The Grid Connection Research On Photovoltaic Power Generation System

With the problems of global energy crisis and environmental pollution increasingly becoming serious,renewable energy has become the current research hotspot because it’s clean,safe,pollution-free,renewable and has other advantages.As a new type of renewable energy,solar energy has great potentials and advantages in dealing with environmental pollution and optimizing the structure of energy.It is one of the most promising and commercial green energy sources in the 21 st century.After years of accumulation in technical research,photovoltaic power generation technology has become a more mature new energy technology.At present,PV cell efficiency,MPPT,control strategy for grid-connected inverter are the key technology.According to photovoltaic effect and the equivalent circuit,the practical mathematical model of the photovoltaic cell is established,and the output characteristics of PV arrays are analyzed under different illumination intensities and different ambient temperatures.The characteristics of observation disturbance and conductance increment method of traditional fixed step are compared.And then,the disadvantages of the maximum power point tracking(MPPT)method of traditional fixed-step-length conditions are analyzed.According to the problems existed in dynamic response of the control algorithm with the traditional variable step-length disturbance observation method in the light mutation,a variable step perturbation observation method is proposed to improve the dynamic response performance of the system,and the output power efficiency of photovoltaic cells is improved.The control method of three-phase photovoltaic grid-connected inverter is researched based on the mathematic model of three-phase grid-connected inverter in the d/q synchronous rotating coordinate system,the model of vector control of grid-connected inverter is established based on grid voltage orientation.In addition,according to the characteristics of virtual grid flux orientation,the vector control of grid-connected inverter is established based on virtual grid flux orientation when there is no grid voltage sensor,which realizes both the decoupling control for d q-axis current and any power factor output control.For the vector control system of the grid-connected inverter directed by virtual grid flux,aiming to solve the existing problem that the low-pass filter flux observer cannot eliminate the DC component,this paper proposes the double low-pass filter method to design virtual grid flux,which can eliminate the DC component thoroughly and improve the accuracy of the virtual grid flux estimation.And then,the validity of the proposed control strategy is verified.