Study On The Grid-Connected Photovoltaic Multilevel Micro Inverter System

For getting higher efficiency of photovoltaic MPPT and circuit as well as lower cost, researchers have been trying to design inverter with new structure. Currently, the structure of PV inverter has a tendency of microminiaturization, and inverter itself have been developing from low-technical-cost type to high-technical-cost type, also known as the change from central inverter to module-level inverter. Though the application of module-level inverter brings high MPPT efficiency for PV generating station, but those inverters barely be used for its high cost,and those inverters have lower efficiency than the conventional ones is the one of reason. Aimed at the contradiction between the development tendency of inverter and factors such as cost and efficiency, this thesis proposed a kind of cascaded micro inverter based on control strategy of voltage phase regulation. In contrast to classical micro inverter, the micro inverter extremely depressed technical integration level in inverter system, its DC/AC part works at a much lower switch frequency compare with normal modulation, in this way, cost and complexity in grid-connected control can be greatly decreased, and circuit efficiency is higher in theory.The main content of this thesis is related to the study of control about the system. In detail, it includes the introduction of the structure of the grid-connected PV cascaded micro inverter, research on grid-connected modulation and control, and experiments based on the inverter experiment platform. So the main work here are the references of the two commonly used modulations of inverter and the contrast of the performances of them, the preliminary establishment and verification of the inverter’s transfer function model on grid-connected control, the design and simulation verification of an islanding detection method compatible with the inverter’s regulation, and the contrast verification between simulation model and experiment platform.