Collective Blade Pitch Control for Wind Turbine Tower Fatigue
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Solution Overview
Problem
Wind turbines experience significant tower fatigue due to high frequency vibrations, particularly when the 3P frequency of the rotor blades coincides with or is close to the coupled mode frequency of the tower and floating platform, leading to reduced lifespan.
Innovation Solution
A controller adjusts the collective pitch of the rotor blades by generating orthogonal components from sensor signals, applying phase shifts and amplitude limits to mitigate high frequency content, specifically using a second-order generalized integrator to reduce tower oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the rotor operates at nominal speed with standard pitch control, then power generation efficiency is maintained, but tower fatigue increases significantly due to resonance between 3P frequency and coupled mode frequency
Solution Approach 1:
The invention actively controls mechanical vibrations by detecting tower oscillations and applying counter-vibrations through rotor blade pitch adjustment. The controller generates a counter-vibration signal that is 180 degrees out of phase with the detected tower oscillation, creating destructive interference that reduces the amplitude of resonant vibrations and protects the tower from fatigue damage while maintaining nominal operating speed
Solution Approach 2:
The invention implements a feedback control system where tower oscillations are continuously monitored by sensors, processed by the controller to determine the magnitude and phase of resonant vibrations, and used to generate appropriate pitch adjustment commands. This closed-loop feedback enables real-time suppression of tower vibrations without affecting the overall power generation efficiency
2Reliability
If active pitch control is applied to dampen tower vibrations, then tower fatigue is reduced, but control system complexity increases
Solution Approach 1:
The invention uses rotor blade pitch angle as an intermediary control variable to indirectly influence tower vibrations. Instead of directly actuating the tower or adding complex vibration damping mechanisms, the system modifies the aerodynamic loading on the blades through pitch adjustment, which in turn creates counter-vibrations that dampen tower oscillations. This indirect control approach simplifies the overall system architecture
Solution Approach 2:
The pitch control system serves multiple functions: it maintains power generation efficiency by controlling rotor speed, and simultaneously reduces tower fatigue by generating counter-vibrations. This multi-functionality eliminates the need for separate vibration damping systems, reducing overall control system complexity while achieving both objectives
3Reliability
If rotor blade pitch is adjusted to counteract tower oscillations, then vibration amplitude is reduced, but precision of pitch control must be increased
Solution Approach 1:
The invention applies periodic pitch adjustments synchronized with the tower oscillation frequency. By detecting the phase and amplitude of tower vibrations and applying pitch commands at the appropriate moments in the oscillation cycle, the system creates periodic counter-vibrations that accumulate destructively over time, effectively reducing vibration amplitude without requiring excessive pitch control precision
Solution Approach 2:
The system dynamically changes pitch angle parameters in response to detected tower oscillations. By continuously adjusting the pitch angle based on real-time vibration measurements, the control system adapts to varying operating conditions and maintains effective vibration suppression without requiring ultra-precise static pitch settings
Data Source
AI summary
The invention relates to adjusting collective pitch of the wind turbine rotor blades. A sensor signal is received, from wind turbine sensors, indicative of wind turbine rotor loading in a fore-aft direction. A first component is determined, based on the received sensor signal, in the fore-aft direction, the first component including high frequency collective content, greater than 2P frequency content, from the received sensor signal. A second component that is orthogonal to the first component is generated. The first and second components are rotated about a phase angle to obtain first and second phase-shifted components. A collective pitch reference offset value is determined for the three rotor blades based on the first or the second phase-shifted component. A control signal is transmitted to adjust collective pitch of the rotor blades based on the determined collective pitch reference offset value.