The best way to reduce global warming is, without any doubt, cutting down our anthropogenic emissions of greenhouse gases. But the world economy is addict to energy, which is mainly produced by fossil carbon fuels. As economic growth and increasing world population require more and more energy, we cannot stop using fossil fuels quickly, nor in a short term. On the one hand, replacing this addiction with carbon dioxide-free renewable energies, and energy efficiency will be long, expensive and difficult. On the other hand, meanwhile effective solutions are developed (i.e. fusion energy), global warming can be alleviated by other methods. Some geoengineering schemes propose solar radiation management technologies that modify terrestrial albedo or reflect incoming shortwave solar radiation back to space. In this paper we analyze the physical and technical potential of several disrupting technologies that could combat climate change by enhancing outgoing longwave radiation and cooling down the Earth. The technologies proposed are power-generating systems that are able to transfer heat from the Earth surface to the upper layers of the troposphere and then to the space. The economical potential of some of these technologies is analyzed as they can at the same time produce renewable energy, thus reduce and prevent future greenhouse gases emissions, and also present a better societal acceptance comparatively to geoengineering.

Fighting global warming by climate engineering: Is the Earth radiation management and the solar radiation management any option for fighting climate change?

Assessment of an “Energy Tower” potential in Australia using a mathematical model and GIS

This paper presents a robust feedback control solution for systems with multiple manipulated inputs and a single measurable output. A structure of parallel controllers achieves robust stability and robust disturbance rejection. Each controller uses the least possible amount of feedback at each frequency. The controller design is carried out in the Quantitative Feedback Theory framework. The method pursues a smart load sharing along the frequency spectrum,
where each branch must either collaborate in the control task or be inhibited
at each frequency. This reduces useless fatigue and saturation risk of actuators. 
Different examples illustrate the ability to deal with complex control problems
that current MISO methodologies cannot solve. Main control challenges arise
due to the uncertainty of plant and disturbance models and when a fast-slow
hierarchy of plants cannot be uniquely established.

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Quantitative Feedback Control of Multiple Input Single Output Systems

: This paper presents a summary of the main concepts and references of the Quantitative Feedback Theory (QFT). It is a frequency domain engineering method to design robust controllers. It explicitly emphasizes the use of feedback to simultaneously reduce the effects of model plant uncertainty and to satisfy performance specifications. QFT highlights the trade-off (quantification) among the simplicity of the controller structure, the minimization of the cost of feedback, the existing model uncertainty and the achievement of the desired performance specifications at every frequency of interest. The technique has been successfully applied to control a wide variety of physical systems. After a brief introduction about the essential aspects of the QFT design methodology, including a wide set of QFT references, this paper presents a new method to extend the classical diagonal QFT controller design method for MIMO plants with model uncertainty to a fully populated matrix controller design method. The paper simultaneously studies three cases: the reference tracking, the external disturbance rejection at plant input and the external disturbance rejection at plant output. The work ends showing several real-world examples where the controllers have been designed using QFT techniques: an industrial SCARA robot manipulator, a wastewater treatment plant, a variable speed wind turbine of 1.65 MW and an industrial furnace of 1 MW.

Quantitative Robust Control Engineering: Theory and Applications

In this paper, recursive extensions to the standard equidistant grid method are proposed whereby the gridding is adapted locally such that a prescribed distance is achieved between neighbouring points in the computed value set (template). Also presented is the Prune algorithm, which finds the outer border of a value set defined by a set of points whose nearest neighbour lies within a prescribed distance. The Prune algorithm is part of the recursive grid methods, but can also be used independently with other methods to compute value sets. As an alternative to analytical or search algorithms, a recursive grid algorithm is presented to compute Horowitz–Sidi bounds (QFT bounds, or boundaries). Isaac Horowitz's contribution to computational methods for QFT is outlined in the perspective of the presented algorithms. Copyright © 2006 John Wiley & Sons, Ltd.

Recursive grid methods to compute value sets and Horowitz–Sidi bounds

The Aero-Electric Power Station is the ultimate solar power station, utilizing the dry, hot air of Earth's desert zones. By spraying water at the top of e.g. a 1200 m tall chimney with a diameter of 400 m, the air is cooled by evaporation and flows downwards through turbines at the bottom, generating 380 MW of net electric power. The Aero-Electric Power Station is still in the planning stage, and this paper belongs to a long series of feasibility studies.



The current ‘truth’ model of the Aero-Electric Power Station is a one-dimensional partial differential equation model. The external slowly changing weather, defined as the mean air pressures, temperatures and humidity at the top and bottom of the tower, determines the optimal operating point, i.e. the optimal water spray flow and turbine velocity that give the largest net power. The gross power produced by the turbine is partly delivered to the grid and partly to pump sea water to spray water reservoirs. The reservoirs make it possible to use the pumping power and the spray flow rate as control.



Wind changes cause significant deviations from the mean external air pressures, requiring closed loop regulation to keep the rotor velocity constant. The Aero-Electric Power Station may be modelled as an uncertain, unstable irrational transfer function, with two disturbances (external air pressure deviations at top and bottom), two control variables (turbine power and spray flow), and one output (rotor velocity), without a cascaded structure, giving rise to a robust load sharing control problem.



A robust linear feedback regulator is designed by QFT, in such a way that the load of regulation is shared between the two control inputs. A closed loop step response simulation for one operating condition, using the ‘truth’ model, demonstrates the design. Copyright © 2003 John Wiley & Sons, Ltd.

Control of the Aero-Electric Power Station—an exciting QFT application for the 21st century

The problem of fuel-optimal attitude maneuvering of a space vehicle (SV) with non-fixed time is considered. The state constraint related to the maintenance of artificial gravitation is imposed. This problem is especially important for long-time space missions. The attitude of the space vehicle is controlled by means of a pair of reactive engines which produce a single control torque with fixed direction in the body-fixed frame. An optimal solution is obtained in the class of trajectories belonging to “swinging mode” two-periodic sliding cycling regimes. The solution is found in analytical form and optimal synthesis is obtained.

Michael Borshchevsky

Papers

Control of the Aero-Electric Power Station—an exciting QFT application for the 21st century

Long time missions and the fuel-optimal attitude maneuvering in a swinging mode