Lookup table-free full-wind-speed fan load reduction operation control method and system

Abstract

The invention relates to a full-wind-speed fan load reduction operation control method and system without a lookup table. The method comprises the following steps: calculating different maximum wind energy utilization coefficients Cpmax in each region by judging wind speed regions; calculating the wind energy utilization coefficient Cp of the fan at the moment; setting a load reduction coefficient kdel, and calculating a load reduction instruction Cp * according to the load reduction coefficient; inputting the difference value between the Cp * and the Cp into a PI module according to a judgment condition Trigger condition to generate a reference value omega ref of a fan rotating speed control loop RSC or a reference value beta ref of a pitch angle control loop PAC; and setting a lower limit area of fan rotating speed according to the wind speed interval to prevent the fan from generating out-of-control positive feedback. According to the strategy, the rotating speed and the pitch angle of the rotor are controlled by introducing a wind energy utilization coefficient Cp control ring, reservation and release of standby power of the draught fan are achieved, a lookup table does not need to be built, flexibility is improved, and a large amount of data does not need to be stored. And the fan can reserve or release standby power according to a dispatching instruction of the station.

Description

Technical Field

[0001] The present invention belongs to the field of motor transmission control, and in particular relates to a load-reduced operation control method and system for a full-wind-speed wind turbine without a lookup table. Background Art

[0002] Traditional power systems are composed of a large number of synchronous generators. When a frequency event occurs in the power grid, the rotor kinetic energy can be actively released to provide a certain amount of energy to the system, and the speed regulator realizes the primary frequency regulation function of the system. Therefore, replacing the generator with renewable energy connected through power electronic equipment will fundamentally change the basic way of operation, control and stability analysis of the power system. In order to simulate the frequency support capability of synchronous generators, wind turbines need to have energy regulation capabilities and can release or absorb power during frequency events.

[0003] In order to achieve load reduction operation, the document WYBao, L Ding, YC. Kang, and L. Sun, "Closed-Loop Synthetic Inertia Control for Wind Turbine Generators in Association With Slightly Over-Speeded Deloading Operation," IEEE Trans. Power Syst., vol. 38, no. 6, pp. 5022-5032, Nov. 2023. proposes a method of reducing the load by changing the operating speed of the fan, but this method is limited by the maximum speed. The literature M. Singh, V. Gevorgian, E. Muljadi, E. Ela, and Ieee, “Variable-Speed ​​Wind Power Plant Operating With Reserve Power Capability,” in Proc. IEEE Energy Convers. Congr.. Expo., 2013, pp. 3305-3310. proposed to reduce the load by changing the pitch angle and reducing the wind energy utilization coefficient, but the frequent operation of the variable pitch system will increase the mechanical loss. The literature LR. Chang-Chien, WTLin, and YCYin, “Enhancing Frequency Response Control by DFIGs in the High Wind Penetrated Power Systems,” IEEE Trans. Power Syst., vol. 26, no. 2, pp. 710-718, May. 2011. proposed a rotor speed and pitch angle coordinated load reduction control strategy, which achieved wind turbine load reduction by using RSC at low wind speed and PAC at high wind speed, but the strategy did not consider the constant speed zone of the wind turbine. Reference X. Zhang, XB Zha, S. Yue, and YL Chen, “A Frequency Regulation Strategy for Wind Power Based 0n Limited Over-Speed ​​De-Loading Curve Partitioning,” IEEE Access, v01.6, pp. 22938-22951, Jun. 2018. The free running area, constant speed area and constant power area of ​​the wind turbine are considered.Since there is no single mapping relationship between the speed and active power in the speed limit area of ​​the wind turbine, the traditional speed limit pitch angle control method cannot achieve accurate load reduction control. Therefore, the traditional method pre-calculates the speed and pitch angle values ​​of the wind turbine at different wind speeds and load reduction factors, and constructs a lookup table to achieve coordinated load reduction. However, this lookup table is usually preset based on specific wind turbine data and working conditions. When the wind turbine operating environment changes, the lookup table method cannot flexibly adjust the wind turbine operating mode, and a large amount of data also increases memory consumption. Summary of the invention

[0004] In order to overcome the problems existing in the related art, the present invention provides a method and system for controlling load reduction operation of a full-wind-speed wind turbine without a lookup table.

[0005] The technical solution is as follows: a method for reducing the load of a full-speed wind turbine without a lookup table, the method comprising the following steps:

[0006] S1, measure the wind speed, and divide the wind speed into low wind speed area, medium wind speed area, high wind speed area and power limit area, and calculate the maximum wind energy utilization coefficient C of each wind speed area pmax , and calculate the wind turbine's current wind energy utilization coefficient C p ;

[0007] S2, set the load reduction factor k del , through formula C p * =k del C pmax , calculate and obtain the fan load reduction reference instruction;

[0008] S3, according to the judgment condition Trigger condition, C p * With C p The difference is input into the PI module to generate the fan speed control loop RSC reference value ω ref Or the pitch angle control loop PAC reference value β ref ;

[0009] S4, sets the lower limit area of ​​the fan speed according to the wind speed range to prevent the fan from having positive feedback out of control and ensure that the fan always maintains stable operation.

[0010] Each wind speed zone and the maximum wind energy utilization coefficient C in the wind speed zone pmax The method of determining is as follows:

[0011] Low wind speed area

[0012] When the fan is running in MPPT state, the tip speed ratio tracks the optimal value λ opt , at this time the maximum value of wind energy utilization coefficient is:

[0013] C pmax =C p (λ opt ,0)

[0014] Medium wind speed range

[0015] When the fan is running in MPPT mode, since the speed has not reached the upper limit, C pmax The calculation method is still:

[0016] C pmax =C p (λ opt ,0)

[0017] High wind speed case v ωmax ≤v<v n

[0018] As the wind speed increases, C p The power gradually increases while decreasing slowly until it reaches the rated power of the wind turbine. The maximum wind energy utilization coefficient is expressed as:

[0019]

[0020] In the formula, ω max is the maximum rotor speed, R is the blade radius, and v is the wind speed.

[0021] Power limit wind speed case v n ≤v

[0022] When the wind speed v n When ≤v, the maximum wind energy that the wind turbine can capture has exceeded the rated power of the wind turbine, so the pitch angle is started to limit the wind turbine capture power. At this time, the maximum value of the wind energy utilization coefficient is:

[0023]

[0024] Where P n is the rated power of the fan, ρ is the air density, S = πR 2 It is the wind swept area of ​​the wind rotor blades.

[0025] Furthermore, the wind energy utilization coefficient C of the wind turbine at this time p The method of determining is as follows:

[0026]

[0027] Furthermore, the determination relationship between the load reduction coefficient and the load reduction instruction is as follows:

[0028]

[0029] According to the judgment condition Trigger condition, C p * With C p The difference is input into the PI module to generate the fan speed control loop RSC reference value ω ref Or the pitch angle control loop PAC reference value β ref , as shown below:

[0030]

[0031] Furthermore, in order to prevent the fan speed from falling into the positive feedback instability region, the lower limit of the fan speed is determined as follows:

[0032]

[0033] The proposed full-wind-speed wind turbine load reduction method without a lookup table can eliminate the traditional wind turbine's reliance on a lookup table for load reduction operation, save data storage space, and flexibly reserve and release standby power according to grid dispatch instructions. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a block diagram of the load reduction control strategy for full wind speed wind turbine without a lookup table;

[0035] Figure 2 It is the wind turbine operation characteristics under MPPT mode and load reduction mode under full wind speed conditions;

[0036] Figure 3 It is the speed instability situation of load reduction control of full wind speed fan without lookup table; DETAILED DESCRIPTION

[0037] The present invention is described in detail below in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention and implement it, but this is not intended to limit the scope of protection of the present application.

[0038] It should be noted that the maximum wind energy utilization coefficient C used in the present invention is pmax Refers to the maximum value that the wind turbine can achieve under constraints such as pitch angle, speed limit, power limit, etc., and does not simply refer to C pmax The value when β = 0°. Similarly, in the present invention, the maximum output power P of the fan mpp It refers to the maximum mechanical power that the fan can output under constraint conditions.

[0039] like Figure 1 As shown, load reduction control is achieved through wind energy utilization coefficient C pThe control link realizes the coordinated control of wind turbine speed and pitch angle. The switching between RSC mode and PAC mode is determined by the judgment condition Trigger condition, RSC mode is 1, and PAC mode is 0. The specific judgment condition of Trigger condition is shown in the following formula:

[0040]

[0041] In the invention, we define the load reduction factor k del belongs to [0, 1], the fan's reserve power P after load reduction del =(1-k del ) mmp . k del The smaller it is, the more reserved power the fan has. In addition, by changing k del The value of is realized, which realizes the release and reservation of the wind turbine reserve power.

[0042] In order to fully utilize the kinetic energy of the wind turbine rotor, the present invention will preferentially reduce the load by increasing the rotor speed. When the rotor speed reaches the upper limit, the pitch angle is started to reduce the load.

[0043] Wind turbine load reduction is essentially to control the wind energy utilization coefficient C by changing λ and β. p The size of (λ, β). We define the load reduction wind energy utilization coefficient as C pdel , so that:

[0044]

[0045] During the load shedding process, the action range of the rotor and the pitch angle is determined by the wind speed. In different wind speed ranges, the load shedding characteristics of WT are different, such as Figure 2 shown.

[0046] Low wind speed area

[0047] When the fan is running in MPPT state, the tip speed ratio tracks the optimal value λ opt ,λ opt The value is generally given by the wind turbine manufacturer. At this time, the maximum value of the wind energy utilization coefficient is:

[0048] C pmax =C p (λ opt ,0)

[0049] When the wind speed is low, the WT's operating speed is also low, so there is sufficient speed margin and the load can be reduced by overspeeding. At this time, the Mode Switch is set to 1, and the active power can be reserved and released only through RSC. By increasing the tip speed ratio to λ del, the pitch angle does not move, so the wind energy utilization coefficient changes to:

[0050] C pdel =C p (λ del ,0)

[0051] λ del When the pitch angle of the wind turbine is zero, C p =C pdel The tip speed ratio needs to be met.

[0052] Medium wind speed range

[0053] In the medium wind speed range, when the fan runs in MPPT mode, since the speed does not reach the upper limit, C pmx The calculation method remains the same as for low wind speeds.

[0054] When the wind speed reaches When k del For a fan with a load reduction factor, the fan speed has reached the upper limit. The fan starts the PAC in load reduction mode to reduce the load. The load reduction wind energy utilization factor is:

[0055]

[0056] In the formula, β del When the fan is at the maximum speed, C p =C pdel The required pitch angle.

[0057] Since the rotor speed does not reach the upper limit in the MPPT mode of the medium wind speed range, the wind turbine needs to convert and cooperate with RSC and PAC to achieve the reservation and release of active power. Assume that in the initial state, the wind turbine running in the MPPT state receives a load reduction instruction. The present invention will give priority to using RSC to reduce the load, and the switch is set to 1 at this time. If the rotor speed reaches the upper limit ω max When Cp still does not meet the load reduction requirement C p * , at this time, the trigger condition is met, the switch is set to 0, and the PAC is started to reduce the load. When the wind turbine receives a dispatching instruction from the station and needs to release the standby power, the present invention will give priority to using the PAC to reduce the pitch angle. When the pitch angle β is detected to be 0, C p Still less than instruction C p * When the Mode Switch is set from 0 to 1, the remaining standby power is released through the RSC.

[0058] High wind speed case v ωmax ≤ v <vn

[0059] The characteristic of this stage is that when the fan operates in MPPT mode, the speed reaches the upper limit ω max , the maximum value of the wind energy utilization coefficient is no longer obtained by the optimal blade tip speed ratio, but gradually becomes smaller than the optimal blade tip speed ratio. Therefore, as the wind speed increases, C p The power gradually increases while decreasing slowly until it reaches the rated power of the wind turbine. At this time, the maximum wind energy utilization coefficient is expressed as:

[0060]

[0061] When the fan is running at reduced load, the speed has reached the upper limit, and the speed limit is ω max , power is reserved and released only through PAC, and Mode Switch is set to 0. Its load-shedding wind energy utilization coefficient is the same as that of medium wind speed.

[0062] Power limit wind speed case v n ≤v

[0063] When the wind speed v n When ≤v, the maximum wind energy that the wind turbine can capture has exceeded the rated power of the wind turbine, so the pitch angle is started to limit the wind turbine to capture power. At this time, the maximum value of the wind energy utilization coefficient can be calculated by the following formula:

[0064]

[0065] At this stage, the present invention still reserves and releases power through PAC, and its load-reducing wind energy utilization coefficient is the same as that of the medium wind speed.

[0066] The specific control strategy of the present invention is as follows:

[0067] First, set the load reduction factor k according to the instruction del and two wind speed thresholds v ωmax and v n ; Secondly, the maximum wind energy utilization coefficient C is calculated according to different wind speed areas pmax ; Then set the load reduction factor k del Obtain the reference value of wind energy utilization coefficient C p * ; Calculate the current wind energy utilization coefficient C p Finally, according to the Trigger condition, it is decided to input the difference between the two into RSC or PAC, so that fan C p Go to track C p * , so that the fan can operate at reduced load according to instructions.

[0068] Since there is a risk of small signal instability when the fan operates on the left side of the MPPT point, most fans operate on the right side of the MPPT point. p and fan speedω r The function is not a single mapping relationship. Figure 3 As shown, in the speed unstable area, C p <C p * , the fan speed controlled by the present invention will further reduce the speed, resulting in the problem of out-of-control of the speed positive feedback reduction, so it is necessary to limit the minimum fan speed reference value. For the sake of conservatism, the present invention sets the fan speed lower limit to ω opt . Under different wind speeds, ω opt The specific value is shown in the following formula.

[0069]

[0070] The present invention breaks away from the traditional way of relying on a lookup table to perform load reduction operation on a wind turbine, saves space for data storage, and can flexibly reserve and release standby power according to grid dispatching instructions.

Claims

1. A method and system for reducing load on a full-speed wind turbine without a lookup table, characterized in that: The method comprises the following steps: S1, measure the wind speed, and divide the wind speed into low wind speed area, medium wind speed area, high wind speed area and power limit area, and calculate the maximum wind energy utilization coefficient C of each wind speed area pmax , and calculate the wind turbine's current wind energy utilization coefficient C p ; S2, set the load reduction factor k del , through formula C p * =k del C pmax , calculate the fan load reduction reference instruction C p * ; S3, according to the judgment condition Trigger condition, C p * With C p The difference is input into the PI module to generate the fan speed control loop RSC reference value ω ref Or the pitch angle control loop PAC reference value β ref ; S4, sets the lower limit area of ​​the fan speed according to the wind speed range to prevent the fan from having positive feedback out of control and ensure that the fan always maintains stable operation.

2. The method for reducing load of a wind turbine at full wind speed without a lookup table according to claim 1, characterized in that: In step S1, each wind speed zone and the maximum wind energy utilization coefficient C of the wind speed zone are pmax The method of determining is as follows: Low wind speed area When the fan is running in MPPT state, the tip speed ratio tracks the optimal value λ opt , the maximum value of wind energy utilization coefficient is: C pmax =C p (l opt ,0) Medium wind speed range In the medium wind speed range, when the fan runs in MPPT mode, since the speed does not reach the upper limit, C pmax The calculation method is still: C pmax =C p (l opt ,0) High wind speed case v ωmax ≤v <v n As the wind speed increases, C p The power gradually increases while decreasing slowly until it reaches the rated power of the wind turbine. The maximum wind energy utilization coefficient is expressed as: In the formula, ω max is the maximum rotor speed, R is the blade radius, and v is the wind speed. Power limit wind speed case v n ≤v At this time, the maximum wind energy that the wind turbine can capture has exceeded the rated power of the wind turbine, and the maximum value of the wind energy utilization coefficient is: Where P n is the rated power of the fan, ρ is the air density, S = πR 2 It is the wind swept area of ​​the wind rotor blades.

3. The method for reducing load on a full-speed wind turbine without a lookup table according to claim 1, characterized in that: In step S1, the wind energy utilization coefficient C of the wind turbine at this time p The method of determining is as follows:

4. The method for reducing load of a wind turbine at full wind speed without a lookup table according to claim 1, characterized in that: In step S2, the determination relationship between the load reduction coefficient and the load reduction instruction is as follows: Among them, the load reduction factor k del Belongs to [0, 1].

5. The method for reducing load of a wind turbine at all wind speeds without a lookup table according to claim 1, characterized in that: In step S3, the Trigger condition is as follows: In the formula, ω ref is the fan speed reference value, ω max is the upper limit of rotor speed, and β is the pitch angle.

6. The method for reducing load of a wind turbine at all wind speeds without a lookup table according to claim 1, characterized in that: In step S4, the fan speed lower limit determination condition is: In the formula, ω opt is the fan speed at the optimal tip speed ratio, v ωmax The wind speed threshold for the fan speed limit.

7. The method for reducing load on a full-speed wind turbine without a lookup table as claimed in claim 1, characterized in that: It can eliminate the traditional wind turbine's reliance on lookup tables for load reduction operation, save data storage space, and flexibly reserve and release standby power according to grid dispatch instructions.

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