CN104319817B - A kind of analytical method for wind energy turbine set and electric iron reciprocal effect - Google Patents
A kind of analytical method for wind energy turbine set and electric iron reciprocal effect Download PDFInfo
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Abstract
The invention discloses a kind of analytical method for wind energy turbine set and electric iron reciprocal effect, it is according to electric railway load character, sets up the mathematics mechanism model containing high ferro and general iron, multiple stage blower fan is equivalent to a certain equivalent parameters
separate unit blower fan set up windfarm system Equivalent Model; Set up unbalanced source voltage that electrified railway traction load causes to running of wind generating set characteristic mathematical analysis model; Set up the mathematic simulated mode that Voltage Drop that electrified railway traction load causes affects Wind turbines, utilize electric locomotive model, the windfarm system Equivalent Model that integrating step 1 is set up, analyzing wind farm wind velocity change affects electrified railway traction load; The unbalanced source voltage that electrified railway traction load causes is analyzed Wind turbines impact the Voltage Drop that running of wind generating set impact, electrified railway traction load cause; Solve imbalance of three-phase voltage and Voltage Drop may cause Wind turbines unstability, have a strong impact on the problem such as safe and stable operation and electrified railway power supply reliability of electrical network.
Description
Technical Field
The invention belongs to the technical field of power grid planning and design, and particularly relates to an analysis method for interaction influence of a wind power plant and a power grid.
Background
Because wind energy has the characteristics of random fluctuation and intermittence, with the large-scale development of wind power generation, wind power brings huge challenges to power grid planning, operation, control and the like, and research and solution of related problems of wind power become new hotspots in the domestic and foreign power industries. The double-fed induction generator is most widely applied to all wind turbine generator types, and mainly has the advantages that flexible alternating current excitation speed regulation is adopted, the rotating speed response is quick along with the change of the outside, the change range is wide, and the change of the outside wind speed can be quickly tracked, so that the optimal operating rotating speed is obtained, and the extremely high wind energy capturing efficiency is obtained. Meanwhile, the capacity of a converter of the double-fed induction generator is only about 30% of the rated capacity of the wind turbine generator, the power control capability of the double-fed induction generator is very flexible, and the cost is low.
After the large-scale nonlinear high-speed rail load is connected into a power grid, the impact of power generated by the power grid, voltage fluctuation and flicker, three-phase asymmetry of the power grid and harmonic waves are mainly influenced. The asymmetry of the high-speed rail load can increase the three-phase imbalance of the system; the generated reactive power impact can cause voltage fluctuation and flicker of the power grid; the generated active power impact can affect the frequency change of the system and change the rotating speed of the rotor of the generator; the generated harmonic waves can generate certain influence on electrical equipment (a generator, a transformer, a capacitor bank and the like) in the power grid, so that the difficulty of operation and control of the power grid is increased, the power quality of the power grid is seriously deteriorated, the safe and stable operation of power grid electrical equipment is reduced, and the power quality of local residents is influenced.
With the increase of the common grid-connected operation conditions of the electrified gasification railway and the wind power plant in recent years, the unbalanced three-phase voltage and the voltage drop generated by the traction load of the electrified railway provide a severe test for the stable operation of the wind turbine generator, and even the instability of the wind turbine generator can be caused, so that the safe and stable operation of a power grid is seriously influenced. When the electrified railway is accessed into the system, the generated voltage unbalance of the power grid can lead the voltage at the end of the wind power station to introduce negative sequence voltage, so that the constraint condition of normal work of the control system is broken, and the operation of the wind turbine generator is adversely affected; the caused voltage drop can cause the voltage at the stator terminal of the double-fed wind generating set to drop rapidly, thereby causing a violent electromagnetic transient process in the generator. The wind power plant is influenced by the fluctuation of the wind speed, the output force also shows fluctuation, and the voltage and current fluctuation of the traction load high-voltage bus of the electrified railway connected into the power grid can be caused, so that the power supply reliability of the electrified railway is influenced.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: the method is used for solving the problems that the instability of a wind turbine generator set is possibly caused by three-phase voltage unbalance and voltage drop generated by traction load of an electrified railway, the safe and stable operation of a power grid is seriously influenced, the power supply reliability of the electrified railway is influenced and the like in the common grid-connected operation of the electrified railway and the wind power field in the prior art.
The technical scheme of the invention is as follows:
an analysis method for interaction influence of a wind power plant and a power station comprises the following steps:
step 1, establishing a mathematical mechanism model containing high-speed rails and ordinary rails according to the load characteristics of the electrified railway, and equating a plurality of fans to be a certain equivalent parameter according to a mathematical formula of a typical double-fed wind driven generatorThe equivalent model of the wind power plant system is established as follows:
in the formula:、、the capacity, the wind sweeping area and the wind energy utilization coefficient of the ith fan in the wind power plant are respectively;、 、respectively equal wind power plant fan capacity, wind sweeping area and wind energy utilization coefficient;
introducing a weighting coefficient into an equivalent parameter X' of the wind turbine generator，
Equivalent of wind power plant to a certain equivalent parameter of single wind turbineAccording to the formulaIt is obtained that,is the ith fan equivalent parameter;
step 2, according to the equivalent model of the wind power plant system established in the step 1, establishing a mathematical analysis model of the power grid voltage unbalance caused by the electric railway load on the operating characteristics of the wind turbine generator:
in the formulaThe coordinate transformation matrix is rotated synchronously for positive sequence,for instantaneous voltage of electric networkThe voltage value converted to the dq synchronous rotation coordinate system,is a two-phase stationary coordinate transformation matrix,is a voltage of the direct-current bus,is a DC capacitor current, p is a positive sequence component, n is a negative sequence component,、respectively converting the positive sequence voltage components of a d axis and a q axis into a dq synchronous rotation coordinate system;、respectively converting the negative sequence voltage components of a d axis and a q axis into a dq synchronous rotating coordinate system;、respectively converting the positive sequence current components of the d axis and the q axis into a dq synchronous rotating coordinate system;、respectively converting the current components into d-axis and q-axis negative sequence current components of a dq synchronous rotating coordinate system;
step 3, according to the equivalent model of the wind power plant system established in the step 1, establishing a mathematical simulation model of the influence of voltage drop caused by the electric railway load on the wind turbine generator, wherein the model comprises the following parts:
an electromagnetic torque and stator flux linkage analysis model of the generator is as follows:
wherein,is the pole pair number of the double-fed motor,the magnetic flux linkage of the stator is provided,for the rotor q-axis current to be,andrespectively excitation and stator inductances
The generator stator outputs an active power and reactive power analysis model:
wherein,in order to be an electromagnetic torque,is the voltage of the stator and is,for rotating electrical angular velocity of stator
Generator rotor motion analysis model:
wherein,in order to be a mechanical torque, the torque,representing the rotor rotational electrical angular velocity;
step 4, analyzing the influence of wind power plant wind speed change on the electric railway load by using an electric locomotive model and combining the wind power plant system equivalent model established in the step 1;
and 5, analyzing the influence of the unbalance of the grid voltage caused by the electric iron load on the operation of the wind turbine generator and the influence of the voltage drop caused by the electric iron load on the wind turbine generator by using the model established in the step 1-3.
The wind power plant system equivalent model in the step 1 further comprises: equivalent impedance parameter of wind power plant
，
，、、Wherein the stator impedance, the rotor impedance and the excitation impedance are respectively,、、respectively the stator impedance, the rotor impedance and the excitation impedance of the equivalent model,、、respectively the stator impedance, the rotor impedance and the excitation impedance of the ith fan,is the equivalent impedance of the fan.
And 4, analyzing the influence of wind speed change of the wind power plant on the electric railway load, wherein the analysis method comprises the following steps: analyzing the influence of wind speed change and normal operation of a power railway load on a wind power plant; and analyzing the influence of wind speed change, half of wind power plant output and normal operation of a power-railway load on the wind speed of the wind power plant.
The invention has the beneficial effects that:
the method can be used for quantitatively and qualitatively analyzing the mutual influence of wind power and an electrified railway, and can better generalize the influence of three-phase imbalance and voltage drop caused by electric iron load on a stator and a rotor of a double-fed fan and a current converter and the influence of the output power change of the fan on the power supply reliability of the electric iron by establishing a mechanism model of the mutual influence of the wind power and the electrified railway so as to better cope with the future coordinated development of the wind power and the electrified railway, and has the following main innovation points:
(1) from the basic principle of operation of a double-fed wind power generation system, equivalence is carried out on a large wind power plant, and an equivalent simulation mathematical model of the wind power plant system is established;
(2) an analysis model for the influence of the power grid voltage unbalance caused by the electric iron load on the output of the double-fed motor is established, and the influence degree of the unbalance caused by the electric iron on the fan is qualitatively and quantitatively researched;
(3) a mathematical analysis model of the change condition of each quantity in the double-fed motor when the voltage drop occurs at the motor end is established, and the change condition of each quantity of the double-fed motor when the voltage drop occurs at the double-fed motor is researched;
(4) an analysis method for the influence of a wind power plant as a fluctuating power supply on the power quality and the power supply reliability of the power supply of the traction load of the electric railway in the power grid is established;
the invention analyzes the influence of the negative sequence component generated by the traction load of the electrified railway and the generated voltage drop on the operating characteristics of the double-fed wind generating set and the output characteristics of the wind power plant, researches the influence of the wind speed change and the wind power plant output power change of the wind power plant on the traction load power supply performance of the electrified railway, and solves the problems that the three-phase voltage unbalance and the voltage drop generated by the traction load of the electrified railway in the common grid-connected operation of the electrified railway and the wind power plant in the prior art can cause the instability of the wind generating set, seriously influence the safe and stable operation of a power grid, influence the power supply reliability of the electrified railway and the like.
Description of the drawings:
FIG. 1 is a schematic diagram of a regional power grid architecture;
FIG. 2 is a diagram of DC voltage spectrum;
FIG. 3 is a graph of the AC side voltage spectrum;
FIG. 4 shows the active power and the reactive power output by the wind turbine;
FIG. 5 is a graph of effective values (taking phase A as an example) of three-phase fundamental voltage of a 110kV bus when a wind power plant is connected to the grid;
FIG. 6 is a graph of the effective value (taking phase A as an example) of three-phase fundamental current of a 110kV bus when a wind power plant is not connected to the grid;
FIG. 7 is a graph of effective values (taking phase A as an example) of three-phase fundamental voltage of a bus with half of 110kV output by grid connection of a wind power plant;
fig. 8 is a graph of three-phase fundamental voltage effective values (taking phase a as an example) of a general 110kV bus output when the wind power plant is not connected to the grid.
Detailed Description
An analysis method for interaction influence of a wind power plant and a power station comprises the following steps:
step 1, establishing a mathematical mechanism model containing high-speed rails and ordinary rails according to the load operation characteristics of the electrified railway, and equating a plurality of fans to be a certain equivalent parameter according to a unit mathematical formula of a typical double-fed wind driven generatorThe equivalent model of the wind power plant system is established as follows:
in the formula:、、the capacity, the wind sweeping area and the wind energy utilization coefficient of the ith fan in the wind power plant are respectively, and n is the total number of the fans.
Equivalent parameter of wind turbine generatorIntroduction of weighting coefficients，
Equivalent of wind power plant to a certain equivalent parameter of single wind turbineAccording to the formulaObtaining;、 、respectively equal wind power plant fan capacity, wind sweeping area and wind energy utilization coefficientIs the ith fan equivalent parameter.
The wind power plant system equivalent model in the step 1 further comprises: equivalent impedance parameter of wind power plant
，
，、、Wherein the stator impedance, the rotor impedance and the excitation impedance are respectively,、、respectively the stator impedance, the rotor impedance and the excitation impedance of the equivalent model;is the equivalent impedance of the fan,、、the stator impedance, the rotor impedance and the excitation impedance of the ith fan are respectively.
Step 2, according to the equivalent model of the wind power plant system established in the step 1, establishing a mathematical analysis model of the power grid voltage unbalance caused by the electric railway load on the operating characteristics of the wind turbine generator:
in the formulaThe coordinate transformation matrix is rotated synchronously for positive sequence,for instantaneous voltage of electric networkThe voltage value converted to the dq synchronous rotation coordinate system,is a two-phase stationary coordinate transformation matrix,is a voltage of the direct-current bus,is a direct current capacitance current, p is a positive sequence component, and n is a negative sequence component;is a d-axis negative-sequence current component,is a q-axis positive sequence current component,、respectively converting the positive sequence voltage components of a d axis and a q axis into a dq synchronous rotation coordinate system;、respectively converting the negative sequence voltage components of a d axis and a q axis into a dq synchronous rotating coordinate system;、respectively converting the positive sequence current components of the d axis and the q axis into a dq synchronous rotating coordinate system;、respectively converting the current components into d-axis and q-axis negative sequence current components of a dq synchronous rotating coordinate system;
in step 2, the mathematical analysis model of the operating characteristics of the wind turbine generator by the unbalanced grid voltage caused by the electric railway load further includes:
、respectively, disturbances of the negative sequence voltage to the electromagnetic torque and reactive power.
The following further detailed description is carried out on a mathematical analysis model of the operating characteristics of the wind turbine generator by the power grid voltage imbalance caused by the electric railway load: because the electric iron is not a three-phase symmetrical load, no matter what wiring mode is adopted by the traction transformer, a larger negative sequence current is injected into the system, and therefore the three-phase voltage of the system is unbalanced.
When the electric iron operates in an asymmetric mode, the stator voltage of the doubly-fed fan contains a negative sequence component, and the negative sequence component can generate high slip, so that the overvoltage and overcurrent of the rotor are more serious. The rapid increase in rotor side current causes the dc side voltage of the rotor exciter converter to rise and the current, active and reactive power of the generator exciter converter oscillate. If the power of the wind turbine is large enough relative to the grid, a wind turbine lacking unbalanced voltage control capability will have to be disconnected from the grid. The unbalance degree caused by the power grid side electric iron can have serious influence on the wind power plant.
The degree of unbalance can be expressed as:
（3）
in the formula (3), the reaction mixture is,is the positive sequence fundamental component square mean root value of the three-phase voltage;is the root mean square value of the negative sequence fundamental component of the three-phase voltage;is the root mean square value of the zero sequence fundamental component of the three-phase voltage.
Because the zero sequence voltage can be eliminated in a transformer wiring mode, when the influence of the unbalanced power grid voltage on the operation of the wind turbine generator is analyzed, the fact that the power grid voltage contains a positive sequence component and a negative sequence component and does not contain a zero sequence component can be only considered. The grid voltage may be expressed as follows:
（4）
in the formula (4), the reaction mixture is,is the voltage of the power grid,andin order to respectively represent the positive sequence fundamental component and the negative sequence fundamental component of the grid voltage, superscripts p and n respectively represent the positive sequence quantity and the negative sequence quantity, which are the same as the following.
Instantaneous voltage of power gridTransformation to dq synchronous rotating coordinate system can be obtained
（5）
In the formula (5), the reaction mixture is,a two-phase stationary coordinate transformation matrix;、respectively positive sequence synchronous rotation coordinate transformation matrix and negative sequence synchronous rotation coordinate transformation matrix.
When the power grid contains negative sequence voltage, the alternating-current side voltage of the power grid side frequency converterAlso contains a negative sequence voltage component:
（6）
at this time, the current of the AC side of the grid side frequency converterAlso contains positive and negative sequence components:
（7）
if the loss is not counted, the transmission power of the DC side and the AC side of the frequency converter on the network side is equal, namely
（8）
In the formula (7), the reaction mixture is,is a voltage of the direct-current bus,is a dc capacitive current.
The current of the direct current capacitor of the network side frequency converter can be obtained by converting the formula (7):
（9）
the formula (9) is developed, and only the output current of the DC side is consideredThe DC component in the DC side current is known as
（10）
The secondary ripple component in the dc side current is:
（11）
considering only the case where the grid voltage contains a negative-sequence fundamental voltage, the dc-side current of the grid-side frequency converter will have a secondary ripple component.
In addition, the analysis only considers the condition that the grid voltage contains the negative-sequence fundamental wave voltage, and does not consider the influence of the current generated by the rotor-side frequency converter on the direct-current capacitor voltage. The rotor side frequency converter is regarded as a load of a direct current capacitor, and the following can be obtained:
（12）
theoretical load currentIs an arbitrary current waveform, so that the second ripple component generated by the network-side frequency converter derived in the foregoing can be considered asIs irrelevant only toIt is related. Therefore, the negative sequence voltage of the power grid can cause the direct current bus of the grid-side frequency converter to have a secondary ripple component.
Let the switching function of the a-phase PWM be:
（13）
by the combined action of the 2-time ripple waves of the voltage at the direct current side of the frequency converter and the positive sequence switching value, the harmonic voltage at the alternating current side of the frequency converter at the network side can be obtained as follows:
（14）
in the formula (14), the compound represented by the formula (I),the amplitude of the direct current voltage ripple is 2 times;the amplitude of the fundamental wave of the positive sequence switching value;is the initial phase angle of 3 harmonic voltage.
From equation (14), it can be found that the 2 nd order ripple component on the dc side of the grid-side inverter will cause the 3 rd order harmonic voltage on the ac side of the grid-side inverter.
Through further calculation, the interaction influence of the alternating current and direct current sides of the network side frequency converter can be deduced, so that the voltage of the direct current side generates even-order ripples, and the alternating current side generates odd-order harmonics.
Step 3, according to the equivalent model of the wind power plant system established in the step 1, establishing a mathematical simulation model of the influence of voltage drop caused by the electric railway load on the wind turbine generator, wherein the model comprises the following parts:
an electromagnetic torque and stator flux linkage analysis model of the generator is as follows:
wherein,is the pole pair number of the double-fed motor,the magnetic flux linkage of the stator is provided,for the rotor q-axis current to be,andrespectively excitation and stator inductances
The generator stator outputs an active power and reactive power analysis model:
wherein,in order to be an electromagnetic torque,is the voltage of the stator and is,for rotating electrical angular velocity of stator
Generator rotor motion analysis model:
wherein,in order to be a mechanical torque, the torque,representing the rotor rotational electrical angular velocity;
the following further detailed description is made on a mathematical simulation model of the influence of voltage drop caused by the electric railway load on the wind turbine generator:
the electrified railway is a typical impact load due to more working conditions, and can cause grid voltage drop. The stator end of the doubly-fed wind generator set is directly connected with a power grid, so that a violent electromagnetic transient process inside the generator can be caused.
The research on the influence of voltage drop on the doubly-fed wind turbine is generally divided into 2 stages: the first stage is a stage of transition from a normal operation state to a voltage drop of the doubly-fed fan, and the second stage is a stage of normal operation after transition from the voltage drop to voltage recovery of the doubly-fed fan.
During voltage sag
The three-phase grounding fault of the power grid causes the voltage of the stator terminal of the double-fed fan to suddenly drop, and the voltage of the generator terminal symmetrically drops in three phases. The voltage drop at the generator end will result in a reduction of the stator flux linkage and thus a corresponding reduction of the electromagnetic torque of the generator.
The three-phase ground fault of the power grid causes the voltage drop of the stator end of the double-fed motor, the voltage of the machine end is three-phase symmetrical, the stator flux linkage quickly reaches a stable state, the rotating speed of the stator magnetic field can be considered to be unchanged during the period, and then the following steps are performed:
(15)
because the doubly-fed motor adopts the stator voltage directional vector control technology, as can be seen from the formula (15), when the stator magnetic field rotating speedInvariable stator flux linkageVoltage following statorIn direct proportion, when the voltage drop of the stator voltage is greatly reduced due to the grid fault, the stator flux linkage is correspondingly reduced almost in proportion.
The electromagnetic torque of the generator is related to the stator flux linkage as follows,
(16)
the drop in terminal voltage results in a proportional reduction in stator flux linkage and a corresponding reduction in generator electromagnetic torque.
During the voltage drop, the change of the wind speed can be considered to be slow relative to the change of the electromagnetic quantity inside the doubly-fed motor, so that the wind speed can be considered to be unchanged when the transient change process of the doubly-fed motor during the voltage drop is analyzed, namely, the mechanical power input by the wind turbine to the generator is unchanged. When the mechanical torque of the doubly-fed motor is not changed, the equation of motion of the rotor of the doubly-fed motor is as follows,
(17)
from the formula (17), the mechanical torqueConstant electromagnetic torqueThe reduction may result in generator speedRises rapidly. Through the connection of a PI control link, the increase of the rotor rotating speed can cause the reference current of the rotor q axisIncrease, and rotor q-axis currentWill also follow the q-axis reference currentIs increased. Meanwhile, it can be seen from equation (18) that the electromagnetic torque of the generatorWill follow the rotor q-axis currentIs increased by an increase in electromagnetic torqueIncrease the rotation speed of the generatorThereby making the rotational speed higherFinally trend towards the reference valueThereby achieving the stability.
When the rotor rotatesWhen the voltage drops and reaches the steady state, the rotating speed can keep the reference rotationSpeed measuring deviceThe method has the advantages of no change, in some cases,
(18)
coupled (17), the electromagnetic torque of the generator should be equal to the mechanical torque during steady state of voltage sag. When the electromagnetic torque is not changed, the d-axis current of the rotor at the steady state is shown by the equation (18)Should be increased accordingly. Because of the q-axis current of the generator rotorControlling reactive power, and keeping the output power factor of the generator constant, i.e. keeping the output reactive power constant, so that the rotor q-axis current is in the period from normal operation to fault dropShould remain substantially unchanged.
The stator of the generator outputs active power and reactive power as follows,
(19)
from the equation (19), it can be seen that when the terminal voltage drops, the terminal voltage is generated due to the electromagnetic torqueThe active power output by the stator side of the generator is reduced under the condition that the rotating speed of the stator magnetic field is not changed; terminal voltage due to voltage dropThe reactive power output by the stator side of the generator is reduced correspondingly.
Because the voltage of the power grid maintains the voltage of the direct current capacitor to be constant, when the voltage of the machine terminal suddenly drops, the voltage of the direct current side capacitor can be reduced; during the steady state of voltage drop, the voltage of the direct-current side bus is restored to be close to a reference value through the adjustment of the PI control link.
After voltage recovery
The method for analyzing the transition of the generator from the voltage drop stage to the normal operation stage after fault clearing is similar to the method for analyzing the voltage drop period at the generator terminal. After the terminal voltage is recovered, the stator flux linkage of the generatorWill follow the terminal voltageIs recovered to the value before the voltage drop and the electromagnetic torque of the generatorBut also increases with increasing stator flux linkage. As can be seen from the operating equation of the generator rotor, an increase in electromagnetic torque will result in a decrease in the rotational speed of the generator. Rotor speedReducing, rotor d-axis reference currentIt is also possible to reduce the number of,can directly influence the change of the electromagnetic torque, thereby leading the rotating speedAnd electromagnetic torque direction reference valueAnd (6) approaching.
After the transient change process after the voltage recovery, each quantity of the generator reaches a new steady state value again, and the electromagnetic torque of the generatorBack to the magnitude before the voltage sag. Generator rotor q-axis reference currentThe reactive power of the generator is controlled through a PI control link, so that the reactive power is basically kept unchanged.
Stator side output active power of generatorThe electromagnetic torque is increased firstly and then returns to a stable value; reactive power output from the stator sideBut also recovers to near steady-state values after increasing with recovery of the termination voltage.
The DC bus voltage is increased in the transient state process of the recovery of the terminal voltage, and then is regulated to be near a reference value through a PI control link when the DC bus voltage is recovered to a steady state.
And 4, analyzing the influence of wind power plant wind speed change on the electric railway load by using the electric locomotive model and combining the wind power plant system equivalent model established in the step 1.
And 4, analyzing the influence of wind speed change of the wind power plant on the electric railway load, wherein the analysis method comprises the following steps: analyzing the influence of wind speed change and normal operation of a power railway load on a wind power plant; and analyzing the influence of wind speed change, half of wind power plant output and normal operation of a power-railway load on the wind speed of the wind power plant.
Under the condition that the external wind speed is constantly changed, the output power of the wind power plant is fluctuated due to wind speed disturbance, so that the tidal current in a power grid is changed, and the fluctuation of the voltage of each node is caused. The fluctuation of the voltage of the power grid can directly influence the running state of the electric locomotive, so that the power electronic devices of the locomotive are frequently impacted, the service life of the locomotive is shortened, the negative sequence current and harmonic waves injected into the power grid by the electric locomotive are increased, and the power supply reliability of the electrified railway is influenced.
In order to research the influence of wind speed change and output change of a wind power plant on the reliability of power supply of a power railway load, the method analyzes from two aspects: firstly, the wind power plant runs normally under the conditions of wind speed change and electric railway load; and secondly, the wind speed of the wind power plant is influenced by half of the wind speed change and the wind power plant output, and the electric railway load normally operates, so that the result of the influence of the wind speed change of the wind power plant on the electric railway load is finally obtained.
And 5, analyzing the influence of the unbalance of the grid voltage caused by the electric iron load on the operation of the wind turbine generator and the influence of the voltage drop caused by the electric iron load on the wind turbine generator by using the model established in the step 1-3.
The invention is further illustrated by the following specific examples: the invention takes a certain area in Hubei as an example for simulation analysis, the area has rich wind resources, the wind power is nearly 300MW and is formed by 183 double-fed wind generating sets of 1.5MW, the outlet ends of all the wind generating sets are connected to the same bus bar, and the wind generating sets are connected to a power grid through a voltage boosting transformer of 0.69/35 kV. The 110kV transformer substation bus is connected with a 35kV bus of a step-up transformer through 121/35kV step-down transformer. Two railway lines pass through the area, and the phenomenon that a wind power plant and a railway traction station are connected to the same public connection point exists. The influence of the regional electric railway load on the wind power plant is simulated based on PSASP software. The monitoring value of the area on the electric energy quality of the electric railway load is shown in a table 1, and the equivalent diagram of the area power grid structure is shown in a figure 1.
(1) Three-phase imbalance simulation
The grid voltage is set to only contain positive sequence fundamental voltage and negative sequence fundamental voltage, harmonic analysis is carried out on the direct-current voltage, and a frequency spectrum diagram of the harmonic analysis is shown in fig. 2.
As can be seen from fig. 2, the dc voltage fluctuates periodically with a period of 0.01 s. The result of the FFT harmonic analysis of the direct current side voltage can obtain that the direct current bus voltage contains even harmonics of 100Hz, 200Hz, 300Hz and the like, the 100Hz harmonic is particularly obvious, and the amplitude basically reaches 1/6 of the amplitude of the direct current voltage. The frequency spectrum analysis result verifies that even-order ripple components are generated by the direct-current side capacitor voltage of the grid side frequency converter under the condition of unbalanced grid voltage.
The frequency spectrum of the ac side voltage (for example, phase a) of the grid side inverter is analyzed, and the result is shown in fig. 3.
From the voltage spectrum analysis result of the alternating-current side of fig. 3, it can be seen that the a-phase voltage contains odd-numbered harmonic voltages such as 150Hz, 250Hz, 350Hz, and the like, and the 3 rd harmonic and 5 th harmonic contents are very large, and the simulation result verifies that the theoretically derived alternating-current side voltage of the grid-side frequency converter can generate odd-numbered harmonics under the condition that the negative-sequence voltage exists in the grid voltage.
(2) Voltage sag simulation
And (4) performing simulation to set the voltage drop at the node 3 to be 40%, wherein the duration time is 1s, and performing simulation analysis on the transient characteristic of the doubly-fed fan when the voltage drop occurs at the stator terminal voltage of the doubly-fed fan.
The outlet of a single 1.5MW doubly-fed fan is connected with a power grid through 0.69/35 step-up transformer, the voltage of a 35kV bus falls to 40% in 8.5s and lasts for 1s, the voltage drop is eliminated in 9.5s, and the voltage of the bus is recovered to the initial value. Simulation setting: simulation (Emulation)Time 12s, simulation step size 50。
The active power and the reactive power output by the wind turbine generator are shown in fig. 4.
In fig. 4, during the voltage drop, the active power output by the wind turbine generator is obviously reduced, and the active power reduction is basically positively correlated with the voltage drop amplitude. The reactive power output by the wind turbine generator set only changes greatly at the moment of voltage drop and recovery, and particularly changes from 0.35MVar to-0.6 MVar at the moment of voltage recovery, but can be quickly recovered to about 0.4MVar after the voltage recovery. However, during the voltage drop, the reactive output is basically maintained at about 0.3MVar and remains unchanged.
(3) Influence of wind farm on electric railway load
Wind power plant normally runs under wind speed change and electric railway load
The change of wind speed of a wind power plant is set in a simulation mode, the wind speed is changed from 5m/s to 25m/s, and both arms of the electric railway load are effective currents. The simulation graphs of the three-phase fundamental voltage and current effective values of the high-voltage bus of the electric railway load are shown as follows.
Fig. 5 and 6 are the effective value of the 110kV bus three-phase fundamental voltage and the effective value of the 110kV bus three-phase fundamental current respectively when the wind farm is connected to the grid and when the wind farm is not connected to the grid. It can be seen from the comparison between fig. 5 and fig. 6 that after the wind speed of the wind farm changes from 5m/s to 25m/s, the fluctuation of the three-phase fundamental voltage and the effective current value of the 110kV bus at the high-voltage side of the electric railway load is intensified, the voltage drop amplitude is increased, the maximum phase current value is increased, and the power quality of the grid-connected voltage is worse. The main reason is that the output power fluctuation is enhanced due to the severe change of the wind speed of the wind power plant, so that the reliability of the traction load power supply of the electrified railway is weakened.
When wind speed of the wind power plant is changed by wind speed and half of the output of the wind power plant and the electric iron load is in normal operation
The change of wind speed of a wind power plant is set in a simulation mode, the wind speed is changed from 5m/s to 25m/s, the output of the wind power plant is 24MW, and both arms of the electric railway load are effective current. The simulation graphs of the three-phase fundamental voltage and current effective values of the iron load high-voltage bus are shown as follows.
As can be seen from comparison between fig. 5 and 6, and between fig. 7 and 8, when the wind speed of the wind farm is not changed but the wind farm output is nearly half, the effective value fluctuation of the three-phase fundamental wave voltage of the 110kV bus at the high-voltage side of the electric railway load is enhanced, the voltage drop amplitude is also reduced, but the power quality of the grid-connected voltage is still deviated. Although the voltage drop of the grid-connected bus of the electric railway load is weakened due to the reduction of the output power, the output power of the wind power plant is changed due to the drastic change of the wind speed of the wind power plant, so that the voltage fluctuation of the grid-connected bus of the electric railway load is enhanced, and the power supply quality and the power supply reliability of the traction load of the electrified railway are also reduced.
Claims (3)
1. An analysis method for interaction influence of a wind power plant and a power station comprises the following steps:
step 1, establishing a mathematical mechanism model containing high-speed rails and ordinary rails according to the load characteristics of the electrified railway, and equating a plurality of fans to be a certain equivalent parameter according to a mathematical formula of a typical double-fed wind driven generatorThe equivalent model of the wind power plant system is established as follows:
in the formula:、、the capacity, the wind sweeping area and the wind energy utilization coefficient of the ith fan in the wind power plant are respectively;、 、respectively equal wind power plant fan capacity, wind sweeping area and wind energy utilization coefficient;
introducing a weighting coefficient into an equivalent parameter X' of the wind turbine generator，
Equivalent of wind power plant to a certain equivalent parameter of single wind turbineAccording to the formulaIt is obtained that,is the ith fan equivalent parameter;
step 2, according to the equivalent model of the wind power plant system established in the step 1, establishing a mathematical analysis model of the power grid voltage unbalance caused by the electric railway load on the operating characteristics of the wind turbine generator:
in the formulaThe coordinate transformation matrix is rotated synchronously for positive sequence,for instantaneous voltage of electric networkThe voltage value converted to the dq synchronous rotation coordinate system,is a two-phase stationary coordinate transformation matrix,is a voltage of the direct-current bus,is a DC capacitor current, p is a positive sequence component, n is a negative sequence component,、respectively converting the positive sequence voltage components of a d axis and a q axis into a dq synchronous rotation coordinate system;、respectively converting the negative sequence voltage components of a d axis and a q axis into a dq synchronous rotating coordinate system;、respectively converting the positive sequence current components of the d axis and the q axis into a dq synchronous rotating coordinate system;、respectively converting the current components into d-axis and q-axis negative sequence current components of a dq synchronous rotating coordinate system;
step 3, according to the equivalent model of the wind power plant system established in the step 1, establishing a mathematical simulation model of the influence of voltage drop caused by the electric railway load on the wind turbine generator, wherein the model comprises the following parts:
an electromagnetic torque and stator flux linkage analysis model of the generator is as follows:
wherein,is the pole pair number of the double-fed motor,the magnetic flux linkage of the stator is provided,for the rotor q-axis current to be,andrespectively excitation and stator inductances
The generator stator outputs an active power and reactive power analysis model:
wherein,in order to be an electromagnetic torque,is the voltage of the stator and is,for rotating electrical angular velocity of stator
Generator rotor motion analysis model:
wherein,in order to be a mechanical torque, the torque,representing the rotor rotational electrical angular velocity;
step 4, analyzing the influence of wind power plant wind speed change on the electric railway load by using an electric locomotive model and combining the wind power plant system equivalent model established in the step 1;
and 5, analyzing the influence of the unbalance of the grid voltage caused by the electric iron load on the operation of the wind turbine generator and the influence of the voltage drop caused by the electric iron load on the wind turbine generator by using the model established in the step 1-3.
2. The analysis method for wind power plant and electric railway interaction influence according to claim 1, characterized in that: the wind power plant system equivalent model in the step 1 further comprises: equivalent impedance parameter of wind power plant
，
，、、Wherein the stator impedance, the rotor impedance and the excitation impedance are respectively,、、respectively the stator impedance, the rotor impedance and the excitation impedance of the equivalent model,、、respectively the stator impedance, the rotor impedance and the excitation impedance of the ith fan,is the equivalent impedance of the fan.
3. The analysis method for wind power plant and electric railway interaction influence according to claim 1, characterized in that: and 4, analyzing the influence of wind speed change of the wind power plant on the electric railway load, wherein the analysis method comprises the following steps: analyzing the influence of wind speed change and normal operation of a power railway load on a wind power plant; and analyzing the influence of wind speed change, half of wind power plant output and normal operation of a power-railway load on the wind speed of the wind power plant.
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