Research On Micro-grid Inverter On Distributed Photovoltaic Generation Systems

It is an important way to solve the problem of environmental pollution and energy issues to make efficient use of solar energy, so photovoltaic power generation receives global attention. The inverter is the core of photovoltaic power generation system, its performance directly affects the quality and of the output power. Compared to the traditional centralized or string inverters,micro-grid inverter has advantages in certain areas such as extending systems,tracking maximum power point,so micro-grid inverter is widely used in distributed photovoltaic power generation system.Focusing on several key technical problems,this paper has done comprehensive analysis in topology and control strategies.A two-stage micro-grid inverter is designed in this paper,which rated power is 220 W.Firstly,this paper establishes the mathematical model of the photovoltaic cell,then analyzes the output characteristics of the PV and the principle of MPPT.This paper propose a improved method to track the maximum power point based on conductance increment,then verify the feasibility through computer simulation.Secondly,this paper compares several common DC-DC converters,and choose the full-bridge circuit as a step-up DC link for the reason that it is easier to use soft-switching technology to reduce losses and improve efficiency。This paper introduces the full-bridge LLC resonant converter to micro-grid inverter,then analyzes its working principle and basic characteristics,then points out the specific design method.Based on the analysis above on,this paper designs a 100V/400 V full-bridge LLC resonant converter,and verify the feasibility of this design through computer simulation.Thirdly,this paper analyzes the control strategy of the current access to the grid.This paper compares the advantages and disadvantages of two commonly used control mode.On the basis of the analysis above on,this paper chooses a controlled object. The design should make sure that the current has the same frequency and phase with the grid voltage as well as the current has high quality.Based on the above scheme,this paper proposes a design that the closed-loop control structure choose current as the inner ring and choose voltage as the outer ring.Then this paper builds a simulation model of the system on the computer simulation platform.The results show that the output current of the micro-grid inverter can track the grid voltage precisely with a low harmonic content based on the design proposed in this paper. In addition to the above advantages,the micro-grid current has a high conversion efficiency as well as meets standards for access to the grid.