Temperature Control of a Solar Furnace with Exact Linearization and Off-Line Identification
The ability to predict the behavior of materials is crucial in several industries due to safety aspects, such as in high temperature furnaces for the production of glass, in the nuclear energy industry or in the high concentrated thermal solar systems. Solar furnaces use concentrated solar radiation that can be used to perform material stress tests with high temperatures. These devices have nonlinear dynamics that are caused by the actuator, the shutter, and by the interaction between the solar energy and the properties of the material. The contribution of this paper consists in the design of a controller for practical use based on the exact linearization method with off-line identification. The aim is to improve the controller performance to track the temperature profile. In this context it is assumed that the thermodynamic properties of the sample material to be tested are unknown.
Singular perturbation stability conditions for adaptive control of a solar furnace with actuator dynamics
A solar furnace is a thermodynamic device that concentrates sun radiation in order to achieve high temperatures at a focus, where a sample of the material to be tested is located. This paper address the problem of designing a control architecture for solar furnaces. It is motivated by the use of a solar furnace as an instrument in material science research to perform two types of experimental tests. In first type, samples are tested in high temperature stress cycles. In these experiments it is important to control the temperature profile. The second test type is characterized by imposing a solar radiation flux profile. On both experiment types there are strong nonlinear effects, a significant degree of parametric uncertainty exists and there are disturbances, such as solar radiation fluctuation due to clouds and to sun's apparent movement. The dominant dynamics is of first order and results from an energy balance performed at the sample. The actuator, consists in a mechanical shutter that reduces the fraction of solar radiation. Although the shutter is much faster than the thermic system, it may severely destabilize the overall controlled system. The contribution of this paper consists in the design of a control architecture for solar furnaces and the application of Singular Perturbation methods in order to derive conditions in the form of bounds for the speed of actuator dynamics so that the closed-loop system is stable.
Solar Processing of Materials: Opportunities and New Frontiers
Abstract Synthesis of materials with unique properties or with a high chemical selectivity is presented as a competitive application domain for concentrated solar energy with respect to laser or plasma systems. To illustrate the general arguments recent experimental data are presented in three domains (1) surface hardening of steel, super hardness of 1000 Hv is obtained without tensile peak at the interface between treated and non treated material (2) oxides nanopowder processing, pure oxide powders and composites are obtained by vapo-condensation with typical size in the range 10–100 nm (3) fullerenes and nanotubes synthesis, a selectivity of 20% for fullerenes is achieved (ratio of fullerenes to soot mass), more recently single wall nanotubes are processed at pressure 450hPa. These results obtained with 2 kW solar furnaces are commented in the view of solar process scalingup.