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.
Temperature control of a solar furnace for material testing
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 article 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 the 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 characterised by imposing a solar radiation flux profile. On both experiment types there are strong nonlinear effects, a significant degree of parametric uncertainty and disturbances, such as solar radiation fluctuation due to clouds and to sun's apparent movement. Although the actuator (shutter) is much faster than the thermic system, it may destabilise the overall controlled system. The contribution of this article 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.
PULSE-STEP CONTROL
Abstract The paper presents a new method for obtaining fast response to set point changes by using a nonlinear feedforward which is obtained by solving a nonlinear equation. Pulse-step control is simple and gives a settling time close to the time where the impulse response reaches its maximum. The fact that the response time is matched to the process dynamics makes the method more robust than time-optimal control. The feedforward generated by pulse-step control can conveniently be combined with feedback based on PID control.