Floating Offshore Wind Turbine MIMO Control for Platform Stability
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Solution Overview
Problem
Floating offshore wind turbines (FOWTs) face instability issues due to non-minimum phase zeros in blade pitch feedback, which complicates control systems and can lead to closed-loop instability, especially at high wind speeds, affecting generator speed and platform motion.
Innovation Solution
A combined gain-scheduled proportional-integral (PI) and platform feedback (PF) control system is implemented, along with a single-input, single-output (SISO) proportional-integral control loop and multi-input, multi-output (MIMO) control loops to stabilize FOWTs by adjusting blade pitch and torque resistance based on wind speed and platform pitch measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If blade pitch feedback is used to control generator speed, then generator speed regulation is improved, but closed-loop instability occurs due to non-minimum phase zeros
Solution Approach 1:
The patent implements a multi-loop feedback control system that includes both blade pitch feedback and platform motion feedback. The platform feedback loop measures platform pitch angle and uses it to adjust blade pitch, creating a compensatory mechanism that stabilizes the system despite the non-minimum phase zeros in the direct blade pitch to generator speed transfer function.
Solution Approach 2:
The patent introduces platform motion measurements as an intermediary variable in the control loop. By measuring platform pitch angle and using it to adjust blade pitch settings, the system creates an indirect control path that compensates for the instability caused by direct blade pitch feedback, effectively using platform motion as a mediator to achieve stable generator speed regulation.
2Stability of the object's composition
If multiple feedback loops are introduced to respond to platform motion, then stability is improved, but control system complexity increases
Solution Approach 1:
The patent segments the control system into distinct functional loops: an inner blade pitch control loop for generator speed regulation and an outer platform feedback loop for stability enhancement. This segmentation allows each loop to be tuned and analyzed independently while maintaining overall system stability, reducing the complexity of controller design compared to a fully coupled multi-variable controller.
Solution Approach 2:
The patent implements gain-scheduled proportional-integral (PI) control where controller gains are adjusted based on operating conditions. This dynamic tuning allows the controller to maintain optimal performance across varying wind speeds and platform motions, improving stability without requiring an overly complex fixed-gain multi-loop controller.
3Reliability
If robust tuning of control gains is applied, then stability robustness is improved, but sensitivity to dimensional scaling increases
Solution Approach 1:
The patent uses gain-scheduled PI control where controller parameters are adjusted based on operating conditions such as wind speed and platform motion. This parameter adaptation allows the controller to maintain robust stability across different scaling conditions without being overly sensitive to dimensional changes, as the gains are dynamically tuned to match the current operating regime.
Data Source
AI summary
A control system for a floating offshore wind turbine (FOWT). The FOWT includes a floating base, a tower, a nacelle, and rotor with blades that harvest energy from wind passing the FOWT. Without a rigid support, however, the FOWT is able to move. The controller uses generator speed and platform pitch position of the FOWT as inputs and manipulates blade pitch and torque resistance to achieve stability.