CN104504285A - Doubly-fed wind power farm equivalent modeling method for crowbar protection - Google Patents

Abstract

The invention discloses a doubly-fed wind power farm equivalent modeling method for crowbar protection. The method is characterized in that a voltage drop criterion capable of representing the crowbar protection action condition of a doubly-fed wind generation set is provided according to the relationship between rotor current increase and set terminal voltage drop amplitude after the doubly-fed wind generation set has three-phase short-circuit faults, the action criterion is modified according to the difference between a single machine infinite bus grid-connected structure and a topological structure of a wind power farm, the crowbar protection action condition of the set is judged according to the action criterion, and further a wind power farm equivalent model is built by taking the crowbar protection action condition as a cluster classification principle. The crowbar protection action condition of the doubly-fed wind power farm internal set is accurately represented, and wind power farm power external characteristic fitting precision of the wind power farm equivalent model is improved.

Description

A kind of double-fed fan motor station equivalent modeling method taking into account crow bar protection

Technical field

The present invention relates to a kind of equivalent modeling method for the grid-connected external characteristics in double-fed fan motor field.

Background technology

The features such as double-fed fan motor unit has maximum power tracing, power decoupled controls, Converter Capacity is little are the mainstream models in current wind energy turbine set.In order to improve the low voltage ride-through capability of double-fed fan motor unit, usually make power converter from the impact of short-circuit current in the protection of its rotor-side installing crow bar.The input of crow bar protection circuit not only makes unit lose control to output power, likely brings out the chain off-grid of unit in wind field, also because the access of crow bar resistance causes the weak feedback degree of wind energy turbine set to strengthen.Therefore, the operation characteristic of action to wind energy turbine set of crow bar protection has material impact.

When carrying out the grid-connected characteristic research of large-scale wind power, in order to reduce exponent number and the simulation calculation time of wind energy turbine set model, wind energy turbine set generally adopts Equivalent Model.At present, the research emphasis of wind energy turbine set multimachine Equivalent Model is, by extracting the quantification of Wind turbines characteristic, to determine criterion index of reasonably hiving off.Conventional criterion index of hiving off has the rotating speed of the input wind speed of wind energy conversion system, the action situation of propeller pitch angle, the direct-axis transient electromotive force of Wind turbines and aerogenerator vectorial.The study hotspot of wind energy turbine set unit Equivalent Model is, by optimizing Equivalent Model parameter, to improve the fitting precision to wind energy turbine set external characteristics further.Optimization object comprises the passive device of equivalent aerogenerator parameter, equivalent controller parameter and wind energy turbine set inside.But current achievement in research does not all take into account crow bar protection to the impact of unit and wind energy turbine set equivalent modeling.Research shows, if consider crow bar protection, traditional criterion index of hiving off is difficult to the crow bar protection act situation of accurate characterization unit, causes wind energy turbine set Equivalent Model to produce comparatively big error.Have scholar the double-fed fan motor set end Voltage Drop degree of depth and crow bar are protected between relation study, but do not consider the impact of wind energy turbine set topological structure on set end Voltage Drop critical value.

Summary of the invention

The present invention, in order to improve double-fed fan motor station equivalent modeling method based on the equivalent thought of the people having the same aspiration and interest to the equivalent accuracy of double-fed fan motor unit crow bar protection act situation, makes the power external characteristics of wind energy turbine set Equivalent Model matching wind energy turbine set more exactly.The invention provides a kind of double-fed fan motor station equivalent modeling method taking into account crow bar protection.

The present invention is that technical solution problem adopts following technical scheme:

The feature that the present invention takes into account the double-fed fan motor station equivalent modeling method of crow bar protection is carried out as follows:

Step 1, add up the actual measurement wind-resources information of wind energy turbine set whole year, described wind-resources information comprises size and the wind direction of wind farm wind velocity, sets up wind energy turbine set wind-resources information database;

Step 2, based on the network topology structure of double-fed fan motor field and model parameter, build wind energy turbine set detailed model;

The operate power factor of step 3, setting unit, the wind speed information of one group of wind energy turbine set is read at random from wind-resources information database, position distribution and the wake effect of foundation unit calculate the input wind speed deriving each unit, are determined the active-power P of each unit by input wind speed correspondence _w, complete the trend initialization of model before dynamic simulation; The wind speed information of described one group of wind energy turbine set refers at unit incision wind speed v _inwith excision wind speed v _outthe combination wind speed information of a certain wind speed direction within the scope of a certain wind speed size in scope and 0 ° to 360 °; Described unit is double-fed fan motor unit;

Terminal voltage U when step 4, each the unit steady-state operation in inside of collection wind energy turbine set _s0;

Grid side generation three phase short circuit fault when step 5, setting 0.1s, Failure elimination after 150ms, after gathering three phase short circuit fault, the terminal voltage of 1ms moment each unit falls value U _sk;

If the described terminal voltage of step 6 falls value U _skbe less than the corresponding terminal voltage before correction and fall critical value U ₀, then judge unit crow bar protection act, crow bar protection act unit incorporated into a crow bar protection act group of planes; Otherwise, then the virtual circuit impedance Z of this unit is calculated _eq-k;

Step 7, the virtual circuit impedance Z of acquisition will be calculated in step 6 _eq-kaccess unit Infinite bus power system also, between the machine end transformer of pessimistic concurrency control and middle pressure bus, falls critical value U to the terminal voltage of unit ₀revise, obtain revised terminal voltage and fall critical value U ₀';

If the set end Voltage Drop value U that step 8 step 5 gathers _skbe less than the revised terminal voltage obtained in step 7 and fall critical value U ₀', then judge unit crow bar protection act, crow bar protection act unit is incorporated into a crow bar protection act group of planes; Otherwise, then judge that the crow bar protection of unit is not operating, protected by crow bar not operating unit to incorporate into crow bar and protect a not operating group of planes;

Step 9, order: the equivalent unit WT of the unit First comprised in a crow bar protection act group of planes _eq1characterize, in the branch road of unit place, its active power flows out line impedance first the equivalent line impedance Z on direction _eq1characterize, the machine end transformer First equivalent machine end transformer T of unit _eq1characterize; Order: crow bar protects unit second the equivalent unit WT comprised in a not operating group of planes _eq2characterize, in the branch road of unit place, its active power flows out line impedance second the equivalent line impedance Z on direction _eq2characterize, machine end transformer second equivalent machine end transformer T of unit _eq2characterize; Utilize the equivalent unit WT of described First _eq1with second equivalent unit WT _eq2, first equivalent line impedance Z _eq1with second equivalent line impedance Z _eq2, First equivalent machine end transformer T _eq1with second equivalent machine end transformer T _eq2equivalent parameters set up take into account crow bar protection double-fed fan motor field Equivalent Model.

The feature that the present invention takes into account the double-fed fan motor station equivalent modeling method of crow bar protection is also: wind energy turbine set described in step 2 is made up of the unit that multiple stage model is identical, and the specified terminal voltage of described unit is U _n, through machine end transformer boost to U _mVbe connected to middle pressure bus by overhead transmission line afterwards, then boost to U through wind energy turbine set main-transformer _hV, eventually through double-circuit line access electrical network; S is spaced apart between adjacent unit; Described wind energy turbine set detailed model comprises circuit model, machine end transformer and main-transformer model between the unit model of each unit in wind energy turbine set, unit.

The feature that the present invention takes into account the double-fed fan motor station equivalent modeling method of crow bar protection is also: in step 3, the input wind speed of each unit is by following process computation:

Upstream and downstream position relationship between the inner unit of wind direction information determination wind energy turbine set in the wind farm wind velocity information that step a, basis are read in;

The size of the input wind speed of step b, wind energy turbine set inner most upstream unit equals the wind speed size in the wind farm wind velocity information of reading in; Setting downstream unit WT _jinput wind speed v _jonly by its upstream unit WT _kthe impact of wake effect, then downstream unit WT _jinput wind speed v _jcalculate by formula (1) and obtain:

$v_j=v_k[1-{\left(\frac{r}{0.08s_{\mathrm{jk}}+r}\right)}^2(1-\sqrt{1-C_t})]---\left(1\right)$

In formula (1), v _kfor upstream unit WT _kinput wind speed; R is the radius that unit circle sweeps wind cross section; s _jkfor upstream unit WT _kwith downstream unit WT _jair line distance; C _tfor thrust coefficient;

Step c, by unit WT _jas upstream unit, determine the input wind speed of its downstream unit according to formula (1), the like, until calculate the input wind speed obtaining the inner each unit of wind energy turbine set.

The feature that the present invention takes into account the double-fed fan motor station equivalent modeling method of crow bar protection is also: the active-power P of unit in described step 3 _wcalculated by formula (2) and obtain:

$P_w=0.5{\mathrm{\ρ\πr}}^2{c}_p{v}_w^3---\left(2\right)$

In formula (2), ρ is atmospheric density; v _wfor the input wind speed of unit; c _pfor power coefficient; Described power coefficient c _pcalculated by formula (3) and obtain:

$\left\{\begin{array}{c}{c}_p=0.22(\frac{116}{\mathrm{\λ}+0.08\mathrm{\β}}-\frac{4.06}{{\mathrm{\β}}^3+1}-0.4\mathrm{\β}-5)e^{-(\frac{12.5}{\mathrm{\λ}+0.08\mathrm{\β}}-\frac{0.4375}{{\mathrm{\β}}^3+1})}\\ \mathrm{\λ}=\frac{{\mathrm{\ω}}_{t}r}{v_w}\end{array}\right.---\left(3\right)$

In formula (3), λ is the tip speed ratio of unit; β is the propeller pitch angle of unit; ω _tfor the wind turbine rotating speed in unit.

The feature that the present invention takes into account the double-fed fan motor station equivalent modeling method of crow bar protection is also: in step 6, unit correction front voltage falls critical value U ₀determine according to the following procedure:

(1), unit Infinite bus power system is built and pessimistic concurrency control, the operate power factor of setting unit; The active-power P of setting unit _wfor 0MW, terminal voltage during steady-state operation is 0.97pu;

(2), setting 0.1s time grid side generation three phase short circuit fault, Failure elimination after 150ms;

(3), after three phase short circuit fault occurs, during 1ms, if the crow bar protection of unit is not operating, then progressively short circuit grounding impedance Z is reduced _f, until crow bar protects lucky action; If the crow bar protection act of unit, then progressively increase short circuit grounding impedance Z _f, until crow bar protection is failure to actuate just;

(4), record crow bar protection by not operating to the lucky action moment, or crow bar protection falls value U by action to the terminal voltage of moment unit of being just failure to actuate _sk, be unit at active-power P _wwith steady-state operation terminal voltage U _s0correction front voltage corresponding under combined situation falls critical value U ₀;

(5), within the scope of unit operation power 0 ~ 2MW, with 0.1MW be the active-power P that step-length increases unit gradually _w, repeat step (2) to step (4);

(6), within the scope of unit steady-state operation terminal voltage 0.97 ~ 1.07pu, with 0.01pu be the steady-state operation terminal voltage U that step-length increases unit gradually _s0, repeat step (2) to step (5);

(7), with active-power P _wfor X-axis, terminal voltage U during steady-state operation _s0for Y-axis, revise front voltage and fall critical value U ₀for Z axis, the terminal voltage set up before unit correction falls critical value three-dimensional coordinate figure.

The feature that the present invention takes into account the double-fed fan motor station equivalent modeling method of crow bar protection is also: the virtual circuit impedance Z of unit in step 6 _eq-kcalculate by formula (4) and obtain:

$Z_{\mathrm{eq}-k}=\frac{\underset{l=k}{\overset{N}{\mathrm{\Σ}}}\left(Z_l\underset{i=1}{\overset{l}{\mathrm{\Σ}}}{S}_i^{*}\right)}{S_k^{*}}---\left(4\right)$

In formula (4), Z _lfor unit WT _lits active-power P in the branch road of place _wflow out the line impedance of branch road; be i-th unit WT _ithe conjugate of applied power; N is unit WT _ithe number of units of the unit on a feeder line at place.

The feature that the present invention takes into account the double-fed fan motor station equivalent modeling method of crow bar protection is also: to set end Voltage Drop critical value U in step 7 ₀correction carry out according to the following procedure:

(a), by the circuit virtual impedance Z of unit _eq-kseries connection access unit Infinite bus power system between the machine end transformer of pessimistic concurrency control and middle pressure bus;

B the operate power factor of (), setting unit is identical with the operate power factor set in step 3, and set unit active-power P _wwith unit active-power P in step 3 _wkeep identical, adjustment line voltage makes terminal voltage U during unit steady-state operation _s0u identical with the terminal voltage that step 4 collects _s0;

Grid side generation three phase short circuit fault when (c), setting 0.1s, Failure elimination after 150ms;

(d), after three phase short circuit fault occurs, during 1ms, if the crow bar protection of unit is not operating, then progressively reduce short circuit grounding impedance Z _f, until crow bar protects lucky action; If crow bar protection act, then progressively increase short circuit grounding impedance Z _f, until crow bar protection is failure to actuate just;

E (), record crow bar are protected by not operating to the lucky action moment, or crow bar protection falls value U by action to the terminal voltage of moment unit of being just failure to actuate _sk, be unit active-power P _wwith steady-state operation terminal voltage U _s0correction rear end Voltage Drop critical value U ' corresponding under combined situation ₀.

The feature that the present invention takes into account the double-fed fan motor station equivalent modeling method of crow bar protection is also: each equivalent parameters that described step 9 medium value unit comprises: applied power S _eq, generator impedance Z _{g_eq}, inertia time constant H _eq, axis rigidity COEFFICIENT K _eq, axle system ratio of damping D _eq, and each equivalent parameters that equivalent machine end transformer comprises: applied power S _{t_eq}, impedance Z _{t_eq}calculate by formula (5) and obtain:

$\left\{\begin{array}{c}{S}_{\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{S}_i,Z_{G\_\mathrm{eq}}=\frac{Z_{\mathrm{Gi}}}{m},H_{\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{H}_i\\ K_{\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{K}_i,D_{\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{D}_i\\ S_{T\_\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{S}_{\mathrm{Ti}},Z_{T\_\mathrm{eq}}=\frac{Z_{\mathrm{Ti}}}{m}\end{array}\right.---\left(5\right)$

In formula (5), S _i, Z _gi, H _i, K _iand D _irepresent the applied power of i-th unit, generator impedance, inertia time constant, axis rigidity coefficient and axle system ratio of damping respectively; S _ti, Z _tibe rated capacity and the impedance of the machine end transformer of i-th unit; M is the number of units of unit in a corresponding group of planes;

The impedance Z of equivalent circuit _l-eqcalculate by formula (6) and obtain:

$Z_{l-\mathrm{eq}}=\frac{\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{Z}_{l-i}{S}_i^{*}{S}_i}{\left(\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{S}_i\right)\left(\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{S}_i^{*}\right)}---\left(6\right)$

In formula (6), Z _l-ibe i-th unit WT _iits active-power P in the branch road of place _wflow out the line impedance on direction.

Compared with the prior art, beneficial effect of the present invention is embodied in:

1, the present invention with unit crow bar protection act situation for group of planes principle of classification sets up double-fed fan motor field Equivalent Model, the terminal voltage in unit 1ms moment after grid side generation three phase short circuit fault is fallen value successively before correction corresponding thereto and fall critical value through revised terminal voltage and carry out two-wheeled and differentiate and compare, effectively can distinguish the inner crow bar protection act of wind energy turbine set and crow bar is protected not operating unit and incorporated into a corresponding group of planes, improve the equivalent accuracy of wind energy turbine set Equivalent Model to unit crow bar protection act, that a kind of equivalent unit number is less, realize more convenient, the more accurately double-fed fan motor station equivalent modeling method of matching wind power plant power external characteristic.

2, the operating criterion protected by unit crow bar of the present invention is reduced to set end Voltage Drop critical value after fault by unit rotor current, and its value is asked for conveniently, is easy to the differentiation of crow bar protection act, has taken into account the high efficiency of terseness that discriminant criterion expresses and execution.

3, the present invention considers that wind energy turbine set internal topology is on the impact of set end Voltage Drop critical value, revising, improve the accuracy that unit crow bar protection act differentiates by introducing virtual circuit impedance to set end Voltage Drop critical value.

Accompanying drawing explanation

Fig. 1 is the double-fed fan motor field equivalent modeling process flow diagram that the present invention takes into account crow bar protection;

Fig. 2 is double-fed fan motor field network topology structure figure in the present invention;

Fig. 3 determines Voltage Drop critical value process flow diagram before unit correction in the present invention;

Fig. 4 is unit Infinite bus power system grid connected structure figure in the present invention;

Fig. 5 is that terminal voltage when unity power factor runs in the present invention before unit correction falls critical value three-dimensional coordinate figure;

Fig. 6 is wind energy turbine set chain structure figure in the present invention;

Fig. 7 is double-fed fan motor field equivalent model structure figure in the present invention;

Fig. 8 is double-fed fan motor field active power dynamic response process when unity power factor runs in the present invention;

Fig. 9 is double-fed fan motor field reactive power dynamic response process when unity power factor runs in the present invention;

Embodiment

As shown in Figure 1, the double-fed fan motor station equivalent modeling method taking into account crow bar protection in the present embodiment carries out as follows:

Step 1, according to weather data convention, the wind direction of 0 °-360 ° is divided into 16 regions, the interval steps of wind speed is taken as 1m/s, the actual measurement wind-resources information of wind energy turbine set whole year is added up, wind-resources information comprises size and the wind direction of wind farm wind velocity, sets up wind energy turbine set wind-resources information database.

Step 2, based on the network topology structure of double-fed fan motor field and model parameter, DIgSILENT/Power Factory software platform is utilized to build wind energy turbine set detailed model.

In this step 2, wind energy turbine set is made up of the unit that multiple stage model is identical, and the specified terminal voltage of unit is U _n, through machine end transformer boost to U _mVbe connected to middle pressure bus by overhead transmission line afterwards, then boost to U through wind energy turbine set main-transformer _hV, eventually through double-circuit line access electrical network; S is spaced apart between adjacent unit; As shown in Figure 2, model parameter is as shown in table 1 for the network topology structure of double-fed fan motor field.When the rotor current of unit is greater than the duration of crow bar shutter threshold value more than 1ms, then crow bar guard signal triggers, and after 2ms, crowbar circuit drops into.Wind energy turbine set detailed model comprises circuit model, machine end transformer and main-transformer model between the unit model of each unit in wind energy turbine set, unit.

The operate power factor of step 3, setting unit, the wind speed information of one group of wind energy turbine set is read at random from wind-resources information database, position distribution and the wake effect of foundation unit calculate the input wind speed deriving each unit, are determined the active-power P of each unit by input wind speed correspondence _w, complete the trend initialization of model before dynamic simulation; The wind speed information of one group of wind energy turbine set refers at unit incision wind speed v _inwith excision wind speed v _outthe combination wind speed information of a certain wind speed direction within the scope of a certain wind speed size in scope and 0 ° to 360 °; Unit is double-fed fan motor unit.

In this step 3, the input wind speed of each unit is by following process computation:

Upstream and downstream position relationship between the inner unit of wind direction information determination wind energy turbine set in the wind farm wind velocity information that step a, basis are read in;

The size of the input wind speed of step b, wind energy turbine set inner most upstream unit equals the wind speed size in the wind farm wind velocity information of reading in; Setting downstream unit WT _jinput wind speed v _jonly by its upstream unit WT _kthe impact of wake effect, then downstream unit WT _jinput wind speed v _jcalculate by formula (1) and obtain:

$v_j=v_k[1-{\left(\frac{r}{0.08s_{\mathrm{jk}}+r}\right)}^2(1-\sqrt{1-C_t})]---\left(1\right)$

In formula (1), v _kfor upstream unit WT _kinput wind speed; R is the radius that unit circle sweeps wind cross section; s _jkfor upstream unit WT _kwith downstream unit WT _jair line distance; C _tfor thrust coefficient; Thrust coefficient C _tthe index provided by unit manufacturing firm, by acquisition of tabling look-up.

Step c, by unit WT _jas upstream unit, determine the input wind speed of its downstream unit according to formula (1), the like, until calculate the input wind speed obtaining the inner each unit of wind energy turbine set.

The active-power P of unit in this step 3 _wcalculated by formula (2) and obtain:

$P_w=0.5{\mathrm{\ρ\πr}}^2{c}_p{v}_w^3---\left(2\right)$

In formula (2), ρ is atmospheric density; v _wfor the input wind speed of unit; c _pfor power coefficient; Described power coefficient c _pcalculated by formula (3) and obtain:

$\left\{\begin{array}{c}{c}_p=0.22(\frac{116}{\mathrm{\λ}+0.08\mathrm{\β}}-\frac{4.06}{{\mathrm{\β}}^3+1}-0.4\mathrm{\β}-5)e^{-(\frac{12.5}{\mathrm{\λ}+0.08\mathrm{\β}}-\frac{0.4375}{{\mathrm{\β}}^3+1})}\\ \mathrm{\λ}=\frac{{\mathrm{\ω}}_{t}r}{v_w}\end{array}\right.---\left(3\right)$

In formula (3), λ is the tip speed ratio of unit; β is the propeller pitch angle of unit; ω _tfor the wind turbine rotating speed in unit.

Terminal voltage U when step 4, each the unit steady-state operation in inside of collection wind energy turbine set _s0.

Grid side generation three phase short circuit fault when step 5, setting 0.1s, Failure elimination after 150ms, after gathering three phase short circuit fault, the terminal voltage of 1ms moment each unit falls value U _sk.

If step 6 terminal voltage falls value U _skbe less than the corresponding terminal voltage before correction and fall critical value U ₀, then judge unit crow bar protection act, crow bar protection act unit incorporated into a crow bar protection act group of planes; Otherwise, then the virtual circuit impedance Z of this unit is calculated _eq-k.

In this step 6, unit correction front voltage falls critical value U ₀really constant current journey as shown in Figure 3, is specifically determined according to the following procedure:

(1), utilize DIgSILENT/Power Factory software platform to build unit Infinite bus power system and pessimistic concurrency control, model structure as shown in Figure 4, sets the operate power factor of unit; The active-power P of setting unit _wfor 0MW, terminal voltage during steady-state operation is 0.97pu;

(2), setting 0.1s time grid side generation three phase short circuit fault, Failure elimination after 150ms;

After grid side generation three phase short circuit fault, the rotor current i of unit _rt () is calculated by formula (4-1) and obtains.

$\begin{array}{c}{i}_r\left(t\right)=-\frac{L_m}{L_s{L}_r-L_m^2}[\frac{u_{\mathrm{sk}}}{{\mathrm{j\ω}}_1}+(\frac{u_{s0}}{{\mathrm{j\ω}}_1}-\frac{u_{\mathrm{sk}}}{{\mathrm{j\ω}}_1})e^{-j{\mathrm{\ω}}_{1}t}{e}^{-\frac{t}{T_s}}]\\ +\frac{L_s}{L_s{L}_r-L_m^2}[\frac{\frac{2}{3}\frac{1}{{\mathrm{\ω}}_1{L}_m\left|u_{s0}\right|}(R_r{\mathrm{\ω}}_1{L}_s{P}_s+R_s{\mathrm{\ω}}_s{L}_r{P}_s+{\mathrm{\ω}}_1{\mathrm{\ω}}_s{L}_s{L}_r{\mathrm{\σQ}}_s-R_s{R}_r{Q}_s+\frac{3}{2}{\mathrm{\ω}}_s{L}_r{\left|u_{s0}\right|}^2)}{{\mathrm{j\ω}}_s+\frac{1}{T_r}}\\ +\frac{j\frac{2}{3}\frac{1}{{\mathrm{\ω}}_1{L}_m\left|u_{s0}\right|}({\mathrm{\ω}}_1{\mathrm{\ω}}_s{L}_s{L}_r{\mathrm{\σP}}_s-R_s{R}_r{P}_s-R_r{\mathrm{\ω}}_1{L}_s{Q}_s-R_s{\mathrm{\ω}}_s{L}_r{Q}_s-\frac{3}{2}{R}_r{\left|u_{s0}\right|}^2)}{{\mathrm{j\ω}}_s+\frac{1}{T_r}}\\ -\frac{{\mathrm{AR}}_r{u}_{\mathrm{sk}}}{{\mathrm{j\ω}}_1({\mathrm{j\ω}}_s+\frac{1}{T_r})}-\frac{{\mathrm{AR}}_r(u_{s0}-u_{\mathrm{sk}})}{{\mathrm{j\ω}}_1(-{\mathrm{j\ω}}_r+\frac{1}{T_r}-\frac{1}{T_s})}{e}^{-{\mathrm{j\ω}}_{1}t}{e}^{-\frac{t}{T_s}}+C_1{e}^{-{\mathrm{j\ω}}_{s}t}{e}^{-\frac{t}{T_r}}\\ =f(R_s,L_s,R_r,L_r,L_m,P_s,Q_s,u_{\mathrm{sk}},u_{s0},{\mathrm{\ω}}_1,{\mathrm{\ω}}_s,{\mathrm{\ω}}_r,t)\end{array}t\≥0.---(4-1)$

In formula (4-1), R _sand R _rbe respectively the resistance of generator stator-rotator side in unit; L _s, L _rand L _mbe respectively self-induction and the mutual inductance of generator stator-rotator side in unit; P _sand Q _sbe respectively active power and reactive power that generator unit sends to electrical network; u _skand u _s0terminal voltage vector when the terminal voltage of unit falls vector steady-state operation after being respectively fault; ω ₁for synchronous rotary angular velocity; ω _sfor the slip angular velocity of unit; ω _rfor the rotor velocity of unit; for stator damping time constant; $T_r=(L_s{L}_r-L_m^2)/\left(L_s{R}_r\right),$ For rotor damping time constant; C ₁for integration constant; $A=-L_m/(L_s{L}_r-L_m^2);$ $\mathrm{\σ}=1-L_m^2/\left(L_s{L}_r\right).$

Known according to formula (4-1), the rotor current i of unit after three phase short circuit fault _rt () is by the resistance R of generator stator-rotator side _sand R _r, the self-induction of generator stator-rotator side and mutual inductance L _sand L _rand L _m, active-power P _sand reactive power Q _s, terminal voltage after fault falls vector u _sk, steady-state operation time terminal voltage vector u _s0and the slip angle rotational speed omega of generator in unit _swith rotor velocity ω _rcommon decision.For the unit with maximum power point tracking characteristic, the slip angle rotational speed omega of its generator _swith rotor velocity ω _rwith active-power P _sbetween there is corresponding relation, the slip angle rotational speed omega of generator _swith rotor velocity ω _rto rotor current i _rt the impact of () can be included in active-power P _sin.By the active-power P that unit operation power factor reflects _sand reactive power Q _sbetween relation, reactive power Q _sto rotor current i _rt the impact of () also can be included in active-power P _sin.Therefore, as the resistance R of generator stator-rotator side _sand R _r, the self-induction of rotor side and mutual inductance L _s, L _rand L _mand rotor current i _rwhen the threshold value of () is fixed t, fault rear end Voltage Drop vector u _skit is only the active-power P of unit _swith terminal voltage vector u during steady-state operation _s0function.When unit adopts stator voltage vector oriented control mode to run, then u _sk=U _sk, u _s0=U _s0.In sum, operating criterion index unit crow bar can protected is by rotor current i _rt () is converted into fault after, the terminal voltage of unit falls value U _sk, and then determine to make crow bar protect terminal voltage during lucky action to fall critical value U ₀.When after fault, the terminal voltage of unit falls value U _sklower than this critical value U ₀time crow bar protection act, otherwise be then failure to actuate.

(3), after three phase short circuit fault occurs, during 1ms, if the crow bar protection of unit is not operating, then pass through progressively to reduce short circuit grounding impedance Z _fthe terminal voltage reducing unit falls value U _sk, until crow bar protects lucky action; If by the crow bar protection act of unit, then progressively increase short circuit grounding impedance Z _fthe terminal voltage promoting unit falls value U _sk, until crow bar protection is failure to actuate just;

(4), record crow bar protection by not operating to the lucky action moment, or crow bar protection falls value U by action to the terminal voltage of moment unit of being just failure to actuate _sk, be unit at active-power P _wwith steady-state operation terminal voltage U _s0correction front voltage corresponding under combined situation falls critical value U ₀;

(5), within the scope of unit operation power 0 ~ 2MW, with 0.1MW be the active-power P that step-length increases unit gradually _w, repeat step (2) to step (4);

(6), within the scope of unit steady-state operation terminal voltage 0.97 ~ 1.07pu, with 0.01pu be the steady-state operation terminal voltage U that step-length increases unit gradually _s0, repeat step (2) to step (5);

(7), with active-power P _wfor X-axis, terminal voltage U during steady-state operation _s0for Y-axis, revise front voltage and fall critical value U ₀for Z axis, the terminal voltage set up before unit correction falls critical value three-dimensional coordinate figure.In one machine infinity bus system, its terminal voltage of unit that unity power factor runs falls critical value as shown in Figure 5.

The virtual circuit impedance Z of unit in this step 6 _eq-kcalculate by formula (4) and obtain:

$Z_{\mathrm{eq}-k}=\frac{\underset{l=k}{\overset{N}{\mathrm{\Σ}}}\left(Z_l\underset{i=1}{\overset{l}{\mathrm{\Σ}}}{S}_i^{*}\right)}{S_k^{*}}---\left(4\right)$

In formula (4), Z _lfor unit WT _lits active-power P in the branch road of place _wflow out the line impedance of branch road; be i-th unit WT _ithe conjugate of applied power; N is unit WT _ithe number of units of the unit on a feeder line at place.

The difference of inner each the set end voltage of wind energy turbine set mainly comes from its difference to middle pressure bus electrical distance.Compared with Infinite bus power system grid connected structure, when grid side generation three phase short circuit fault, under wind energy turbine set chain topology as shown in Figure 6, single unit makes line impedance can not be ignored to the increase effect of middle pressure bus electrical distance.Now, to have connected between unit with short dot line impedance.Based on the functional form of formula (4), if this impedance is incorporated to the stator side of generator, then generator unit stator side resistance R _swith reactance L _schange will affect stator damping time constant T _swith rotor damping time constant T _r, thus the terminal voltage affecting unit falls value U _skwith rotor current i _rthe relation of (t).Therefore, need to fall critical value U to the terminal voltage of unit ₀revise.

Step 7, the virtual circuit impedance Z of acquisition will be calculated in step 6 _eq-kaccess unit Infinite bus power system also, between the machine end transformer of pessimistic concurrency control and middle pressure bus, falls critical value U to the terminal voltage of unit ₀revise, obtain revised terminal voltage and fall critical value U ₀'.

To set end Voltage Drop critical value U in this step 7 ₀correction carry out according to the following procedure:

(a), by the circuit virtual impedance Z of unit _eq-kseries connection access unit Infinite bus power system between the machine end transformer of pessimistic concurrency control and middle pressure bus.

B the operate power factor of (), setting unit is identical with the operate power factor set in step 3, and set unit active-power P _wwith unit active-power P in step 3 _wkeep identical, adjustment line voltage makes terminal voltage U during unit steady-state operation _s0u identical with the terminal voltage that step 4 collects _s0.

Grid side generation three phase short circuit fault when (c), setting 0.1s, Failure elimination after 150ms.

(d), after three phase short circuit fault occurs during 1ms, if the crow bar protection of unit is not operating, then by progressively reducing short circuit grounding impedance Z _fthe terminal voltage reducing unit falls value U _sk, until crow bar protects lucky action; If crow bar protection act, then by progressively increasing short circuit grounding impedance Z _fthe terminal voltage promoting unit falls value U _sk, until crow bar protection is failure to actuate just.

E (), record crow bar are protected by not operating to the lucky action moment, or crow bar protection falls value U by action to the terminal voltage of moment unit of being just failure to actuate _sk, be unit active-power P _wwith steady-state operation terminal voltage U _s0correction rear end Voltage Drop critical value U ' corresponding under combined situation ₀.

If the set end Voltage Drop value U that step 8 step 5 gathers _skbe less than the revised terminal voltage obtained in step 7 and fall critical value U ₀', then judge unit crow bar protection act, crow bar protection act unit is incorporated into a crow bar protection act group of planes; Otherwise, then judge that the crow bar protection of unit is not operating, protected by crow bar not operating unit to incorporate into crow bar and protect a not operating group of planes.

Step 9, order: the equivalent unit WT of the unit First comprised in a crow bar protection act group of planes _eq1characterize, in the branch road of unit place, its active power flows out line impedance first the equivalent line impedance Z on direction _eq1characterize, the machine end transformer First equivalent machine end transformer T of unit _eq1characterize; Order: crow bar protects unit second the equivalent unit WT comprised in a not operating group of planes _eq2characterize, in the branch road of unit place, its active power flows out line impedance second the equivalent line impedance Z on direction _eq2characterize, machine end transformer second equivalent machine end transformer T of unit _eq2characterize; Utilize the equivalent unit WT of First _eq1with second equivalent unit WT _eq2, first equivalent line impedance Z _eq1with second equivalent line impedance Z _eq2, First equivalent machine end transformer T _eq1with second equivalent machine end transformer T _eq2equivalent parameters set up take into account crow bar protection double-fed fan motor field Equivalent Model.The structure of wind energy turbine set Equivalent Model as shown in Figure 7.

Each equivalent parameters that this step 9 medium value unit comprises: applied power S _eq, generator impedance Z _{g_eq}, inertia time constant H _eq, axis rigidity COEFFICIENT K _eq, axle system ratio of damping D _eq, and each equivalent parameters that equivalent machine end transformer comprises: applied power S _{t_eq}, impedance Z _{t_eq}calculate by formula (5) and obtain:

$\left\{\begin{array}{c}{S}_{\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{S}_i,Z_{G\_\mathrm{eq}}=\frac{Z_{\mathrm{Gi}}}{m},H_{\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{H}_i\\ K_{\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{K}_i,D_{\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{D}_i\\ S_{T\_\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{S}_{\mathrm{Ti}},Z_{T\_\mathrm{eq}}=\frac{Z_{\mathrm{Ti}}}{m}\end{array}\right.---\left(5\right)$

In formula (5), S _i, Z _gi, H _i, K _iand D _irepresent the applied power of i-th unit, generator impedance, inertia time constant, axis rigidity coefficient and axle system ratio of damping respectively; S _ti, Z _tibe rated capacity and the impedance of the machine end transformer of i-th unit; M is the number of units of unit in a corresponding group of planes;

The impedance Z of equivalent circuit _l-eqcalculate by formula (6) and obtain:

$Z_{l-\mathrm{eq}}=\frac{\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{Z}_{l-i}{S}_i^{*}{S}_i}{\left(\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{S}_i\right)\left(\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{S}_i^{*}\right)}---\left(6\right)$

In formula (6), Z _l-ibe i-th unit WT _iits active-power P in the branch road of place _wflow out the line impedance on direction.

For in checking the present invention, the revised terminal voltage of unit falls critical value U ' ₀to the accuracy that crow bar protection act situation differentiates, set the active-power P of the unit that 66 unity power factors run according to table 2 _w, grid side generation three-phase shortcircuit during 0.1s, Failure elimination after 150ms.Consider that short circuit grounding impedance is respectively Z _f=j5.5 Ω and Z _f=j7 Ω two kinds of situations, now press busbar voltage U in wind energy turbine set _mVcorrespondingly drop to 53.7% and 55.7% of its ratings.The terminal voltage of unit is fallen value U _skcritical value U is fallen respectively with before its correction with revised terminal voltage ₀with U ' ₀compare, judge the action situation that crow bar is protected, and with the simulation result of detailed model for benchmark, the correctness that above-mentioned crow bar protection act situation judges is added up, as shown in table 3.Can find out, work as Z _f=j5.5 Ω and Z _fduring=j7 Ω, fall critical value U according to the terminal voltage before revising ₀, the unit number of units of crow bar protection act erroneous judgement is respectively 8 and 7; Revised terminal voltage is used to fall critical value U ' ₀, erroneous judgement number of units is decreased to 2 and 0 respectively.Visible, adopt revised terminal voltage to fall critical value U ' ₀the accuracy that unit crow bar protection act situation in wind energy turbine set is differentiated can be improved.

For setting up the validity of wind energy turbine set Equivalent Model in checking the present invention according to the classification of crow bar protection act situation, the probability distribution according to wind energy turbine set actual measurement air speed data produces the initial wind speed of wind energy turbine set (wind speed 11m/s, wind direction 0 °) at random.Unit adopts the unity power factor method of operation.The wind energy turbine set Equivalent Model of classifying based on the crow bar classification of motion, wind speed classification, rotating speed vector and the power response process of detailed model in wind energy turbine set exit are as shown in Figure 8 and Figure 9.In Fig. 8, curve a is the active power response process of detailed model in wind energy turbine set exit, curve b is based on the active power response process of crow bar classification of motion Equivalent Model in wind energy turbine set exit, curve c is based on the active power response process of wind speed classification Equivalent Model in wind energy turbine set exit, and curve d is based on the active power response process of rotating speed vector classification Equivalent Model in wind energy turbine set exit.In Fig. 9, curve a is the reactive power response process of detailed model in wind energy turbine set exit, curve b is based on the reactive power response process of crow bar classification of motion Equivalent Model in wind energy turbine set exit, curve c is based on the reactive power response process of wind speed classification Equivalent Model in wind energy turbine set exit, and curve d is based on the reactive power response process of rotating speed vector classification Equivalent Model in wind energy turbine set exit.

With wind energy turbine set detailed model simulation result for benchmark, the error criterion of definition Equivalent Model is:

$E_r=\frac{1}{n}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\left|\frac{Y_{\mathrm{fi}}\left(k\right)-Y_i\left(k\right)}{Y_i\left(k\right)}\right|---\left(7\right)$

$\mathrm{\δ}=\underset{1\≤i\≤n}{\max }|Y_{\mathrm{fi}}\left(k\right)-Y_i\left(k\right)|---\left(8\right)$

In formula (7) and formula (8), Y _i(k), Y _fik () is respectively wind energy turbine set detailed model, the electric parameters of Equivalent Model in wind energy turbine set exit; N is sampling number.

Wind energy turbine set Equivalent Model to the equivalent accuracy of unit crow bar action situation in detailed model and model error index as shown in table 4, wherein scope analysis time of model error index tends towards stability the moment (0.6s) from fault initial time (0.1s) to system, and data sampling step-length is 0.2ms.Between age at failure, whether unit crow bar protection act decides its reactive power support ability to system, and then affects the Voltage Drop degree of depth of wind energy turbine set and the active power of wind energy turbine set.Because institute of the present invention extracting method has higher crow bar action situation equivalence accuracy, the therefore matching power external characteristics of wind energy turbine set better.

Table 1 double-fed fan motor unit and circuit model parameter

Table 2 double-fed fan motor unit active power

The double-fed fan motor unit of table 3 crow bar protection act

The equivalent accuracy of table 4 crow bar action situation and model error index

Claims (8)

1. take into account a double-fed fan motor station equivalent modeling method for crow bar protection, it is characterized in that described method is carried out as follows:

Step 1, add up the actual measurement wind-resources information of wind energy turbine set whole year, described wind-resources information comprises size and the wind direction of wind farm wind velocity, sets up wind energy turbine set wind-resources information database;

Step 2, based on the network topology structure of double-fed fan motor field and model parameter, build wind energy turbine set detailed model;

The operate power factor of step 3, setting unit, the wind speed information of one group of wind energy turbine set is read at random from wind-resources information database, position distribution and the wake effect of foundation unit calculate the input wind speed deriving each unit, are determined the active-power P of each unit by input wind speed correspondence _w, complete the trend initialization of model before dynamic simulation; The wind speed information of described one group of wind energy turbine set refers at unit incision wind speed v _inwith excision wind speed v _outthe combination wind speed information of a certain wind speed direction within the scope of a certain wind speed size in scope and 0 ° to 360 °; Described unit is double-fed fan motor unit;

Terminal voltage U when step 4, each the unit steady-state operation in inside of collection wind energy turbine set _s0;

Grid side generation three phase short circuit fault when step 5, setting 0.1s, Failure elimination after 150ms, after gathering three phase short circuit fault, the terminal voltage of 1ms moment each unit falls value U _sk;

If the described terminal voltage of step 6 falls value U _skbe less than the corresponding terminal voltage before correction and fall critical value U ₀, then judge unit crow bar protection act, crow bar protection act unit incorporated into a crow bar protection act group of planes; Otherwise, then the virtual circuit impedance Z of this unit is calculated _eq-k;

Step 7, the virtual circuit impedance Z of acquisition will be calculated in step 6 _eq-kaccess unit Infinite bus power system also, between the machine end transformer of pessimistic concurrency control and middle pressure bus, falls critical value U to the terminal voltage of unit ₀revise, obtain revised terminal voltage and fall critical value U ₀';

If the set end Voltage Drop value U that step 8 step 5 gathers _skbe less than the revised terminal voltage obtained in step 7 and fall critical value U ₀', then judge unit crow bar protection act, crow bar protection act unit is incorporated into a crow bar protection act group of planes; Otherwise, then judge that the crow bar protection of unit is not operating, protected by crow bar not operating unit to incorporate into crow bar and protect a not operating group of planes;

Step 9, order: the equivalent unit WT of the unit First comprised in a crow bar protection act group of planes _eq1characterize, in the branch road of unit place, its active power flows out line impedance first the equivalent line impedance Z on direction _eq1characterize, the machine end transformer First equivalent machine end transformer T of unit _eq1characterize; Order: crow bar protects unit second the equivalent unit WT comprised in a not operating group of planes _eq2characterize, in the branch road of unit place, its active power flows out line impedance second the equivalent line impedance Z on direction _eq2characterize, machine end transformer second equivalent machine end transformer T of unit _eq2characterize; Utilize the equivalent unit WT of described First _eq1with second equivalent unit WT _eq2, first equivalent line impedance Z _eq1with second equivalent line impedance Z _eq2, First equivalent machine end transformer T _eq1with second equivalent machine end transformer T _eq2equivalent parameters set up take into account crow bar protection double-fed fan motor field Equivalent Model.

2. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, it is characterized in that wind energy turbine set described in step 2 is made up of the unit that multiple stage model is identical, the specified terminal voltage of described unit is U _n, through machine end transformer boost to U _mVbe connected to middle pressure bus by overhead transmission line afterwards, then boost to U through wind energy turbine set main-transformer _hV, eventually through double-circuit line access electrical network; S is spaced apart between adjacent unit; Described wind energy turbine set detailed model comprises circuit model, machine end transformer and main-transformer model between the unit model of each unit in wind energy turbine set, unit.

3. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, is characterized in that the input wind speed of each unit in step 3 is by following process computation:

Upstream and downstream position relationship between the inner unit of wind direction information determination wind energy turbine set in the wind farm wind velocity information that step a, basis are read in;

The size of the input wind speed of step b, wind energy turbine set inner most upstream unit equals the wind speed size in the wind farm wind velocity information of reading in; Setting downstream unit WT _jinput wind speed v _jonly by its upstream unit WT _kthe impact of wake effect, then downstream unit WT _jinput wind speed v _jcalculate by formula (1) and obtain:

$v_j=v_k[1-{\left(\frac{r}{0.08s_{\mathrm{jk}}+r}\right)}^2(1-\sqrt{1-C_t})]---\left(1\right)$

In formula (1), v _kfor upstream unit WT _kinput wind speed; R is the radius that unit circle sweeps wind cross section; s _jkfor upstream unit WT _kwith downstream unit WT _jair line distance; C _tfor thrust coefficient;

Step c, by unit WT _jas upstream unit, determine the input wind speed of its downstream unit according to formula (1), the like, until calculate the input wind speed obtaining the inner each unit of wind energy turbine set.

4. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, is characterized in that the active-power P of unit in described step 3 _wcalculated by formula (2) and obtain:

$P_w=0.5\mathrm{\ρ\π}{r}^2{c}_p{v}_w^3---\left(2\right)$

In formula (2), ρ is atmospheric density; v _wfor the input wind speed of unit; c _pfor power coefficient; Described power coefficient c _pcalculated by formula (3) and obtain:

$\left\{\begin{array}{c}{c}_p=0.22(\frac{116}{\mathrm{\λ}+0.08\mathrm{\β}}-\frac{4.06}{{\mathrm{\β}}^3+1}-0.4\mathrm{\β}-5)e^{-(\frac{12.5}{\mathrm{\λ}+0.08\mathrm{\β}}-\frac{0.4375}{{\mathrm{\β}}^3+1})}\\ \mathrm{\λ}=\frac{{\mathrm{\ω}}_{t}r}{v_w}\end{array}\right.---\left(3\right)$

In formula (3), λ is the tip speed ratio of unit; β is the propeller pitch angle of unit; ω _tfor the wind turbine rotating speed in unit.

5. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, is characterized in that in step 6, unit correction front voltage falls critical value U ₀determine according to the following procedure:

(1), unit Infinite bus power system is built and pessimistic concurrency control, the operate power factor of setting unit; The active-power P of setting unit _wfor 0MW, terminal voltage during steady-state operation is 0.97pu;

(2), setting 0.1s time grid side generation three phase short circuit fault, Failure elimination after 150ms;

(3), after three phase short circuit fault occurs, during 1ms, if the crow bar protection of unit is not operating, then progressively short circuit grounding impedance Z is reduced _f, until crow bar protects lucky action; If the crow bar protection act of unit, then progressively increase short circuit grounding impedance Z _f, until crow bar protection is failure to actuate just;

(4), record crow bar protection by not operating to the lucky action moment, or crow bar protection falls value U by action to the terminal voltage of moment unit of being just failure to actuate _sk, be unit at active-power P _wwith steady-state operation terminal voltage U _s0correction front voltage corresponding under combined situation falls critical value U ₀;

(5), within the scope of unit operation power 0 ~ 2MW, with 0.1MW be the active-power P that step-length increases unit gradually _w, repeat step (2) to step (4);

(6), within the scope of unit steady-state operation terminal voltage 0.97 ~ 1.07pu, with 0.01pu be the steady-state operation terminal voltage U that step-length increases unit gradually _s0, repeat step (2) to step (5);

(7), with active-power P _wfor X-axis, terminal voltage U during steady-state operation _s0for Y-axis, revise front voltage and fall critical value U ₀for Z axis, the terminal voltage set up before unit correction falls critical value three-dimensional coordinate figure.

6. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, is characterized in that the virtual circuit impedance Z of unit in step 6 _eq-kcalculate by formula (4) and obtain:

$Z_{\mathrm{eq}-k}=\frac{\underset{l=k}{\overset{N}{\mathrm{\Σ}}}\left(Z_l\underset{i=1}{\overset{l}{\mathrm{\Σ}}}{S}_i^{*}\right)}{S_k^{*}}---\left(4\right)$

In formula (4), Z _lfor unit WT _lits active-power P in the branch road of place _wflow out the line impedance of branch road; be i-th unit WT _ithe conjugate of applied power; N is unit WT _ithe number of units of the unit on a feeder line at place.

7. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, is characterized in that in step 7 set end Voltage Drop critical value U ₀correction carry out according to the following procedure:

(a), by the circuit virtual impedance Z of unit _eq-kseries connection access unit Infinite bus power system between the machine end transformer of pessimistic concurrency control and middle pressure bus;

B the operate power factor of (), setting unit is identical with the operate power factor set in step 3, and set unit active-power P _wwith unit active-power P in step 3 _wkeep identical, adjustment line voltage makes terminal voltage U during unit steady-state operation _s0u identical with the terminal voltage that step 4 collects _s0;

Grid side generation three phase short circuit fault when (c), setting 0.1s, Failure elimination after 150ms;

(d), after three phase short circuit fault occurs, during 1ms, if the crow bar protection of unit is not operating, then progressively reduce short circuit grounding impedance Z _f, until crow bar protects lucky action; If crow bar protection act, then progressively increase short circuit grounding impedance Z _f, until crow bar protection is failure to actuate just;

E (), record crow bar are protected by not operating to the lucky action moment, or crow bar protection falls value U by action to the terminal voltage of moment unit of being just failure to actuate _sk, be unit active-power P _wwith steady-state operation terminal voltage U _s0correction rear end Voltage Drop critical value U ' corresponding under combined situation ₀.

8. the double-fed fan motor station equivalent modeling method taking into account crow bar protection according to claim 1, is characterized in that each equivalent parameters that described step 9 medium value unit comprises: applied power S _eq, generator impedance Z _{g_eq}, inertia time constant H _eq, axis rigidity COEFFICIENT K _eq, axle system ratio of damping D _eq, and each equivalent parameters that equivalent machine end transformer comprises: applied power S _{t_eq}, impedance Z _{t_eq}calculate by formula (5) and obtain:

$\left\{\begin{array}{c}{S}_{\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{S}_i,Z_{G\_\mathrm{eq}}=\frac{Z_{\mathrm{Gi}}}{m},H_{\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{H}_i\\ K_{\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{K}_i,D_{\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{D}_i\\ S_{T\_\mathrm{eq}}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{S}_{\mathrm{Ti}},Z_{T\_\mathrm{eq}}=\frac{Z_{\mathrm{Ti}}}{m}\end{array}\right.---\left(5\right)$

In formula (5), S _i, Z _gi, H _i, K _iand D _irepresent the applied power of i-th unit, generator impedance, inertia time constant, axis rigidity coefficient and axle system ratio of damping respectively; S _ti, Z _tibe rated capacity and the impedance of the machine end transformer of i-th unit; M is the number of units of unit in a corresponding group of planes;

The impedance Z of equivalent circuit _l-eqcalculate by formula (6) and obtain:

$Z_{l-\mathrm{eq}}=\frac{\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{Z}_{l-i}{S}_i^{*}{S}_i}{\left(\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{S}_i\right)\left(\underset{i=1}{\overset{m}{\mathrm{\Σ}}}{S}_i^{*}\right)}---\left(6\right)$

In formula (6), Z _l-ibe i-th unit WT _iits active-power P in the branch road of place _wflow out the line impedance on direction.