A droop control frequency modulation method with pitch angle protection function for a wind farm

Abstract

The invention is a kind of wind farm droop control frequency modulation method with pitch angle protection function, wind farm control center receives the load shedding mode and adjustable power of wind turbine; the wind turbine is divided into two groups by whether to use pitch angle load shedding, and the total frequency modulation power of the wind farm and the two groups is calculated according to the calculation; the control center determines the total droop coefficient of the wind farm according to the total adjustable power of the wind farm; the total droop coefficient of the two groups is determined according to the adjustable power of the two groups, and the relationship between the frequency modulation participation rate ρ and σ and the maximum adjustable frequency modulation power of G1, G2 and the maximum adjustable frequency modulation power of the wind farm is calculated; the droop coefficient of the wind turbine is determined according to the adjustable power of the wind turbine, and it is sent to each wind turbine; finally, the wind turbine adjusts the droop coefficient in real time according to the received information, and completes the frequency modulation work. The invention preferentially makes the wind turbine without pitch angle load shedding to perform frequency modulation, reduces the pitch angle action amplitude and frequency of the wind turbine with pitch angle load shedding, protects the mechanical device of the wind turbine, and prolongs the service life of the wind turbine.

Description

Technical Field

[0001] This invention relates to the field of wind farm participation in power system frequency regulation technology, specifically a wind farm droop control frequency regulation method with pitch angle protection function. Background Technology

[0002] As the scale of wind power grid connection increases, the intermittent and random nature of wind power generation poses an increasingly prominent threat to the frequency stability of the power system. Therefore, enabling wind farms to possess primary frequency regulation capabilities similar to traditional power generation units has become a crucial issue. To address this, many countries stipulate that when the output of a grid-connected wind farm reaches a certain value, the wind turbines within the farm must have a certain percentage of reserve power for frequency regulation.

[0003] Due to the large distances involved, the wind speeds accessed by the turbines within a wind farm vary. Turbines operating at lower wind speeds can reduce load through overspeed control to provide reserve power; however, turbines operating at higher wind speeds require a combination of pitch angle load reduction and overspeed load reduction to provide a specified percentage of reserve power. Turbines employing pitch angle load reduction inevitably require pitch angle adjustments to release reserve power during frequency regulation. These frequent adjustments exacerbate wear on the turbine's mechanical components, increase maintenance costs, and reduce the turbine's service life. Summary of the Invention

[0004] This invention addresses the technical problem that frequent operation of wind turbines using pitch angle reduction during frequency regulation exacerbates the wear of wind turbine mechanical devices and increases wind turbine maintenance costs. It provides a wind farm droop control frequency regulation method with pitch angle protection function to reduce wind turbine maintenance costs.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A frequency regulation method for droop control in wind farms with pitch angle protection includes the following steps:

[0007] (1) The wind farm control center receives the wind turbine's load reduction mode and adjustable power: The wind farm control center starts frequency regulation control and periodically exchanges information with the doubly fed induction wind turbine units in the field. The wind turbine units send their own load reduction mode and adjustable power to the control center. The adjustable power includes the maximum adjustable power and the remaining adjustable power.

[0008] (2) The control center divides the wind turbines into two groups according to the load reduction method and calculates the total adjustable power of the wind farm and each group: wind turbines that use pitch angle control and those that do not use pitch angle control for load reduction. Based on the collected adjustable power of the wind turbines, the total maximum adjustable power of the wind farm, the maximum adjustable power of the two groups of wind turbines, the total remaining adjustable power of the wind farm, and the remaining adjustable power of the two groups of wind turbines are calculated.

[0009] (3) The control center determines the total droop coefficient of the wind farm: The control center determines the total droop coefficient of the wind farm based on the adjustable power of the wind farm, so that it is proportional to the maximum adjustable power of the wind farm.

[0010] (4) The control center determines the total droop coefficient of the two sets of wind turbines and calculates the maximum adjustable frequency power of the two sets: The control center determines the total droop coefficient of the two sets of wind turbines based on the adjustable power of the two sets of wind turbines. The frequency regulation participation degree ρ and σ of the two sets of wind turbines are determined by the membership function. Then, the relationship between ρ and σ and the maximum adjustable frequency power of G1 and G2 and the maximum adjustable frequency power of the wind farm is calculated.

[0011] (5) The control center determines the droop coefficient of each fan and sends the droop coefficient to each fan: The control center determines the droop coefficient of each fan according to its adjustable power, so that the droop coefficient of each fan is proportional to its remaining adjustable power, and sends it to each fan.

[0012] (6) The fan receives information and adjusts the droop coefficient in real time to complete the frequency modulation: The fan adjusts the droop coefficient in real time according to the information received from the control center and completes the frequency modulation through droop control.

[0013] The adjustable power of the fan mentioned in step (1) includes the maximum adjustable power and the remaining adjustable power, and their relationship is as follows:

[0014]

[0015] In the above formula: This is the maximum adjustable power of the fan. This refers to the remaining adjustable power of the fan. This represents the actual frequency regulation power of the fan, which varies with frequency deviation.

[0016] The wind turbine load reduction methods described in step (2) are divided into those without pitch angle load reduction and those with pitch angle load reduction; the grouping method is represented by S. When S is 0, it means that the wind turbine does not use pitch angle load reduction; when S is 1, the wind turbine uses pitch angle load reduction, specifically expressed as follows:

[0017] G1={i|S i =0}

[0018] G2={i|S i =1}

[0019] In the formula: G1 and G2 are wind turbine units that do not use and use pitch angle load reduction, respectively, and i is the number of the wind turbine.

[0020] The calculation methods for the total maximum adjustable power of the wind farm, the maximum adjustable power of the two sets of wind turbines, the total remaining adjustable power of the wind farm, and the remaining adjustable power of the two sets of wind turbines mentioned in step (2) are as follows:

[0021] The maximum adjustable power of the wind farm are as follows:

[0022]

[0023] The maximum adjustable power of the two wind turbine units are as follows:

[0024]

[0025]

[0026] The remaining adjustable power of the wind farm is as follows:

[0027]

[0028] The remaining adjustable power of the two wind turbine units are as follows:

[0029]

[0030]

[0031] In the formula: and Let be the maximum adjustable power and the remaining adjustable power of the i-th wind turbine, respectively, and n be the number of wind turbines in the wind farm that can participate in frequency regulation.

[0032] The calculation method for the total droop coefficient of the wind farm mentioned in step (3) is as follows:

[0033]

[0034] In the formula: Let |Δf| be the total droop coefficient of the wind farm. m | represents the maximum acceptable frequency deviation for the power system. When the frequency deviation is greater than |Δf m At this time, low-frequency load shedding will be initiated to prevent the frequency from dropping further.

[0035] The total droop coefficient for each group in step (4) is calculated as follows:

[0036]

[0037]

[0038] In the formula, the sum of the droop coefficients of the fans within a group represents the droop coefficient of each group, which reflects the degree to which each group participates in frequency regulation. and These are the sag coefficients for the first and second groups of fans, respectively. Let be the sag coefficient of the i-th fan.

[0039] Based on the grouping within the wind farm, the sum of the droop coefficients of the two groups of wind turbines should also satisfy the following formula:

[0040]

[0041] The membership function is calculated as follows:

[0042]

[0043] In the formula: When the membership function ρ = 1, it means that a group of wind turbines that do not use pitch angle load reduction participate in frequency regulation. When the membership function σ = 1, it means that the remaining adjustable power of the group that does not use pitch angle load reduction is exhausted. At this time, a group of wind turbines that use pitch angle load reduction participate in frequency regulation, thereby reducing the pitch angle action amplitude of the wind turbines.

[0044] So, and It can be obtained from the following formula:

[0045]

[0046]

[0047] The sag coefficient of each fan in step (5) is calculated using the following formula:

[0048]

[0049] In step (6), frequency regulation is completed through droop control. Therefore, the real-time frequency regulation power of the fan is:

[0050]

[0051] In the formula: Δf is the frequency deviation of the system.

[0052] The beneficial effects of this invention are as follows: This invention collects the adjustable frequency power and load reduction methods of the wind turbines in the wind farm through the wind farm control center, assigns a droop coefficient to them for frequency adjustment, prioritizes the frequency adjustment of wind turbines that do not use pitch angle load reduction, reduces the pitch angle action amplitude and frequency of wind turbines that use pitch angle load reduction, protects the mechanical devices of the wind turbines, and extends the service life of the wind turbines. Attached Figure Description

[0053] Figure 1 This is the control flowchart of the wind farm control center.

[0054] Figure 2 This is a schematic diagram of information exchange between the wind farm control center and the wind turbines.

[0055] Figure 3 This is a schematic diagram showing the control center allocating the total droop coefficient to the two sets of fans. Detailed Implementation

[0056] To better understand the above-mentioned objectives, features and advantages of the present invention, the technical solution of the present invention will be further described in a non-limiting manner below with reference to the accompanying drawings and specific embodiments.

[0057] The wind farm droop control frequency regulation method with pitch angle protection function according to the present invention includes the following steps:

[0058] (1) The wind farm control center receives the wind turbine's load reduction mode and adjustable power: The wind farm control center starts frequency regulation control and conducts periodic information exchange with the doubly fed induction wind turbine units in the field. The wind turbine units send their own load reduction mode and adjustable power to the control center. The adjustable power includes the maximum adjustable power and the remaining adjustable power.

[0059] As attached Figure 1 and Figure 2 As shown: The wind farm control center activates frequency regulation mode and periodically exchanges information in real time with the wind turbines within the farm. Each turbine sends its load shedding mode (S) and adjustable power to the control center. When S is 0, it indicates that the turbine is not using pitch angle load shedding; when S is 1, the turbine is using pitch angle load shedding. The turbine's adjustable power includes maximum adjustable power and remaining adjustable power, represented by... and The relationship between the two is as follows:

[0060]

[0061] In the above formula: The frequency regulation power of the fan varies with the frequency deviation.

[0062] (2) The control center divides the wind turbines into two groups according to the load reduction method and calculates the total adjustable power of the wind farm and each group: wind turbines that use pitch angle control and those that do not use pitch angle control for load reduction. Based on the collected adjustable power of the wind turbines, the total maximum adjustable power of the wind farm, the maximum adjustable power of the two groups of wind turbines, the total remaining adjustable power of the wind farm, and the remaining adjustable power of the two groups of wind turbines are calculated.

[0063] Based on the wind turbine unloading method S, the wind turbines in the field are divided into two groups, as shown below:

[0064] G1={i|S i =0}

[0065] G2={i|S i =1}

[0066] In the above formula: G1 and G2 are wind turbine units that do not use and use pitch angle load reduction, respectively, and i is the number of the wind turbine.

[0067] The maximum adjustable power of the wind farm are as follows:

[0068]

[0069] The maximum adjustable power of the two wind turbine units are as follows:

[0070]

[0071]

[0072] The remaining adjustable power of the wind farm is as follows:

[0073]

[0074] The remaining adjustable power of the two wind turbine units are as follows:

[0075]

[0076]

[0077] In the formula: and Let be the maximum adjustable power and the remaining adjustable power of the i-th wind turbine, respectively, and n be the number of wind turbines in the wind farm that can participate in frequency regulation.

[0078] (3) Determine the total droop coefficient of the wind farm so that the total droop coefficient of the wind farm is proportional to the total maximum adjustable power of the wind farm: The control center determines the total droop coefficient of the wind farm based on the adjustable power of the wind farm so that it is proportional to the maximum adjustable power of the wind farm.

[0079] The control center determines the total droop coefficient of the wind farm based on the sum of its maximum adjustable power, which can be calculated using the following formula:

[0080]

[0081] In the formula: |Δf m | represents the maximum acceptable frequency deviation for the power system. When the frequency deviation is greater than |Δf m At this time, low-frequency load shedding will be initiated to prevent the frequency from dropping further.

[0082] (4) The control center determines the total droop coefficient of the two sets of wind turbines and calculates the maximum adjustable frequency power of the two sets: The control center determines the total droop coefficient of the two sets of wind turbines based on the adjustable power of the two sets of wind turbines. The frequency regulation participation degree ρ and σ of the two sets of wind turbines are determined by the membership function. Then, the relationship between ρ and σ and the maximum adjustable frequency power of G1 and G2 and the maximum adjustable frequency power of the wind farm is calculated.

[0083] The control center determines the sum of the droop coefficients of the two groups based on the adjustable frequency power of each group. and It satisfies the following formula:

[0084]

[0085]

[0086] In the formula, the sum of the droop coefficients of the fans within a group represents the droop coefficient of each group, which reflects the degree to which each group participates in frequency regulation. and These are the sag coefficients for the first and second groups of fans, respectively. Let be the sag coefficient of the i-th fan.

[0087] Based on the grouping within the wind farm, the sum of the droop coefficients of the two groups of wind turbines should also satisfy the following formula:

[0088]

[0089] The frequency regulation participation ρ and σ of the two sets of wind turbines are determined by membership functions, and their independent variable x is calculated by the following formula:

[0090]

[0091] The function expression is:

[0092]

[0093] See function graph Figure 3 When x is greater than 0.1, G1 still has sufficient frequency regulation resources, and its frequency regulation participation ρ is equal to 1, taking over the entire droop control task of the wind farm. As x decreases to around 0.1, it indicates that the frequency regulation resources in G1 are becoming scarce, so ρ should gradually decrease, and the frequency regulation task undertaken by G2 gradually decreases. At the same time, the frequency regulation participation σ of G2 gradually increases, and its frequency regulation task also gradually increases. To ensure stable operation of the wind turbine, the slopes of both curves around 0.1 are sufficiently large. As x further decreases, the resources of both G1 and G2 are about to decrease to 0, and ρ and σ converge to... and This indicates that when frequency regulation resources are about to be exhausted, the frequency regulation participation of ρ and σ is the ratio of the maximum adjustable frequency power of G1 and G2 to the maximum adjustable frequency power of the wind farm. and Calculate according to the following formula:

[0094]

[0095]

[0096] (5) Determine the droop coefficient for each fan and send the droop coefficient to each fan: The control center determines the droop coefficient of each fan based on its adjustable power, ensuring that the droop coefficient of each fan is proportional to its remaining adjustable power, and sends this coefficient to each fan. The droop coefficient is calculated using the following formula:

[0097]

[0098] (6) The wind turbine receives information and adjusts its droop coefficient in real time to complete the frequency modulation: The control center periodically calculates the droop coefficient of each wind turbine according to the above steps and sends it to the wind turbine. The wind turbine adjusts its frequency according to the received droop coefficient through droop control. The frequency modulation power of the wind turbine is:

[0099]

[0100] In the formula: Δf is the frequency deviation of the system.

[0101] In summary, this invention collects the adjustable power and load reduction methods of wind turbines in the wind farm through the wind farm control center, assigns droop coefficients to them for frequency regulation, prioritizes the frequency regulation of wind turbines that do not use pitch angle load reduction, reduces the pitch angle action amplitude and frequency of wind turbines that use pitch angle load reduction, protects the mechanical devices of the wind turbines, and extends the service life of the wind turbines.

[0102] It should be noted that the above are merely preferred embodiments of the present invention, intended to illustrate the technical concept and features of the present invention, and should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A droop control frequency modulation method with pitch angle protection function for a wind farm, characterized in that, It comprises the following steps: (1) The wind farm control center receives the load shedding mode of the wind turbine and the adjustable power: the wind farm control center opens the frequency modulation control, and periodically interacts with the double-fed induction wind turbine in the field. The wind turbine sends its load shedding mode and adjustable power to the control center. The adjustable power includes the maximum adjustable power and the remaining adjustable power; (2) The control center divides the wind turbines into two groups G1 and G2 according to the load shedding mode, calculates the total regulating power of the wind farm and each group: G1 and G2 are respectively the groups of wind turbines without and with pitch angle control for load shedding, calculates the maximum adjustable power of the wind farm according to the collected adjustable power of the wind turbines , the maximum adjustable power of the two groups of wind turbines , , the remaining adjustable power of the wind farm , and the remaining adjustable power of the two groups of wind turbines , ; (3) The control center determines the total droop coefficient of the wind farm : The control center determines the total droop coefficient of the wind farm according to the adjustable power of the wind farm , which is proportional to the maximum adjustable power of the wind farm ; (4) The control center determines the droop coefficients of the two groups of wind turbines , , and calculates the maximum adjustable power of the two groups , : The control center determines the droop coefficients of the two groups of wind turbines according to the adjustable power of the two groups of wind turbines, wherein the frequency modulation participation of the two groups of wind turbines is determined by a membership function and , and then the relationship between and and , the maximum adjustable power of each and the maximum adjustable power of the wind farm is calculated. (5) The control center determines the droop coefficient of each wind turbine and sends the droop coefficient to each wind turbine: the control center determines the droop coefficient of each wind turbine according to its adjustable power, so that the droop coefficient of each wind turbine is proportional to its remaining adjustable power, and sends it to each wind turbine; (6) The wind turbine receives information and adjusts the droop coefficient in real time to complete the frequency modulation work: the wind turbine adjusts the droop coefficient in real time according to the information received from the control center, and completes the frequency modulation work through droop control; The calculation method of the membership function is as follows: ， wherein: ; membership function = 1 indicates that the group of wind turbines without pitch angle reduction participates in frequency regulation, the membership function = 1 indicates that the remaining adjustable power of the group without pitch angle reduction is exhausted, at this time the group of wind turbines with pitch angle reduction participates in frequency regulation, thereby reducing the pitch angle action amplitude of the wind turbines; So, and According to the following formula: ， ， The droop coefficient of each wind turbine in step (5) is calculated by the following formula: ， wherein: is the droop coefficient of the i-th wind turbine, is the remaining adjustable power of the i-th wind turbine; The real-time frequency modulation power of the fan in step (6) is completed by droop control, so the real-time frequency modulation power of the fan is: Pf = P0- Kf (P0- P) ， In the formula: is the frequency deviation of the system.

2. The droop control frequency modulation method with pitch angle protection function for wind farm according to claim 1, characterized in that, The adjustable power of the wind turbine in step (1) includes the maximum adjustable power and the remaining adjustable power, and their relationship is as follows: ， In the above formulae: is the maximum adjustable power of the fan, is the remaining adjustable power of the fan, is the actual frequency-regulated power of the fan, which varies with the frequency deviation.

3. The droop control frequency modulation method with pitch angle protection function for wind farm according to claim 1, characterized in that, The wind turbine load shedding mode in step (2) is divided into not using pitch angle load shedding and using pitch angle load shedding; Grouping mode uses S to represent, when S is 0, it means that the wind turbine does not use pitch angle load shedding; When S is 1, the wind turbine uses pitch angle load shedding, which is specifically expressed as: ， ， In the formula: i is the number of wind turbines.

4. The droop control frequency modulation method with pitch angle protection function for wind farm according to claim 1, characterized in that, The total maximum adjustable power of the wind farm, the maximum adjustable power of the two groups of wind turbines, the total remaining adjustable power of the wind farm and the remaining adjustable power of the two groups of wind turbines in step (2) are calculated as follows: The maximum adjustable power of the wind farm is respectively: ， The maximum adjustable power of the two groups of wind turbines is respectively: ， ， The remaining adjustable power of the wind farm is respectively: ， The remaining adjustable power of the two groups of wind turbines is respectively: ， ， In the formula: and Pmaxi and Presiduali are the maximum adjustable power and the remaining adjustable power of the ith wind turbine, respectively, and n is the number of wind turbines in the wind farm that can participate in frequency regulation.

5. The droop control frequency modulation method with pitch angle protection function for wind farm according to claim 1, characterized in that, The total droop coefficient of the wind farm in step (3) is calculated as follows: ， wherein is the total droop coefficient of the wind farm, is the maximum frequency deviation acceptable by the power system, when the frequency deviation is greater than the under-frequency load shedding will be activated to prevent further frequency drop.

6. The droop control frequency modulation method with pitch angle protection function for wind farm according to claim 1, characterized in that, The total droop coefficient of each group in step (4) is calculated as follows: ， ， In the formula, the sum of the droop coefficients of the fans in the group represents the droop coefficient of each group, which reflects the strength of each group participating in frequency modulation, wherein and are the droop coefficients of the fans in the G1 group and the G2 group, respectively, is the droop coefficient of the i-th fan. According to the grouping in the wind farm, the sum of the droop coefficients of the two groups of wind turbines should also satisfy the following formula: 。

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