CN106452263A - Extended active power-based sliding mode variable structure direct power control (DPC) method for DFIG in unbalanced power grid - Google Patents

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

A DFIG based on sliding mode variable structure direct expansion of active power under unbalanced power grid power control method

technical field

The invention belongs to the technical field of motor control, and in particular relates to a DFIG-based sliding mode variable structure direct power control method based on expanded active power under an unbalanced power grid.

Background technique

Modern wind power generation systems mainly adopt two types of doubly-fed induction generators and permanent magnet synchronous generators. In order to improve power generation efficiency, both adopt variable-speed and constant-frequency power generation operation modes. Among them, the doubly-fed induction generator (DFIG) has the most applications and the most mature technology, and is the current mainstream model. The structure of the DFIG system is shown in Figure 1. DFIG can realize variable speed and constant frequency control, reduce the capacity of the converter, and realize decoupling control of active power and reactive power. This flexibility of power control is very beneficial to the power grid. However, in an unbalanced grid, since the stator side of DFIG is directly connected to the grid, the operation performance of DFIG will be greatly affected. Therefore, it is of great significance to study the improved control strategy of DFIG in unbalanced grid.

For a long time, vector control (VC) has been the mainstream control strategy of doubly-fed wind power generation system. VC decouples the active and reactive currents through two PI controllers, which has excellent steady-state performance, but the dynamic performance of VC is not satisfactory due to the hysteresis effect of the integral link. Aiming at the improved control strategy of VC under unbalanced power grid, some scholars proposed an improved strategy using two sets of PI controllers to control the positive and negative sequence current components respectively. However, the process of separating the positive and negative sequences of voltage and current greatly increases the complexity of the system, and if the separation is inaccurate, it will seriously affect the control performance of the system. In recent years, direct power control strategy (DPC) has attracted more and more attention, and its direct and effective control of power is more in line with the requirements of the grid for wind power generation systems. Some scholars have aimed at the application of DPC in unbalanced grids. A power compensation measure is proposed. By adding different compensations to the power reference value, different control objectives can be achieved respectively. However, the calculation process of power compensation value in this control strategy still needs to use the positive and negative sequence components of voltage and current. Resonant controller (R) has been widely used in the study of improved control strategies in unbalanced power grids because of its characteristic of large gain only for specific frequency variables. In both VC and DPC, the PI controller and R controller are combined to control the DC component and the double frequency pulsating component respectively, so as to realize the effective control of DFIG under unbalanced power grid. However, in this control strategy, the calculation of the current reference value still needs to utilize the negative sequence component of the current. From the above analysis, it can be seen that the research on the improved control strategy of DFIG under the unbalanced power grid is based on the separation of the positive and negative sequences of the grid voltage and current, which will not only increase the complexity of the system, but also have a greater impact on the accuracy of the separation process. Big dependency. Therefore, it is of great significance for the further development of the improved control strategy of DFIG under the unbalanced power grid to study how to realize the effective control of DFIG without the separation of positive and negative sequences of grid voltage and current.

Contents of the invention

In view of the above, the present invention provides a sliding mode variable structure direct power control method based on extended active power of DFIG in an unbalanced power grid, which does not require the separation of positive and negative sequences of the grid voltage and current, and the control structure is very simple, which can be used in unbalanced power grids. Under the stable electromagnetic torque, reactive power and sinusoidal stator current.

A sliding mode variable structure direct power control method based on DFIG extended active power under an unbalanced power grid, comprising 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 (Space Vector Pulse Width Modulation) algorithm to construct a set of PWM signals To control the generator-side converter of DFIG.

In the step (2), Clark transformation is carried out to the three-phase stator voltage U _sabc and the three-phase stator current I _sabc according to the following formula:

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.

In the step (3), the stator voltage vector U _sαβ is integrated according to the following formula:

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.

In the step (4), the extended active power P _s ^new and reactive power Q _s output by the DFIG stator are calculated by the following formula:

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 .

In the step (5), the sliding mode variable structure direct power control is carried out based on the following equations to expand the active power P _s ^new and the reactive power Q _s :

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.

In the step (6), Park transformation is carried out to the modulation voltage vector U _rαβ according to the following formula:

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 .

The present invention proposes an expanded active power based on the DFIG mathematical model under the unbalanced power grid, and takes the expanded active power and the traditional reactive power as control objects, and combines the sliding mode variable structure algorithm with the DPC technology, and then proposed an improved sliding mode variable structure direct power control strategy based on extended active power; the method of the present invention can realize DFIG under the unbalanced power grid without separating the positive and negative sequences of the grid voltage and current The effective control can obtain stable electromagnetic torque, reactive power and sinusoidal stator current; the control system of the present invention is extremely simple to implement, and does not need a phase-locked loop to monitor the frequency of the grid voltage in real time.

The extended power theory proposed in the present invention can not only be combined with the sliding mode variable structure direct power control strategy, but also can be combined with multiple direct power control strategies to form an improved control strategy under unbalanced power grid. Its control idea has wider applicability.

Description of drawings

Figure 1 is a schematic diagram of the structure of the DFIG system.

Fig. 2 is a schematic diagram of the system realization principle of the control method of the present invention.

Fig. 3 is the steady-state response waveform figure of the DFIG sliding mode variable structure direct power control system based on the expansion of active power of the present invention under the unbalanced grid where the stator voltage unidirectionally drops 50%; wherein, U _sabc is the three-phase stator voltage, I _sabc is the three-phase stator current, I _rabc is the three-phase rotor current, P is the active power, Q is the reactive power, and Te is the electromagnetic torque.

Fig. 4 is a spectrum analysis diagram of stator A-phase current of the DFIG sliding mode variable structure direct power control system based on extended active power in an unbalanced power grid where the stator voltage unidirectionally drops 50%.

detailed description

In order to describe the present invention more specifically, the technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

The system realization of the DFIG sliding mode variable structure direct power control method based on the expanded active power of the present invention is shown in Fig. The voltage sensor 3 for the three-phase voltage of the stator, the current Hall sensor 4 for detecting the three-phase current of the DFIG stator, the encoder 12 for detecting the position angle of the DFIG rotor, the differentiator 11 for obtaining the rotational speed of the unit, and the realization of DFIG output active power and reactive power Control loop for power regulation. The control loop is composed of a feedback signal processing channel and a forward control channel, wherein the forward control channel includes a SVPWM signal generator 5, a sliding mode variable structure control operation module 6, and a two-phase stationary/rotating coordinate transformation module 13; the feedback signal processing channel includes A three-phase/two-phase static coordinate transformation module 7, a lagging stator voltage calculation module 8, a power calculation module 9, and a flux linkage calculation module 10 for obtaining stator voltage and stator current vector signals in a stator two-phase static coordinate system.

As shown in Figure 2, the DFIG sliding mode direct power control method of the present invention comprises the following steps:

(1) Utilize three voltage Hall sensors 3 to collect the DFIG three-phase stator voltage signal U _sabc ; utilize the three-phase current Hall sensor 4 to collect the three-phase stator current signal I _sabc ;

(2) Use the encoder 12 to detect the rotor position θ _r of DFIG, and then calculate the angular frequency ω _r of the rotor through the differentiator 11;

(3) Pass the collected three-phase stator voltage signal U _sabc and three-phase stator current signal I _sabc through the static three-phase to two-phase coordinate transformation module 7 to obtain the stator voltage vector U _sαβ and stator current vector I in the stator coordinate system _sαβ ; taking the stator voltage as an example, the expression of coordinate transformation from static three-phase to two-phase is:

(4) The stator voltage vector U _sαβ that is collected is passed through the stator voltage calculation module 8 of the lag, and it is lagged by a quarter cycle to obtain the stator voltage vector U' _sαβ of the lag;

(5) Pass the collected stator voltage vector U _sαβ through the flux linkage calculation module 10 to obtain the stator flux linkage vector ψ _sαβ , and the calculation formula of the flux linkage is:

(6) The acquired stator voltage vector U _sαβ , stator current vector I _sαβ and lagged stator voltage vector U' _sαβ are calculated through the rotor side power calculation module 9 to calculate the expanded active power and reactive power signals output by the stator Q _s , the calculation formula of active and reactive power is:

(7) Combine the extended active power, reactive power P _s ^new , Q _s output by the stator to the grid obtained according to step (4) and the given stator extended active power and reactive power reference value Q _sref and stator voltage vector U _sαβ , lagging stator voltage vector U' _sαβ , stator current vector I _sαβ , stator flux vector ψ _sαβ , grid voltage angular frequency ω ₁ and rotor angular frequency ω _r are input to the sliding mode variable structure power The control module 6 calculates the modulation voltage vector U _rαβ of DFIG;

The calculation principle of the sliding mode variable structure direct power control module 6 is as follows:

7.1 The control target is that the active and reactive power of the stator follow its reference value, that is, the power error is zero, so the sliding mode surface is defined as:

S＝[S ₁ S ₂ ] ^T

Among them, K _p and K _q are the integral adjustment parameters of extended active power and reactive power respectively, and K _p >0, K _q >0, e _p and e _q are the errors of extended active power and reactive power respectively, that is:

When e _p and e _q tend to zero, the control objective can be achieved.

7.2 In order to make the state of the system close to the sliding surface, the Lyapunov function can be constructed as follows:

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

Among them, it can be obtained from the formula in 7.1:

7.3 From the DFIG mathematical model, the expansion rate of active and reactive power can be obtained as:

7.4 Bring the formula in 7.3 into 7.2 to get:

in:

According to the Lyapunov stability, when W is greater than or equal to zero and its derivative is less than zero, the system tends to be stable.

7.5 Construct the following relational formula:

Among them: K _ps and K _qs are the switching function adjustment parameters for expanding the active power and reactive power respectively, and K _ps >0, K _qs >0, sgn(S ₁ ) and sgn(S ₂ ) are the expansion of active power and reactive power Switching function for work power:

Wherein, λ _j is the boundary value of the switch function, j=1,2.

Put this equation into the equation in 7.4 to get:

It can ensure that the derivative of W is less than zero and the system is stable.

(8) Transform the modulation voltage vector U _rαβ to the rotor reference coordinate system through the two-phase stationary/rotating coordinate transformation module 13 to obtain U _rdq , and the calculation formula from the two-phase stationary coordinate system to the two-phase rotating coordinate system is:

(9) Use the value of U _rdq as the reference value of the SVPWM signal generation module 5, and modulate to obtain the switching signals S _a , S _b , and S _c of the DFIG rotor side converter;

(10) The obtained switching signals S _a , S _b , and S _c are driven through the driving module to drive the switching devices, so as to realize the sliding mode variable structure direct power control based on the expanded active power.

Referring to Fig. 3, under the DFIG sliding mode variable structure direct power control method based on the expanded active power of the present invention, the reactive power and electromagnetic torque waveforms of the control system in this embodiment are Stable; the stator three-phase current waveform is sinusoidal, and the overall control effect is very ideal.

Referring to Figure 4, it can be seen that under the DFIG sliding mode variable structure direct power control method based on expanded active power in the present invention, the harmonic content of the stator current in the control system of this embodiment under the unbalanced power grid where the stator voltage drops 50% in one direction THD is very small.

In summary, the DFIG sliding mode variable structure direct power control method based on the expanded active power in the present invention can realize the effective control of DFIG under the unbalanced power grid without the separation of the positive and negative sequences of the grid voltage and current, and obtain a stable Electromagnetic torque, reactive power and sinusoidal stator current; the control structure of the invention is extremely simple, and no phase-locked loop is needed to monitor the frequency of the grid voltage in real time.

Claims (6)

1. a kind of sliding moding structure direct Power Control method based on expansion active power for the DFIG under unbalanced power grid, including such as Lower step：

(1) gather the threephase stator voltage U of DFIG_sabcWith threephase stator electric current I_sabc, and turning of DFIG is calculated by detection Sub- 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 static Stator voltage vector U under alpha-beta coordinate system_sαβWith stator current vector I_sαβ；And then by described stator voltage vector U_sαβDelayed four In/mono- cycle, 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 DFIG The expansion active-power P of 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, thus counting Calculate the modulation voltage vector U obtaining DFIG_rαβ；

(6) utilize rotor position angle θ to described modulation voltage vector U_rαβCarry out Park conversion, obtain under rotor reference coordinate system Modulation voltage vector U_rdq, and then go out one group of pwm signal using SVPWM algorithm construction and carried out with the machine-side converter to DFIG Control.

2. sliding moding structure direct Power Control method according to claim 1 it is characterised in that：In described step (2) According to following formula to threephase stator voltage U_sabcWith threephase stator electric current I_sabcCarry out Clark conversion：

$\begin{array}{cc}\left[\begin{array}{c}{U}_{s\mathrm{\α}}\\ U_{s\mathrm{\β}}\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{U}_{sa}\\ U_{sb}\\ U_{sc}\end{array}\right]& \left[\begin{array}{c}{I}_{s\mathrm{\α}}\\ I_{s\mathrm{\β}}\end{array}\right]=\frac{2}{3}\left[\begin{array}{ccc}1& -\frac{1}{2}& -\frac{1}{2}\\ 0& \frac{\sqrt{3}}{2}& -\frac{\sqrt{3}}{2}\end{array}\right]\left[\begin{array}{c}{I}_{sa}\\ I_{sb}\\ I_{sc}\end{array}\right]\end{array}$

Wherein：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_sa、U_sb、U_scIt is respectively threephase stator voltage U_sabcPhase on corresponding A, B, C three-phase Voltage, I_sa、I_sb、I_scIt is respectively threephase stator electric current I_sabcPhase current on corresponding A, B, C three-phase.

3. sliding moding structure direct Power Control method according to claim 1 it is characterised in that：In described step (3) According to following formula to stator voltage vector U_sαβIt is integrated：

$\left\{\begin{array}{c}{\mathrm{\ψ}}_{s\mathrm{\α}}={\∫}_0^t{U}_{s\mathrm{\α}}\left(\mathrm{\τ}\right)d\mathrm{\τ}\\ {\mathrm{\ψ}}_{s\mathrm{\β}}={\∫}_0^t{U}_{s\mathrm{\β}}\left(\mathrm{\τ}\right)d\mathrm{\τ}\end{array}\right.$

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) when corresponding to τ Carve stator voltage vector U_sαβα axle component and beta -axis component, t be system operation duration.

4. sliding moding structure direct Power Control method according to claim 1 it is characterised in that：In described step (4) Calculate the expansion active-power P of DFIG stator output by below equation_s ^newAnd reactive power Q_s：

$P_s^{new}=\frac{3}{2}\[{U^{\′}}_{s\mathrm{\α}}{I}_{s\mathrm{\β}}-{U^{\′}}_{s\mathrm{\β}}{I}_{s\mathrm{\α}}\]$

$Q_s=-\frac{3}{2}\[U_{s\mathrm{\α}}{I}_{s\mathrm{\β}}-U_{s\mathrm{\β}}{I}_{s\mathrm{\α}}\]$

Wherein：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 β axle Component.

5. sliding moding structure direct Power Control method according to claim 1 it is characterised in that：In described step (5) Based on below equation to expansion active-power P_s ^newAnd reactive power Q_sCarry out sliding moding structure direct Power Control：

$U=-D^{-1}\{G+\left[\begin{array}{cc}{K}_{ps}& 0\\ 0& K_{qs}\end{array}\right]\left[\begin{array}{c}\mathrm{sgn}\left(S_1\right)\\ \mathrm{sgn}\left(S_2\right)\end{array}\right]\}$

$\begin{array}{cc}U=\left[\begin{array}{c}{U}_{r\mathrm{\α}}\\ U_{r\mathrm{\β}}\end{array}\right]& D=\frac{3}{2{\mathrm{\σ}}^{\′}{L}_m}\left[\begin{array}{cc}-{U^{\′}}_{s\mathrm{\β}}& {U^{\′}}_{s\mathrm{\α}}\\ U_{s\mathrm{\β}}& -U_{s\mathrm{\α}}\end{array}\right]\end{array}$

$\begin{array}{c}G=-\frac{3L_r}{2{\mathrm{\σ}}^{\′}{L}_m^2}\left[\begin{array}{c}{U}_{s\mathrm{\β}}{U^{\′}}_{s\mathrm{\α}}-U_{s\mathrm{\α}}{U^{\′}}_{s\mathrm{\β}}\\ 0\end{array}\right]+\frac{3L_r{\mathrm{\ω}}_r}{2{\mathrm{\σ}}^{\′}{L}_m^2}\left[\begin{array}{c}{\mathrm{\ψ}}_{s\mathrm{\β}}{U^{\′}}_{s\mathrm{\α}}-{\mathrm{\ψ}}_{s\mathrm{\α}}{U^{\′}}_{s\mathrm{\β}}\\ {\mathrm{\ψ}}_{s\mathrm{\α}}{U}_{s\mathrm{\β}}-{\mathrm{\ψ}}_{s\mathrm{\β}}{U}_{s\mathrm{\α}}\end{array}\right]\\ -\left[\begin{array}{c}-{\mathrm{\ω}}_1{Q}_s-3/2{\mathrm{\ω}}_r({U^{\′}}_{s\mathrm{\α}}{I}_{s\mathrm{\β}}-{U^{\′}}_{s\mathrm{\β}}{I}_{s\mathrm{\α}})\\ {\mathrm{\ω}}_1{P}_s^{new}+3/2{\mathrm{\ω}}_r(U_{s\mathrm{\α}}{I}_{s\mathrm{\α}}+U_{s\mathrm{\β}}{I}_{s\mathrm{\β}})\end{array}\right]+\left[\begin{array}{c}{K}_p{e}_p\\ K_q{e}_q\end{array}\right]\end{array}$

$\begin{array}{ccc}\left\{\begin{array}{c}{e}_p=P_{sref}^{new}-P_s^{new}\\ e_q=Q_{sref}-Q_s\end{array}\right.& \left\{\begin{array}{c}{S}_1=e_p+K_p{\&Integral;}_0^t{e}_p\left(\mathrm{\&tau;}\right)d\mathrm{\&tau;}\\ S_2=e_q+K_q{\&Integral;}_0^t{e}_q\left(\mathrm{\&tau;}\right)d\mathrm{\&tau;}\end{array}\right.& \mathrm{sgn}\left(S_j\right)=\left\{\begin{array}{cc}1,& S_j>{\mathrm{\&lambda;}}_j\\ \frac{S_j}{{\mathrm{\&lambda;}}_j},& \left|S_j\right|\&le;{\mathrm{\&lambda;}}_j\\ -1,& S_j<-{\mathrm{\&lambda;}}_j\end{array}\right.\end{array}$

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'_sα And 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 parameter that active power and reactive power give, K_ps And K_qsCorrespond to extend the switch function regulation parameter that active power and reactive power give,L_mFor The rotor mutual inductance of DFIG, L_rAnd L_sIt is respectively inductor rotor and the stator inductance of DFIG,And Q_srefIt is respectively given opening up Exhibition 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 reactive power Error amount, ω₁For the angular frequency of line voltage, j=1 or 2, λ_jThe boundary value giving for switch function, when t is system operation Long.

6. sliding moding structure direct Power Control method according to claim 1 it is characterised in that：In described step (6) According to following formula to modulation voltage vector U_rαβCarry out Park conversion：

$\left[\begin{array}{c}{U}_{rd}\\ U_{rq}\end{array}\right]=\left[\begin{array}{cc}{\mathrm{cos\&theta;}}_r& {\mathrm{sin\&theta;}}_r\\ -{\mathrm{sin\&theta;}}_r& {\mathrm{cos\&theta;}}_r\end{array}\right]\left[\begin{array}{c}{U}_{r\mathrm{\&alpha;}}\\ U_{r\mathrm{\&beta;}}\end{array}\right]$

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