| In the growing shortage of traditional energy sources, environmental pollution is worsening in the background. Because the distribution of a wide range of photovoltaic power generation, large reserves, no pollution, etc., it is more and more national attention. Throughout the photovoltaic power generation systems, photovoltaic grid-connected inverter is to achieve energy conversion and control of the core components of the grid, which largely determines the performance and the stability and efficiency of the grid system, therefore, PV grid-connected inverter is very important.This research designs a 3kW PV grid-connected inverter.After comparison and analysis, the main circuit uses two scale but non-isolated structure. The first stage uses DC / DC boost converter to complete the function of the output DC voltage of the PV array, as well as the maximum power point tracking(MPPT). The second stage uses a single-phase full-bridge inverter to complete network control and islanding detection. The research carries out a depth study on the photovoltaic grid-connected inverter maximum power point tracking(MPPT) and islanding detection technology. In the research of the maximum power point tracking, I firstly analyzes the impact of external factors on the output characteristics of the PV array and load impedance affect the output power of the PV array, and then analyzes the PV maximum output power control algorithm. In the study, compared to the current mainstream several algorithms, such as the constant voltage method, fixed step disturbance observation, This paper analyzes the different control algorithms during the MPPT control advantages and disadvantages. In front of the theoretical basis of MPPT control algorithm, introduced two improved algorithm, By Matlab / Simulink simulation to verify the superiority of the improved algorithm, and determine the fuzzy control algorithm used in this research. In islanding detection technology research, analyzeing the causes of islanding and explaining the dangers and the need to study it islanding protection,then islanding detection method used to detect passive and active assay were analyzed and compared. For defects and the actual operation of the power grid of traditional detection methods, this research proposes a modified two-way cycle perturbations active frequency shift method,by Matlab / Simulink simulation proved,the improved control algorithm is verified to be feasible.Finally, through research on the overall system solution, the hardware and software of a 3kW single phase photovoltaic grid inverter has been designed, then the prototype has been built and tested ultimately, it validates the subject of the proposed technical indicators. Prototype validation results show that: the use of the system design and control strategy can meet the state requirements of the network, and can get a higher quality net current. |
