Research On Key Technologies Of Modularization Of New Photovoltaic Cascade Power Generation Unit

The world energy problem is becoming more and more serious.The development and utilization of photovoltaic grid-connected power generation has been greatly developed by various countries.Grid-connected inverter,the core component of photovoltaic grid-connected system,has been widely studied.The cascaded grid-connected inverter can be connected to the highvoltage grid without transformer,which reduces the volume and cost of the system.Its power unit of each level adopts independent MPPT control to ensure maximum output power.This paper takes cascade photovoltaic gridconnected inverter as the research object,conducts in-depth research on its key technologies,designs a new type of photovoltaic cascade generation unit module,and carries out the following work:(1)The background,research significance and research status of power imbalance of unisolated multilevel cascade inverter are described.Then,the main circuit topology of single-phase and three-phase new photovoltaic cascade inverter is designed,the mathematical model is built,the working principle is analyzed,and the single-stage frequency doubling modulation strategy of horizontal carrier movement is discussed,which provides the theoretical basis for the following paper.(2)In view of the poor response effect caused by the traditional MPPT in poor environment,an improved method based on the derivative adjusting duty cycle between power and voltage is proposed from the perspective of adaptive step length disturbance.The simulation results of photovoltaic panel and Boost circuit show that the improved method can improve the tracking speed and accuracy of maximum power.(3)Aiming at the possible over-modulation problem of cascaded gridconnected inverter,a control strategy based on centralized communication is proposed to correct the power balance through active power component of duty cycle.Simulation results show that the proposed control strategy can effectively solve the power imbalance problem and improve the overall stability of the system.(4)The simulation model and experimental platform are designed and built.The experimental results verify the correctness of the theoretical analysis and the effectiveness of the improved MPPT modulation strategy and power balance strategy proposed in chapter 3.(5)According to the real-time demand of the system,a real-time monitoring system based on Lab VIEW is designed.Experimental results show that the monitoring system is real-time and convenient.