A method for setting frequency regulation parameters of wind turbines based on available frequency regulation energy constraints

Abstract

A method for setting frequency regulation parameters of a wind turbine generator set based on available frequency regulation energy constraints relates to the technical field of frequency regulation energy optimization for wind farms, and is used to solve the problem that none of the frequency regulation parameter setting methods for wind turbine generator sets have established a coupling relationship between the frequency regulation parameters and the available frequency regulation energy behind them, and cannot reflect the actual frequency regulation capability that the wind turbine generator set can bear. It includes (1) evaluating the available frequency regulation energy of wind power in the entire network; and (2) optimizing the frequency regulation parameters of wind power in the power grid. The wind power frequency regulation parameter optimization method proposed in this patent establishes a coupling relationship with the frequency regulation capability of wind power in the entire network. Making full use of the frequency regulation energy to improve the system frequency response, while avoiding the risk of wind turbine generator speed exceeding the limit, can effectively reflect the actual frequency regulation capability of the wind turbine generator set.

Description

Technical Field

[0001] The invention relates to the technical field of wind farm station frequency regulation energy optimization, and in particular to a method for setting frequency regulation parameters of a wind turbine generator set based on available frequency regulation energy constraints. Background Art

[0002] In recent years, the penetration rate of wind and solar power generation has gradually increased. Since renewable energy generation is connected to the power system through power electronic equipment, it does not have the inertia and primary frequency regulation capability of traditional synchronous machines under conventional control strategies. As the proportion of renewable energy generation increases, the system inertia level and frequency regulation response capability will decrease, and the frequency safety characteristics will deteriorate.

[0003] The currently widely used strategies for wind turbines to participate in frequency regulation include adding a power loop to the rotor-side inverter control, introducing virtual inertia control, droop control, or a combination of the two to simulate the frequency regulation response process of the synchronous machine. Its operating modes include load reduction operation and non-load reduction operation. Load reduction operation abandons the maximum capture of wind energy, allowing the wind turbine to maintain a certain level of reserve capacity to reduce power generation efficiency. Regarding how to set the frequency control parameters of wind turbines, the literature [J. Vande Vyver, JDM De Kooning, B. Meersman, L. Vandevelde and TLVandoorn, "Droop Control as an Alternative Inertial Response Strategy for the Synthetic Inertia on Wind Turbines," in IEEE Transactions on Power Systems, vol. 31, no. 2, pp. 1129-1138, March 2016.] and [J. Morren, S. Haan, WL Kling and JAFerreira, "Windturbines emulating inertia and supporting primary frequency control", IEEE Trans. Power Syst., vol. 21, no. 1, pp. 433-434, Feb. 2006.] proposed that fixed wind turbine virtual inertia and droop gain parameters participate in frequency modulation. However, the energy source of wind turbine frequency modulation is mainly the blade kinetic energy stored in the wind turbine, and its size is affected by the wind speed at the height of the wind turbine hub. The fixed frequency modulation parameters ignore the coupling relationship with the kinetic energy of the rotor behind. If the parameters are too large, the wind turbine speed will exceed the limit under low wind speed operation conditions. If the parameters are too small, the wind turbine cannot fully participate in frequency modulation under high wind speed operation conditions. Therefore, the fixed frequency modulation parameters cannot adapt to the operating conditions of wind turbines under different wind speeds. For this reason, some studies have proposed variable parameter wind power frequency modulation control strategies to improve wind turbine control and stability. The literature [M. Garmroodi, G. and DJ Hill,"Frequency support from wind turbine generators with a time-variable droop characteristic",IEEE Trans. Sustain. Energy, vol. 9, no. 2, pp. 676-684, April 2018.] and [Y.-L. Hu and Y.-K. Wu,"Approximation to Frequency Control Capability of a DFIG-Based Wind Farm Using a Simple Linear Gain Droop Control," in IEEE Transactions on Industry Applications, vol. 55, no. 3, pp. 2300-2309, May-June 2019.] proposed a linear gain droop control strategy considering the kinetic energy of the wind turbine rotor. Reference

[14] proposed setting the virtual inertia and droop control parameters as functions of the wind turbine speed. Reference [M. Hwang, E. Muljadi, J. W Park, P. Srensen, and Y. C. Kang, “Dynamic droop–based inertial control of a doubly-fed induction generator,”IEEE Trans. Sustain. Energy, vol. 7, no. 3, pp. 924–933, Jul. 2016.] and [M. Hwang, E. Muljadi, G. Jang, and Y C Kang, “Disturbance-adaptive short-term frequency support of aDFIG associated with the variable gain based on the ROCOF and rotor speed,” IEEE Trans. Power Syst., vol. 32, no. 3, pp. 1873–1881, May 2017.] proposed setting the wind turbine droop control parameters as a function that considers the dynamics of the frequency change rate. Compared with the fixed parameter setting method, variable parameter frequency regulation improves the adaptability of wind turbines to different operating conditions and avoids the risk of wind turbine instability. The wind turbine frequency regulation parameter setting methods proposed in the above studies have not established the coupling relationship between the frequency regulation parameters and the available frequency regulation energy behind them, and cannot reflect the actual frequency regulation capacity that the wind turbine can bear. Summary of the invention

[0004] The purpose of the present invention is to provide a method for setting frequency modulation parameters of a wind turbine generator set based on available frequency modulation energy constraints, so as to solve the problem that the frequency modulation parameter setting methods of the wind turbine generator set fail to establish a coupling relationship between the frequency modulation parameters and the available frequency modulation energy behind them, and fail to reflect the actual frequency modulation capacity that the wind turbine generator set can bear.

[0005] The technical solution adopted by the present invention to solve the technical problem is: a method for setting frequency modulation parameters of a wind turbine generator set based on available frequency modulation energy constraints, comprising the following steps:

[0006] 1. Evaluate the available frequency regulation energy of wind power in the whole grid

[0007] S1.1 Use the following formula to calculate the rotor kinetic energy ΔE that can be released by the wind turbine k0

[0008] ΔE k0 =0.5J(w r 2 -w min 2 )

[0009] Among them, w r is the fan speed, w min is the minimum speed of the wind turbine, J is the inherent moment of inertia of the wind turbine;

[0010] S1.2 Calculate the mechanical energy loss ΔE of the wind turbine using the following formula m

[0011]

[0012] Among them, T is the time for the wind turbine to participate in frequency modulation, P0 is the mechanical power at the initial moment of frequency modulation, ρ is the air density, A is the swept area of ​​the wind turbine blades, v is the current wind speed, C P is the wind energy utilization coefficient, λ0 is the tip speed ratio at the initial moment of frequency modulation, w r0 is the speed at the initial moment of frequency modulation, β is the pitch angle;

[0013] S1.3 Calculate the net released rotor kinetic energy ΔE of the wind turbine using the following formula k

[0014] ΔE k =ΔE k0 -ΔE m ;

[0015] S1.4 Use the following formula to calculate the available frequency regulation energy of wind power in the whole grid

[0016]

[0017] Among them, M is the number of wind turbines in the wind farm, and v is the predicted wind speed;

[0018] 2. Optimize wind power frequency regulation parameters in the power grid

[0019] S2.1 Establishment of wind power frequency regulation parameter optimization model for power grid

[0020]

[0021] Where Δf nadir1 is the lowest frequency point after the disturbance occurs, Δf st is the steady-state frequency point after disturbance, λ is the weight coefficient, kp is the wind power virtual inertia coefficient, and kd is the droop coefficient;

[0022] S2.2 Use the following formula to calculate the energy of wind power participating in frequency regulation in the power grid

[0023]

[0024] Among them, T is the time when wind power participates in frequency regulation, η is the wind power penetration rate, and Δf is the frequency offset;

[0025] S2.3 Wind farm frequency regulation parameter setting and single machine control implementation

[0026] Assume that the frequency regulation parameters of each wind farm are standardized based on the system capacity as the reference value S SB , the wind power frequency regulation energy can be expressed by the energy aggregation of each wind farm:

[0027]

[0028] The equivalent frequency modulation parameters of each wind farm are calculated using the following formula:

[0029]

[0030] Among them, ΔE kj is the frequency regulation energy of each wind farm, S B is the capacity of each wind farm, S SB =∑S B .

[0031] Furthermore, according to the wind turbine output power, the blade operating conditions are divided into a starting area, a maximum power point tracking (MPPT) area, a constant speed area, and a constant power area;

[0032] In the start-up area, the wind turbine is connected to the grid and its output power is 0, so it cannot participate in frequency regulation.

[0033] In the constant power area, the wind speed exceeds the rated wind speed, and the fan output power reaches the rated value and no longer increases. At this time, the rotor speed is the maximum, and the power increment of the fan participating in the frequency regulation depends on the limit power.

[0034] In the MPPT area, the wind energy utilization coefficient is kept optimal to achieve maximum wind energy tracking control, and the tip speed ratio is the optimal λ opt , according to the definition of tip speed ratio, the fan speed ω r It is expressed as: v is the current wind speed, r is the radius of the fan blade;

[0035] In the constant speed area, the fan speed changes little with the wind speed, but the fan capture power shows an upward trend. The rotor speed can be expressed as a linear function of the wind speed: Among them, ω max is the maximum speed of the fan rotor, ω1 is the initial speed when entering the constant speed zone, v n is the rated wind speed, v1 is the lower limit of wind speed in the constant speed zone;

[0036] Therefore, the wind turbine can release the rotor kinetic energy ΔE k0 It is converted into a function of wind speed for calculation, that is,

[0037]

[0038] Furthermore, the calculation formula for the mechanical energy loss of a wind turbine is:

[0039]

[0040] Among them, T is the time for the wind turbine to participate in frequency modulation, T = 30s; P0 is the mechanical power at the initial moment of frequency modulation, λ0 is the tip speed ratio at the initial moment of frequency modulation, W ro is the speed at the initial moment of frequency modulation.

[0041] Furthermore, taking the lowest frequency drop point and steady-state frequency as optimization targets, a wind power frequency regulation parameter optimization model based on the SFR model is established to achieve the optimal allocation of wind power frequency regulation energy in the inertial response and primary frequency regulation links.

[0042] Furthermore, the wind turbines and synchronous machines in the power grid are dynamically aggregated into a single unit, and a power grid frequency response model is established;

[0043] (1) Establish the system frequency dynamic equation:

[0044]

[0045] Where Δf is the frequency offset, ΔP g is the equivalent synchronous machine power change, ΔP w is the power change of the equivalent wind turbine participating in frequency regulation, ΔP l is the load disturbance, H is the grid equivalent synchronous machine inertia time constant, D is the damping coefficient, and η is the wind power penetration rate;

[0046] Establish the equivalent synchronous generator prime mover mechanical power dynamic equation:

[0047]

[0048] Among them, T g is the equivalent synchronous machine time constant, k g is the power-frequency static characteristic coefficient;

[0049] Establish the equivalent wind turbine frequency modulation output electromagnetic power increment equation:

[0050]

[0051] Among them, k d k is the droop coefficient of wind power participating in frequency regulation in the grid to be determined; p is the virtual inertia coefficient;

[0052] Assume that at time t0 the system experiences a power step disturbance ΔP l , the system frequency time domain analytical expression is expressed as

[0053] in,

[0054]

[0055] According to the time domain expression of frequency, the time domain analytical expression of frequency change rate is as follows:

[0056] Find the extreme point of the above formula and get the analytical expression of the lowest point of system frequency drop:

[0057]

[0058] (2) Upper and lower limits of equivalent fan output:

[0059] P wmin ≤P w ≤P wmax

[0060] (3) Frequency modulation energy constraint

[0061] ΔE w =ΔE k

[0062] The energy formula for wind power participating in frequency regulation of the power grid is obtained by integrating the incremental equation of electromagnetic power output of equivalent wind turbines participating in frequency regulation.

[0063] The beneficial effects of the present invention are as follows: the method of setting wind power frequency regulation parameters from the system level based on the SFR model realizes the setting of frequency regulation parameters at the wind farm level and the single machine level, and the method has guiding significance for power grid dispatching to timely grasp the wind power frequency regulation capability. The wind power frequency regulation parameter optimization method proposed in this patent establishes a coupling relationship with the wind power frequency regulation capability of the entire network. Through simulation example analysis, it is further verified that the wind power frequency regulation parameters under different wind speed conditions can adapt to the time-varying nature of wind speed, make full use of frequency regulation energy to improve the system frequency response, and avoid the risk of wind turbine speed exceeding the limit, which can effectively reflect the actual frequency regulation capability of the wind turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is a schematic diagram of the operating status of the DFIG unit under all wind conditions;

[0065] Figure 2 The block diagram of wind turbine participating in frequency regulation control;

[0066] Figure 3 It is the simulation structure diagram of the two-area system;

[0067] Figure 4a It is the frequency response curve at low wind speed;

[0068] Figure 4b It is the speed response curve diagram under low wind speed;

[0069] Figure 4c It is the electromagnetic power response curve at low wind speed;

[0070] Figure 5a It is the frequency response curve at medium wind speed;

[0071] Figure 5b This is the speed response curve at medium wind speed;

[0072] Figure 5c It is the electromagnetic power response curve at medium wind speed;

[0073] Figure 6 This is the time-varying frequency modulation parameter curve of the wind turbine for 10 minutes. DETAILED DESCRIPTION

[0074] In order to study the parameter setting method that reflects the wind power frequency regulation capability of the power grid, the constraint of the available frequency regulation energy of the wind farm cannot be ignored. The present invention uses the evaluated frequency regulation energy of multiple wind farms in the entire network to propose a method for setting the wind power frequency regulation parameters of the power grid, so that the power grid dispatcher can grasp the actual frequency regulation capability of the wind farm and even the entire power grid in real time. First, a method for evaluating the available frequency regulation energy of wind power in the entire network is proposed. This method analyzes the rotor kinetic energy that can be released by each wind turbine in the wind farm to participate in frequency regulation. Then, based on the evaluation of wind power frequency regulation energy and the SFR model to analyze the system frequency response, a method for optimizing the wind power frequency regulation parameters of the power grid is proposed, and a method for setting the frequency regulation parameters of a single machine layer is proposed to realize the application of the single machine frequency regulation control strategy.

[0075] 1. Evaluation of available frequency regulation energy of wind power in the whole grid considering the operating point deviation

[0076] The energy source for wind turbines to participate in frequency regulation is the kinetic energy of the blade rotor. However, due to the influence of speed limit, it cannot be fully used to provide frequency support. In addition, the release of rotor kinetic energy will cause the operating point of the wind turbine to shift and generate mechanical energy loss. The energy difference between the releasable rotor kinetic energy and the mechanical energy loss is the net release of rotor kinetic energy of the wind turbine.

[0077] Known actual fan speed w r Since the kinetic energy of the blade rotor cannot be fully released, there is a minimum speed limit of W min , the wind turbine blade rotor kinetic energy ΔE is expressed by the available rotor kinetic energy, the available rotor speed change and the inherent moment of inertia J of the wind turbine. k0 :

[0078] ΔE k0 =0.5J(w r 2 -w min 2 ) (1)

[0079] In order to express the blade rotor kinetic energy as a function of wind speed, the rotor speed w under different operating conditions is analyzed. r Relationship with wind speed. According to the fan output power, such as Figure 1 As shown, its operating conditions are divided into a starting area, a maximum power point tracking (MPPT) area, a constant speed area, and a constant power area. In the starting area, the wind turbine realizes grid-connected control, the output power is 0, and it cannot participate in frequency modulation. In the constant power area, the wind speed exceeds the rated wind speed, and the wind turbine output power reaches the rated value and no longer increases. At this time, the rotor speed is the maximum, and the power increment of the wind turbine participating in frequency modulation depends on its limit power. Therefore, the present invention sets the wind turbine to provide a fixed 0.1pu frequency modulation power increment under this condition.

[0080] In the MPPT area, the wind energy utilization coefficient is kept optimal to achieve maximum wind energy tracking control, the pitch angle remains unchanged at 0°, and the tip speed ratio is the optimal λ opt, according to the definition of tip speed ratio, the fan speed ω r It is expressed as: Where r is the radius of the fan blade.

[0081] In the constant speed area, the fan speed changes little with the wind speed, but the fan capture power shows an upward trend. The rotor speed can be expressed as a linear function of the wind speed:

[0082] Based on the above analysis, substituting the above two equations into equation (1), the kinetic energy of the wind turbine blade rotor can be expressed as a function of wind speed:

[0083]

[0084] In the formula, ω max is the maximum speed of the fan rotor, ω1 is the initial speed when entering the constant speed zone, v n is the rated wind speed, v1 is the lower limit of the wind speed in the constant speed zone; v is the current wind speed.

[0085] The mechanical power expression of the fan is known:

[0086]

[0087] Where P m is the mechanical power captured by the fan, ρ is the air density, C P is the wind energy utilization coefficient, β is the pitch angle, and A is the swept area of ​​the wind turbine blades.

[0088] Since the frequency modulation time is short, it can be assumed that the wind speed remains unchanged during the frequency modulation period. The released blade rotor kinetic energy provides frequency modulation support energy on the one hand, and on the other hand, it causes the rotor speed to drop. The blade tip speed ratio λ decreases with the speed change, and the wind energy utilization coefficient decreases. Therefore, the mechanical power captured by the wind turbine decreases. This part of the energy loss cannot be ignored when evaluating the wind power frequency modulation energy. Therefore, the wind turbine net releases the rotor kinetic energy ΔE k It is expressed as follows, where ΔE m is the mechanical energy loss:

[0089] ΔE k =ΔE k0 -ΔE m (4)

[0090] To calculate the mechanical energy loss ΔE m Assuming that the wind power participation frequency regulation time is T, the mechanical power change is integrated to obtain Where P m (t) Wind energy utilization coefficient C P Influence, when the pitch angle β remains unchanged, C PIt is a function of λ(t). Assuming that λ(t) changes uniformly during frequency modulation and is linearized, the mechanical energy loss of the wind turbine can be expressed as:

[0091]

[0092] In the formula, the wind turbine participating in frequency modulation time T is set to 30s; P0 is the mechanical power at the initial moment of frequency modulation, λ0 is the tip speed ratio at the initial moment of frequency modulation, and w r0 is the speed at the initial moment of frequency modulation.

[0093] Based on the ultra-short-term wind speed forecast information of the wind farm, the net rotor kinetic energy that can be released by each wind turbine in the wind farm is evaluated using formulas (2)-(5), and the available frequency modulation energy of the wind farm is obtained by superposition, which is expressed as follows:

[0094]

[0095] Where M is the number of wind turbines in the wind farm, and v is the predicted wind speed. This can further evaluate the available frequency regulation energy of multiple wind farms in the entire network.

[0096] 2. Optimization of wind power frequency regulation parameters in power grid and setting of field-machine layered frequency regulation parameters

[0097] When the wind turbine participates in system frequency regulation through comprehensive inertia control in non-load reduction operation mode, if the control parameters of the two frequency regulation links are set subjectively, when the parameters are too large, the wind power cannot actually provide the corresponding energy support, and when the parameters are too small, it will cause waste of wind power frequency regulation energy.

[0098] In order to solve the above parameter setting problems, the relationship between frequency regulation parameters and available frequency regulation energy is established. The SFR aggregation model is used to analyze the impact of wind power frequency regulation parameters on system frequency response from the system level. According to the above evaluation, the available wind power frequency regulation energy of the whole network is used as the energy constraint. The optimization method is used to achieve the reasonable allocation of wind power frequency regulation energy in the two frequency regulation links, and the equivalent wind power frequency regulation parameters of the power grid are solved. Therefore, the power grid dispatcher can grasp the actual frequency regulation capability of wind power in the power grid and further realize the parameter setting of wind farm layer and single machine layer.

[0099] 2.1 Establishment of wind power frequency regulation parameter optimization model for power grid

[0100] In order to establish the coupling relationship between wind power frequency regulation energy and the parameters of the inertial response link and the primary frequency regulation link, based on the above-assessed available frequency regulation energy of wind power in the whole network, considering the maximum power disturbance of the power grid N-1, the lowest point of frequency drop and steady-state frequency are selected as the optimization targets, and a wind power frequency regulation parameter optimization model based on the SFR model is established to achieve the optimal allocation of wind power frequency regulation energy in the inertial response and primary frequency regulation links, and obtain the optimal frequency regulation parameters.

[0101] There are two optimization control objectives: maximum frequency deviation and minimum frequency steady-state deviation. Explanation of setting optimization control objectives:

[0102] 1) To ensure the stable operation of the power system, the system frequency should always be kept within a safe range. When a frequency disturbance occurs, if the system frequency response is lower than a certain threshold, it will cause low-frequency load reduction and cause frequency safety. Therefore, it is considered to increase the lowest frequency point after the disturbance.

[0103] 2) The system steady-state frequency is required not to exceed ±0.2Hz during load disturbance, so consider increasing the steady-state value of the frequency during the frequency modulation process.

[0104] The objective function is expressed as follows:

[0105]

[0106] Where Δf nadir1 is the lowest frequency point after the disturbance occurs, Δf st Here, improving the lowest frequency point of the system is the main optimization goal, and improving the steady-state frequency point is the auxiliary optimization goal. Therefore, the weight coefficient λ is introduced, and the decision quantity is the wind power virtual inertia coefficient kp and the droop coefficient kd.

[0107] 2.2 Constraints and Solutions

[0108] In order to obtain the wind power frequency regulation parameters of the power grid to characterize the wind power frequency regulation capability of the entire grid, based on the traditional SFR model, the wind turbines and synchronous machines in the power grid are dynamically aggregated into a single unit, and a power grid frequency response model is established.

[0109] (1) Establish the system frequency dynamic equation:

[0110]

[0111] Where Δf is the frequency offset; ΔP g is the equivalent synchronous machine power change; ΔP w is the power change of equivalent wind turbine participating in frequency regulation; ΔP l is the load disturbance; H is the grid equivalent synchronous machine inertia time constant, and D is the damping coefficient.

[0112] Dynamic equation of mechanical power of equivalent synchronous generator prime mover:

[0113]

[0114] Where, T g is the equivalent synchronous machine time constant; k g is the power frequency static characteristic coefficient; η is the wind power penetration rate.

[0115] The incremental equation of electromagnetic power output when the equivalent fan participates in frequency modulation is:

[0116]

[0117] Where kd is the droop coefficient of wind power participating in frequency regulation of the grid to be determined; kp is the virtual inertia coefficient.

[0118] Assume that at time t0 the system experiences a power step disturbance ΔP l , combined with equations (6)-(8), the system frequency time domain analytical expression can be expressed as

[0119] in,

[0120]

[0121] By observing formula (9), it is found that the system frequency dynamics is a sinusoidal damping expression related to the wind power penetration rate η and wind power frequency regulation parameters.

[0122] According to the time domain expression of frequency, the time domain analytical expression of frequency change rate is as follows:

[0123] By finding the extreme point of equation (11), we can get the analytical expression of the lowest point of system frequency drop:

[0124]

[0125] (2) Upper and lower limits of equivalent fan output:

[0126] P wmin ≤P w ≤P wmax (12)

[0127] (3) Frequency modulation energy constraint

[0128] ΔE w =ΔE k (13)

[0129] Among them, ΔE k It is the frequency regulation energy available for wind power in the entire grid.

[0130] The energy of wind power participating in frequency regulation in the power grid is obtained by integrating equation (8), which is expressed as equation (14). The integral of the first part is the frequency regulation energy of wind power participating in inertia response, and the second part is the energy of wind power participating in primary frequency regulation.

[0131]

[0132] In the formula, T is the time for wind power to participate in frequency regulation. Since the energy support of the speed recovery stage after the wind turbine exits frequency regulation mainly depends on the fuel response on the synchronous machine boiler side, and the fuel response time is relatively slow, in order to ensure the energy supply connection within the frequency regulation time scale, T is set to 30s. ΔE k In order to evaluate the available frequency regulation energy of wind power, it is necessary to point out that ΔE k Perform normalization processing.

[0133] From equations (13) and (14), we can see that, subject to the wind power frequency regulation energy constraint, the wind power frequency regulation parameter k d , k p They restrict each other and affect the distribution of wind power frequency regulation energy between the two links, which in turn jointly affects the lowest point of frequency drop after the system is disturbed.

[0134] Combined with the constraints of formulas (6)-(14), based on the N-1 principle of the power grid, the particle swarm optimization method is used to obtain the optimal results of wind power frequency regulation parameters kd and kp under the maximum disturbance of the power grid. The frequency regulation parameters obtained by optimization are the optimal parameter boundaries, which reflect the actual frequency regulation capability of wind power in the power grid to cope with the maximum power disturbance of the power grid N-1.

[0135] 2.3 Wind farm frequency regulation parameter setting and single machine control implementation

[0136] Based on the above analysis, the wind power frequency regulation parameters of the power grid are obtained by optimizing the single-machine model based on the aggregation of each wind farm, which represents the frequency regulation capability of the whole network wind energy. In order to realize the frequency regulation parameter setting of the wind farm layer and the single machine layer, this section first calculates the frequency regulation energy weight ratio of each wind farm in the power grid. According to formula (14), it is assumed that the frequency regulation parameters of each wind farm are standardized based on the system capacity as the reference value S SB , the wind power frequency regulation energy can be expressed by the energy aggregation of each wind farm:

[0137]

[0138] Where ΔE kj is the frequency regulation energy of each wind farm, S B is the capacity of each wind farm; S SB =∑S B .

[0139] According to equations (14) and (15), the equivalent frequency modulation parameters of each wind farm can be expressed as follows:

[0140]

[0141] like Figure 2As shown, when the wind farm dispatching layer obtains the frequency regulation parameters of the wind farm, the frequency regulation parameters of each wind turbine in the farm can be obtained based on the frequency regulation energy weight ratio of each wind turbine, thereby realizing the frequency regulation control of the wind turbine set.

[0142] 3. Example Analysis

[0143] In order to verify the above-mentioned optimization frequency modulation parameter setting method, this paper builds the following in MATLAB / simulink: Figure 3 The simulation model of the two-region system is shown in Figure 1. The installed capacity of the synchronous generator is 100MW, and the export voltage is 13.8kV; the wind farm contains 10 double-fed wind turbines with a rated capacity of 1.5MW and an export voltage of 0.575Kv; the initial load of the system is 97MW, and the reference frequency is 50Hz; the operating parameters of the synchronous machine and the double-fed wind turbine are shown in Table 1. To simplify the problem, the simulation uses a single wind turbine operation mode to replace the wind farm. After the system is running stably, the frequency disturbance time is simulated by a sudden increase in load. The time T for the wind turbine to participate in frequency regulation is 30s.

[0144] Table 1 Synchronous machine and wind turbine operating parameters

[0145]

[0146] 3.1 Analysis of FM effect

[0147] In order to verify the proposed method for setting the frequency regulation parameters of wind turbines, the following simulation examples are set to compare and analyze the frequency regulation effects under different wind speed conditions: Example 1: the frequency regulation parameter optimization method of this patent; Example 2: the fixed frequency regulation parameters of the wind turbine [25, 4] (simulating the regulation coefficient and inertia time constant of the traditional synchronous machine); Example 3: wind power does not participate in frequency regulation.

[0148] 1) Analysis of frequency modulation effect at low wind speed

[0149] When the wind speed is 9m / s, the frequency modulation parameters kp and kd optimized by the patent method are [12.1, 10]. The simulation results are as follows: Figure 4a , Figure 4b and Figure 4c As shown. From the frequency response curve, it can be seen that both Example 1 of the method in this paper and Example 2 of the method using fixed frequency modulation parameters can effectively improve the lowest frequency point, and the fixed parameter method has the best improvement effect. However, in the frequency response process of Example 2, the release of the kinetic energy of the fan rotor cannot support the whole process of frequency modulation. At 15s, the fan speed reaches the minimum allowable lower limit and triggers protection, forcing it to exit the frequency modulation and causing a secondary drop in frequency. This shows that the parameter setting of Example 2 is too large, which does not match the actual frequency modulation capability of the fan, increasing the risk of secondary frequency drop. Compared with Example 2, Example 1 of the method proposed in this paper can more reasonably release the kinetic energy of the fan rotor at low wind speed, participate in the whole process of frequency response, and avoid the secondary drop in frequency caused by triggering the lower limit of speed protection, ensuring a relatively stable recovery of frequency.

[0150] 2) Analysis of frequency modulation effect at medium wind speed

[0151] When the wind speed is 11m / s, the frequency modulation parameters kp and kd optimized by the patent method are [15.67, 10]. The simulation results are as follows: Figure 5a , Figure 5b and Figure 5c The frequency response curve shows that the frequency modulation parameter method of this patent can effectively improve the lowest frequency point and steady-state frequency value after the disturbance, while the traditional fixed frequency modulation parameter setting method avoids the risk of speed over-limit at medium wind speed compared with the speed response curve at low wind speed. However, the lowest frequency point is lower than that of the patent method. This is because the available frequency modulation energy of the wind turbine is not fully utilized, which shows the effectiveness of the frequency modulation parameter setting method of this patent.

[0152] In addition, the optimization method of this patent is used to obtain the time-varying frequency modulation parameter curve of the wind turbine for 10 minutes, such as Figure 6 shown.

[0153] In summary, the participation of wind power in grid frequency regulation can effectively improve the frequency dynamic response after disturbance, reduce the risk of grid frequency exceeding the limit, and improve the frequency safety of the grid. The frequency regulation parameter setting method proposed in this patent can better reflect the frequency regulation capability of wind turbines, and can make full use of the frequency regulation energy of wind turbines, and adapt to the time-varying volatility of wind power frequency regulation energy caused by wind speed changes, and effectively avoid the problem of poor frequency response effect caused by wind turbine speed exceeding the limit and insufficient utilization of frequency regulation energy.

[0154] In response to the problem of frequency regulation parameter setting for wind turbines, this patent proposes a method for setting wind power frequency regulation parameters at the system level based on the SFR model, taking into account the time-varying frequency regulation energy of the wind farm, and realizing the frequency regulation parameter setting at the wind farm level and the single machine level. This method has guiding significance for power grid dispatching to timely grasp the wind power frequency regulation capability. The wind power frequency regulation parameter optimization method proposed in this patent establishes a coupling relationship between it and the wind power frequency regulation capability of the entire network. Through simulation example analysis, it is further verified that the wind power frequency regulation parameters under different wind speed conditions can adapt to the time-varying nature of wind speed, make full use of the frequency regulation energy to improve the system frequency response, and avoid the risk of wind turbine speed exceeding the limit, which can effectively reflect the actual frequency regulation capability of the wind turbine.

Claims

1. A method for setting frequency modulation parameters of a wind turbine generator set based on available frequency modulation energy constraints, characterized in that: The following steps are involved:

1. Evaluate the available frequency regulation energy of wind power in the whole grid S1.1 Use the following formula to calculate the rotor kinetic energy ΔE that can be released by the wind turbine k0 ΔE k0 =0.5J(in r 2 -In min 2 ) Among them, w r is the fan speed, w min is the minimum speed of the wind turbine, J is the inherent moment of inertia of the wind turbine; S1.2 Calculate the mechanical energy loss ΔE of the wind turbine using the following formula m Among them, T is the time for the wind turbine to participate in frequency modulation, P0 is the mechanical power at the initial moment of frequency modulation, ρ is the air density, A is the swept area of ​​the wind turbine blades, v is the current wind speed, C P is the wind energy utilization coefficient, λ0 is the tip speed ratio at the initial moment of frequency modulation, w r0 is the speed at the initial moment of frequency modulation, β is the pitch angle; S1.3 Calculate the net released rotor kinetic energy ΔE of the wind turbine using the following formula k ΔE k =ΔE k0 -ΔE m ; S1.4 Use the following formula to calculate the available frequency regulation energy of wind power in the whole grid Among them, M is the number of wind turbines in the wind farm, and v is the predicted wind speed; 2. Optimize wind power frequency regulation parameters in the power grid S2.1 Establishment of wind power frequency regulation parameter optimization model for power grid Where Δf nadir1 is the lowest frequency point after the disturbance occurs, Δf st is the steady-state frequency point after disturbance, λ is the weight coefficient, kp is the wind power virtual inertia coefficient, and kd is the droop coefficient; S2.2 Use the following formula to calculate the energy of wind power participating in frequency regulation in the power grid Among them, T is the time when wind power participates in frequency regulation, η is the wind power penetration rate, and Δf is the frequency offset; S2.3 Wind farm frequency regulation parameter setting and single machine control implementation Assume that the frequency regulation parameters of each wind farm are standardized based on the system capacity as the reference value S SB , the wind power frequency regulation energy can be expressed by the energy aggregation of each wind farm: The equivalent frequency modulation parameters of each wind farm are calculated using the following formula: Where, ΔE kj is the frequency regulation energy of each wind farm, S B is the capacity of each wind farm, S SB =∑S B ; According to the wind turbine output power, the blade operating conditions are divided into the starting area, the maximum power tracking MPPT area, the constant speed area and the constant power area; In the start-up area, the wind turbine is connected to the grid and its output power is 0, so it cannot participate in frequency regulation. In the constant power area, the wind speed exceeds the rated wind speed, and the fan output power reaches the rated value and no longer increases. At this time, the rotor speed is the maximum, and the power increment of the fan participating in frequency regulation depends on the limit power. In the MPPT area, the wind energy utilization coefficient is kept optimal to achieve maximum wind energy tracking control, and the tip speed ratio is the optimal λ opt , according to the definition of tip speed ratio, the fan speed ω r It is expressed as: v is the current wind speed, r is the radius of the fan blade; In the constant speed area, the fan speed changes little with the wind speed, but the fan capture power shows an upward trend. The rotor speed can be expressed as a linear function of the wind speed: Among them, ω max is the maximum speed of the fan rotor, ω1 is the initial speed when entering the constant speed zone, v n is the rated wind speed, v1 is the lower limit of wind speed in the constant speed zone; The wind turbine can release the rotor kinetic energy ΔE k0 It is converted into a function of wind speed for calculation, that is, The calculation formula of mechanical energy loss of wind turbine is: Among them, T is the time for the wind turbine to participate in frequency modulation, T = 30s; P0 is the mechanical power at the initial moment of frequency modulation, λ0 is the tip speed ratio at the initial moment of frequency modulation, w r0 is the speed at the initial moment of frequency modulation; Taking the lowest frequency drop point and steady-state frequency as optimization targets, a wind power frequency regulation parameter optimization model based on the SFR model is established to achieve the optimal allocation of wind power frequency regulation energy in the two links of inertial response and primary frequency regulation. The wind turbines and synchronous machines in the power grid are dynamically aggregated into a single unit, and a power grid frequency response model is established; (1) Establish the system frequency dynamic equation: Where Δf is the frequency offset, ΔP g is the equivalent synchronous machine power change, ΔP w is the power change of the equivalent wind turbine participating in frequency regulation, ΔP l is the load disturbance, H is the grid equivalent synchronous machine inertia time constant, D is the damping coefficient, and η is the wind power penetration rate; Establish the equivalent synchronous generator prime mover mechanical power dynamic equation: Among them, T g is the equivalent synchronous machine time constant, k g is the power-frequency static characteristic coefficient; Establish the equivalent wind turbine frequency modulation output electromagnetic power increment equation: Among them, k d k is the droop coefficient of wind power participating in frequency regulation in the grid to be determined; p is the virtual inertia coefficient; Assume that at time t0 the system experiences a power step disturbance ΔP l , the system frequency time domain analytical expression is expressed as in, According to the time domain expression of frequency, the time domain analytical expression of frequency change rate is as follows: Find the extreme point of the above formula and get the analytical expression of the lowest point of system frequency drop: (2) Upper and lower limits of equivalent fan output: P wmin ≤P w ≤P wmax (3) Frequency modulation energy constraint ΔE w =ΔE k The energy formula for wind power participating in frequency regulation of the power grid is obtained by integrating the incremental equation of electromagnetic power output of equivalent wind turbines participating in frequency regulation.

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