Research Of Related Issues In Large-capacity Photovoltaic System

With the global economic and social development, the energy crisis and environmental pollution problems are becoming increasingly prominent. The solar energy, as one of the renewable resources, is vast reserves and non-polluting, and will play a vital role in the energy structure and planning in the future. There are many ways to develop and utilize the solar resources, and in which PV is a very important and potential way. Currently, photovoltaic technology is relatively mature in the small and medium scale. In the foreseeable future, photovoltaic power system will gradually enter large-capacity grid-connected application, the large-scale grid-connected PV system will become an important trend in the PV industry. Based on this, several key problems of the large-capacity photovoltaic system are analyzed and studied in this paper.In the large-capacity photovoltaic power occasion, the problem of partially shading of the photovoltaic arrays will be more prominent, previous studies have generally focused on the output characteristics of photovoltaic array under the uniform illumination condition, but under the partially shading condition, the situation will be different. The first part of this paper did some researches on this problem, through the MATLAB simulation, we gained the output characteristic curves of photovoltaic array under the partially shading condition, and for more, some meaningful conclusions was obtained.The output characteristics of photovoltaic array under the partially shading condition was gained in the latest part, we can see that there are multiple power peaks on the P-V characteristic curve. In this case, the traditional maximum power point tracking method may find a local maximum power point only, this will cause large power losses. Therefore, we propose a new maximum power point tracking methods to adapt this situation and ensure that the global maximum power point will be found quickly and efficiently under any illumination condition.To increase the griding capacity, the usual way is to make the inverters parallelled, but this will lead to serious circulation problems, there will be some problems in the stability and efficiency. In this paper, we presented a multiplex transformer scheme with square wave inverter, the system efficiency and circulation problem have greatly improved. Through analysis and simulation, the program can achieve good results, having greate prospects for development.In order to realize parameter measurement, performance evaluation, optimized design, and qualification authentication of PV inverter, an accurate and efficient testing platform is needed. For requirements of large-capacity inverter testing, we proposed a testing system solution based on the high-frequency PWM rectifier, the feasibility and accuracy of the platform is confirmed by simulation. For more, we built such a testing platform. Using this testing platform, we tested the related parameters of the griding reactor, this will be a foundation for the optimization of reactor design and testing of other performance parameters of the PV inverter.