Research On Series Power Optimizer In Photovoltaic Grid Connected System

Energy is the basis of human survival,fossil energy will eventually be exhausted,and the development and use of new energy is very urgent.At present,photovoltaic power generation technology is the research hotspot and the development key point of various countries.Photovoltaic cells are based on photovoltaic effect,at present,most of the photovoltaic cells′photoelectric conversion efficiency are less than 20%.so maximizing the output power of photovoltaic cells is the most effective way to improve the power generation of photovoltaic power station.In photovoltaic power generation system,there are many factors that reduce the output power of photovoltaic array,such as inconsistent attenuation speed of photovoltaic cells or shadowing.through the centralized maximum power tracking of inverter,the output power of each photovoltaic cell can not be maximized.This paper will study the key technology to maximize the output power of each photovoltaic cell through series power optimizer.Firstly,the problems of photovoltaic cell model establishment and photovoltaic array shadow shading are studied.The photovoltaic effect is introduced,and the physical model and engineering model of photovoltaic cells are discussed.Based on the mathematical expression of physical model,the simulation model of photovoltaic cell is established,the relationships among among power,voltage and current is analyzed.Based on the simulation model of photovoltaic cells,different shading degrees are simulated by changing the light intensity,and the relationship between shading degree and output power reduction ratio is analyzed.Aiming at the problem of MPPT algorithm selection,this paper introduces the working principles,advantages and disadvantages of several algorithms,and selects disturbance observation method as the algorithm of power optimizer.Aiming at the contradiction between tracking speed and tracking accuracy of fixed step disturbance observation method,the fixed step disturbance observation method is improved to make the disturbance step change every time.The simulation results show that the improved algorithm can ensure the tracking speed and decrease Oscillation at low maximum power point at the same time.At the same time,experiments verify the effectiveness of the variable step disturbance observation method.Aiming at the problem that the voltage fluctuation on the DC side of the inverter will reduce the power quality,this paper analyzes the working principle of the power optimizer when the shadow is obscured and the influence of the grid connected inverter on the power optimizer,and puts forward the voltage self-adjusting control method;aiming at the defect that the photovoltaic power generation system can not carry out on-site rescue in case of fire,this paper puts forward the method of combining the optimizer circuit with the self holding relay In order to solve the problem of capacitor discharge in inverter during instantaneous short circuit,a control method of sequential short circuit is proposed.Finally,based on the simulation and experimental platform,it is verified that the power optimizer can maximize the output power of each photovoltaic cell.