CN104917201A - Controller and method for simulating active power frequency of double-fed induction generator (DFIG) in combination with inertia and over speed - Google Patents

Abstract

The invention discloses a controller and method for simulating the active power frequency of a double-fed induction generator (DFIG) in combination with inertia and over speed. The controller comprises a frequency deviation detecting module, a blocking module, a regulating variable setting module, a time delay module and a speed protecting module which are connected in sequence, wherein a real-time grid frequency signal and a frequency setting value are respectively input in the frequency deviation detecting module to obtain the frequency deviation signal of the grid at that time; the frequency deviation signal enters the regulating variable setting module through the blocking module, and the regulating variable setting module obtains a speed regulating variable according to the frequency deviation signal; and the speed protecting module enables the DFIG unit to exit frequency modulation under an abnormal speed condition, and can put into the frequency modulation again after time delay for a period of time. The controller has the beneficial effects that large-scale double-fed wind power integration takes the place of a conventional synchronous generator to cause that the system inertia is reduced and thus the transient stability of system frequency is worsened, and the comprehensive frequency controller provided by the invention can effectively solve the problem.

Description

Simulation inertia and the double-fed blower fan active power and frequency control device and method that combine of exceeding the speed limit

Technical field

The present invention relates to double-fed wind power generator technical field, particularly relate to a kind of inertia and double-fed blower fan that hypervelocity method controls to combine of simulating and to gain merit frequency synthesis controller and method.

Background technology

Wind power generation is as current the most ripe, the generation of electricity by new energy mode most with scale development condition, and the region permeability that especially wind energy resources is abundant in electric power system constantly increases.The develop rapidly of wind power generation scale brings huge environmental benefit and economic benefit, but brings new challenge also to the safe and stable operation of electric power system.

Double-fed wind power generator (doubly fed induction generation, DFIG) has the little feature of generating efficiency height frequency inverter capacity, one of main force's type having become current Large Scale Wind Farm Integration.Its power electronics converter is while realizing maximal power tracing, also make no longer there is coupled relation between rotor speed and mains frequency, can not be discharged by rotor as conventional synchronization generator or store kinetic energy damping system frequency change, namely Wind turbines rotor kinetic energy by frequency converter completely " hiding ".From total system angle, the moment of inertia of Wind turbines is zero, and the wind energy turbine set based on DFIG unit accesses the frequency dynamic response characteristic of the obvious attenuation systems of meeting on a large scale.And efficiency has reached the primary frequency modulation maximizing and cannot participate in system when it operates in maximal power tracing (Maximum Power Point Tracking, MPPT) pattern.

In order to reduce the impact of extensive DFIG unit access on mains frequency stability, common has improved one's methods:

1, the kinetic energy utilizing rotor to store carries out short time frequency modulation, and additional meritorious frequency control link, to simulate the frequency response characteristic of synchronous generator, makes speed-changing draught fan have certain virtual inertia;

2, reduce generator efficiency by the method at hypervelocity or variable pitch angle, make it leave the primary frequency modulation of surplus energy participation system;

3, the method utilizing the energy-storage system such as flywheel, battery pack to assist wind energy turbine set to participate in system frequency adjustment have also been obtained the concern of Many researchers.

DFIG unit set inertia is large, rotational speed regulation wider range, and therefore said method can simulate " simulated inertia " larger than synchronous machine in theory; But the kinetic energy that DFIG unit can provide when rotating speed is lower is limited, after exiting frequency modulation, rotating speed recovery process power output reduces and will the secondary of mains frequency be caused to fall, and in frequency-modulating process, operating point departs from maximal power tracing point and also will deepen this adverse effect.Further, perfect wind energy turbine set frequency regulation capability, requires that Wind turbines possesses controlled inertial response and Primary frequency control ability simultaneously, and the integrated control method that after off-load, primary frequency modulation and inertia control to organically combine is comparatively rare.

Summary of the invention

In order to overcome the above problems, the invention provides and a kind ofly simulate inertia and exceed the speed limit the double-fed blower fan active power and frequency control device that combines and method.The method can make double-fed blower fan utilize the inertia frequency modulation of rotor kinetic energy and the effective back-up system of off-load reserve capacity, reduce static frequency error, and avoids the system frequency secondary pulse that excessive frequency modulation may bring.

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

Simulate inertia and the double-fed blower fan active power and frequency control device that combines of exceeding the speed limit, comprising: the frequency departure detection module connected successively, to adjust module, time delay module and speed protection module every straight module, regulated quantity;

Real-time grid frequency signal f _meawith frequency setting value f _refincoming frequency separate-blas estimation module obtains the frequency departure signal delta f of now electrical network respectively; Frequency departure signal delta f to adjust module through entering regulated quantity every straight module, and regulated quantity module of adjusting obtains rotational speed regulation amount according to frequency departure signal delta f; Rotating speed protection module makes DFIG unit exit frequency modulation under rotating speed abnormal conditions, and again could drop into frequency modulation after time delay certain hour.

Simulate inertia and a control method for the double-fed blower fan active power and frequency control device combined that exceeds the speed limit, comprise the following steps:

(1) determine the most strong wind power that double-fed wind power generator is caught, and obtain double-fed wind power generator maximum power tracking curve equation;

(2) when mains frequency normally works, Wind turbine operates in hypervelocity off-load state, improves rotor store kinetic energy and obtain frequency modulation reserve capacity by hypervelocity method;

(3) when detecting that system frequency deviation exceedes controlling dead error, according to frequency departure size, rotor speed, hypervelocity off-load amount determination rotational speed regulation amount, double-fed Wind turbine determines given active power of output reference value according to rotational speed regulation amount and rotor speed.

(4) static difference coefficient during double-fed Wind turbine participation system primary frequency modulation is adjusted, make it have the droop characteristic the same with conventional electric generators;

The most strong wind power of catching of wind-driven generator is in described step (1):

$\left\{\begin{array}{c}{P}_{opt}=\frac{1}{2}{\mathrm{\ρC}}_{p_{opt}}({\mathrm{\λ}}_{opt},\mathrm{\β}){\mathrm{AU}}_w^3\\ C_{p_{opt}}({\mathrm{\λ}}_{opt},\mathrm{\β})=0.22(\frac{116}{{\mathrm{\λ}}_i}-0.4\mathrm{\β}-5)e^{\frac{-12.5}{{\mathrm{\λ}}_i}}\\ \frac{1}{{\mathrm{\λ}}_i}=\frac{1}{{\mathrm{\λ}}_{opt}+0.08\mathrm{\β}}-\frac{0.035}{{\mathrm{\β}}^3+1}\\ {\mathrm{\λ}}_{opt}=\frac{w_{t_{opt}}R}{U_w}\end{array}\right.$

Wherein, P _optfor the maximum power that given wind speed apparatus for lower wind machine is caught, ρ is atmospheric density, C _optfor with tip speed ratio λ _opt, optimum Wind resource change rate coefficient that propeller pitch angle β is relevant, A is the inswept area of blower fan, U _wfor wind speed, w _toptfor blower fan angular velocity of rotation, R is blade radius.

In described step (1), double-fed wind power generator maximum power tracking curve equation is specially:

$P_{opt}=k_{opt}{w}_r^3$

In formula:

$k_{opt}=\frac{1}{2}\mathrm{\ρ}\left(\frac{C_{P_{opt}}}{{\mathrm{\λ}}_{opt}^3}\right){\mathrm{\πR}}^5$

${\mathrm{\ω}}_r=\left(\frac{p}{2}\right){\mathrm{G\ω}}_t$

In formula: P _optfor the maximum power that wind energy conversion system is caught, k _optfor by the determined power tracking coefficient of wind energy conversion system aerodynamics, ρ is atmospheric density, C _poptoptimal power conversion coefficient, λ _optfor optimum tip speed ratio, R is blade radius, ω _rfor rotor speed, p is power generator electrode logarithm, and G is gear box carry-over factor, w _tfor blower fan angular velocity of rotation.

Rotational speed regulation amount in described step (3) is:

$\mathrm{\Δ}w=\frac{k_{opt}-k_{de}}{3k_{opt}(1-d\%)}\×w_r\×\frac{\mathrm{\Δ}f}{f_b-f_a}$

Wherein, k _optk _debe respectively power tracking coefficient before and after off-load, d% represents off-load amount size, w _rfor rotor speed, Δ f is frequency departure amount size, f _bf _afor mains frequency regulates bound under normal circumstances, mains frequency decline does not allow more than 0.5Hz under normal circumstances.

Beneficial effect of the present invention:

1, extensive double-fed fan motor grid-connected replacement conventional synchronous generator will cause system inertia to reduce thus worsen system frequency transient stability, and the collective frequency controller that the present invention proposes can effectively improve this problem.

2, the simulation inertia that the present invention proposes controls and the comprehensive frequency modulation control method that combines of hypervelocity method, has that frequency modulation function is perfect, the stable feature of frequency-modulating process, can effectively reduce frequency fluctuation amplitude and static frequency error that load disturbance causes.The controlled quentity controlled variable setting method researched and proposed further makes DFIG unit participation frequency-modulating process have the droop characteristic the same with conventional electric generators.

3, after demonstrating DFIG unit employing rotational speed regulation general controller by simulation analysis, system response is effectively improved.Participating in frequency-modulating process medium speed maintains in safety zone, overcomes general kinetic energy control method frequency modulated time short and easily cause the problem of machine of cutting.

Accompanying drawing explanation

Fig. 1 is typical simulation inertia integrated control method schematic diagram;

Fig. 2 is the sagging frequency characteristics control curve of conventional generator of band speed regulator;

Fig. 3 is under same wind conditions, DFIG off-load schematic diagram;

Fig. 4 is DFIG rotational speed regulation Comprehensive Control schematic diagram of the present invention;

When Fig. 5 is sudden load increase, DFIG participates in power output in frequency-modulating process, catch relation schematic diagram between power and rotating speed;

Fig. 6 is changed power schematic diagram in moderating process and accelerator;

Fig. 7 is analogue system example structural representation of the present invention;

Fig. 8 be embodiment of the present invention load L2 uprush 100MW time system frequency response comparison diagram;

Fig. 9 is embodiment of the present invention DFIG unit active power of output change curve;

Figure 10 is embodiment of the present invention DFIG generating unit speed change curve;

Figure 11 is that embodiment of the present invention DFIG unit participates in inputting mechanical changed power curve in frequency-modulating process.

Embodiment

Below in conjunction with accompanying drawing and embodiment, the invention will be further described.

1, DF I G unit set inertia frequency modulation and primary frequency modulation specificity analysis

1.1 rotor kinetic energy control methods

The kinetic energy that wind-driven generator stores in the rotor is:

$E=\frac{1}{2}{\mathrm{J\ω}}^2$

In formula: J is mechanical rotation inertia, ω is rotating speed.The rotational speed regulation scope of DFIG unit is generally synchronous speed ± 0.2pu, and participate in system frequency modulation by controlling rotor speed change release or absorbing rotor kinetic energy, before and after rotating speed changes, the kinetic energy increment of rotor is:

$\mathrm{\Δ}E=\frac{1}{2}J({\mathrm{\ω}}_2^2-{\mathrm{\ω}}_1^2)$

In formula: Δ E is the kinetic energy change amount of rotor, ω ₁and ω ₂be respectively rotor speed before and after frequency modulation.By increasing an additional active power reference value changing to be associated with system frequency on the active power reference value of DFIG rotor-side converter, speed-changing draught fan can be made to utilize the kinetic energy active response system frequency change of storage, the frequency response characteristic of simulation conventional generator.Be typical simulation inertial frequency controller in dotted line frame in following Fig. 1, complete additional meritorious frequency controller also comprise rotating speed protection module, rotating speed recovers module, and the secondary control module such as conventional power unit Coordination module.

In Fig. 1, additional frequency controller gained active power is:

$\mathrm{\Δ}P=-(\mathrm{\Δ}f*\frac{1}{R}+K_f\frac{d\mathrm{\Δ}f}{dt})$

Ignore system loss, write as and be similar to conventional generator equation of rotor motion form and can obtain:

$(2H_s+K_f)\frac{d\mathrm{\Δ}f}{dt}=P_M-P_E-(D+\frac{1}{R})\mathrm{\Δ}f---\left(1\right)$

In formula: H _sfor the inertia constant of conventional generator, K _ffor proportionality coefficient, 1/R is sagging coefficient, and Δ f is system frequency variable quantity, P _mfor wind energy conversion system input machine torque, P _efor exporting electromagnetic torque, D is load damping coefficient.From (1) formula, work as K _fthe moment of inertia similar with conventional electric generators can be produced when being greater than zero, damping coefficient can be increased when 1/R is greater than zero and improve frequency dynamic response performance.

When system frequency is undergone mutation, simulation inertia control given full play to DFIG can quick adjustment gain merit export characteristic, the meritorious support that the kinetic energy utilizing rotor to store makes Wind turbine can provide of short duration, improves the transient stability of system frequency.But due to without active reserve capacity, the system that therefore cannot be continuously provides fm role, and rotation speed of fan enters rotating speed Restoration stage lower than exiting frequency modulation during threshold values.

1.2 Control of decreasing load methods

Conventional generator can change air intake valve aperture to regulate input mechanical output by speed regulator thus make generator participate in primary frequency modulation, conventional generator with speed regulator has droop characteristic, its incremental delivered power is the proportional variation relation with frequency departure as shown in Figure 2, that is:

ΔP＝-K _G*Δf

In formula, K _gthe unit power regulation of unit, K _ginverse be exactly the static difference coefficient of conventional power generation usage unit, that is:

$\mathrm{\δ}=\frac{1}{K_G}=\frac{\mathrm{\Δ}f}{\mathrm{\Δ}P}$

In order to have identical sagging frequency modulation characteristic, certain reserve capacity should be had when DFIG unit is in maximal power tracing operational mode, otherwise it can only play a role when frequency raises, and can not play a role when frequency reduces.The method obtaining reserve capacity feasible has two kinds: a kind of method is hypervelocity method, make its normally work time the optimized rotating speed of speed of service when being greater than maximal power tracing thus reduce the efficiency of Wind turbine, need to control again when increasing power output rotating speed and reduce and make blower fan can catch more mechanical output; Another kind method is that the propeller pitch angle increasing blower fan catches wind power with reduction.Be illustrated in fig. 3 shown below as Control of decreasing load schematic diagram:

Hypervelocity method is based on a.c.frequency converting control technology, and control rate is fast more than award setting speed, and it mainly has certain the blind area of control by maximum (top) speed restriction, is therefore applicable to rated wind speed with lower area.Variable pitch method actuator is mechanical part, the relatively slow DeGrain causing the Wind turbines adopting direct award setting to participate in frequency modulation of propeller pitch angle governing speed, and pitch-controlled system is action aggravation mechanical loss frequently, adds recondition expense and easily shortens service life of fan.Therefore, when conditions permit, the preferential method of hypervelocity that uses obtains reserve capacity.

2, DFIG generating unit speed regulates Comprehensive Control

Wind energy turbine set possesses inertial response ability can reduce the transient stability that system frequency rate of change improves system frequency, have active power for subsequent use and can increase/reduce the primary frequency modulation that input mechanical output participates in system, therefore perfect wind energy turbine set frequency adjustment strategy should possess this two kinds of abilities simultaneously.As mentioned before, blower fan obtains reserve capacity can pass through hypervelocity method and variable pitch method, and the method that variable pitch method combines with simulation inertia is subject to variable pitch method self-defect and limits obviously.Hypervelocity method is mainly subject to velocity limits restriction, and according to wind-powered electricity generation department operating statistic, the probability of blower fan power output overrate 80% is generally no more than 10% of running time, and thus hypervelocity controls can be suitable in most cases.Rotating speed improves also makes blower fan store the kinetic energy that can be used for frequency modulation more, and what therefore the present invention adopted is the method that hypervelocity method and simulation inertia control to combine.

2.1 rotational speed regulation Comprehensive Control principles and frequency modulation dynamic process analysis

The most strong wind power of catching of wind-driven generator can be expressed as:

$\left\{\begin{array}{c}{P}_{opt}=\frac{1}{2}{\mathrm{\ρC}}_{p_{opt}}({\mathrm{\λ}}_{opt},\mathrm{\β}){\mathrm{AU}}_w^3\\ C_{p_{opt}}({\mathrm{\λ}}_{opt},\mathrm{\β})=0.22(\frac{116}{{\mathrm{\λ}}_i}-0.4\mathrm{\β}-5)e^{\frac{-12.5}{{\mathrm{\λ}}_i}}\\ \frac{1}{{\mathrm{\λ}}_i}=\frac{1}{{\mathrm{\λ}}_{opt}+0.08\mathrm{\β}}-\frac{0.035}{{\mathrm{\β}}^3+1}\end{array}\right.---\left(2\right)$

In formula: P _optfor the maximum power that given wind speed apparatus for lower wind machine is caught, ρ is atmospheric density, C _optfor optimum wind power conversion efficiency, λ _optfor optimum tip speed ratio, β is propeller pitch angle, and A is the inswept area of blower fan, U _wfor wind speed.Tip speed ratio λ _opt=w _toptr/U _w, w _toptfor blower fan angular velocity of rotation, R is blade radius.

Due to the more difficult accurate detection of wind speed in actual motion, cannot directly provide the optimum speed corresponded, therefore generally directly not take speed closed loop to control, but balance by control inputs mechanical output and electromagnetic power the indirect control realizing rotating speed with this.Under not considering the condition of loss, DFIG unit is with current rotor rotational speed omega _runiquely determine P _optas the meritorious reference value P in rotor-side active power controller system _ref, adjusting rotary speed can regulation output power easily and directly.Can obtain maximum power tracking curve equation by (2) formula is:

$P_{opt}=k_{opt}{w}_r^3$

In formula:

$k_{opt}=\frac{1}{2}\mathrm{\ρ}\left(\frac{C_{P_{opt}}}{{\mathrm{\λ}}_{opt}^3}\right){\mathrm{\πR}}^5$

${\mathrm{\ω}}_r=\left(\frac{p}{2}\right){\mathrm{G\ω}}_t$

In formula: k _optfor by the determined constant of wind energy conversion system aerodynamics, usually given by producer, p is power generator electrode logarithm, and G is gear box carry-over factor.

Be illustrated in figure 4 the theory diagram of controller: when mains frequency is normal, Wind turbine operates in hypervelocity off-load state, when detecting that system frequency deviation exceedes controlling dead error, by (5) formula according to current rotating speed and off-load situation output speed regulated quantity Δ w, DFIG unit is according to (w _r+ Δ w) determine given power output reference value.

Specifically comprise: the frequency departure detection module connected successively, to adjust module, time delay module and speed protection module every straight module, regulated quantity;

Real-time grid frequency signal f is obtained by detection of grid frequency _meainput control device, by frequency signal and frequency setting value f _refrelatively obtain the frequency departure signal delta f of now electrical network; Regulated quantity module of adjusting obtains rotational speed regulation amount size delta ω according to frequency departure signal delta f and other parameter by following (5) formula; Double-fed Wind turbine is according to (w _r+ Δ ω) determine new optimal power reference value P _refgive rotor side converter, finally reach double-fed blower fan power output responsive electricity grid frequency fluctuation object.Wherein: the impact that Power System Steady-state frequency error can be eliminated every straight link, deviation signal Δ f is made to be greater than the just action of controlling dead error Time Controller.Rotating speed protection module makes DFIG unit exit frequency modulation under rotating speed abnormal conditions, and again could drop into frequency modulation after time delay certain hour.

From generally simulate inertia control method different, adjustment process rotating speed is in safety zone always herein, the just action in case of a fault of rotating speed protection module.Time delay module can prevent frequent switching in rotating speed recovery process.

DFIG unit frequency modulation overall process power-rotation speed change schematic diagram when Figure 5 shows that system loading is uprushed.

Before frequency modulation, DFIG unit operation is at hypervelocity off-load point 2, and when system frequency generation larger fluctuation, electromagnetic power increases Δ P immediately by putting 2 _mto point 3, now catch mechanical output because output electromagnetic power is greater than blower fan, rotor is by deceleration release kinetic energy; As seen from the figure rotating speed be reduced to optimized rotating speed before the blower fan mechanical output of catching will with w _rreduce to increase Δ P by point 2 _warrive point 4, electromagnetic power is then with w _rreduce to be reduced to a little 4 (being the fm capacity limit when point 4 overlaps with MPPT point), final Δ P by point 3 _w=Δ P _mtime generator power reach new poised state, power output maintains increases Δ P _wparticipate in primary frequency modulation.Generally, Δ f reduces Δ w gradually and also declines thereupon under secondary system fm role, under the effect of Wind turbine self regulating and controlling, slow Accelerating running is returned off-load operating point by rotor, accelerator is longer relative to the time moderating process, avoids rotation speed of fan recovery process and causes power output to reduce impacting the frequency of system.

DFIG participates in the whole process of frequency modulation, and power output is along 2 → 3 → 4 → 2 changes, and input power is along 2 → 4 → 2 changes, and this process had both released the power of rotor kinetic energy sharing system sudden change, also takes full advantage of reserve capacity and participates in system primary frequency modulation.Frequency-modulating process when system frequency is uprushed is contrary with said process, and in like manner known rotor first accelerates rear deceleration and finally returns balance point.Changed power curve is illustrated in fig. 6 shown below:

In Fig. 6, area S ₁for the kinetic energy of rotor moderating process release, area S ₂for the kinetic energy that rotor accelerator absorbs, accelerate operating point final return to origin when area equals retardation area, that is:

$\mathrm{\Δ}E=\frac{1}{2}J(W_2^2-W_4^2)={\∫}_{t_1}^{t_2}(P_m-P_w)dt={\∫}_{t_3}^{t_4}(P_w-P_m)dt$

In sum, after taking rotational speed regulation integrated control strategy, DFIG unit catches mechanical output, effective back-up system frequency stabilization according to system frequency fluctuation size release rotor kinetic energy and increase, thus reduces the adverse effect of system inertia after improving wind energy turbine set access electrical network.Because DFIG stores more kinetic energy by improving rotating speed and leaves certain reserve capacity, whole frequency-modulating process rotor speed is positioned at safety zone, does not therefore exist after blower fan participation frequency modulation and cuts machine risk.DFIG unit participates in a secondary frequencies adjustment and also needs rational static frequency characteristic of adjusting out, makes it have with the same droop characteristic of conventional electric generators.

2.2 Comprehensive Control specificity analysis and controls

Static difference coefficient size has material impact to maintenance system frequency is stable.Static difference coefficient is less, generating set fm capacity is stronger, more easily ensure frequency stabilization, but in actual motion, too small static difference coefficient may to cause in system sharing of load between each generating set unreasonable, make set speed adjustment system cannot stable operation, therefore DFIG unit participates in system primary frequency modulation and rationally need adjust to its difference coefficient.If power tracking curvilinear equation is after hypervelocity off-load:

$P_{del}=k_{de}{w}_r^3$

In formula: k _defor off-load power tracking coefficient.Represent off-load amount size with d%, maximal power tracing point with hypervelocity point power relation is:

P ₂＝(1-d％)P ₁(3)

Then sagging coefficient can be expressed as:

${\mathrm{\δ}}_{*}=\frac{1}{{K_G}_{*}}=\frac{{\mathrm{\Δf}}_{*}}{{\mathrm{\ΔP}}_{*}}=\frac{\mathrm{\Δ}f}{f_{0}d\%}$

3%-5% is generally for conventional generator δ value, the frequency of electric power system is fallen amplitude and is not generally allowed more than 0.5Hz, if therefore Wind turbines possesses the static frequency characteristic similar to usual turbo generator set, the off-load level of unit should be 20%-33%, by regulating power aircraft pursuit course.In order to make DFIG unit have the droop characteristic the same with generator shown in Fig. 2, then need the position controlling stable operating point 4 in frequency-modulating process.The position of point 4 not easily directly controls, and to be directly proportional and then the position at control point 4 by the power of uprushing at control point 3 to Δ f.Operate in off-load point 2 before DFIG unit frequency modulation, after frequency disturbance, Wind turbines power output becomes:

$P_2^{\′}=P_2+\mathrm{\Δ}P=k_{del}{(w_r+\mathrm{\Δ}w)}^3=k_{del}(w_r^3+3w_r^2\mathrm{\Δ}w+3w_r{\mathrm{\Δw}}^2+{\mathrm{\Δw}}^3)$

When rotational speed regulation scope is little, w can be thought _r> > Δ w, so:

$k_{del}(w_r^3+3w_r^2\mathrm{\Δ}w+3w_r{\mathrm{\Δw}}^2+{\mathrm{\Δw}}^3)\≈k_{del}(w_r^3+3w_r^2\mathrm{\Δ}w)$

That is:

$\mathrm{\Δ}P=k_{de}3w_r^2\mathrm{\Δ}w=\frac{{\mathrm{\ΔP}}_{max}}{f_b-f_a}*\mathrm{\Δ}f---\left(4\right)$

In formula: Δ P _maxfor the power Δ P that uprushes in Fig. 5 _mthe limiting value that can reach, referred to as limit frequency modulation power, limit frequency modulation power should not be too large in order to avoid rotating speed ingoing power unstable region.As seen from Figure 5, limit frequency modulation power is power difference between point (putting 5) that maximal power tracing point (point 1) is identical with rotating speed in off-load power curve.Maximal power tracing point and hypervelocity off-load point power are respectively:

$P_1=k_{opt}{\mathrm{\ω}}_1^3$

$P_2=k_{de}{\mathrm{\ω}}_2^3$

The rotation speed relation of 2 can be obtained by the power relation of (3) formula 2:

${\mathrm{\ω}}_1={\mathrm{\ω}}_5=\sqrt[3]{\frac{k_{de}}{k_{opt}(1-d\%)}}{\mathrm{\ω}}_2$

Point 5 rotating speed is substituted into off-load power tracking curvilinear equation can obtain:

$P_5=k_{de}\frac{k_{de}}{k_{opt}(1-d\%)}{\mathrm{\ω}}_2^3=\frac{k_{de}}{k_{opt}(1-d\%)}{P}_2$

So:

${\mathrm{\ΔP}}_{max}=P_1-P_5=\frac{1}{1-d\%}{P}_2-\frac{k_{de}}{k_{opt}(1-d\%)}{P}_2=\frac{k_{opt}-k_{de}}{k_{opt}(1-d\%)}{P}_2$

By Δ P _max(4) formula of substitution also can obtain after abbreviation:

$\mathrm{\Δ}w=\frac{k_{opt}-k_{de}}{3k_{opt}(1-d\%)}\×w_r\×\frac{\mathrm{\Δ}f}{f_b-f_a}---\left(5\right)$

Wherein, k _optk _debe respectively power tracking coefficient before and after off-load, d% represents off-load amount size, w _rfor rotor speed, Δ f is frequency departure amount size, f _bf _afor mains frequency regulates bound under normal circumstances, mains frequency decline does not allow more than 0.5Hz under normal circumstances.

By (4) (5) two formula can find out, power tracking coefficient and frequency-tuning range are setting parameter, can adjust according to static difference coefficient.Δ f ∝ Δ w ∝ Δ P in frequency-tuning range, thus DFIG unit participation system primary frequency modulation has the droop characteristic the same with conventional electric generators.

3, simulation analysis

The present invention is based on classical four machine two district systems, example system has as shown in Figure 7 been built in MATLAB/Simulink, wherein G1, G3 and G4 capacity of being respectively is the thermal power plant of 400MW and 1000MW, No. 2 Nodes G2 are wind energy turbine set (wind energy turbine set is made up of the double-fed wind power generator of 200 1.5MW), and wind energy turbine set rated capacity is overall system capacity 14.2%.Load L1 and L2 is that constant burden with power is respectively 500MW and 1000MW.Choose the rated capacity in each power plant for its power base value, rotating speed base value is the rated speed of DFIG unit.

Frequency response simulation analysis during 3.1 system loading sudden change

Wind speed is 9m/s, and tuning range is ± 0.5Hz, DFIG unit is in 11% off-load state by the method for hypervelocity, and load L2 to be uprushed to 1100MW by 1000MW in the 10.0s moment, caused system frequency to reduce.Fig. 8 is that DFIG unit is taked to control without additional frequency respectively, general simulation inertia controls, rotational speed regulation Comprehensive Control three kinds of control modes time, system frequency curve of cyclical fluctuations contrast situation after load disturbance, can find out by figure:

The out-of-control situation lower frequency of DFIG unit declines the fastest and the range of decrease is comparatively large, and fluctuation amplitude has exceeded requirement;

Take generally to simulate inertia control method and can make the frequency fluctuation of Wind turbine responding system, restrained effectively frequency fluctuation maximum amplitude.But the kinetic energy that can provide because rotation speed of fan is lower is limited, after about 10s, Wind turbine exits frequency modulation and causes secondary pulse to system frequency, also will aggravate along with wind energy turbine set scale strengthens impact effect thereupon;

Take rotational speed regulation integrated control strategy, frequency departure exceed frequency modulation control dead band (± 0.2Hz) afterwards frequency modulation control have an effect.The frequency modulation initial stage relies on rotor release kinetic energy effectively to inhibit system frequency to fluctuate, and frequency minima is promoted to 49.66Hz by 49.38Hz, and the change amplitude of frequency decreases 45.1%, obvious to system inertia supporting function, can by FREQUENCY CONTROL in claimed range.Wind turbine not only falls initial stage oscillation suppression in system frequency, shares the imbalance power of frequency modulation generator in system primary frequency modulation process for a long time, and with compared with additional control, static frequency deviation reduces about 0.05Hz.Because hypervelocity method makes generator store more kinetic energy and operating point is close to maximal power tracing point gradually, therefore DFIG unit whole process avoids the secondary pulse that general simulation inertia control method is brought, and frequency retrieval process is improved.

3.2 active power Output Characteristic

Fig. 9 is in glitch perturbation process, the power output situation of change of DFIG unit under three kinds of control modes.When DFIG unit controls without additional frequency, Wind turbine operates in maximal power point tracking control model, and its power output keeps 0.225pu to system frequency change without response.Adopt general simulation inertia control method, power output when storing kinetic energy responding system frequency change therefore frequency modulation starts can be utilized to increase, but when 20s, frequency control link is forced excision because rotating speed is too low, and this result also in the secondary pulse of system frequency.Adopt rotational speed regulation integrated control method, time normal, power output is reduced to 0.2pu (off-load 11%) by 0.225, frequency modulation starts rear power output responding system frequency change to be increased fast, along with rotating speed and frequency departure reduce reduction gradually, still less speed is relative slower, final power output becomes power before off-load, reserve capacity plays a role completely, and therefore DFIG unit energy effectively participates in the long-term frequency modulation of system.

3.3 rotation speed change process analysis procedure analyses

Figure 10 is that DFIG unit participates in frequency-modulating process medium speed situation of change.DFIG unit is without in additional frequency control situation, and running of wind generating set is in maximal power point tracking control model, and unit is to system frequency change without response, and its rotating speed only adjusts according to the change of wind speed, keeps optimum tip speed ratio, to follow the trail of maximal wind-energy.Under adopting general simulation inertia control situation, the kinetic energy that rotating part stores is limited and do not have controlled energy source, if frequency modulation is excessive, finally excises frequency control link by force because rotating speed is too low, causes the secondary of system frequency to fluctuate.When adopting rotational speed regulation integrated control method, during stable operation, rotating speed is increased to 1.02pu by 0.85 and stores more kinetic energy and be conducive to frequency modulation, and final rotating speed levels off to optimized rotating speed instead of lower rotation speed limit value therefore and without cutting machine risk.

The mechanical power characteristic analysis of 3.4 input

Figure 11 is that DFIG unit participates in inputting mechanical changed power situation in frequency-modulating process.As can be seen from the figure, the wind power that DFIG unit adopts general simulation inertia control method to catch in frequency-modulating process is reducing until exit frequency modulation to enter rotating speed Restoration stage always, a kinetic energy part for rotor losses is used for the other part of system frequency modulation and is used for making up mechanical output loss, and this factor reduce further the Wind turbine Frequency Adjustable time.DFIG unit adopts the method for rotational speed regulation Comprehensive Control, and catching wind power in frequency-modulating process is increasing amplitude peak always and be about 0.05pu.

After demonstrating DFIG unit employing rotational speed regulation integrated control strategy by simulation analysis, frequency characteristic is effectively improved.Participating in frequency-modulating process medium speed maintains in safety zone, overcomes general kinetic energy control method frequency modulated time short and easily cause the problem of machine of cutting.

By reference to the accompanying drawings the specific embodiment of the present invention is described although above-mentioned; but the restriction not to invention protection range; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various amendment or distortion that creative work can make still within protection scope of the present invention.

Claims (6)

1. simulate inertia and the DFIG unit active power and frequency control device that combines of exceeding the speed limit, it is characterized in that, comprising: the frequency departure detection module connected successively, to adjust module, time delay module and speed protection module every straight module, regulated quantity;

Real-time grid frequency signal and frequency setting value respectively incoming frequency separate-blas estimation module obtain the frequency departure signal of now electrical network; Frequency departure signal to be adjusted module through entering regulated quantity every straight module, and regulated quantity module of adjusting obtains rotational speed regulation amount according to frequency departure signal; Rotating speed protection module makes DFIG unit exit frequency modulation under rotating speed abnormal conditions, and again could drop into frequency modulation after time delay certain hour.

2. a kind of inertia and double-fed blower fan of combining of exceeding the speed limit of simulating as claimed in claim 1 is gained merit the control method of frequency synthesis controller, it is characterized in that, comprises the following steps:

(1) determine the most strong wind power that double-fed wind power generator is caught, and obtain double-fed wind power generator maximum power tracking curve equation;

(2) when mains frequency normally works, Wind turbine operates in hypervelocity off-load state, improves rotor store kinetic energy and obtain frequency modulation reserve capacity by hypervelocity method;

(3) when detecting that system frequency deviation exceedes controlling dead error, according to frequency departure size, rotor speed, hypervelocity off-load amount determination rotational speed regulation amount, double-fed Wind turbine determines given active power of output reference value according to rotational speed regulation amount and rotor speed;

(4) static difference coefficient during double-fed Wind turbine participation system primary frequency modulation is adjusted, make it have the droop characteristic the same with conventional electric generators.

3. a kind of inertia and double-fed blower fan of combining of exceeding the speed limit of simulating as claimed in claim 2 is gained merit frequency synthesis control method, it is characterized in that, in described step (1), the most strong wind power of catching of wind-driven generator is:

$\left\{\begin{array}{c}{P}_{opt}=\frac{1}{2}{\mathrm{\ρC}}_{p_{opt}}\left({\mathrm{\λ}}_{opt},\mathrm{\β}\right){\mathrm{AU}}_w^3\\ C_{p_{opt}}\left({\mathrm{\λ}}_{opt},\mathrm{\β}\right)=0.22\left(\frac{116}{{\mathrm{\λ}}_i}-0.4\mathrm{\β}-5\right)e^{\frac{-12.5}{{\mathrm{\λ}}_i}}\\ \frac{1}{{\mathrm{\λ}}_i}=\frac{1}{{\mathrm{\λ}}_{opt}+0.08\mathrm{\β}}-\frac{0.035}{{\mathrm{\β}}^3+1}\\ {\mathrm{\λ}}_{opt}=\frac{w_{t_{opt}}R}{U_w}\end{array}\right.$

Wherein, P _optfor the maximum power that given wind speed apparatus for lower wind machine is caught, ρ is atmospheric density, C _optfor with tip speed ratio λ _opt, optimum Wind resource change rate coefficient that propeller pitch angle β is relevant, A is the inswept area of blower fan, U _wfor wind speed, for blower fan angular velocity of rotation, R is blade radius.

4. a kind of inertia and double-fed blower fan of combining of exceeding the speed limit of simulating as claimed in claim 2 is gained merit frequency synthesis control method, and it is characterized in that, in described step (1), double-fed wind power generator maximum power tracking curve equation is specially:

$P_{opt}=k_{opt}{w}_r^3$

In formula:

$k_{opt}=\frac{1}{2}\mathrm{\ρ}\left(\frac{C_{P_{opt}}}{{\mathrm{\λ}}_{opt}^3}\right){\mathrm{\πR}}^5$

${\mathrm{\ω}}_r=\left(\frac{p}{2}\right){\mathrm{G\ω}}_t$

In formula: P _optfor the maximum power that wind energy conversion system is caught, k _optfor by the determined power tracking coefficient of wind energy conversion system aerodynamics, ρ is atmospheric density, optimal power conversion coefficient, λ _optfor optimum tip speed ratio, R is blade radius, ω _rfor rotor speed, p is power generator electrode logarithm, and G is gear box carry-over factor, w _tfor blower fan angular velocity of rotation.

5. a kind of inertia and double-fed blower fan of combining of exceeding the speed limit of simulating as claimed in claim 2 is gained merit frequency synthesis control method, and it is characterized in that, the rotational speed regulation amount in described step (3) is:

$\mathrm{\Δ}w=\frac{k_{opt}-k_{de}}{3k_{opt}(1-d\%)}\×w_r\×\frac{\mathrm{\Δ}f}{f_b-f_a}$

Wherein, k _opt, k _debe respectively the forward and backward power tracking coefficient of off-load, d% represents off-load amount size, w _rfor rotor speed, Δ f is frequency departure amount size, f _b, f _abe respectively mains frequency under normal circumstances and regulate upper and lower limit.

6. a kind of inertia and double-fed blower fan of combining of exceeding the speed limit of simulating as claimed in claim 2 is gained merit frequency synthesis control method, it is characterized in that, in order to make double-fed Wind turbine have the droop characteristic the same with conventional electric generators in described step (4), need to be directly proportional to frequency departure amount Δ f by the power of uprushing of power points of controlling to uprush, and then the position of control stable operating point.