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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Advanced rotor technologies' taking place on Tuesday, 11 March 2014 at 11:15-12:45. The meet-the-authors will take place in the poster area.

Ricard Buils Urbano DNV GL Renewables Advisory, United Kingdom
Co-authors:
Barbara Savini (1) F P Alexey Vinogradov (2) Ian Woodrow (1)
(1) DNV GL Renewables Advisory, Bristol, United Kingdom (2) GL Renewables Certification, Hamburg, Germany

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Abstract

Integrated design optimisation and pitch system safety feathering with individual pitch control

Introduction

In recent years Individual Pitch Control (IPC) has attracted growing interest as the size of wind turbines increases and load sensor technology becomes more reliable.This is true both for new projects and in cases where manufacturers choose to fit larger rotors on existing turbines. The control methodology is mature and the focus is now moving towards exploring technologies or removing existing limitations in sensor choice, pitch actuators and safety system functionality to further reduce turbine cost of energy. Further reduction in the offshore cost of energy is achievable through the utilization of 2P-IPC during the support structure design process.

Approach

GL Garrad Hassan has been involved in many IPC projects from control design to field testing and has experience across a variety of applications and turbine configurations. In recent years GH focused on identifying areas where IPC can significantly reduce turbine costs through an integrated design approach of control, subsystems and turbine structure driven by cost of energy analysis. Examples described in the paper include significant reduction of off-shore jacket support structure cost through the use of 2P IPC control, as well as alternative choices for load sensors and pitch actuation systems and their interaction with the safety system.

Main body of abstract

Although the ability of IPC to reduce rotor asymmetric fatigue loads is well known there are still concerns regarding the possible impact on rotor extreme loads in cases of shutdowns with the blades misaligned, typically during safety shutdowns. This paper shows that if IPC is used in conjunction with a blade alignment strategy during safety system shutdowns
rotor extreme loads can actually be reduced compared to collective pitch control. The paper discusses the technical feasibility of introducing such an alignment strategy in the context of current certification requirements.
To address concerns over the cost and reliability of the blade root load sensors used for IPC,GH has looked at alternative sensor arrangements and in particular this paper describes how the use of simpler tower top gauges may be beneficial while preserving the controller performance in terms of load reduction, including the additional benefits of using 2P IPC. This can be particularly important in some offshore applications, for example when using a jacket substructure which can be susceptible to torsional vibration. This paper shows how an integrated approach to the design of the whole structure in combination with its controller can lead to significant cost reduction especially if 2P IPC is included in the design.
The benefits of integrated design also extend to pitch actuators and bearings, particularly when considering increased pitch activity for IPC, or the requirements of large offshore turbines. Using two actuators per blade can have advantages while introducing new certification issues with respect to safety feather reliability.


Conclusion

The work reported here aims to further improve and encourage the use of IPC in the wind industry, and addresses certification issues around safety feathering. The use of 2P IPC may be particularly beneficial in reducing torsional loading of offshore jacket structures. Fatigue load reduction from IPC is well known, but extreme loads can also be reduced by using a blade alignment strategy during safety system shutdowns, and the certification implications of this strategy are discussed. Consideration of cost and reliability may lead to the use of simple tower top gauges instead of blade root sensors.


Learning objectives
This paper presents technology solutions and alternatives to existing IPC control system set-ups, consistent with the certification requirements, which can reduce costs and maximise the benefits of an IPC control strategy. Alternative load sensor and actuator arrangements as well as safety system philosophy are presented, to reduce extreme loads and the costs associated with sensors and actuators. The case study of particular interest to the offshore market demonstrates the particular benefits of 2P IPC.