MW Multi-level Photovoltaic Converter And Its Grid-connected Technology

With the increasing of power generation scale,large-scale photovoltaic power generation is the trend of the development of the world's photovoltaic power generation.As the core of PV grid-connected system,large-scale PV grid-connect converter becomes a hot research.Taking the cascaded multilevel photovoltaic converter as the study object,and is carried out with depth research in the dissertation.This paper studies the mathematical model of PV-array and its output characteristics.In this paper,the maximum power tracking method is introduced and does a key research on the improved perturbation and observation which has good maximum power tracking performance tested by experiment.This paper study on the cascade multi-level converter topology.The operation principle and mathematical model of cascaded multilevel converter is analyzed in detail.This paper has introduced the converter's PWM control method,the method of carrier phase shift control for multilevel converter is studied which can effectively reduce the harmonic output of the converter and improve the power quality.Based on the characteristic analysis of the cascade multilevel converter,this paper has described the structure and control method of the MW multi-level photovoltaic converter connected to the grid,studied the control strategy of the converter with the grid control signal,and did a research on using the converter to compensate the load reactive.The feasibility of the control method is proved by simulation.In addition,the paper has studied the island effect of converter,analyzed the mechanism of the island effect.This paper has introduced the detection method of the island effect and its standards.Based on the research,the paper has did a research on the method of periodic disturbance detection.The simulation shows that the method can detect the island state of the system,and make the response to ensure the security and stability of the system in time.