Transformador diferencial linear variável em rastreador solar para um sistema de energia solar concentrada do tipo refletor linear Fresnel

Abstract

This work proposes a solution to increase the efficiency of the tracking process of a Linear Fresnel Reflector (LFR) type of concentrated solar energy (CSP). A linear variable differential transformer (LVDT) was coupled to the axis of the reflecting mirror to indicate its angular position during the period of operation. The position obtained through the LVDT is input from a control system that has been developed to compensate for the angular position of the reflecting mirror at times when there are external perturbations or problems in the mechanical positioning system. It was necessary to construct a low cost LVDT, as well as the mechanical structure of the reflector system and the instrumentation circuit. The matlab/simulink was used to simulate the electric and geometric models of the LVDT and the electronic circuit of instrumentation. Regarding the coupling of the sensor to the axis of the reflector mirror, it was done through a pulley. A simulation evaluation of the influence of the pulley radius on the error of the mirror position reading was performed for a same sensor accuracy value. The influence of the sensor’s accuracy value on the inclination error of the reflector mirror was also checked. To determine the accuracy of the transducer in practice, a repeatability test was performed. Ten calibration curves were obtained and then the margin of error was calculated, with a confidence level of 99%. It was then found that a pulley having a radius of 8.5 cm would be sufficient to control the position of the mirror with a 0.21◦ error. The accuracy of the concentrator system was determined with the LVDT coupled to the structure, also using repeatability test. Ten calibration curves were obtained and the margin of error was determined, also with a confidence level of 99%. An evaluation of the best installation height of the receiver was also made to reduce the radiation losses. In addition, the relationship between the radiation losses and the horizontal installation distance of the reflecting mirrors was determined in relation to the receiver. In practice the maximum error in reading the angular position of the reflecting mirror was 0.27 ◦ , which makes it possible for 96.92% of the radiation reflected by the farthest mirror, and 100% of the radiation reflected by the other mirrors, to reach the receiver positioned at 3.47 m height.