CN106452263A

CN106452263A - A Sliding Mode Variable Structure Direct Power Control Method Based on DFIG Expanded Active Power in Unbalanced Grid

Info

Publication number: CN106452263A
Application number: CN201611032917.5A
Authority: CN
Inventors: 孙丹; 王霄鹤; 蒋天龙
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2016-11-15
Filing date: 2016-11-15
Publication date: 2017-02-22
Anticipated expiration: 2036-11-15
Also published as: CN106452263B

Abstract

The invention discloses an extended active power-based sliding mode variable structure direct power control (DPC) method for a DFIG in an unbalanced power grid. Extended active power is provided on the basis of a mathematical model of the DFIG in the unbalanced power grid, the extended active power and conventional reactive power are taken as control objects, a sliding mode variable structure algorithm and a DPC technology are combined, and an improved extended active power-based sliding mode variable structure DPC strategy is further provided. According to the method, the DFIG in the unbalanced power grid can be effectively controlled to obtain stable electromagnetic torque and reactive power as well as sinusoidal stator current on the premise of no positive and negative sequence separation of the voltage and current of the power grid; control can be systematically implemented simply without monitoring the frequency of the voltage of the power grid in real time by a phase-locked loop.

Description

Under a kind of unbalanced power grid, DFIG is direct based on the sliding moding structure expanding active power Poewr control method

Technical field

The invention belongs to motor control technology field is and in particular to DFIG is based on expansion wattful power under a kind of unbalanced power grid The sliding moding structure direct Power Control method of rate.

Background technology

Modern wind electricity generation system mainly adopts double fed induction generators and magneto alternator two types, for improving Generating efficiency, all using the variable speed constant frequency generator method of operation.Wherein, at most, technology is for double fed induction generators (DFIG) application For maturation, it is current mainstream model.DFIG system architecture, as shown in figure 1, DFIG can achieve that variable speed constant frequency controls, reduces conversion The capacity of device, also can achieve active, idle uneoupled control, and the flexibility of this Power Control is highly beneficial to electrical network.However, Under unbalanced power grid, because the stator side of DFIG and electrical network are joined directly together, the runnability of DFIG can be greatly affected, because This, research improvement control strategy under unbalanced power grid for the DFIG has great importance.

Vector controlled (VC) is all the main flow control strategy of dual feedback wind power generation system for a long time.VC passes through two PI controls Device processed carries out uneoupled control to active reactive electric current respectively, has excellent steady-state behaviour, but due to integral element exist delayed Effect, the dynamic property of VC is simultaneously not fully up to expectations.For improvement control strategy under unbalanced power grid for the VC, scholar is had to propose A kind of improvement strategy respectively positive- and negative-sequence currents being controlled using two groups of PI controllers.However, entering to voltage, electric current The detached process of row positive-negative sequence considerably increases the complexity of system, also can be to the control performance of system if separation is inaccurate Cause to have a strong impact on.In recent years, direct Power Control strategy (DPC) is more and more paid close attention to by people, and it is direct to power Effectively control and also more meet the requirement for wind generator system for the electrical network, have scholar to be directed to DPC under unbalanced power grid Application, it is proposed that a kind of power back-off measure, by adding different compensation in value and power reference, can realize difference respectively Control targe.However, the calculating process of power compensating value still needs and is just using voltage and current in this control strategy Negative sequence component.Resonant controller (R) has the characteristic of larger gain due to it to the variable of CF, in unbalanced power grid It is used widely in the research of lower improvement control strategy.In VC and DPC, have and mutually tied with R controller by PI controller Close, respectively DC component and two frequency multiplication flutter components are implemented to control, to realize the effective control of DFIG under unbalanced power grid.So And, in this control strategy, calculating of current reference value still needs the negative sequence component utilizing electric current.Can by above analysis Know, under numerous unbalanced power grid, the research of the improvement control strategy of DFIG is all intended to based on line voltage, electric current positive-negative sequence at present Detached, not only can increase the complexity of system, the accuracy for separation process also has larger dependence.Therefore, study How not need under the premise of line voltage, electric current positive-negative sequence are detached, to realize the effective control of DFIG, DFIG is being existed The development further of the improvement control strategy under unbalanced power grid is significant.

Content of the invention

In view of above-mentioned, the invention provides under a kind of unbalanced power grid, DFIG is based on the sliding moding structure expanding active power Direct Power Control method, the positive-negative sequence without line voltage, electric current separates, and control structure very simple, can be in injustice Stable electromagnetic torque, reactive power and sinusoidal stator current is realized under weighing apparatus electrical network.

A kind of sliding moding structure direct Power Control method based on expansion active power for the DFIG under unbalanced power grid, including Following steps：

(1) gather the threephase stator voltage U of DFIG_sabcWith threephase stator electric current I_sabc, and DFIG is calculated by detection Rotor angular frequency_rWith rotor position angle θ_r；

(2) respectively to described threephase stator voltage U_sabcWith threephase stator electric current I_sabcCarry out Clark conversion, correspondence obtains Stator voltage vector U under static alpha-beta coordinate system_sαβWith stator current vector I_sαβ；And then by described stator voltage vector U_sαβStagnant In a quarter cycle afterwards, obtain delayed stator voltage vector U'_sαβ；

(3) to described stator voltage vector U_sαβIt is integrated, obtain stator magnetic linkage vector ψ_sαβ；

(4) according to stator voltage vector U_sαβ, delayed stator voltage vector U'_sαβWith stator current vector I_sαβCalculate The expansion active-power P of DFIG stator output_s ^newAnd reactive power Q_s；

(5) by described expansion active-power P_s ^newAnd reactive power Q_sCarry out sliding moding structure direct Power Control, from And it is calculated the modulation voltage vector U of DFIG_rαβ；

(6) utilize rotor position angle θ to described modulation voltage vector U_rαβCarry out Park conversion, obtain rotor reference coordinate Modulation voltage vector U under system_rdq, and then using SVPWM (space vector pulse width modulation) algorithm construction go out one group of pwm signal with The machine-side converter of DFIG is controlled.

According to following formula to threephase stator voltage U in described step (2)_sabcWith threephase stator electric current I_sabcCarry out Clark Conversion：

Wherein：U_sαAnd U_sβCorrespond to stator voltage vector U_sαβα axle component and beta -axis component, I_sαAnd I_sβCorrespond to stator Current phasor I_sαβα axle component and beta -axis component, U_sa、U_sb、U_scIt is respectively threephase stator voltage U_sabcOn corresponding A, B, C three-phase Phase voltage, I_sa、I_sb、I_scIt is respectively threephase stator electric current I_sabcPhase current on corresponding A, B, C three-phase.

According to following formula to stator voltage vector U in described step (3)_sαβIt is integrated：

Wherein：ψ_sαAnd ψ_sβCorrespond to stator magnetic linkage vector ψ_sαβα axle component and beta -axis component, U_sα(τ) and U_sβ(τ) corresponding For τ moment stator voltage vector U_sαβα axle component and beta -axis component, t be system operation duration.

Calculate the expansion active-power P of DFIG stator output by below equation in described step (4)_s ^newAnd reactive power Q_s：

Wherein：U_sαAnd U_sβCorrespond to stator voltage vector U_sαβα axle component and beta -axis component, I_sαAnd I_sβCorrespond to stator Current phasor I_sαβα axle component and beta -axis component, U'_sαAnd U'_sβCorrespond to delayed stator voltage vector U'_sαβα axle component And beta -axis component.

It is based on below equation to expansion active-power P in described step (5)_s ^newAnd reactive power Q_sCarry out sliding moding structure Direct Power Control：

Wherein：U_rαAnd U_rβCorrespond to modulation voltage vector U_rαβα axle component and beta -axis component, U_sαAnd U_sβCorrespond to stator Voltage vector U_sαβα axle component and beta -axis component, I_sαAnd I_sβCorrespond to stator current vector I_sαβα axle component and beta -axis component, U'_sαAnd U'_sβCorrespond to delayed stator voltage vector U'_sαβα axle component and beta -axis component, ψ_sαAnd ψ_sβCorrespond to stator magnetic linkage Vector ψ_sαβα axle component and beta -axis component, K_pAnd K_qCorrespond to extend the integral adjustment ginseng that active power and reactive power give Number, K_psAnd K_qsCorrespond to extend the switch function regulation parameter that active power and reactive power give, L_mRotor mutual inductance for DFIG, L_rAnd L_sIt is respectively inductor rotor and the stator inductance of DFIG,And Q_srefIt is respectively given Expansion active power reference value and reactive power reference qref, e_p(τ) and e_q(τ) corresponding to the τ moment extends active power and idle The error amount of power, ω₁For the angular frequency of line voltage, j=1 or 2, λ_jThe boundary value giving for switch function, t transports for system Row duration.

According to following formula to modulation voltage vector U in described step (6)_rαβCarry out Park conversion：

Wherein：U_rαAnd U_rβCorrespond to modulation voltage vector U_rαβα axle component and beta -axis component, U_rdAnd U_rqCorrespond to modulate Voltage vector U_rdqD axle component and q axle component.

It is proposed that a kind of active power of expansion on the basis of the present invention is DFIG Mathematical Modeling under unbalanced power grid, And using the active power of this expansion and traditional reactive power as control object, by sliding-mode variable structure algorithm and DPC technology Combine, and then propose a kind of improved sliding moding structure direct Power Control strategy based on expansion active power；This Bright method is under the premise of detached without line voltage electric current positive-negative sequence it is possible to realize DFIG effective under unbalanced power grid Control, obtain the stator current of stable electromagnetic torque and reactive power and sine；Control system of the present invention realizes extremely letter List is it is not necessary to phaselocked loop carries out real-time monitoring to the frequency of line voltage.

The expansion Power Theory proposing in the present invention, not only can be tied with sliding moding structure direct Power Control strategy phase Close, can also be combined the improvement control strategy being formed under unbalanced power grid with multiple direct Power Control strategies.It controls thinks Want that there is relatively broad applicability.

Brief description

Fig. 1 is the structural representation of DFIG system.

Fig. 2 is that the system of control method of the present invention realizes principle schematic.

Fig. 3 is the DFIG sliding moding structure direct Power Control system based on expansion active power for the present invention in stator voltage The unidirectional steady-state response oscillogram fallen under 50% unbalanced power grid；Wherein, U_sabcFor threephase stator voltage, I_sabcFor three-phase Stator current, I_rabcFor three-phase rotor current, P is active power, and Q is reactive power, and Te is electromagnetic torque.

Fig. 4 is the DFIG sliding moding structure direct Power Control system based on expansion active power for the present invention in stator voltage The unidirectional spectrum analysis figure falling the stator A phase current under 50% unbalanced power grid.

Specific embodiment

In order to more specifically describe the present invention, below in conjunction with the accompanying drawings and specific embodiment is to technical scheme It is described in detail.

The system based on the DFIG sliding moding structure direct Power Control method expanding active power for the present invention realizes such as Fig. 2 Shown, DFIG1 that system includes a 2kW, the voltage source type converter 2 being connected with DFIG rotor windings, it is used for detecting DFIG The voltage sensor 3 of stator three-phase voltage, for detecting the current Hall sensor 4 of DFIG stator three-phase current, be used for detecting The encoder 12 of DFIG rotor position angle, obtain generating unit speed differentiator 11 and realize DFIG export active, reactive power The control loop adjusting.Control loop is by feeding back signal processing channel and forward direction control passage is constituted, wherein forward direction control passage Including SVPWM signal generator 5, Sliding mode variable structure control computing module 6, two-phase static/rotating coordinate transformation module 13；Feedback Signal processing channel include for obtain the stator voltage in stator two-phase rest frame, stator current vector signal three Phase/two-phase static coordinate conversion module 7, delayed stator voltage computing module 8, power computation module 9, flux linkage calculation module 10.

As shown in Fig. 2 DFIG sliding formwork direct Power Control method of the present invention comprises the following steps：

(1) three voltage hall sensors 3 are utilized to gather DFIG threephase stator voltage signal U_sabc；Using three-phase current suddenly You are sensor 4 collection threephase stator current signal I_sabc；

(2) encoder 12 is adopted to detect the rotor position of DFIG_r, then calculate rotor angular frequency through differentiator 11_r；

(3) by the threephase stator collecting voltage signal U_sabcWith threephase stator current signal I_sabcArrive through static three-phase Two-phase coordinate transformation module 7, obtains the stator voltage vector U under stator coordinate_sαβWith stator current vector I_sαβ；With stator electricity As a example pressure, from static three-phase, the expression formula to two-phase coordinate transform is：

(4) by the stator voltage vector collecting U_sαβThrough delayed stator voltage computing module 8, by its delayed four In/mono- cycle, obtain delayed stator voltage vector U'_sαβ；

(5) by the stator voltage vector collecting U_sαβThrough flux linkage calculation module 10, obtain stator magnetic linkage vector ψ_sαβ, magnetic The computing formula of chain is：

(6) by the stator voltage vector collecting U_sαβ, stator current vector I_sαβWith delayed stator voltage vector U'_sαβCalculate expansion active power, the reactive power signals of stator output by rotor-side power computation module 9Q_s, have Work(, reactive power calculate formula：

(7) the expansion active power that will be exported to electrical network according to the stator that step (4) obtain, reactive power P_s ^new、Q_sWith give Fixed stator expands active power, reactive power reference qrefQ_srefAnd stator voltage vector U_sαβ, delayed stator voltage arrow Amount U'_sαβ, stator current vector I_sαβ, stator magnetic linkage vector ψ_sαβ, line voltage angular frequency₁With rotor angular frequency_rIt is input to Sliding moding structure power control module 6, is calculated the modulation voltage vector U of DFIG_rαβ；

The Computing Principle of sliding moding structure direct Power Control module 6 is as follows：

7.1 control targes are that stator is active, reactive power follows its reference value, and that is, power error is zero, and therefore definition is slided Die face is：

S=[S₁S₂]^T

Wherein, K_pAnd K_qIt is respectively extension active power and reactive power integral adjustment parameter, and K_p>0、K_q>0, e_pAnd e_q It is respectively extension active power and reactive power error, that is,：

Work as e_p、e_qGo to zero, you can realize control targe.

7.2, in order that the state of system levels off to sliding-mode surface, can construct Lyapunov function as follows：

The derived function of this Lyapunov function can be calculated as follows：

Wherein, can be obtained by formula in 7.1：

7.3 can expand active and reactive power rate of change by DFIG Mathematical Modeling is：

7.4 bring formula in 7.3 into 7.2 obtains：

Wherein：

From Lyapunov stability, when W is more than or equal to zero and its derivative is less than zero, system tends towards stability.

The 7.5 following relational expressions of structure：

Wherein：K_psAnd K_qsIt is respectively the switch function regulation parameter expanding active power and reactive power, and K_ps>0、K_qs> 0, sgn (S₁) and sgn (S₂) it is the switch function expanding active power and reactive power：

Wherein, λ_jFor the boundary value of this switch function, j=1,2.

The equation is brought into equation in 7.4 obtain：

Can ensure that the derivative of W is less than zero, system stability.

(8) by modulation voltage vector U_rαβBy two-phase static/rotating coordinate transformation module 13 transforms to rotor reference coordinate System, obtains U_rdq, the computing formula from two-phase rest frame to two-phase rotating coordinate system is：

(9) by U_rdqValue as SVPWM signal generator module 5 reference value, modulation obtain DFIG rotor side converter Switching signal S_a、S_b、S_c；

(10) by switching signal S obtaining_a、S_b、S_cThrough drive module driving switch device, realize active based on expanding The sliding moding structure direct Power Control of power.

Referring to Fig. 3, under the DFIG sliding moding structure direct Power Control method based on expansion active power for the present invention, this Embodiment control system under the unidirectional unbalanced power grid falling 50% of stator voltage, put down by reactive power and electromagnetic torque waveform Surely；Stator three-phase current waveform is sinusoidal, and overall control effect is very good.

Referring to Fig. 4 it can be seen that the present invention based on expand active power DFIG sliding moding structure direct Power Control Under method, Stator Current Harmonic under the unidirectional unbalanced power grid falling 50% of stator voltage for the present embodiment control system contains Amount THD very little.

In sum, the present invention is based on expanding the DFIG sliding moding structure direct Power Control method of active power need not It is possible to realize effective control under unbalanced power grid for the DFIG under the premise of line voltage electric current positive-negative sequence is detached, put down Steady electromagnetic torque and the stator current of reactive power and sine；Control structure of the present invention extremely simple it is not necessary to phaselocked loop Real-time monitoring is carried out to the frequency of line voltage.

Claims

1. DFIG is based on the sliding mode variable structure direct power control method of expanding active power under a kind of unbalanced grid, comprises the following steps:

(1) Collect the three-phase stator voltage U _sabc and the three-phase stator current I _sabc of DFIG, and obtain the rotor angular frequency ω _r and rotor position angle θ _r of DFIG through detection and calculation;

(2) Perform Clark transformation on the three-phase stator voltage U _sabc and the three-phase stator current I _sabc respectively, correspondingly obtain the stator voltage vector U _sαβ and the stator current vector I _sαβ under the static α-β coordinate system; The stator voltage vector U _sαβ is delayed by a quarter cycle, and the lagged stator voltage vector U' _{sαβ is obtained} ;

(3) integrating the stator voltage vector U _sαβ to obtain the stator flux vector ψ _sαβ ;

(4) Calculate the extended active power P _s ^new and reactive power Q _s output by the DFIG stator according to the stator voltage vector U _sαβ , the lagging stator voltage vector U' _sαβ and the stator current vector I _sαβ ;

(5) By performing sliding mode variable structure direct power control on the expanded active power P _s ^new and reactive power Q _s , the modulated voltage vector U _rαβ of DFIG is calculated;

(6) Use the rotor position angle θ to perform Park transformation on the modulation voltage vector U _rαβ to obtain the modulation voltage vector U _rdq in the rotor reference coordinate system, and then use the SVPWM algorithm to construct a set of PWM signals to transform the machine side of DFIG device to control.

2. sliding mode variable structure direct power control method according to claim 1, is characterized in that: in described step (2), according to following formula, three-phase stator voltage U _sabc and three-phase stator current I _sabc carry out Clark transformation:

\begin{matrix} [\begin{matrix} {U u}_{s the s α α} \\ {U u}_{s the s β β} \end{matrix}] = = \frac{22}{33} [\begin{matrix} 11 & - - \frac{11}{22} & - - \frac{11}{22} \\ 00 & \frac{\sqrt{33}}{22} & - - \frac{\sqrt{33}}{22} \end{matrix}] [\begin{matrix} {U u}_{s the s a a} \\ {U u}_{s the s b b} \\ {U u}_{s the s c c} \end{matrix}] & [\begin{matrix} {I I}_{s the s α α} \\ {I I}_{s the s β β} \end{matrix}] = = \frac{22}{33} [\begin{matrix} 11 & - - \frac{11}{22} & - - \frac{11}{22} \\ 00 & \frac{\sqrt{33}}{22} & - - \frac{\sqrt{33}}{22} \end{matrix}] [\begin{matrix} {I I}_{s the s a a} \\ {I I}_{s the s b b} \\ {I I}_{s the s c c} \end{matrix}] \end{matrix}

Among them: U _sα and U _sβ correspond to the α-axis component and β-axis component of the stator voltage vector U _sαβ , I _sα and I _sβ correspond to the α-axis component and β-axis component of the stator current vector I _sαβ , U _sa , U _sb , U _sc is the three-phase stator voltage U _sabc corresponding to the phase voltage on the three phases A, B, and C, I _sa , I _sb , and I _sc are the three-phase stator current I _sabc corresponding to the phases on the three phases A, B, and C current.

3. the sliding mode variable structure direct power control method according to claim 1, is characterized in that: in described step (3), stator voltage vector U _{s α β} is integrated according to following formula:

\{\begin{matrix} {ψ ψ}_{s the s α α} = = {&Integral; &Integral;}_{00}^{t t} {U u}_{s the s α α} ((τ τ)) d d τ τ \\ {ψ ψ}_{s the s β β} = = {&Integral; &Integral;}_{00}^{t t} {U u}_{s the s β β} ((τ τ)) d d τ τ \end{matrix}

Among them: ψ _sα and ψ _sβ correspond to the α-axis component and β-axis component of the stator flux vector ψ _sαβ , U _sα (τ) and U _sβ (τ) correspond to the α-axis component and β of the stator voltage vector U _sαβ at time τ axis component, and t is the running time of the system.

4. the sliding mode variable structure direct power control method according to claim 1, is characterized in that: in the described step (4), calculate the expanded active power P _s ^new and the reactive power Q _s of DFIG stator output by following formula:

{P P}_{s the s}^{n no e e w w} = = \frac{33}{22} [[{U u}^{' '}_{s the s α α} {I I}_{s the s β β} - - {U u}^{' '}_{s the s β β} {I I}_{s the s α α}]]

{Q Q}_{s the s} = = - - \frac{33}{22} [[{U u}_{s the s α α} {I I}_{s the s β β} - - {U u}_{s the s β β} {I I}_{s the s α α}]]

Among them: U _sα and U _sβ correspond to the α-axis component and β-axis component of the stator voltage vector U _sαβ , I _sα and I _sβ correspond to the α-axis component and β-axis component of the stator current vector I _sαβ , U' _sα and U' _sβ corresponds to the α-axis component and β-axis component of the delayed stator voltage vector U' _sαβ .

5. the sliding mode variable structure direct power control method according to claim 1, is characterized in that: in the described step (5), carry out sliding mode variable structure to expanding active power P _s ^new and reactive power Q _s based on following equation Direct Power Control:

U u = = - - {D D.}^{- - 11} {{G G + + [\begin{matrix} {K K}_{p p s the s} & 00 \\ 00 & {K K}_{q q s the s} \end{matrix}] [\begin{matrix} sgn sgn (({S S}_{11})) \\ sgn sgn (({S S}_{22})) \end{matrix}]}}

\begin{matrix} U u = = [\begin{matrix} {U u}_{r r α α} \\ {U u}_{r r β β} \end{matrix}] & D D. = = \frac{33}{22 {σ σ}^{' '} {L L}_{m m}} [\begin{matrix} - - {U u}^{' '}_{s the s β β} & {U u}^{' '}_{s the s α α} \\ {U u}_{s the s β β} & - - {U u}_{s the s α α} \end{matrix}] \end{matrix}

\begin{matrix} G G = = - - \frac{33 {L L}_{r r}}{22 {σ σ}^{' '} {L L}_{m m}^{22}} [\begin{matrix} {U u}_{s the s β β} {U u}^{' '}_{s the s α α} - - {U u}_{s the s α α} {U u}^{' '}_{s the s β β} \\ 00 \end{matrix}] + + \frac{33 {L L}_{r r} {ω ω}_{r r}}{22 {σ σ}^{' '} {L L}_{m m}^{22}} [\begin{matrix} {ψ ψ}_{s the s β β} {U u}^{' '}_{s the s α α} - - {ψ ψ}_{s the s α α} {U u}^{' '}_{s the s β β} \\ {ψ ψ}_{s the s α α} {U u}_{s the s β β} - - {ψ ψ}_{s the s β β} {U u}_{s the s α α} \end{matrix}] \\ - - [\begin{matrix} - - {ω ω}_{11} {Q Q}_{s the s} - - 33 / / 22 {ω ω}_{r r} (({U u}^{' '}_{s the s α α} {I I}_{s the s β β} - - {U u}^{' '}_{s the s β β} {I I}_{s the s α α})) \\ {ω ω}_{11} {P P}_{s the s}^{n no e e w w} + + 33 / / 22 {ω ω}_{r r} (({U u}_{s the s α α} {I I}_{s the s α α} + + {U u}_{s the s β β} {I I}_{s the s β β})) \end{matrix}] + + [\begin{matrix} {K K}_{p p} {e e}_{p p} \\ {K K}_{q q} {e e}_{q q} \end{matrix}] \end{matrix}

\begin{matrix} \{\begin{matrix} {e e}_{p p} = = {P P}_{s the s r r e e f f}^{n no e e w w} - - {P P}_{s the s}^{n no e e w w} \\ {e e}_{q q} = = {Q Q}_{s the s r r e e f f} - - {Q Q}_{s the s} \end{matrix} & \{\begin{matrix} {S S}_{11} = = {e e}_{p p} + + {K K}_{p p} {&Integral; &Integral;}_{00}^{t t} {e e}_{p p} ((τ τ)) d d τ τ \\ {S S}_{22} = = {e e}_{q q} + + {K K}_{q q} {&Integral; &Integral;}_{00}^{t t} {e e}_{q q} ((τ τ)) d d τ τ \end{matrix} & sgn sgn (({S S}_{j j})) = = \{\begin{matrix} 11,, & {S S}_{j j} > > {λ λ}_{j j} \\ \frac{{S S}_{j j}}{{λ λ}_{j j}},, & | | {S S}_{j j} | | \leq \leq {λ λ}_{j j} \\ - - 11,, & {S S}_{j j} < < - - {λ λ}_{j j} \end{matrix} \end{matrix}

Among them: U _rα and U _rβ correspond to the α-axis component and β-axis component of the modulation voltage vector U _rαβ , U _sα and U _sβ correspond to the α-axis component and β-axis component of the stator voltage vector U _sαβ , and I _sα and I _sβ correspond to is the α-axis component and β-axis component of the stator current vector I _sαβ , U' _sα and U' _sβ correspond to the α-axis component and β-axis component of the lagging stator voltage vector U' _sαβ , and ψ _sα and ψ _sβ correspond to the stator magnetic The α-axis component and β-axis component of the chain vector ψ _sαβ , K _p and K _q correspond to the integral adjustment parameters of the extended active power and reactive power, and K _ps and K _qs correspond to the extended active power and reactive power given The switching function of the adjustment parameter, L _m is the stator-rotor mutual inductance of DFIG, L _r and L _s are the rotor inductance and stator inductance of DFIG respectively, and Q _sref are the given extended active power reference value and reactive power reference value respectively, e _p (τ) and e _q (τ) correspond to the error values of extended active power and reactive power at time τ, and ω ₁ is the power grid The angular frequency of the voltage, j = 1 or 2, λ _j is the boundary value given by the switching function, and t is the operating time of the system.

6. sliding mode variable structure direct power control method according to claim 1, is characterized in that: in described step (6), according to following formula, modulating voltage vector U _{r α β} is carried out Park transformation:

[\begin{matrix} {U u}_{r r d d} \\ {U u}_{r r q q} \end{matrix}] = = [\begin{matrix} {cosθ cosθ}_{r r} & {sinθ sinθ}_{r r} \\ - - {sinθ sinθ}_{r r} & {cosθ cosθ}_{r r} \end{matrix}] [\begin{matrix} {U u}_{r r α α} \\ {U u}_{r r β β} \end{matrix}]

Among them: U _rα and U _rβ correspond to the α-axis component and β-axis component of the modulation voltage vector U _rαβ , U _rd and U _rq correspond to the d-axis component and q-axis component of the modulation voltage vector U _rdq .