Project

The pitch system of a wind turbine is one of the systems used for regulating the power production of the wind turbine. The Pitch system may turn the blades of the turbine from approximately 0 to 90 degrees around its own axis and thus regulate the energy input from the wind to the turbine. If the blades are turned into a 90 degree position the turbine will stop rotating and the energy production is stopped. If an error occurs in the turbine and it is necessary to shut the turbine down before extensive damage occurs, an emergency stop is performed by turning the blades to their 90 degree position. The pitch system is the primary safety system of the turbine.

As the pitch system has an essential function of the wind turbine it is extremely important that the system is reliable and available. Especially for offshore wind turbines it is extremely important that no other maintenance than the scheduled has to be performed. Research shows that pitch systems are currently responsible for 22% of wind turbines' total downtime.
A combination of lower cost and increased reliability and availability on the hydraulic pitch system will reduce both the total cost of ownership (TCO) and Total Cost of Energy (TCE).

This project aims to significantly increase the reliability and availability of the pitch systems compared to current hydraulic and electric pitch systems. This is done through a modular way of thinking in which the entire system is brought out in the rotating hub and distributed in three individual systems - one for each wing. Through this transformation it is the goal to reduce the price by 20% while the number of components is lowered by 10%.

To increase uptime for a hydraulic pitch system, external leakage from the hydraulic components must be eliminated. This will be achieved through reductions in external leakage paths to both the environment in the hub of the turbine and nature where the turbine is erected. In 2012, 74% of the offshore wind turbines were installed with hydraulic pitch systems. Of the total offshore capacity, 86% of the turbines are controlled by hydraulic pitch systems (2012). It is the goal for the new hydraulic pitch system that it must be in new offshore wind turbines already being installed with hydraulic pitch, but by the modular thinking and plug and play setup it is possible to access turbine manufacturers who use electric pitch and thus take greater market share.

The technical challenge in designing a lasting structure and PTO is the key issue for any wave energy concept. The project aims at solving this main hindrance for wave energy converters. The intention with the project is to further develop a digital hydraulic PTO system with focus on the mechanical implementation.

It is also the intention of the project to broaden the knowledge to more than just a single absorber system. In reality, a WEC most often consists of several moving parts in the water, such as several floats which strongly interact hydrodynamically and possibly also mechanically. The focus in the project is, therefore, also on array effects.

The purpose of the project is to:

Perform numerical and small-scale laboratory array interaction tests with several
absorbers in an array consisting of multiple closely spaced point absorbers. Experimental tests will be performed at small scale in a wave basin on 5 existing experimental set-ups which are available at the Department of Civil Engineering, Aalborg University.

Further develop full-scale digital hydraulic PTO system. The use of better and
cheaper components, and including further measurements of forces and accelerations. This is achieved by upgrading, improving and further developing the digital hydraulic PTO-system, which is tested at the Department of Energy Technology, Aalborg University. Development will have a strong focus on the valve control strategies to reduce and minimize the loads on the structure by more intelligent switching of the valves, while maintaining a high power output.

Apply existing methods and do further development on fatigue analysis, reliability and risk assessment strategies for a digital hydraulic PTO. Tools like Fault Three Analysis (FTA)/Failure Mode and Effects Analysis (FMEA) will be used to define critical failure modes of the PTO system and their influence on the structural loads. The fatigue analysis of the structural parts is performed using existing probabilistic reliability methods.

Measure in reality prototype performance of the digital hydraulic PTO which
Wavestar plans on implementing at their demonstrator test machine at Hanstholm. Sensors for measuring forces, pressures and accelerations will be implemented in the demonstrator, thereby enabling real investigations on the behaviour of the system and making further development possible.

Investigate new control strategies to maximize the power output of a highly
efficient PTO while the minimization of structural loads is taken into account. Relevant parameters such as PTO efficiency, motion and force constraints are included in the design. The strategies are to be implemented in the wave basin and ultimately in Wavestar test machine at Hanstholm.