Method for controlling minimum overturning force of vertical axis wind turbine

Abstract

The invention provides a minimum overturning force control method for a vertical axis wind turbine, which relates to the technical field of wind power generation and comprises four steps of determining a target shutdown position, executing shutdown variable pitch control, completing minimum overturning force shutdown and executing starting variable pitch control. According to the method, the shutdown overturning force of the vertical axis wind turbine is fundamentally reduced, specifically, the blades are accurately rotated to the chord length position parallel to the wind direction through active variable pitch control, the static overturning force can be reduced to be 20% or below of the maximum value of a traditional fixed wing mode according to calculation of a typical aerodynamic model, and the core mechanical property is improved, so that the stability of the shutdown overturning force of the vertical axis wind turbine is greatly improved. The main shaft, the bearing and the supporting structure of the wind turbine are subjected to lightweight design according to the remarkably reduced load, so that the material consumption and the manufacturing cost are greatly reduced, meanwhile, the rotational inertia is effectively reduced due to the reduction of the overall weight of the unit, and the starting performance and the energy capture efficiency at the low wind speed are improved.

Description

Technical Field

[0001] This invention relates to the field of wind power generation technology, and in particular to a method for controlling the minimum overturning force of a vertical axis wind turbine. Background Technology

[0002] A vertical axis wind turbine is a wind turbine generator with its rotating axis perpendicular to the horizontal plane. It converts wind energy into electrical energy by rotating its blades under the aerodynamic force of the incoming wind, driving the rotor and generator to rotate. In distributed energy and multi-energy power supply systems, such as remote mountainous areas and islands where access to traditional power grids is difficult, vertical axis wind turbines are ideal independent power supply devices due to their compact structure and good adaptability to wind direction. However, while converting wind energy into mechanical energy, the aerodynamic loads acting on the blades in a vertical axis wind turbine generate thrust along the wind direction on the rotating axis, creating an overturning moment. When this moment exceeds the yield limit of the main shaft and its supporting structure, it will cause the unit to tip over and be damaged. The magnitude of this overturning force is closely related to the wind speed and the angular position of the blades on the rotation circumference. Currently, medium and large vertical axis wind turbines generally use a fixed-wing structure, meaning the blades are rigidly connected to the support frame by bolts, and their windward angle is not adjustable.

[0003] For the shutdown control of vertical axis wind turbines, there are two main existing solutions: one is the resistance energy-consuming braking used in small units, which keeps the unit rotating at a low speed, but this method will continuously wear down the bearings and affect the service life; the other is the mechanical brake used in medium and large units, which keeps the wind turbine completely stationary, but it cannot control the circumferential position of the blades after shutdown, so the unit may stop in the direction of the greatest overturning moment.

[0004] To ensure that the turbine can withstand the maximum torque under extreme wind speeds, the main shaft, bearings, and support structure of the wind turbine often need to be reinforced for extreme loads. This results in high material consumption, increased weight, and higher manufacturing costs. At the same time, the increased moment of inertia deteriorates the turbine's starting performance at low wind speeds. Therefore, this invention proposes a method for controlling the minimum overturning force of a vertical axis wind turbine to solve the problems existing in the prior art. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to propose a method for controlling the minimum overturning force of a vertical axis wind turbine. This invention can actively adjust the blade position during the shutdown phase to minimize the overturning force, and on this basis, achieve structural lightweighting, cost reduction, and improved start-up performance, thereby solving the problems existing in the prior art.

[0006] To achieve the objectives of this invention, the invention is implemented through the following technical solution: a method for controlling the minimum overturning force of a vertical axis wind turbine, comprising a control system, wherein the control system performs the following steps: Step 1: Determine the target stopping location The control system determines the feathering position that makes the chord length of each blade parallel to the wind direction based on the aerodynamic model of the vertical axis wind turbine, and sets this position as the target stopping position. Step 2: Execute shutdown pitch control Upon receiving a shutdown command, the control system sends control signals and power to the pitch drive mechanism corresponding to each blade via slip rings, driving each blade to rotate independently from the working position to the feathering position. The pitch drive mechanism includes a drive motor and a reduction mechanism. Step 3: Stop the machine after achieving minimum overturning force. After the control system confirms that each blade has reached the feathering position through the position detection device, it stops the pitch drive. Step 4: Execute start pitch control Upon receiving the start command, the control system drives each blade to rotate in the opposite direction from the feathering position to the preset working windward position.

[0007] A further improvement is that in step two, the pitch drive mechanism is a servo drive system, which includes a servo driver, a servo motor, and a reduction mechanism, wherein the servo motor meshes with the internal gear bearing at the root of the blade through the reduction mechanism.

[0008] A further improvement is that, in step two, the power supplied by the slip ring includes the main power supply and the emergency power supply. When the main power supply fails, the power supply automatically switches to the emergency power supply.

[0009] A further improvement is that, in step three, the position detection device is an angle encoder or a position limit switch mounted on the blade shaft.

[0010] A further improvement is made in step three, where, after stopping the pitch drive, the wind turbine is controlled to yaw in a controlled manner until it comes to a stop, wherein controllable damping is applied to the main shaft of the wind turbine.

[0011] A further improvement is that the controllable damping is applied through a braking system, and the damping magnitude is adjusted according to the real-time wind direction and wind speed.

[0012] A further improvement is that the braking system is a hydraulic braking system or an electromagnetic braking system.

[0013] A further improvement is that, in step four, the start command is automatically triggered when the wind speed sensor detects that the wind speed has reached the start threshold, or it is manually triggered by the operator.

[0014] A further improvement is that the control system is configured to continuously monitor wind direction and wind speed, and automatically generate and execute a shutdown command when it is determined that the extreme wind speed is about to occur.

[0015] The beneficial effects of this invention are as follows: By combining aerodynamic model-based feathering position calculation, independent closed-loop servo pitch drive, reliable emergency power switching, and controllable damped yaw, this invention achieves a fundamental reduction in the shutdown overturning force of vertical axis wind turbines. Specifically, active pitch control precisely rotates the blades to a position where the chord length is parallel to the wind direction. Based on typical aerodynamic model calculations, the static overturning force can be reduced to less than 20% of the maximum value of traditional fixed-wing systems. This improvement in core mechanical properties allows for lightweight design of the wind turbine's main shaft, bearings, and support structures to accommodate significantly reduced loads, thereby greatly reducing material consumption and manufacturing costs. Simultaneously, the reduced overall weight of the unit effectively lowers the moment of inertia, improving start-up performance and energy capture efficiency at low wind speeds. Furthermore, the emergency power supply ensures the completion of pitch control actions in extreme conditions, while the controllable damped yaw mechanism ensures a smooth and controlled shutdown process. The synergy of these two mechanisms significantly enhances safety and operational reliability under fault conditions and severe wind conditions, ultimately achieving comprehensive optimization of safety, economy, and performance. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the control method of the present invention.

[0017] Figure 2 This is a schematic diagram of the control framework of the present invention.

[0018] Figure 3 This is a schematic diagram comparing the overturning force waveforms of two different wind turbines according to the present invention. Detailed Implementation

[0019] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0020] To implement the control method of the present invention, it includes a control system, which includes: Control unit: As the core execution entity of the control method, it is used to perform calculations, judgments and issue instructions. It can be a programmable logic controller (PLC), an industrial computer or a dedicated embedded controller. Sensing and input unit: including wind speed sensor and wind direction sensor, used to provide environmental parameters to control unit, and may also include human-machine interface for receiving manual commands; The execution unit includes a pitch drive module and a yaw damping module. The pitch drive module is configured for each blade and is used to drive the blade to rotate around its own axis. The yaw damping module is used to apply controllable rotational resistance to the main rotating shaft of the wind turbine. Signal and energy transmission unit: mainly refers to slip rings, used to transmit control signals and power between the rotating impeller section and the stationary tower section; Energy protection unit: includes the main power supply for the main circuit and the emergency power supply (such as uninterruptible power supply UPS or battery pack) for emergency situations.

[0021] It should be noted that all of the above units are functional modules. For example, the "pitch drive module" can physically be a system consisting of a servo driver, a motor, and a reducer, or it can be other forms of electric, hydraulic, or pneumatic drive devices; the "yaw damping module" can physically be a hydraulic brake, an electromagnetic brake, or other devices that can generate controllable resistance.

[0022] Example 1 according to Figures 1-2 As shown in the figure, this embodiment proposes a method for controlling the minimum overturning force of a vertical axis wind turbine, including the following steps: Step 1: Determine the target stopping location The control system has a pre-stored aerodynamic model based on a vertical axis wind turbine. This model is based on blade geometry parameters and can calculate the angle at which the chord length of each blade is parallel to the wind direction, i.e., the feathering position, based on the input real-time wind direction data. This position is then set as the target position for the current shutdown. Accordingly, the aerodynamic model can be a mathematical model based on classical blade momentum theory or a simplified model calibrated with experimental data, which is a well-known tool in the field of wind energy technology.

[0023] Step 2: Execute shutdown pitch control When the control unit receives a shutdown command (which can be determined automatically or triggered manually), it sends a control signal containing the target angle (feather position) and drive power to the pitch drive module of each blade through the slip ring.

[0024] The pitch control process is as follows: Taking a common servo drive system as an example, a control signal is sent to the servo driver to drive the servo motor to rotate. Then, the output of the servo motor transmits torque through a reduction mechanism (planetary gearbox). The output end of the reduction mechanism drives the blade to rotate through a rotary drive interface (the output gear meshes with an internal gear ring fixed on the shaft at the root of the blade). The servo motor, reducer, internal gear ring, and their connection methods are conventional designs in the field of mechanical transmission.

[0025] The power supply is ensured as follows: drive power is transmitted from the bottom of the tower to the rotating hub via slip rings, with the power source being the main power supply. An emergency power supply is also included; when the control system detects a main power failure, it immediately and uninterruptedly activates the emergency power supply via a power switching circuit, ensuring the pitch control process is not interrupted.

[0026] Step 3: Stop the machine after achieving minimum overturning force. The control system obtains the actual angle of the blade through a position detection device. Specifically, an angle encoder is installed at the tail of the servo motor, and its signal is fed back to the control unit. Alternatively, a mechanical limit switch may be triggered when the blade shaft reaches the feathering position, and the switch signal may be transmitted back through a slip ring. Then, once the control system confirms that all blades have reached the feathering position, it sends a stop command to the pitch drive module.

[0027] Furthermore, once the blades stop in the feathering position, the wind turbine begins to yaw under the action of the wind. At this time, the control system activates the yaw damping module. Accordingly, in this embodiment, this module is a hydraulic braking system.

[0028] Therefore, the control system calculates the required damping force based on the current wind speed and direction, and sends a control signal to the proportional valve of the hydraulic system to adjust the hydraulic pressure, so that the brake caliper applies a corresponding clamping force to the brake disc mounted on the main shaft, thereby generating controllable frictional damping. As a result, the wind turbine smoothly yaws and decelerates under this damping action until it comes to a complete stop, effectively avoiding yaw oscillation.

[0029] Step 4: Execute start pitch control When the start-up conditions are met (the control system detects that the wind speed is continuously higher than the start-up threshold through the wind speed sensor or receives a manual start-up command), the control system drives each blade to rotate in the opposite direction from the feathering position to the preset working windward position (i.e., the power generation position), thus completing the start-up preparation.

[0030] During the entire operation, the control unit continuously monitors wind speed and direction. When it determines, based on a preset algorithm (wind speed trend prediction), that an extreme wind speed that threatens structural safety is about to occur, it automatically generates and executes the above-mentioned shutdown procedure without external instructions, thereby achieving proactive safety protection.

[0031] It should be noted that: Regarding the "aerodynamic model" involved in this embodiment: its specific form does not affect the implementation of the method; any algorithm or lookup table method that can output the "feather position" is acceptable.

[0032] Regarding the "pitch drive module" involved in this embodiment: Although the embodiment uses a servo system as an example, any drive device that can achieve the function of "receiving electrical signals and driving the blades to rotate precisely to a specified angle" is applicable.

[0033] Regarding the "position detection device" involved in this embodiment: the angle encoder and limit switch are only examples. Any sensor that can provide information on "whether the blade has reached the specified position" (such as a rotary transformer or a combination of multiple proximity switches) can be used.

[0034] Regarding the physical implementation of the control system involved in this embodiment: the above-mentioned functional modules (control unit, sensing unit, execution unit, etc.) can be integrated in a cabinet or installed in a distributed manner. The signal connection between them can be a wired industrial bus or wireless communication.

[0035] Example 2 The difference between this embodiment and Embodiment 1 is that an electromagnetic braking system is used to apply controllable damping. When the control unit needs to apply damping, it supplies power to the coil of the electromagnetic brake. The coil generates a magnetic field, attracting the armature to drive the friction pads to press against the brake disc on the main shaft, generating braking torque. The magnitude of the damping force is achieved by the control unit adjusting the current in the coil (using PWM pulse width modulation control).

[0036] according to Figure 3 As shown, and taking Example 1 as an example, the aerodynamic model involved can be used for theoretical estimation of overturning force. Taking a typical three-bladed vertical axis wind turbine with equal chord length as an example, the maximum wind pressure on a single blade under a given wind speed is... F Estimate using the following formula: In the formula, air density, The drag coefficient of the blade is... This is the projected area of ​​the blade on a plane perpendicular to the wind direction. The incoming air velocity. To simplify the analysis and highlight the main trends, per-unit calculations are often used.

[0037] For traditional fixed-wing aircraft parking methods, the overturning force analysis is specifically as follows: when the blades are fixed at any angle, at the extreme wind speed... V max Below, the sum of the projected areas of the three blades along the circumference and the direction of the force vary periodically with the rotation angle α. By performing vector synthesis calculations on the wind pressure on each blade within one period (0° to 120°), the maximum static overturning force it can withstand can be obtained. F max For easier comparison, this maximum value can be normalized to 1.0 (per unit).

[0038] Regarding the feathering shutdown method described in Embodiment 1, the overturning force analysis is as follows: When all blades actively rotate to the feathering position where the chord length is parallel to the wind direction, the effective windward area of ​​the blades is significantly reduced. Taking the representative NACA0018 airfoil as an example, its maximum thickness is 18% of the chord length. In the feathering position, the projected area of ​​the blade is approximately the projection of its maximum thickness direction, that is, the projected area of ​​a single blade is approximately 0.18A, and for a three-bladed wind turbine, the total effective projected area is approximately 0.54A.

[0039] At this point, the wind pressure on each blade is in essentially the same direction and parallel to the wind direction, therefore there is no significant periodic variation. At the same limiting wind speed... V max Static overturning force at the feathering position F min The theoretical estimate (per unit value) can be simplified to: The coefficient 0.366 originates from the comprehensive calculation of the drag coefficient and projected area relationship under feathering conditions (corresponding to the wind pressure under the maximum projected area being converted to the wind pressure under the projected area in the thickness direction). Based on this calculation, the static overturning force under feathering position... F min The per-unit value is approximately 0.1978.

[0040] Therefore, the simplified theoretical analysis based on the above aerodynamic model and typical airfoil parameters shows that by controlling all blades to reach the feathering position using the method of this invention, the static overturning force during shutdown can be reduced to less than 20% of the maximum overturning force under the traditional fixed-wing shutdown method. This provides a direct theoretical basis for the lightweight design of the wind turbine main shaft, bearings and support structure.

[0041] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the present invention without departing from its framework and scope of application, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling the minimum overturning force of a vertical axis wind turbine, comprising a control system, characterized in that: The control system performs the following steps: Step 1: Determine the target stopping location The control system determines the feathering position that makes the chord length of each blade parallel to the wind direction based on the aerodynamic model of the vertical axis wind turbine, and sets this position as the target stopping position. Step 2: Execute shutdown pitch control Upon receiving a shutdown command, the control system sends control signals and power to the pitch drive mechanism corresponding to each blade via slip rings, driving each blade to rotate independently from the working position to the feathering position. The pitch drive mechanism includes a drive motor and a reduction mechanism. Step 3: Stop the machine after achieving minimum overturning force. After the control system confirms that each blade has reached the feathering position through the position detection device, it stops the pitch drive. Step 4: Execute start pitch control Upon receiving the start command, the control system drives each blade to rotate in the opposite direction from the feathering position to the preset working windward position.

2. The method for controlling the minimum overturning force of a vertical axis wind turbine according to claim 1, characterized in that: In step two, the pitch drive mechanism is a servo drive system, which includes a servo driver, a servo motor, and a reduction mechanism. The servo motor meshes with the internal gear bearing at the root of the blade through the reduction mechanism.

3. The method for controlling the minimum overturning force of a vertical axis wind turbine according to claim 1, characterized in that: In step two, the power supplied by the slip ring includes the main power supply and the emergency power supply. When the main power supply fails, it automatically switches to the emergency power supply.

4. The method for controlling the minimum overturning force of a vertical axis wind turbine according to claim 1, characterized in that: In step three, the position detection device is an angle encoder or a position limit switch installed on the blade shaft.

5. The method for controlling the minimum overturning force of a vertical axis wind turbine according to claim 1, characterized in that: In step three, after stopping the pitch drive, the wind turbine is controlled to yaw in a controlled manner until it comes to a stop, wherein controllable damping is applied to the main shaft of the wind turbine.

6. The method for controlling the minimum overturning force of a vertical axis wind turbine according to claim 5, characterized in that: The controllable damping is applied through a braking system, and its damping magnitude is adjusted according to the real-time wind direction and wind speed.

7. The method for controlling the minimum overturning force of a vertical axis wind turbine according to claim 6, characterized in that: The braking system is either a hydraulic braking system or an electromagnetic braking system.

8. The method for controlling the minimum overturning force of a vertical axis wind turbine according to claim 1, characterized in that: In step four, the start command is automatically triggered when the wind speed sensor detects that the wind speed has reached the start threshold, or it is manually triggered by the operator.

9. The method for controlling the minimum overturning force of a vertical axis wind turbine according to claim 1, characterized in that: The control system is configured to continuously monitor wind direction and wind speed, and automatically generate and execute a shutdown command when it is determined that the extreme wind speed is about to occur.

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