Implementation of the ‘smart’ rotor concept - Wind Power Generation and Wind Turbine Design - page 493

A rib-spar structure has also been proven to be the optimal topology for load
transfer through the blade [106] (see Fig. 16). The rib-spar concept can therefore
also be applied throughout the whole blade, in conjunction with a thermoplastic
composite (TPC) material [107]. TPC materials are more feasible for the multi-
component rib-spar concept because TPC parts can be assembled by means
of welding, which is much faster than adhering and - if done well - leads to a
stronger bond.
Alternatively, the trailing edge can be extended with a fl at morphing surface as
was done by Bak et al. [108] in their load control experiment. Structurally it is a
very favorable solution because only minor adaptations to the blade are required.
The active surface is simply added. The fl at surface could be activated by piezo-
electrics or SMA wires. However, an aerofoil with fl at trailing edge will have to be
developed and a transition to parts of the aerofoil with non-fl at trailing edge will
have to be made. The load carrying part of the cord at sections with control surfaces
is also reduced, assuming that the total cord length must remain the same.
5 Control and dynamics
An important aspect of the smart rotor is the sensor and control strategy for the
load control features. In Fig. 17 the possible control possibilities can be observed.
Implementation of sensors that measure the structural response is most straight-
forward. They can be embedded in or attached to the structure. The problem with
fl ow measurements techniques is that they add complexity to the system and some,
like Lidar or pressure taps, are not reliable enough yet. However, Lidars have
been shown to show great correspondence with cup anemometer data [109] and a
nacelle mounted Lidar that measured turbulence in the infl ow has been reported
[ 110 ]. On the other hand, Lidars do not work under all atmospheric condi-
tions. Pitot tubes may be more feasible and are already suggested for control
purposes by Larsen et al. [111]. Larsen also mentions that the drawback of
measuring the structural response is the phase difference between the load
fl uctuation and the blade response.
With sensors that measure the blade's mechanical loading, such as strain gages,
already some implementations have been seen on wind turbine blades, but not for
control purposes. Here the goal was to measure loads to validate the load assumptions
Figure 17: Various sensor concepts for feedback and feedforward control.