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Delegates are invited to meet and discuss with the poster presenters during the poster presentation sessions between 10:30-11:30 and 16:00-17:00 on Thursday, 19 November 2015.

Lead Session Chair:
Stephan Barth, ForWind - Center for Wind Energy Research, Germany
Sirko Bartholomay cp.max Rotortechnik GmbH & Co. KG, Germany
Sirko Bartholomay (1) F Mathias Hillmann (1) Erik Miersch (1) Thomas Rische (1)
(1) cp.max Rotortechnik GmbH & Co. KG, Dresden, Germany

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2015 and are published here unedited

Sirko Bartholomay studied aeronautics at the TU Dresden, ISAE Toulouse and DTU Denmark. In his studies he concentrated on aerodynamics and aeroelastics of wings. In his current position at cp.max he works on new approaches to eliminate imbalances of wind turbines. Furthermore, he coordinates a project with different entities to develop a movable trailing edge flap for wind turbines.


Poster Download poster (5.21 MB)


Self-Balancing Power-Optimized Windturbine Control Concept


Windturbines are subject to mass and aerodynamic imbalances which may lead to increased wear of all components of the machine and thereby reduce the operational life span significantly. Furthermore, misaligned pitch zero angles may lead to power losses, as the rated power is achieved at higher wind speeds as previsioned or the flow is stalled over parts of the blade.
The classical approach to eliminate aerodynamic imbalances is the use of optical methods in order to measure the blade pitch alignment. However, numerous measurements of cp.max have shown, that with raising rotor diameter small deviations in geometry or twist lead to severe aerodynamic imbalances. Yet, the latter mentioned effects are not captured by classical optical methods.
cp.max has therefore developed a new approach to eliminate aerodynamic imbalances, which takes the aforementioned effects into account.
This method can easily be automated in the turbine control and the reduced vibration level can be used as a starting point to find the optimal blade pitch zero angle for maximum power output, resulting in a low vibration, power optimized wind turbine. cp.max has filed the aforementioned concept for patent.


Aerodynamic imbalances are caused by errors in the zero blade pitch angle alignment between the blades to one another, differences in twist or geometry, such as different thicknesses, missing/defect flow elements or erosion.
Yet, mostly aerodynamic imbalances are only tried to correct for by measuring the blade angle alignment, often by an optical measurement, which relies only on a measurement at one single radial position. Hereby, the aforementioned effects cannot be corrected for and an onsite intervention is necessary. Especially, on very large turbines, measurements have shown, that small manufacturing tolerances lead to significant aerodynamic issues which demand a new approach.
cp.max has developed a method which is based on the consideration of integrating all acting forces on the blades as one resultant force. A test-pitch method is then used to calculate the optimal blade pitch zero angle adjustment to bring the turbine to an optimal vibration level.
As cp.max has introduced and validated this method on numerous turbines, it has become a standard on-site maintenance procedure.

Main body of abstract

The new procedure has proven its effectiveness to reduce aerodynamic imbalances on numerous turbines in on-site interventions. The procedure is based on a photometric measurement to analyze blade pitch zero angles combined with a vibration analysis. After the blade pitch angles are set to the same zero position, a test pitch is introduced on at least one blade. With the result from vibration analysis before and after the test pitch is introduced, a tare value and tare pointer are used to calculate the optimal blade zero position. The result from this procedure is a turbine with an optimal aerodynamic vibration level.
In contrast to a time consuming on-site intervention, the obvious next step is to introduce this procedure in the control mechanisms of a wind turbine. Thereby, on a regular basis the turbine control can adjust itself to minimal vibration level.
Furthermore, from this low vibration starting point, an optimal blade pitch zero angle can be found iteratively by taking the power curve into consideration.
Finally, a low vibration, power optimized wind turbine is achieved.


A new approach to eliminate aerodynamic imbalances is presented, which has proven its effectiveness a large number of turbines. Especially on large turbines, where classical approaches fail, the new approach is necessary, as it does not only take one discrete blade pitch zero angle into account.
The concept was validated on numerous turbines and is a promising concept to be implemented into wind turbine control mechanisms.
Furthermore, the low vibration level is an excellent starting point to find the power optimized setting of the blade pitch zero angles.

Learning objectives
- Imbalances of Wind turbines
- Classical Methods to eliminate vibrations
- New Approach based on test-pitch
- Integration of the new approach into the control mechanism
- Power optimization