CN104037806B - A kind of electric power system tide computational methods based on wind turbine generator basic model - Google Patents

Abstract

The invention discloses the research method of a kind of wind turbine generator basic model and Power Flow Problem, carried out detailed analysis and elaboration for the structure of wind-driven generator and model, four component Models based on wind speed determine the update equation formula of Wind speed model, the basis of labor wind-driven generator output mechanical power proposes the dissimilar steady-state load flow model such as asynchronous system wind-driven generator and double-feedback aerogenerator, on this basis in conjunction with existing Load flow calculation determine dissimilar wind-driven generator grid-connected after power flow algorithm, and according to the emulation needs of reality, propose simplify processes model and the flow process of asynchronous wind driven generator, by the system load flow computational methods after research wind-electricity integration, be conducive to the connect-in strategy determining wind energy turbine set, and be study it further to the stability of a system, the work of the aspects such as reliability lays the foundation.

Description

A kind of electric power system tide computational methods based on wind turbine generator basic model

Technical field

The present invention relates to a kind of wind turbine generator research method, specifically a kind of electric power system tide computational methods based on wind turbine generator basic model.

Background technology

At present at world wide, in order to ensure energy security, realizing energy sources diversification, and tackling climate change, each national capital develop actively regenerative resource.Wind energy is inexhaustible clean, pollution-free, regenerative resource, and thus wind power generation occupies 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, and due to the impact of oil crisis, be exploitation alternative energy source, 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 obtains development at full speed, for realizing the target of carbon dioxide isothermal chamber gas abatement, Europe using Wind Power Development as an important measure, wherein for ensureing that wind-powered electricity generation grows continuously and fast, the country such as Germany, Denmark, Spain has all formulated higher wind-powered electricity generation purchasing price.Known according to " global wind report in 2011 " that Global Wind-energy council (GWEC) issues, by the end of the year 2011, world's installed capacity of wind-driven power will reach 2.38 hundred million kW, average annual growth about 28% during increasing by 20.6%, 2001-2011 on a year-on-year basis.

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 first time and Second National Wind Energy Resources Survey respectively, show that China's land 10m height layer wind energy resources theory development reserves can be respectively 3226GW and 4350GW.According to statistics, the land wind-powered electricity generation developed of China is about 2.5 hundred million kw, and sea is land three times, i.e. 750GW, and total amount is the conclusion of 1000GW.Because THE WIND ENERGY RESOURCES IN CHINA mainly concentrates on " three Norths " area, mostly away from load center.Wind-powered electricity generation cause development since " Renewable Energy Law " is promulgated 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, the wind energy turbine set that the province ,city and area introducing wind-powered electricity generation all starts building and propose meter is studied each side impact that electrical network brings with regard to grid connected wind power.

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

(1) the wind power generation addressing area that wind resource is abundant in coastal, mountain area etc., and these areas are often away from major network, the injection of wind power will change the trend distribution of local electrical network, cause the node voltage of partial electric grid to produce fluctuation.Angle that collateral security wind energy turbine set and electric power system normally run is considered, determines that the maximum injection power of a wind energy turbine set and influencing factor thereof need the problem solved when becoming planning and designing wind energy turbine set.

(2) wind turbine generator (wind turbine generator) change of exerting oneself, the operational mode of conventional power unit in net is changed, therefore can cause certain influence to the low frequency oscillation mode of electrical network and oscillating characteristic after wind farm grid-connected, some local oscillation patterns even may be caused to occur or disappear.

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

Therefore, for after wind-electricity integration to the influence research analysis of original system, there is good economic implications and good social effect.Then a underlying issue that need first solve on the impact of system load flow analysis and calculation after wind-electricity integration.On the one hand by the trend analyzed containing wind turbine generator can determine wind energy turbine set connect-in strategy and can Efficient Evaluation blower fan be grid-connected Power System Steady-state is run to the impact produced afterwards, comprise the problems such as the realistically displayed of node busbar voltage mutation analysis and line power and the node voltage caused by wind energy turbine set; Power Flow Problem after analyzing wind-electricity integration on the other hand is also its working foundation affected the aspect such as the stability of a system, reliability of analyzing and researching further.

After wind farm grid-connected, in the Load flow calculation carrying out electric power system, adopt which kind of wind energy turbine set model most important.Document [1-3] proposes following several model: the first is simple PQ model, in conjunction with the specified meritorious and power factor of wind energy turbine set, extrapolate the reactive power that wind energy turbine set absorbs, and then in Load flow calculation, it can be used as common PQ load bus to process.Another kind is the function slippage of induction machine being expressed as terminal voltage, active power and equivalent branch impedance, is called RX model, is calculated electrical power and the mechanical output of blower fan by initial slippage and wind speed, and continuous 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 then 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. the combined iteration method that the electric power system tide containing wind energy turbine set calculates and application [J]. electric power network technique, 2005,29 (18): 59-62.

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

Summary of the invention

For the deficiencies in the prior art, the invention provides a kind of electric power system tide computational methods based on wind turbine generator basic model, by the electric power system tide computational methods after research wind-electricity integration, be conducive to the connect-in strategy determining wind energy turbine set.

The present invention solves the technical scheme that its technical problem takes: a kind of electric power system tide computational methods based on wind turbine generator basic model, is characterized in that, 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, and a part is the wind energy conversion system of mechanical energy by wind energy transformation, and another part is generator mechanical energy being transferred to electric energy; Wind power generation process is the moment of inertia and the mechanical energy that by impeller, wind energy are changed into wind wheel, by the gearing of main shaft, after the rotating speed that the effect of gear box makes asynchronous generating machine rotor reach suitable, rotor driven generates electricity, and through exciter converter, stator electric energy is injected electrical network;

2) based on the update equation formula of four component Model determination Wind speed model of wind speed: current Wind speed model often adopts four international component Models, namely comprise basic wind, fitful wind, gradual change wind, random noise wind four part, basic wind, fitful wind, gradual change wind, random noise wind four part sum constitute the wind speed of normal wind machine; The wind speed of normal wind machine residing for hub height is Vw, needs to revise it in actual analysis processing procedure, the update equation formula of Wind speed model as shown in Equation 1:

$V_w=V_{w0}{\[\frac{H}{H_0}\]}^{\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 asynchronous wind driven generator is proposed:

3.1) machine output power 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;

Machine output power or employing the second of wind-driven generator analyze expression way, as shown in Equation 3:

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

In formula, P _mthe wind speed of wind energy conversion system wheel hub and meritorious power output is respectively 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) carry out the equivalent electric circuit of asynchronous wind driven generator to simplify the Γ type equivalent circuit obtaining asynchronous wind driven generator, the complex power formula of Γ type equivalent circuit as shown in Equation 4:

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

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; 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 sending the simultaneously stability reactive power of active power;

Revolutional slip s and the tg φ of corresponding asynchronous wind driven generator can be derived according to formula 3 and formula 4, embody respectively such as formula shown in 5 and formula 6:

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

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

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, then reactive power express for mechanical active power of output function 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 asynchronous wind driven generator stable state equivalent circuit is as shown in Equation 8:

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

In formula, for stator terminal voltage; for stator current; for the voltage of rotor windings 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 windings; S is revolutional slip;

The total active-power P of asynchronous wind driven 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 windings sends or absorbs _rthe reactive power that the reactive power of asynchronous wind driven generator is sent by generator unit stator side or the reactive power that absorbs and current transformer send in generator amature side or absorb forms, by regulating amplitude and the phase angle of rotor additional power source voltage, stator side can be changed send 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 is such as formula shown in 9 and formula 10:

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

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

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 sending for rotor windings or absorb;

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 the relation with voltage, wind speed, revolutional slip, Load flow calculation is carried out to the electric power system containing asynchronous wind driven generator group;

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

Q _s＝P _stgφ(11)

Expression formula as shown in Equation 12 can be obtained:

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

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

Convolution 10 and formula 12, carry out Load flow calculation to the electric power system containing double-fed type asynchronous wind driven generator group under constant power factor mode;

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

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

Because rotor current transformer maximum current limits the range of operation expression formula of formation as shown in Equation 14:

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

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

Convolution 13 and formula 14, carry out Load flow calculation to the electric power system containing double-fed type asynchronous wind driven generator group under constant voltage operational mode;

5) simplify processes is carried out to the model of asynchronous wind driven generator:

To formula 7 simplify processes further, formula as shown in Equation 15 can be obtained:

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

Traditional Load flow calculation formula is as shown in Equation 16:

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

In formula, Δ P and Δ Q represents the amount of unbalance injecting active power and reactive power respectively, and Δ V and Δ θ is then expressed as the correction of voltage magnitude and phase angle;

Power flow equation shown in convolution 16 pairs of formulas 15 carries out simplify processes, simplifies power flow equation as shown in Equation 17:

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

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, the wind turbine generator after grid-connected 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 part always existed during wind energy conversion system normally runs, and determines the rated power that wind turbine generator exports; The part of gustiness compounent for reflecting that in real process, wind speed changes suddenly; Gradual change wind is then used for describing the roll-off characteristic of wind energy; The stochastic behaviour of wind energy change is then described by random noise wind component.

In said method, described the process that Load flow calculation is carried out in the electric power system containing asynchronous wind driven generator group to be comprised 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, determines the reactive power of the active power that wind turbine generator sends and absorption by formula 3 and formula 8;

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, then calculates end, otherwise with new magnitude of voltage as initial value, repeats step S14, till calculating terminates.

In said method, the described process that Load flow calculation is carried out in the electric power system containing double-fed type asynchronous wind driven generator group is comprised the following steps under constant power factor mode:

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

S22, obtains P according to double-fed type asynchronous wind driven generator 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 _ssubstitute into electric power system with PQ form of bus bars, 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 to perform step S24 and S25, until the difference of voltage is less than ε;

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

In said method, the described process that Load flow calculation is carried out in the electric power system containing double-fed type asynchronous wind driven generator group is comprised the following steps under constant voltage operational mode:

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

S32, obtains P according to double-fed type asynchronous wind driven generator wind speed power curve _e;

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

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

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 determine the update equation formula of Wind speed model, the basis of labor wind-driven generator output mechanical power proposes the dissimilar steady-state load flow model such as asynchronous wind driven generator and double-fed type asynchronous wind driven generator, on this basis in conjunction with existing Load flow calculation determine dissimilar wind-driven generator grid-connected after power flow algorithm, and according to the emulation needs of reality, propose simplify processes model and the flow process of asynchronous wind driven generator, by the system load flow computational methods after research wind-electricity integration, be conducive to the connect-in strategy determining wind energy turbine set, and be study it further to the stability of a system, the work of the aspects such as reliability lays the foundation.

Accompanying drawing explanation

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 simplifying equivalent circuit;

Fig. 3 is the schematic diagram of asynchronous wind driven 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 hereafter provides many different embodiments or example is used for realizing different structure of the present invention.Of the present invention open in order to simplify, hereinafter the parts of specific examples and setting are described.In addition, the present invention can in different example repeat reference numerals and/or letter.This repetition is to simplify and clearly object, itself does not indicate the relation between discussed various embodiment and/or setting.It should be noted that parts illustrated in the accompanying drawings are not necessarily drawn in proportion.Present invention omits the description of known assemblies and treatment technology and process to avoid unnecessarily limiting the present invention.

As shown in Figure 1, a kind of electric power system tide computational methods based on wind turbine generator basic model of the present invention, it comprises following process:

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

Usual 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 Load flow calculation after analysis and research wind-electricity integration, first need the operation characteristic analysing in depth 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 two parts thus, and a part is the wind energy conversion system of mechanical energy by wind energy transformation, and another part is generator mechanical energy being transferred to electric energy.A wind-energy changing system in essence.Typical wind power generator incorporated in power network group 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 the moment of inertia and the mechanical energy that by impeller, wind energy are changed into wind wheel, by the gearing of main shaft, after the rotating speed that the effect of gear box makes asynchronous generating machine rotor reach suitable, rotor driven generates electricity, and through exciter converter, stator electric energy is injected electrical network.

Two, based on the update equation formula of four component Model determination Wind speed model of wind speed

Current Wind speed model often adopts four international component Models, and namely comprise basic wind, fitful wind, gradual change wind, random noise wind four part, basic wind is the part always existed during wind energy conversion system normally runs, and determines the rated power that wind turbine generator exports; The part of gustiness compounent for reflecting that in real process, wind speed changes suddenly; Gradual change wind is then used for describing the roll-off characteristic of wind energy; The stochastic behaviour of wind energy change is then described by random noise wind component.In fact, basic wind, fitful wind, gradual change wind, random noise wind four part sum constitute the wind speed of normal wind machine; The wind speed of normal wind machine residing for hub height is Vw, needs to revise it in actual analysis processing procedure, the update equation formula of Wind speed model as shown in Equation 1:

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

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 machine output power 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;

Machine output power or employing the second of wind-driven generator analyze expression way, as shown in Equation 3:

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

In formula, P _mthe wind speed of wind energy conversion system wheel hub and meritorious power output is respectively 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 wind driven generator group Mathematical Modeling

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

The Mathematical Modeling of asynchronous wind driven generator group 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, total iterations is many, and convergence rate is slow.PQ model considers wind power plant reactive power and is subject to the impact such as busbar voltage and slippage, compares RX model, and when 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 be simplified, as shown in Fig. 2 (b).

Carry out the equivalent electric circuit of asynchronous wind driven generator to simplify the Γ type equivalent circuit obtaining asynchronous wind driven generator, the complex power formula of Γ type equivalent circuit can be obtained as shown in Equation 4 by foregoing circuit relation:

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

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; 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 sending the simultaneously stability reactive power of active power.

According to the characteristic relation of the wind-driven generator machine output power of formula 3 known itself and wind speed, can obtain the power output of every platform wind turbine generator under different wind speed, then 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.Suppose in the application that wind turbine generator is yi word pattern arrangement substantially, therefore can ignore the impact that wake effect produces power stage.By the circuit relationships that Fig. 2 and Shi 4 presents, in conjunction with the set end voltage U of output power value P and wind turbine generator, revolutional slip s and the tg φ of corresponding asynchronous wind driven generator can be derived thus, embody respectively such as formula shown in 5 and formula 6:

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

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

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, then reactive power express for mechanical active power of output function 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 wind driven generator group Mathematical Modeling

Double-fed type asynchronous wind driven generator group is in running, and be improve the service efficiency of wind energy, its rotating speed can regulate with the change of different wind speed, thus ensure blower fan running status at Best Point.Compared to asynchronous wind driven generator group, because double-fed type asynchronous wind driven generator group adds exciter control system, by the exciting current of suitable power electronic equipment regulator generator rotor, when ensureing generator unit stator output voltage and frequency is constant, the power stage of wind turbine generator can also be regulated.

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

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

In formula, for stator terminal voltage; for stator current; for the voltage of rotor windings 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 windings; S is revolutional slip.

The rotating speed n of double-fed type asynchronous wind power generator rotor is change, and in the three-phase symmetric winding of rotor, pass 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 rotating speed n ₂rotating magnetic field, i.e. n2=60f ₁× s/p, p are number of pole-pairs, then relative to stator winding, the rotating magnetic field relative rotation speed that rotor current produces is n ± n ₂=n ₁, n ₁for synchronous speed.Thus, in rotor variable-speed operation situation, stator winding still can produce the electric energy of fixed frequency 50Hz.

According to the change of double-fed type asynchronous wind power generator rotor rotating speed, double-fed type asynchronous wind driven generator has three kinds of running statuses.Metasynchronism is run, 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 wind driven 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 windings sends or absorbs _r.When rotating speed is higher than synchronous speed, rotor windings sends active power; When rotating speed is lower than synchronous speed, rotor windings absorbs active power.

The reactive power that the reactive power of double-fed type asynchronous wind driven generator is sent by generator unit stator side or the reactive power that absorbs and current transformer send in generator amature side or absorb forms.Regulate amplitude and the phase angle of rotor additional power source voltage, stator side can be changed and send 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 is such as formula shown in 9 and formula 10:

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

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

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 sending for rotor windings or absorb.

The exciter control system of double-fed type asynchronous wind driven generator 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 Reactive-power control ability, can maintain set end voltage and stablize in a certain degree.But this control model complex structure, and the Reactive-power control ability of wind turbine generator is very limited.Current double-fed type asynchronous wind driven generator group seldom adopts this control model, and adopts constant power factor control model.Under steady preview roadway, this control model can make the power factor of wind turbine generator maintain near 1.0, namely from electrical network angle, and wind turbine generator not absorbing reactive power substantially while sending active power.

But reaching incision wind speed when wind speed, the moment that wind turbine generator starts, control system fails to get involved in time, and double-fed type asynchronous wind driven generator group still synchronous and asynchronous wind turbine generator is the same, needs to absorb a large amount of idlely to carry out excitation.Therefore analyze fan starting on system voltage cause affect time, the power flow algorithm of asynchronous wind driven generator group can be adopted.

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

4.1) electric power system tide containing asynchronous system Wind turbines calculates

System busbar is divided into PQ bus, PV bus and balance bus three major types by conventional Load flow calculation.But asynchronous system Wind turbines can not belong to certain class bus simply, when solving the electric power system tide comprising wind energy turbine set, must consider the feature of Wind turbines itself: send meritorious simultaneously stability idle, and the size of absorbing reactive power is relevant to set end voltage, the active power sent and slippage.

In conjunction with the active power of above-mentioned asynchronous wind driven generator group and reactive power and the relation with voltage, wind speed, revolutional slip, the step of the electric power system containing asynchronous wind driven generator group being carried out to Load flow calculation 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, determines the reactive power of the active power that wind turbine generator sends and absorption by formula 3 and formula 8;

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, then calculates end, otherwise with new magnitude of voltage as initial value, repeats step S14, till calculating terminates.

Because double-fed type asynchronous wind driven 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, Load flow calculation is carried out to the electric power system containing double-fed type asynchronous wind driven generator group

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

Q _s＝P _stgφ(11)

Expression formula as shown in Equation 12 can be obtained:

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

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

Under constant power factor mode to carry out the step of Load flow calculation to the electric power system containing double-fed type asynchronous wind driven generator group as follows:

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

S22, obtains P according to double-fed type asynchronous wind driven generator 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 _ssubstitute into electric power system with PQ form of bus bars, 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 to perform step S24 and S25, until the difference of voltage is less than ε;

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

4.3) under constant voltage operational mode, Load flow calculation is carried out to the electric power system containing double-fed type asynchronous wind driven generator group

Under constant voltage operational mode, double-fed type asynchronous wind driven generator can absorb or send reactive power, constant to maintain set end voltage.Within the scope of Wind turbines Reactive-power control, wind energy turbine set can be considered PV bus.For double-fed type asynchronous wind driven generator, its reactive power adjustable range by the restriction of stator winding thermal current limit, rotor windings thermal current limit and current transformer maximum current, but main be the restriction of current transformer maximum current.

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

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

Because rotor current transformer maximum current limits the range of operation expression formula of formation as shown in Equation 14:

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

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

Under constant voltage operational mode to carry out the step of Load flow calculation to the electric power system containing double-fed type asynchronous wind driven generator group as follows:

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

S32, obtains P according to double-fed type asynchronous wind driven generator wind speed power curve _e;

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

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

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 the emulation needs of reality, simplify processes is carried out to the model of asynchronous wind driven generator

Operation in conjunction with actual wind energy turbine set is known, can by stator reactance in Fig. 2 and rotor reactance merging treatment, and namely circuit can simplify processes further, and after simplifying, asynchronous generator equivalent circuit as shown in Figure 4.

To formula 7 simplify processes further, formula as shown in Equation 15 can be obtained:

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

Traditional Load flow calculation formula is as shown in Equation 16:

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

In formula, Δ P and Δ Q represents the amount of unbalance injecting active power and reactive power respectively, and Δ V and Δ θ is then expressed as the correction of voltage magnitude and phase angle;

When carrying out Load flow calculation after Wind turbines is grid-connected, need revise above-mentioned conventional Load Flow equation, it is the function of node voltage because node injection is idle, then inject the idle derivative to voltage by increasing blower fan node in Jacobian matrix continuous item, power flow equation shown in convolution 16 pairs of formulas 15 carries out simplify processes, simplifies power flow equation as shown in Equation 17:

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

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.

Electrical network example below by reality proves the validity of the application's research method.

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, and account for about 10% of this area's generating total capacity, it is connected by 110kV circuit with area power grid.

Adopt said method to calculate the system load flow under various typical wind speed, analyze the impact of wind energy turbine set operation on system load flow, voltage.Table 1 and table 2 sets forth the result of calculation under various typical wind speed.It should be noted that, in flow calculation program, have employed the measure of excision wind turbine generator automatically, 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, and voltage can be caused to decline to a great extent.If voltage drop to a certain extent, unit internal control system can be forced wind turbine generator is stopped transport, and is separated by unit with electrical network.Therefore the application processes like this and conforms to actual conditions.

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

, reactive power meritorious as can be seen from wind energy turbine set in table 1 and maximumly start number of units, along with wind speed gradually changes from low to high, the active power that wind turbine generator sends is ever-increasing.Meanwhile, the reactive power that wind turbine generator absorbs also is 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 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 a class, hereinafter if no special instructions all by this principle process.

In addition, when 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 operation of wind turbine generator can not cause obvious impact to voltage level of power grid.When the situation that wind speed is higher or fluctuations in wind speed is violent (wind speed is greater than 6m/s), the startup simultaneously of whole wind turbine generator can to making line voltage obviously reduce.As shown in table 2, when wind speed is 24m/s, in order to maintain normal voltage level, system starts 50 wind turbine generator (for main flow 800kW asynchronous wind driven generator group) at most simultaneously.With the installed capacity that this area is current, when strong wind weather, wind energy turbine set can be one batch according to the wind energy turbine set installed capacity of about 25%, and grouping starts wind turbine generator.Along with economic development, the installed capacity of this area will increase further, then 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
1# power plant 110kV 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, when 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 absorbed due to wind turbine generator increases, and declines gradually with the busbar voltage level that wind energy turbine set electrical distance is nearer.Such as when wind speed reaches 12m/s, comprise 4-7# node 110kV busbar voltage level and all have decreased near 0.9p.u..Wherein 5# node 110kV bus is the access point of above-mentioned wind energy turbine set, and voltage is down to 0.885p.u..If wind speed continues to improve, and wind turbine generator does not now have automatic logout or do not limit fan starting quantity, so voltage can decline further, and system local voltage level will worsen.When wind speed is 24m/s, the startup number of units of wind energy turbine set due to system constraint, system voltage level is restored.

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

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

Table 3: two kinds of computational methods Comparative result

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 because RX computation model only completes the correction of change in voltage in iterative process each time, revised PQ model then considers the change of voltage and slip simultaneously, therefore convergence rate is faster, and when 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 determine the update equation formula of Wind speed model, the basis of labor wind-driven generator output mechanical power proposes the dissimilar steady-state load flow model such as asynchronous wind driven generator and double-fed type asynchronous wind driven generator, on this basis in conjunction with existing Load flow calculation determine dissimilar wind-driven generator grid-connected after power flow algorithm, and according to the emulation needs of reality, propose simplify processes model and the flow process of asynchronous wind driven generator, by the system load flow computational methods after research wind-electricity integration, be conducive to the connect-in strategy determining wind energy turbine set, and be study it further to the stability of a system, the work of the aspects such as reliability lays the foundation.Last the present invention demonstrates the validity of the application's research method by actual electric network example.

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

Claims (7)

1. based on electric power system tide computational methods for wind turbine generator basic model, it is characterized in that, 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, and a part is the wind energy conversion system of mechanical energy by wind energy transformation, and another part is generator mechanical energy being transferred to electric energy; Wind power generation process is the moment of inertia and the mechanical energy that by impeller, wind energy are changed into wind wheel, by the gearing of main shaft, after the rotating speed that the effect of gear box makes asynchronous generating machine rotor reach suitable, rotor driven generates electricity, and through exciter converter, stator electric energy is injected electrical network;

2) based on the update equation formula of four component Model determination Wind speed model of wind speed: current Wind speed model often adopts four international component Models, namely comprise basic wind, fitful wind, gradual change wind, random noise wind four part, basic wind, fitful wind, gradual change wind, random noise wind four part sum constitute the wind speed of normal wind machine; The wind speed of normal wind machine residing for hub height is Vw, needs to revise it in actual analysis processing procedure, the update equation formula of Wind speed model as shown in Equation 1:

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

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 asynchronous wind driven generator is proposed:

3.1) machine output power 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;

Machine output power or employing the second of wind-driven generator analyze expression way, as shown in Equation 3:

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

In formula, P _mthe wind speed of wind energy conversion system wheel hub and meritorious power output is respectively 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) carry out the equivalent electric circuit of asynchronous wind driven generator to simplify the Γ type equivalent circuit obtaining asynchronous wind driven generator, the complex power formula of Γ type equivalent circuit as shown in Equation 4:

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

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; 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 sending the simultaneously stability reactive power of active power;

Revolutional slip s and the tg φ of corresponding asynchronous wind driven generator can be derived according to formula 3 and formula 4, embody respectively such as formula shown in 5 and formula 6:

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

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

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, then reactive power express for mechanical active power of output function 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 wind driven generator stable state equivalent circuit is as shown in Equation 8:

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

In formula, for stator terminal voltage; for stator current; for the voltage of rotor windings 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 windings; S is revolutional slip;

The total active-power P of double-fed type asynchronous wind driven 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 windings sends or absorbs _rthe reactive power that the reactive power of double-fed type asynchronous wind driven generator is sent by generator unit stator side or the reactive power that absorbs and current transformer send in generator amature side or absorb forms, by regulating amplitude and the phase angle of rotor additional power source voltage, stator side can be changed send 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 is such as formula shown in 9 and formula 10:

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

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

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 sending for rotor windings or absorb;

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 the relation with voltage, wind speed, revolutional slip, Load flow calculation is carried out to the electric power system containing asynchronous wind driven generator group;

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

Q _s＝P _stgφ(11)

Expression formula as shown in Equation 12 can be obtained:

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

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

Convolution 10 and formula 12, carry out Load flow calculation to the electric power system containing double-fed type asynchronous wind driven generator group under constant power factor mode;

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

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

Because rotor current transformer maximum current limits the range of operation expression formula of formation as shown in Equation 14:

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

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

Convolution 13 and formula 14, carry out Load flow calculation to the electric power system containing double-fed type asynchronous wind driven generator group under constant voltage operational mode;

5) simplify processes is carried out to the model of asynchronous wind driven generator:

To formula 7 simplify processes further, formula as shown in Equation 15 can be obtained:

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

Traditional Load flow calculation formula is as shown in Equation 16:

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

In formula, Δ P and Δ Q represents the amount of unbalance injecting active power and reactive power respectively, and Δ V and Δ θ is then expressed as the correction of voltage magnitude and phase angle;

Power flow equation shown in convolution 16 pairs of formulas 15 carries out simplify processes, simplifies power flow equation as shown in Equation 17:

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

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. a kind of electric power system tide computational methods based on wind turbine generator basic model according to claim 1, is characterized in that, the span of described altitude correction factor α is 0.10-0.40.

3. a kind of electric power system tide computational methods based on wind turbine generator basic model according to claim 1, it is characterized in that, the wind turbine generator after grid-connected mainly comprises: wind turbine, pylon, power transmission shaft, gear box, generator and corresponding control system.

4. a kind of electric power system tide computational methods based on wind turbine generator basic model according to claim 1, it is characterized in that, basic wind in described Wind speed model is the part always existed during wind energy conversion system normally runs, and determines the rated power that wind turbine generator exports; The part of gustiness compounent for reflecting that in real process, wind speed changes suddenly; Gradual change wind is then used for describing the roll-off characteristic of wind energy; The stochastic behaviour of wind energy change is then described by random noise wind component.

5. a kind of electric power system tide computational methods based on wind turbine generator basic model according to claim 1, is characterized in that, describedly comprise the following steps the process that Load flow calculation is carried out in the electric power system containing asynchronous wind driven generator group:

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, determines the reactive power of the active power that wind turbine generator sends and absorption by formula 3 and formula 8;

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, then calculates end, otherwise with new magnitude of voltage as initial value, repeats step S14, till calculating terminates.

6. a kind of electric power system tide computational methods based on wind turbine generator basic model according to claim 1, it is characterized in that, the described process that Load flow calculation is carried out in the electric power system containing double-fed type asynchronous wind driven generator group is comprised the following steps under constant power factor mode:

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

S22, obtains P according to double-fed type asynchronous wind driven generator 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 _ssubstitute into electric power system with PQ form of bus bars, 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 to perform step S24 and S25, until the difference of voltage is less than ε;

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

7. a kind of electric power system tide computational methods based on wind turbine generator basic model according to claim 1, it is characterized in that, the described process that Load flow calculation is carried out in the electric power system containing double-fed type asynchronous wind driven generator group is comprised the following steps under constant voltage operational mode:

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

S32, obtains P according to double-fed type asynchronous wind driven generator wind speed power curve _e;

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

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

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.