate axis system to forward and reverse synchronous angular speed rotating coordinate axis system, and 2 omega conversioneFiltering by a wave trap to obtain dq axis components of the output current of the grid-side converter under a forward and reverse synchronous angular velocity rotating coordinate system, namely
Figure BDA0001445755580000031
A7) The dq axis component of the voltage of the grid-connected point of the permanent magnet direct-drive wind turbine generator obtained in the step A4) under the reverse synchronous angular velocity rotating coordinate system, namely
Figure BDA0001445755580000032
The voltage unbalance of the grid-connected point can be restrained to zero by the grid-side converter during the operation period of the asymmetrical fault of the power grid according to the following formula, and the output negative sequence current reference value without amplitude limitation is required to be output
Figure BDA0001445755580000033
Figure BDA0001445755580000034
In the formula, Kp1And τi1Respectively calculating a proportional coefficient and an integral time constant of a PI regulator of the module for calculating the reference value of the negative sequence current;
A8) the dq axis component of the wind power plant grid-connected point voltage obtained in the step A4) under the forward and reverse synchronous angular velocity rotating coordinate system
Figure BDA0001445755580000035
And the non-amplitude-limited negative sequence current reference value of the network side converter obtained in the step A7)
Figure BDA0001445755580000036
The amplitude of the positive sequence current which can be output by the permanent magnet direct-drive wind power system under the limitation of the negative sequence current is determined according to the following formula:
Figure BDA0001445755580000037
wherein, | igmaxI is the maximum current amplitude allowed to flow by the grid-side converter;
A9) carrying out the dq axis voltage component of the permanent magnet direct-drive wind turbine generator grid-side converter obtained in the step A4) under the reverse synchronous angular velocity rotating coordinate system
Figure BDA0001445755580000038
And the dq axis current components of the permanent magnet direct-drive wind turbine grid-side converter obtained in the step A6) and the step A8) under the forward and reverse synchronous angular velocity rotating coordinate system
Figure BDA0001445755580000039
Maximum current i allowed by the grid-side converter to operategmaxThe reference values are transmitted to a positive sequence current reference value calculation module and a negative sequence current reference value calculation module of the grid-side converter to determine the positive sequence current reference value and the negative sequence current reference value of the grid-side converter
Figure BDA00014457555800000310
Figure BDA00014457555800000311
A10) Respectively transmitting the positive sequence current reference value and the negative sequence current reference value of the network side converter obtained by calculation in the step A9) to a positive sequence current inner loop control link and a negative sequence current inner loop control link of the network side converter, and obtaining positive sequence control voltage dq axis component and negative sequence control voltage dq axis component of the network side converter under the control of a positive synchronous speed angular speed rotating coordinate system and a reverse synchronous speed rotating coordinate system according to the following formula
Figure BDA00014457555800000312
Figure BDA00014457555800000313
Figure BDA00014457555800000314
In the formula, Kp3And τi3Respectively is the proportional coefficient and the integral time constant, K, of a current inner loop PI controller in a positive sequence control system of a network side converterp4And τi4L are respectively proportional coefficient and integral time constant of a current loop PI controller in a negative sequence control system of the network side convertergThe inductance of an incoming line reactor of the network side converter;
A11) using the positive and negative sequence control voltage dq axis components of the network side converter obtained in the step A10)
Figure BDA0001445755580000041
Figure BDA0001445755580000042
And
Figure BDA0001445755580000043
respectively obtaining positive and negative sequence control voltages under a stationary two-phase αβ coordinate axis system through constant power conversion from a forward synchronous angular velocity rotating coordinate axis system and a reverse synchronous angular velocity rotating coordinate axis system to a stationary two-phase αβ coordinate axis system
Figure BDA0001445755580000044
A12) Controlling the positive and negative sequence control voltage of the network side converter obtained in the step A11)
Figure BDA0001445755580000045
And DC bus voltage UdcGenerating a PWM driving signal of a grid-side converter through space vector modulation so as to inhibit the voltage unbalance degree of a power grid;
(B) the control steps of the permanent magnet direct-drive wind turbine generator side converter are as follows:
B1) the machine side converter of the permanent magnet direct-drive wind turbine generator adopts a vector control strategy, and the control voltage of the machine side converter generates a PWM (pulse width modulation) driving signal through space vector pulse width modulation so as to maintain the stability of the direct current bus voltage of the permanent magnet direct-drive wind turbine generator during the asymmetric fault period.
Further, the step a9) comprises the following steps:
a9.1) during the asymmetrical fault operation of the power grid, the reference value of the negative sequence current dq axis of the non-amplitude-limited grid-side converter obtained in the step A7) is utilized
Figure BDA0001445755580000046
Calculating the amplitude of the negative sequence current reference value of the network side converter
Figure BDA0001445755580000047
Amplitude of positive sequence current reference value of sum network side converter
Figure BDA0001445755580000048
Figure BDA0001445755580000049
And the following judgments were made:
Figure BDA00014457555800000410
in the formula (I), the compound is shown in the specification,
Figure BDA00014457555800000411
the d-axis current positive sequence component at the lower net side of a positive synchronous angular velocity rotating coordinate system when the permanent magnet direct-drive wind turbine generator realizes the maximum wind energy tracking,
Figure BDA00014457555800000412
a q-axis current positive sequence component at the lower network side of the forward synchronous angular velocity rotating coordinate system when no reactive power is output;
a9.2) if the constraint condition in A9.1) is met, outputting the positive and negative sequence dq axis current reference values of the grid-side converter according to the following steps:
Figure BDA00014457555800000413
in the formula (I), the compound is shown in the specification,
Figure BDA00014457555800000414
positive and negative sequence dq axis current reference values output by the module are calculated for the positive and negative sequence current reference values of the network side converter;
a9.3) if the constraint condition in A9.1) is not satisfied, judging the amplitude of the negative sequence current reference value of the grid-side converter of the permanent magnet direct-drive wind turbine generator obtained in the step A9.1)
Figure BDA00014457555800000415
Whether a constraint condition shown as the following formula is satisfied:
Figure BDA00014457555800000416
a9.4) if the constraint condition in A9.3) is met, outputting the positive and negative sequence dq axis current reference values of the grid-side converter according to the following steps:
Figure BDA0001445755580000051
a9.5) if the constraint condition in A9.3) is not satisfied, outputting the positive and negative sequence dq axis current reference values of the grid-side converter according to the following steps:
Figure BDA0001445755580000052
the step B1) comprises the following steps:
b1.1) during the asymmetric fault operation of the power grid, setting a voltage reference instruction of a machine side converter as follows:
Figure BDA0001445755580000053
in the formula, #sFor permanent magnet flux linkage, LsIs the stator reactance, ωsFor the synchronous electrical angular velocity, K, of the permanent-magnet direct-drive wind turbine generatorp5、τi5And Kp6、τi6The proportional coefficient and the integral time constant of the dq-axis voltage loop PI regulator and the current loop PI regulator are respectively. u. ofsd，usqRespectively d-axis and q-axis voltage reference values of the machine side converter,
Figure BDA0001445755580000054
is the machine side converter q-axis current reference value,
Figure BDA0001445755580000055
is the reference value of the DC bus voltage isdAnd isqAre the machine side converter d-axis and q-current reference values.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, through controlling the machine side converter and the grid side converter of the permanent magnet direct-drive wind turbine generator, on the basis of fully considering the converter capacity and the unit operation condition, the given instructions of the positive and negative-sequence dq-axis currents of the grid side converter of the permanent magnet direct-drive wind turbine generator are obtained, so that the permanent magnet direct-drive wind turbine generator can inhibit the voltage unbalance of a grid-connected point and provide active current to a power grid to the maximum extent, and the low-voltage ride through capability of the permanent magnet direct-drive wind turbine generator under the power grid asymmetric fault and the power quality of the power grid connected with the grid are obviously enhanced.
Drawings
Fig. 1 is a schematic structural diagram of a permanent magnet direct-drive wind turbine generator set connected to a power system.
Fig. 2 is a block diagram of an asymmetric fault ride-through control method of the permanent magnet direct-drive wind turbine generator set.
FIG. 3 is a module for calculating the reference values of the positive sequence current and the negative sequence current of the grid-side converter of the permanent magnet direct-drive wind turbine generator system.
Fig. 4 is a simulation waveform diagram of the permanent magnet direct-drive wind turbine generator without the control method and with the control method when the voltage unbalance of the grid-connected point is 12% and the voltage positive sequence component drops to 0.9 pu.
Fig. 5 is a simulation waveform diagram of the permanent magnet direct-drive wind turbine generator without the control method and with the control method when the voltage unbalance of the grid-connected point is 16% and the voltage positive sequence component drops to 0.85 pu.
Detailed Description
The following detailed description of specific embodiments of the invention refers to the accompanying drawings.
Fig. 1 is a schematic structural diagram of a permanent magnet direct-drive wind turbine generator set connected to a power system, wherein the permanent magnet direct-drive wind turbine generator set is connected to a large power grid through a Point of Common Coupling (PCC). When the power grid is in asymmetric fault, the permanent magnet direct-drive wind turbine generator fully utilizes the capacity of a grid-side converter, and provides active current to the power grid to the maximum extent while ensuring that the voltage unbalance degree of a grid-connected point is restrained, so that the fault ride-through capability and the grid-connected electric energy quality of the permanent magnet direct-drive wind turbine generator are improved.
Referring to fig. 2, the control objects of the enhanced low voltage ride through control method of the permanent magnet direct drive wind turbine generator set under the power grid asymmetric fault comprise a direct current link capacitor 1, a machine side converter 2, a grid side converter 3, a space vector modulation module 4, a permanent magnet direct drive wind turbine generator set 5, a voltage sensor 6, a current sensor 7, a grid side converter positive sequence current reference value calculation module 8, a grid side converter negative sequence current reference value calculation module 9, a positive sequence current maximum amplitude calculation module 10, a wave trap 11, a constant power conversion module 12 from a forward synchronous speed rotating coordinate axis system to a static two-phase αβ coordinate axis system, a constant power conversion module 13 from a reverse synchronous angular speed rotating coordinate axis system to a static two-phase αβ coordinate axis system, a constant power conversion module 14 from a static abc three-phase coordinate axis system to a static two-phase αβ coordinate axis system, a constant power conversion module 15 from a static two-phase αβ coordinate axis system to a forward synchronous angular speed rotating coordinate axis system, a constant power conversion module 16 from a static two-phase αβ coordinate axis to a reverse synchronous angular speed rotating coordinate axis system, and a phase-.
The method comprises the following specific implementation steps:
(A) the control steps of the permanent magnet direct-drive wind turbine generator system grid-side converter are as follows:
A1) using voltage sensors 6Collecting wind power plant grid-connected point three-phase voltage signal ugabcAnd a DC bus voltage signal UdcAcquiring three-phase current signals i output by a grid-side converter by using a current sensor 7gabc；
A2) Collected permanent magnet direct-drive wind turbine generator grid-connected point three-phase voltage signal ugabcObtaining the electrical angle theta of the positive sequence voltage vector of the wind power plant grid-connected point after passing through a digital phase-locked loop (P LL) 17gAnd synchronous electrical angular velocity omegae；
A3) Direct-drive permanent magnet wind turbine generator grid-connected point three-phase voltage signal ugabcThe voltage signals are converted into voltage signals under a stationary two-phase αβ coordinate axis system, namely u, through a constant power coordinate conversion module 14 from a stationary three-phase abc coordinate system to a stationary two-phase αβ coordinate axis systemgα、ugβ；
A4) Adopting a direct drive permanent magnet wind turbine generator grid-connected point positive sequence voltage d-axis orientation mode, and enabling the voltage signal u under the static two-phase αβ coordinate axis system obtained in the step A3)gα、ugβPassing through constant power conversion modules 15 and 16 from a static two-phase αβ coordinate axis system to a forward direction and a reverse direction synchronous angular velocity rotating coordinate axis system, and passing through a2 omegaeFiltering by a wave trap 11 to obtain dq axis components of the wind power plant grid-connected point three-phase voltage in the forward and reverse synchronous angular speed rotating coordinate axis system during operation under the condition of asymmetric fault of a power grid, namely
Figure BDA0001445755580000071
A5) Collected three-phase current signals i of the grid-side convertergabcObtaining the current i under the stationary two-phase αβ coordinate axis system through the constant power coordinate transformation module 14 from the stationary three-phase abc coordinate axis system to the stationary two-phase αβ coordinate axis systemgα、igβ；
A6) Outputting current i of the grid-down side converter of the stationary two-phase αβ coordinate axis system obtained in the step A5)gα、igβPassing through constant power conversion modules 15 and 16 from a static two-phase αβ coordinate axis system to a forward direction and a reverse direction synchronous angular velocity rotating coordinate axis system, and passing through a2 omegaeThe wave trap 11 filters to obtain the forward and reverse synchronization of the output current of the grid-side converterThe dq-axis component of the rotating coordinate system of angular velocity, i.e.
Figure BDA0001445755580000072
A7) The dq axis component of the voltage of the grid-connected point of the permanent magnet direct-drive wind turbine generator obtained in the step A4) under the reverse synchronous angular velocity rotating coordinate system, namely
Figure BDA0001445755580000073
The voltage unbalance of the grid-connected point can be restrained to zero by the grid-side converter during the operation period of the asymmetric fault of the power grid according to the following formula, and the output negative sequence current reference value which is not limited is required to be output
Figure BDA0001445755580000074
Figure BDA0001445755580000075
In the formula, Kp1And τi1Respectively calculating a proportional coefficient and an integral time constant of a PI regulator of the module for calculating the reference value of the negative sequence current;
A8) the dq axis components of the wind power plant grid-connected point voltages obtained in the steps A4) and A7) under the forward and reverse synchronous angular speed rotating coordinate systems
Figure BDA0001445755580000076
And a negative sequence current reference value i of the grid-side converter
Figure BDA0001445755580000077
The amplitude of the positive sequence current which can be output by the permanent magnet direct-drive wind power system under the limitation of the negative sequence current can be determined according to the following formula:
Figure BDA0001445755580000078
wherein, | igmaxI is a netThe maximum current amplitude allowed to flow by the side converter;
A9) the dq axis voltage reference value of the permanent magnet direct-drive wind turbine generator grid-side converter obtained in the step A4) under the reverse synchronous angular velocity rotating coordinate system
Figure BDA0001445755580000079
And the dq axis current reference values of the permanent magnet direct-drive wind turbine grid-side converter obtained in the step A6) and the step A8) under the forward and reverse synchronous angular velocity rotating coordinate system
Figure BDA00014457555800000710
Maximum current i allowed by the grid-side converter to operategmaxThe reference values are transmitted to positive and negative sequence current reference value calculation modules 8 and 9 (see figure 3) of the grid-side converter to determine the reference values of the positive and negative sequence current of the grid-side converter
Figure BDA00014457555800000711
The invention relates to a positive sequence current reference value calculation module and a negative sequence current reference value calculation module 8 and 9 of a network side converter, which have the following concrete implementation steps:
a9.1) during the asymmetrical fault operation of the power grid, the reference value of the negative sequence current dq axis of the non-amplitude-limited grid-side converter obtained in the step A7) is utilized
Figure BDA00014457555800000712
Calculating the amplitude of the negative sequence current reference value of the network side converter
Figure BDA00014457555800000713
Amplitude of positive sequence current reference value of sum network side converter
Figure BDA0001445755580000081
Figure BDA0001445755580000082
And the following judgments were made:
Figure BDA0001445755580000083
in the formula (I), the compound is shown in the specification,
Figure BDA0001445755580000084
the d-axis current positive sequence component at the lower net side of a positive synchronous angular velocity rotating coordinate system when the permanent magnet direct-drive wind turbine generator realizes the maximum wind energy tracking,
Figure BDA0001445755580000085
a q-axis current positive sequence component at the lower network side of the forward synchronous angular velocity rotating coordinate system when no reactive power is output;
a9.2) if the constraint condition in a9.1) is satisfied, the grid-side converter positive and negative sequence dq-axis current command values are output as follows:
Figure BDA0001445755580000086
in the formula (I), the compound is shown in the specification,
Figure BDA0001445755580000087
positive and negative sequence dq axis current reference values output by the module are calculated for the positive and negative sequence current reference values of the network side converter;
a9.3) if the constraint condition in A9.1) is not met, judging the amplitude of the negative sequence current reference value of the grid-side converter of the permanent magnet direct-drive wind turbine generator
Figure BDA0001445755580000088
Whether a constraint condition shown as the following formula is satisfied:
Figure BDA0001445755580000089
a9.4) if the constraint condition in A9.3) is met, outputting the positive and negative sequence dq axis current reference values of the grid-side converter according to the following steps:
Figure BDA00014457555800000810
a9.5) if the constraint condition in A9.3) is not satisfied, outputting the positive and negative sequence dq axis current reference values of the grid-side converter according to the following steps:
Figure BDA0001445755580000091
A10) respectively transmitting the positive sequence current reference value and the negative sequence current reference value of the grid-side converter obtained by the calculation in the steps A7) and A9) to a positive sequence current inner loop control link and a negative sequence current inner loop control link of the grid-side converter, and obtaining positive sequence voltage dq and negative sequence voltage dq axial component controlled by a positive synchronous angular speed rotating coordinate system and a negative synchronous angular speed rotating coordinate system of the grid-side converter according to the following formula
Figure BDA0001445755580000092
Figure BDA0001445755580000093
Figure BDA0001445755580000094
In the formula, Kp3And τi3Respectively is the proportional coefficient and the integral time constant, K, of a current inner loop PI controller in a positive sequence control system of a network side converterp4And τi4L are respectively proportional coefficient and integral time constant of a current loop PI controller in a negative sequence control system of the network side convertergThe inductance of an incoming line reactor of the parallel network side converter;
A11) using the positive and negative sequence control voltage dq axis components of the network side converter obtained in the step A10)
Figure BDA0001445755580000095
Figure BDA0001445755580000096
And
Figure BDA0001445755580000097
constant power from rotating coordinate axis system to stationary two-phase αβ coordinate axis system through forward and reverse synchronous angular velocity respectivelyThe transformation modules 12 and 13 obtain positive and negative sequence control voltages under a static two-phase αβ coordinate axis system
Figure BDA0001445755580000098
A12) Controlling the positive and negative sequence control voltage of the network side converter obtained in the step A11)
Figure BDA0001445755580000099
And DC bus voltage UdcGenerating a PWM driving signal of a network side converter through a space vector modulation module 4; so as to restrain the voltage unbalance degree of the power grid;
(B) the control steps of the machine side converter of the permanent magnet direct-drive wind power system are as follows:
B1) the permanent magnet direct-drive wind power system machine side converter 2 adopts a vector control strategy, and the control voltage of the permanent magnet direct-drive wind power system machine side converter adopts space vector pulse width modulation to generate a motor side converter PWM driving signal so as to maintain the stability of the direct current bus voltage of the permanent magnet direct-drive wind power system during the asymmetric fault period. The specific implementation step B1) is as follows:
b1.1) during the asymmetric fault operation of the power grid, setting a voltage reference instruction of a machine side converter as follows:
Figure BDA00014457555800000910
in the formula, #sFor permanent magnet flux linkage, LsIs the stator reactance, ωsFor the synchronous electrical angular velocity, K, of the permanent-magnet direct-drive wind turbine generatorp5、τi5And Kp6、τi6The proportional coefficient and the integral time constant of the dq-axis voltage loop PI regulator and the current loop PI regulator are respectively.
According to the invention, on the premise of not adding hardware equipment, the enhanced low voltage ride through control of the permanent magnet direct-drive wind turbine generator is realized under the condition of asymmetrical faults of a power grid, the voltage unbalance degree of a grid-connected point is inhibited to the greatest extent by fully utilizing the capacity of a grid-side converter of the permanent magnet direct-drive wind turbine generator, and meanwhile, a certain active power is provided for the power grid, so that the non-grid-disconnection safe and stable operation capability of the permanent magnet direct-drive wind turbine generator and the power quality of the power grid connected with the permanent magnet direct-drive wind turbine generator.
Fig. 4 shows that the voltage unbalance of the grid-connected point reaches 12% and the voltage positive sequence component falls to 0.9pu, wherein the PMSG wind power system does not adopt any control strategy for inhibiting the voltage unbalance during 1.5s-2s, and the PMSG system effectively reduces the voltage unbalance of the power grid from 12% to 0 and the voltage waveform recovers symmetry during 2s-2.5s by using the control method provided by the present invention, so that the transient voltage level of the grid-connected point is significantly improved, and at this time, the PMSG still realizes the maximum wind energy tracking control. FIG. 5 shows that the voltage unbalance of the grid-connected point reaches 16% and the voltage positive sequence component falls to 0.85pu, wherein the PMSG wind power system does not adopt any control strategy for inhibiting the voltage unbalance during 1.5s-2s, and the PMSG system can still effectively reduce the voltage unbalance of the power grid from 16% to 0 during 2s-2.5s failure by adopting the control method provided by the invention; at the moment, the PMSG can not realize maximum wind energy tracking control any more, only a GSC current margin is used for outputting a certain active power average value, the voltage unbalance of a grid-connected point is restrained, meanwhile, a certain active support is provided for a power grid, and the grid-connected power quality of a unit is effectively improved.
Finally, it should be noted that the above-mentioned examples of the present invention are only examples for illustrating the present invention, and are not intended to limit the embodiments of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it will be apparent to those skilled in the art that other variations and modifications can be made based on the above description. Not all embodiments are exhaustive. All obvious changes and modifications of the present invention are within the scope of the present invention.

Claims (2)

1. The control method for enhancing the low voltage ride through of the permanent magnet direct-drive wind turbine generator under the asymmetric fault of the power grid is characterized by comprising the following steps: the method relates to the control of a network side converter and a machine side converter of a permanent magnet direct-drive wind turbine generator;
(A) the control steps of the permanent magnet direct-drive wind turbine generator system grid-side converter are as follows:
A1) collecting grid-connected point three-phase power of permanent magnet direct-drive wind turbine generatorPressure signal ugabcThree-phase current signal i output by grid-side convertergabcAnd a DC bus voltage signal Udc；
A2) Collected permanent magnet direct-drive wind turbine generator grid-connected point three-phase voltage signal ugabcObtaining the electrical angle theta of the positive sequence voltage vector of the grid-connected point of the permanent magnet direct-drive wind turbine generator after passing through the digital phase-locked loop P LLgAnd synchronous electrical angular velocity omegae；
A3) Direct-drive permanent magnet wind turbine generator grid-connected point three-phase voltage signal ugabcThrough constant power coordinate transformation from a static three-phase abc coordinate system to a static two-phase αβ coordinate system, the constant power coordinate transformation is converted into a voltage signal under a static two-phase αβ coordinate system, namely ugα、ugβ；
A4) Respectively carrying out the voltage signal u under the stationary two-phase αβ coordinate axis system obtained in the step A3) in a positive sequence voltage d-axis orientation mode of a grid-connected point of a permanent-magnet direct-drive wind turbine generatorgα、ugβConstant power conversion from static two-phase αβ coordinate axis system to forward and reverse synchronous angular speed rotating coordinate axis system, and 2 omega conversioneFiltering by a wave trap to obtain dq axis components of three-phase voltages of grid-connected points of the permanent-magnet direct-drive wind turbine generator in the operation period under the condition of asymmetric faults of a power grid, namely, the dq axis components under a forward and reverse synchronous angular speed rotating coordinate axis system
Figure FDA0002502290690000011
A5) Collected three-phase current signals i of the grid-side convertergabcObtaining output current i under a stationary two-phase αβ coordinate axis system through constant power coordinate transformation from the stationary three-phase abc coordinate axis system to the stationary two-phase αβ coordinate axis systemgα、igβ；
A6) Outputting current i of the grid-down side converter of the stationary two-phase αβ coordinate axis system obtained in the step A5)gα、igβConstant power conversion from static two-phase αβ coordinate axis system to forward and reverse synchronous angular speed rotating coordinate axis system, and 2 omega conversioneFiltering by a wave trap to obtain dq axis components of the output current of the grid-side converter under a forward and reverse synchronous angular velocity rotating coordinate system, namely
Figure FDA0002502290690000012
Figure FDA0002502290690000013
A7) The dq axis component of the voltage of the grid-connected point of the permanent magnet direct-drive wind turbine generator obtained in the step A4) under the reverse synchronous angular velocity rotating coordinate system, namely
Figure FDA0002502290690000014
The voltage unbalance of the grid-connected point can be restrained to zero by the grid-side converter during the operation period of the asymmetrical fault of the power grid according to the following formula, and the output negative sequence current reference value without amplitude limitation is required to be output
Figure FDA0002502290690000015
Figure FDA0002502290690000016
In the formula, Kp1And τi1Respectively calculating a proportional coefficient and an integral time constant of a PI regulator of the module for calculating the reference value of the negative sequence current;
A8) the dq axis component of the voltage of the grid-connected point of the permanent magnet direct-drive wind turbine generator obtained in the step A4) under the forward and reverse synchronous angular velocity rotating coordinate system
Figure FDA0002502290690000017
And the non-amplitude-limited negative sequence current reference value of the network side converter obtained in the step A7)
Figure FDA0002502290690000018
The amplitude of the positive sequence current which can be output by the permanent magnet direct-drive wind turbine generator under the limitation of the negative sequence current is determined according to the following formula:
Figure FDA0002502290690000019
wherein, | igmaxI is the maximum current amplitude allowed to flow by the grid-side converter;
A9) carrying out the dq axis voltage component of the permanent magnet direct-drive wind turbine generator grid-side converter obtained in the step A4) under the reverse synchronous angular velocity rotating coordinate system
Figure FDA0002502290690000021
And the dq axis current components of the permanent magnet direct-drive wind turbine grid-side converter obtained in the step A6) and the step A8) under the forward and reverse synchronous angular velocity rotating coordinate system
Figure FDA0002502290690000022
Maximum current i allowed by the grid-side converter to operategmaxThe reference values are transmitted to a positive sequence current reference value calculation module and a negative sequence current reference value calculation module of the grid-side converter to determine the positive sequence current reference value and the negative sequence current reference value of the grid-side converter
Figure FDA0002502290690000023
A10) Respectively transmitting the positive sequence current reference value and the negative sequence current reference value of the network side converter obtained by calculation in the step A9) to a positive sequence current inner loop control link and a negative sequence current inner loop control link of the network side converter, and obtaining positive sequence control voltage dq axis component and negative sequence control voltage dq axis component of the network side converter under the control of a positive synchronous speed angular speed rotating coordinate system and a reverse synchronous speed rotating coordinate system according to the following formula
Figure FDA0002502290690000024
Figure FDA0002502290690000025
In the formula, Kp3And τi3Respectively is the proportional coefficient and the integral time constant, K, of a current inner loop PI controller in a positive sequence control system of a network side converterp4And τi4Respectively a current loop in a negative sequence control system of a network side converterProportional coefficient and integral time constant of PI controller, LgThe inductance of an incoming line reactor of the network side converter;
A11) using the positive and negative sequence control voltage dq axis components of the network side converter obtained in the step A10)
Figure FDA0002502290690000026
And
Figure FDA0002502290690000027
respectively obtaining positive and negative sequence control voltages under a stationary two-phase αβ coordinate axis system through constant power conversion from a forward synchronous angular velocity rotating coordinate axis system and a reverse synchronous angular velocity rotating coordinate axis system to a stationary two-phase αβ coordinate axis system
Figure FDA0002502290690000028
A12) Controlling the positive and negative sequence control voltage of the network side converter obtained in the step A11)
Figure FDA0002502290690000029
And DC bus voltage UdcGenerating a PWM driving signal of a grid-side converter through space vector modulation so as to inhibit the voltage unbalance degree of a power grid;
(B) the control steps of the permanent magnet direct-drive wind turbine generator side converter are as follows:
B1) the machine side converter of the permanent magnet direct-drive wind turbine generator adopts a vector control strategy, and the control voltage of the machine side converter generates a PWM (pulse width modulation) driving signal through space vector pulse width modulation so as to maintain the stability of the direct current bus voltage of the permanent magnet direct-drive wind turbine generator during the asymmetric fault period;
the step A9) comprises the following steps:
a9.1) during the asymmetrical fault operation of the power grid, the reference value of the negative sequence current dq axis of the non-amplitude-limited grid-side converter obtained in the step A7) is utilized
Figure FDA00025022906900000210
Calculating the amplitude of the negative sequence current reference value of the network side converter
Figure FDA00025022906900000211
Amplitude of positive sequence current reference value of sum network side converter
Figure FDA00025022906900000212
Figure FDA00025022906900000213
And the following judgments were made:
Figure FDA00025022906900000214
in the formula (I), the compound is shown in the specification,
Figure FDA00025022906900000215
the d-axis current positive sequence component at the lower net side of a positive synchronous angular velocity rotating coordinate system when the permanent magnet direct-drive wind turbine generator realizes the maximum wind energy tracking,
Figure FDA00025022906900000216
a q-axis current positive sequence component at the lower network side of the forward synchronous angular velocity rotating coordinate system when no reactive power is output;
a9.2) if the constraint condition in A9.1) is met, outputting the positive and negative sequence dq axis current reference values of the grid-side converter according to the following steps:
Figure FDA0002502290690000031
in the formula (I), the compound is shown in the specification,
Figure FDA0002502290690000032
positive and negative sequence dq axis current reference values output by the module are calculated for the positive and negative sequence current reference values of the network side converter;
a9.3) if the constraint condition in A9.1) is not satisfied, judging the amplitude of the negative sequence current reference value of the grid-side converter of the permanent magnet direct-drive wind turbine generator obtained in the step A9.1)
Figure FDA0002502290690000033
Whether a constraint condition shown as the following formula is satisfied:
Figure FDA0002502290690000034
a9.4) if the constraint condition in A9.3) is met, outputting the positive and negative sequence dq axis current reference values of the grid-side converter according to the following steps:
Figure FDA0002502290690000035
a9.5) if the constraint condition in A9.3) is not satisfied, outputting the positive and negative sequence dq axis current reference values of the grid-side converter according to the following steps:
Figure FDA0002502290690000036
2. the method for controlling the enhanced low voltage ride through of the permanent magnet direct-drive wind turbine generator under the asymmetric fault of the power grid according to claim 1, wherein the step B1) comprises the following steps:
b1.1) during the asymmetric fault operation of the power grid, setting a voltage reference instruction of a machine side converter as follows:
Figure FDA0002502290690000041
in the formula, #sFor permanent magnet flux linkage, LsIs the stator reactance, ωsFor the synchronous electrical angular velocity, K, of the permanent-magnet direct-drive wind turbine generatorp5、τi5And Kp6、τi6Proportional coefficients and integral time constants of the dq-axis voltage loop PI regulator and the current loop PI regulator are respectively set; u. ofsd，usqRespectively d-axis and q-axis voltage reference values of the machine side converter,
Figure FDA0002502290690000042
is the machine side converter q-axis current reference value,
Figure FDA0002502290690000043
is the reference value of the DC bus voltage isdAnd isqAre the machine side converter d-axis and q-current reference values.
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