Reliability Evaluation Of Photovoltaic Converter Power Devices

The converter is the core and the most vulnerable component of photovoltaic power generation system.In recent years,as the cost of photovoltaic power generation continues decreasing,the total installed capacity of grid-connected solar power generation system has increased significantly,and the reliability of the converter also has an increasing impact on the power system.Existing research shows that the faults of photovoltaic power generation system mainly come from grid-connected inverters.As the core module of the converter,power devices are the most vulnerable to failure.Life prediction is an important part of reliability research and plays an important role in the design and maintenance of photovoltaic power generation system.Therefore,it is necessary to carry out research on the reliability of photovoltaic power generation system in order to improve the security and support the operation and maintenance of it.This research mainly focuses on the life prediction method of power modules in converter for photovoltaic grid-connected system and its related contents.The specific work contents are as follows:The effects of photovoltaic cell modeling and its model parameters on the system output characteristics are analyzed.An engineering model of photovoltaic cell output power and voltage is presented and then it is established in MATLAB/Simulink.The effectiveness of the engineering model is verified by simulation and experiment.At the same time,the effects of illumination intensity and temperature on the output of photovoltaic cells are simulated.Furthermore,based on the engineering model,a fast calculation method of photovoltaic output power and voltage is proposed,which is applicable for long-time scale data(such as one-year data)of photovoltaic power generation system,and the rapidity and effectiveness of the method are verified.This method can effectively reduce the simulation workload of the maximum output power and voltage under actual working conditions of long time scales for IGBT module reliability evaluation in photovoltaic converter,which can avoid the shortcomings of slow speed and long time in circuit model simulation.Junction temperature is the key physical parameter for reliability evaluation and life prediction of power devices.Based on the above-mentioned fast algorithm of photovoltaic output and photovoltaic power generation conditions,the loss calculation and electro-thermal coupling model of power devices in photovoltaic converter are studied.The thermal network model considering the self-heating effect and aging process of the module is constructed,and the influence of self-heating effect and aging process on the junction temperature of the module are quantitatively analyzed,as well as the fluctuation history of junction temperature load of power module under operating conditions.The IGBT module FF300R07ME4＿B11 of Infineon Company is selected as the research object and the loss model and thermal network model of the module are built in MATLAB/Simulink.The effects of illumination intensity,ambient temperature and weather conditions on the junction temperature of the IGBT module are analyzed by simulation.Based on failure physical model and damage linear accumulation principle,a life prediction method for power devices considering the actual photovoltaic working conditions and the fatigue accumulation of the devices is proposed.The multiscale statistical characteristics of junction temperature stress series are analyzed by rain flow counting method,and then the life evaluation results of power devices can be obtained by damage accumulation.Taking Alice Springs in Australia as an example,the life assessment based on one-year illumination intensity and temperature data is carried out.The junction temperature fluctuations are divided into three scales according to the time scale: fundamental junction temperature,low-frequency junction temperature and ultra-low-frequency junction temperature.The comprehensive life assessment considering three scales of junction temperature fluctuations is realized.The evaluation results show that the lifetime consumption of IGBT modules in photovoltaic inverters mainly comes from the fluctuation of base frequency junction temperature,and the self-heating of thermal resistance and the aging process have great influence the life consumption.Compared with the existing research results,the evaluation results in this paper are closer to the actual results.