CN108923443B - Lyapunov coordination control method for DFIG (distributed feed control group) by adopting PGSC (PGSC) and SGSC (SGSC) - Google Patents

Lyapunov coordination control method for DFIG (distributed feed control group) by adopting PGSC (PGSC) and SGSC (SGSC) Download PDF

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CN108923443B
CN108923443B CN201810664090.2A CN201810664090A CN108923443B CN 108923443 B CN108923443 B CN 108923443B CN 201810664090 A CN201810664090 A CN 201810664090A CN 108923443 B CN108923443 B CN 108923443B
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CN108923443A (en
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程启明
程尹曼
陈路
孙伟莎
李涛
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Shanghai University of Electric Power
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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
    • H02J3/26—Arrangements for eliminating or reducing asymmetry in polyphase 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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H02J3/386—
    • 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
    • Y02E40/40—Arrangements for reducing harmonics
    • 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

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Abstract

The invention relates to a Lyapunov coordination control method for a DFIG (doubly Fed Generator) by adopting a PGSC (grid tied capacitor) and an SGSC (doubly Fed Generator), which is characterized in that a series transformer and the SGSC are added on the side of a DFIG stator, the secondary of the series transformer is connected between the DFIG stator and a power grid in series, the input end of the SGSC is connected with the input end of the PGSC, the output end of the SGSC is connected with the primary end of the series transformer through an inductor L, the SGSC adopts Lyapunov-based control, double-frequency harmonic waves of the PGSC can be counteracted by utilizing harmonic waves generated by the SGSC, the stator voltage is easy to control, so that the suppression of double-frequency fluctuation of the total output power of a system is realized, the influence of unbalanced grid voltage on an RSC system is reduced, the ride-through operation capability of the unbalanced grid voltage of the RSC system is improved, and the global stability of the system is realized at the same time. Compared with the prior art, the method has the advantages of high response speed, strong robustness, few control parameters and the like. Compared with the prior art, the invention has the advantages of and the like.

Description

Lyapunov coordination control method for DFIG (distributed feed control group) by adopting PGSC (PGSC) and SGSC (SGSC)
Technical Field
The invention relates to a distributed power generation control technology, in particular to a Lyapunov coordination control method for DFIG (distributed generation control) by adopting PGSC (PGSC) and SGSC (SGSC).
Background
Along with the increase of the influence of the wind turbine generator on the stability of the power system, the wind turbine generator is guaranteed not to run off the grid when the voltage of the power grid is unbalanced. Among the wind power generators, Doubly Fed Induction Generators (DFIGs) are widely used due to their relatively low cost. The Rotor of the DFIG employs two PWM converters, namely a Rotor-Side Converter (RSC) and a Grid-Side Converter (GSC). Because the two converters are connected with the large capacitor through the middle direct current bus, the independent decoupling control of the network side can be realized through the network side converter, the control target of the network side is obtained, and the control quality is improved. The existing doubly-fed asynchronous motor has low response speed and low robustness due to the fact that the stator voltage is difficult to control.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a Lyapunov coordination control method for DFIG adopting PGSC and SGSC.
The purpose of the invention can be realized by the following technical scheme:
a Lyapunov coordination control method of a DFIG (doubly fed induction generator) adopting PGSC (grid generator) and SGSC (doubly fed induction generator) is used for carrying out coordination control on a generator side converter and a grid side converter of the DFIG under the condition of unbalanced grid voltage, RSC and parallel grid side converters (parallel GSC, PGSC) connected with the RSC are adopted in a rotor of the DFIG, the two converters are connected with a large capacitor through a middle direct-current bus, a series transformer and a series grid side converter (series GSC, SGSC) are added on the stator side of the DFIG, a secondary side of the series transformer is connected between a stator of the DFIG and a grid in series, an input end of the SGSC is connected with an input end of the PGSC, an output end of the SGSC is connected with a primary side of the series transformer through an inductor L, and the method for carrying out coordination control on the generator side converter and the grid side converter of the DFIG comprises the specific steps of:
s1: and (3) establishing a positive sequence model and a negative sequence model for the SGSC by adopting Lyapunov-based coordinated control, and calculating a control target of the SGSC and network side current reference values under different control targets.
The control objectives of the SGSC are:
positive sequence component u of stator side voltage of DFIGs+With positive sequence component u of the network voltageg+Always consistent, and controls the negative sequence component u of the voltage at the stator sides-To zero, i.e.:
Figure GDA0003231694330000021
the instantaneous power S output to the PGSC by the power grid under the voltage unbalance is arranged into a matrix form as follows:
Figure GDA0003231694330000022
in the formula, onThe indices p, n represent positive and negative sequence components, respectively, the indices d, q represent dq axis components, +, -represent positive and negative directions of the coordinate axes, respectively,
Figure GDA0003231694330000023
the net side voltage components of the positive sequence component on the d-axis and q-axis of the positive coordinate system respectively,
Figure GDA0003231694330000024
the net side voltage components of the negative sequence component on the d axis and the q axis of the negative transfer coordinate system respectively,
Figure GDA0003231694330000025
the net side current components of the positive sequence component on the d axis and the q axis of the positive coordinate system respectively,
Figure GDA0003231694330000026
the network side current components of the negative sequence component on the d axis and the q axis of the positive coordinate system are respectively shown, subscripts g _ av, g _ sin2 and g _ cos2 respectively represent a direct current component, a frequency-doubled sine component and a frequency-doubled cosine component of PGSC power, and P, Q respectively represent active power and reactive power.
The control targets of the SGSC include:
the first target is: the current input at the net side does not contain a negative sequence component, namely:
Figure GDA0003231694330000027
Figure GDA0003231694330000028
in the formula, subscripts series _ av, series _ sin2 and series _ cos2 represent a direct current component, a frequency-doubled sine component and a frequency-doubled cosine component of the SGSC power respectively;
and a second target: the network side input active power only contains a direct current component, namely:
Pg_sin2-Pseries_sin2＝0，Pg_cos2-Pseries_cos2＝0
Figure GDA0003231694330000031
wherein D is1、D2Are respectively:
Figure GDA0003231694330000032
Figure GDA0003231694330000033
if u is to beg+Oriented on d-axis by regulating the DC voltage UdcThe regulator ensures that the voltage value has no harmonic wave, and the instantaneous power of the direct current bus capacitor of the system is the sum of the instantaneous power of PGSC instantaneous power minus RSC and SGSC, namely:
Figure GDA0003231694330000034
in the formula: pg、PseriesInput power, P, of PGSC, SGSC, respectivelyrThe output power of the rotor side is C, and the capacitance of the direct current bus is C;
u under the condition of stable operation of power griddcIncluding a DC voltage average component and a ripple component dUdcTwo parts of/dt, namely:
Udc＝Udc_av+dUdc/dt＝Udc_av+1/2ωUdc_av[(Pg_sin2-Pseries_sin2)+(Pg_cos2-Pseries_cos2)]
and a third target: DC bus voltage without frequency doubling sine udc_sin2Cosine component udc_cos2Namely:
udc_sin2＝udc_cos2＝0
Figure GDA0003231694330000041
and a fourth target: the reactive power input by the network side only contains a direct current component, namely:
Qg_sin2-Qseries_sin2＝0，Qg_cos2-Qseries_cos2＝0
Figure GDA0003231694330000042
s2: and controlling the AC component at the SGSC side by adopting a PIR controller.
The transfer function for controlling the AC component at the SGSC side by adopting the PIR controller is as follows:
Figure GDA0003231694330000043
in the formula: kpAnd KiRespectively is a proportionality coefficient and an integral coefficient; krIs the resonance coefficient of the resonance regulator; omegacIs the cut-off frequency.
S3: and controlling the PGSC by adopting a Lyapunov controller.
The net-side Lyapunov positive sequence model is as follows:
Figure GDA0003231694330000044
where ω is the grid angular frequency, LgBeing the inductance of a filter reactor, RgIs the sum of the impedance on the line and the equivalent series resistance of the inductor, and:
Figure GDA0003231694330000051
Figure GDA0003231694330000052
in the formula, x1、x2The difference value x between the actual value and the instruction value of the current component of the positive sequence component on the net side of the d axis and the q axis of the positive coordinate system3Is the difference between the actual value and the command value of the DC bus voltage, udc、
Figure GDA0003231694330000053
Respectively an actual value, a command value, S of the DC bus voltaged、
Figure GDA0003231694330000054
Δ d is the actual value, the command value and the difference between the two, S, of the d-axis switching function, respectivelyq、
Figure GDA0003231694330000055
Δ q is an actual value, a command value and a difference value between the actual value and the command value of the q-axis switching function respectively;
constructing a Lyapunov function energy function as follows:
Figure GDA0003231694330000056
the derivative of the Lyapunov function energy function is:
Figure GDA0003231694330000057
when x is not 0, V (x) > 0, dV (x)/dt > 0, assuming:
Figure GDA0003231694330000058
Figure GDA0003231694330000059
Figure GDA00032316943300000510
Figure GDA00032316943300000511
Figure GDA00032316943300000512
in the formula, beta1、β2For the scaling factor, ignoring ripple, the ripple value of the switching function is taken as:
Figure GDA00032316943300000513
in the formula, alpha1、α2Two proportionality coefficients are respectively;
dV (x)/dt can be expressed as:
Figure GDA0003231694330000061
in the formula:
Figure GDA0003231694330000062
Figure GDA0003231694330000063
let z3＝m1z1＝m2z2And m is1、m2>0, then:
Figure GDA00032316943300000610
Figure GDA00032316943300000611
in the formula, λ1min(r1,β1,m1) > 0 is related to the independent variable m1A quadratic function of (a)2min(r2,β2,m2) > 0 is related to the independent variable m2A quadratic function of (a);
when getting m1(0)＝(1+β1)/(2β1) The method comprises the following steps:
λ1min(r1,β1,m1)＝Rg+r1[1-(1+β1)2/(4β1)]
in the same way, when m is taken2(0)＝(1+β2)/(2β2) The method comprises the following steps:
λ2min(r2,β2,m2)＝Rg+r2[1-(1+β2)2/(4β2)]
when in use
Figure GDA0003231694330000064
When is lambda1min(r1,β1,m1) > 0, beta0＝1+2Rg/r1；
For a desired uncertainty interval 1-epsilon < beta1＜1+ε，1-ε＜β2< 1+ ε, and
Figure GDA0003231694330000065
Figure GDA0003231694330000066
then alpha can be deduced1、α2The value range is as follows:
Figure GDA0003231694330000067
then the positive sequence control is derived as:
Figure GDA0003231694330000068
the same reasoning can be concluded that negative sequence control is:
Figure GDA0003231694330000069
s4: RSC is controlled by adopting inner ring Lyapunov control and outer ring PI control.
Compared with the prior art, the invention has the following advantages:
(1) the invention has fast response speed, strong robustness and few control parameters;
(2) according to the invention, the harmonic generated by the SGSC is utilized to offset the double-frequency harmonic of the PGSC, and the stator voltage is easy to control, so that the suppression of the double-frequency fluctuation of the total output power of the system is realized, the influence of the unbalanced grid voltage on the RSC system is reduced, the ride-through operation capability of the unbalanced grid voltage of the RSC system is improved, and the overall stability and robustness of the system are improved.
Drawings
FIG. 1 is a diagram of a topology of a DFIG system employing an SGSC;
FIG. 2 is a block diagram of a network-side converter;
FIG. 3 is a block diagram of a SGSC based DFIG coordination control;
fig. 4 is a simulation result diagram when the first to fourth control targets are selected on the network side and the fourth control target is selected on the rotor side, where fig. 4(a) is a simulation result diagram of rotor current and fig. 4(b) is a simulation result diagram of stator side power; FIG. 4(c) is a diagram showing the results of electromagnetic torque simulation;
FIG. 5 is a DC bus voltage waveform diagram under three control strategies of SGSC + PID control, Lyapunov control and SGSC + Lyapunov control;
FIG. 6 is a net side current waveform diagram controlled by SGSC + PID;
FIG. 7 is a net side current waveform diagram using Lyapunov control;
FIG. 8 is a network side current waveform diagram of an SGSC + Lyapunov control strategy;
fig. 9 is a waveform diagram of network-side active power under three control strategies of SGSC + PID control, Lyapunov control, and SGSC + Lyapunov control;
fig. 10 is a network side reactive power waveform diagram under three control strategies of SGSC + PID control, Lyapunov control, and SGSC + Lyapunov control.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments.
Examples
Fig. 1 is a topological structure diagram of a DFIG system using SGSC. Compared with a classical double-fed fan system, the topological structure of the system has the advantage that a series transformer and a series network side converter (series GSC, SGSC) are additionally arranged on the stator side of the fan. The secondary of the series transformer is connected in series between a fan stator and a power grid, the input end of the SGSC of the series network side converter is connected with the input end of a parallel network side converter (parallel GSC, PGSC), the output end of the SGSC of the series network side converter is connected with the primary of the series transformer through an inductor L, the added SGSC can inject proper series compensation voltage into a stator loop to counteract the negative sequence voltage of the stator and can also control the SGSC to inject a positive sequence compensation voltage vector into the stator loop to eliminate the influence of the leakage impedance voltage drop of the series transformer on the stator voltage of the DFIG, thereby ensuring the positive sequence component u of the stator voltage of the DFIGs+With positive sequence component u of the network voltageg+The same is true. The output control voltage vector of the SGSC under the unbalanced network voltage is as follows:
useries＝ucom+-ug-
in the formula useriesIs the output voltage of the series transformer; u. ofcom+A positive sequence voltage vector to be compensated for the SGSC; u. ofg-Is the negative sequence component of the grid voltage.
FIG. 2 is a block diagram of a network-side converter, in which ua、ub、ucFor the mains voltage, va、vb、vcIs GSC AC side voltage, RgIs the sum of the line impedance and the equivalent series resistance of the inductor, LgFor filtering inductance, i, at the output of GSCa、ib、icFor GSC input current, C is the capacitance of the DC bus, udcIs straightVoltage of the current busbar, iloadThe current flowing to RSC is on the net side.
The positive and negative sequence mathematical models of PGSC on dq axis are:
Figure GDA0003231694330000081
Figure GDA0003231694330000082
Figure GDA0003231694330000083
in the formula, superscripts p and n respectively represent positive and negative sequence components, subscripts d and q respectively represent dq axis components, and +, -respectively represent positive and reverse directions of coordinate axes;
Figure GDA0003231694330000084
and
Figure GDA0003231694330000085
respectively a network side voltage component, a GSC alternating current side voltage component and a network side current component of the positive sequence component on a d axis and a q axis of a positive rotation coordinate system;
Figure GDA0003231694330000086
and
Figure GDA0003231694330000087
respectively a network side voltage component, a GSC alternating current side voltage component and a network side current component of the negative sequence component on a d axis and a q axis of a negative transfer coordinate system; and omega is the angular frequency of the power grid.
If the state variables defining the positive sequence closed loop system are:
Figure GDA0003231694330000088
Figure GDA0003231694330000091
the positive order math block could instead:
Figure GDA0003231694330000092
for SGSC, there are:
Figure GDA0003231694330000093
for PGSC, the PGSC outputs a negative sequence current component, the power of which multiplied by the voltage across it must have a double frequency, that is:
Figure GDA0003231694330000094
in the formula: the subscript "g _ av" represents the average component of power; "g _ sin2, g _ cos 2" represent the sine and cosine of the wave component. The amplitude of each power component in the above equation is expressed in a matrix form:
Figure GDA0003231694330000095
according to the analysis, in the DFIG wind power control system, because the double-frequency oscillation in the output power of the SGSC and the PGSC accounts for a certain proportion, the output power of the whole structure necessarily contains oscillation components, and serious threats can be brought to safe and stable operation of a power grid and electric energy quality. Meanwhile, the active power in the middle dc bus capacitor C includes the amount of SGSC and PGSC injected into it, and therefore, the stability of the dc link voltage must be disturbed. Based on the above, the invention provides a Lyapunov coordination control method for DFIG adopting PGSC and SGSC, which specifically comprises the following steps:
step S1: and establishing a positive-negative sequence model of the converter structure of the series network side based on the coordination control of the Lyapunov control strategy according to the unbalanced voltage condition of the power grid, and calculating a control target of the converter of the series network side and network side current reference values under different control targets.
The control objectives of the SGSC are: positive sequence component u of stator side voltage of DFIGs+With positive sequence component u of the network voltageg+Always consistent, and controls the negative sequence component u of the voltage at the stator sides-To zero, i.e.:
Figure GDA0003231694330000101
the instantaneous power S output to the PGSC under the voltage unbalance by the power grid is arranged into a matrix form as follows:
Figure GDA0003231694330000102
in the formula, subscripts g _ av, g _ sin2, and g _ cos2 represent a direct current component, a frequency-doubled sine component, and a frequency-doubled cosine component of PGSC power, respectively.
The first target is: the current input at the net side does not contain a negative sequence component, namely:
Figure GDA0003231694330000103
Figure GDA0003231694330000104
in the formula, subscripts series _ av, series _ sin2 and series _ cos2 represent a direct current component, a frequency-doubled sine component and a frequency-doubled cosine component of the SGSC power respectively;
and a second target: the network side input active power only contains a direct current component, namely:
Pg_sin2-Pseries_sin2＝0，Pg_cos2-Pseries_cos2＝0
Figure GDA0003231694330000111
wherein D is1、D2Are respectively:
Figure GDA0003231694330000112
Figure GDA0003231694330000113
if u is to beg+Oriented in the d-axis, usually by regulating the DC voltage UdcThe regulator of (2) ensures that the voltage value is free of harmonics. As can be seen from fig. 1, the instantaneous power of the dc bus capacitor of the system is PGSC instantaneous power minus the sum of instantaneous power of both RSC and SGSC, that is:
Figure GDA0003231694330000114
in the formula: pg、PseriesInput power, P, of PGSC, SGSC, respectivelyrIs the output power on the rotor side. U under the condition of stable operation of power griddcIncluding a DC voltage average component and a ripple component dUdcTwo parts of/dt, namely:
Udc＝Udc_av+dUdc/dt＝Udc_av+1/2ωUdc_av[(Pg_sin2-Pseries_sin2)+(Pg_cos2-Pseries_cos2)]
from the above equation, the second harmonic ripple of the dc bus voltage can be suppressed to some extent even if the PGSC target two is satisfied.
And a third target: DC bus voltage without frequency doubling sine udc_sin2Cosine component udc_cos2Namely:
udc_sin2＝udc_cos2＝0
Figure GDA0003231694330000121
and a fourth target: the reactive power input by the network side only contains a direct current component, namely:
Qg_sin2-Qseries_sin2＝0，Qg_cos2-Qseries_cos2＝0
Figure GDA0003231694330000122
step S2: because the traditional PI control has certain limit on the bandwidth of the regulator, the Proportional Integral Resonance (PIR) controller is adopted to realize effective control on the AC component at the SGSC side, and the phase sequence separation is not needed, so that the transient performance of the system is improved. Its transfer function can be expressed as:
Figure GDA0003231694330000123
in the formula: kpAnd KiRespectively are proportional and integral coefficients; krIs the resonance coefficient of the resonance regulator; omegacIs the cut-off frequency.
Step S3: and controlling the PGSC by adopting a Lyapunov controller.
The net-side Lyapunov positive sequence model is as follows:
Figure GDA0003231694330000124
in the formula:
Figure GDA0003231694330000131
Figure GDA0003231694330000132
constructing a Lyapunov function energy function as follows:
Figure GDA0003231694330000133
the derivative of the Lyapunov function energy function is:
Figure GDA0003231694330000134
when x is not 0, V (x) > 0, dV (x)/dt > 0, and therefore the Lyapunov global progressive stability condition is satisfied.
For the inaccuracy problem of the reference value x, assume:
Figure GDA0003231694330000135
Figure GDA0003231694330000136
Figure GDA0003231694330000137
Figure GDA0003231694330000138
Figure GDA0003231694330000139
ignoring the ripple, the ripple value of the switching function is taken as:
Figure GDA00032316943300001310
dV (x)/dt can be expressed as:
Figure GDA00032316943300001311
in the formula:
Figure GDA0003231694330000141
Figure GDA0003231694330000142
from the above formula, the function f1、f2Must be greater than zero to ensure dv (x)/dt > 0. Let z3＝m1z1＝m2z2And m is1、m2>0, then:
Figure GDA0003231694330000149
Figure GDA00032316943300001410
in the formula, λ1min(r1,β1,m1) > 0 is related to the independent variable m1A quadratic function of (a)2min(r2,β2,m2) > 0 is related to the independent variable m2Is a quadratic function of (a).
When getting m1(0)＝(1+β1)/(2β1) The method comprises the following steps:
λ1min(r1,β1,m1)＝Rg+r1[1-(1+β1)2/(4β1)]
in the same way, when m is taken2(0)＝(1+β2)/(2β2) The method comprises the following steps:
λ2min(r2,β2,m2)＝Rg+r2[1-(1+β2)2/(4β2)]
when in use
Figure GDA0003231694330000143
When is lambda1min(r1,β1,m1) > 0, beta0＝1+2Rg/r1. Therefore, when r1The asymptotic stability of the uncertainty interval is greatest at the lowest.
For a desired uncertainty interval 1-epsilon < beta1＜1+ε，1-ε＜β2< 1+ ε, and
Figure GDA0003231694330000144
Figure GDA0003231694330000145
then alpha can be deduced1、α2The value range is as follows:
Figure GDA0003231694330000146
this can be extrapolated to positive sequence control:
Figure GDA0003231694330000147
the same reasoning can be concluded that negative sequence control is:
Figure GDA0003231694330000148
step S4: FIG. 3 is a block diagram of coordination control of the DFIG side and the grid side based on the SGSC. In the figure, 3s/2r is the operation from three-phase stationary to two-phase rotation. For RSC, due to the special structure of the grid-connected DFIG, even under the condition of unbalanced power grid, the terminal voltage of the DFIG is still symmetrical, so that the vector strategy of inner ring Lyapunov control and outer ring PI control similar to PGSC is adopted for RSC.
In the embodiment, simulation research is carried out on the feasibility and the effectiveness of the control method of the DFIG adopting the combination of the SGSC and the Lyapunov in an MATLAB/Simulink simulation platform. The given power grid voltage unbalance degree of the system is 15%, and the main simulation parameter values of the doubly-fed motor are shown in table 1; the control parameters for PIR in the voltage loop for SGSC and PGSC are shown in table 2.
Table 1 main simulation parameters of a doubly-fed machine
Figure GDA0003231694330000151
TABLE 2 control parameters for PIR in voltage loop for SGSC and PGSC
Figure GDA0003231694330000152
In order to prove the superiority of the control method adopting combination of SGSC and Lyapunov, simulation comparison is respectively carried out on three control methods, namely SGSC and Lyapunov combined control, SGSC and PI combined control only and Lyapunov only, which are provided by the invention. During the period of time t being 0-0.4 s, three control strategies are adopted to realize operation under unbalanced power grid, and four different control targets are realized in different periods, namely:
1) t is 0-0.1 s: selecting a first control target to eliminate a negative sequence component of the current on the network side;
2) t is 0.1-0.2 s: operating according to the control target II to eliminate the network side active power double frequency;
3) t is 0.2-0.3 s: operating according to the control target III to eliminate the double frequency of the direct current bus voltage;
4) t is 0.3-0.4 s: and controlling the target four to eliminate the network side reactive power double frequency.
In addition, the rotor side selects a control target: the constant electromagnetic torque reduces the mechanical load on the wind system shaft.
The specific experimental effects are as follows:
fig. 4(a), 4(b), and 4(c) are graphs showing simulation results of the rotor current, the stator-side power, and the electromagnetic torque when the grid-side selection control target one to the target four and the rotor-side selection control target four are selected, respectively. A, B, C in FIG. 4(a) show three phases, respectively, and as can be seen from FIG. 4(a), the requirement of eliminating the negative sequence component of the grid-side current can be achieved; as can be seen from fig. 4(b), 4(c), the goal of eliminating harmonics of the doubly fed electromechanical torque and the stator output reactive power can be achieved.
Fig. 5 shows dc bus voltage waveforms under three control strategies. It can be seen that under the same voltage imbalance condition, when the control target is selected, the dc bus voltage reaches a stable value of 700V at 20ms under the SGSC + PID control strategy, whereas with Lyapunov and the control strategy herein, it is stable at 3.2 ms. When the control targets two to four are selected, the oscillation of the control strategy is smaller and the waveform is smoother than that of the control strategies of the two previous control strategies. Therefore, the control strategy provided by the patent can increase the bandwidth, accelerate the response speed and improve the anti-interference capability of the system.
Comparing fig. 6, fig. 7 and fig. 8, it can be known that, under the control target, the SGSC + PID control strategy is adopted, the overshoot is large when the current value on the network side is 0-0.06 s, which easily causes the converter to be saturated, and the Lyapunov control strategy and the control strategy in this text are adopted without overshoot; the effects of the three control strategies are similar under control objectives two and three. When the control target is selected, the current on the network side reaches relative balance when being 0.35s under the first control strategy, the Lyapunov control is balanced with the control strategy provided by the invention when being 0.32s, but the two-phase drop currents in the separate Lyapunov control strategies are respectively 15.5A and 15.9A and do not reach complete balance like the control strategy provided by the invention. Therefore, the control strategy of the patent has obvious advantages in both dynamic response speed and stability.
Table 3 is a table of the ratio of the active and reactive double frequency harmonic ripple components to the average power when three control strategies are employed under four different control objectives. Fig. 9 and fig. 10 are waveform diagrams of active power and reactive power of the grid side under three control methods, respectively. As can be seen from comparison of fig. 9, fig. 10 and table 3, under the control target one to target four, compared with the SGSC + PID control and the Lyapunov control, the active and reactive adjustment time, overshoot and harmonic content under the SGSC + Lyapunov control strategy provided herein are smaller. Therefore, the network side power of the control method proposed by the patent is superior to the first two control methods in control performance.
TABLE 3 ratio of active and reactive double-frequency harmonic ripple component to average power for three control methods
Figure GDA0003231694330000161
Figure GDA0003231694330000171
While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and those skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (2)

1. A Lyapunov coordination control method for a DFIG (doubly fed induction generator) adopting PGSC (grid generator converter) and SGSC (grid side converter), wherein the PGSC is a parallel grid side converter, the SGSC is a series grid side converter and is used for carrying out coordination control on a machine side converter and a grid side converter of the DFIG under the condition of unbalanced grid voltage, the method is characterized in that RSC and PGSC (grid side converter) connected with the RSC in parallel are adopted for a rotor of the DFIG, the two converters are connected with a large capacitor through a middle direct current bus, a series transformer and an SGSC (grid side converter) are added on a stator side of the DFIG, a secondary side of the series transformer is connected between a stator of the DFIG and a grid in series, an input end of the SGSC is connected with an input end of the PGSC, and an output end of the SGSC is connected with a primary side of the series transformer through an inductor L, and the method comprises the specific steps of carrying out coordination control on the machine side converter and the grid side converter of the DFIG, wherein:
1) establishing a positive sequence model and a negative sequence model for the SGSC by adopting Lyapunov-based coordinated control, and calculating a control target of the SGSC and network side current reference values under different control targets;
2) controlling an alternating current component at the SGSC side by adopting a PIR controller;
3) a Lyapunov controller is adopted to control PGSC;
4) RSC is controlled by adopting inner ring Lyapunov control and outer ring PI control;
in step 1), the control targets of the SGSC are:
positive sequence component u of stator side voltage of DFIGs+With positive sequence component u of the network voltageg+Always consistent, and controls the negative sequence component u of the voltage at the stator sides-To zero, i.e.:
Figure FDA0003374366380000011
the instantaneous power S output to the PGSC by the power grid under the voltage unbalance is arranged into a matrix form as follows:
Figure FDA0003374366380000012
in the formula, the superscripts p and n represent positive and negative sequence components respectively, the subscripts d and q represent dq axis components, and + and-represent positive and negative directions of coordinate axes respectively,
Figure FDA0003374366380000013
the net side voltage components of the positive sequence component on the d-axis and q-axis of the positive coordinate system respectively,
Figure FDA0003374366380000014
the net side voltage components of the negative sequence component on the d axis and the q axis of the negative transfer coordinate system respectively,
Figure FDA0003374366380000021
the net side current components of the positive sequence component on the d axis and the q axis of the positive coordinate system respectively,
Figure FDA0003374366380000022
the network side current components of the negative sequence component on the d axis and the q axis of the positive rotation coordinate system are respectively shown, subscripts g _ av, g _ sin2 and g _ cos2 respectively represent a direct current component, a frequency-doubled sine component and a frequency-doubled cosine component of PGSC power, and P, Q respectively represent active power and reactive power;
the control targets of the SGSC include:
the current of the first target and the net side input does not contain a negative sequence component, namely:
Figure FDA0003374366380000023
Figure FDA0003374366380000024
in the formula, subscripts series _ av, series _ sin2 and series _ cos2 represent a direct current component, a frequency-doubled sine component and a frequency-doubled cosine component of the SGSC power respectively;
Figure FDA0003374366380000025
is the negative sequence component of the net side current on the dq axis of the negative coordinate system,
Figure FDA0003374366380000026
is the negative sequence component of the stator side current on the dq axis of the negative coordinate system;
and a second target, namely, the network side input active power only contains a direct current component, namely:
Pg_sin2-Pseries_sin2＝0，Pg_cos2-Pseries_cos2＝0
Figure FDA0003374366380000027
wherein D is1、D2Are respectively:
Figure FDA0003374366380000028
Figure FDA0003374366380000031
if u is to beg+Oriented on d-axis by regulating the DC voltage UdcThe regulator ensures that the voltage value has no harmonic wave, and the instantaneous power of the direct current bus capacitor of the system is the sum of the instantaneous power of PGSC instantaneous power minus RSC and SGSC, namely:
Figure FDA0003374366380000032
in the formula: pg、PseriesInput power, P, of PGSC, SGSC, respectivelyrThe output power of the rotor side is C, and the capacitance of the direct current bus is C;
u under the condition of stable operation of power griddcIncluding a DC voltage average component and a ripple component dUdcTwo parts of/dt, namely:
Udc＝Udc_av+dUdc/dt＝Udc_av+1/2ωUdc_av[(Pg_sin2-Pseries_sin2)+(Pg_cos2-Pseries_cos2)]
in the formula, omega is the angular frequency of the power grid; u. ofdc_avIs a DC voltage udcThe average component of;
target three, DC bus voltage does not contain frequency doubling sine udc_sin2Cosine component udc_cos2Namely:
udc_sin2＝udc_cos2＝0
Figure FDA0003374366380000033
and target four, reactive power input by the network side only contains a direct-current component, namely:
Qg_sin2-Qseries_sin2＝0，Qg_cos2-Qseries_cos2＝0
Figure FDA0003374366380000034
the specific content of the step 3) is as follows:
the net-side Lyapunov positive sequence model is as follows:
Figure FDA0003374366380000041
where ω is the grid angular frequency, LgBeing the inductance of a filter reactor, RgIs the sum of the impedance on the line and the equivalent series resistance of the inductor, and:
Figure FDA0003374366380000042
Figure FDA0003374366380000043
in the formula, x1、x2The difference value x between the actual value and the instruction value of the current component of the positive sequence component on the net side of the d axis and the q axis of the positive coordinate system3Is the difference between the actual value and the command value of the DC bus voltage, udc、
Figure FDA0003374366380000044
Respectively an actual value, a command value, S of the DC bus voltaged、
Figure FDA0003374366380000045
Δ d is the actual value, the command value and the difference between the two, S, of the d-axis switching function, respectivelyq、
Figure FDA0003374366380000046
Δ q is an actual value, a command value and a difference value between the actual value and the command value of the q-axis switching function respectively;
constructing a Lyapunov function energy function as follows:
Figure FDA0003374366380000047
the derivative of the Lyapunov function energy function is:
Figure FDA0003374366380000048
when x is not 0, V (x) > 0, dV (x)/dt > 0, assuming:
Figure FDA0003374366380000049
Figure FDA00033743663800000410
Figure FDA00033743663800000411
Figure FDA0003374366380000051
Figure FDA0003374366380000052
in the formula, z1The ratio of the difference value between the actual value and the command value of the current on the d-axis network side of the positive sequence component in the positive rotation coordinate system to the actual value is obtained; z is a radical of2Is divided into positive sequenceMeasuring the ratio of the difference value between the actual value and the command value of the q-axis network side current in the forward coordinate system to the actual value; z is a radical of3The ratio of the difference value between the actual value and the command value of the direct current bus voltage to the actual value; beta is a1、β2For the scaling factor, ignoring ripple, the ripple value of the switching function is taken as:
Figure FDA0003374366380000053
in the formula, alpha1、α2Two scaling factors, dv (x)/dt, can be expressed as:
Figure FDA0003374366380000054
in the formula:
Figure FDA0003374366380000055
Figure FDA0003374366380000056
let z3＝m1z1＝m2z2And m is1、m2>0, then:
Figure FDA00033743663800000511
Figure FDA00033743663800000512
in the formula, λ1min(r1,β1,m1) > 0 is related to the independent variable m1A quadratic function of (a)2min(r2,β2,m2) > 0 is related to the independent variable m2A quadratic function of (a);
when getting m1(0)＝(1+β1)/(2β1) The method comprises the following steps:
λ1min(r1,β1,m1)＝Rg+r1[1-(1+β1)2/(4β1)]
in the same way, when m is taken2(0)＝(1+β2)/(2β2) The method comprises the following steps:
λ2min(r2,β2,m2)＝Rg+r2[1-(1+β2)2/(4β2)]
when in use
Figure FDA0003374366380000057
When is lambda1min(r1,β1,m1) > 0, beta0＝1+2Rg/r1；
For a desired uncertainty interval 1-epsilon < beta1＜1+ε，1-ε＜β2< 1+ ε, and
Figure FDA0003374366380000058
Figure FDA0003374366380000059
then alpha can be deduced1、α2The value range is as follows:
Figure FDA00033743663800000510
then the positive sequence control is derived as:
Figure FDA0003374366380000061
the same reasoning can be concluded that negative sequence control is:
Figure FDA0003374366380000062
2. the Lyapunov coordinated control method for DFIG adopting PGSC and SGSC according to claim 1, wherein in step 2), the transfer function for controlling the ac component at the SGSC side by using the PIR controller is:
Figure FDA0003374366380000063
in the formula: kpAnd KiRespectively is a proportionality coefficient and an integral coefficient; krIs the resonance coefficient of the resonance regulator; omegacIs the cut-off frequency.
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