CN101986552B - Rotor current control method of double-fed wind driven generator under power grid faults - Google Patents

Abstract

The invention belongs to the field of controlling a power conversion device of a wind driven generator, relating to a rotor current control method of a double-fed wind driven generator under power grid faults. The method comprises the following steps: obtaining the stator voltage and the rotor current under a two-phase static coordinates by utilizing the detected three-phase stator voltage and the three-phase rotor current through a 3/2 conversion module; calculating the stator magnetic flux linkage and the position angle; calculating the slip frequency angle and the slip frequency angular velocity; summating the stator magnetic flux linkage position angle and the rotor position angle, and then carrying out differentiation to obtain the sum of the magnetic flux linkage angular velocity and the rotor angular velocity; calculating the rotor current set values under the two-phase static coordinates of a rotor; respectively subtracting the rotor current set values under the two-phase static coordinates of the rotor with the rotor current under the two-phase static coordinates and obtaining the reference value of the rotor voltage under the two-phase static coordinates through the calculation by utilizing a performance requirement (PR) controller; and generating the switching signal of a control power device. The rotor current control method has the advantages that the rotor current oscillation of a double-fed induction generator (DFIG) resulted from power grid faults can be effectively inhibited, the grid in-service operation of the double-fed wind driven generator, and the operation performance of the DFIG under the power grid faults is enhanced.

Description

Double-fed wind power generator rotor current control method under the electric network fault

Technical field

The present invention relates to the control method of double-fed wind power generator under a kind of electric network fault (DFIG) rotor side inverter, belong to wind-driven generator control field.

Background technology

Because it is the stator side of double fed induction generators (DFIG) directly links to each other with electrical network, very responsive to electric network fault.Electric network fault can cause the generator unit stator voltage jump, and stator current produces vibration, and generator unit stator is meritorious simultaneously also oscillatory occurences can occur with reactive power and electromagnetic torque.In addition, because the close coupling between rotor and the stator, the stator voltage of sudden change can cause the rotor current fluctuation, has influence on the running status of double feedback electric engine.When electric network fault acquires a certain degree, be the security of operation of protection converter plant, the wind-powered electricity generation unit off-the-line in the electrical network of will having no alternative but to comply.The large-scale wind power unit will further worsen electrical network from grid disconnection, the stable operation of electrical network caused have a strong impact on.To this, the power grid operation merchant requires the wind-powered electricity generation unit when line voltage falls fault, and wind-driven generator can not break away from electrical network within the specific limits, and to electrical network meritorious and idle support is provided.For example, National Grid requirement wind energy turbine set in voltage range shown in Figure 1 can be incorporated into the power networks.The voltage range indication is a wind energy turbine set tie point voltage among the figure because there are electrical isolation in generator and tie point, during electric network fault generator terminal voltage fall degree can be less than tie point electric voltage dropping degree.

The home and abroad mainly is to have adopted the rotor short-circuit resist technology to the control method of DFIG rotor-side under the electric network fault at present.This method is when electric network fault, though protected exciter converter and rotor winding, generator operation need absorb a large amount of reactive powers from electrical network in the induction motor mode at this moment, and this will further worsen electrical network; The second, the switching operation of protective circuit can produce transient state to system and impact; In addition, add new protective device and improved system cost.Have the scholar to introduce novel topological structure, this scheme control is complicated, and because the generator off-grid operation when the transmission system fault of this scheme, therefore normal operation does not have positive support effect to power system restoration; Equally, this scheme need increase the cost of system.

Adopt improved excitation control algolithm through can remedy the influence that operation is caused to double feedback electric engine of line voltage fault to a certain extent to being controlled at of rotor-side.Its advantage is to need not to improve system cost, and when electrical network falls, can meritorious idle support be provided to electrical network.Therefore, be necessary to design the control method of DFIG rotor current under a kind of electric network fault.

Summary of the invention

The objective of the invention is to solve the problem that exists in the prior art; DFIG rotor current control method under a kind of electric network fault is provided; This method need not added the additional hardware device; Can effectively suppress the DFIG rotor current vibration that electric network fault causes, realize being incorporated into the power networks under the double-fed wind power generator fault, improve the runnability of DFIG under electric network fault.

To achieve these goals, the present invention takes following technical scheme:

The double-fed wind power generator rotor current control method may further comprise the steps under a kind of electric network fault

(1) detect threephase stator voltage, three-phase rotor current and rotor position angle also calculate angular velocity of rotation;

(2) detected threephase stator voltage and three-phase rotor current are obtained two stator voltage and rotor currents under the rest frame mutually through 3/2 conversion module;

(3) with the stator voltage signal under the stator two phase rest frames through software phase-lock loop, obtain the stator magnetic linkage position angle; The rotor position angle that obtains according to step (1) calculates the slippage angle, and slippage angle differential is obtained slippage angular speed; Obtain magnetic linkage angular speed and rotor velocity sum with carrying out differential after stator magnetic linkage position angle and the rotor position angle summation;

(4) be that angle of transformation carries out anti-Park conversion with d, q axle rotor current reference value under the rotating coordinate system with the slippage angle, obtain the rotor current set-point under the rotor two phase rest frames;

(5) with the rotor current set-point under the rotor that calculates in the step (4) the two phase rest frames respectively with step (2) calculated two mutually the rotor current under the rest frame subtract each other, pass through the reference value that ratio resonance (PR) controller calculates two phase rest frame lower rotor part voltages then;

(6) the rotor voltage signal under the two phase rest frames that step (5) obtained produces the switching signal of power controlling device through after the space vector pulse width modulation.

As further execution mode, the PR controller described in the step (5), its transfer function does

$K_p+\frac{K_{\mathrm{<figure-callout\; id="2"\; label="r\; S\; S"\; filenames="HDA00000299037500013.png,HDA00000299037500041.png"\; state="\{\{state\}\}">r</figure-callout>}}S}{S^{}}+\frac{K_{r1}\mathrm{<figure-callout\; id="2"\; label="S\; S"\; filenames="HDA00000299037500013.png,HDA00000299037500041.png"\; state="\{\{state\}\}">S</figure-callout>}}{S^{}}+\frac{K_{r2}\mathrm{<figure-callout\; id="2"\; label="S\; S"\; filenames="HDA00000299037500013.png,HDA00000299037500041.png"\; state="\{\{state\}\}">S</figure-callout>}}{S^{}}$

PR controller medium frequency ω _c, ω _C1, ω _C2Be set to slippage angular speed, rotor velocity and rotor velocity and synchronous angular velocity sum respectively.

Control method of the present invention is under the situation of not changing hardware configuration; Only two PI controllers of the vector control through tradition is meritorious, reactive power decoupling zero replace with the PR controller of band compensation term; Its compensation term is used for the influence that compensation network instant of failure stator magnetic linkage DC component and negative sequence component produce generator amature; Suppress the rotor overcurrent that the line voltage fault is brought, be incorporated into the power networks under the stable control of realization double-fed wind power generator and the fault.Simultaneously, because rotor current obtains fine inhibition, stator current, the vibration that stator is meritorious, reactive power and electromagnetic torque produce when the electrical network symmetry is fallen fault is also improved accordingly.

Description of drawings

Fig. 1 is the voltage range requirement of National Grid wind farm grid-connected operation during to electric network fault.

Fig. 2 is a double-fed wind power generator rotor Current Control schematic diagram under the electric network fault.

Fig. 3 is PR controller principle figure among the present invention.

Fig. 4 is the stator voltage 80% 3 symmetrical design sketch that adopts the conventional vector control method under the fault that falls, and (a) is stator three-phase voltage u among the figure _Sabc(KA); (b) be the rotor three-phase current i _Rabc(KA); (c) be stator three-phase current i _Sabc(KA); (d) be motor speed n (r/min); (e) be electromagnetic torque T _e(KNm); (f) be stator active power P _s(MW); (g) be the stator reactive power Q _s(MVar).

Fig. 5 is the stator voltage 80% 3 symmetrical design sketch that adopts control method of the present invention under the fault that falls, and (a) is stator three-phase voltage u among the figure _Sabc(KA); (b) be the rotor three-phase current i _Rabc(KA); (c) be stator three-phase current i _Sabc(KA); (d) be motor speed n (r/min); (e) be electromagnetic torque T _e(KNm); (f) be stator active power P _s(MW); (g) be the stator reactive power Q _s(MVar).

Fig. 6 relatively falls the design sketch that adopts the conventional vector control method under the fault for 80% liang of stator voltage, and (a) is stator three-phase voltage u among the figure _Sabc(KA); (b) be the rotor three-phase current i _Rabc(KA); (c) be stator three-phase current i _Sabc(KA); (d) be motor speed n (r/min); (e) be electromagnetic torque T _e(KNm); (f) be stator active power P _s(MW); (g) be the stator reactive power Q _s(MVar).

Fig. 7 relatively falls the design sketch that adopts control method of the present invention under the fault for 80% liang of stator voltage, and (a) is stator three-phase voltage u among the figure _Sabc(KA); (b) be the rotor three-phase current i _Rabc(KA); (c) be stator three-phase current i _Sabc(KA); (d) be motor speed n (r/min); (e) be electromagnetic torque T _e(KNm); (f) be stator active power P _s(MW); (g) be the stator reactive power Q _s(MVar).

Embodiment

Below in conjunction with accompanying drawing and embodiment the present invention is further specified.

Electric network fault generally is divided into symmetric fault and unbalanced fault, and symmetric fault generally is to be caused by electrical network three relative ground circuits, and unbalanced fault is divided into single-phase shorted to earth fault, two relative ground circuit fault and phase faults.Falling of the generator unit stator voltage that electric network fault can cause, the variation of stator voltage will cause that the generator unit stator magnetic linkage changes.Normal condition issues the motor stator voltage equation can be expressed as the space vector form:

$u_s=R_s{i}_s+\frac{{\mathrm{d\&psi;}}_s}{\mathrm{dt}}---\left(1\right)$

In the formula: u _s, i _s, ψ _s, R _sRepresent stator voltage under the rest frame, electric current, magnetic linkage and resistance respectively.

When electric network fault took place, stator voltage moment was fallen, and is ignoring under the situation of stator resistance, can find out that by formula (1) stator magnetic linkage will and then change.Yet, can know that according to superconductor closed-loop path magnetic linkage conservation principle and Lenz's law though sudden change has taken place stator voltage, instant of failure generator unit stator magnetic linkage will keep invariable.Be to produce transient DC component and negative sequence component (unbalanced fault) in the stator magnetic linkage to keep electric voltage dropping moment generator unit stator magnetic linkage constant.If consider the influence of stator resistance, this DC component and negative sequence component can be decayed in time.

Suppose that in fault taking place moment only considers electromagnetic transient, and disregard mechanical transient process, promptly generator keeps rotating speed constant during transient process.Because when fault took place, also with rotating speed rotation before the fault, the relative velocity of stator magnetic linkage DC component and rotor was a motor speed to generator amature, the relative velocity of same stator magnetic linkage negative sequence component and rotor is synchronous rotary speed and motor speed sum.Stator magnetic linkage DC component and negative sequence component can produce the influence that frequency is rotor speed, synchronous rotary speed and motor speed sum respectively to rotor flux.According to closed-loop path magnetic linkage conservation principle; In order to keep the rotor flux conservation; In the rotor loop frequency of occurrences is respectively the motor speed and the synchronous alternating current component of rotary speed and motor speed sum, the magnetic linkage that these two alternating current components will produce two corresponding frequencies is respectively offset the influence of stator magnetic linkage to rotor.Rotor produced the main cause of big electric current when the alternating current that rotor is inducted promptly was the fault generation.

The analysis of the inner transient state electromagnetic relationship of wind-driven generator can be known during according to above electric network fault; If suppress the induced current of rotor through compensation to rotor-exciting voltage; Can offset the harmful effect of stator magnetic linkage transient DC component and negative sequence component, double-fed generator can be fallen at the line voltage three-phase guarantee being incorporated into the power networks of generator when fault takes place the generator amature side.

Fig. 2 is a double-fed wind power generator rotor Current Control schematic diagram under the electric network fault.Its control method specifically comprises the steps:

(1) adopt voltage sensor and current sensor to detect threephase stator voltage u respectively _Sabc, three-phase rotor current i _Rabc, adopt encoder detection rotor angular position theta _rAnd calculating angular velocity of rotation ω _r

(2) with the detected threephase stator voltage of step (1) u _SabcWith three-phase rotor current i _RabcObtain the stator voltage u under the two phase rest frames through 3/2 conversion module _{S α}, u _{S β}With rotor current i _{R α}, i _{R β}

(3) with the stator voltage signal u under the stator two phase rest frames _{S α}, u _{S β}Through software phase-lock loop, obtain the stator magnetic linkage angular position theta _sThe rotor position angle θ that obtains according to step (1) _rCalculate slippage angle θ _s-θ _r, slippage angle differential is obtained the slippage angular velocity omega _SlWith the stator magnetic linkage angular position theta _sWith rotor position angle θ _rCarry out differential after the summation and obtain magnetic linkage angular speed and rotor velocity sum ω _Sr

(4) with d, q axle rotor current reference value i under the rotating coordinate system _Rd ^*And i ^Rq*With the slippage angle is that angle of transformation carries out anti-Park conversion, obtains the rotor current set-point i under the rotor two phase rest frames _{R α} ^*, i _{R β} ^*

(5) with the rotor current set-point i under the rotor that calculates in the step (4) the two phase rest frames _{R α} ^*, i _{R β} ^*The two rotor current i under the rest frame mutually that calculated with step (2) respectively _{R α}, i _{R β}Subtract each other, calculate the reference value u of two phase rest frame lower rotor part voltages then through the PR controller _{S α} ^*, u _{S β} ^*

(6) the rotor voltage signal u under the two phase rest frames that step (5) obtained _{S α} ^*, u _{S β} ^*Through after the space vector pulse width modulation, produce the switching signal of power controlling device.

The concrete form of PR controller is as shown in Figure 3 among Fig. 2, and its transfer function does

$K_p+\frac{K_{\mathrm{<figure-callout\; id="2"\; label="r\; S\; S"\; filenames="HDA00000299037500013.png,HDA00000299037500041.png"\; state="\{\{state\}\}">r</figure-callout>}}S}{S^{}}+\frac{K_{r1}\mathrm{<figure-callout\; id="2"\; label="S\; S"\; filenames="HDA00000299037500013.png,HDA00000299037500041.png"\; state="\{\{state\}\}">S</figure-callout>}}{S^{}}+\frac{K_{r2}\mathrm{<figure-callout\; id="2"\; label="S\; S"\; filenames="HDA00000299037500013.png,HDA00000299037500041.png"\; state="\{\{state\}\}">S</figure-callout>}}{S^{}}---\left(2\right)$

For suppressing the rotor current that stator causes under the electric network fault stationary rotor coordinate system lower frequency is respectively motor speed and motor speed and synchronous angular velocity sum, PR controller medium frequency ω _c, ω _C1, ω _C2Be set to the slippage angular velocity omega respectively _Sl, rotor velocity ω _rWith rotor velocity and synchronous angular velocity sum ω _Sr

Key points in design of the present invention promptly is under above-mentioned electric network fault in the double-fed wind power generator rotor current control method; Through analyzing the reason that overcurrent produces and the characteristics of overcurrent, the induced current of the particular frequencies that the compensation term of utilizing the PR controller produces during to rotor fault suppresses.Realized being incorporated into the power networks of double-fed wind power generator under the electric network fault.

Be the correctness of proof theory and the validity of compensation control strategy; Suppose that electric network fault makes under the condition that the generator unit stator set end voltage falls; The method that adopts the present invention to propose is the control of 1.5MW DFIG system implementation to a rated power, and rotor current has been converted stator side.Be located in the control procedure and keep wind-driven generator to be incorporated into the power networks all the time, and frequency converter operate as normal all the time.

Electric network fault lower rotor part Current Control Strategy to traditional stator flux linkage orientation vector control strategy and proposition compares, and Fig. 4 and Fig. 5 are respectively and adopt traditional double-fed wind powered generator control method and control method of the present invention at the stator voltage 80% 3 symmetrical operation result that falls under the condition that electric network fault causes.Line voltage falls at 0.1s constantly, recovers normal constantly at 0.3s.When traditional control method of Fig. 3 takes place in the electric network electric voltage drop fault; Because stator voltage changes the influence of the stator magnetic linkage DC component that is produced; The stator and rotor electric current of DFIG significantly increases during electric network electric voltage drop, will surpass the current limit value of converter plant in the real system, causes wind turbine generator will have to and grid disconnection; This both had been unfavorable for the stable operation of generator, also was unfavorable for the fault recovery and the stable operation of electrical network.Stator is meritorious, reactive power and electromagnetic torque have all produced thermal agitation, and vibration significantly meritorious, reactive power will influence stablizing of electrical network, and the thermal agitation of electromagnetic torque will cause the generator mechanical failure.Compare with traditional control method; Fig. 5 control method has effectively been eliminated the rotor current pulsation under the electric network fault; Suppressed the generation of rotor overcurrent; Simultaneously stator current, meritorious, reactive power and electromagnetic torque pulsation obviously reduce, and motor can send the recovery that lasting meritorious, reactive power are supported electrical network.The wind turbine generator of this method control satisfies the condition that is incorporated into the power networks under the fault, has improved the operation control ability of DFIG under the electric network fault condition, has improved the dynamic quality of control system.

Fig. 6 and Fig. 7 are respectively and adopt traditional double-fed wind powered generator control method and the inventive method at 80% liang of operation result that falls mutually under the condition of stator voltage that electric network fault causes.Line voltage falls at 0.1s constantly, recovers normal constantly at 0.3s.Find out that by Fig. 6 electric network fault takes place and the recovery moment, stator and rotor electric current generation thermal agitation produces serious overcurrent, and at this moment protective device must start the safety with the protection frequency converter.Necessary and the grid disconnection of generating set has further influenced the recovery of electric network fault.

Fig. 7 is the control design sketch of the inventive method, takes place and recovers constantly at electric network fault among the figure, the pulsation of the rotor current that this control method has effectively suppressed to be caused by stator magnetic linkage DC component and negative sequence component.The vibration of electric current is very little, does not influence the operation of wind turbine generator.By finding out among Fig. 7, after line voltage recovered, rotating speed was controlled very soon, satisfies the requirement that wind-driven generator is incorporated into the power networks under the electrical network catastrophe failure.

In sum; Control method of the present invention is compared with traditional stator flux linkage orientation vector control, and under electric network fault, control system can effectively be eliminated the current fluctuation of rotor; Suppress the generation of rotor overcurrent, strengthened the run without interruption ability of DFIG wind-powered electricity generation unit under electric network fault; Institute's control system algorithm of carrying is simple; Only need tradition is meritorious, the PI controller of electric current loop changes the PR controller that contains the harmonic compensation item in the reactive power decoupling zero vector control; Just can suppress the rotor overcurrent that electric network fault brings; And the rotor current that reduces makes the stator overcurrent also obtain obvious inhibition to the influence of stator magnetic linkage.

Claims (1)

1. double-fed wind power generator rotor current control method under the electric network fault is characterized in that may further comprise the steps:

(1) detect threephase stator voltage, three-phase rotor current and rotor position angle also calculate angular velocity of rotation;

(2) detected threephase stator voltage and three-phase rotor current are obtained two stator voltage and rotor currents under the rest frame mutually through 3/2 conversion module;

(3) with the stator voltage under the stator two phase rest frames through software phase-lock loop, obtain the stator magnetic linkage position angle; The rotor position angle that obtains according to step (1) calculates the slippage angle, and slippage angle differential is obtained slippage angular speed; Obtain magnetic linkage angular speed and rotor velocity sum with carrying out differential after stator magnetic linkage position angle and the rotor position angle summation;

(4) be that angle of transformation carries out anti-Park conversion with d, q axle rotor current reference value under the rotating coordinate system with the slippage angle, obtain the rotor current set-point under the rotor two phase rest frames;

(5) with the rotor current set-point under the rotor that calculates in the step (4) the two phase rest frames respectively with step (2) calculated two mutually the rotor current under the rest frame subtract each other, calculate the reference value of two phase rest frame lower rotor part voltages then through the ratio resonant controller;

The reference value of the two phase rest frame lower rotor part voltages that (6) step (5) obtained produces the switching signal of power controlling device through after the space vector pulse width modulation.

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