CN108035848A - Independent variable pitch control method of wind generating set based on tower top load - Google Patents

Abstract

The invention discloses an independent variable pitch control method for a wind turbine generator set based on a tower top load, the method comprising: firstly, mounting a sensor on the top of a tower, directly collecting the tower top bending moments M _x , _My , and M _z through the sensor, and then calculating the D-axis load and the Q-axis load, i.e., the D-Q-axis load, through the collected tower top load; secondly, the D-axis load and the Q-axis load are respectively output as variable pitch instructions of the D-Q-axis through a filter, a PI controller, and a limiting output; finally, the variable pitch instructions of the D-Q-axis are inversely transformed through the D-Q-axis to obtain the variable pitch instructions on each blade, which are superimposed on the unified variable pitch instructions. The method of the invention adopts the tower top load as the feedback amount of the independent variable pitch control, and the number of load sensors is reduced from three groups to one group, which significantly reduces the cost while also improving the reliability.

Description

An independent pitch control method for wind turbines based on tower top loads

technical field

The present invention relates to the technical field of pitch control of wind power generators, in particular to an independent pitch control method for wind power generators based on tower top loads.

Background technique

It is known in the industry that with the development of wind power technology, wind turbines gradually tend to be designed with large megawatts, high towers, large impellers, and lightweight. For a large turbine unit, the fatigue load My of the blade root, the unbalanced load of the hub and the unbalanced load of the yaw will increase significantly. In order to realize the lightweight design of the impeller and the tower, the unit needs to adopt an independent pitch control strategy to reduce the fatigue load.

The traditional independent pitch control mainly relies on mounting load sensors at the root of the fan blades, and by measuring the loads in the flapping direction and shimmy direction of the blade roots, it is converted into out-of-plane loads of the fan impeller plane, and the unbalanced load on the impeller plane is obtained.

Among them, the first-order, asymmetric wind field on the impeller plane can be linearized and described by two mutually perpendicular components, and the blade load is closely related to the wind speed. Therefore, the unbalanced load of the impeller plane can be expressed as a "load action field", and any instantaneous load of the blade is regarded as its sampling value at the corresponding position of the load field. In addition, the additional pitch action used to compensate for asymmetric loads can also be expressed as a "pitch action field" covering the sweep plane of the impeller, and the additional pitch action required by the blade can be expressed by its corresponding position of the pitch action field Sampling is obtained. Each field can be described as two perpendicular components. Generating the pitch action field from the load action field requires only a dual-input dual-output controller, and this is independent of the number of blades and the impeller rotational speed. For a three-bladed rotor, the three measured blade root loads can be used to calculate the two components of the instantaneous load field. From the dual components of the load field, the pitch field is generated. From the dual The components can be transformed into three independent pitch increments, a process known as classical independent pitch control.

This independent pitch control mainly takes the blade root load as the input quantity, and eliminates the unbalanced load on the impeller plane by applying an additional pitch angle on each blade to achieve the purpose of load reduction. However, how to ensure the reliability of the independent pitch control and reduce the cost of the independent pitch control has been puzzling technicians.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art, and proposes a method for independent pitch control of wind turbines based on tower top loads. The method uses tower top loads as the feedback of independent pitch control. The number has been reduced from three to one, increasing reliability while significantly reducing costs.

In order to achieve the above object, the technical solution provided by the present invention is: an independent pitch control method for a wind turbine based on a tower top load, comprising the following steps:

1) First, mount the sensor on the top of the tower, and directly collect the tower top bending moments M _x , M _y , M _z through the sensor, and then calculate the D-axis load and Q-axis load from the collected tower top load, that is, the DQ axis The details of the load are as follows:

The D-axis load reflects the unbalance of the wind rotor plane pitch direction, and the Q-axis load reflects the unbalance of the impeller plane yaw direction load. In the wind turbine hub coordinate system, the D-axis load refers to the hub M _y , and The Q-axis load refers to the hub M _z , the hub coordinate system is the GL coordinate system, the X coordinate axis points from the nose to the tail along the hub centerline, the Y coordinate axis is horizontal and perpendicular to the X axis, and the Z coordinate axis points vertically upward; independent pitch The purpose of control is to eliminate the unbalanced load on the impeller plane, so it is necessary to know the load reflecting the unbalanced impeller plane, that is, the D-axis load and the Q-axis load. Therefore, how to obtain the DQ-axis load through the tower top load is particularly critical;

The loads collected at the top of the tower include: tower top bending moments M _x , M _y , M _z , the tower coordinate system is a fixed coordinate system, that is, the GL coordinate system, the X coordinate axis points south, the Y coordinate axis points east, and the Z axis is vertical Upwards, the coordinate origin is on the central axis of the tower, and the tower coordinate system is different from the hub coordinate system, because the hub coordinate system is fixed on the cabin and rotates with the yaw of the cabin, while the tower coordinate system is relatively stationary with the ground;

The Q-axis load of the DQ axis is directly related to the tower top load Mz, and the Q-axis load is equal to _Mz . The tower top load collected by the sensor is used as the input signal of the independent pitch control. According to the yaw of the tower top coordinate system and the hub coordinate system, The relationship between the angles, the load M _x and M _y on the top of the tower are rotated and transformed, and the D-axis load of the DQ axis is calculated. In the process of transformation, the additional bending moment of the gravity of the cabin on the top of the tower is considered. Therefore, when calculating the D-axis load In the process, it is also necessary to subtract the additional bending moment exerted by the gravity of the cabin on the top of the tower; among them, the coordinate rotation transformation is required to obtain the DQ axis load from the transformation of the load on the top of the tower, and the transformation is as follows:

In the formula, M _D represents the D-axis load, M _Q represents the Q-axis load; M _x , M _y , and M _z represent the loads in the three directions of the tower top; φ represents the yaw angle of the cabin; F _G represents the gravity of the cabin, and L represents The distance from the center of gravity of the nacelle to the central axis of the tower; in this transformation formula, not only the rotation transformation caused by the yaw of the nacelle is considered, but also the additional bending moment caused by the gravity of the nacelle;

2) Pass the load of the D-Q axis through the low-pass filter, notch filter, and PI controller to generate the D-Q axis pitch command and limit the output. The specific conditions are as follows:

Knowing the DQ shaft load, that is, knowing the unbalanced load on the impeller plane, to eliminate the unbalanced load on the impeller plane, it is necessary to design a controller from the DQ shaft load to the DQ shaft pitch command. Here, the PI controller is used to control the DQ shaft. The pitch command is used to eliminate the unbalanced load of the DQ axis. Since the load signal contains high-frequency noise, these high-frequency components are useless for load reduction and will only disturb the control system. Therefore, low-pass filters and traps need to be added to the controller. frequency filter, for the sake of safety, the pitch command output by the PI controller needs to be limited, and the limited DQ axis pitch command is obtained; among them, since the DQ axes are mutually independent and completely decoupled, therefore, The D-axis load and the Q-axis load are controlled separately, that is, the D-axis load outputs the D-axis pitch command θ _D after passing through the PI controller, and the Q-axis load generates the Q-axis pitch command θ _Q through the PI controller;

3) Invert the pitch command of the D-Q axis to obtain the pitch command on each blade, and then superimpose it on the unified pitch command. The specific conditions are as follows:

The transformation from the D-Q axis pitch action field to the pitch increment of the three rotating blades is called the D-Q axis rotation inverse transformation, and the formula is as follows:

where {θ ₁ θ ₂ θ ₃ } is the pitch angle increment of each blade, is the azimuth angle of the impeller; considering the time delay, an azimuth offset δ needs to be introduced at the impeller azimuth angle of the DQ axis rotation inverse transformation formula, and an azimuth offset δ is added to the azimuth angle of the impeller to offset the controller’s The various time delays in the control loop, therefore, the inverse transformation formula is rewritten as:

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1. Mount the sensor on the top of the tower instead of mounting the sensor at the root of each blade. Since the sensor is only installed on the top of the tower, the number of sensors is significantly reduced and the cost is also significantly reduced compared to mounting sensors on the root of the blade. , and the process is relatively easy.

2. The independent pitch control scheme with sensors mounted on the top of the tower is more reliable, because it is only necessary to ensure that the load sensors mounted on the top of the tower work normally. If the independent pitch control scheme with blade root loads is adopted, each The blade root load sensors are functioning normally.

3. Using the tower top load as the input of independent pitch control, the D-Q axis load can be obtained more directly, and the control loop is simpler and more reliable; while using the blade root load as the input of independent pitch control, it is necessary to first convert the blade root load from the rotation coordinate The system is transformed into a fixed coordinate system, which increases the complexity of the control.

Description of drawings

Fig. 1 is a schematic diagram of the hub load reference coordinate system of the present invention.

Fig. 2 is a schematic diagram of the tower load reference coordinate system of the present invention.

Fig. 3 is a schematic diagram of the independent pitch D-Q axis controller of the present invention.

Fig. 4 is a schematic diagram of the overall loop of the independent pitch control of the present invention.

Detailed ways

The present invention will be further described below in conjunction with specific examples.

Referring to Figure 4, the wind turbine generator set provided in this embodiment is based on the independent pitch control method of the tower top load, including the following steps:

1) First, mount the sensor on the top of the tower, and directly collect the tower top bending moments M _x , M _y , M _z through the sensor, and then calculate the D-axis load and Q-axis load from the collected tower top load, that is, the DQ axis The details of the load are as follows:

The D-axis load reflects the unbalance of the wind rotor plane pitch direction, and the Q-axis load reflects the unbalance of the impeller plane yaw direction load. In the wind turbine hub coordinate system, the D-axis load refers to the hub M _y , and the Q-axis load refers to the hub M _z . The hub coordinate system (GL coordinate system) X coordinate axis points from the nose to the tail along the hub centerline, the Y coordinate axis is horizontal and perpendicular to the X axis, and the Z coordinate axis points vertically upward. The hub coordinate system is shown in Figure 1. The purpose of independent pitch control is to eliminate the unbalanced load on the impeller plane, so it is necessary to know the loads that reflect the unbalanced impeller plane, namely the D-axis load and Q-axis load. For this reason, how to obtain the DQ shaft load through the measured tower top load is particularly critical.

The loads collected at the top of the tower include: tower top bending moments M _x , M _y , and M _z . The tower coordinate system is a fixed coordinate system (GL coordinate system), the X coordinate axis points to the south, the Y coordinate axis points to the east, the Z axis is vertically upward, and the coordinate origin is on the central axis of the tower, as shown in Figure 2. The tower coordinate system is different from the hub coordinate system, because the hub coordinate system is fixed on the nacelle and rotates with the yaw of the cabin, while the tower coordinate system is relatively stationary with the ground.

The Q-axis load of the DQ axis is directly related to the tower top load _Mz , and the Q-axis load is equal to _Mz . The tower top load collected by the sensor is used as the input signal of the independent pitch control. According to the deflection of the tower top coordinate system and the hub coordinate system The relationship between the navigation angle, the load M _x and M _y on the top of the tower are rotated and transformed, and the D-axis load of the DQ axis is calculated. In the process of transformation, the additional bending moment of the gravity of the cabin on the top of the tower is considered. Therefore, when calculating the D-axis During the loading process, the additional bending moment imposed by the gravity of the nacelle on the top of the tower needs to be subtracted; among them, the coordinate rotation transformation is required to obtain the DQ axis load from the transformation of the load on the top of the tower, and the transformation is as follows:

In the formula, M _D represents the D-axis load, M _Q represents the Q-axis load; M _x , M _y , and M _z represent the loads in the three directions of the tower top; φ represents the yaw angle of the cabin; F _G represents the gravity of the cabin, and L represents The distance from the center of gravity of the nacelle to the central axis of the tower. In this transformation formula, not only the rotation transformation caused by the yaw of the nacelle is considered, but also the additional bending moment caused by the gravity of the nacelle is considered.

2) Pass the load of the D-Q axis through the low-pass filter, notch filter, and PI controller to generate the D-Q axis pitch command and limit the output. The specific conditions are as follows:

The DQ shaft load is known, that is, the unbalanced load on the impeller plane is known. To eliminate the unbalanced load on the impeller plane, it is necessary to design a controller from the DQ shaft load to the DQ shaft pitch command. In this embodiment, a classical PI controller is used to control the pitch command of the DQ axis to eliminate the unbalanced load of the DQ axis. Since the load signal contains high-frequency noise, these high-frequency components are useless for load reduction and will only disturb the control system, so a low-pass filter needs to be added to the controller (the main function is to eliminate high-frequency noise in the load signal) , Notch filter, the main function of the notch filter is to filter out 3P (three times the frequency of the impeller rotation frequency), because the energy of the 3P frequency is generally higher, and the load after the low-pass filter A considerable component of the 3P frequency is still preserved in the signal, so a notch filter is required to filter it out. The filtered DQ axis load is sent to the PI (proportional + integral) controller, and the output of the PI controller is the pitch command of the DQ axis. In addition, for the sake of safety, the pitch change command output by the PI controller needs to be limited to obtain the limited DQ axis pitch command. Since the D and Q axes are mutually independent and completely decoupled, the D-axis load and the Q-axis load are controlled separately, that is, the D-axis load outputs the D-axis pitch command θ _D after passing through the PI controller, and the Q-axis load passes through the PI controller Generate the Q-axis pitch command θ _Q , and the specific control is shown in Figure 3.

3) Invert the pitch command of the D-Q axis to obtain the pitch command on each blade, and then superimpose it on the unified pitch command. The specific conditions are as follows:

The transformation from the D-Q axis pitch action field to the pitch increment of the three rotating blades is called the D-Q axis rotation inverse transformation, where the D-Q axis rotation inverse transformation formula is as follows:

where {θ ₁ θ ₂ θ ₃ } is the pitch angle increment of each blade, is the impeller azimuth angle. Considering the time delay, an azimuth offset δ needs to be introduced in the impeller azimuth angle of the DQ axis rotation inverse transformation formula. The various time delays of the controller in the control loop are offset by adding an azimuth offset δ at the impeller azimuth. Therefore, the inverse transformation formula is rewritten as:

The independent pitch control is mainly used to reduce the 1P frequency component of the blade out-of-plane load, and also reduce the bending moment of the hub and the main shaft. It has been verified by practice that in the method of the present invention, these loads can be basically eliminated at the peak frequency spectrum of 1P frequency, so that the independent pitch control can significantly reduce the fatigue load, because the 1P frequency load is the dominant component in fatigue, generally Next, the bending moment outside the root of the impeller can be reduced by 20%, while the shaft bending moment can be reduced by 30% to 40%. Compared with the prior art, the method of the present invention can ensure the reliability of the independent pitch control and effectively reduce the cost of the independent pitch control, which has practical promotion value and is worthy of popularization.

The implementation examples described above are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Therefore, all changes made according to the shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims (1)

1. an independent pitch control method based on a tower top load for a wind turbine, characterized in that it may further comprise the steps: 1) First, mount the sensor on the top of the tower, and directly collect the tower top bending moments M _x , M _y , M _z through the sensor, and then calculate the D-axis load and Q-axis load from the collected tower top load, that is, the DQ axis The details of the load are as follows: The D-axis load reflects the unbalance of the wind rotor plane pitch direction, and the Q-axis load reflects the unbalance of the impeller plane yaw direction load. In the wind turbine hub coordinate system, the D-axis load refers to the hub M _y , and The Q-axis load refers to the hub M _z , the hub coordinate system is the GL coordinate system, the X coordinate axis points from the nose to the tail along the hub centerline, the Y coordinate axis is horizontal and perpendicular to the X axis, and the Z coordinate axis points vertically upward; independent pitch The purpose of control is to eliminate the unbalanced load on the impeller plane, so it is necessary to know the load reflecting the unbalanced impeller plane, that is, the D-axis load and the Q-axis load. Therefore, how to obtain the DQ-axis load through the tower top load is particularly critical; The loads collected at the top of the tower include: tower top bending moments M _x , M _y , M _z , the tower coordinate system is a fixed coordinate system, that is, the GL coordinate system, the X coordinate axis points south, the Y coordinate axis points east, and the Z axis is vertical Upwards, the coordinate origin is on the central axis of the tower, and the tower coordinate system is different from the hub coordinate system, because the hub coordinate system is fixed on the cabin and rotates with the yaw of the cabin, while the tower coordinate system is relatively stationary with the ground; The Q-axis load of the DQ axis is directly related to the tower top load _Mz , and the Q-axis load is equal to _Mz . The tower top load collected by the sensor is used as the input signal of the independent pitch control. According to the deflection of the tower top coordinate system and the hub coordinate system The relationship between the navigation angle, the load M _x and M _y on the top of the tower are rotated and transformed, and the D-axis load of the DQ axis is calculated. In the process of transformation, the additional bending moment of the gravity of the cabin on the top of the tower is considered. Therefore, when calculating the D-axis During the loading process, the additional bending moment imposed by the gravity of the nacelle on the top of the tower needs to be subtracted; among them, the coordinate rotation transformation is required to obtain the DQ axis load from the transformation of the load on the top of the tower, and the transformation is as follows: <mfenced open = "{" close = ""><mtable><mtr><mtd><mrow><msub><mi>M</mi><mi>D</mi></msub><mo>=</mo><msub><mi>M</mi><mi>y</mi></msub><mi>c</mi><mi>o</mi><mi>s</mi><mrow><mo>(</mo><mi>&amp;phi;</mi><mo>)</mo></mrow><mo>+</mo><msub><mi>M</mi><mi>x</mi></msub><mi>s</mi><mi>i</mi><mi>n</mi><mrow><mo>(</mo><mi>&amp;phi;</mi><mo>)</mo></mrow><mo>-</mo><msub><mi>F</mi><mi>G</mi></msub><mi>L</mi></mrow></mtd></mtr><mtr><mtd><mrow><msub><mi>M</mi><mi>Q</mi></msub><mo>=</mo><msub><mi>M</mi><mi>z</mi></msub></mrow></mtd></mtr></mtable></mfenced> In the formula, M _D represents the D-axis load, M _Q represents the Q-axis load; M _x , M _y , and M _z represent the loads in the three directions of the tower top; φ represents the yaw angle of the cabin; F _G represents the gravity of the cabin, and L represents The distance from the center of gravity of the nacelle to the central axis of the tower; in this transformation formula, not only the rotation transformation caused by the yaw of the nacelle is considered, but also the additional bending moment caused by the gravity of the nacelle; 2) Pass the load of the D-Q axis through the low-pass filter, notch filter, and PI controller to generate the D-Q axis pitch command and limit the output. The specific conditions are as follows: Knowing the DQ shaft load, that is, knowing the unbalanced load on the impeller plane, to eliminate the unbalanced load on the impeller plane, it is necessary to design a controller from the DQ shaft load to the DQ shaft pitch command. Here, the PI controller is used to control the DQ shaft. The pitch command is used to eliminate the unbalanced load of the DQ axis. Since the load signal contains high-frequency noise, these high-frequency components are useless for load reduction and will only disturb the control system. Therefore, low-pass filters and traps need to be added to the controller. frequency filter, for the sake of safety, the pitch command output by the PI controller needs to be limited, and the limited DQ axis pitch command is obtained; among them, since the DQ axes are mutually independent and completely decoupled, therefore, The D-axis load and the Q-axis load are controlled separately, that is, the D-axis load outputs the D-axis pitch command θ _D after passing through the PI controller, and the Q-axis load generates the Q-axis pitch command θ _Q through the PI controller; 3) Invert the pitch command of the D-Q axis to obtain the pitch command on each blade, and then superimpose it on the unified pitch command. The specific conditions are as follows: The transformation from the D-Q axis pitch action field to the pitch increment of the three rotating blades is called the D-Q axis rotation inverse transformation, and the formula is as follows: where {θ ₁ θ ₂ θ ₃ } is the pitch angle increment of each blade, is the azimuth angle of the impeller; considering the time delay, an azimuth offset δ needs to be introduced at the impeller azimuth angle of the DQ axis rotation inverse transformation formula, and an azimuth offset δ is added to the azimuth angle of the impeller to offset the controller’s The various time delays in the control loop, therefore, the inverse transformation formula is rewritten as: