Advanced Controller Optimization

◀ Back to projects overview P201103-001-2BE

2-B Energy is developing a dedicated offshore wind turbine with a lower Cost of Energy (CoE) based on: a full jacket support structure concept with integrated design of support structure and foundation; suitable for large distance from the coast with helicopter access; sophisticated control system to reduce dynamic and extreme loads; and optimized for high availability by efficient service & maintenance & repair. The turbine is categorized as a 6MW, 2 blade horizontal axis wind turbine. The turbine is referred to as 2B6.

Main objective of the project
The main objective of this project was to reduce the Cost of Energy by optimization of the basic “conventional” wind turbine control system. Advanced “non-conventional” control strategies were investigated in order to achieve reduction in the fatigue and extreme load spectrum; and where possible improve the annual energy production (AEP) of the 2B6 turbine. Different types of advanced control strategies were investigated with the following objectives:

Reducing extreme loads during extreme events (mainly wind gusts) and avoiding unnecessary shutdowns during normal operational conditions caused by overspeed or overpower.
Reducing the fatigue loads upon the support structure by damping the motion in the fore-aft and side-side direction of the turbine.
Reducing the fatigue loads by mitigation of the negative effects of rotor imbalance, support structure wake, wind shear and other exitations.
Reducing the activation of the yaw motors, and thereby reducing the fatigue loading on the yaw system by controlling the yaw misalignment by pitch motion.

Reduction in the load spectrum results in reduction of the Rotor-Nacelle Assembly (RNA) mass and the support structure mass due to lighter components resulting in reduced capital expenditures (CAPEX).

The approach and the results obtained
The approach is to develop advanced control algorithms and investigate their effectiveness to decrease fatigue or extreme load levels of the 2B6 wind turbine, using full or reduced load simulation. In parallel to adding advanced control algorithms, the structure and functionality of the controller were re-evaluated and improved to make the system more robust, easier to handle and easier to implement in the controller hardware of the wind turbine. The optimized dynamic-link library (DLL) has been connected to Bladed; GL Garrad Hassan’s Bladed is the industry standard integrated software package for the design and certification of onshore and offshore turbines.

Different control algorithms were developed in different work packages.

By implementating an algorithm which is able to detect a wind gust, the control system can perform a load elevating action up to 2 s earlier compared to the regular overspeed limit. This algorithm and the appropriate measure were able to reduce the overall loads upon the turbine with 20% in some of the extreme wind conditions. Blade mass reduction of 14% was achieved with this algorithm. The availability of the turbine improved by avoiding unnecessary shutdowns.
By implementating an algorithm, to reduce the fore-aft motion of the RNA, the fatigue loads on support structure was reduced with approximately 7% compared to a control system without such an algorithm. Additional investigations to achieve better performance resulted in an increase of fatigue loads of other components.
Reducing the fatigue loads by mitigation of the negative effects of rotor imbalance, support structure wake, wind shear and other exitationsactions were proven not to be effective for the 2B6.
Implementing an algorithm which is able to control the yaw misalignment by pitch motion, was proven to be very effective. The activation of the yaw motors could be reduced to zero without an increase of fatigue levels upon the wind turbine or support structure. Not activating the yaw motors reduces the need of internal consumption of produced wind energy and the alignment of the turbine with the wind is better. A limited increase in pitch activity was noted.

The integrated design approach of wind turbine, support structure and control system enabled 2-B Energy to improve the control behavior of the turbine to achieve reductions with respect to loading upon the wind turbine. These reductions in loading enhance reduction of mass of individual components, and thereby reduce the material costs. All these improvements lead to a reduction in Cost of Energy. This project was initiated after FLOW Project P201101-002-2BE, Controller Optimization for 6MW 2 Bladed Offshore Wind Turbine, because the results of that FLOW Project showed significant reductions in loads when optimizing the control design tools. This project is part of the two-folded path with a focus upon the control system while the other FLOW project of 2-B Energy focused on the upgrade to a 140 meter rotor diameter which improved annual energy production significantly. Both projects are interlinked due to this common goal: Improving the 2B6 design.

Contribution of the project results to cost and risk reduction for Far-offshore wind energy
The estimated reduction in CAPEX and the increase in AEP for this project are quantified as:

CAPEX Blade mass reduction of 5% due to lowering extreme loads

AEP Availability increase of 0.5% due to avoiding unnecessary shutdown.

The Cost of Energy reduction over the entire lifetime was quantified by using the FLOW Cost Model which shows a reduction of CoE of 1% compared to the baseline for Dutch wind farms in 2010. Although the comparison made here is between two 2-B Energy concepts/designs the results achieved could also be applicable in a broader sense as improvement are mainly related to controller optimizations.