Research On MPPT Control And Islanding Detection Technology Of PV Grid Connected System

In recent years,solar energy,as an inexhaustible energy,has attracted more and more attention.Although the use of solar energy has a very far-reaching significance in alleviating the world energy crisis,but with the continuous use of solar energy,the problems in the use of solar energy technologies are increasingly prominent.The research in this dissertation is aimed at the problem of improving the power generation efficiency in the process of solar power generation and detecting the islanding effect problem which has the great harm in the process of grid connected operation.Because the islanding effect is produced in the operation of the distributed generation grid connected system,so the PV generation grid connected system is first modeled in this dissertation.In this part,aiming at the problems of tracking speed,tracking accuracy and power oscillation existing in the control process of PV cells MPPT,this dissertation proposes a MPPT control method based on CBAS algorithm,which reduces the complexity of the algorithm compared with other group control methods by introducing the advantages of single search of bas algorithm,and reduces the requirements of the controller.In addition,in the process of algorithm operation,the logistic model of chaos algorithm is introduced to expand the scope of algorithm search,effectively avoiding the premature problem of the original bas algorithm.First of all,CBAS algorithm is mathematically verified by using two categories and four kinds typical functions,and then CBAS algorithm is applied to MPPT control,and its advantages in speed and accuracy in MPP tracking process are verified by simulation.In the research process of islanding effect detection technology,this dissertation aims at the common islanding detection methods which have the problems of large detection blind area,great impact on the power quality of power grid in the application process,and poor parameter setting may lead to slow detection speed.In this dissertation,firstly,an islanding detection method with the second quarter cycle and the fourth quarter cycle current amplitude disturbance is introduced,which effectively reduces the impact on the power quality of the power grid under the same power factor as other detection methods.In order to reduce the blind area of the original current amplitude disturbance method,an adaptive current amplitude disturbance method is proposed,then,combined with the above methods,a new islanding detection method based on Fuzzy low harmonic control is proposed by using fuzzy control,that is,by introducing the fuzzy control based on the change of PCC voltage frequency and the change rate of frequency,to control the initial disturbance factor of adaptive current amplitude disturbance method to reduce the impact of islanding detection method on power quality of power grid andislanding detection blind area in normal operation of the system,and there is no problem of bad parameter setting on the impact of detection speed.Finally,in order to further reduce the impact on the power quality of the power grid,a hybrid fuzzy low harmonic islanding detection method is proposed based on the passive islanding detection method.Firstly,the passive islanding detection blind area is used to select the detection method,that is to say,passive islanding detection method is preferred to reduce the harmonic output.If it is in the passive islanding detection blind area,then fuzzy low harmonic islanding detection method is used to further reduce the impact on power quality of power grid to a certain extent.The effectiveness of the above method is verified by simulation.The dissertation has 76 pictures,11 tables,and 58 references.