Research On The Automatic Calibration Method Of Pitch-azimuth Two-axis Heliostat

The tracking accuracy of the heliostat is an important guarantee for the efficiency of the solar tower thermal power plant.In this method,we use the deviation of the calibration target and the reflecting spot of the heliostat on the calibration target to automatically calculate the error parameters in the tracking error model of the heliostat.Then the parameterized error model is used to modify the control formula of the heliostat's tracking motion and realize the automatic calibration of the heliostat's tracking error.Firstly,we analyze the mechanical-electrical structure of pitch-azimuth two-axis heliostat,and find out the causes of heliostat tracking errors,and quantify the sources of these errors.According to the coordinates of heliostat and the solar astronomical motion formula,the tracking motion formula of pitch-azimuth two-axis heliostat is established.According to the deviation between the reflecting spot center of heliostat and the focus target center,the least square estimation model of error parameters is established,and the realization algorithm of least square estimation is given.The deviation of reflective spot center needs to be obtained by image processing and image analysis.In this paper,we analyze and process the reflection spot image of heliostat.The position of four corners on the focusing target is determined by integral graph method.The energy center of the reflection spot is calculated by two-dimensional Gauss fitting method.Then we introduce the calibration method of camera parameters which suitable for this system.The error parameters in the tracking formula of heliostat can be estimated according to the measured spot deviation and the reflection spot error model of heliostat.The whole automatic calibration system includes image acquisition hardware and software.The software includes the modules of spot image acquisition,spot image analysis,error parameter estimation,image acquisition system calibration,database management and OPC communicationAt the end of this paper,the development platform and graphical user interface of the whole software are introduced.The software basically realizes several functional modules mentioned above.This system can be used for automatic error calibration of the two-axis tracking heliostat in tower solar thermal power plant,and improve the tracking accuracy of the heliostat.