Photovoltaic Maximum Power Point Tracking And Research Of Grid Inverter

After the second industrial revolution, the age of electricity had come. From then on, science&technology advanced rapidly and new inventions continuously emerged in. With the development of new technologies, the consumption of electricity keeps growing. The lack of electricity, limited natural resources and environment pollution has become an energy security issue worldwide. Today, academics and experts agree that solar power, wind power and hydroelectric can take the place of coal&petroleum as renewable energy sources. Thus, it is worth promoting and employing. Grid-connected photovoltaic system is studied in this paper.Photovoltaic system is composed of photovoltaic arrays, maximum power point tracking (MPPT) logic and grid-connected inverters. The volt-ampere characteristic curve of photovoltaic arrays is non-linear. Many scholars home and abroad have done a lot of work on studying the output characteristic of photovoltaic cells. Mathematical models have been set up for photovoltaic cells according to the physical properties. In this paper, the5-Parameter model is used in Matlab/Simulink to simulate the output characteristic of photovoltaic arrays under both uniform insolation and partially shaded conditions. The output values are used in analyzing the performance of different MPPT algorithms.The shadow effect is a common problem in grid-connected photovoltaic systems. Under uniform insolation conditions, there is only one peak value on the Power-Voltage curve of photovoltaic arrays. The classic MPPT algorithms are correct and reliable. Under partially shaded conditions, there are multiple peak values on the Power-Voltage curve of photovoltaic arrays. The operating point may be located at the local maximum power point rather than the real maximum power point when classic MPPT algorithms are employed. In order to solve this problem, a new MPPT strategy is proposed in this paper. The tracking process is divided in four stages. In each stage, a specific MPPT algorithm is used. The simulation results prove that this method can not only handle the multiple extreme problem but also has the advantage of great convergence rate and no oscillation in the vicinity of the maximum power point.Finally, a mathematical model of grid-connected inverter is set up in Matlab/Simulink. Voltage oriented control scheme is used to realize the direct control of grid current. Simulation results show that the gird-connected inverter designed in the paper can achieve no static error in steady state and has short response time in transient changing conditions.