Title: Research on Airborne Wind Energy Systems at University of Porto
and
Automatic Circular Take-off and Landing of Tethered Aircraft
Abstract:
In this talk, I start by describing the research context and interests of our
group at University of Porto, in particular the research on Airborne Wind
Energy Systems.
In second part of the talk, I describe a specific
recent work: the development of an automatic take-off and landing framework
for tethered airplanes. In particular, we develop a control system for
circular take-off and landing of a self-propelled, fixed-wing, tethered
aircraft. The aim is to include the framework in an Airborne Wind Energy
System.
Airborne Wind Energy Systems (AWES) are devices
that convert wind energy into electricity using autonomous aircraft attached to
the ground by a tether. These devices can harvest wind energy at high
altitudes, where the wind is stronger and more consistent, being able to generate
electricity from a yet unexplored renewable energy resource. One of the main
challenges in the development of AWES into a commercially viable and
competitive renewable energy technology is the ability to operate safely,
reliably, and autonomously for long periods of time in several weather and
environmental conditions. To achieve fully autonomous operation it is crucial
to develop reliable Automatic Take-Off and Landing (ATOL) schemes for tethered
aircraft.
In the developed control system, we use a hierarchical
control architecture. In the top layer, we design a supervisory controller that
is responsible for governing the transition between flight phases, for
path-planning, and for setting the references to the lower-level controllers at
each phase of operation. The controllers designed for each phase range from
simple PID, designed for one control-variable, to multivariable optimal
regulators for the locally linearized systems.The developed framework has been
tested in simulations and in a small-scale prototype. The results show the
viability of the approach to take-off, attain a certain altitude, and landing.
The analysis also reveals the limits on the maximum altitude attainable with a
fixed-tether length as a function of the path radius.