The Research of a Three-phase Single-stage Grid-connected Photovoltaic Inverter

A three-phase single-stage grid-connected photovoltaic inverter is introduced.The inverter starts up with voltage loop control and after start-up it changes to current loop control with MPPT starting to work.According to the characteristics of the MPPT methods,a method combining CVT,IncCond and fast-regulation is chosen with a good re-sult of MPPT.The inverter puts out active power to the electricity grid and it also can be conveniently controlled to put out certain reactive power for local loads as the reactive power compensation.A software phase-locked method is introduced.In this simple and applicable method,the phase and frequency of the inverter output is regulated by changing the zero point and step length of the pointer,with the switching frequency unchanged.The invereter obtains a good experimental result in the lab with simple structure and control.