CN106786807B - A kind of wind power station active power control method based on Model Predictive Control - Google Patents
A kind of wind power station active power control method based on Model Predictive Control Download PDFInfo
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Abstract
The invention discloses a kind of wind power station active power control methods based on Model Predictive Control, the wind speed according to locating for Wind turbines classifies Wind turbines, and the local linearization state-space model of every class unit is established using equivalent modeling method and is based on this predictive controller that designs a model, consider the dynamic response characteristic of inhomogeneity unit, dispatching of power netwoks value is distributed into every class unit by certain priority, every obtained active reference value of class unit is revised by model predictive controller again, is revised value and is proportionately distributed to all units in such.The present invention considers the operation difference between unit using active power of wind power field control as target, and is based on Model Predictive Control, makes it quickly to track dispatching of power netwoks value.
Description
Technical Field
The invention belongs to the technical field of wind power plant active power control, and particularly relates to a wind power plant active power control method based on model predictive control.
Background
Wind power generation has been rapidly developed as the most important form of renewable energy utilization. The traditional wind power plant control mode is an autonomous active power control mode, and each fan in the wind power plant is allowed to generate electricity as much as possible according to the change of wind energy. With the gradual increase of the wind power penetration level, the fluctuation of the active power of the wind power plant caused by the uncertainty of the wind energy brings great challenges to the safe operation of the power grid. The realization of controllable operation of the wind power plant gradually becomes the development trend of grid-connected operation of a large wind power plant, and the key technology of the controllable operation of the wind power plant is active power control of the wind power plant.
The active power control of the wind power plant, namely the wind power plant can track the power grid regulation value as far as possible. In order to smooth the active output fluctuation of the wind power plant, a common method is to use a large energy storage device, but the equipment cost, the technical cost and the maintenance cost of the method are high. Another more economical method is a method of cooperative control of wind turbines. The method utilizes the collective effect of the wind power plant, distributes a power reference value to each fan through a control unit of a wind electric field layer, takes each wind turbine as an actuator, and the sum of the active output of each wind turbine is the total active power of the wind power plant.
Scholars at home and abroad develop a series of discussion on the active power cooperative control method of the wind turbine, and most commonly, a proportional-integral control mode is adopted according to the deviation between the power grid modulation value and the active output of the wind power plant measured by a common link point, and then an active reference value is distributed to each unit by using a proportional distribution mode. The wind power plant is a multivariable strong coupling system with constraint, so that the wind power plant is very suitable for being controlled by a model predictive control method. Recently, researchers propose that a model prediction control mode is applied to wind power plant control, and two schemes of centralized model prediction control and distributed model prediction control are provided. Because the wind power plant model is a multi-input multi-output system, the order is obviously increased along with the increase of the number of fans, and the calculation amount of the distributed model prediction scheme can be reduced compared with the centralized model prediction control scheme. Generally, the wind power plants are uniformly controlled by the researches at present, and the differences of different wind conditions and the like of different positions where the units are located are not considered. However, if the difference between the units is not considered, the power distribution is not proper, and the total active power tracking effect is not good. In addition, the current research neglects the response time of the unit, the active output of the unit can reach the reference value instantly, and the research focuses on the load control of the fan under the condition of power traceability. There has been little research aimed at quickly tracking grid dispatch.
Therefore, the active power control method has important significance for classifying the wind turbine generators under different wind conditions and reasonably distributing the active adjustment quantity based on the model prediction control mode, so that the wind power plant can quickly track the power grid dispatching command.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a wind power plant active power control method based on model predictive control, so that the wind power plant can quickly respond, unnecessary actions of a unit are avoided, and the tracking of a grid regulation value is realized.
In order to achieve the purpose, the active power control method of the wind power plant based on model predictive control is characterized by comprising the following steps of:
(1) according to the factory parameters of the fan, the cut-in wind speed vinTo rated wind speed vratedThen to cut-out wind speed voutClassifying the wind conditions of the wind turbine generator, and then scheduling the active power from the grid scheduling center according to the classification resultAnd the real-time active output of the wind power plant measured from the common link pointThe wind power plant level active reference value is distributed, so that each type of wind turbine generator is distributed to the active power reference valueWherein i is 1,2, …, n, n represents the total number of the wind turbine classification;
(2) carrying out equivalent modeling on each classified wind turbine generator according to classification, designing a model prediction controller of each wind turbine generator on the basis of the equivalent modeling, and finally, designing a model prediction controller of each wind turbine generatorController pair using model predictionThe power is corrected to obtain the active power value
(3) The active power value is calculatedDistributing the output power of a single wind turbine generator to a single wind turbine generator according to the output proportion of the single wind turbine generator in the wind turbine generator, and enabling each wind turbine generator to be distributed to an output power valuemiThe total number of the ith type wind turbines is represented;
(4) each wind turbine generator set outputs power values according to the distributionAnd outputting to finish active power control of the whole wind power plant.
In the step (1), each type of wind turbine generator is allocated to an active power reference valueThe method comprises the following specific steps:
(2.1) Power Pre-treatment
Calculating the active power output of each type of wind turbine generator
Wherein,m represents the output of the jth wind turbine generator in the ith wind turbine generatoriThe total number of the ith type wind turbines is represented;
calculating the active output of the whole wind power plant
Wherein,the active power output of the ith type of wind turbine generator is shown, and n represents the total number of the wind turbine generator categories;
calculating the to-be-regulated quantity delta P of the wind power plant:
wherein,is active dispatching power from a power grid dispatching center;
(2.2) distributing active power reference values of each type of wind turbine generator
(2.2.1) when Δ P > 0, it indicatesActive power reference value of each type of wind turbineThe distribution steps are as follows:
1) calculating the power per liter capacity of each type of wind turbine generator:
2) sequentially accumulating the power rise capacity of each type of wind turbine generator according to a preset regulation and control sequenceAnd then, the active reference value of each type of wind turbine generator is obtained by distribution according to the following formula
Wherein,the capacity of the ith type wind turbine generator for increasing the power is shown,the maximum value of the active output of the ith type wind turbine generator is represented, and t represents that the active output is sequentially accumulated to the t type wind turbine generator to meet the dispatching target;
(2.2.2) when Δ P < 0, it is indicatedActive power reference value of each type of wind turbineThe distribution steps are as follows:
1) calculating the power reduction capability of each type of wind turbine generator:
2) according to a preset regulation and control sequenceSequentially accumulating the power reduction capability of each type of wind turbine generatorAnd then, the active reference value of each type of wind turbine generator is obtained by distribution according to the following formula
Wherein,the capacity of the class i unit for reducing power is shown,and expressing the minimum value of the active output of the ith type unit.
Further, in the step (2), the method for performing equivalent modeling on each type of wind turbine generator according to the classification category includes:
(3.1) dividing the wind conditions of the wind turbine generator set in the step (1) into n types, wherein the low wind speed area generator set occupies k-1 type and is represented as T1,T2,…Tk-1(ii) a The units in the region close to the rated wind speed are in one category, denoted as Tk(ii) a The high wind speed area unit occupies n-k type and is represented as Tk+1,Tk+2,…Tn；
(3.2) equivalence is carried out on various wind turbine generators
(3.2.1) respectively equating various wind turbine generators on the premise of capacity equivalence;
1) equating the unit in the low wind speed area:
1.1) equivalent of wind speed
According to wind speed-power function meterCalculating the power of each wind turbine in the ith type of wind turbine: pij＝F(vij)
Calculating the equivalent active power of the ith wind turbine generator
Calculating equivalent wind speed of the ith wind turbine generator by adopting a back-stepping method
Wherein j represents the j th wind turbine generator in the ith wind turbine generator, miIndicates the total number of the i-th wind turbines, F (v)ij) As a function of wind speed-power, vijRepresenting the wind speed of a jth wind turbine generator in the ith type wind turbine generator;
1.2) torque equivalence
Wherein,the equivalent torque of the wind generation set of the ith class corresponds to the specific set j of the ith class*The torque of (d);
2) equating the unit close to the rated wind speed and the unit in the high wind speed area;
2.1), wind speed equivalent:
2.2), torque equivalence:
(3.3) establishing a state space model according to the equivalence
(3.3.1) mechanical torque of fanThe first order Taylor expansion approximation at a given stable operating point yields:
where δ represents the deviation of the variable from its stable operating point, ρ is the air density, R is the wind wheel radius, v is the wind speed, Cp(λ, β) is the power utilization coefficient, β is the pitch angle, λ is the tip speed ratio,ωtis the fan speed, TtCan be regarded as relating to the fan speed omegatAngle of pitch β and wind speed v, upper lineRepresenting its steady state operating point;
(3.3.2) establishing a state space model
y＝δPg＝Cx
Wherein,d＝δv
wherein, ω isgIs the motor speed, TgIs the electromagnetic torque, and the electromagnetic torque,the upper scale indicates the given value, KsAnd BsRespectively representing the equivalent elastic coefficient and the equivalent damping coefficient of the rotating shaft, JtAnd JgRespectively representing the rotational inertia of the fan and the motor, taugAnd τ represent the electromechanical time constant and pitch angle time constant, respectively, η is the motor efficiency.
Further, in the step (2), the design process of the model predictive controller is as follows:
(4.1) discretizing the state space model to obtain:
x(k+1)＝A′x(k)+Bu′u(k)+Bd′d(k)
y(k+1)＝C′x(k)
(4.2) designing and optimizing objective function and constraint condition
The optimization objective function is:
the constraint conditions are as follows:
wherein n isc,npRepresenting the control and prediction time domains, Q, respectivelyP，QR，QSThe weight coefficients are respectively represented by the weight coefficients,respectively represents the maximum values of the electromagnetic torque and the pitch angle of the i-th wind turbine generator, andrespectively representing the electromagnetic torque set value and the pitch angle set value of the ith type wind turbine generator, and knowing the sampling time and the change rate constraintThe multiplication of the two can be calculated The minimum value and the maximum value of the electromagnetic torque change rate of the ith type wind turbine generator and the minimum value and the maximum value of the pitch angle change rate are respectively represented.
The invention aims to realize the following steps:
the invention relates to a wind power plant active power control method based on model predictive control, which classifies wind turbines according to the wind speeds of the wind turbines, establishes a local linear state space model of each type of the wind turbines by adopting an equivalent modeling method, designs a model predictive controller based on the model predictive controller, considers the dynamic response characteristics of different types of the wind turbines, distributes a power grid dispatching value to each type of the wind turbines according to a certain priority, modifies an active reference value obtained by each type of the wind turbines by the model predictive controller, and distributes the modified value to all the wind turbines in the type according to a proportion. The method takes the active power control of the wind power plant as a target, considers the operation difference between the units, and is based on model prediction control, so that the method can quickly track the power grid regulation value.
Meanwhile, the wind power plant active power control method based on model predictive control also has the following beneficial effects:
(1) compared with the existing PI control method, the power is distributed according to the operation difference of the wind generation sets by classifying the wind generation sets according to the different wind speeds;
(2) compared with the existing PI control method, the power distribution has priority, so that unnecessary frequent actions of the pitch angle of the unit (especially the actions of the pitch angle of the unit in a region close to the rated wind speed) are reduced on the whole, the response speed is accelerated, and the service life of the unit is prolonged;
(3) a model predictive controller used which essentially optimizes the controlled variable on the basis of a prediction of the future behavior of the process; the prediction has no harsh requirement on the accuracy of the model based on, and a certain fault-tolerant space is provided for modeling a high-order nonlinear complex system of the wind power plant; the optimization is to determine the future control action through the optimization of a certain performance index in a limited time in the future, and the optimization is repeatedly carried out on line and has global optimization different from the traditional meaning; and the model predictive control is a closed-loop control algorithm, and the actual output error is fully utilized for feedback correction, so that a good control effect can be obtained.
Drawings
FIG. 1 is a system block diagram of a wind power plant active power control method based on model predictive control;
FIG. 2 is a system block diagram of a prior PI control method;
FIG. 3 is a graph of wind speed conditions within a wind farm used for simulation verification;
FIG. 4 is a graph comparing the effect of tracking grid regulation values;
FIG. 5 is a comparison graph of changes of the pitch angles of the units in a near-rated wind speed region;
fig. 6 is a graph comparing changes of active output of the unit.
Detailed Description
The following description of the embodiments of the present invention is provided in order to better understand the present invention for those skilled in the art with reference to the accompanying drawings. It is to be expressly noted that in the following description, a detailed description of known functions and designs will be omitted when it may obscure the subject matter of the present invention.
Examples
FIG. 1 is a system block diagram of a wind power plant active power control method based on model predictive control.
In this embodiment, as shown in fig. 1, a system architecture of the wind farm active power control method based on model predictive control mainly includes: firstly, distributing an active reference value of a wind power plant level; secondly, modifying a reference value based on model predictive control; and thirdly, distributing active reference fixed values among the units. The three sections are explained in detail below.
Wind power plant level active reference value distribution
The wind power plant level active reference value distribution is based on unit classification. Because the wind speed of each fan cannot be completely the same due to factors such as geographical position and the like even in a very small wind power plant, all the wind power plants in the wind power plant are classified into a plurality of subclasses according to the fact that the wind speed of the wind power plant corresponds to different preset wind speed intervals, but the wind power plants can be divided into three categories according to a control mode in general:
the low wind speed area unit: the wind turbine generator runs between cut-in wind speed and rated wind speed, the pitch angle is kept at 0 degree, active power control is achieved by controlling the torque of the fan to adjust the rotating speed to change the wind energy utilization coefficient, the inertia time constant is small, and the response speed is high.
Near the rated wind speed area unit: the wind speed-power combined type wind turbine generator set runs in an interval which is small near a rated wind speed, and the working state of the wind speed-power combined type wind turbine generator set is likely to be changed greatly when the wind speed-power combined type wind turbine generator set is disturbed by small wind speed due to the fact that the wind speed-power combined type wind turbine generator set is located near an inflection point of a wind speed-power curve, so that the pitch angle is changed continuously, unnecessary mechanical actions of the wind turbine generator set are caused, and response time is prolonged.
High wind speed district unit: the wind turbine generator set runs between a rated wind speed and a cut-out wind speed and is in a rated rotating speed constant power generation state, active power control is realized by adjusting a pitch angle, the change of the pitch angle is mechanical action, an inertia time constant is large, and the response speed is low; because the rotating speed of the unit in the high wind speed area reaches a rated value, the higher the wind speed, the more sensitive the output power of the unit is to the change of the pitch angle, namely, the angle with the same size is changed, and the higher the wind speed, the larger the power change of the unit is.
In the embodiment, the wind conditions of the wind turbine generator are divided into n types, wherein the low wind speed zone generator occupies k-1 type and is represented as T1,T2,…Tk-1(ii) a The units in the region close to the rated wind speed are in one category, denoted as Tk(ii) a The high wind speed area unit occupies n-k type and is represented as Tk+1,Tk+2,…Tn；
When the wind power plant receives active dispatching power from a power grid dispatching centerAnd the real-time active output of the wind power plant measured from the common link pointThen, obtaining the deviation delta P between the power grid regulation value and the real-time active output of the wind power plant, namely the quantity to be regulated of the wind power plant, judging whether the wind power plant needs to carry out power-up or power-down control, and controlling according to the response speed of each type of unitIs characterized by being given a certain priorityDistributing to each type of unit so as to obtain an active power reference value of each type of unitIn order to accelerate the response speed of the wind power plant, obviously, the pitch angle should be adjusted as little as possible, the priority order of each type of unit participating in adjustment is that the unit in the low wind speed area participates in the adjustment firstly, the unit in the lowest wind speed area and the unit in the next lower wind speed area are sequentially added in the adjustment according to the wind speed increasing direction until the certain type of unit in the low wind speed area with the wind speed closest to the rated wind speed is added in the active power adjustment, if the active power control target is not reached, the unit in the high wind speed area participates in the adjustment again, and the unit in the highest wind speed area and the unit in the next higher wind speed area are sequentially added in the active power adjustment according to the wind speed decreasing direction until the certain type. After a certain type of unit participates in regulation, the power grid dispatching requirement can be met, and the active output of the following units maintains the original value according to the priority sequence.
Active power reference value is distributed to each type of wind turbine generatorThe specific steps are explained in detail, and specifically:
(1) calculating the active power output of each type of wind turbine generator
Wherein,m represents the output of the jth wind turbine generator in the ith wind turbine generatoriRepresenting class i wind powerThe total number of the units;
calculating the active output of the whole wind power plant
Wherein,the active power output of the ith type of wind turbine generator is shown, and n represents the total number of the wind turbine generator categories;
calculating the to-be-regulated quantity delta P of the wind power plant:
wherein,is active dispatching power from a power grid dispatching center;
(2) and distributing the active power reference value of each type of wind turbine generator
(2.1) when Δ P > 0, it indicatesThe active power reference value of each type of wind turbine generator is shown by indicating that the active power output needs to be increased at the moment in the wind power plant in order to track the power grid regulation valueThe distribution steps are as follows:
1) calculating the power per liter capacity of each type of wind turbine generator:
2) sequentially accumulating the power rise capacity of each type of wind turbine generator according to a preset regulation and control sequenceAnd then, the active reference value of each type of wind turbine generator is obtained by distribution according to the following formula
Wherein,the capacity of the ith type wind turbine generator for increasing the power is shown,the maximum value of the active output of the ith type wind turbine generator is represented, and t represents that the active output is sequentially accumulated to the t type wind turbine generator to meet the dispatching target;
(2.2) when Δ P < 0, it indicatesThe active power reference value of each type of wind turbine generator is shown to indicate that the active power output of the wind power plant needs to be reduced at the moment in order to track the power grid regulation valueThe distribution steps are as follows:
1) calculating the power reduction capability of each type of wind turbine generator:
2) according to a preset regulation and control sequenceSequentially accumulating the power reduction capability of each type of wind turbine generatorAnd then, the active reference value of each type of wind turbine generator is obtained by distribution according to the following formula
Wherein,the capacity of the class i unit for reducing power is shown,and the minimum value of the active output of the ith type of unit is represented, and t represents that the active output is sequentially accumulated to the t type of wind generation unit so as to meet the dispatching target.
Reference value modification based on model predictive control
In order to design a model predictive controller, equivalent modeling must be performed on each type of wind turbine generator, and the following method is divided into two cases and is explained on the premise of capacity equivalence, namely:
1) equating the unit in the low wind speed area:
1.1) equivalent of wind speed
Calculating the power P of each wind turbine in the ith wind turbine according to the wind speed-power functionij：Pij＝F(vij)
Calculating the equivalent active power of the ith wind turbine generator
Calculating equivalent wind speed of the ith wind turbine generator by adopting a back-stepping method
Wherein j represents the j th wind turbine generator in the ith wind turbine generator, miIndicates the total number of the i-th wind turbines, F (v)ij) As a function of wind speed-power, vijRepresenting the wind speed of a jth wind turbine generator in the ith type wind turbine generator;
if two units with wind speeds of 6m/s and 8m/s respectively perform wind speed equivalence, the wind speed-power function isAir density ρ 1.2231kg/m3The radius R of the wind wheel is 63m, and the maximum value C of the power utilization coefficient is obtained because the unit is positioned in a low wind speed areap＝Cpmax0.482, v is wind speed. The power of the two units, 0.793872MW and 1.881772MW, is calculated respectively according to the wind speed-power function. And solving the sum, and obtaining the equivalent wind speed of about 9m/s according to the inverse solution of the wind speed-power function.
1.2) torque equivalence
Wherein,the equivalent torque of the wind generation set of the ith class corresponds to the specific set j of the ith class*The torque of (d);
2) equating the unit close to the rated wind speed area and the unit in the high wind speed area;
2.1), wind speed equivalent:
2.2), torque equivalence:
3) establishing a state space model according to the equivalence
3.1) because the accuracy requirement of model predictive control on a predictive model is not high, the mechanical torque of the fan is directly appliedPerforming first-order Taylor expansion at a given stable operation point, and performing T expansiontThe partial linearization approximation near the stable operating point yields:
where δ represents the deviation of the variable from its stable operating point, ρ is the air density, R is the wind wheel radius, v is the wind speed, Cp(λ, β) is the power utilization coefficient, β is the pitch angle, λ is the tip speed ratio,ωtis the fan speed, TtCan be regarded as relating to the fan speed omegatAngle of pitch β and wind speed v, upper lineRepresenting its steady state operating point;
3.2) establishing a state space model
y＝δPg＝Cx
Wherein,d＝δv
wherein, ω isgIs the motor speed, TgIs the electromagnetic torque, and the electromagnetic torque,the upper scale indicates the given value, KsAnd BsRespectively representing the equivalent elastic coefficient and the equivalent damping coefficient of the rotating shaft, JtAnd JgRespectively representing the rotational inertia of the fan and the motor, taugAnd τ represent the electromechanical time constant and pitch angle time constant, respectively, η is the motor efficiency.
4) And then designing a model predictive controller according to the state space model, wherein the design process is as follows:
4.1), discretizing the state space model to obtain:
x(k+1)＝A′x(k)+Bu′u(k)+Bd′d(k)
y(k+1)＝C′x(k)
4.2), design optimization objective function and constraint condition
The optimization objective function is:
the constraint conditions are as follows:
wherein n isc,npRepresenting the control and prediction time domains, Q, respectivelyP，QR，QSThe weight coefficients are respectively represented by the weight coefficients,respectively represents the maximum values of the electromagnetic torque and the pitch angle of the i-th wind turbine generator, andrespectively representing the difference between the electromagnetic torque given value and the pitch angle given value of the ith wind turbine generator at two sampling moments,respectively representing electromagnetic torque set value and pitch angle set value of the ith type wind turbine generator, and knowing sampling time and change rate constraintsThe multiplication of the two can be calculated The minimum value and the maximum value of the electromagnetic torque change rate of the ith type wind turbine generator and the minimum value and the maximum value of the pitch angle change rate are respectively represented.
Third, distribution of active reference modification values among units
In order to ensure the fairness of the distribution among the units in the similar operation state, the modification value of the active reference value of each type of unit obtained by the model predictive controllerDistributing the output power of a single wind turbine generator to a single wind turbine generator according to the output proportion of the single wind turbine generator in the wind turbine generator, and enabling each wind turbine generator to be distributed to an output power value
Fig. 2 is a system block diagram of a conventional PI control method.
According to the method, control is performed in a proportional-integral control mode only according to the deviation between the power grid modulation value and the active output of the wind power plant measured by the common link point, and then the active reference value is distributed to each unit in a proportional distribution mode. According to the method, the difference between the units is not considered, no priority is provided in the adjusting process, the active reference values of all the units fluctuate along with the fluctuation of the grid adjusting value, so that the pitch angles of some units, particularly the units in a region close to a rated wind speed, frequently act, the response time must be prolonged, the wind power plant is not beneficial to quickly tracking the grid adjusting value, the service life of the units is damaged, and the cost of the wind power plant is increased.
Examples
In order to illustrate the technical effect of the invention, the active power control method is applied to a wind power plant with the capacity of 5MW and 14 wind power units for simulation verification. And assuming that the wind speed measured by the wind farm is as shown in FIG. 3, according to the wind turbine parameters (cut-in wind speed v) used in the simulationinRated wind speed v of 3m/sratedCutting at 11.4m/sWind outlet velocity vout25m/s) the wind speed is divided into 5 subclasses, as shown in table 1, 14 units in the wind farm are divided into 5 subclasses according to the initial wind speed, and the unit classification is shown in table 2. The effectiveness of the method is illustrated by taking the example that the power grid dispatching value is changed from 50MW-42MW-36MW-40MW-45MW-52 MW.
TABLE 1 divide 5 subclasses by wind speed
TABLE 2 wind farm Unit Classification
Fig. 4 is a graph comparing the effect of tracking the grid regulation values. As can be seen from FIG. 4, the wind power plant performs active power control according to the method of the present invention, and the response speed is faster than that of the existing PI control method. The time that the active power of the wind power plant reaches and then stabilizes within an error band range of +/-5% of a power grid dispatching value is defined as the adjusting time, the index of the method is 1.27s, the index of the PI control method is 2.4s, and the rapidity of the method is improved by 47.2% compared with the existing method.
FIG. 5 is a graph comparing changes of the pitch angle of the unit in a near-rated wind speed region. As can be seen from FIG. 5, the wind farm performs active power control according to the method of the present invention, and the active reference value allocated to each unit in the units in the area adjacent to the rated wind speed is always 5MW, so that the pitch angle is always kept at 0 °, which is beneficial to the fast response of the wind farm; the PI control method does not consider the sensitivity characteristic of the unit to wind speed disturbance, and continuously distributes a power reference value to the unit, so that the pitch angle is frequently changed, and the quick response of a wind power plant is not facilitated.
Fig. 6 is a graph comparing changes of active output of the unit. From fig. 6, it can be seen that under the two methods, the power variation trends of the five types of units are shown. Described in terms of its power value at six sampling instants of stable operation. The six moments are 5s, 15s, 25s, 35s, 45s, 55s and 65s respectively. The first three histograms of each class describe the output of each class of units as the wind farm tracks the power of the grid schedule that is progressively decreasing (the grid schedule value abruptly changes from the initial 50MW to 42MW and then 36 MW). When the dispatching value is suddenly changed to 42MW from the initial 50MW, the active power control is carried out by using the method, the first type of unit and the second type of unit in the low wind speed area are firstly reduced to the minimum value, because the power reduction quantity is not met, the fifth type of unit in the highest wind speed in the high wind speed area participates in the regulation, the fifth type of unit still cannot meet the regulation quantity after the power reduction quantity is reduced to the minimum power, then the fourth type of unit in the second highest wind speed in the high wind speed area also reduces the output to participate in the regulation, and the process can be seen through a first bar chart to a second bar chart of each type of unit; when the power grid dispatching value is suddenly changed from 42MW to 36MW, only the fourth unit has the adjustment margin because the first, second and fifth units are all reduced to the set minimum power value, the fourth unit continues to reduce the output power to finish the tracking target, and the process can be seen from the second bar chart to the third bar chart of each unit. Similar to power reduction, in the power increasing process, active power control is carried out according to the method, and each type of unit still participates in regulation according to a preset priority sequence, namely the first type, the second type, the fifth type and the fourth type of unit act in sequence, and the expected effect is met. The active output of each type of unit using the PI control method changes continuously along with the change of the power grid dispatching value, and the system stability is poor.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, and various changes may be made apparent to those skilled in the art as long as they are within the spirit and scope of the present invention as defined and defined by the appended claims, and all matters of the invention which utilize the inventive concepts are protected.
Claims (3)
1. A wind power plant active power control method based on model predictive control is characterized by comprising the following steps:
(1) according to the factory parameters of the fan, the cut-in wind speed vinTo rated wind speed vratedThen to cut-out wind speed voutClassifying the wind conditions of the wind turbine generator, and then scheduling the active power from the grid scheduling center according to the classification resultAnd from a common chainWind power plant real-time active output obtained by contact measurementThe wind power plant level active reference value is distributed, so that each type of wind turbine generator is distributed to the active power reference valueWherein i is 1,2, …, n, n represents the total number of the wind turbine classification;
(2) carrying out equivalent modeling on each classified wind turbine generator according to classification, designing a model prediction controller of each wind turbine generator on the basis of the equivalent modeling, and finally utilizing the model prediction controller to carry out equivalent modeling on each classified wind turbine generatorThe power value P is obtained by trimmingi ref；
(3) The value P of active poweri refDistributing the output power of a single wind turbine generator to a single wind turbine generator according to the output proportion of the single wind turbine generator in the wind turbine generator, and enabling each wind turbine generator to be distributed to an output power valuej＝1,2,…,mi，miThe total number of the ith type wind turbines is represented;
(4) each wind turbine generator set outputs power values according to the distributionOutputting to complete active power control of the whole wind power plant;
wherein each type of wind turbine generator is allocated to an active power reference valueThe method comprises the following specific steps:
(2.1) Power Pre-treatment
Calculating the active output of each type of wind turbine generatorForce Pi out：
Wherein,m represents the output of the jth wind turbine generator in the ith wind turbine generatoriThe total number of the ith type wind turbines is represented;
calculating the active output of the whole wind power plant
Wherein, Pi outThe active power output of the ith type of wind turbine generator is shown, and n represents the total number of the wind turbine generator categories;
calculating the to-be-regulated quantity delta P of the wind power plant:
wherein,is active dispatching power from a power grid dispatching center;
(2.2) distributing active power reference values of each type of wind turbine generator
(2.2.1) when Δ P > 0, it indicatesActive power reference value of each type of wind turbineThe distribution steps are as follows:
1) calculating the power per liter capacity of each type of wind turbine generator: delta Pi up＝Pi max-Pi out
2) Sequentially accumulating the power rise capacity of each type of wind turbine generator according to a preset regulation and control sequenceAnd then, the active reference value of each type of wind turbine generator is obtained by distribution according to the following formula
Wherein, Δ Pi upIndicating the capacity of a wind turbine of class i, Pi maxThe maximum value of the active output of the ith type wind turbine generator is represented, and t represents that the active output is sequentially accumulated to the t type wind turbine generator to meet the dispatching target;
(2.2.2) when Δ P < 0, it is indicatedActive power reference value of each type of wind turbineThe distribution steps are as follows:
1) calculating the power reduction capability of each type of wind turbine generator: delta Pi down＝Pi out-Pi min
2) Sequentially accumulating the power reduction capacity of each type of wind turbine generator according to a preset regulation and control sequence, and performing the operation when the power reduction capacity of each type of wind turbine generator is equal to the preset regulation and control sequenceAnd then, the active reference value of each type of wind turbine generator is obtained by distribution according to the following formula
Wherein, Δ Pi downIndicating the power-down capability of the i-th unit, Pi minAnd expressing the minimum value of the active output of the ith type unit.
2. The wind power plant active power control method based on model predictive control according to claim 1, wherein in the step (2), the method for performing equivalent modeling on each type of wind power generation set according to classification categories comprises the following steps:
(3.1) dividing the wind conditions of the wind turbine generator set in the step (1) into n types, wherein the low wind speed area generator set occupies k-1 type and is represented as T1,T2,…Tk-1(ii) a Units of one type, denoted T, close to rated wind speedk(ii) a The high wind speed area unit occupies n-k type and is represented as Tk+1,Tk+2,…Tn；
(3.2) equivalence is carried out on various wind turbine generators
(3.2.1) respectively equating various wind turbine generators on the premise of capacity equivalence;
1) equating the unit in the low wind speed area:
1.1) equivalent of wind speed
Calculating the power of each wind turbine in the ith wind turbine according to the wind speed-power function: pij＝F(vij)
Calculating equivalent active power P of ith wind turbine generatori eq：
Calculating equivalent wind speed of the ith wind turbine generator by adopting a back-stepping method
Wherein j represents the ith in the ith type wind turbine generatorj wind turbine generators, miIndicates the total number of the i-th wind turbines, F (v)ij) As a function of wind speed-power, vijRepresenting the wind speed of a jth wind turbine generator in the ith type wind turbine generator;
1.2) torque equivalence
Wherein,the equivalent torque of the wind generation set of the ith class corresponds to the specific set j of the ith class*The torque of (d);
2) equating the unit close to the rated wind speed and the unit in the high wind speed area;
2.1), wind speed equivalent:
2.2), torque equivalence:
(3.3) establishing a state space model according to the equivalence
(3.3.1) mechanical torque of fanThe first order Taylor expansion approximation at a given stable operating point yields:
where delta represents the deviation of the variable from its steady operating point,ρ is the air density, R is the rotor radius, v is the wind speed, Cp(λ, β) is the power utilization coefficient, β is the pitch angle, λ is the tip speed ratio,ωtis the fan speed, TtViewed as relating to fan speed ωtPitch angle β and wind speed v, with an upper line-representing its steady state operating point, Kω、KvAnd KβCoefficients relating to fan speed, pitch angle and wind speed, respectively;
(3.3.2) establishing a state space model
y＝δPg＝Cx
Wherein,represents the derivative of x over time t;
wherein, PgAs generator power, ωgIs the motor speed, TgIs the electromagnetic torque, and the electromagnetic torque,the upper scale indicates the given value, KsAnd BsRespectively representing the equivalent elastic coefficient and the equivalent damping coefficient of the rotating shaft, JtAnd JgRespectively representing the rotational inertia of the fan and the motor, taugAnd τ represent the electromechanical time constant and pitch angle time constant, respectively, η is the motor efficiency.
3. The method for controlling the active power of the wind power plant based on the model predictive control according to claim 2, wherein in the step (2), the design process of the model predictive controller is as follows:
(4.1) discretizing the state space model to obtain:
x(k+1)＝A′x(k)+Bu′u(k)+Bd′d(k)
y(k+1)＝C′x(k)
(4.2) designing and optimizing objective function and constraint condition
The optimization objective function is:
the constraint conditions are as follows:
wherein, | | | represents norm, nc,npRepresenting the control and prediction time domains, Q, respectivelyP，QR，QSThe weight coefficients are respectively represented by the weight coefficients,respectively represents the maximum values of the electromagnetic torque and the pitch angle of the i-th wind turbine generator, andrespectively representing the difference between the electromagnetic torque given value and the pitch angle given value of the ith wind turbine generator at two sampling moments,respectively representing given electromagnetic torque values, known sampling time and known change rate constraints of the ith type wind turbine generatorThe two are multiplied to obtain Respectively representing the minimum value and the maximum value of the electromagnetic torque of the ith type wind turbine generator set and the minimum value and the maximum value of the pitch angle; pi maxRepresents the maximum value of the active output of the i-th wind turbine generator, Pi minAnd expressing the minimum value of the active output of the ith type unit.
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