CN104037806A - Research method for basic model and flow problems of wind generating sets - Google Patents

Abstract

The invention discloses a research method for basic model and flow problems of wind generating sets; detailed analysis and explanation are performed aiming at the structure and the model of a wind driven generator, and the modified equation of a wind speed model is determined based on a four-component model of wind speed. A steady-state flow model for various types of wind driven generators such as the asynchronous wind driven generator and the double-feed wind driven generator is provided based on detailed analysis of output mechanical power of the wind driven generators, on the above basis, a flow computation model for different types of wind driven generators after being grid-connected is determined in combination with existing flow computation, and a simplified processing module and a simplified processing procedure for the asynchronous wind driven generator are provided according to the actual simulation requirement; through researching the flow computation method of the system after the grid connection of wind power, determination of the grid connection scheme of a wind power plant is facilitated, and a foundation is laid for work of further researching stability, reliability and other aspects of the system.

Description

The research method of a kind of wind turbine generator basic model and Power Flow Problem

Technical field

The present invention relates to a kind of wind turbine generator research method, specifically the research method of a kind of wind turbine generator basic model and Power Flow Problem.

Background technology

At world wide, in order to ensure energy security, realize energy sources diversification, and tackle climate change at present, each national capital develop actively regenerative resource.Wind energy is inexhaustible clean, pollution-free, regenerative resource, thereby wind power generation has occupied preferential and leading status in the development and utilization of new forms of energy.

Wind power generation worldwide true development starts from 20 century 70s, due to the impact of oil crisis, is exploitation alternative energy source, and the developed countries such as USA and Europe drop into a large amount of funds, utilize multiple advanced technology to develop modern wind generating set.Since the nineties, Global Wind Power Industry has obtained development at full speed, for realizing the target of carbon dioxide isothermal chamber gas abatement, Europe is using Wind Power Development as an important measure, wherein, for ensureing that wind-powered electricity generation grows continuously and fast, the countries such as Germany, Denmark, Spain have all formulated higher wind-powered electricity generation purchasing price." 2011 global wind report " of issuing according to Global Wind-energy council (GWEC) are known, and by the end of the year 2011, world's installed capacity of wind-driven power reaches 2.38 hundred million kW, increase by a year-on-year basis to increase approximately 28% every year during 20.6%, 2001-2011.

China is vast in territory, seashore line length, wind energy resources abundant.At the later stage eighties 20th century and 2004-2005, China Meteorological Administration has organized respectively for the first time and Second National Wind Energy Resources Survey, show that China's land 10m height layer wind energy resources theory can development reserves be respectively 3226GW and 4350GW.According to statistics, the land wind-powered electricity generation developing of China is about 2.5 hundred million kw, and sea is land three times, i.e. 750GW, the conclusion that total amount is 1000GW.Because THE WIND ENERGY RESOURCES IN CHINA mainly concentrates on " three Norths " area, mostly away from load center.The development since " Renewable Energy Law " promulgated of the wind-powered electricity generation cause of China rapidly, according to the planning of the Committee of Development and Reform of state, will be increased to 3,000 ten thousand kilowatts to the year two thousand twenty China wind-powered electricity generation installation total amount.Current, the wind power generation of China is in Rapid development stage, along with the increase of wind energy turbine set capacity and the appearance of related specifications, introduce the province ,city and area of wind-powered electricity generation and all start built and propose the each side impact that the wind energy turbine set of meter brings electrical network with regard to grid connected wind power and study.

Because wind-powered electricity generation is intermittent power supply, and normal together with power electronic equipment connecting system, therefore, the access of wind energy turbine set is influential to the operation of electric power system, likely affects reliability, stability and the quality of power supply of original system.Along with the increase of wind turbine generator single-machine capacity and wind energy turbine set scale, the shortcoming of randomness, intermittence and the non-scheduling of wind energy makes its grid-connected rear impact on electric power system also more and more obvious.These impacts show following several respects:

(1) wind power generation addressing in coastal, mountain area etc. the abundant area of wind resource, and these areas are often away from major network, the trend that the injection of wind power will change local electrical network distributes, and causes that the node voltage of partial electric grid produces fluctuation.The angle of the normal operation of collateral security wind energy turbine set and electric power system considers, determines the problem that the maximum injecting power of a wind energy turbine set and influencing factor thereof need to solve while becoming planning and designing wind energy turbine set.

(2) variation that wind turbine generator (wind turbine generator) is exerted oneself, the operational mode of netting interior conventional unit is changed, therefore after wind farm grid-connected, can low frequency oscillation mode and oscillating characteristic to electrical network cause certain influence, even may cause some local oscillation patterns to occur or disappear.

(3) wind-powered electricity generation is as the intermittent power supply of one, and the reliability of wind energy turbine set exists certain impact to the formulation of system operation mode, therefore need to take into full account the reliability of its power supply in the design phase.

Therefore, research and analyse for the impact on original system after wind-electricity integration, there is good economic implications and good social effect.After wind-electricity integration, be a underlying issue that need first solve on the impact of system load flow analysis and calculation.The trend that on the one hand contain wind turbine generator by analysiss can determine wind energy turbine set grid-connected scheme and can the grid-connected rear impact that Power System Steady-state is moved to generation of Efficient Evaluation blower fan, comprise the problem such as node busbar voltage mutation analysis and the emulation verification of line power and node voltage being caused by wind energy turbine set; The Power Flow Problem of analyzing on the other hand after wind-electricity integration is also its working foundation on the impact of the aspect such as the stability of a system, reliability of further analyzing and researching.

After wind farm grid-connected, in the trend of carrying out electric power system is calculated, adopt which kind of wind energy turbine set model most important.Document [1-3] has proposed following several models: the first is simple PQ model, in conjunction with the specified meritorious and power factor of wind energy turbine set, extrapolates the reactive power that wind energy turbine set absorbs, and then in trend is calculated, sets it as common PQ load bus and process.Another kind is the function that the slippage of induction machine is expressed as to terminal voltage, active power and equivalent branch impedance, is called RX model, calculates electrical power and the mechanical output of blower fan by initial slippage and wind speed, and constantly iteration is until convergence.Actual simulation result shows, the iterative step that PQ model needs is less, and its result meets the demands equally, and the amount of calculation of RX model is larger.

Document [1]: Wu Yichun, Ding Ming, Zhang Lijun. the electric power system tide containing wind energy turbine set calculates [J]. Proceedings of the CSEE .2005,25 (4): 36-39.

Document [2]: Wang Haichao, Zhou Shuanxi, Lu Zongxiang, etc. combined iteration method and the application [J] of calculating containing the electric power system tide of wind energy turbine set. electric power network technique, 2005,29 (18): 59-62.

Document [3]: Chen Jinfu, Chen Haiyan, Duan Xianzhong. containing the multi-period Dynamic Optimal Load Flow of electric power system [J] of Large Scale Wind Farm Integration. Proceedings of the CSEE, 2006,26 (3): 31-35.

Summary of the invention

For the deficiencies in the prior art, the invention provides the research method of a kind of wind turbine generator basic model and Power Flow Problem, by the electric power system tide computational methods after research wind-electricity integration, be conducive to determine the grid-connected scheme of wind energy turbine set.

The present invention solves the technical scheme that its technical problem takes: the research method of a kind of wind turbine generator basic model and Power Flow Problem, it is characterized in that, and comprise following process:

1) structure of wind energy turbine set wind turbine generator is studied with model: described wind turbine generator is connected side by side, and jointly accesses network system; The conversion process of energy of the wind turbine generator of whole wind energy turbine set is wind energy-mechanical energy-electric energy, and wind turbine generator can be divided into two parts, the wind energy conversion system that a part is is mechanical energy by wind energy transformation, and another part is the generator that mechanical energy is transferred to electric energy; Wind power generation process is that the moment of inertia that changes wind energy into wind wheel by impeller is mechanical energy, by the gearing of main shaft, through the effect of gear box, asynchronous generating machine rotor is reached after suitable rotating speed, rotor driven generating, and through exciter converter, stator electric energy is injected to electrical network;

2) four component Models based on wind speed are determined the update equation formula of wind speed model: four international component Models of the normal employing of current wind speed model, comprise basic wind, fitful wind, gradual change wind, random noise wind four parts, basic wind, fitful wind, gradual change wind, random noise wind four part sums have formed the wind speed of normal wind machine; Normal wind machine is Vw at the residing wind speed of hub height, in actual analysis processing procedure, need it to revise, the update equation formula of wind speed model as shown in Equation 1:

$V_w=V_{w0}{\left[\frac{H}{H_0}\right]}^{\mathrm{\α}}---\left(1\right)$

In formula: H is hub height, H ₀for surveying wind height, V _w0for surveying the wind speed of wind height, α is altitude correction factor;

3) the steady-state load flow model of proposition asynchronous wind driven generator:

3.1) the mechanical power output of wind-driven generator adopts the first to analyze expression way, as shown in Equation 2:

P _m＝0.5ρSC _pV ³ (2)

In formula, ρ is atmospheric density (kg/m ³); S is the swept area (m of pneumatic equipment blades made ²); C _pfor the power coefficient of wind energy conversion system, can be expressed as the function of tip speed ratio, V is wind speed;

The mechanical power output of wind-driven generator adopts the second to analyze expression way, as shown in Equation 3:

$P_m=\left\{\begin{array}{cc}0& V<V_{\mathrm{cin}},V>V_{\mathrm{cout}}\\ \frac{V^3-{V_{\mathrm{cin}}}^3}{{V_r}^3-{V_{\mathrm{cin}}}^3}{P}_r& V_{\mathrm{cin}}\&le;V<V_r\\ P_r& V_r\&le;V\&le;V_{\mathrm{cout}}\end{array}\right.---\left(3\right)$

In formula, P _mbe respectively wind speed and the meritorious power output of wind energy conversion system wheel hub with V; V _cin, V _r, V _cout, P _rfor being expressed as wind energy conversion system incision wind speed, rated wind speed, cut-out wind speed, rated power;

3.2) equivalent electric circuit of asynchronous wind driven generator is simplified to the Γ type equivalent circuit that obtains asynchronous wind driven generator, the complex power formula of Γ type equivalent circuit as shown in Equation 4:

$\begin{array}{c}\tilde{S}=\stackrel{\&CenterDot;}{U}\stackrel{*}{I}=\stackrel{\&CenterDot;}{U}\frac{-\stackrel{*}{U}}{j(x_1+x_2)+r_2/s}+j\frac{U^2}{x_m}-\\ \frac{U^2\frac{r_2}{s}}{{\left(\frac{r_2}{s}\right)}^2+{(x_1+x_2)}^2}+j(\frac{U^2}{{\left(\frac{r_2}{s}\right)}^2+{(x_1+x_2)}^2}+\frac{U^2}{x_m})=P+\mathrm{jQ}\end{array}---\left(4\right)$

In formula, x _mfor excitation reactance; r _mfor excitation resistance; r ₁for stator resistance; x ₁for stator reactance; x ₂for rotor reactance; r ₂for rotor resistance; S is revolutional slip, s=(n _s-n)/n _s, n _sfor synchronous speed, n is asynchronous generator rotating speed, and j is imaginary unit, with be respectively line voltage and line current; Known according to formula 4, the active power of asynchronous wind driven generator and the direction of reactive power are contrary, and wind turbine generator is absorbing reactive power in sending active power;

Can derive revolutional slip s and the tg φ of corresponding asynchronous wind driven generator according to formula 3 and formula 4, embody respectively suc as formula 5 and formula 6 shown in:

$s=\frac{U^2{r}_2-\sqrt{U^4{r}_2^2-4P^2{(x_1+x_2)}^2{r}_2^2}}{2P{(x_1+x_2)}^2}---\left(5\right)$

$\mathrm{tg\&phi;}=\frac{Q}{P}=\frac{s^2(x_1+x_2)(x_m+x_1+x_2)+r_2^2}{r_2{x}_{m}s}---\left(6\right)$

In formula, r ₁for stator resistance; x ₁for stator reactance; Φ is power-factor angle, and s is revolutional slip, and Q is reactive power, and P is active power;

Simultaneous formula 5 and formula 6, eliminate revolutional slip s, reactive power express for the function of mechanical active power of output as shown in Equation 7:

$Q=\frac{2P^2{(x_1+x_2)}^2}{r_2^2{x}_m(-U^2{r}_2^2+\sqrt{U^4{r}_2^2-4P^2{(x_1+x_2)}^2{r}_2^2})}---\left(7\right)$

From formula 7, the reactive power Q that wind turbine generator absorbs is not only relevant with the active-power P of generating set, and also has substantial connection with set end voltage U;

3.3) expression formula of double-fed type asynchronous generator stable state equivalent circuit is as shown in Equation 8:

$\left\{\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_1={\stackrel{\&CenterDot;}{I}}_1(r_1+j{x}_1)+({\stackrel{\&CenterDot;}{I}}_1+{\stackrel{\&CenterDot;}{I}}_2)j{x}_m\\ \frac{{\stackrel{\&CenterDot;}{U}}_2}{s}={\stackrel{\&CenterDot;}{I}}_2(\frac{r_1}{s}+j{x}_2)+({\stackrel{\&CenterDot;}{I}}_1+{\stackrel{\&CenterDot;}{I}}_2)j{x}_m\end{array}\right.---\left(8\right)$

In formula, for stator terminal voltage; for stator current; for the voltage of rotor winding external power supply; for rotor current; r ₁and x ₁be respectively resistance and the reactance of stator winding; r ₂and x ₂be respectively resistance and the reactance of rotor winding; S is revolutional slip;

The total active-power P of double-fed type asynchronous generator injected system _ebe made up of two parts, a part is the active-power P that stator winding sends _s, another part is the active-power P that rotor winding sends or absorbs _rthe reactive power of double-fed type asynchronous generator is sent by generator unit stator side or the reactive power that absorbs and current transformer send or the reactive power that absorbs forms in generator amature side, by regulating amplitude and the phase angle of rotor additional power source voltage, can change that stator side is sent or the size of absorbing reactive power, the reactive power Q of speed-variable frequency-constant wind-driven generator group _ecan be approximated to be the reactive power Q of stator winding _s, the power expression of double-fed type asynchronous wind driven generator suc as formula 9 and formula 10 shown in:

$P_r=\frac{r_r{x}_{\mathrm{ss}}^2(P_s^2+Q_s^2)}{x_m^2{\left|U_s\right|}^2}+\frac{2r_r{x}_{\mathrm{ss}}}{x_m^2}{Q}_s-s{P}_s+\frac{r_r{\left|U_s\right|}^2}{x_m^2}---\left(9\right)$

$P_e=P_s+P_r=\frac{r_r{x}_{\mathrm{ss}}^2(P_s^2+Q_s^2)}{x_m^2{\left|U_s\right|}^2}+\frac{2r_r{x}_{\mathrm{ss}}}{x_m^2}{Q}_s+(1-s)P_s+\frac{r_r{\left|U_s\right|}^2}{x_m^2}---\left(10\right)$

In formula, x _ss=x _s+ x _m, r _mfor excitation resistance, x _mfor excitation reactance, P _efor total active power, P _sfor the active power that stator winding sends, P _rthe active power of sending or absorbing for rotor winding;

4) the wind-driven generator tide model after grid-connected is calculated:

4.1) in conjunction with the active power of above-mentioned asynchronous wind driven generator group and reactive power and with the relation of voltage, wind speed, revolutional slip, the electric power system that contains asynchronous system wind turbine generator is carried out to trend calculating;

4.2) wind turbine generator power factor set point is cos φ, convolution 11 expression formulas:

Q _s＝P _stgφ ( ₁₁)

Can obtain expression formula as shown in Equation 12:

$\begin{array}{c}{P}_e=P_s+P_r\\ =\frac{r_r{x}_{\mathrm{ss}}^2{P}_s^2}{x_m^2{\left|U_s\right|}^2}(1+{\mathrm{tg}}^2\mathrm{\&phi;})+\\ (1+\frac{2r_r{x}_{\mathrm{ss}}\mathrm{tg\&phi;}}{x_m^2}-s)P_s+\frac{r_r{\left|U_s\right|}^2}{x_m^2}\end{array}---\left(12\right)$

In formula, P _efor total active power, P _sfor the active power that stator winding sends, P _rthe active power of sending or absorbing for rotor winding;

Convolution 10 and formula 12 are carried out trend calculating to the electric power system that contains double-feedback aerogenerator group under constant power factor mode;

4.3) due to Q _ebe approximately Q _s, just Q _ewith Q _ssubstitution formula (10), obtains expression formula as shown in Equation 13:

$\begin{array}{c}{P}_e=P_s+P_r\\ =\frac{r_r{x}_{\mathrm{ss}}^2(P_s^2+Q_s^2)}{x_m^2{\left|U_s\right|}^2}+\frac{2r_r{x}_{\mathrm{ss}}}{x_m^2}{Q}_s+\\ (1-s)P_s+\frac{r_r{\left|U_s\right|}^2}{x_m^2}\end{array}---\left(13\right)$

Because of rotor current transformer maximum current limit form range of operation expression formula as shown in Equation 14:

$P_s^2+{(Q_s+\frac{{\left|U_s\right|}^2}{x_{\mathrm{ss}}})}^2\&le;\frac{x_m^2{\left|U_s\right|}^2}{x_{\mathrm{ss}}}{I}_{r\max }^2---\left(14\right)$

In formula, I _rmaxfor rotor current transformer maximum current limit value;

Convolution 13 and formula 14 are carried out trend calculating to the electric power system that contains double-feedback aerogenerator group under constant voltage operational mode;

5) model of asynchronous wind driven generator is simplified to processing:

Formula 7 is further simplified and is processed, can obtain formula as shown in Equation 15:

$Q=\frac{U^2}{x_m}+\frac{s^2{(x_1+x_2)}^2}{{r_2}^2+s^2{(x_1+x_2)}^2}{U}^2---\left(15\right)$

Traditional trend computing formula is as shown in Equation 16:

$\left[\begin{array}{c}\mathrm{\&Delta;P}\\ \mathrm{\&Delta;Q}\end{array}\right]=\left[\begin{array}{cc}H& N\\ M& J\end{array}\right]\left[\begin{array}{c}\mathrm{\&Delta;\&theta;}\\ \mathrm{\&Delta;U}/U\end{array}\right]---\left(16\right)$

In formula, Δ P and Δ Q represent respectively to inject the amount of unbalance of active power and reactive power, and Δ V and Δ θ are expressed as the correction of voltage magnitude and phase angle;

Convolution 16 is simplified processing to the power flow equation shown in formula 15, simplifies power flow equation as shown in Equation 17:

$\frac{\&PartialD;Q}{\&PartialD;U}=\frac{2U}{x_m}+U(1-\frac{U^2}{\sqrt{U^4-4{(x_1+x_2)}^2{P}^2}})---\left(17\right)$

In formula, x _mfor excitation reactance, x ₁for stator reactance, x ₂for rotor reactance, U is set end voltage, and Q is reactive power, and P is active power.

In said method, the span of described altitude correction factor α is 0.10-0.40.

In said method, described grid-connected Wind turbine mainly comprises: wind turbine, pylon, power transmission shaft, gear box, generator and corresponding control system.

In said method, the basic wind in described wind speed model is the normal part always existing in service of wind energy conversion system, has determined the rated power of wind turbine generator output; The part of gustiness compounent for reflecting that real process wind speed changes suddenly; Gradual change wind is used for describing the roll-off characteristic of wind energy; The stochastic behaviour that wind energy changes is described by random noise wind component.

In said method, the described process that the electric power system that contains asynchronous system wind turbine generator is carried out to trend calculating comprises the following steps:

S11, forms bus admittance matrix;

S12, sets the voltage initial value of each bus: phase angle and amplitude;

S13, the wind speed of given wind energy turbine set;

S14, the active power of sending by formula 3 and the definite wind turbine generator of formula 8 and the reactive power of absorption;

S15, asks the meritorious and idle amount of unbalance in formula 1, and obtains Jacobian matrix element;

S16, solves formula 1 by Newton-Raphson method, and revises each busbar voltage and phase angle;

S17, whether verification trend restrains, if convergence, calculate finish, otherwise with new magnitude of voltage as initial value, repeating step S14, until calculating finish.

In said method, the described process that the electric power system that contains double-feedback aerogenerator group is carried out to trend calculating under constant power factor mode comprises the following steps:

S21, wind speed setting and wind energy turbine set voltage initial value U _s;

S22, obtains P according to double-feedback aerogenerator wind speed power curve _e;

S23, according to the rotating speed control law formula (10) of wind turbine generator, calculates revolutional slip s;

S24, calculates P according to formula (12) _s, and calculate Q according to formula (11) _s;

S25, by P _e, Q _swith PQ form of bus bars substitution electric power system, calculate wind energy turbine set busbar voltage U ' _s, judge that the difference of voltage is in the error range of setting, i.e. U ' _s-U _s< ε;

S26, if U ' _s≠ U _s, make U _s=0.5 (U _s+ U ' _s), turn back to step S24 and continue execution step S24 and S25, until the difference of voltage is less than ε;

S27, obtains the final calculated value of Us, and substitution formula (12), obtains P _s, P _rdistribution situation.

In said method, the described process that the electric power system that contains double-feedback aerogenerator group is carried out to trend calculating under constant voltage operational mode comprises the following steps:

S31, wind speed setting, sets constant working voltage U _s;

S32, obtains P according to double-feedback aerogenerator wind speed power curve _e;

S33, by P _e, U _swith PV form of bus bars substitution electric power system, calculate wind energy turbine set bus and inject reactive power Q _e;

S34, calculates revolutional slip s according to the rotating speed control law of wind turbine generator;

S35, calculates P according to formula 13 _s;

S36, by P _s, Q _e, U _ssubstitution formula 14 checks that whether electric current is out-of-limit.

The invention has the beneficial effects as follows: the structure and the model that the present invention is directed to wind-driven generator have carried out detailed analysis and elaboration, and four component Models based on wind speed have been determined the update equation formula of wind speed model, the dissimilar steady-state load flow models such as asynchronous system wind-driven generator and double-feedback aerogenerator have been proposed on the basis of labor wind-driven generator output mechanical power, on this basis in conjunction with existing trend calculative determination the power flow algorithm of dissimilar wind-driven generator after grid-connected, and according to actual emulation needs, simplification transaction module and the flow process of asynchronous wind driven generator have been proposed, by the system load flow computational methods after research wind-electricity integration, be conducive to determine the grid-connected scheme of wind energy turbine set, and be further to study it to the stability of a system, the work of the aspects such as reliability lays the foundation.

Brief description of the drawings

Fig. 1 is method flow diagram of the present invention;

Fig. 2 is asynchronous generator equivalent circuit of the present invention and the schematic diagram of simplifying equivalent circuit;

Fig. 3 is the schematic diagram of double-fed type asynchronous generator stable state equivalent circuit of the present invention;

Fig. 4 is the schematic diagram of asynchronous wind driven generator equivalent circuit after simplification of the present invention;

Fig. 5 is the schematic diagram of part busbar voltage calculation of tidal current in example of the present invention.

Embodiment

For clearly demonstrating the technical characterstic of this programme, below by embodiment, and in conjunction with its accompanying drawing, the present invention will be described in detail.Disclosing below provides many different embodiment or example to be used for realizing different structure of the present invention.Of the present invention open in order to simplify, hereinafter the parts to specific examples and setting are described.In addition, the present invention can be in different examples repeat reference numerals and/or letter.This repetition is in order to simplify and object clearly, itself do not indicate the relation between discussed various embodiment and/or setting.It should be noted that illustrated parts are not necessarily drawn in proportion in the accompanying drawings.The present invention has omitted the description of known assemblies and treatment technology and technique to avoid unnecessarily limiting the present invention.

As shown in Figure 1, the research method of a kind of wind turbine generator basic model of the present invention and Power Flow Problem, it comprises following process:

One, the structure to wind energy turbine set wind turbine generator and model are studied

Conventionally wind energy turbine set often comprises multiple wind turbine generator, and carries out side by side through the suitable mode of connection, and is jointly connected with network system.The problems such as the trend calculating of analysis and research after wind-electricity integration, first need to analyse in depth the operation characteristic of wind energy turbine set.The conversion process of energy of whole wind turbine generator is wind energy-mechanical energy-electric energy, can be divided into thus two parts, the wind energy conversion system that a part is is mechanical energy by wind energy transformation, and another part is the generator that mechanical energy is transferred to electric energy.A wind-energy changing system in essence.Typical grid-connected Wind turbine mainly comprises following a few part: wind turbine, pylon, power transmission shaft, gear box, generator and corresponding control system.

Whole wind power generation process is that the moment of inertia that changes wind energy into wind wheel by impeller is mechanical energy, by the gearing of main shaft, through the effect of gear box, asynchronous generating machine rotor is reached after suitable rotating speed, rotor driven generating, and through exciter converter, stator electric energy is injected to electrical network.

Two, four component Models based on wind speed are determined the update equation formula of wind speed model

Four international component Models of the normal employing of current wind speed model, comprise basic wind, fitful wind, gradual change wind, random noise wind four parts, and basic wind is the normal part always existing in service of wind energy conversion system, have determined the rated power of wind turbine generator output; The part of gustiness compounent for reflecting that real process wind speed changes suddenly; Gradual change wind is used for describing the roll-off characteristic of wind energy; The stochastic behaviour that wind energy changes is described by random noise wind component.In fact wind, fitful wind, gradual change wind, random noise wind four part sums have formed the wind speed of normal wind machine, substantially; Normal wind machine is Vw at the residing wind speed of hub height, in actual analysis processing procedure, need it to revise, the update equation formula of wind speed model as shown in Equation 1:

$V_w=V_{w0}{\left[\frac{H}{H_0}\right]}^{\mathrm{\&alpha;}}---\left(1\right)$

In formula: H is hub height, H ₀for surveying wind height, V _w0for surveying the wind speed of wind height, α is altitude correction factor, and the span of α is 0.10-0.40.

Three, the steady-state load flow model of asynchronous wind driven generator is proposed

3.1) power out-put characteristic of wind-driven generator

The mechanical power output of wind-driven generator adopts the first to analyze expression way, as shown in Equation 2:

P _m＝0.5ρSC _pV ³ (2)

In formula, ρ is atmospheric density (kg/m ³); S is the swept area (m of pneumatic equipment blades made ²); C _pfor the power coefficient of wind energy conversion system, can be expressed as the function of tip speed ratio, V is wind speed;

The mechanical power output of wind-driven generator adopts the second to analyze expression way, as shown in Equation 3:

$P_m=\left\{\begin{array}{cc}0& V<V_{\mathrm{cin}},V>V_{\mathrm{cout}}\\ \frac{V^3-{V_{\mathrm{cin}}}^3}{{V_r}^3-{V_{\mathrm{cin}}}^3}{P}_r& V_{\mathrm{cin}}\&le;V<V_r\\ P_r& V_r\&le;V\&le;V_{\mathrm{cout}}\end{array}\right.---\left(3\right)$

In formula, P _mbe respectively wind speed and the meritorious power output of wind energy conversion system wheel hub with V; V _cin, V _r, V _cout, P _rfor being expressed as wind energy conversion system incision wind speed, rated wind speed, cut-out wind speed, rated power.

3.2) asynchronous system wind turbine generator Mathematical Modeling

Wind turbine generator is divided into fixed rotating speed and two kinds of forms of speed change conventionally, and the wind turbine generator of fixed rotating speed generally adopts asynchronous generator, and its power out-put characteristic is absorbing reactive power in sending active power.

The Mathematical Modeling of asynchronous system wind turbine generator mainly contains RX model and PQ model.Iterative process is divided into two steps by RX model: the slippage iterative computation of conventional Load Flow iterative computation and asynchronous wind driven generator, and total iterations is many, and convergence rate is slow.PQ model has considered that wind energy turbine set reactive power is subject to the impact such as busbar voltage and slippage, compares RX model, and in the situation that not affecting computational accuracy, iterations greatly reduces, and computational speed is significantly improved.

The equivalent electric circuit of asynchronous wind driven generator as shown in Fig. 2 (a), wherein x _m>>x ₁, ignore r ₁, r _mafter field excitation branch line can be moved to circuit head end, the asynchronous wind driven generator Γ type equivalent circuit being simplified, as shown in Fig. 2 (b).

The equivalent electric circuit of asynchronous wind driven generator is simplified to the Γ type equivalent circuit that obtains asynchronous wind driven generator, the complex power formula that can obtain Γ type equivalent circuit by foregoing circuit relation as shown in Equation 4:

$\begin{array}{c}\tilde{S}=\stackrel{\&CenterDot;}{U}\stackrel{*}{I}=\stackrel{\&CenterDot;}{U}\frac{-\stackrel{*}{U}}{j(x_1+x_2)+r_2/s}+j\frac{U^2}{x_m}-\\ \frac{U^2\frac{r_2}{s}}{{\left(\frac{r_2}{s}\right)}^2+{(x_1+x_2)}^2}+j(\frac{U^2}{{\left(\frac{r_2}{s}\right)}^2+{(x_1+x_2)}^2}+\frac{U^2}{x_m})=P+\mathrm{jQ}\end{array}---\left(4\right)$

In formula, x _mfor excitation reactance; r _mfor excitation resistance; r ₁for stator resistance; x ₁for stator reactance; x ₂for rotor reactance; r ₂for rotor resistance; S is revolutional slip, s=(n _s-n)/n _s, n _sfor synchronous speed, n is asynchronous generator rotating speed, and j is imaginary unit, with be respectively line voltage and line current; Known according to formula 4, the active power of asynchronous wind driven generator and the direction of reactive power are contrary, and wind turbine generator is absorbing reactive power in sending active power.

According to the characteristic relation of known itself and wind speed of the wind-driven generator machinery power output of formula 3, under different wind speed, can obtain the power output of every wind turbine generator, the power output of whole wind energy turbine set is the power output that the number of units of wind energy turbine set Wind turbine is multiplied by separate unit Wind turbine.In the application, suppose that wind turbine generator is substantially yi word pattern and arranges, therefore can ignore the impact that wake effect produces power stage.The circuit relationships presenting by Fig. 2 and Shi 4, in conjunction with the set end voltage U of output power value P and wind turbine generator, can derive revolutional slip s and the tg φ of corresponding asynchronous wind driven generator thus, embody respectively suc as formula 5 and formula 6 shown in:

$s=\frac{U^2{r}_2-\sqrt{U^4{r}_2^2-4P^2{(x_1+x_2)}^2{r}_2^2}}{2P{(x_1+x_2)}^2}---\left(5\right)$

$\mathrm{tg\&phi;}=\frac{Q}{P}=\frac{s^2(x_1+x_2)(x_m+x_1+x_2)+r_2^2}{r_2{x}_{m}s}---\left(6\right)$

In formula, r ₁for stator resistance; x ₁for stator reactance; Φ is power-factor angle, and s is revolutional slip, and Q is reactive power, and P is active power;

Simultaneous formula 5 and formula 6, eliminate revolutional slip s, reactive power express for the function of mechanical active power of output as shown in Equation 7:

$Q=\frac{2P^2{(x_1+x_2)}^2}{r_2^2{x}_m(-U^2{r}_2^2+\sqrt{U^4{r}_2^2-4P^2{(x_1+x_2)}^2{r}_2^2})}---\left(7\right)$

From formula 7, the reactive power Q that wind turbine generator absorbs is not only relevant with the active-power P of generating set, and also has substantial connection with set end voltage U.

3.3) double-fed type asynchronous generating unit Mathematical Modeling

Double-feedback aerogenerator group, in running, is to improve the service efficiency of wind energy, and its rotating speed can regulate with the variation of different wind speed, thus ensure blower fan running status at Best Point.Than asynchronous wind driven generator group, because double-feedback aerogenerator group has increased exciter control system, can be by the exciting current of suitable power electronic equipment regulator generator rotor, in the situation that ensureing that generator unit stator output voltage and frequency are constant, can also regulate the power stage of wind turbine generator.

Double-fed type asynchronous generator stable state equivalent circuit as shown in Figure 3, its expression formula as shown in Equation 8:

$\left\{\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_1={\stackrel{\&CenterDot;}{I}}_1(r_1+j{x}_1)+({\stackrel{\&CenterDot;}{I}}_1+{\stackrel{\&CenterDot;}{I}}_2)j{x}_m\\ \frac{{\stackrel{\&CenterDot;}{U}}_2}{s}={\stackrel{\&CenterDot;}{I}}_2(\frac{r_1}{s}+j{x}_2)+({\stackrel{\&CenterDot;}{I}}_1+{\stackrel{\&CenterDot;}{I}}_2)j{x}_m\end{array}\right.---\left(8\right)$

In formula, for stator terminal voltage; for stator current; for the voltage of rotor winding external power supply; for rotor current; r ₁and x ₁be respectively resistance and the reactance of stator winding; r ₂and x ₂be respectively resistance and the reactance of rotor winding; S is revolutional slip.

The rotation speed n of double-fed type asynchronous generating machine rotor changes, and in the three-phase symmetric winding of rotor, passing into frequency is f ₁the electric current of × s, wherein f ₁for work frequency, s is revolutional slip, s=(n _s-n)/n _s, n _sfor synchronous speed.F in rotor ₁× s frequency current produces rotation speed n ₂rotating magnetic field, i.e. n2=60f ₁× s/p, p is number of pole-pairs, with respect to stator winding, the rotating magnetic field relative rotation speed that rotor current produces is n ± n ₂=n ₁, n ₁for synchronous speed.Thereby in rotor variable-speed operation situation, stator winding still can produce the electric energy of fixed frequency 50Hz.

According to the variation of double-fed type asynchronous generator rotor speed, double-fed type asynchronous generator has three kinds of running statuses.Metasynchronism operation, now n<n ₁; Supersynchronous operation, now n>n ₁; Synchronous operation state, now n=n ₁.

The total active-power P of double-fed type asynchronous generator injected system _ebe made up of two parts, a part is the active-power P that stator winding sends _s, another part is the active-power P that rotor winding sends or absorbs _r.Rotating speed is during higher than synchronous speed, and rotor winding sends active power; Rotating speed is during lower than synchronous speed, and rotor winding absorbs active power.

The reactive power of double-fed type asynchronous generator is sent by generator unit stator side or the reactive power that absorbs and current transformer send or the reactive power that absorbs forms in generator amature side.Regulate amplitude and the phase angle of rotor additional power source voltage, can change that stator side is sent or the size of absorbing reactive power.The reactive power Q of speed-variable frequency-constant wind-driven generator group _ecan be approximated to be the reactive power Q of stator winding _s.The power expression of double-fed type asynchronous wind driven generator suc as formula 9 and formula 10 shown in:

$P_r=\frac{r_r{x}_{\mathrm{ss}}^2(P_s^2+Q_s^2)}{x_m^2{\left|U_s\right|}^2}+\frac{2r_r{x}_{\mathrm{ss}}}{x_m^2}{Q}_s-s{P}_s+\frac{r_r{\left|U_s\right|}^2}{x_m^2}---\left(9\right)$

$P_e=P_s+P_r=\frac{r_r{x}_{\mathrm{ss}}^2(P_s^2+Q_s^2)}{x_m^2{\left|U_s\right|}^2}+\frac{2r_r{x}_{\mathrm{ss}}}{x_m^2}{Q}_s+(1-s)P_s+\frac{r_r{\left|U_s\right|}^2}{x_m^2}---\left(10\right)$

In formula, x _ss=x _s+ x _m, r _mfor excitation resistance, x _mfor excitation reactance, P _efor total active power, P _sfor the active power that stator winding sends, P _rthe active power of sending or absorbing for rotor winding.

The exciter control system of double-feedback aerogenerator group has two kinds of control models: constant voltage control model and constant power factor control model.Constant voltage control model can make wind turbine generator have certain idle regulating power, can in to a certain degree, maintain set end voltage stable.But this control model complex structure, and the idle regulating power of wind turbine generator is very limited.Double-feedback aerogenerator group seldom adopts this control model at present, and adopts constant power factor control model.Under steady operation mode, this control model can make the power factor of wind turbine generator maintain near 1.0, from electrical network angle, and wind turbine generator absorbing reactive power not substantially in sending active power.

Reach incision wind speed but work as wind speed, the moment that wind turbine generator starts, control system fails to get involved in time, and double-feedback aerogenerator group still synchronous and asynchronous formula wind turbine generator is the same, need to absorb a large amount of idle excitations of carrying out.Therefore in the time analyzing affecting that fan starting causes system voltage, can adopt the power flow algorithm of asynchronous system wind turbine generator.

Four, the wind-driven generator tide model after grid-connected is calculated

4.1) electric power system tide that contains asynchronous system wind-powered electricity generation unit calculates

Conventional trend is calculated system busbar is divided into PQ bus, PV bus and balance bus three major types.But asynchronous system wind-powered electricity generation unit can not belong to certain class bus simply, while solving the electric power system tide that comprises wind energy turbine set, must consider the feature of wind-powered electricity generation unit itself: send and absorb meritorious time idlely, and the size of absorbing reactive power is relevant to set end voltage, the active power of sending and slippage.

In conjunction with the active power of above-mentioned asynchronous wind driven generator group and reactive power and with the relation of voltage, wind speed, revolutional slip, the step of the electric power system that contains asynchronous system wind turbine generator being carried out to trend calculating is as follows:

S11, forms bus admittance matrix;

S12, sets the voltage initial value of each bus: phase angle and amplitude;

S13, the wind speed of given wind energy turbine set;

S14, the active power of sending by formula 3 and the definite wind turbine generator of formula 8 and the reactive power of absorption;

S15, asks the meritorious and idle amount of unbalance in formula 1, and obtains Jacobian matrix element;

S16, solves formula 1 by Newton-Raphson method, and revises each busbar voltage and phase angle;

S17, whether verification trend restrains, if convergence, calculate finish, otherwise with new magnitude of voltage as initial value, repeating step S14, until calculating finish.

Because double-fed type asynchronous generator has two kinds of operational modes, i.e. constant power factor mode and constant voltage operational mode.

4.2) under constant power factor mode, the electric power system that contains double-feedback aerogenerator group is carried out to trend calculating

Wind turbine generator power factor set point is cos φ, convolution 11 expression formulas:

Q _s＝P _stgφ (11)

Can obtain expression formula as shown in Equation 12:

$\begin{array}{c}{P}_e=P_s+P_r\\ =\frac{r_r{x}_{\mathrm{ss}}^2{P}_s^2}{x_m^2{\left|U_s\right|}^2}(1+{\mathrm{tg}}^2\mathrm{\&phi;})+\\ (1+\frac{2r_r{x}_{\mathrm{ss}}\mathrm{tg\&phi;}}{x_m^2}-s)P_s+\frac{r_r{\left|U_s\right|}^2}{x_m^2}\end{array}---\left(12\right)$

In formula, P _efor total active power, P _sfor the active power that stator winding sends, P _rthe active power of sending or absorbing for rotor winding;

Under constant power factor mode that the electric power system that contains double-feedback aerogenerator group is carried out to the step of trend calculating is as follows:

S21, wind speed setting and wind energy turbine set voltage initial value U _s;

S22, obtains P according to double-feedback aerogenerator wind speed power curve _e;

S23, according to the rotating speed control law formula (10) of wind turbine generator, calculates revolutional slip s;

S24, calculates P according to formula (12) _s, and calculate Q according to formula (11) _s;

S25, by P _e, Q _swith PQ form of bus bars substitution electric power system, calculate wind energy turbine set busbar voltage U ' _s, judge that the difference of voltage is in the error range of setting, i.e. U ' _s-U _s< ε;

S26, if U ' _s≠ U _s, make U _s=0.5 (U _s+ U ' _s), turn back to step S24 and continue execution step S24 and S25, until the difference of voltage is less than ε;

S27, obtains the final calculated value of Us, and substitution formula (12), obtains P _s, P _rdistribution situation.

4.3) under constant voltage operational mode, the electric power system that contains double-feedback aerogenerator group is carried out to trend calculating

Under constant voltage operational mode, double-feedback aerogenerator can absorb or send reactive power, constant to maintain set end voltage.In the idle adjustable range of wind-powered electricity generation unit, wind energy turbine set can be considered PV bus.For double-fed type asynchronous generator, its reactive power adjustable range is subject to the restriction of stator winding thermal current limit, rotor winding thermal current limit and current transformer maximum current, but main be current transformer maximum current limit.

Due to Q _ebe approximately Q _s, just Q _ewith Q _ssubstitution formula (10), obtains expression formula as shown in Equation 13:

$\begin{array}{c}{P}_e=P_s+P_r\\ =\frac{r_r{x}_{\mathrm{ss}}^2(P_s^2+Q_s^2)}{x_m^2{\left|U_s\right|}^2}+\frac{2r_r{x}_{\mathrm{ss}}}{x_m^2}{Q}_s+\\ (1-s)P_s+\frac{r_r{\left|U_s\right|}^2}{x_m^2}\end{array}---\left(13\right)$

Because of rotor current transformer maximum current limit form range of operation expression formula as shown in Equation 14:

$P_s^2+{(Q_s+\frac{{\left|U_s\right|}^2}{x_{\mathrm{ss}}})}^2\&le;\frac{x_m^2{\left|U_s\right|}^2}{x_{\mathrm{ss}}}{I}_{r\max }^2---\left(14\right)$

In formula, I _rmaxfor rotor current transformer maximum current limit value;

Under constant voltage operational mode that the electric power system that contains double-feedback aerogenerator group is carried out to the step of trend calculating is as follows:

S31, wind speed setting, sets constant working voltage U _s;

S32, obtains P according to double-feedback aerogenerator wind speed power curve _e;

S33, by P _e, U _swith PV form of bus bars substitution electric power system, calculate wind energy turbine set bus and inject reactive power Q _e;

S34, calculates revolutional slip s according to the rotating speed control law of wind turbine generator;

S35, calculates P according to formula 13 _s;

S36, by P _s, Q _e, U _ssubstitution formula 14 checks that whether electric current is out-of-limit.

5) according to actual emulation needs, the model of asynchronous wind driven generator is simplified to processing

Operation in conjunction with actual wind energy turbine set is known, stator reactance in Fig. 2 and rotor reactance can be merged to processing, and circuit can further be simplified processing, and after simplifying, asynchronous generator equivalent circuit as shown in Figure 4.

Formula 7 is further simplified and is processed, can obtain formula as shown in Equation 15:

$Q=\frac{U^2}{x_m}+\frac{s^2{(x_1+x_2)}^2}{{r_2}^2+s^2{(x_1+x_2)}^2}{U}^2---\left(15\right)$

Traditional trend computing formula is as shown in Equation 16:

$\left[\begin{array}{c}\mathrm{\&Delta;P}\\ \mathrm{\&Delta;Q}\end{array}\right]=\left[\begin{array}{cc}H& N\\ M& J\end{array}\right]\left[\begin{array}{c}\mathrm{\&Delta;\&theta;}\\ \mathrm{\&Delta;U}/U\end{array}\right]---\left(16\right)$

In formula, Δ P and Δ Q represent respectively to inject the amount of unbalance of active power and reactive power, and Δ V and Δ θ are expressed as the correction of voltage magnitude and phase angle;

By after wind-powered electricity generation set grid-connection, carry out trend calculate time, need revise above-mentioned conventional Load Flow equation, the function of node voltage because node injects idle, can inject the idle derivative to voltage by increase blower fan node in Jacobian matrix continuous item, convolution 16 is simplified processing to the power flow equation shown in formula 15, simplifies power flow equation as shown in Equation 17:

$\frac{\&PartialD;Q}{\&PartialD;U}=\frac{2U}{x_m}+U(1-\frac{U^2}{\sqrt{U^4-4{(x_1+x_2)}^2{P}^2}})---\left(17\right)$

In formula, x _mfor excitation reactance, x ₁for stator reactance, x ₂for rotor reactance, U is set end voltage, and Q is reactive power, and P is active power.

Prove the validity of the application's research method below by actual electrical network example.

Analyze for a certain actual electric network, the wind energy turbine set that this area puts into operation has nine, and blower fan total amount amounts to 180, and installation total capacity is about 160MW, accounts for 10% left and right of this area's generating total capacity, and it is connected by 110kV circuit with area power grid.

Adopt said method to calculate the system load flow under various typical wind speed, analyzed wind energy turbine set and moved the impact on system load flow, voltage.Table 1 and table 2 have provided respectively the result of calculation under various typical wind speed.It should be noted that, in flow calculation program, adopted the measure of automatic excision wind turbine generator, to maintain system voltage level within the acceptable range, be generally 0.9～1.1 (perunit value).When wind speed is very high, too much wind turbine generator is connected to the grid simultaneously needs absorption idle in a large number, can cause voltage to decline to a great extent.If voltage drop to a certain extent, unit internal control system can force to make wind turbine generator to be stopped transport, and unit is separated with electrical network.Therefore the application processes and conforms to actual conditions like this.

Table 1: wind energy turbine set is meritorious, reactive power and maximum can start number of units

, reactive power meritorious by wind energy turbine set in table 1 and maximum can start number of units can be found out, along with wind speed gradually changes from low to high, the active power that wind turbine generator is sent is ever-increasing.Meanwhile, the reactive power that wind turbine generator absorbs is also ever-increasing.Wind speed and active power of wind power field in certain wind speed range (0～14m/s) present cubic function relation substantially.When wind speed is during lower than 3m/s or higher than 25m/s, wind turbine generator is subject to protective device effect autostop in unit, therefore two kinds of situations is classified as to a class, hereinafter if no special instructions all by this principle processing.

In addition, in the time that wind speed is lower (wind speed range is 0～6m/s), wind turbine generator absorbs idle less, and system voltage level is in normal range (NR).With the existing installed capacity of wind-driven power in Area in Yantai Region, the whole start-up and operations of wind turbine generator can not cause obvious impact to line voltage level.When the situation (wind speed is greater than 6m/s) that wind speed is higher or fluctuations in wind speed is violent, all wind turbine generator startup meeting is simultaneously to obviously reducing line voltage.As shown in table 2, in the time that wind speed is 24m/s, in order to maintain normal voltage level, system starts 50 wind turbine generator (taking main flow 800kW asynchronous system wind turbine generator as example) at most simultaneously.With the current installed capacity in this area, in the time of strong wind weather, wind energy turbine set can be one batch according to the wind energy turbine set installed capacity of 25% left and right, and grouping starts wind turbine generator.Along with economic development, the installed capacity of this area will further increase, and this ratio also needs suitable reduction.

Table 2: part busbar voltage calculation of tidal current

Bus sequence number	Wind speed is lower than 3m/s	Wind speed 6m/s	Wind speed 12m/s	Wind speed 24m/s
					1# node 110kV bus	0.9738	0.9529	0.8966	0.9443
2# node 110kV bus	0.9757	0.9506	0.8851	0.9398
					3# node 110kV bus	0.9759	0.9555	0.9006	0.9471
4# node 110kV bus	0.9751	0.9547	0.8997	0.9463
					5# node 110kV bus	0.9648	0.9441	0.8885	0.9356
6# node 110kV bus	0.9754	0.9550	0.9001	0.9466
					7# node 110kV bus	0.9686	0.9481	0.8927	0.9396
8# node 110kV bus	0.9991	1.0002	0.9991	1.0000
					9# node 110kV bus	0.9873	0.9870	0.9862	0.9868
The 110kV of 1# power plant bus	0.9917	0.9907	0.9884	0.9904

10# node 220kV bus	0.9876	0.9865	0.9837	0.9860
					11# node 220kV bus	0.9753	0.9833	0.9798	0.9827
12# node 220kV bus	0.9887	0.9878	0.9854	0.9874
					13# node 220kV bus	0.9904	0.9894	0.9868	0.9890

As seen from Figure 5, in the situation that not accessing wind turbine generator, system voltage level is good, and each busbar voltage maintains near 1.0p.u. substantially.When wind speed improves gradually, the reactive power absorbing due to wind turbine generator increases, and the busbar voltage level nearer with wind energy turbine set electrical distance declines gradually.For example, in the time that wind speed reaches 12m/s, comprise that 4-7# node 110kV busbar voltage level has all dropped near 0.9p.u..Wherein 5# node 110kV bus is the access point of above-mentioned wind energy turbine set, and voltage has been down to 0.885p.u..If wind speed continues to improve, and wind turbine generator now do not have automatic logout or fan starting quantity do not limited, and voltage can further decline so, and system local voltage level will worsen.In the time that wind speed is 24m/s, due to system constraint the startup number of units of wind energy turbine set, system voltage level is restored.

Can find out simultaneously, the obvious impact that wind turbine generator causes system voltage has certain effect scope, for with the nearer bus of wind energy turbine set access point electrical distance, be down to 0.9001p.u. as the voltage of 6# node 110kV bus by 0.976p.u., reached voltage levvl lower limit.And for distant bus, as 12# node 220kV bus and 8#, 9# basic point 110kV bus, although voltage levvl along with wind speed increases the decline having to a certain degree, fall is very little, changes not obvious.This is because reactive power is difficult for long-distance transmissions, has that locality and dispersed feature cause.This feature that access only has a significant effect near the busbar voltage level in some areas access point for wind energy turbine set can arrange reactive power compensator, to improve local voltage level near wind energy turbine set access point.

To above-mentioned electrical network, adopt respectively the model of above-mentioned revised PQ method and existing RX to contrast, its result is as shown in table 3.

Table 3: two kinds of computational methods result contrasts

From the above results, the simulation result under two kinds of methods is basically identical, but revised PQ model has convergence rate faster.This is the correction that has only completed change in voltage due to RX computation model in iterative process each time, revised PQ model has been considered the variation of voltage and slip simultaneously, therefore convergence rate is faster, and in the time of same convergence precision, the result of two kinds of methods should be more or less the same.

The structure and the model that the present invention is directed to wind-driven generator have carried out detailed analysis and elaboration, and four component Models based on wind speed have been determined the update equation formula of wind speed model, the dissimilar steady-state load flow models such as asynchronous system wind-driven generator and double-feedback aerogenerator have been proposed on the basis of labor wind-driven generator output mechanical power, on this basis in conjunction with existing trend calculative determination the power flow algorithm of dissimilar wind-driven generator after grid-connected, and according to actual emulation needs, simplification transaction module and the flow process of asynchronous wind driven generator have been proposed, by the system load flow computational methods after research wind-electricity integration, be conducive to determine the grid-connected scheme of wind energy turbine set, and be further to study it to the stability of a system, the work of the aspects such as reliability lays the foundation.Last the present invention has proved the validity of the application's research method by actual electric network example.

The above is the preferred embodiment of the present invention, for those skilled in the art, under the premise without departing from the principles of the invention, can also make some improvements and modifications, and these improvements and modifications are also regarded as protection scope of the present invention.

Claims (7)

1. a research method for wind turbine generator basic model and Power Flow Problem, is characterized in that, comprises following process:

1) structure of wind energy turbine set wind turbine generator is studied with model: described wind turbine generator is connected side by side, and jointly accesses network system; The conversion process of energy of the wind turbine generator of whole wind energy turbine set is wind energy-mechanical energy-electric energy, and wind turbine generator can be divided into two parts, the wind energy conversion system that a part is is mechanical energy by wind energy transformation, and another part is the generator that mechanical energy is transferred to electric energy; Wind power generation process is that the moment of inertia that changes wind energy into wind wheel by impeller is mechanical energy, by the gearing of main shaft, through the effect of gear box, asynchronous generating machine rotor is reached after suitable rotating speed, rotor driven generating, and through exciter converter, stator electric energy is injected to electrical network;

2) four component Models based on wind speed are determined the update equation formula of wind speed model: four international component Models of the normal employing of current wind speed model, comprise basic wind, fitful wind, gradual change wind, random noise wind four parts, basic wind, fitful wind, gradual change wind, random noise wind four part sums have formed the wind speed of normal wind machine; Normal wind machine is Vw at the residing wind speed of hub height, in actual analysis processing procedure, need it to revise, the update equation formula of wind speed model as shown in Equation 1:

$V_w=V_{w0}{\left[\frac{H}{H_0}\right]}^{\mathrm{\&alpha;}}---\left(1\right)$

In formula: H is hub height, H ₀for surveying wind height, V _w0for surveying the wind speed of wind height, α is altitude correction factor;

3) the steady-state load flow model of proposition asynchronous wind driven generator:

3.1) the mechanical power output of wind-driven generator adopts the first to analyze expression way, as shown in Equation 2:

P _m＝0.5ρSC _pV ³ (2)

In formula, ρ is atmospheric density (kg/m ³); S is the swept area (m of pneumatic equipment blades made ²); C _pfor the power coefficient of wind energy conversion system, can be expressed as the function of tip speed ratio, V is wind speed;

The mechanical power output of wind-driven generator adopts the second to analyze expression way, as shown in Equation 3:

$P_m=\left\{\begin{array}{cc}0& V<V_{\mathrm{cin}},V>V_{\mathrm{cout}}\\ \frac{V^3-{V_{\mathrm{cin}}}^3}{{V_r}^3-{V_{\mathrm{cin}}}^3}{P}_r& V_{\mathrm{cin}}\&le;V<V_r\\ P_r& V_r\&le;V\&le;V_{\mathrm{cout}}\end{array}\right.---\left(3\right)$

In formula, P _mbe respectively wind speed and the meritorious power output of wind energy conversion system wheel hub with V; V _cin, V _r, V _cout, P _rfor being expressed as wind energy conversion system incision wind speed, rated wind speed, cut-out wind speed, rated power;

3.2) equivalent electric circuit of asynchronous wind driven generator is simplified to the Γ type equivalent circuit that obtains asynchronous wind driven generator, the complex power formula of Γ type equivalent circuit as shown in Equation 4:

$\begin{array}{c}\tilde{S}=\stackrel{\&CenterDot;}{U}\stackrel{*}{I}=\stackrel{\&CenterDot;}{U}\frac{-\stackrel{*}{U}}{j(x_1+x_2)+r_2/s}+j\frac{U^2}{x_m}-\\ \frac{U^2\frac{r_2}{s}}{{\left(\frac{r_2}{s}\right)}^2+{(x_1+x_2)}^2}+j(\frac{U^2}{{\left(\frac{r_2}{s}\right)}^2+{(x_1+x_2)}^2}+\frac{U^2}{x_m})=P+\mathrm{jQ}\end{array}---\left(4\right)$

In formula, x _mfor excitation reactance; r _mfor excitation resistance; r ₁for stator resistance; x ₁for stator reactance; x ₂for rotor reactance; r ₂for rotor resistance; S is revolutional slip, s=(n _s-n)/n _s, n _sfor synchronous speed, n is asynchronous generator rotating speed, and j is imaginary unit, with be respectively line voltage and line current; Known according to formula 4, the active power of asynchronous wind driven generator and the direction of reactive power are contrary, and wind turbine generator is absorbing reactive power in sending active power;

Can derive revolutional slip s and the tg φ of corresponding asynchronous wind driven generator according to formula 3 and formula 4, embody respectively suc as formula 5 and formula 6 shown in:

$s=\frac{U^2{r}_2-\sqrt{U^4{r}_2^2-4P^2{(x_1+x_2)}^2{r}_2^2}}{2P{(x_1+x_2)}^2}---\left(5\right)$

$\mathrm{tg\&phi;}=\frac{Q}{P}=\frac{s^2(x_1+x_2)(x_m+x_1+x_2)+r_2^2}{r_2{x}_{m}s}---\left(6\right)$

In formula, r ₁for stator resistance; x ₁for stator reactance; Φ is power-factor angle, and s is revolutional slip, and Q is reactive power, and P is active power;

Simultaneous formula 5 and formula 6, eliminate revolutional slip s, reactive power express for the function of mechanical active power of output as shown in Equation 7:

$Q=\frac{2P^2{(x_1+x_2)}^2}{r_2^2{x}_m(-U^2{r}_2^2+\sqrt{U^4{r}_2^2-4P^2{(x_1+x_2)}^2{r}_2^2})}---\left(7\right)$

From formula 7, the reactive power Q that wind turbine generator absorbs is not only relevant with the active-power P of generating set, and also has substantial connection with set end voltage U;

3.3) expression formula of double-fed type asynchronous generator stable state equivalent circuit is as shown in Equation 8:

$\left\{\begin{array}{c}{\stackrel{\&CenterDot;}{U}}_1={\stackrel{\&CenterDot;}{I}}_1(r_1+j{x}_1)+({\stackrel{\&CenterDot;}{I}}_1+{\stackrel{\&CenterDot;}{I}}_2)j{x}_m\\ \frac{{\stackrel{\&CenterDot;}{U}}_2}{s}={\stackrel{\&CenterDot;}{I}}_2(\frac{r_1}{s}+j{x}_2)+({\stackrel{\&CenterDot;}{I}}_1+{\stackrel{\&CenterDot;}{I}}_2)j{x}_m\end{array}\right.---\left(8\right)$

In formula, for stator terminal voltage; for stator current; for the voltage of rotor winding external power supply; for rotor current; r ₁and x ₁be respectively resistance and the reactance of stator winding; r ₂and x ₂be respectively resistance and the reactance of rotor winding; S is revolutional slip;

The total active-power P of double-fed type asynchronous generator injected system _ebe made up of two parts, a part is the active-power P that stator winding sends _s, another part is the active-power P that rotor winding sends or absorbs _rthe reactive power of double-fed type asynchronous generator is sent by generator unit stator side or the reactive power that absorbs and current transformer send or the reactive power that absorbs forms in generator amature side, by regulating amplitude and the phase angle of rotor additional power source voltage, can change that stator side is sent or the size of absorbing reactive power, the reactive power Q of speed-variable frequency-constant wind-driven generator group _ecan be approximated to be the reactive power Q of stator winding _s, the power expression of double-fed type asynchronous wind driven generator suc as formula 9 and formula 10 shown in:

$P_r=\frac{r_r{x}_{\mathrm{ss}}^2(P_s^2+Q_s^2)}{x_m^2{\left|U_s\right|}^2}+\frac{2r_r{x}_{\mathrm{ss}}}{x_m^2}{Q}_s-s{P}_s+\frac{r_r{\left|U_s\right|}^2}{x_m^2}---\left(9\right)$

$P_e=P_s+P_r=\frac{r_r{x}_{\mathrm{ss}}^2(P_s^2+Q_s^2)}{x_m^2{\left|U_s\right|}^2}+\frac{2r_r{x}_{\mathrm{ss}}}{x_m^2}{Q}_s+(1-s)P_s+\frac{r_r{\left|U_s\right|}^2}{x_m^2}---\left(10\right)$

In formula, x _ss=x _s+ x _m, r _mfor excitation resistance, x _mfor excitation reactance, P _efor total active power, P _sfor the active power that stator winding sends, P _rthe active power of sending or absorbing for rotor winding;

4) the wind-driven generator tide model after grid-connected is calculated:

4.1) in conjunction with the active power of above-mentioned asynchronous wind driven generator group and reactive power and with the relation of voltage, wind speed, revolutional slip, the electric power system that contains asynchronous system wind turbine generator is carried out to trend calculating;

4.2) wind turbine generator power factor set point is cos φ, convolution 11 expression formulas:

Q _s＝P _stgφ (11)

Can obtain expression formula as shown in Equation 12:

$\begin{array}{c}{P}_e=P_s+P_r\\ =\frac{r_r{x}_{\mathrm{ss}}^2{P}_s^2}{x_m^2{\left|U_s\right|}^2}(1+{\mathrm{tg}}^2\mathrm{\&phi;})+\\ (1+\frac{2r_r{x}_{\mathrm{ss}}\mathrm{tg\&phi;}}{x_m^2}-s)P_s+\frac{r_r{\left|U_s\right|}^2}{x_m^2}\end{array}---\left(12\right)$

In formula, P _efor total active power, P _sfor the active power that stator winding sends, P _rthe active power of sending or absorbing for rotor winding;

Convolution 10 and formula 12 are carried out trend calculating to the electric power system that contains double-feedback aerogenerator group under constant power factor mode;

4.3) due to Q _ebe approximately Q _s, just Q _ewith Q _ssubstitution formula (10), obtains expression formula as shown in Equation 13:

$\begin{array}{c}{P}_e=P_s+P_r\\ =\frac{r_r{x}_{\mathrm{ss}}^2(P_s^2+Q_s^2)}{x_m^2{\left|U_s\right|}^2}+\frac{2r_r{x}_{\mathrm{ss}}}{x_m^2}{Q}_s+\\ (1-s)P_s+\frac{r_r{\left|U_s\right|}^2}{x_m^2}\end{array}---\left(13\right)$

Because of rotor current transformer maximum current limit form range of operation expression formula as shown in Equation 14:

$P_s^2+{(Q_s+\frac{{\left|U_s\right|}^2}{x_{\mathrm{ss}}})}^2\&le;\frac{x_m^2{\left|U_s\right|}^2}{x_{\mathrm{ss}}}{I}_{r\max }^2---\left(14\right)$

In formula, I _rmaxfor rotor current transformer maximum current limit value;

Convolution 13 and formula 14 are carried out trend calculating to the electric power system that contains double-feedback aerogenerator group under constant voltage operational mode;

5) model of asynchronous wind driven generator is simplified to processing:

Formula 7 is further simplified and is processed, can obtain formula as shown in Equation 15:

$Q=\frac{U^2}{x_m}+\frac{s^2{(x_1+x_2)}^2}{{r_2}^2+s^2{(x_1+x_2)}^2}{U}^2---\left(15\right)$

Traditional trend computing formula is as shown in Equation 16:

$\left[\begin{array}{c}\mathrm{\&Delta;P}\\ \mathrm{\&Delta;Q}\end{array}\right]=\left[\begin{array}{cc}H& N\\ M& J\end{array}\right]\left[\begin{array}{c}\mathrm{\&Delta;\&theta;}\\ \mathrm{\&Delta;U}/U\end{array}\right]---\left(16\right)$

In formula, Δ P and Δ Q represent respectively to inject the amount of unbalance of active power and reactive power, and Δ V and Δ θ are expressed as the correction of voltage magnitude and phase angle;

Convolution 16 is simplified processing to the power flow equation shown in formula 15, simplifies power flow equation as shown in Equation 17:

$\frac{\&PartialD;Q}{\&PartialD;U}=\frac{2U}{x_m}+U(1-\frac{U^2}{\sqrt{U^4-4{(x_1+x_2)}^2{P}^2}})---\left(17\right)$

In formula, x _mfor excitation reactance, x ₁for stator reactance, x ₂for rotor reactance, U is set end voltage, and Q is reactive power, and P is active power.

2. the research method of a kind of wind turbine generator basic model according to claim 1 and Power Flow Problem, is characterized in that, the span of described altitude correction factor α is 0.10-0.40.

3. the research method of a kind of wind turbine generator basic model according to claim 1 and Power Flow Problem, is characterized in that, described grid-connected Wind turbine mainly comprises: wind turbine, pylon, power transmission shaft, gear box, generator and corresponding control system.

4. the research method of a kind of wind turbine generator basic model according to claim 1 and Power Flow Problem, it is characterized in that, basic wind in described wind speed model is the normal part always existing in service of wind energy conversion system, has determined the rated power of wind turbine generator output; The part of gustiness compounent for reflecting that real process wind speed changes suddenly; Gradual change wind is used for describing the roll-off characteristic of wind energy; The stochastic behaviour that wind energy changes is described by random noise wind component.

5. the research method of a kind of wind turbine generator basic model according to claim 1 and Power Flow Problem, is characterized in that, the described process that the electric power system that contains asynchronous system wind turbine generator is carried out to trend calculating comprises the following steps:

S11, forms bus admittance matrix;

S12, sets the voltage initial value of each bus: phase angle and amplitude;

S13, the wind speed of given wind energy turbine set;

S14, the active power of sending by formula 3 and the definite wind turbine generator of formula 8 and the reactive power of absorption;

S15, asks the meritorious and idle amount of unbalance in formula 1, and obtains Jacobian matrix element;

S16, solves formula 1 by Newton-Raphson method, and revises each busbar voltage and phase angle;

S17, whether verification trend restrains, if convergence, calculate finish, otherwise with new magnitude of voltage as initial value, repeating step S14, until calculating finish.

6. the research method of a kind of wind turbine generator basic model according to claim 1 and Power Flow Problem, it is characterized in that, the described process that the electric power system that contains double-feedback aerogenerator group is carried out to trend calculating under constant power factor mode comprises the following steps:

S21, wind speed setting and wind energy turbine set voltage initial value U _s;

S22, obtains P according to double-feedback aerogenerator wind speed power curve _e;

S23, according to the rotating speed control law formula (10) of wind turbine generator, calculates revolutional slip s;

S24, calculates P according to formula (12) _s, and calculate Q according to formula (11) _s;

S25, by P _e, Q _swith PQ form of bus bars substitution electric power system, calculate wind energy turbine set busbar voltage U ' _s, judge that the difference of voltage is in the error range of setting, i.e. U ' _s-U _s< ε;

S26, if U ' _s≠ U _s, make U _s=0.5 (U _s+ U ' _s), turn back to step S24 and continue execution step S24 and S25, until the difference of voltage is less than ε;

S27, obtains the final calculated value of Us, and substitution formula (12), obtains P _s, P _rdistribution situation.

7. the research method of a kind of wind turbine generator basic model according to claim 1 and Power Flow Problem, it is characterized in that, the described process that the electric power system that contains double-feedback aerogenerator group is carried out to trend calculating under constant voltage operational mode comprises the following steps:

S31, wind speed setting, sets constant working voltage U _s;

S32, obtains P according to double-feedback aerogenerator wind speed power curve _e;

S33, by P _e, U _swith PV form of bus bars substitution electric power system, calculate wind energy turbine set bus and inject reactive power Q _e;

S34, calculates revolutional slip s according to the rotating speed control law of wind turbine generator;

S35, calculates P according to formula 13 _s;

S36, by P _s, Q _e, U _ssubstitution formula 14 checks that whether electric current is out-of-limit.