Design And Implementation Of The Current Source Type Large Capacity Of Photovoltaic Inverter

A new type large-capacity converter of current source with five electrical level is presented, it is based on the theory of current re-injection. In order to develop the new type converter easily, the injection circuit switch in the conduction state adjusts the output current of DC side evenly. It reduces the required current capacity of branch switch components, changes the current through the wire, eliminates the need for large-capacity multi-tap reactor, reduces the inconvenience in the manufacturing design.In this master’s thesis, the photovoltaic power generation and grid inverter are studied, the problem of maximum power point tracking is analyzed, the mathematical model of photovoltaic cells is explored. The explanations of the principle and characteristics about the maximum power point tracking are presented, the corresponding control process and strategy for each kind of way are offered simultaneously. Using the simple and improved method, the problem of lack of the traditional ways to detect island has been solved. By studying the modified principle of island detection and operation and the frequency deviation track after losing voltage, the constraints that islanding detection should be satisfied are deduced, the improved algorithm of meeting detection requirements is obtained. The current distortion caused by the active phase shifting island detection algorithm is discussed. On the basis of relevant data, choosing the appropriate method can alleviate the impact on electric power network.The MATLAB simulation has confirmed that the multi-stage injection current source type current transformer has the high quality of the current voltage waveform, it can control capacitive and inductive reactive power flexibly, and has the fast dynamic response. By controlling the maximum power point tracking, the conversion efficiency of photovoltaic cells is improved obviously. Using the island detection, it can ensure the security of power grid, reasonable compensation of reactive power, improve voltage stability of the public access points.