Research And Analysis Of The Output Characteristics Of Photovoltaic Grid-connected Inverter

Under the condition of serious energy crisis and the advocation of using green energy around the world,the photovoltaic(PV)industry has developed rapidly.As the green and clean energy,solar enenrgy has the advantages at renewable and high development potential.We can increase energy utilization rate of PV through the distributed micro-grid technology of renewable energy,so PV industry had been widely concerned in power industry at home and abroad.Taking the PV inverter as the reaserch object,this paper is mainly focused on study the working characteristics of PV grid-connected system and the harmonics output characteristics of PV grid-connected inverter.Firstly,it has introduced the importance of photovoltaic grid-connected inverter during the development process of intelligent electric grid and microgrid.Then,some aspects of PV grid-connected system,such as the topology,working characteristics,maximum power point tracking(MPPT)control strategy,double-loop control strategy and grid-connected strategy,has been analyzed.A PV grid-connection system has been realized by simulation.For establishing a more precise model of two-stage three-phase PV systems,an proposed output harmonic model of single-phase inverter is presented.And based on the characteristics of two-stage photovoltaic systems,a model is established which is more suitable for the features of two-stage three-phase PV systems.To describe the modeling process clearly,the ideal mathematics model of PV inverter has been deduced,the dead-time effects and power devices characteristics on the output voltage has been studied,and the DC side ripple voltage caused by the DC/DC link has been studied.The output filter can reduce the harmonic content of the inverter current to a utmost extent,so the output filter is an essential part of the PV system.The characteristics and design methods of L and LC output filter has been analysed comparatively.Taking the parameters' characteristics of the LCL output filter into account,a analysis and design method,which determine the filter inductor near the inverter firstly,has been proposed.The filtering principle of LCL filter and the parameters' characteristics of the LCL filter has been analyzed in detail by using the method.Finally,a simple design flow has been shown.