What an incredible article. A positive and insightful tour de force of AWES academic research.
I find it an astonishingly honest account of AWES history from the academic viewpoint.
I’m going to give a big response to
Electricity in the air: Insights from two decades of advanced control research
and experimental flight testing of airborne wind energy systems.
The title tells you what to expect.
I’m going to be quite blunt
The clarity with which the authors present the breadth of work is brilliant.
This is how AWES was laid out in the books. This is a great guide to consult if you need to know the development of most any particular aspect of AWES research.
The progress, breadth and quality of research work into control systems over those two decades has been incredible. It’s a huge and valuable lot of work. Ground-breaking in many cases. With uses applicable in other industries too.
It’s a remarkable account of a huge academic journey. But it leaves me as ever questioning the logic of the overall approach in academic work, how deep these insights were and how broadly the Kite and AWES research communities outside of academia were consulted or observed.
The abstract is inspiring but foretells the conclusion
we start with…
> Because the flight operation of tethered devices can be adjusted to a varying wind resource, the energy availability increases in comparison to conventional wind turbines. Ultimately, this represents a rich topic for the study of real-time optimal control strategies that must function robustly in a spatiotemporally varying environment. With all of the opportunities that airborne wind energy systems bring, however, there are also a host of challenges, particularly those relating to robustness in extreme operating conditions and launching/landing the system (especially in the absence of wind). Thus, airborne wind energy systems can be viewed as a control system designer’s paradise or nightmare, depending on one’s perspective.
And in the Conclusion
Conclusions
Airborne wind energy (AWE) represents a promising technology that has grown over the past decade from a tight cluster of organizations pursuing initial concept designs to a thriving research and development field consisting of over 60 institutions worldwide. Just as the size of the AWE community has grown over the past decade, so has the maturity of both the control architectures used to harvest the wind energy and the prototypes –
We are stuck in the single line single kite control loop.
You can see why AWES research would start from a controls perspective. Control is a very appealing hammer to wield on this problem. We can control planes and kites, we can control wind turbines - Lets control a flying wind turbine.
There is recognition of early alternative concepts especially laddermill and kitegen carousel - even saying
It is worth noting, however, that several multi-kite setups are still under consideration in recent literature
but then with regard to multi-kites
An examination of the aforementioned concepts, along with the timeline along which the concepts were introduced and (where relevant) experimentally prototyped reveals that last decade has seen a gradual transition towards the utilization of crosswind flight, both with airborne and ground-based generation. Due to this trend and the relative dominance of crosswind systems within the AWE control literature, these types of systems will serve as the focus of the technical content in this review article.
We are stuck in a single kite control loop again
with this thing called crosswind flight which none of these single line kites seem capable of
Do we need controls?
Well you would think so when the standard control model of kite dynamics is called
The Unicycle model yet it ignores side slip
For me this is personally very frustrating I genuinely fell of my downhill unicycle about 10 times yesterday. Don’t worry it was mostly over heather. I also have a simple electric unicycle. Amazing machine, just needs an IMU. Thing about unicycling is holding a rail, or holding another unicyclists hand makes unicycle easier… There’s a clue there.
Still on the question do we need controls?
It is also shown in van der Vlugt et al. (2019) that for the ideal case of a massless wing that is not actuated, the angle of attack stays constant on any 3D flight trajectory.
Not really if you just fix a broad enough bridle set. Kites can plough on through an extraordinary wind range … just match the tether angle to keep it in an efficient operational mode.
Here’s more evidence toward AWES research laser focus on power.
Not looking at AWES in the whole.
However, in the scientific literature, the contributions related to launch and landing of AWE systems are by far less numerous than those pertaining to crosswind flight control and power generation, both for ground-gen and fly-gen systems. One reason for this gap is that launch and landing phases can be initially carried out by a human pilot, where the system is subsequently switched to autonomous operation. Indeed, launch and landing phases are rather short and carried out at relatively low speeds, so that a pilot can execute them effectively, in contrast with the power generation phase, which requires a continuous, high level of attention to obtain good orbit repeatability and stabilize the flight pattern. For small-scale systems employing a soft kite, one business model even assumes that re-positioning of the kite after landing is eventually carried out by a crew, thus having non-fully-autonomous operation (see Fig. 26).
As a consequence of the aforementioned factors, the study of the automation problem of launch and landing started several years after that of crosswind flight. For the same reason, the design of systems suitable for fully autonomous, repeatable launch and landing has started in relatively recent times, first for fly-gen systems around 2010, and then for ground-gen systems from around 2014 onward.
OK I’ve been very harsh on AWES academia.
I may have upset some.
That this paper is being shared openly is a great sign of the enthusiasm of AWES academia to progress and develop these incredible technologies cooperatively.
We can only welcome that in these urgent times.
I really appreciate the value of this paper as a guide to the copious valuable works it references so clearly.
I’ll give the last word of my review of this paper back to the paper itself.
Given this record of progress, as documented in this survey paper, a bright future exists for the field.