Research On Island Protection Technology Of Grid-connected Inverter Based On FPGA

In the power structure of our country,thermal power accounts for more than 80%of the total.However,the consumption of non-renewable resources and environmental pollution of thermal power have affected the environment-friendly development strategy of our country.In order to optimize the existing energy structure,new power generation methods such as wind and light have the advantages of clean,environmental protection and renewable,and have gradually become the mainstream means of power generation.As one of the methods of new energy power generation,photovoltaic distributed power generation has gradually become the research focus of professional scholars.In this paper,focusing on the three-phase grid-connected inverter and its island protection in photovoltaic system,the theoretical and experimental research is carried out from the following aspects:First of all,the working principle,mathematical modeling,control method and modulation algorithm of the diode clamped three-level inverter are studied.The cause of the voltage imbalance of the split bus is analyzed,and an open-loop correction scheme is designed to balance the positive and negative half-bus voltage.At the same time,according to the requirements of grid-connected standards in different countries,the popular research directions of grid-connected inverter: island effect and anti-island strategy are analyzed deeply.and an active island detection scheme using reactive current disturbance to shift the frequency is proposed,which disturbs the frequency and phase of the voltage by injecting reactive current into the power grid.When the frequency and phase lose the support of the large power grid,the offset will occur,and then the passive island protection method is used to start the island protection.Secondly,because the active island detection uses the frequency protection method,the dynamic response speed of the phase-locked loop plays an important role in the detection effect.Therefore,this paper makes an in-depth analysis of three-phase DQ-PLL and single-phase software phase-locked loop SOGI-PLL,FFT-PLL,and compares the phase-locked effects of several common phase-locked loops.The simulation models are built in Matlab/Simulink,and the simulation results are compared.Finally,based on the above research,the island hardware experiment platform of three-phase inverter is built,the software design is completed,and the island experiment is carried out.the experimental results meet the requirements of grid-connected detection and protection in different countries.the effectiveness and feasibility of the protection method proposed in this paper are verified.