The Correction Method Research For Heliostat System With Polar Axis

As one of the most important parts in tower solar thermal power station,heliostat is a kind of energy collecting device which can track the sun and reflect solar radiation on collector.The control accuracy of heliostat tracking control system will directly affect the collecting efficiency of collector.Due to the heliostat system is a multiple degree of freedom and the complex structure of multiple segments.The tracking error is a variety of composite errors caused by mechanical structure,as well as measurement and other aspects.Only heliostat tracking precision of reflection is high enough,higher solar-thermal conversion efficiency can be obtained.Therefore,to reduce the heliostat tracking error and improve the tracking accuracy of heliostat has a great significance to improve the power efficiency of the system.A error of polar axis heliostat tracking control system is analyzed in this paper,it concludes main error sources as follow,1、Measurement error of gravity acceleration,2、Heliostat eccentricity reflecting error.3、zero-point drift of heliostat installed in the South.This Project has mainly established the error model and designed the correction scheme for corresponding error.(1)It is divided into three parts to correct the measurement error of the gravity acceleration sensor:1)For the proportional deviation and zero deviation of gravity acceleration sensor,linear calibration is carried out by using the least square method.2)The non-orthogonal error of the three axis of the needle sensor is corrected by the space coordinate transformation.3)In order to solve the problem of the nonlinear characteristics of the temperature drift of the sensor,this project has designed a new method for measuring angel by double fusion based on gravity sensor and magnetic sensor.(2)For the heliostat reflection eccentricity error,an iterative error compensation algorithm is designed in this paper,after verification,the algorithm can effectively reduce the influence of eccentricity on tracking accuracy.(3)For the zero deviation of heliostat installed in the south,a zero error correction scheme by taking the sun as a reference is designed in this paper.The method mounted a camera on mirror,measure the position of the sun in the camera field of vision to calculate the error and correct the zero deviation.Compared with traditional method,it does not need to install a large calibrating board under the collector,and improves work efficiency though the way of many sets of calibrating system work at the same time.After completing the theoretical derivation and simulation in this paper,by combining the actual project,the heliostats of ShanXiGuoJin have been corrected and tested.The actual operation shows that the correction method in this paper can effectively improve the heliostat tracking accuracy,the heliostat can reflect the sun light on the collector accurately for a long time,and feasibility of the whole scheme is verified.