CN101917130A - Quick energy response method for grid-side converter in DFIG (Doubly-Fed Induction Generator) low-voltage ride-through (LVRT) process - Google Patents

Abstract

The invention discloses a quick energy response method for a grid-side converter in a DFIG (Doubly-Fed Induction Generator) low-voltage ride-through (LVRT) process on the basis of an optimized reactive power input method. The quick energy response method is characterized in that in the control of the grid-side converter, when a double-fed wind power generation system is in the LVRT process, a unit power factor control policy is utilized if the fluctuation error evaluation function value of the voltage at a direct current side of the converter is in a control target range; and when the fluctuation error evaluation function value of the voltage at the direct current side of the converter exceeds the control range, the quick energy response method for the grid-side converter in the DFIG LVRT process on the basis of the optimized reactive power input method is utilized to improve the flowing response speed of the active power energy of the grid-side converter. The invention obviously enhances the robustness of the control of direct current link of the double-fed wind power generation converter.

Description

DFIG low pressure crossing process net side converter energy fast response method

Technical field

The present invention relates to a kind of DFIG low pressure crossing process net side converter energy fast response method, belong to the power electronics applied technical field based on optimization reactive power injection method.

Background technology

The four-quadrant rectification is adjustable with its power factor, energy can two-way flow etc. advantage become the preferred option of net side converter in the dual feedback wind power generation system.The controlled target of DFIG (Doubly-Fed Induction Generator double-fed generator) net side converter is: (1) keeps dc voltage stability and has the good dynamic response ability by control AC side active current; (2) guarantee the sinusoidal degree of ac-side current, and to make the AC side power factor be 1.Therefore ac-side current being implemented effectively control is the key of four-quadrant rectification control.In actual applications, the control to output current is to realize by the output voltage of regulating current transformer.Because the utilizable direct voltage of current transformer is fixed, so no matter adopt which kind of PWM modulation system, the maximum of AC side of converter output voltage is also fixed.Work as electric network electric voltage drop, in the DFIG system implementation low pressure crossing process, the dc voltage fluctuation will exceed the safety zone, current transformer need be exported the fluctuation that bigger active current suppresses direct voltage, and this moment, the AC side of converter output voltage reached capacity easily, and conventional unity power factor control algolithm often seems that response speed is slow excessively.

Summary of the invention

The objective of the invention is to shortcoming at above prior art existence, a kind of DFIG low pressure crossing process net side converter energy fast response method is proposed, with the direct voltage utilance that improves dual feedback wind power generation system net side converter, the response speed that improves its direct voltage in the low pressure crossing process.

In order to reach above purpose, the present invention takes following technical scheme to realize:

DFIG low pressure crossing process net side converter energy fast response method is characterized in that: may further comprise the steps:

1) obtains the active current set-point after the error process pi regulator adjusting by direct voltage sampled value and set-point;

2) according to dc voltage fluctuation error assessment function setup reactive current set-point, if the fluctuating error evaluation function value of direct voltage is in the controlled target scope, the set-point of reactive current is made as zero, the control of implementation unity power factor, control AC side of converter power factor is 1, if the fluctuating error evaluation function value of direct voltage exceeds the controlled target scope, then force given reactive current to carry out energy and respond fast;

3) set-point of active current and reactive current is compared with corresponding value of feedback respectively, and generated error is exported two cordic phase rotator voltage given values through pi regulator, obtains current transformer three-phase alternating current side output voltage through coordinate transform.

Aforesaid dc voltage fluctuation error assessment function is:

$\mathrm{\ξ}=\frac{\mathrm{\ϵ}}{u_{\mathrm{dc}}^{*}}+\frac{\mathrm{\Δ}{u}_{\mathrm{dc}}}{T_s}+\underset{n=1}{\overset{\∞}{\mathrm{\Σ}}}\mathrm{\ϵ}\left(n\right)$

Wherein: $\mathrm{\ϵ}=u_{\mathrm{dc}}-u_{\mathrm{dc}}^{*};$

Δu _dc＝u _dc(n)-u _dc(n-1)；

u _DcBe the direct voltage value of feedback;

Be the direct voltage set-point.

The DFIG low pressure crossing process net side converter energy fast response method of optimizing based on reactive power of the present invention, by forcing given reactive current, it is saturated to avoid the current transformer output voltage to occur, guaranteed the output active current is implemented booster response control, with the quick response of realization energy Flow and the fast and stable of dc voltage.

Description of drawings

Fig. 1 is four-quadrant rectification current transformer main circuit structure figure;

Fig. 2 is a four-quadrant rectification current transformer first-harmonic equivalent circuit diagram;

Fig. 3 is a four-quadrant rectification current transformer control principle block diagram;

Fig. 4 is four-quadrant rectification current transformer d, q shaft voltage resolution of vectors schematic diagram.

Embodiment

In conjunction with the accompanying drawings the specific embodiment of the present invention is described below:

Fig. 1 is four-quadrant rectification current transformer main circuit structure figure.Can determine four-quadrant rectification current transformer first-harmonic equivalent circuit diagram according to Fig. 1, as shown in Figure 2.The present invention adopts the control of line voltage directional vector to realize the four-quadrant rectification, and control principle figure as shown in Figure 3.Can draw four-quadrant rectification current transformer output current according to control principle figure and satisfy following formula:

$\left\{\begin{array}{c}{u}_{\mathrm{dr}}=-u_{\mathrm{dr}}^{\′}+\mathrm{\Δ}{u}_{\mathrm{dr}}+u_s\\ u_{\mathrm{qr}}=-u_{\mathrm{qr}}^{\′}-\mathrm{\Δ}{u}_{\mathrm{qr}}\end{array}\right.$ ... ... ... .... formula 1

Wherein:

$\left\{\begin{array}{c}{u}_{\mathrm{dr}}^{\′}=L\frac{{\mathrm{di}}_d}{\mathrm{dt}}+{\mathrm{Ri}}_d\\ u_{\mathrm{qr}}^{\′}=L\frac{{\mathrm{di}}_q}{\mathrm{dt}}+{\mathrm{Ri}}_q\end{array}\right.$ ... ... ... ... .. formula 2

$\left\{\begin{array}{c}\mathrm{\Δ}{u}_{\mathrm{dr}}={\mathrm{\ω}}_1{\mathrm{Li}}_q\\ \mathrm{\Δ}{u}_{\mathrm{qr}}={\mathrm{\ω}}_1{\mathrm{Li}}_d\end{array}\right.$ ... ... ... ... .... formula 3

$\left\{\begin{array}{c}{u}_{\mathrm{dr}}=S_d{u}_{\mathrm{dc}}\\ u_{\mathrm{qr}}=S_q{u}_{\mathrm{dc}}\end{array}\right.$ ... ... ... ... .... formula 4

Each variable-definition in the formula is as follows:

i _d: d shaft current component under the two-phase rotating coordinate system;

i _q: q shaft current component under the two-phase rotating coordinate system;

u _s: line voltage;

U ' _Dr: d shaft voltage component decoupling zero item;

U ' _Qr: q shaft voltage component decoupling zero item;

Δ u _Dr: d shaft voltage compensating for coupling item;

Δ u _Qr: q shaft voltage compensating for coupling item;

u _Dr: current transformer output d shaft voltage component;

u _Qr: current transformer output q shaft voltage component.

According to shown in Figure 3, The whole control system is a double circle structure, and outer shroud is that Voltage loop, interior ring are electric current loop.The given voltage of DC link

With feedback voltage u _DcError after comparing is regulated the set-point of output active current through pi regulator

And the set-point of reactive current

Character by power factor in conventional power factor controlling algorithm determines.In this algorithm then according to dc voltage fluctuation error assessment function setup.

When dual feedback wind power generation system is in the low pressure crossing process, can cause rising sharply or rapid drawdown of direct voltage, make the fluctuating error evaluation function value of direct voltage exceed the controlled target scope.

If the fluctuating error evaluation function value of direct voltage exceeds the controlled target scope, make u ' _Qr=-0.1 ξ.

When direct voltage rises sharply, current transformer output i _dFor negative value to suppress build-up of voltage.If the fluctuating error of direct voltage exceeds the controlled target scope, the output voltage of current transformer will reach capacity.Saturated for withdrawing from, in the output current scope that current transformer allows, force given negative reactive current i _qi _d, i _qBe negative value, according to formula 2 and formula 3, u ' _Dr, Δ u _DrAlso be negative value.According to formula 1, Δ u _DrMake current transformer output d shaft voltage component u _DrReduce.According to formula 2, q shaft voltage component decoupling zero item u ' _QrBe negative value, make current transformer output q shaft voltage component u _QrIncrease.Because u ' _QrTo i _qFast-response control, u ' _QrThe absolute value increment much smaller than Δ u _DrAbsolute value recruitment, so u _QrThe absolute value recruitment be far smaller than u _DrThe absolute value decrease, its resultant vector length still reduces, so the output voltage of AC side of converter reduces, improved current transformer dc voltage utilance greatly, has significantly reduced the current transformer output voltage and saturated probability occurred.

When the direct voltage rapid drawdown, current transformer need be exported i _dFor on the occasion of, reduce to stop direct voltage.If the fluctuating error evaluation function value of direct voltage exceeds the controlled target scope.Force given positive reactive current i this moment _qAccording to formula 1, because u ' _DrMuch larger than u _sSo, current transformer output d shaft voltage component u _DrBe negative value, at this moment given positive reactive current i _q, make current transformer output d shaft voltage component u _DrReduce.Equally, given positive reactive current i _q, make current transformer output q shaft voltage component u _QrIncrease.Because u ' _QrTo i _qFast-response control, u ' _QrThe absolute value increment much smaller than Δ u _DrThe absolute value recruitment, u _QrRecruitment be far smaller than u _DrReduction, so the output voltage of AC side of converter reduces, improved current transformer dc voltage utilance greatly, significantly reduced the current transformer output voltage and saturated probability occurred.

After the DFIG low pressure crossing process net side converter energy fast response method calculating of adopting reactive power optimization, the current transformer output voltage is reduced, avoid the output voltage of AC side of converter saturated.Thereby guaranteed the electric current of current transformer output is implemented control fast and effectively, also the speed and the size that flow of control energy effectively just kept the stable of dc voltage.

Below disclose the present invention with preferred embodiment, so it is not in order to restriction the present invention, and all employings are equal to replaces or technical scheme that the equivalent transformation mode is obtained, all drops within protection scope of the present invention.

Claims (2)

1. DFIG low pressure crossing process net side converter energy fast response method is characterized in that: may further comprise the steps:

1) obtains the active current set-point after the error process pi regulator adjusting by direct voltage sampled value and set-point;

2) according to dc voltage fluctuation error assessment function setup reactive current set-point, if the fluctuating error evaluation function value of direct voltage is in the controlled target scope, the set-point of reactive current is made as zero, control AC side of converter power factor is 1, if the fluctuating error evaluation function value of direct voltage exceeds the controlled target scope, then force given reactive current to carry out energy and respond fast;

3) set-point of active current and reactive current is compared with corresponding value of feedback respectively, and generated error is exported two cordic phase rotator voltage given values through pi regulator, obtains current transformer three-phase alternating current side output voltage through coordinate transform.

2. DFIG low pressure crossing process net side converter energy fast response method according to claim 1, it is characterized in that: described dc voltage fluctuation error assessment function is:

$\mathrm{\ξ}=\frac{\mathrm{\ϵ}}{u_{\mathrm{dc}}^{*}}+\frac{\mathrm{\Δ}{u}_{\mathrm{dc}}}{T_s}+\underset{n=1}{\overset{\∞}{\mathrm{\Σ}}}\mathrm{\ϵ}\left(n\right)$

Wherein: $\mathrm{\ϵ}=u_{\mathrm{dc}}-u_{\mathrm{dc}}^{*};$

Δu _dc＝u _dc(n)-u _dc(n-1)；

u _DcBe the direct voltage value of feedback;

Be the direct voltage set-point.

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