A Coordinated Control Method for Active Power of a Wind Turbine with Pitch System Load Optimization

Abstract

The present invention relates to the technical field of variable-speed wind turbine generator control, and particularly to a coordinated active power control method for a wind turbine with optimized pitch system load. The method includes two parts: designing a fuzzy controller to update the pitch range limit parameter and using the rotational speed range limit parameter for coordinated control of the pitch angle and torque to achieve accurate tracking of the active power command issued by the wind farm by the unit and reduce the pitch system load. The method uses the rotational speed and the change in rotational speed as input variables of the fuzzy controller, establishes fuzzy rules to dynamically update the pitch range limit parameter, further introduces the rotational speed range limit parameter, redefines the rotational speed regulation error at this time, and designs an active power control with coordinated pitch angle and torque based on this rotational speed regulation error. The method is simple and easy to implement, effectively expands the range of rotational speed participating in active power regulation at any pitch angle, and reduces the pitch system load.

Description

Technical Field

[0001] The present invention relates to the technical field of variable-speed wind turbine generator control, and particularly relates to a coordinated active power control method for a wind turbine with optimized pitch system load. Background Art

[0002] Facing the challenges brought by global climate change and sustainable development goals, wind energy, as an important renewable energy source, is gradually increasing its proportion in the global energy structure. However, due to the inherent randomness and intermittency of wind speed, the impact of wind power generation systems on grid frequency and voltage stability is becoming increasingly significant. Therefore, the active power control of wind turbines remains a challenging topic.

[0003] To ensure that the wind turbine can track the active power command issued by the wind farm center, a proportional-integral control strategy is usually adopted to adjust the pitch angle to adapt to the change of power output. At the same time, the rotational speed is maintained at a non-optimal reference value to ensure the safety of the unit in high-wind-speed environments and to track the active power command. To further improve the power tracking effect, scholars have introduced a control strategy that uses linear matrix inequality methods to optimize the control performance and smooths the power fluctuations caused by wind speed fluctuations by more finely adjusting the pitch angle. However, the above methods all rely on adjusting the pitch angle to smooth the power fluctuations to achieve active power control, which greatly increases the pitch angle adjustment frequency and causes significant wear on the key components of the unit.

[0004] To reduce the pitch angle adjustment frequency, scholars have proposed a rotor speed control method that can smooth the power fluctuations only by adjusting the speed at low wind speeds, effectively reducing the pitch adjustment frequency. However, in high-wind-speed environments, it still relies on adjusting the pitch angle to smooth the power fluctuations, and its effect on reducing the pitch system load is limited. To more effectively reduce the load of the pitch system without significantly increasing the burden on the drive train, further research is needed, which is also the main problem to be solved by the present invention. Summary of the Invention

[0005] To expand the range of rotational speed participating in active power regulation at any pitch angle and reduce the pitch angle adjustment frequency, the present invention provides a simple, easy-to-implement, and low-cost coordinated active power control method for a wind turbine oriented to optimized pitch system load. Using the rotational speed and the change in rotational speed as the inputs of a fuzzy controller, fuzzy rules are established to dynamically update the pitch range limit parameters At the same time, to reduce the increased part of the drive train load, a rotational speed range limit parameter is further introduced, effectively expanding the range of rotational speed participating in active power adjustment, thereby reducing the pitch angle adjustment frequency and reducing the pitch system load.

[0006] The technical solution adopted by the present invention to solve its technical problems is: a method for coordinated control of active power of a wind turbine with optimized pitch system load, including the following steps:

[0007] A method for coordinated control of active power of a wind turbine with optimized pitch system load, the method includes the following steps:

[0008] (1) Using a wind power technology simulation platform, under turbulent wind conditions, according to the wind turbine speed , calculate the speed change amount, denoted by , and the expression is:

[0009] ;

[0010] Wherein, is the wind turbine speed at the current sampling moment, is the wind turbine speed at the previous sampling moment;

[0011] (2) According to the speed and the speed change amount obtained in step 1, respectively design the proportionality factors and to normalize them to obtain better responses in transient and steady states, and the expressions are:

[0012] ;

[0013] ;

[0014] Wherein, the role of the proportionality factors and is to normalize the data (that is, to limit the data far greater than plus or minus 1 within plus or minus 1 through the proportionality factor) to obtain better responses in transient and steady states. Since the speed and speed change amount of a variable-speed wind turbine are both limited physical quantities, the proportionality factor generally takes a positive constant to achieve the purpose of normalization;

[0015] (3) Use the normalized speed and the speed change amount in step 2 as the inputs of the fuzzy controller, and the pitch range limit parameter as the output of the fuzzy controller. Design the fuzzy sets of the inputs and outputs. Among them, the pitch range limit parameter is updated in real time by the speed and speed change amount, and the update strategy is realized by establishing fuzzy rules, that is, taking the speed and speed change amount as the inputs of the fuzzy controller, and the pitch range limit parameter as the output of the fuzzy controller. Establish fuzzy rules before the inputs and outputs to update the pitch range limit parameter in real time; use triangular membership functions with overlap, and the linguistic variables are represented by negative big (NB), negative small (NS), zero (ZO), positive small (PS), and positive big (PB);

[0016] (4) Based on the linguistic variables obtained in step 3, fuzzy rules were established to dynamically update the pitch range limit parameters , and its expression is:

[0017] ;

[0018] where is the scaling factor, is the total number of rules, represents the th rule, is the output of the th rule, represents the weight of the th rule, is the normalized pitch range limit parameter;

[0019] (5) In order to reduce the increased part of the drive train load, the rotational speed regulation range limit parameters and were further introduced, effectively expanding the rotational speed range participating in active power regulation at any pitch angle;

[0020] (6) Using the pitch range limit parameter and the rotational speed regulation range limit parameter introduced in step 4 and step 5, the regulation error was redefined, and its expression is:

[0021] ;

[0022] where is the rated rotational speed, is the intersection point of the optimal power curve and the reference power ;

[0023] (7) Using the regulation error obtained in step 6, a pitch angle controller was designed, adopting the PI control mode, and its specific expression is:

[0024] ;

[0025] where, and are the proportional and integral control parameters respectively;

[0026] (8) Further design a multi-mode torque controller to work together with the pitch angle controller designed in step 7 to ensure the efficient and stable operation of the wind turbine in the full wind speed range, and its expression is:

[0027] ;

[0028] where, is the active power command issued by the wind farm, is the optimal wind turbine speed control gain, is the generator torque.

[0029] Preferably, in the step 4, the established fuzzy rule table is as follows:

[0030]

[0031] In the designed fuzzy controller, the if-then statement is applied, that is, if is NB and is NB, then α1 is PS, and so on; where the linguistic variables NB, NS, ZO, PS, and PB of the input and output have been established in Figure 12 , 13, and 14.

[0032] Preferably, in the step 6, is the intersection point of the optimal power curve and the reference power , and its specific expression is:

[0033] ;

[0034] wherein, is the optimal wind turbine speed control gain.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] In view of the current situation that the RSC method can only buffer the unbalanced power between the input and output by adjusting the speed only at the zero pitch angle, which increases the load of the pitch system, the present invention designs an active power coordinated control method for a wind turbine generator set oriented to the optimization of the pitch system load. By using the speed regulation range limit parameter and the pitch range limit parameter, the speed participation in the active power regulation range at any pitch angle is effectively extended without significantly increasing the load of the drive train, and the pitch frequency is significantly reduced; in view of the fact that the RSC method can ensure that the wind turbine generator set accurately tracks the active power command issued by the center of the wind farm, a multi-mode torque controller is further designed to work in coordination with the designed pitch angle controller to ensure the efficient and stable operation of the wind turbine generator set in the full wind speed range. Description of the Drawings

[0037] The present invention will be further described below with reference to the drawings.

[0038] Figure 1 is the true wind speed diagram;

[0039] Figure 2 is the design flow chart of the active power coordinated control method for a wind turbine generator set oriented to the optimization of the pitch system load;

[0040] Figure 3 Controller block diagram of the active power coordinated control method for a wind turbine for pitch system load optimization;

[0041] Figure 4 Wind turbine speed comparison chart;

[0042] Figure 5 Pitch angle comparison chart;

[0043] Figure 6 Power generation comparison chart;

[0044] Figure 7 Pitch angle change rate comparison chart;

[0045] Figure 8 Pitch bearing friction comparison chart;

[0046] Figure 9 Blade root Mx comparison chart;

[0047] Figure 10 Blade root My comparison chart;

[0048] Figure 11 Blade root Mz comparison chart;

[0049] Figure 12 Membership function of the normalized speed;

[0050] Figure 13 Membership function of the normalized speed change;

[0051] Figure 14 Membership function of the normalized pitch range limit parameter. Specific implementation mode

[0052] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] Embodiment 1

[0054] A method for active power coordinated control of a wind turbine for pitch system load optimization provided by the present invention includes the following steps:

[0055] Step 1, taking the turbulent wind with a time of 600 s and an average wind speed of 9 m / s as the input of the GH Bladed wind power technology simulation platform, and calculating the speed change according to the wind turbine speed , which is represented by , and the expression is:

[0056] ;

[0057] Among them, is the wind turbine rotational speed at the current sampling moment, and

[0058] is the wind turbine rotational speed at the previous sampling moment. Step 2, according to the rotational speed and rotational speed change obtained in Step 1, and scale factors are designed respectively to normalize them to obtain better responses under transient and steady states. The expression is:

[0059] ;

[0060] .

[0061] Step 3, the normalized rotational speed and rotational speed change obtained in Step 2 are used as the inputs of the fuzzy controller, and the pitch range limit parameter is used as the output of the fuzzy controller to design the fuzzy sets of the inputs and outputs. Triangular membership functions with overlaps are used, and the linguistic variables are represented by Negative Big (NB), Negative Small (NS), Zero (ZO), Positive Small (PS), and Positive Big (PB).

[0062] Step 4, based on the linguistic variables obtained in Step 3, fuzzy rules are established to dynamically update the pitch range limit parameter , and its expression is:

[0063] ;

[0064] where is the scale factor, is the total number of rules, represents the th rule, is the output of the th rule, represents the weight of the th rule. The established fuzzy rule table is:

[0065] ;

[0066] Step 5, in order to reduce the increased part of the drive train load, the rotational speed adjustment range limit parameters and are further introduced to effectively expand the rotational speed range participating in the active power regulation at any pitch angle.

[0067] Step 6, using the pitch range limit parameter and rotational speed adjustment range limit parameter introduced in Step 4 and Step 5, the adjustment error is redefined, and its expression is:

[0068] ;

[0069] Wherein is the rated rotational speed, is the intersection point of the optimal power curve and the reference power , and its specific expression is:

[0070] .

[0071] Step 7: Using the regulation error obtained in Step 6, a pitch angle controller is designed, adopting the PI control method, and its specific expression is:

[0072] ;

[0073] Wherein, and are the proportional and integral control parameters respectively.

[0074] Step 8: Further design a multi-mode torque controller to work in coordination with the pitch angle controller designed in Step 7 to ensure the efficient and stable operation of the wind turbine within the full wind speed range. The expression of the torque controller is:

[0075] ;

[0076] Wherein, is the active power command issued by the wind farm center, is the optimal wind turbine rotational speed control gain.

[0077] The pitch angle controller and the rotational speed controller designed in the present invention work in coordination to achieve accurate tracking of the active power control command issued by the wind farm and reduce the pitch system load. Under the action of the set rotational speed range limit parameter and pitch range limit parameter, it can effectively expand the rotational speed participation in the active power regulation range at any pitch angle without significantly increasing the drivetrain load. This method is simple and easy to implement. It can not only ensure that the wind turbine accurately tracks the active power command issued by the wind farm, but also significantly reduce the pitch angle adjustment frequency and the load of the pitch system. The final controller block diagram of the active power coordination control method for the wind turbine optimized for the pitch system load is as shown in Figure 3 .

[0078] To quantitatively compare the control effects of the active power coordination control method for the wind turbine optimized for the pitch system load proposed in the present invention and the RSC method, it is necessary to explain the evaluation index of the pitch angle load. In practice, frequent adjustment of the pitch angle will accelerate the wear of the key components of the unit, thereby shortening its service life. Therefore, the present invention uses the following index (PF, Pitch Fatigue) to evaluate the pitch system load:

[0079] ;

[0080] Among them, represents the pitch angle of the wind turbine generator set, with the unit of , so the unit of this index is , which quantifies the change amount of the pitch angle per second on average within the operation time period seconds of the unit, and can effectively evaluate the load of the pitch system. In addition, the present invention respectively compares the moment changes at the blade root to more comprehensively evaluate the fatigue degree of the blade.

[0081] Embodiment 2

[0082] In this embodiment, the wind power technology development software GH bladed simulation platform is used to verify the effectiveness of the method of the present invention.

[0083] In the embodiment, a 1.5MW three-blade horizontal axis variable speed wind turbine generator set model is used, and its main parameters are shown in the following table:

[0084]

[0085] The controller parameters are selected as follows:

[0086] .

[0087] For the sake of simplified description, in the comparison results, the name of the RSC method is replaced by RSC, and the name of the method of the present invention is replaced by fuzzy.

[0088] Figure 1 is the true wind speed diagram.

[0089] Figure 2 is the design flow chart of the active power coordinated control method for the wind turbine generator set for pitch system load optimization. Using the GH bladed simulation platform, under the condition of turbulent wind, according to the wind turbine speed, the change amount of the speed is calculated, and the speed and the change amount of the speed are normalized. The normalized speed and the change amount of the speed are used as the inputs of the fuzzy controller, and the pitch range limit parameter is used as the output. The fuzzy sets of the inputs and outputs are designed, and the linguistic variables are established. According to the linguistic variables, the fuzzy rules are established to dynamically update the pitch range limit parameter . In order to reduce the increased part of the drive train load, the speed range limit parameter is further introduced, effectively expanding the speed participation range in active power regulation at any pitch angle. The speed regulation error is further redefined, and the active power control coordinated by the pitch angle and the torque is designed according to this regulation error.

[0090] Figure 3It is a block diagram of the active power coordinated control method for a wind turbine for pitch system load optimization. In the pitch angle controller, first, according to the wind turbine speed, the speed change amount is calculated, and the speed and the speed change amount are normalized. Then, the normalized speed and speed change amount are used as the inputs of the fuzzy controller, and the pitch range limit parameter is used as the output to establish fuzzy rules and dynamically update the pitch range limit parameter . To reduce the increased part of the drive train load, a speed regulation range limit parameter is further introduced and , and the corresponding speed regulation error is redefined at this time. The torque controller switches different control modes according to the speed and works in coordination with the pitch angle controller; in practice, this control framework can effectively expand the speed participation range in active power regulation at any pitch angle, while ensuring tracking of the active power command issued by the wind farm, significantly reducing the pitch angle adjustment frequency and reducing the pitch system load

[0091] Figure 4 It is a comparison chart of wind turbine speeds

[0092] Figure 5 It is a comparison chart of pitch angles. After calculation, the total pitch angle adjustment amount of the traditional RSC method is 95.11 , and the total pitch angle adjustment amount of the method of the present invention is 57.94 , a reduction of 39.08%

[0093] Figure 6 It is a comparison chart of generated powers. It can be seen that the method of the present invention can accurately track the active power command issued by the wind farm

[0094] Figure 7 It is a comparison chart of pitch angle change rates. After calculation, the pitch system load evaluation index PF of the traditional RSC method is 0.192 , and the pitch system load evaluation index PF of the method of the present invention is 0.097 , a reduction of 49.6%

[0095] Figure 8 It is a comparison chart of pitch bearing friction. It can be seen that compared with the traditional RSC method, the method of the present invention significantly reduces the friction at the pitch bearing

[0096] Figure 9 It is a comparison chart of the Mx moment at the blade root. After calculation, the equivalent fatigue load of the RSC method in the Mx direction of the blade root when the material coefficient is 10 is 1841000 Nm, and the equivalent fatigue load of the method of the present invention in the Mx direction of the blade root when the material coefficient is 10 is 1836000 Nm, a reduction of 2.72%

[0097] Figure 10The figure is a comparison of the My moment at the root of the blade. After calculation, the equivalent fatigue load of the RSC method when the material coefficient in the My direction of the blade root is 10 is 1942000Nm, and the equivalent fatigue load of the method of the present invention when the material coefficient in the My direction of the blade root is 10 is 1492000Nm, which is reduced by 23.17%.

[0098] Figure 11 The figure is a comparison of the Mz moment at the root of the blade. After calculation, the equivalent fatigue load of the RSC method when the material coefficient in the Mz direction of the blade root is 10 is 16182Nm, and the equivalent fatigue load of the method of the present invention when the material coefficient in the Mz direction of the blade root is 10 is 13978.8Nm, which is reduced by 13.62%.

[0099] Figure 12 , Figure 13 and Figure 14 are the normalized speed, speed change and membership function of the pitch range limit parameter, that is, Figure 12 , Figure 13 and Figure 14 These are the membership functions of the input (normalized speed and speed change) and output (normalized pitch range limit parameter) established respectively. To design a fuzzy controller, the membership functions of the input and output must be established respectively before the fuzzy rules between them can be established.

Claims

1. A wind turbine active power coordinated control method with load optimization of a variable pitch system, characterized in that: The method comprises the following steps: (1) Using the wind power technology simulation platform, under turbulent wind conditions, the wind rotor speed , calculate the speed change, and use Indicates that the expression is: ； in, is the wind wheel speed at the current sampling time, is the wind wheel speed at the last sampling moment; (2) The speed obtained in step 1 and speed change , respectively design the proportional factors and It is normalized to obtain better response in transient and steady state, and the expression is: ； ； (3) Normalize the speed after step 2 and speed change As the input of the fuzzy controller, the pitch range limit parameter is used as the output of the fuzzy controller, and the fuzzy sets of input and output are designed; using triangular membership functions with overlap, the linguistic variables are represented by negative large NB, negative small NS, zero ZO, positive small PS, and positive large PB; (4) Based on the language variables obtained in step 3, fuzzy rules are established to dynamically update the pitch range limit parameters. , whose expression is: ； in is the scale factor, is the total number of rules, Indicates Rules, For the The output of the rule, Indicates The weight of the rule, is the normalized pitch range limit parameter; (5) In order to reduce the increase in the load on the transmission chain, the speed adjustment range limit parameter is further introduced and , effectively expanding the range of speed participation in active power regulation at any pitch angle; (6) Redefine the adjustment error by using the pitch range limit parameters and speed adjustment range limit parameters introduced in steps 4 and 5 , whose expression is: ； in is the speed rating, is the optimal power curve and the reference power The intersection of (7) Using the adjustment error obtained in step 6, the pitch angle controller is designed using the PI control method. The specific expression is: ； in, and are the proportional and integral control parameters respectively; (8) Further design a multi-mode torque controller to work in conjunction with the pitch angle controller designed in step 7 to ensure efficient and stable operation of the wind turbine in the full wind speed range. The expression is: ； in, It is the active power instruction issued by the wind farm. is the optimal wind wheel speed control gain, is the generator torque.

2. The method for coordinated control of active power of wind turbines with optimized pitch system load according to claim 1, characterized in that: In step 6, is the optimal power curve and the reference power The specific expression is: ； in, is the optimal wind wheel speed control gain.

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