Network And Islanding Detection Technique Based On The Micro-grid Photovoltaic Power

In the recent30years, with the development of Chinese society, contradictions exist among resources, economy, and environment are becoming increasingly obvious, so more and more attention is attracted by applying of new resources. Solar energy have the characteristics as pollution-free and inexhaustible, and photovoltaic power generation is one of the important ways to utilize solar energy. Therefore, the study of photovoltaic power generation is of great significant.Firstly, in this paper, according to the characteristic of P-V and the traditional maximum power point tracking (MPPT) method, the new MPPT method is realized by improving the perturbation step of perturbation and observation method (P&O). Utilizing the relationship of the power variation and the setting threshold to change the perturbation step, the tracking speed of the MPPT method is improved. The photovoltaic cell equivalent mathematical model with P-V and V-I characteristics is built in Matlab/Simulink. The simulation results show that this method possesses high calculation speed and accuracy.Secondly, in order to realize the stable operation of stand-alone photovoltaic power system, constant power control is adopted in this paper.This method can make the voltage and frequency remain in a stable range.Thirdly, in order to realize single-phase grid-connection with photovoltaic power generation, this paper adopt the synthesis of current method and voltage feed-forward compensation method to control the inverter in photovoltaic system. The control method makes the grid current and the gird voltage have same frequency, and satisfies the requirement of single-phase grid. In order to realize three-phase photovoltaic power generation to connect power grid, PQ control method is adopted to control inverter in photovoltaic system. The control method can fast-track the grid frequency, achieves phase-locked control and satisfies three-phase photovoltaic grid-connected requirements.Finally, in this paper, the principle of positive feedback voltage islanding detection method is analyzed in the photovoltaic power generation system. The situation of unavailable for detecting island detection can be effectively avoided because the output power of photovoltaic power generation system is close to the local load. The simulation results show that this method is feasible in the photovoltaic grid-connected system islanding detection. At the same time, the positive feedback voltage islanding detection method may produce island miscarriage. The method of periodic sampling detection voltage signal to detect island is applied. The simulation results show that this method can effectively avoid misjudgment island.