Wind Turbine Rotor Blade Pitch Control for Extreme Load Mitigation
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Solution Overview
Problem
Conventional wind turbine systems face challenges in effectively mitigating rotor blade loads, particularly during extreme turbulence and wind shear conditions, relying solely on collective or cyclic pitching, which can lead to structural damage and inefficiencies in energy production.
Innovation Solution
A system and method that harmonizes collective and cyclic pitching modes through a hierarchical approach, using cyclic pitching as a primary lever to reduce imbalance loads, with collective pitching addressing pitch system saturation and mean thrust, and coordinating these modes based on load types to minimize extreme loads and energy production loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional wind turbine systems rely solely on collective or cyclic pitching to mitigate rotor blade loads, then the control system structure remains simple, but the system cannot effectively reduce extreme loads during turbulence and wind shear conditions
Solution Approach 1:
The control system is segmented into two independent controllers: a cyclic pitch controller that processes blade deflection signals to reduce imbalance loads, and a collective pitch controller that processes thrust signals to reduce mean thrust. This segmentation allows each controller to specialize in specific load types without requiring complex integrated control logic, thereby improving load mitigation effectiveness while maintaining reasonable system complexity
Solution Approach 2:
The control system achieves multi-functionality by enabling the pitch control mechanism to simultaneously address multiple load types (imbalance loads from blade deflection and mean thrust from wind pressure) through coordinated cyclic and collective pitching actions, rather than requiring separate control mechanisms for each function
2Measurement precision
If additional sensors are installed to measure rotor blade loads accurately, then measurement precision improves, but system cost and complexity increase
Solution Approach 1:
The system uses blade deflection and thrust as intermediary measurements that can be obtained from existing sensors, rather than directly measuring complex load parameters. These intermediaries serve as proxies for the actual loads, allowing accurate load estimation without requiring complex load measurement systems
Solution Approach 2:
Instead of directly measuring the complex rotor blade loads with specialized sensors, the system creates a computational model that copies and reconstructs load information from simpler, already-available measurements of blade deflection and thrust, thereby obtaining accurate load data without additional expensive sensors
3Length of moving object
If cyclic pitching is used to increase tip clearance, then tip clearance improves, but blade root bending moments are not effectively reduced
Solution Approach 1:
The control functions are segmented and assigned to appropriate pitch modes: cyclic pitching is dedicated to tip clearance control while collective pitching handles blade root bending moment reduction. This segmentation allows each control mode to optimize its specific function without compromising the other, resolving the contradiction between tip clearance and bending moment reduction
4Strength
If collective pitching is used to reduce blade root bending moments, then bending moments are reduced, but tip clearance is not effectively increased
Solution Approach 1:
The control system segments the pitch control functions by assigning collective pitching specifically to blade root bending moment reduction and cyclic pitching specifically to tip clearance maintenance. This functional segmentation ensures that each pitch mode addresses its designated objective effectively without interfering with the other control goal
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
Effectively reduces tip clearance loading and blade root bending moments with minimal impact on annual energy production, utilizing existing components without additional sensors, and enhancing energy production in the power curve's knee region.
Implementation Method 1
The rotor blades are the primary elements for converting wind energy into electrical energy. The blades typically have the cross-sectional profile of an airfoil such that, during operation, air flows over the blade producing a pressure difference between its sides. Consequently, a lift force, which is directed from the pressure side towards the suction side, acts on the blade.
Implementation Method 2
providing a first pitching mode, comprising a cyclic pitching mode, for reducing the first type of load, comprising a rotor imbalance; providing a different, second pitching mode, comprising a collective pitching mode, for reducing the different, second type of load, comprising a thrust of the rotor; and coordinating the first and second pitching modes based on the type of the at least first type of load and second type of load to mitigate the loads acting on the rotor blade
Data Source
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AI summary
A method for mitigating loads acting on a rotor blade of a wind turbine includes receiving a plurality of loading signals and determining at least one load acting on the rotor blade based on the loading signals. Further, the method includes determining a type of the load(s) acting on the rotor blade. Moreover, the method includes comparing the load(s) to a loading threshold, such as an extreme loading threshold. In addition, the method includes implementing a control scheme when the load(s) exceeds the loading threshold. More specifically, the control scheme includes providing a first pitching mode for reducing a first type of load, providing a different, second pitching mode for reducing a different, second type of load, and coordinating the first and second pitching modes based on the type of the at least one load to mitigate the loads acting on the rotor blade.