Inverter Control And Islanding Detection Of Photovoltaic Generation System

With the increasing concern about global environmental protection, the solar energy, clean, pollution-free and inexhaustible, has received great interest as an alternative source of energy for the future. In an effort to use the solar energy effectively, a great deal of research has been done on the photovoltaic (PV) generation systems.This dissertation focuses on two stage of single-phase grid-connected PV system. The photovoltaic array, the maximum power point tracking (MPPT) strategy and islanding detection method have been investigated. The main work and achievements in this dissertation are as follows:(1) The model of the photovoltaic cells is analyzed and verified by simulation. The result shows that, with the voltage increasing, the output power of photovoltaic cells increases firstly and decreases afterwards, which provides the basis for MPPT. The Perturb & observe algorithm of MPPT is selected to simulate. The power of the system has small fluctuation in the range of the maximum power when it reaches at the point of the maximum power.(2) The inverter in grid-connected PV is important since it is related to the power quality of the system's output. In this dissertation, major attention is given to the hysteresis current-controlled method and SPWM method. Comparing the simulation results of hysteresis current-controlled method with SPWM method, the latter is better since the inverter's output is unity power factor.(3) A model of two-stage single-phase PV system is built up based on the simulation of PV cells, the Boost circuit and inverter. The simulation result demonstrates that the output current of the inverter is in phase with grid voltage after a period of adjustment.(4) Anti-islanding protection plays an important role in grid-connected PV system. This dissertation provides profound research on the slip mode frequency shift method (SMS) and active frequency shift method (AFD). Simulations of the AFD method with the single inverter and the five-level cascaded inverter are respectively performed,whose results turn out that the AFD method with five-level cascaded inverter is still effective, although the detection time is longer than the AFD method with the single inverter.