Research On Hot Spot Fault Diagnosis Of Crystalline Silicon Components In Photovoltaic Power Plants

Energy crisis has become a topic of widespread concern since from 21st century.In the past decades,solar photovoltaic energy,as a kind of clean and renewable energy,has been developed rapidly under the advocacy and support of governments all over the world.In order to ensure the long term stable and efficient operation of PV generation system,researchers and institutes are concerned about the development of new type photovoltaic cell and the improvement of MPPT control method.Meanwhile,module failures like hot spot heating,EVA encapsulation film yellowing,cell crack also received more and more attention.The hot spot heating,also known as localized heating,is caused by the current mismatching inside the PV module.Hot spot heating occurs commonly in the practical application of PV modules,it not only dissipates the power generated by other cells in the form of heat,but also causes the melt deformation or burnout of the solar cells.In severe cases,the hot spot heating can lead to fire and other irreversible damage,which seriously threatens the stability and security of the PV generation system.Hot spot endurance test has become an important part during the PV module certification test.Analyzing the causes of the hot spot heating and developing a hot spot inspection system are quite significant to ensure the performance and quality of the PV modules.The main work of this thesis is as follows:This thesis focuses on the diagnosis of hot spot failures inside the crystalline silicon PV modules.On the fundamental of mastering the mechanism and characteristics of the hot spot heating,a current-based hot spot inspection system is developed for single module by using projector as the light source.Furthermore,we improved the current-based method into voltage-based inspection method for better stability.The validity of the method is verified by experiments.The main work of this thesis is as follows:(1)Study the mechanism and characteristics of the hot spot failure.According to the phenomenon of hot spot failure,combined with the output ?-? curves of it,the sufficient test has been carried out to confirm that crystal defect negates the bypass diode and causes the hot spot failure.(2)Based on the output ?-? characteristics of the hot spot failure,we proposed a current-based hot spot inspection method,and defined a risk factor named HSI(Hot Spot Index).Using a projector as the light,applying Labview and DAQ(Data Acquisition),a current-based hot spot inspection system is developed for single module by using projector as the light source.The validity of the method is verified by experiments.(3)After discover the disadvantage of the current-based method under low illuminance situation,by analyzing the relationship between the ?-? characteristic and illuminance intensity,we have improved and proposed a voltage-based inspection method,and updated the formula of HSI.Furthermore,we have investigated the threshold value of this method.(4)The construction of voltage-based hot spot inspection system is completed.Through the field test of a PV array,the validity of the voltage-based hot spot inspection system is verified.