Comprehensive Error Analysis And Compensation Strategy Research Of Parallel Concentrated Photovoltaic Tracking Mechanism

With the vigorous development of China’s photovoltaic power generation industry,the technology of concentrated photovoltaic power generation with higher power generation efficiency and lower production cost is increasingly valued.However,due to the structural characteristics of the concentrated photovoltaic power generation systems,the tracking accuracy of the tracking mechanisms is required to be high,and the existing error modeling and error compensation methods cannot meet the tracking requirements.Based on the U-PRU-PUS parallel mechanism developed by the research group in the early stage,this paper proposed a comprehensive error modeling method,carried out a comprehensive error compensation strategy study,and based on the concentrated photovoltaic power generation system,the performances of the parallel mechanism were optimized.Built a parallel configuration machine,and completed the comprehensive error compensation test.The main research contents are as follows:1.By analyzing the vector relationship of each branch chain of the U-PRU-PUS parallel mechanism,the mapping relationship between the driving joints and the attitude of the moving platform was obtained.Based on this,the velocity Jacobian matrix was established,and the workspace was solved using the space boundary search method.Secondly,the differential kinematics equations of U branch chain,PRU branch chain,PUS branch chain and moving platform were established by using the finite element method and substructure synthesis thought,and the differential kinematics equation of the system was obtained by introducing the deformation compatibility condition.The established finite element model was verified by using Abaqus and Adams software for joint simulation.2.Based on the performance requirements of the concentrated photovoltaic system for the parallel tracking mechanism,the dexterity of the parallel mechanism was analyzed using the speed Jacobian matrix.and the dexterity evaluation index was established.The stiffness evaluation index was established by extracting the stiffness sub-matrix.Based on the motion law of parallel mechanism,a workspace evaluation index was proposed.Finally,taking the dexterity,stiffness and workspace of the parallel mechanism as the objective of size optimization,the genetic algorithm was used for multi-objective optimization.Under this optimization strategy,the dexterity and rigidity of the parallel mechanism were increased by 4.9% and 8.5% respectively,and the overall height and length of the driving rod of the parallel mechanism were reduced,which improved the stability and compactness of the parallel mechanism.Although the workspace was relatively small,the reduced area was concentrated in the area with low irradiance in a day.3.Based on the U-PRU-PUS parallel mechanism,a unified error model was proposed.The error model included the elastic deformation under the force of the system and the geometric errors of the components caused by manufacturing.The geometric error model was constructed based on the vector method and the differential kinematics of the parallel mechanism.By analyzing the action mode of elastic deformations and geometric errors on the rods and the coupling mechanism between them,a method of rod position vector correction was proposed,and a unified error model was established by introducing the correction parameters of the rods.The joint simulation was carried out by Abaqus and Adams software,and the geometric error parameters were simulated by adding design variables to Adams software.Finally,the results of the joint simulation were compared with those of Matlab software,and the unified error model was verified.4.The comprehensive error identification method and compensation strategy of the parallel mechanism were studied.The workspace of the parallel mechanism was divided into 100 groups of Euler angles.The positions and attitudes were optimized based on the optimization index O.When the number of optimal positions and attitudes was 18,the geometric error parameters identification requirement was met and the optimization index O tended to be stable.The least square method was used to identify the error parameters of the constructed geometric error model and the modified geometric error model,and then a quasi-static partition method was proposed based on the distribution law of the influence errors.This method improved the efficiency of error parameters identification under the premise of ensuring the compensation accuracy.Finally,by integrating geometric error parameters,elastic deformation and influence error parameters,a comprehensive error compensation strategy was proposed.5.Based on the results of size optimization,a parallel mechanism prototype was developed,and the moving platform was improved for the convenience of measurement.The zero point calibration of the parallel mechanism was completed by multiple measurements of the moving platform with the laser tracker.Then 18 groups of preferred positions and orientations of the parallel mechanism were measured by the proposed Euler angle measurement method of the moving platform.Based on the measured Euler angles,the comprehensive error parameter identification was carried out.Finally,based on the identification results,the comprehensive error compensation test was carried out.Through the compensation,the tracking accuracy of the two Euler angle directions of the parallel mechanism was improved by 75.50% and 81.94% respectively,and the comprehensive error compensation strategy was verified.