Research On MPPT And Anti-islanding Of Grid-Connected Photovoltaic Power Generation System

In recent years, there has been an increase in the use of renewable energy due to the growing concern for the pollution caused by fossil-fuel-based energy. On-site power generation using sources like photovoltaic (PV) arrays can be used to reduce the dependence on energy from the grid as well as provide back up power for critical systems during grid outages.This thesis proposed a PV grid-connected power generation system that can be used in stand-alone mode and grid-connected mode, to convert the DC power output of the PV arrays to the more useful 220V AC. The operation and design of the various stages of the system are discussed. During the processes of developing PV energy generation system, maximum power point tracking, anti-islanding equipment, novel topology for AC photovoltaic module system and the control of inverter are researched. And some valuable results are obtained.In the first part of this paper, to extract more power from PV arrays, two novel MPPT methods are presented: asymmetric fuzzy maximum power point tracking (MPPT) method and two-mode maximum power point tracking method. Simulation and experimental results show that the PV power generation system has good steady state and transient characteristics with the control of the two proposed MPPT control methods.In the second part of this paper, the active frequency drift with periodical disturbance and positive feedback method is provided to detect islanding based on the active frequency drift (AFD) anti-islanding method. This new anti-islanding method can reduce the non-detection zone (NZD) and increase the speed of anti-islanding detection compare to the AFD method. In the third part of this paper, a PV grid-connected power generation system is designed based on the above work. It is composed of a MPPT circuit, an inverter, filter, control circuits and protection circuits. It can work under the stand-alone mode and the grid-connected mode according to the choice of user. The PV power generation system sets up a good base for the next work.At last, a novel topology for ACM( AC photovoltaic module) system is presented. The new topology consists of a BUCK-BOOST converter and a current source inverter. The BUCK-BOOST circuit implements maximum power point tracking of PV array well due to eliminateing the power perturbation from inverter. The current source inverter transforms this DC power into the 220V and 50Hz AC power at last. The effectiveness of the proposed inverter is confirmed experimentally and through simulation results.