Wind storage fuzzy control frequency modulation method considering fatigue load of transmission shaft

Abstract

The invention discloses a wind storage fuzzy control frequency modulation method considering a fatigue load of a transmission shaft, and the method comprises the following steps: 1, building a dynamic model of a wind turbine generator set by considering the dynamic characteristics and frequency response behaviors of the wind turbine generator set; 2, analyzing the influence of the primary frequency modulation of the wind turbine generator on the fatigue load of the transmission shaft based on the participation of the wind turbine generator in the primary frequency modulation process; 3, analyzing operation characteristics of the wind turbine generator set under different working conditions, and dividing a generator rotating speed area; and 4, constructing a super capacitor energy storage model, designing a wind storage combined primary frequency modulation control strategy based on fuzzy control according to the operation conditions of the wind turbine generator at different wind speeds, performing frequency response by using super capacitor energy storage, improving the system stability and reducing the fatigue load of the generator. The method provided by the invention is obviously superior to a traditional wind power primary frequency modulation method in the aspects of reducing frequency deviation and reducing fatigue load.

Description

Technical Field

[0001] The invention belongs to the technical field of power system operation control, and relates to a wind storage fuzzy control frequency modulation method considering the fatigue load of a transmission shaft. Background Art

[0002] As the penetration rate of wind power gradually increases, the system inertia decreases and the frequency deviation increases, the difficulty of frequency regulation increases, and the frequency stability of the power system decreases. Most studies use simplified wind turbine models, which do not fully consider the dynamic characteristics and complex frequency response behaviors of wind turbines. There are few studies on the primary frequency regulation capability of wind turbines under dynamic conditions and their impact on system frequency characteristics. At the same time, when wind turbines participate in frequency regulation, the frequency regulation controller will often change the power reference value of the unit to adapt to changes in the grid frequency, which will cause the pitch angle and generator torque of the wind turbine to frequently operate, thereby increasing the fatigue load of the wind turbine, and in severe cases directly reducing the service life of the unit. Since the primary frequency regulation capability of wind turbines is related to wind speed, the randomness of wind speed leads to the limitation of insufficient primary frequency regulation capability and increased fatigue load when only performing primary frequency regulation through wind turbines. Summary of the invention

[0003] In order to solve the problem of aggravated fatigue load of the transmission shaft when a wind turbine performs primary frequency modulation, the present invention provides a wind storage fuzzy control frequency modulation method taking into account the fatigue load of the transmission shaft.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] A wind storage fuzzy control frequency modulation method considering the fatigue load of the transmission shaft comprises the following steps:

[0006] Step 1: Considering the dynamic characteristics and frequency response behavior of the wind turbine, the following wind turbine dynamic model is constructed:

[0007] Aerodynamic torque model:

[0008]

[0009] Drive shaft model:

[0010]

[0011] Generator torque model:

[0012] P g =T g ω g ;

[0013] Where R is the blade radius; ρ is the air density; v is the wind speed; C p is the wind energy utilization coefficient; ωr is the rotor speed; J r , J g are the rotational inertia of the rotor and the generator respectively; T g is the electromagnetic torque of the generator; T s is the transmission shaft torque; ω g is the generator speed; K s is the rigidity coefficient of the transmission shaft; D s is the mutual damping coefficient of the transmission shaft; n g is the gearbox speed ratio; P g Output power for the generator;

[0014] Step 2: Based on the wind turbine participating in the primary frequency modulation process, analyze the impact of the wind turbine primary frequency modulation on the fatigue load of the transmission shaft. The specific steps are as follows:

[0015] Step 21: As the system frequency fluctuates, the wind turbine output active power changes, and the frequency characteristic formula of the unit is expressed as:

[0016]

[0017] In the formula, K is the primary frequency modulation coefficient of the generator; ΔP is the change in the active power output of the generator; Δf is the frequency change;

[0018] Step 2: Considering the generator electromagnetic torque T g , Active power P g and generator speed ω g The functional relationship between g =T g ×ω g , the frequency characteristic formula of the unit is rewritten as:

[0019]

[0020] In the formula, ΔT g K is the change of electromagnetic torque of the generator; P is the frequency modulation coefficient; Δω g is the change in generator speed; Δf is the change in frequency;

[0021] Step 2: According to the transmission shaft model formula, the linearization of the transmission shaft torque is:

[0022]

[0023] In the formula, J t is the equivalent inertia;

[0024] Step 3: Analyze the operating characteristics of wind turbines under different working conditions and divide the generator speed zones:

[0025] Region I: Constant speed operation area, ω in ≤ω<ω opt,min , ω is the generator speed of the wind turbine, ω in is the generator grid-connected cut-in speed, ω opt,min The cut-in speed for the generator with the best tip speed ratio;

[0026] Region II: Maximum Power Tracking Region, ω opt,min ≤ω<ω opt,max ,ω opt,max The cut-out speed for the generator's optimum tip speed ratio section;

[0027] Region III: Constant speed control area, ω opt,max ≤ω<ω N ,ω N is the rated speed of the generator;

[0028] Region IV: Constant power region, ω N ≤ω<ω out ,ω out Cut out the speed for the generator;

[0029] Step 4: Construct a supercapacitor energy storage model. According to the operating conditions of wind turbines at different wind speeds, design a wind-storage combined primary frequency modulation control strategy based on fuzzy control. Use supercapacitor energy storage for frequency response, improve system stability and reduce unit fatigue load. The specific steps are as follows:

[0030] Step 41: Build a supercapacitor energy storage model:

[0031] When constructing the supercapacitor energy storage model, it is equivalent to a circuit model of parallel resistors and capacitors. In order to quickly stabilize the voltage, a voltage feedback loop is introduced. The relationship between the supercapacitor current change rate and the reference power and voltage change is shown in the following formula:

[0032]

[0033] In the formula, ΔI d is the current change; ΔE d is the voltage change; T c is the time constant; P sc-ref is the reference power of the supercapacitor; K P is the power control gain; K V is the voltage control gain;

[0034] The actual output of a supercapacitor is shown below:

[0035] P sc (s)=(ΔE d +E d0 )ΔI d

[0036] Among them, P s (s) represents the actual output power of the supercapacitor; E d0 Represents the initial voltage of the supercapacitor;

[0037] Supercapacitor energy storage is connected to the grid through a power conversion system during the grid connection process. When supercapacitor energy storage is connected to the grid, the energy conversion efficiency of the capacitor itself and the energy conversion efficiency of the power conversion system are comprehensively considered. The mathematical model of energy storage charging and discharging is shown in the following formula:

[0038]

[0039] Where: SOC(k) is the SOC of energy storage at time k; P sc (k) is the power instruction of energy storage at time k; P b (k)<0 means the energy storage is in charging state, P sc (k)>0 means the energy storage is in the discharge state; E reted is the rated capacity of the capacitor energy storage system;

[0040] Step 4.2: Design a wind-storage combined primary frequency regulation control strategy based on fuzzy control

[0041] On the basis of generator speed partitioning, fuzzy controllers FLC1 and FLC2 are designed, where FLC1 is used to determine the total active power of the short-term frequency response of the wind storage system, and FLC2 is used to derive the participation coefficient of the wind turbine frequency regulation. During the frequency regulation process, the output power of the supercapacitor system in the frequency response process is jointly determined by FLC1 and FLC2.

[0042] For FLC1: Input variables are frequency deviation Δf and generator speed ω g , the output variable is the total active power output ΔP of the wind-storage system in the short-term frequency response sum ; Design 7 fuzzy sets: NL (negative large), NM (negative medium), NS (negative small), M (medium), PS (positive small), PM (positive medium) and PL (positive large) to describe Δf and ΔP sum The state of the generator is designed, and 7 fuzzy sets are designed to describe the generator speed ω: VS (minimum), MS (small), S (small), M (medium), L (large), ML (large) and VL (maximum). g Status;

[0043] The fuzzy logic control rule of FLC1 is established as follows: When Δf is negative, the output ΔP sum is a positive value; when Δf is positive, the output ΔP sum is a negative value; and when the absolute value of Δf is larger, the output ΔP sum The larger the value, the smaller the absolute value of Δf is.sum Smaller;

[0044] For FLC2: the input variable is the generator speed ω g And the output power P w , the output variable is the wind turbine participating frequency modulation coefficient a, and the fuzzy set of FLC2 has the same meaning as FLC1;

[0045] According to the generator speed division in step 3, the basic fuzzy rule of FLC2 is as follows: w Larger g When it is larger, the frequency modulation coefficient a is larger; when ω g When P is small, the kinetic energy stored in DFIG is not enough to support the frequency, and the frequency modulation coefficient a should be small. w When it is very large, the DFIG output power reaches the rated value. If the DFIG releases additional energy, the power may exceed the limit, so the frequency modulation coefficient a is very small;

[0046] The output power of wind turbines in the wind-storage combined system that can provide frequency regulation is shown in the following formula:

[0047] ΔP w =a·ΔP sum

[0048] Where ΔP w The power change requirements for wind turbine frequency regulation;

[0049] The output power of the supercapacitor is shown as follows:

[0050] P sc-ref =(1-a)·ΔP sum

[0051] Step 43. By applying fuzzy controllers FLC1 and FLC2 in the wind storage system, the DFIG gives priority to the supercapacitor for frequency response according to its current operating status, and determines the degree of participation in the unit frequency regulation through real-time frequency deviation and generator speed, avoiding excessive participation of the DFIG in the frequency regulation process. The total active output increment of the combined system is determined in real time by FLC1.

[0052] Compared with the prior art, the present invention has the following advantages:

[0053] The present invention fully considers the dynamic characteristics and frequency response behavior of the wind turbine set, establishes a wind turbine model, analyzes the influence of the primary frequency regulation behavior on the fatigue load of the transmission shaft, and forms a wind-storage combined primary frequency regulation control strategy based on fuzzy control according to the operating conditions of the wind turbine set at different wind speeds, establishes a supercapacitor energy storage model, and the method of the present invention is significantly superior to the traditional wind power primary frequency regulation method in reducing frequency deviation and reducing fatigue load. The minimum value of the traditional wind power primary frequency regulation method is -0.0069pu, and the fatigue load of the transmission shaft is 925469.64Nm. The minimum frequency value of the present invention is -0.0054pu, which is reduced by 21.74% compared with the traditional method, and the fatigue load of the transmission shaft is 654648.44Nm, which is reduced by 29.26%. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a flow chart of the wind storage fuzzy control frequency modulation method considering the fatigue load of the transmission shaft;

[0055] Figure 2 is the wind turbine speed-torque curve;

[0056] Figure 3 is the fuzzy logic controller FLC1;

[0057] Figure 4 It is the fuzzy logic controller FLC2. DETAILED DESCRIPTION

[0058] The technical solution of the present invention is further described below in conjunction with the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

[0059] The present invention provides a wind storage fuzzy control frequency modulation method considering the fatigue load of the transmission shaft, such as Figure 1 As shown, the method comprises the following steps:

[0060] Step 1: Consider the dynamic characteristics and frequency response behavior of the wind turbine and build a frequency response model of the wind turbine.

[0061] As the proportion of wind power increases, its own dynamic changes caused by participating in frequency modulation and its impact on system frequency cannot be ignored. A frequency response model of wind turbines considering dynamic characteristics is established. When wind turbines are manufactured, mechanical power and input wind speed generally satisfy a certain mathematical relationship. An empirical formula is usually used to describe the aerodynamic system characteristics of wind turbines. Aerodynamic torque refers to the torque generated by wind acting on the blades. Aerodynamic torque is:

[0062]

[0063] Where R is the blade radius (m); ρ is the air density (kg / m 3 );v is wind speed (m / s); C p is the wind energy utilization coefficient, which is related to λ and β; λ is the tip speed ratio, β is the pitch angle, which can be obtained by λ=ω r R / v calculation; ω r is the rotor speed (rad / s).

[0064] The mechanical transmission structure of the doubly-fed wind turbine generator system includes a multi-stage transmission structure such as a low-speed mechanical transmission shaft, a gearbox, a high-speed mechanical transmission shaft, and an asynchronous induction generator. The transmission shaft model adopts a two-mass block model, and the mathematical expression is shown in equations (2)-(4):

[0065]

[0066] In the formula, J r , J g The moments of inertia of the rotor and generator are (kg·m 2 );T g is the electromagnetic torque of the generator (Nm); T s is the transmission shaft torque (Nm); ω g is the generator speed (rad / s); K s is the rigidity coefficient of the transmission shaft (Nm / rad); D s is the mutual damping coefficient of the transmission shaft (Nm·s / rad); n g is the gearbox speed ratio; the subscript s represents the word shaft, and is the integral in the formula.

[0067] The generator is a device that converts mechanical energy into electrical energy. Vector control is usually used to ensure its fast and accurate response. Only the active control link of the unit is considered. Therefore, the generator torque model can be expressed by the following formula:

[0068] P g =T g ω g (5)

[0069] Where P g Output power for the generator.

[0070] Step 2: Based on the wind turbine participating in the primary frequency modulation process, analyze the impact of the wind turbine primary frequency modulation on the fatigue load of the transmission shaft.

[0071] The primary frequency regulation capability of a wind turbine refers to the ability of a wind turbine to respond to changes in grid frequency in a short period of time and maintain grid frequency stability by adjusting output power. As the system frequency fluctuates, the wind turbine output active power changes, and the frequency characteristic formula of the unit can be expressed as:

[0072]

[0073] Where K is the primary frequency modulation coefficient of the generator; ΔP is the change in the active power output of the generator (W); and Δf is the frequency change (Hz).

[0074] Considering the generator electromagnetic torque T g , Active power P g and generator speed ω g The functional relationship between them, formula (6) can be rewritten as:

[0075]

[0076] Where, ΔT g is the change of electromagnetic torque of the generator (Nm); K P is the frequency modulation coefficient; Δω g is the change in generator speed (rad / s); Δf is the change in frequency (Hz).

[0077] Since the main shaft torque cannot be measured directly, the fatigue load can be reflected by other variables. According to equations (2)-(4), the linearization of the transmission shaft torque is:

[0078]

[0079] In the formula, J t is the equivalent inertia, J t =J r +n g 2 J g .

[0080] The fluctuation of the transmission shaft torque is related to the wind speed, rotor speed, pitch angle and generator torque changes. The generator torque is greatly affected by the frequency response, and the transmission shaft is easily affected by the frequency response. In addition, since the torque fluctuation is in both positive and negative directions, the transmission shaft torque fluctuation will increase, resulting in an increase in the fatigue load of the transmission shaft.

[0081] Step 3: Analyze the operating characteristics of wind turbines under different working conditions and divide the generator speed zones.

[0082] According to the operating status of the wind turbine, the generator speed area is divided. The operating status of the generator changes with the change of wind speed, and its ability to support frequency is also enhanced or weakened due to different wind speeds. Under different working conditions, different control methods should be used to classify the generator speed and output power under different wind speeds so that its working curve shows the expected working characteristics.

[0083] At different wind speeds, wind turbines operate in different states. Figure 2 Analyze the wind turbine output and generator speed. Where ω is the wind turbine generator speed, ω in is the generator grid-connected cut-in speed, ω opt,min is the generator’s optimal tip speed ratio cut-in speed, ω opt,max is the generator's optimal tip speed ratio cut-out speed, ω N is the rated speed of the generator, ω out is the generator cut-out speed, and the unit of the above variables is rad / s.

[0084] Region I: Constant speed operation area, ω in ≤ω<ω opt,min In the low speed range above the cut-in speed, the wind turbine runs at a constant speed at the minimum speed, which can compensate for the wind turbine's own losses, but cannot respond to frequency modulation requirements by reducing the speed to release rotational kinetic energy.

[0085] Region II: Maximum Power Tracking Region, ω opt,min ≤ω<ω opt,max In this area, the rotor speed is controlled in proportion to the wind speed by controlling the electromagnetic torque of the generator to achieve the best tip speed ratio. At this time, the wind energy captured by the wind turbine is the largest, that is, the maximum power tracking mode, and the load reduction response frequency fluctuations can be used.

[0086] Region III: Constant speed control area, ω opt,max ≤ω<ω N , limited by the mechanical strength and converter capacity of the wind turbine, the wind turbine reaches the maximum speed of the maximum wind energy capture mode. Although the rated wind speed has not been reached at this time, it must maintain the rated speed.

[0087] Region IV: Constant power region, ω N ≤ω<ω out , the generator torque reaches the rated value, and the wind power output is kept at the rated value by changing the pitch angle. The torque can be set to the rated value, i.e. constant torque control, or it can be adjusted slightly according to the speed change, which is inversely proportional to the speed change, to maintain the rated power output.

[0088] Step 4: Construct a supercapacitor energy storage model. According to the operating conditions of wind turbines at different wind speeds, design a wind-storage combined primary frequency regulation control strategy based on fuzzy control. Use supercapacitor energy storage for frequency response, improve system stability and reduce unit fatigue load.

[0089] When constructing a supercapacitor energy storage model, it is usually equivalent to a circuit model of parallel resistors and capacitors. In order to quickly stabilize the voltage, a voltage feedback loop needs to be introduced. The relationship between the supercapacitor current change rate and the reference power and voltage change is shown in formula (9):

[0090]

[0091] In the formula, ΔI d is the current change; ΔE d is the voltage change; T c is the time constant; P sc-ref is the reference power of the supercapacitor; K P is the power control gain; K V is the voltage controlled gain.

[0092] In the circuit, the relationship between the voltage change and the current change is as shown in formula (10).

[0093]

[0094] Where R and C are the equivalent resistance and equivalent capacitance respectively.

[0095] The actual output of the supercapacitor can be expressed by equation (11):

[0096] P sc (s)=(ΔE d +E d0 )ΔI d (11)

[0097] Among them, P s (s) represents the actual output power of the supercapacitor; E d0 Indicates the initial voltage of the supercapacitor.

[0098] Supercapacitor energy storage needs to be connected to the grid through a power conversion system during the grid connection process. Therefore, when capacitor energy storage is connected to the grid, the energy conversion efficiency of the capacitor itself and the energy conversion efficiency of the power conversion system must be considered comprehensively. The mathematical model of energy storage charging and discharging is shown in formula (12).

[0099]

[0100] Where: SOC(k) is the SOC of energy storage at time k; P sc (k) is the power instruction for energy storage at time k; and P b (k)<0 means the energy storage is in charging state, P sc (k)>0 means the energy storage is in the discharge state; E reted is the rated capacity of the capacitor energy storage system.

[0101] A wind-storage combined primary frequency regulation method based on fuzzy control is proposed. Two fuzzy controllers are designed based on the generator speed partitioning. Figure 3 and Figure 4As shown in the figure, FLC1 is used to determine the total active power of the short-term frequency response in the wind storage system, while FLC2 is used to derive the participation coefficient of the wind turbine frequency regulation. In addition, during the frequency regulation process, the output power of the supercapacitor during the frequency response process is jointly determined by FLC1 and FLC2.

[0102] For FLC1: Determine the short-term total frequency power demand of the DFIG-ES system according to the system frequency change. The input variables are the frequency deviation Δf and the generator speed ω g , the value range is [-0.01, 0.01] pu and [0.5, 1.15] pu respectively, and the output variable is the total active power output ΔP of the wind-storage system in the short-term frequency response sum , the value range is [-1,1]pu. FLC1 designed 7 fuzzy sets, namely NL (negative large), NM (negative medium), NS (negative small), M (medium), PS (positive small), PM (positive medium) and PL (positive large) to describe Δf and ΔP sum , another 7 fuzzy sets are designed, namely VS (minimum), MS (small), S (small), M (medium), L (large), ML (large) and VL (maximum) to describe the generator speed ω g status.

[0103] The fuzzy logic rules of FLC1 are shown in Table 1. The fuzzy control rules are established as follows: When Δf is negative, the system needs to obtain more energy from the wind-storage combined system, so the output ΔP sum is a positive value; when Δf is positive, the system needs to reduce the energy obtained from the wind-storage combined system, so the output ΔP sum is a negative value; and when the absolute value of Δf is larger, the output ΔP sum The larger the value, the smaller the absolute value of Δf is. sum A smaller value is beneficial to the system frequency stability.

[0104] Table 1 Fuzzy logic control rules of FLC1

[0105]

[0106] For FLC2: the input variable is the generator speed ω g And the output power P w , the value range is [0.5,1.15]pu and [0.2,1]pu. These two variables reflect the short-term frequency response capability of the wind turbine in the current operating state. The output variable is the wind turbine participation frequency modulation coefficient a, which has a value range of [0,1]pu, indicating the degree of participation of the wind turbine in responding to frequency fluctuations. The fuzzy set of FLC2 has the same meaning as FLC1.

[0107] According to the generator speed division in step 3, the basic fuzzy rule of FLC2 is as follows: w Larger g When it is larger, the frequency modulation coefficient a is larger; when ω g When P is small, the kinetic energy stored in DFIG is not enough to support the frequency, and the frequency modulation coefficient a should be small. w When is large, the DFIG output power reaches the rated value. If the DFIG releases additional energy, the power may exceed the limit, so the frequency modulation coefficient a is small. The basic fuzzy rules of FLC2 are shown in Table 2.

[0108] Table 2 Fuzzy logic control rules of FLC2

[0109]

[0110] The output power that wind turbines can provide for frequency regulation in the wind-storage combined system is shown in formula (13).

[0111] ΔP w =a·ΔP sum (13)

[0112] Where ΔP w It is the power change requirement for frequency regulation of wind turbines.

[0113] The output power of the energy storage system can be calculated as:

[0114] P sc-ref =(1-a)·ΔP sum (14)

[0115] By applying two fuzzy logic controllers in the wind-storage system, the DFIG can give priority to the frequency response of the energy storage system according to its current operating status, and determine the degree of participation in the frequency regulation of the unit through real-time frequency deviation and generator speed, so as to avoid excessive participation of the DFIG in the frequency regulation process. The total active output increment of the frequency regulation of the combined system is determined in real time by FLC1. Therefore, the frequency regulation demand that the energy storage needs to bear in the wind-storage system is also determined accordingly. The energy storage system can flexibly cooperate with the operating status of the DFIG to achieve coordinated operation of the DFIG and the energy storage, so that the system frequency can be stabilized.

[0116] Example:

[0117] In this embodiment, the average wind speed is set to 6 m / s, and a random step load is used for simulation analysis.

[0118] Table 3 Frequency peak and valley values ​​under 6 m / s random step load

[0119]

[0120] Table 4 Equivalent fatigue load under 6 m / s random step load

[0121]

[0122] As can be seen from Table 3, the minimum deviation of the system frequency under the wind-storage joint control strategy is -0.0054pu, which is higher than the traditional wind power frequency control method, and the frequency deviation is reduced by 21.74%; the maximum deviation of the system frequency is 0.0049pu, which is lower than the traditional wind power frequency control method. Relative to the wind power participating in frequency regulation, it is reduced by 23.44%. The control strategy proposed in this invention effectively improves the system frequency stability. Table 4 shows the fatigue load of the transmission shaft. When the frequency increases, the wind-storage joint control can still reduce the torque amplitude of the transmission shaft. When the frequency decreases, the conclusion is consistent with that under the step load. The wind-storage joint control method greatly reduces the fatigue load of the transmission shaft, and the load reduction reaches 29.26%.

[0123] Embodiment 2:

[0124] In this embodiment, an average wind speed of 9m / s is selected for simulation analysis. At this time, the speed of the generator is in the second zone. At this stage, the wind turbine has a certain margin for active power generation, which can be used to respond to frequency fluctuations. However, in order to reduce the harm of increased fatigue load on the transmission shaft caused by wind power frequency regulation, and because the rotor speed is relatively low and the stored rotational kinetic energy is relatively small, it is difficult to effectively respond by relying solely on the unit's own regulation capabilities. In this case, the wind turbine unit itself cannot be completely relied upon for frequency regulation. The wind-storage combined system needs to make full use of the energy storage system as a supplement to the wind turbine's participation in frequency regulation to ensure the effect of frequency regulation and reduce the impact of frequency response on the mechanical structure of the wind turbine. This is the main control goal of the control strategy in this section.

[0125] Table 5 Frequency peak and valley values ​​under 9m / s random step load

[0126]

[0127] Table 6 DEL under 9m / s random step load

[0128]

[0129] Table 5 shows the system frequency values. The lowest point of system frequency fluctuation under the wind-storage coordinated control mode is still higher than the lowest point of system frequency when wind power participates in frequency regulation. The peak value is reduced by 12.5%, and the valley value is reduced by 6.25%. The fatigue load of the transmission shaft is shown in Table 6. The torque fatigue load of the transmission shaft under the wind-storage combined frequency regulation method is smaller than that under the traditional wind power frequency regulation control method, with a load reduction of 16.44%.

Claims

1. A wind storage fuzzy control frequency modulation method considering the fatigue load of the transmission shaft, characterized in that The method comprises the following steps: Step 1: Consider the dynamic characteristics and frequency response behavior of the wind turbine and build a dynamic model of the wind turbine; Step 2: Based on the wind turbine generator system participating in the primary frequency modulation process, the influence of the primary frequency modulation of the wind turbine generator system on the fatigue load of the transmission shaft is analyzed; Step 3: Analyze the operating characteristics of wind turbines under different working conditions and divide the generator speed zones; Step 4: Construct a supercapacitor energy storage model. According to the operating conditions of wind turbines at different wind speeds, design a wind-storage combined primary frequency regulation control strategy based on fuzzy control. Use supercapacitor energy storage for frequency response, improve system stability and reduce unit fatigue load.

2. The wind storage fuzzy control frequency modulation method considering the fatigue load of the transmission shaft according to claim 1 is characterized in that In the step 1, the wind turbine dynamics model includes: Aerodynamic torque model: Drive shaft model: Generator torque model: P g =T g oh g ; Where R is the blade radius; ρ is the air density; v is the wind speed; C p is the wind energy utilization coefficient; ω r is the rotor speed; J r , J g are the rotational inertia of the rotor and the generator respectively; T g is the electromagnetic torque of the generator; T s is the transmission shaft torque; ω g is the generator speed; K s is the rigidity coefficient of the transmission shaft; D s is the mutual damping coefficient of the transmission shaft; n g is the gearbox speed ratio; P g Output power for the generator.

3. The wind storage fuzzy control frequency modulation method considering the fatigue load of the transmission shaft according to claim 2 is characterized in that The specific steps of step 2 are as follows: Step 21: As the system frequency fluctuates, the wind turbine output active power changes, and the frequency characteristic formula of the unit is expressed as: In the formula, K is the primary frequency modulation coefficient of the generator; ΔP is the change in the active power output of the generator; Δf is the frequency change; Step 2: Considering the generator electromagnetic torque T g , Active power P g and generator speed ω g The functional relationship between g =T g ×ω g , the frequency characteristic formula of the unit is rewritten as: In the formula, ΔT g K is the change of electromagnetic torque of the generator; P is the frequency modulation coefficient; Δω g is the change in generator speed; Δf is the change in frequency; Step 2: According to the transmission shaft model formula, the linearization of the transmission shaft torque is: In the formula, J t is the equivalent inertia.

4. The wind storage fuzzy control frequency modulation method considering the fatigue load of the transmission shaft according to claim 3 is characterized in that In step 3, the generator speed range includes: Region I: Constant speed operation area, ω in ≤ω<ω opt,min , ω is the generator speed of the wind turbine, ω in is the generator grid-connected cut-in speed, ω opt,min The cut-in speed for the generator with the best tip speed ratio; Region II: Maximum Power Tracking Region, ω opt,min ≤ω<ω opt,max ,ω opt,max The cut-out speed for the generator's optimum tip speed ratio section; Region III: Constant speed control area, ω opt,max ≤ω<ω N ,ω N is the rated speed of the generator; Region IV: Constant power region, ω N ≤ω<ω out ,ω out Cut out speed for the generator.

5. The wind storage fuzzy control frequency modulation method considering the fatigue load of the transmission shaft according to claim 4 is characterized in that The specific steps of step 4 are as follows: Step 41: Build a supercapacitor energy storage model: When constructing the supercapacitor energy storage model, it is equivalent to a circuit model of parallel resistors and capacitors. In order to quickly stabilize the voltage, a voltage feedback loop is introduced. The relationship between the supercapacitor current change rate and the reference power and voltage change is shown in the following formula: In the formula, ΔI d is the current change; ΔE d is the voltage change; T c is the time constant; P sc-ref is the reference power of the supercapacitor; K P is the power control gain; K V is the voltage control gain; The actual output of a supercapacitor is shown below: P sc (s)=(ΔE d +E d0 )ΔI d Among them, P s (s) represents the actual output power of the supercapacitor; E d0 Represents the initial voltage of the supercapacitor; Supercapacitor energy storage is connected to the grid through a power conversion system during the grid connection process. When supercapacitor energy storage is connected to the grid, the energy conversion efficiency of the capacitor itself and the energy conversion efficiency of the power conversion system are comprehensively considered. The mathematical model of energy storage charging and discharging is shown in the following formula: Where: SOC(k) is the SOC of energy storage at time k; P sc (k) is the power instruction of energy storage at time k; P b (k)<0 means the energy storage is in charging state, P sc (k)>0 means the energy storage is in the discharge state; E reted is the rated capacity of the capacitor energy storage system; Step 4.2: Design a wind-storage combined primary frequency regulation control strategy based on fuzzy control On the basis of generator speed partitioning, fuzzy controllers FLC1 and FLC2 are designed, where FLC1 is used to determine the total active power of the short-term frequency response of the wind storage system, and FLC2 is used to derive the participation coefficient of the wind turbine frequency regulation. During the frequency regulation process, the output power of the supercapacitor system in the frequency response process is jointly determined by FLC1 and FLC2. For FLC1: Input variables are frequency deviation Δf and generator speed ω g , the output variable is the total active power output ΔP of the wind-storage system in the short-term frequency response sum ; Design 7 fuzzy sets: NL: negative large, NM: negative medium, NS: negative small, M: median, PS: positive small, PM: positive medium and PL: positive large to describe Δf and ΔP sum The state of the design is VS: minimum, MS: smaller, S: small, M: median, L: large, ML: larger and VL: maximum 7 fuzzy sets to describe the generator speed ω g Status; The fuzzy logic control rule of FLC1 is established as follows: When Δf is negative, the output ΔP sum is a positive value; when Δf is positive, the output ΔP sum is a negative value; and when the absolute value of Δf is larger, the output ΔP sum The larger the value, the smaller the absolute value of Δf is. sum Smaller; For FLC2: the input variable is the generator speed ω g And the output power P w , the output variable is the wind turbine participating frequency modulation coefficient a, and the fuzzy set of FLC2 has the same meaning as FLC1; According to the generator speed division in step 3, the basic fuzzy rule of FLC2 is as follows: w Larger g When it is larger, the frequency modulation coefficient a is larger; when ω g When P is small, the kinetic energy stored in DFIG is not enough to support the frequency, and the frequency modulation coefficient a should be small. w When it is very large, the DFIG output power reaches the rated value. If the DFIG releases additional energy, the power may exceed the limit, so the frequency modulation coefficient a is very small; The output power of wind turbines in the wind-storage combined system that can provide frequency regulation is shown in the following formula: ΔP w =a·ΔP sum In the formula, ΔP w The power change requirements for wind turbine frequency regulation; The output power of the supercapacitor is shown as follows: P sc-ref =(1-a)·ΔP sum Step 43. By applying fuzzy controllers FLC1 and FLC2 in the wind storage system, the DFIG gives priority to the supercapacitor for frequency response according to its current operating status, and determines the degree of participation in the unit frequency regulation through real-time frequency deviation and generator speed, avoiding excessive participation of the DFIG in the frequency regulation process. The total active output increment of the combined system is determined in real time by FLC1.

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