Wind Turbine Rotor Emergency Stop Pitching Control
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Solution Overview
Problem
Existing wind turbine stop processes, particularly during emergency stops, apply extreme bending moments to the tower, which can lead to damage and reduced lifespan, as rapid pitching and thrust changes cause significant pendulum motion and bending moments at the tower root.
Innovation Solution
A method involving fast pitching of rotor blades at 10-15°/s to a position where rotor acceleration is zero, followed by a temporary stop and resumption after a predetermined time period, measured to align with the tower's natural eigen-frequency mode, to minimize aerodynamic thrust and bending moments, using angular acceleration measurements and on-off control for robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If rapid pitching is applied during emergency stop, then stopping time is reduced, but extreme bending moments are generated at the tower root
Solution Approach 1:
The patent applies periodic action by implementing a stop-resume-stop pitching sequence. The pitching motion is interrupted at specific moments (when angular acceleration is zero) to allow the tower to settle, then resumed after a predetermined time period. This periodic interruption pattern reduces extreme bending moments while maintaining reasonable stopping time.
Solution Approach 2:
The patent uses preliminary action by stopping the pitching motion before reaching the final parking position when angular acceleration is zero. This preliminary stop allows the tower to settle and reduces the accumulation of bending moments before the final positioning phase begins.
2Device complexity
If constant angular pitching rate is applied, then control simplicity is maintained, but huge bending moments reach 2.5 times maximum bending moment under ordinary operation
Solution Approach 1:
The patent implements feedback by continuously monitoring angular acceleration and using this information to control the pitching motion. The control system adjusts the pitching rate based on real-time measurements of angular acceleration, stopping when acceleration is zero and resuming after predetermined periods, thereby reducing extreme bending moments.
Solution Approach 2:
The patent applies dynamics by transitioning from a constant pitching rate to a variable pitching rate that responds to real-time conditions. The pitching motion is dynamically adjusted based on angular acceleration measurements, creating a more complex but safer control strategy that prevents extreme loading.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces the magnitude of bending moments at the tower root, preventing potential failure, prolonging the turbine's lifespan, and allowing for less reinforced tower designs by controlling the pitching process to avoid negative thrust forces during the stop process.
Implementation Method 1
aerodynamic forces from the wind on the blades will not cause harm to the wind turbine
Implementation Method 2
account is taken to reduce the pendulum motion of the wind turbine tower that is caused when the positive thrust on the rotor during normal operation providing a deflection of the tower in the downwind direction is replaced by a negative thrust
Data Source
AI summary
A method for controlling a pitch angle of blades of a wind turbine rotor during an emergency stop process of the rotor from an operating state, includes the steps of: (i) continuously determining a measure of an angular acceleration of the rotor, (ii) initiating pitching of the rotor blades and continuing pitching until a time (t2) where the determined angular acceleration of the rotor is substantially zero, and (iii) resuming pitching of the rotor blades at the end of a predetermined time period (t3-t2) after the time (t2) where the determined angular acceleration of the rotor was substantially zero. A wind turbine including an emergency stop control system having a mechanism for controlling an emergency stop process of the wind turbine rotor according to such a method is also contemplated.