Wind power frequency modulation control method for reducing fatigue load of wind driven generator

Abstract

The invention discloses a wind power frequency modulation control method for reducing the fatigue load of a wind driven generator, and belongs to the technical field of wind power generation. Wind energy is captured by blades of the wind driven generator and converted into mechanical power, and corresponding tower thrust and blade tip speed ratio are obtained; in consideration of a connection relation in a transmission chain structure of a wind turbine generator, the whole transmission system is simplified into a dual-mass-block model; establishing a simplified generator first-order inertia model, a simplified pitch angle adjusting system first-order inertia model and a simplified tower model; establishing a linear state space model of the wind turbine generator by using a small signal analysis method according to the model; and solving a target function and designing a constraint equation according to the model. A power regulation control strategy is provided for the whole operation area (namely partial and full-load states) of the wind driven generator, so that the problem of the service life of the wind driven generator is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of wind power generation, and in particular relates to a wind power frequency modulation control method for reducing fatigue load of a wind turbine. Background Art

[0002] As the capacity of fluctuating renewable energy sources connected to the grid increases, the frequency stability of the power system faces the risk of decline. Therefore, the frequency response capabilities of renewable energy sources have gradually become a hot topic. To improve the overall stability of the power system, wind turbines must be able to regulate frequency. During the frequency response process, wind turbines need to actively adjust their power output to match power demand. However, this process will lead to a significant increase in wind turbine fatigue loads, especially in extremely cold regions where wind speeds fluctuate significantly under extreme weather conditions. The frequent operation of the variable pitch device during frequency response further shortens the service life of the wind turbine, which does not meet the long-term operation requirements of wind farm developers. To effectively extend the service life of wind turbines, certain measures must be taken to suppress wind turbine fatigue loads.

[0003] Although existing wind turbine frequency regulation strategies can provide stable active power regulation, they do not take into account the service life of wind turbines. There is a significant need to develop a wind power frequency regulation control strategy that takes into account both wind turbine frequency regulation capabilities and fatigue load suppression.

[0004] The problem with existing technologies is that, in order to address the contradiction between power fluctuation and power generation efficiency of large-inertia wind turbines below the rated wind speed, existing technologies mostly adopt maximum power point tracking control strategies, but do not consider the fatigue load during system operation.

[0005] Using the algorithm optimization solution as the set value of the speed and pitch control loop does not fully consider the operation mechanism of the wind turbine. Frequent changes in the optimization solution can easily cause frequent movements of the pitch angle and aggravate the wear of mechanical components. Summary of the Invention

[0006] The present invention provides a name for a power regulation control strategy for the entire operating range of a wind turbine (i.e., partial load and full load states) to overcome the service life problem of the wind turbine.

[0007] The present invention is achieved through the following technical solutions:

[0008] A wind power frequency modulation control method for reducing fatigue load of a wind turbine generator, the method comprising the following steps:

[0009] Step 1: Wind energy is captured by the wind turbine blades and converted into mechanical power, resulting in the corresponding tower thrust and tip speed ratio;

[0010] Step 2: Based on the speed ratio obtained in step 1 and taking into account the connection relationship in the transmission chain structure of the wind turbine, the entire transmission system is simplified into a dual-mass block model;

[0011] Step 3: Based on the dual-mass model in step 2, establish a simplified first-order inertia model of the generator, a first-order inertia model of the pitch angle adjustment system, and a tower model;

[0012] Step 4: Based on the above model, use the small signal analysis method to establish the linear state space model of the wind turbine;

[0013] Step 5: Design the objective function and constraint equations based on the above model.

[0014] Furthermore, the tower thrust and tip speed ratio corresponding to step 1 are specifically:

[0015]

[0016]

[0017]

[0018] (4)

[0019] (5)

[0020] in, is the mechanical power of the fan; is the air density; is the blade radius; is the wind energy utilization coefficient; is the tip speed ratio; is the pitch angle; is the wind speed; is the tower thrust; is the thrust coefficient; is the rotor speed; To simplify the calculation parameters.

[0021] Furthermore, the dual-mass model in step 2 is specifically as follows:

[0022] (6)

[0023] in, ; is the gear ratio; is the generator torque; is the rotor inertia; is the main shaft torque; is the spindle spring coefficient; is the spindle viscous friction coefficient; is the transmission chain torque; is the generator inertia; is the generator speed; is the mechanical torque; is the rotor speed.

[0024] Furthermore, the step 3 is specifically as follows:

[0025] (7)

[0026] (8)

[0027] (9)

[0028] (10)

[0029] in, is the generator inertia time constant; is the generator efficiency; is the generator torque reference value; is the active power; is the pitch angle reference value; is the pitch angle inertia time constant; is the tower bending moment; The tower is high.

[0030] Furthermore, the step 4 is specifically as follows:

[0031] (11)

[0032] in, ; ; ; ;

[0033] ;

[0034] ;

[0035] ;

[0036] ;

[0037] ;

[0038] .

[0039] Furthermore, the zero-order holder is used to discretize Equation (11):

[0040] (12)

[0041] Among them, the discretized state space matrix is ; ; ; ; ;; .

[0042] Furthermore, the step 5 is specifically to solve the objective function design and constraint equations as follows:

[0043] (13)

[0044] (14)

[0045] in, To control the time domain; is the output weight matrix; is the input weight matrix; The change of wind turbine power reference value for each control interval; Changes in the bending moment of the wind turbine in each control interval; Changes in wind turbine torque in each control interval; The change of wind turbine pitch angle in each control interval.

[0046] The beneficial effects of the present invention are:

[0047] The present invention optimizes the classical frequency modulation control method of wind turbines and designs a pitch angle controller using the MPC algorithm, thereby avoiding the frequent switching of the pitch angle in the traditional frequency modulation method.

[0048] The wind turbine of the present invention can take into account the influence of fatigue load while completing power reference tracking. A linearized state-space equation model of the wind turbine considering fatigue load is derived, which can improve the computational efficiency of the local controller and extend the service life of the wind turbine within this framework. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a flow chart of the method of the present invention.

[0050] Figure 2 It is a simulation flow chart of the present invention.

[0051] Figure 3 This is a schematic diagram of the optimization results of the tower bending moment comparison between traditional PI control and MPC-based control.

[0052] Figure 4This is a schematic diagram comparing the spindle torque optimization results under traditional PI control and MPC-based control.

[0053] Figure 5 is a schematic diagram of the torque and bending moment rain flow fatigue counting results under traditional PI control and MPC control. Figure 5a This is a schematic diagram of the torque rain flow fatigue counting results. Figure 5b Schematic diagram of bending moment rain flow fatigue counting results.

[0054] Figure 6 It is a schematic diagram of wind turbine power output based on MPC control of the present invention. DETAILED DESCRIPTION

[0055] The following is a clear and complete description of the technical solutions in the embodiments of this application in conjunction with the drawings in the specification of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0056] In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0057] The present invention controls the pitch angle and generator torque, captures power to the greatest extent, reduces the instantaneous load of the transmission chain, and smoothes the power curve while reducing the action frequency of the pitch actuator. It can effectively respond to frequency events and extend the service life of the wind turbine.

[0058] The present invention mainly considers the frequency modulation control optimization strategy to reduce fatigue load during the operation of wind turbines. The simulation module consists of a frequency response module, a fan module, and an MPC module. The proposed frequency modulation control optimization method flow chart is as follows: Figure 1 shown.

[0059] The method comprises the following steps:

[0060] Step 1: Wind energy is captured by the wind turbine blades and converted into mechanical power. The corresponding tower thrust and tip speed ratio can be expressed as:

[0061]

[0062]

[0063]

[0064] (4)

[0065] (5)

[0066] in, is the mechanical power of the fan; is the air density; is the blade radius; is the wind energy utilization coefficient; is the tip speed ratio; is the pitch angle; is the wind speed; is the tower thrust; is the thrust coefficient; is the rotor speed.

[0067] Step 2: Considering that the main shaft is the core connecting component in the wind turbine's transmission chain structure, one end is rigidly coupled to the rotor hub, and the other end forms a power transmission link with the gearbox. The degree of tower damage also affects the life of the wind turbine. The entire transmission system is usually simplified into a dual-mass model:

[0068] (6)

[0069] in, ; is the gear ratio; is the generator torque; is the rotor inertia; is the main shaft torque; is the spindle spring coefficient; is the spindle viscous friction coefficient; is the transmission chain torque; is the generator inertia; is the generator speed.

[0070] Step 3: Establish a simplified first-order inertia model of the generator, a first-order inertia model of the pitch angle adjustment system, and a tower model as follows:

[0071] (7)

[0072] (8)

[0073] (9)

[0074] (10)

[0075] in, is the generator inertia time constant; is the generator efficiency; is the generator torque reference value; is the active power; is the pitch angle reference value; is the pitch angle inertia time constant; is the tower bending moment; The tower is high.

[0076] Step 4: Based on the above model, use the small signal analysis method to establish the linear state space model of the wind turbine:

[0077] (11)

[0078] in, ; ; ; ;

[0079] ;

[0080] ;

[0081] ;

[0082] ;

[0083] ;

[0084] .

[0085] The zero-order holder is used to discretize Equation (11):

[0086] (12)

[0087] in, ; ; ; ; ; .

[0088] Step 5: To reduce the fatigue load generated by the operation of the wind turbine, while providing frequency response power regulation, it is necessary to reduce the fluctuation of the tower bending moment and torque, and at the same time avoid large-scale switching of the pitch angle. Therefore, the objective function design and constraint equations proposed by this method are as follows:

[0089] (13)

[0090] (14)

[0091] The fluctuation of wind speed causes the mechanical torque on the rotor side to fluctuate continuously, while the power tracking control requires that the electromagnetic torque of the generator strictly matches the power instruction. When the mechanical torque is transmitted to the generator through the gearbox, a dynamic torque imbalance will be generated on both sides of the main shaft (mechanical side and electromagnetic side). The alternating stress formed by this periodic torque difference is the main cause of the fatigue load of the transmission chain. The bending moment of the tower mainly comes from the axial thrust generated by the wind wheel, which is transmitted to the tower structure through the rigid connection between the cabin base and the top of the tower. The fluctuation of wind speed causes the fatigue damage of the tower to show significant uncertainty. Therefore, the fluctuation of the tower bending moment and the main shaft torque become important indicators for quantifying fatigue loads, and they can be subjected to rain flow counting analysis based on the equivalent damage load theory. The simulation results of the example of the present invention are shown in Figure 2. Figure 3 、 4 , 5, and 6.

[0092] Depend on Figure 3 and Figure 4 It can be seen that this optimization strategy can effectively reduce the fluctuation of tower bending moment and main shaft torque. As shown in Figure 5, the number of rain flow cycles of bending moment and torque under the MPC control strategy is reduced compared with the traditional PI control strategy, which effectively suppresses the fatigue load of the wind turbine. Figure 6 It can be seen that this optimization strategy takes into account the frequency regulation and power following function of the wind turbine.

Claims

1. A wind power frequency modulation control method for reducing fatigue load of wind turbines, characterized in that: The method comprises the following steps: Step 1: Wind energy is captured by the wind turbine blades and converted into mechanical power, resulting in the corresponding tower thrust and tip speed ratio; Step 2: Based on the speed ratio obtained in step 1 and taking into account the connection relationship in the transmission chain structure of the wind turbine, the entire transmission system is simplified into a dual-mass block model; Step 3: Based on the dual-mass model in step 2, establish a simplified first-order inertia model of the generator, a first-order inertia model of the pitch angle adjustment system, and a tower model; Step 4: Based on the above model, use the small signal analysis method to establish the linear state space model of the wind turbine; Step 5: Design the objective function and constraint equations based on the above model.

2. The method according to claim 1, characterized in that The tower thrust and tip speed ratio corresponding to step 1 are specifically: ； ； ； (4)； (5) in, is the mechanical power of the fan; is the air density; is the blade radius; is the wind energy utilization coefficient; is the tip speed ratio; is the pitch angle; is the wind speed; is the tower thrust; is the thrust coefficient; is the rotor speed; To simplify the calculation parameters.

3. The method according to claim 2, characterized in that The dual-mass model in step 2 is specifically as follows: (6) in, ; is the gear ratio; is the generator torque; is the rotor inertia; is the main shaft torque; is the spindle spring coefficient; is the spindle viscous friction coefficient; is the transmission chain torque; is the generator inertia; is the generator speed; is the mechanical torque; is the rotor speed.

4. The method according to claim 3, characterized in that The step 3 is specifically as follows: (7) (8) (9) (10) in, is the generator inertia time constant; is the generator efficiency; is the generator torque reference value; is the active power; is the pitch angle reference value; is the pitch angle inertia time constant; is the tower bending moment; The tower is high.

5. The method according to claim 4, characterized in that: The step 4 is specifically as follows: (11) in, ; ; ; ; ； ； ； ； ； 。 6. The method according to claim 5, characterized in that The zero-order holder is used to discretize Equation (11): (12) Among them, the discretized state space matrix is ; ; ; ; ;; .

7. The method according to claim 2, characterized in that: Specifically, step 5 is to solve the objective function design and constraint equations as follows: (13) (14) in, To control the time domain; is the output weight matrix; is the input weight matrix; The change of wind turbine power reference value for each control interval; Changes in the bending moment of the wind turbine in each control interval; Changes in wind turbine torque in each control interval; The change of wind turbine pitch angle in each control interval.

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