Steady-state distribution and transient utilization method and system for standby power of multi-terminal wind power system

Abstract

The invention relates to a multi-terminal wind power system standby power steady state distribution and transient state utilization method and system, and the method comprises the following steps: obtaining historical wind speed data and real-time load data of each fan in a multi-terminal wind power system, and carrying out the clustering through employing a clustering algorithm, and obtaining a system total standby power instruction in a steady state; according to the rated capacity of each fan, performing standby power steady-state distribution on the total standby power instruction of the system among the fans to obtain a standby power instruction of each fan; a frequency supporting capacity evaluation method based on the rotor rotating speed and the pitch angle position is adopted to evaluate the frequency supporting capacity of the fan, and an evaluation result is obtained; and based on an evaluation result, distributing the total additional power required by meeting the frequency safety boundary constraint among the fans to realize the transient utilization of the standby power. Compared with the prior art, the method has the advantages that the additional power of each fan is matched with the actual operation condition, and the better economic performance is achieved while the frequency supporting effect is guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of new energy technology, and in particular to a method and system for steady-state distribution and transient utilization of standby power of a multi-terminal wind power system. Background Art

[0002] With the increase in the penetration rate of new energy, the power system faces the risk of reduced inertia and frequency instability, and new energy systems are needed to provide frequency support. In order to strengthen the frequency support capability, wind power systems usually need to reserve some power, that is, to reduce load on the basis of the maximum power point and release the required power when the grid needs it. In multi-terminal offshore wind power systems, there are differences in the physical design of different wind turbines, wind speed and direction in the area where they are located, etc. The use of equal reserve power allocation method makes energy utilization inefficient and increases wind turbine wear. In addition, the release of wind turbine reserve power in transient state also determines the economic operation of the system. Therefore, how to economically and efficiently allocate steady-state power reserves for each wind turbine in a multi-terminal system with multiple wind turbines interconnected, and how to orderly release reserve power during transient frequency support become the key.

[0003] With the increasing penetration of wind power systems and the continuous investment in power electronic equipment, the rotational inertia of the power system is gradually decreasing, and the system is gradually evolving towards a low-inertia system, which will increase the unbalanced power impact of the system, weaken the system frequency support capability, and threaten the system frequency security. In order to ensure the safe and stable operation of the system and improve the frequency stability and security of the power grid, the offshore wind power system should provide frequency support for the power grid.

[0004] Generally, wind turbines use maximum power point tracking (MPPT) to calculate output power during steady-state operation. They cannot provide additional power to cope with frequency disturbances when the grid needs it. Therefore, wind turbines need to reserve a certain amount of power during steady-state operation. When frequency disturbances occur, this part of the reserve power is used through additional frequency control of the converter to output additional power to support the grid frequency. However, although designing a larger steady-state reserve power is beneficial to the frequency support performance, it also reduces the economic efficiency of system operation. On the other hand, an unreasonable reserve power release strategy for each wind turbine during transient state may also lead to extreme situations where low-output wind turbines have low output and high-output wind turbines have high output, resulting in low energy utilization. Therefore, it is necessary to reasonably allocate steady-state reserve power and transient additional power. Existing technologies have also been improved through various measures. For example, measure 1: The document "A Two-Stage Power Distribution Scheme of Multiple Wind Farms Participating in Primary Frequency Regulation" aims to minimize frequency deviation and establishes a two-layer power control strategy of steady-state control of wind power system and transient control of wind turbine frequency support, which effectively improves frequency stability, but ignores the actual operating conditions of wind turbines. Long-term operation will lead to increased wear and tear of wind turbines and reduced health, thereby increasing operating and maintenance costs. Measure 2: The document "Active power dispatch optimization for offshore wind farms considering fatigue distribution" and the document "Fast active power distribution method for wind farms considering unit fatigue load" establish models of wind turbine shaft system and tower fatigue loads, and dispatch with the minimum total fatigue load of the wind farm and its distribution within the station as the optimization goal. However, the control method is too complicated to calculate, and does not consider the impact of synchronous changes in standby power instructions on wind turbine failure rate and system stability when wind speed changes frequently and irregularly. Measure 3: The document "Coordinated Power Reserve Control of Wind Farm for Frequency Regulation" linearizes the mathematical relationship between the change in rotor speed and the change in power, and uses the maximization of the linear part of the rotor kinetic energy that can be released as the objective function for linear programming solution. However, when there are large differences in wind turbine designs, the amount of calculation is too large, the process is too complicated, and the system response speed is slow.Measure 4: The document "Research on wind farm active power dispatching algorithm based on fuzzy evaluation" distributes active power by average or according to wind speed ratio. However, it does not take into account the randomness of wind speed and the differences in unit operating conditions, resulting in low wind turbine energy utilization. In addition, too frequent unit power adjustment may lead to an increase in the unit's failure rate. Summary of the invention

[0005] The purpose of the present invention is to provide a method and system for steady-state distribution and transient utilization of standby power in a multi-terminal wind power system, which can improve the energy utilization rate and economic performance of the system.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A method for steady-state distribution and transient utilization of reserve power in a multi-terminal wind power system comprises the following steps:

[0008] Obtain the historical wind speed data and real-time load data of each wind turbine in the multi-terminal wind power system, perform clustering using a clustering algorithm, and obtain the system total standby power command in steady state;

[0009] According to the rated capacity of each wind turbine, the total standby power command of the system in the steady state is distributed among the wind turbines to obtain the standby power command of each wind turbine;

[0010] According to the standby power instructions of each wind turbine, a frequency support capability evaluation method based on rotor speed and pitch angle position is used to evaluate the frequency support capability of the wind turbine to obtain an evaluation result;

[0011] Based on the evaluation results, the total additional power required to meet the frequency safety boundary constraint is distributed among the wind turbines to achieve transient utilization of the reserve power.

[0012] Furthermore, the step of obtaining the system total standby power instruction in a steady state includes:

[0013] The maximum power of the wind turbine in each time period under the MPPT mode is calculated based on the historical wind speed data of each wind turbine, and the total maximum power of the system in each time period is further obtained, wherein the calculation expression of the maximum power is:

[0014]

[0015] Where P MPPT is the maximum power value of the fan, ρ is the air density, R is the radius of the fan blade, C pmax is the maximum wind energy utilization coefficient, v wis the wind speed;

[0016] Based on the total maximum power of the system in each time period and the real-time load data, a comparison is performed to obtain the system power surplus in each time period;

[0017] The system power surplus of each time period is used as a data set of the K-means algorithm to cluster the power surplus points, obtain the cluster centers and the corresponding power surpluses, and further obtain the total standby power instruction of the system in steady state.

[0018] Furthermore, the step of clustering using the K-means algorithm includes:

[0019] (1) Randomly select K power surplus points as initial cluster centers;

[0020] (2) Calculate the Euclidean distance between each power surplus point and each initial cluster center, and assign each power surplus point to the cluster center closest to it, where the calculation expression of the Euclidean distance is:

[0021]

[0022] Where X is the data object, i.e., the power surplus point, C i is the i-th cluster center, m is the dimension of the data object, X j , C ij X, C i The jth attribute value of is the time value and power corresponding to the power surplus point, and d is the Euclidean distance;

[0023] (3) Each cluster center and the allocated power surplus point are regarded as a cluster. Each time a power surplus point is allocated, the cluster center of the cluster is recalculated based on the average value of the existing power surplus points.

[0024] (4) Calculate the sum of the squares of the distances between the new cluster center and the previous cluster center, and determine whether the sum of the squares of the distances is less than a set value. If so, stop the iteration and obtain each cluster center and the corresponding power surplus. If not, repeat steps (2)-(4) until the iteration stops.

[0025] Furthermore, the expression for the steady-state allocation of the standby power is:

[0026]

[0027] Where P res,i is the standby power command assigned to the i-th wind turbine, n is the total number of wind turbines, P rated,i is the rated power of the i-th fan, P res It is the total standby power command of the system when the system is in steady state.

[0028] Furthermore, the step of performing steady-state allocation of standby power also includes:

[0029] A steady-state power compensation coefficient is applied to each wind turbine to compensate for the imbalance between the generated power and the load power, wherein the expression of the steady-state power compensation coefficient is:

[0030]

[0031] In the formula, k m，i is the steady-state power compensation coefficient of the i-th wind turbine, k0 represents the corresponding system power droop coefficient when the system frequency deviation fluctuates to the safety boundary, n represents the number of wind turbines, ω r Indicates the speed, the subscript 0 indicates the speed before the disturbance, the subscript min / max indicates the minimum / maximum speed, P res,i The reserve power command assigned to the i-th wind turbine, P res It is the total standby power command of the system when the system is in steady state.

[0032] Furthermore, the step of obtaining the evaluation result includes:

[0033] Based on the standby power instructions of each wind turbine, according to the power standby principle, the wind turbine operation increases the rotor speed to achieve overspeed load reduction to meet the standby power demand. When the rotor speed reaches the maximum value within the allowable range and still cannot meet the standby power demand, the pitch control is activated to coordinate to meet the standby power demand.

[0034] According to the rotor speed and pitch control of the wind turbine during operation, the frequency support capability of the wind turbine is evaluated and an evaluation result is obtained.

[0035] Furthermore, the evaluation expression is:

[0036]

[0037] In the formula, G e represents the frequency support capability of the wind turbine, β represents the pitch angle, and β min Indicates the minimum allowable value of the pitch angle, β max Indicates the maximum allowable value of the pitch angle, ω r Indicates the speed. The subscript 0 indicates the speed before the disturbance, and the subscript min / max indicates the minimum / maximum speed.

[0038] Furthermore, the step of realizing transient utilization of the reserve power includes:

[0039] According to the evaluation results, the primary frequency modulation coefficient is set based on the total additional power required to meet the frequency safety boundary constraint, so that the wind turbine can cope with the frequency disturbance event;

[0040] Based on the primary frequency modulation coefficient, the additional power supported by the transient frequency of the wind turbine is calculated to achieve transient utilization. Further, the calculation expression of the additional power supported by the transient frequency of the wind turbine is:

[0041] ΔP PFC,i =-k PFC,i ·(f-f0)

[0042]

[0043] In the formula, ΔP PFC,i represents the additional power of the primary frequency regulation control of the i-th fan, k PFC,i represents the primary frequency modulation coefficient of the i-th wind turbine, f is the real-time system frequency, f0 is the rated frequency, k0 represents the corresponding system power droop coefficient required when the system frequency deviation fluctuates to the safety boundary, n represents the number of wind turbines, G e,i Represents the frequency support capacity of the i-th fan.

[0044] The present invention also provides a system for steady-state distribution and transient utilization of standby power of a multi-terminal wind power system, comprising:

[0045] Steady-state allocation layer: obtain the historical wind speed data and real-time load data of each wind turbine in the multi-terminal wind power system, cluster them using a clustering algorithm, and obtain the system total standby power instruction in steady state; according to the rated capacity of each wind turbine, the system total standby power instruction in steady state is distributed among the wind turbines to obtain the standby power instruction of each wind turbine;

[0046] Transient utilization layer: According to the backup power instructions of each wind turbine, the frequency support capability of the wind turbine is evaluated by using a frequency support capability evaluation method based on rotor speed and pitch angle position to obtain an evaluation result; based on the evaluation result, the total additional power required to meet the frequency safety boundary constraint is allocated among the wind turbines to achieve transient utilization of the backup power.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) The present invention obtains the total system reserve power instruction by using a clustering algorithm, and then allocates it according to the rated capacity of each fan, sets the steady-state reserve power task of each fan, and then evaluates the frequency support capacity of the fan. Then, based on the total additional power required to meet the frequency safety boundary constraint, the additional power supported by the transient frequency is allocated to each fan, thereby realizing the transient utilization of the reserve power of each fan. The present invention improves the output of the fan through a reasonable reserve power release strategy, and improves the energy utilization rate of the system through additional power allocation.

[0049] (2) When the wind turbine of the present invention is in steady-state operation, the rotor speed is increased to achieve overspeed load reduction. When the rotor speed reaches the maximum value within the allowable range and still cannot meet the standby power demand, the variable pitch control is activated for coordination. This method of preferentially changing the rotor speed and then changing the pitch angle takes into account the physical properties of the pitch angle, improves the response speed, and reduces the degree of wind turbine wear. The frequency support capacity evaluation method used can accurately evaluate the frequency support capacity of each wind turbine, and based on this, the transient use of standby power is more economical and efficient.

[0050] (3) The present invention uses the k-means algorithm to cluster the power surplus, which can fix the size of the standby power within a certain period of time, without the need to frequently change the standby power of the unit, thereby reducing the unit failure rate and improving system reliability.

[0051] (4) The present invention simplifies the calculation process and has a fast response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a schematic diagram of the method flow of the present invention;

[0053] Figure 2 The fan power curve and power reserve principle of the present invention;

[0054] Figure 3 The fan standby power utilization principle of the present invention;

[0055] Figure 4 A case study system for an embodiment of the present invention;

[0056] Figure 5 is the frequency simulation result of the embodiment of the present invention;

[0057] Figure 6 5% load step disturbance system simulation results of an embodiment of the present invention, wherein (a) is a 75MW wind turbine output power comparison diagram, (b) is a 100MW wind turbine output power comparison diagram, (c) is a 75MW wind turbine pitch angle comparison diagram, (d) is a 100MW wind turbine pitch angle comparison diagram, (e) is a 75MW wind turbine rotor speed comparison diagram, and (f) is a 100MW wind turbine rotor speed comparison diagram. DETAILED DESCRIPTION

[0058] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0059] Example 1

[0060] This embodiment provides a method for steady-state allocation and transient utilization of the reserve power of a multi-terminal wind power system. The method uses the K-means algorithm of historical wind speed to obtain a reference value for the total reserve power of the multi-terminal wind power system in steady state, and then allocates the total reserve power according to the rated capacity of each wind turbine, and sets the steady-state reserve power task of each wind turbine; then the frequency support capability of the wind turbine is evaluated based on the real-time speed and pitch angle position, and then the additional power supported by the transient frequency is allocated to each wind turbine based on the total additional power required to meet the frequency safety boundary constraint, so as to realize the transient utilization of the reserve power of each wind turbine. The technical solution of the present invention is mainly divided into two parts. The first part is the principle of steady-state reserve power control and transient utilization of wind turbines, and the second part is the specific implementation process of the method.

[0061] Part 1: Principles of steady-state standby power control and transient utilization of wind turbines.

[0062] The active power reference value of the wind turbine will be calculated according to the MPPT algorithm, and the speed will be changed according to the imbalance between the electromagnetic torque and mechanical torque of the wind turbine at this time, so that it can finally reach the maximum power operating point under the current wind speed. When the wind turbine needs to reserve a certain amount of power according to the grid dispatching requirements, it is impossible to continue to use MPPT to control the output power. Instead, it is necessary to reduce a certain amount of power output based on the maximum real-time capture power. The reduction corresponds to the power reserve demand, thereby achieving power reserve.

[0063] Wind turbine power curve and power reserve principle Figure 2 As shown in the figure. MPPT Represents the power command obtained by the MPPT algorithm, P res It means that after the wind turbine reserves the reserve power, it refers to the power command. The wind turbine initially runs at point A of the mechanical power curve, corresponding to the pitch angle of β2 and the rotor speed of ω. opt2 .like Figure 2 As shown, there are three ways for wind turbines to achieve power reserve, namely rotor overspeed, pitch control, and rotor deceleration, corresponding to Figure 2 Points C, D, and B in the figure can all make the wind turbine output power increase from P at point A to MPPT Reduce to P res In the rotor overspeed mode, the rotor reduces its output power by increasing the speed. opt2 Increase to ω2, the operating point changes from point A to point C. It can be seen that overspeed load reduction can store part of the energy in the form of rotor kinetic energy, which can be used as a frequency support energy source; in variable pitch control mode, the wind turbine increases the blade pitch angle to make the wind energy utilization coefficient C p Reduce, reduce the wind turbine capture power to the suboptimal power point D, the corresponding pitch angle is β1, the optimal speed is ω opt1. However, pitch control is a mechanical control with slow response speed, mechanical fatigue and physical wear, and frequent changes will increase operation and maintenance costs. The rotor deceleration method is the same as the rotor overspeed, but it should be noted that the rotor deceleration operating point B is an unstable operating point. During the system frequency drop, the electromagnetic torque of the wind turbine will increase suddenly, while the mechanical torque cannot change suddenly. The electromagnetic torque is greater than the mechanical torque, which will cause the wind turbine to release the rotor kinetic energy. The rotor will further decelerate and there is a risk of stalling and collapse. In summary, the best way for the wind turbine to reach the power reserve point is through rotor overspeed. If the rotor still cannot meet P after overspeeding to the maximum speed. res If the output requirement is met, the speed can be kept unchanged and the pitch angle position can be changed.

[0064] The principle of standby power utilization is as follows Figure 3 Taking rotor overspeed as an example, the wind turbine runs at overspeed from the maximum power point A to point B. At this time, the maximum speed has been reached but the reserve power requirement is still not met. At this time, the pitch angle is changed from β0 to β1, and the operating point is changed from point B to point C, leaving a reserve power of ΔP res =P MPPT -P res When the disturbance comes, the wind turbine reserve power is used, and the wind turbine will obtain a new reference power value P under the frequency support control strategy. cmd , the traditional standby power utilization method will change the speed and pitch at the same time, so that the power operating point changes directly from point C to point D, causing greater physical wear on the wind turbine blades and slow response speed. The present invention improves the standby power utilization control. The improved standby power utilization control will give priority to changing the rotor speed so that it reaches the maximum power point under the current pitch angle first. If the maximum power still cannot meet the frequency support requirements at this time, the pitch angle will be changed again, that is, the speed is first changed from point C to the current pitch angle optimal point E, and then the pitch control is activated to the final point. This method takes into account the physical properties of the pitch angle, improves the response speed, and reduces the degree of wind turbine wear.

[0065] Part II: Specific implementation process of the method.

[0066] like Figure 1 As shown, the specific steps of the method include:

[0067] S1. Establish a wind turbine power-time clustering model based on historical wind speed and K-means clustering algorithm.

[0068] The maximum output power of the wind turbine operating in MPPT mode in each period is calculated based on the historical wind speed data. The maximum power value of the wind turbine at each wind speed can be obtained by formula (1):

[0069]

[0070] Where P MPPT Indicates the maximum power value of the fan.

[0071] Comparing the total maximum power of the wind farm with the load demand can obtain the system power surplus in each period. The power surplus points of the offshore multi-terminal wind power system at each moment are used as data sets. The K-means algorithm is used to cluster the power surplus points. The wind farm will use the power surplus at the cluster center as the backup power instruction. The specific clustering process is as follows:

[0072] 1) Randomly select K power surplus points as initial cluster centers;

[0073] 2) Calculate the Euclidean distance between each power surplus point and each initial cluster center, and assign each power surplus point to the cluster center closest to it; the Euclidean distance calculation formula between the data object and the cluster center in the space is:

[0074]

[0075] Where: X is the data object, i.e. the power surplus point, C i is the i-th cluster center, m is the dimension of the data object, X j , C ij For X and C i The j-th attribute value of , that is, the time value and power value corresponding to the power surplus point.

[0076] 3) The cluster center and the power surplus points assigned to it represent a cluster. Each time a power surplus point is assigned, the cluster center of the cluster will be recalculated based on the average value of the existing power surplus points in the cluster.

[0077] Repeat steps 2) and 3). If the sum of the squares of the distances between the new cluster center and the previous cluster center is less than the set value, the algorithm stops and the wind farm uses the power surplus of each cluster center as a reference value for power reserve.

[0078] In different time periods in the same cluster, the wind turbines will uniformly allocate backup power according to the power surplus of the cluster center, and the power surplus of the cluster center in the time period will replace the original real-time changing power surplus.

[0079] S2. Calculate the steady-state standby power command of each wind turbine in the multi-terminal wind power system.

[0080] The clustering algorithm is used to obtain the steady-state total reserve power command P of the multi-terminal wind power system in a certain period of time. res After that, each fan will be assigned tasks according to its rated capacity:

[0081]

[0082] Where P res,i is the standby power command of the ith fan, n is the total number of fans, P rated,iis the rated power of the i-th wind turbine. However, since the total reserve power of the wind farm calculated by the clustering algorithm may cause an imbalance between the power generation and load power in the system, it is necessary to apply a steady-state power compensation coefficient to the wind turbine to compensate for the unbalanced power. The power compensation coefficient can be set according to the reserve capacity of each wind turbine:

[0083]

[0084] In the formula, k m，i is the steady-state compensation coefficient of the i-th wind turbine, k0 represents the system power droop coefficient required when the system frequency deviation fluctuates to the safety boundary, n represents the number of wind turbines, ω represents the speed, the subscript 0 represents the speed before the disturbance, and the subscript min / max represents the minimum / maximum speed.

[0085] S3. Frequency support capability assessment method based on steady-state operating conditions of wind turbines.

[0086] According to the power reserve principle, the wind turbine will first increase the rotor speed to achieve overspeed load reduction. When the rotor speed reaches the maximum value within the allowable range and still cannot meet the reserve power demand, the variable pitch control needs to be activated for coordination. Based on this variable speed and variable pitch logic, it can be considered that when the pitch angle is constant, the greater the rotor speed, the greater the mechanical kinetic energy that can be used to support the frequency; according to the wind turbine control principle, when the rotor speed is constant, the greater the pitch angle, the smaller its output power, and it can be considered that the potential power that can be provided is greater. Therefore, the frequency support capability of the wind turbine can be evaluated based on the rotor speed and pitch angle position. The specific formula is:

[0087]

[0088] In the formula, G e represents the frequency support capability of the wind turbine, β represents the pitch angle, and β min Indicates the minimum allowable value of the pitch angle, which can be 0°, β max Indicates the maximum allowable value of the pitch angle, which is generally 28°.

[0089] S4. A method for transient utilization of standby power based on frequency support capability assessment for frequency control.

[0090] Assume that the system suddenly experiences ΔP L If there is a sudden increase in load, the fan will allocate reserve power according to formula (6) to compensate for the sudden increase in load.

[0091]

[0092] In the formula, ΔP i It is the additional power that should be allocated to each wind turbine based on the frequency support capacity assessment results.

[0093] However, in actual operation, it is impossible to accurately predict the sudden increase in load, and it is impossible to accurately preset the power addition in the fan power control loop. Therefore, the fan can only respond to frequency disturbance events by setting the frequency modulation coefficient once. The frequency modulation coefficient of the i-th fan is calculated as

[0094]

[0095] In the formula, k PFC,i represents the primary frequency modulation coefficient of the i-th wind turbine, and the corresponding transient frequency support additional power is calculated according to formula (8).

[0096] ΔP PFC,i =-k PFC,i ·(f-f0) (8)

[0097] In the formula, ΔP PFC,i It represents the additional power of the primary frequency modulation control of the i-th wind turbine. Each wind turbine outputs additional power according to formula (8), and the wind farm will continue to output power.

[0098] Similarly, if the system suddenly appears ΔP L In the case of a sudden load drop, the standby power is still allocated according to formula (8) to compensate for the sudden load drop. Different from the case of a sudden load increase, the fan will reduce its output power at this time. The power reduction of each fan is equal to the calculated result of formula (6) ΔP i The subsequent process is the same as the load surge. The whole process flow chart is as follows: Figure 1 As shown, in the figure, m represents the number of fans and k represents the number of loads.

[0099] The embodiment of the present invention verifies the proposed method for steady-state allocation and transient utilization of reserve power in a multi-terminal wind power system in PSCAD / EMTDC. Figure 4 As shown, WT1 represents 50 1.5MW PMSG wind turbines, so the total rated capacity of WT1 is 75MW, WT2 represents 50 2MW PMSG wind turbines, so the total rated capacity of WT2 is 100MW, SG is used for equivalent onshore AC generators, and the rated capacity is 100MW, PL1 and PL2 are fixed loads, both of which have a load value of 175MW, totaling 350MW, PL3 is a 5% load that can be switched on and off, with a size of 8.75MW, and the switchable load PL3 is put into use at the simulation time t = 30s. The parameters of the synchronous generator are shown in Table 1.

[0100] Table 1 Example system parameters

[0101]

[0102] Verification scheme:

[0103] In this case study, the initial cluster number K of the clustering algorithm is set to 24. Three groups of simulations are set: a. The wind turbine MPPT is running without frequency support control; b. The wind turbine uses the average allocation method for standby power; c. The wind turbine uses the proposed standby power steady-state allocation and transient utilization method. For the convenience of comparison, the average allocation method uses the K-means clustering algorithm with the same parameters as the proposed method when calculating the steady-state standby power size. The frequency simulation results are shown in Figure 2. Figure 5 As shown in Figure 2, the wind turbine output power, pitch angle and rotor speed are as follows: Figure 6 shown.

[0104] Figure 5 The frequency change waveforms under three different control modes are shown. When the total power reserve and the total additional power of the wind farm are the same, the frequency change waveforms are consistent. In terms of frequency, since the wind farm cannot respond to the frequency changes of the AC system under MPPT control, cutting off the load seriously affects the frequency of the AC system. The lowest frequency point is 49.51Hz. Since the total additional power of the multi-terminal wind power system of the average distribution method and the proposed method is the same, the frequency support effect is the same, and the lowest frequency point is increased to 49.80Hz. The frequency deviation is reduced by 59.18% compared with the previous method, which has a significant effect. Figure 6 The output power, pitch angle and rotor speed of the wind turbine in three different control modes are shown. Figure 6 As can be seen from Figures (a) and (b) in the figure, since the system has no frequency support loop under MPPT control, its output power is constant. The average allocation method and the proposed method use the same clustering algorithm with the same parameters to calculate the steady-state reserve power. Therefore, the output power is the same before the disturbance. After the disturbance, the 75MW wind turbine outputs more power using the proposed method compared to the average allocation method, while the 100MW wind turbine outputs less power, but the total additional power of the two is the same. In terms of pitch angle, Figure 6 As shown in Figures (c) and (d) in Figure 1, the pitch angle change of the wind turbine under the proposed method is smaller than that of the average distribution method, the physical change is smaller, and the economic performance is better. Although the pitch angle is greatly reduced under the MPPT method, considering that frequency stability is the priority, the MPPT method is not included in the comparison. In terms of rotor speed, Figure 6 As shown in Figures (e) and (f) in Figure 3, the change in wind turbine speed is smaller for the 75MW wind turbine using the proposed method, while the change in the 100MW wind turbine using the average distribution method is smaller, and the difference between the two changes is small.

[0105] Since the differences in frequency, rotor speed and pitch angle between the average distribution method and the proposed method are small, the evaluation index of the wind turbine "fatigue coefficient" can be used to show the advantages and disadvantages of the two and quantify the economic performance of wind turbine operation. The fatigue coefficient corresponding to the simulation process in this example is shown in Table 2. Table 2 lists the simulation results of the fatigue coefficient of the average distribution method and the proposed method. It can be seen that compared with the average distribution method, the total fatigue of the wind farm is not much different between the proposed method and the average distribution method, while the standard deviation of the fatigue load is reduced by about 16.5%. In general, the proposed method can reduce the total fatigue and fatigue standard deviation of the wind farm while ensuring frequency stability, making the wear degree of each wind turbine more similar and reducing the operation and maintenance cost of the wind farm.

[0106] Table 2 Fatigue coefficient related results during simulation time (unit: per unit value)

[0107]

[0108] In summary, this embodiment takes into account the actual operating conditions of the wind turbine. First, the K-means algorithm based on the historical wind speed is used to obtain the total standby power of the multi-terminal system in a steady state, and then the standby power is allocated among the wind turbines according to the rated capacity of each wind turbine. Subsequently, a frequency support capacity evaluation method based on the rotor speed and pitch angle position is proposed. Based on the evaluation results, the total additional power required to meet the frequency safety boundary constraint is allocated among the wind turbines to achieve transient utilization of the standby power. Compared with measure 1 in the background technology, the present invention proposes a frequency support capacity evaluation method based on the rotor speed and pitch angle, which can accurately evaluate the frequency support capacity of each wind turbine, and based on this, the transient utilization of the standby power is more economical and efficient; compared with measure 3, the present invention not only simplifies the calculation process, but also takes into account the historical wind speed to achieve a faster response speed; compared with measures 2 and 4, the present invention proposes a K-means algorithm based on the historical wind speed, which can fix the standby power size within a certain period of time, without frequently changing the standby power of the unit, reducing the unit failure rate and improving the system reliability.

[0109] Example 2

[0110] This embodiment provides a system for steady-state distribution and transient utilization of backup power of a multi-terminal wind power system, including a steady-state distribution layer and a transient utilization layer.

[0111] Steady-state allocation layer: obtain the historical wind speed data and real-time load data of each wind turbine in the multi-terminal wind power system, cluster them using a clustering algorithm, and obtain the system total standby power instruction in steady state; according to the rated capacity of each wind turbine, the system total standby power instruction in steady state is distributed among the wind turbines to obtain the standby power instruction of each wind turbine;

[0112] Transient utilization layer: According to the backup power instructions of each wind turbine, the frequency support capability of the wind turbine is evaluated by using a frequency support capability evaluation method based on rotor speed and pitch angle position to obtain an evaluation result; based on the evaluation result, the total additional power required to meet the frequency safety boundary constraint is allocated among the wind turbines to achieve transient utilization of the backup power.

[0113] The rest is the same as in Example 1.

[0114] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0115] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A method for steady-state allocation and transient utilization of reserve power in a multi-terminal wind power system, characterized in that: The following steps are involved: Obtain the historical wind speed data and real-time load data of each wind turbine in the multi-terminal wind power system, perform clustering using a clustering algorithm, and obtain the system total standby power command in steady state; According to the rated capacity of each wind turbine, the total standby power command of the system in the steady state is distributed among the wind turbines to obtain the standby power command of each wind turbine; According to the standby power instructions of each wind turbine, a frequency support capability evaluation method based on rotor speed and pitch angle position is used to evaluate the frequency support capability of the wind turbine to obtain an evaluation result; Based on the evaluation results, the total additional power required to meet the frequency safety boundary constraint is distributed among the wind turbines to achieve transient utilization of the reserve power.

2. A method for steady-state allocation and transient utilization of reserve power in a multi-terminal wind power system according to claim 1, characterized in that: The step of obtaining the system total standby power instruction in steady state comprises: The maximum power of the wind turbine in each time period under the MPPT mode is calculated based on the historical wind speed data of each wind turbine, and the total maximum power of the system in each time period is further obtained, wherein the calculation expression of the maximum power is: Where P MPPT is the maximum power value of the fan, ρ is the air density, R is the radius of the fan blade, C pmax is the maximum wind energy utilization coefficient, v w is the wind speed; Based on the total maximum power of the system in each time period and the real-time load data, a comparison is performed to obtain the system power surplus in each time period; The system power surplus of each time period is used as a data set of the K-means algorithm to cluster the power surplus points, obtain the cluster centers and the corresponding power surpluses, and further obtain the total standby power instruction of the system in steady state.

3. A method for steady-state allocation and transient utilization of reserve power in a multi-terminal wind power system according to claim 2, characterized in that: The steps of clustering using the K-means algorithm include: (1) Randomly select K power surplus points as initial cluster centers; (2) Calculate the Euclidean distance between each power surplus point and each initial cluster center, and assign each power surplus point to the cluster center closest to it, where the calculation expression of the Euclidean distance is: Where X is the data object, i.e., the power surplus point, C i is the i-th cluster center, m is the dimension of the data object, X j , C ij X, C i The jth attribute value of is the time value and power corresponding to the power surplus point, and d is the Euclidean distance; (3) Each cluster center and the allocated power surplus point are regarded as a cluster. Each time a power surplus point is allocated, the cluster center of the cluster is recalculated based on the average value of the existing power surplus points. (4) Calculate the sum of the squares of the distances between the new cluster center and the previous cluster center, and determine whether the sum of the squares of the distances is less than a set value. If so, stop the iteration and obtain each cluster center and the corresponding power surplus. If not, repeat steps (2)-(4) until the iteration stops.

4. A method for steady-state allocation and transient utilization of reserve power in a multi-terminal wind power system according to claim 1, characterized in that: The expression of the reserve power steady-state allocation is: Where P res,i is the standby power command assigned to the i-th wind turbine, n is the total number of wind turbines, P rated,i is the rated power of the i-th fan, P res It is the total standby power command of the system when the system is in steady state.

5. A method for steady-state allocation and transient utilization of reserve power in a multi-terminal wind power system according to claim 1, characterized in that: The step of performing steady-state allocation of standby power also includes: A steady-state power compensation coefficient is applied to each wind turbine to compensate for the imbalance between the generated power and the load power, wherein the expression of the steady-state power compensation coefficient is: In the formula, k m，i is the steady-state power compensation coefficient of the i-th wind turbine, k0 represents the corresponding system power droop coefficient required when the system frequency deviation fluctuates to the safety boundary, n represents the number of wind turbines, ω r Indicates the speed, the subscript 0 indicates the speed before the disturbance, the subscript min / max indicates the minimum / maximum speed, P res,i The reserve power command assigned to the i-th wind turbine, P res It is the total standby power command of the system when the system is in steady state.

6. A method for steady-state allocation and transient utilization of reserve power in a multi-terminal wind power system according to claim 1, characterized in that: The step of obtaining the evaluation result comprises: Based on the standby power instructions of each wind turbine, according to the power standby principle, the wind turbine operation increases the rotor speed to achieve overspeed load reduction to meet the standby power demand. When the rotor speed reaches the maximum value within the allowable range and still cannot meet the standby power demand, the pitch control is activated to coordinate to meet the standby power demand. According to the rotor speed and pitch control of the wind turbine during operation, the frequency support capability of the wind turbine is evaluated and an evaluation result is obtained.

7. A method for steady-state allocation and transient utilization of reserve power in a multi-terminal wind power system according to claim 6, characterized in that: The evaluated expression is: In the formula, G e represents the frequency support capability of the wind turbine, β represents the pitch angle, and β min Indicates the minimum allowable value of the pitch angle, β max Indicates the maximum allowable value of the pitch angle, ω r Indicates the speed. The subscript 0 indicates the speed before the disturbance, and the subscript min / max indicates the minimum / maximum speed.

8. A method for steady-state allocation and transient utilization of reserve power in a multi-terminal wind power system according to claim 1, characterized in that: The steps of realizing transient utilization of standby power include: According to the evaluation results, the primary frequency modulation coefficient is set based on the total additional power required to meet the frequency safety boundary constraint, so that the wind turbine can cope with the frequency disturbance event; Based on the primary frequency modulation coefficient, the additional power supported by the transient frequency of the wind turbine is calculated to achieve transient utilization.

9. A method for steady-state allocation and transient utilization of reserve power in a multi-terminal wind power system according to claim 8, characterized in that: The calculation expression of the additional power supported by the transient frequency of the wind turbine is: ΔP PFC,i =-k PFC,i ·(f-f0) Where ΔP PFC,i represents the additional power of the primary frequency regulation control of the i-th fan, k PFC,i represents the primary frequency modulation coefficient of the i-th wind turbine, f is the real-time grid frequency, f0 is the rated frequency, k0 represents the corresponding system power droop coefficient when the system frequency deviation fluctuates to the safety boundary, n represents the number of wind turbines, G e,i Represents the frequency support capacity of the i-th fan.

10. A system for steady-state distribution and transient utilization of reserve power in a multi-terminal wind power system, characterized in that: include: Steady-state allocation layer: obtain the historical wind speed data and real-time load data of each wind turbine in the multi-terminal wind power system, cluster them using a clustering algorithm, and obtain the system total standby power instruction in steady state; according to the rated capacity of each wind turbine, the system total standby power instruction in steady state is distributed among the wind turbines to obtain the standby power instruction of each wind turbine; Transient utilization layer: According to the backup power instructions of each wind turbine, the frequency support capability of the wind turbine is evaluated by using a frequency support capability evaluation method based on rotor speed and pitch angle position to obtain an evaluation result; based on the evaluation result, the total additional power required to meet the frequency safety boundary constraint is allocated among the wind turbines to achieve transient utilization of the backup power.

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