The objective of DOWEC task 3 of work package 1 has been defined as
?research and devel-opment of wind turbine (power) control algorithms
to maximize energy yield and reduction of turbine fatigue load, and
its optimisation for offshore operation?. In accordance with the DOWEC
baseline turbine and the related DOWEC turbine all activities were focused
on active pitch to vane, variable speed concept. The results of this
task contribute to the:
? set-up of a modular control structure based on theoretical analysis
and industrial needs;
? increase of turbine performance (power production,
load reduction) by additional control features and actions.
It can be concluded that the control structure is superior to ordinary
PD feedback control of the rotor speed. An independent comparison for
the DOWEC turbine using an aerodynamic code, with a state-of-the-art
control structure, has resulted in improvements concerning:
? extreme fore-aft tower bending moment (-40%);
? fatigue fore-aft
tower bottom bending equivalent moment (-50%);
? variations in blade
pitch rate (standard dev. -0.65 dg/s);
? tilt moment (-10%).
The mean power production (10min) in above rated wind speeds was over
99% of its rated value. Opposite to the improvements it has brought
about larger variations in generator speed (standard dev. .5 rpm),
increase of yaw moment (12% ) and radial blade forces (14% ).
The underlying approach of the control structure divides the multivariable
wind turbine system into different independent scalar subsystems by
band fil-tering. As a consequence the resulting setpoints, the pitch
rate and electrictorque, consist of additive contributions of the different
control actions.
Concerning power control, ordinary rotor speed feedback has proved to
be a robust core. However, valuable extensions were developed by wind
speed feed forward control (pitch control) and optimisation around rated
condition (electric torque control).
Promising results have been achieved on fore-aft tower damping by pitch
control. Electric torque control has enabled considerable damping results
of (collective) drive train resonances and possibilities for badly damped
sideward tower vibrations.