A Novel Transformer less Grid-Tied Inverter with Effective Power Control

Abstract

Three-phase transformerless inverter is widely used in low-power photovoltaic (PV) grid-connected systems due to its small size, high efficiency and low cost. When no transformer is used in a grid connected photovoltaic (PV) system, a galvanic connection between the grid and PV array exists. In these conditions, dangerous leakage currents  (common-mode currents) can appear  through  the  stray  capacitance  between  the  PV array  and  the  ground. The  former,  in  order  to  create  a  galvanic isolation  between  the  input  and  the  output  include  a transformer (mandatory in some countries) that limits the whole system performances in terms of efficiency, weight, size  and  cost.  On  the  contrary,  transformerless  inverters do not present any isolation and are characterized  by little size,  lower  cost  and  higher  efficiency  (more  than  2% higher).  Nevertheless, the lack of transformers leads to leakage currents that can be harmful to the human body, as well as for the whole conversion system integrity. In order to minimize the ground leakage current and improve the efficiency of the converter system, transformerless PV inverters utilizing unipolar PWM control. In this project it presents a high-reliability single-phase transformerless grid-connected inverter that operate super junction MOSFETs to accomplish high efficiency for photovoltaic applications. In this paper proposed converter tested for the three phase system and it is analyzed.kept constant at midpoint of dc input voltage, results low leakage current. Finally, to validate the proposed topology, a 1 kW laboratory prototype is built and tested.