Integration of Isolation for Grid-Tied Photovoltaic Inverters

IDEA IN BRIEF The photovoltaic (PV) industry has been enjoying great growth over the past few years, mostly driven by high oil prices and environmental concerns. However, PV cost remains to be the greatest barrier for further expansion, and it needs to come down further to compete with traditional coal based grid electricity. Besides solar panels, the electronic components, such as PV inverters, are the major cost components. For safety and operational concerns, gridtied PV converters need to have harvested dc be isolated from the ac grid. Isolation is usually required to satisfy safety regulation to prevent dc injection into the ac grid that may impact distribution transformers and traditional watt-hour meters. Traditional isolation solutions such as optocouplers can’t satisfy the 25 year warranty typical for PV panels. Microinverters also become the trend where the system availability is improved and performance under shading condition is also dramatically improved. In those cases, the PV inverter is installed at the back of the PV panel where the high temperature there can accelerate the degradation of the optocouplers. This paper discusses the signal and power isolation needs in PV inverters and how integration of isolation functions using microtransformers can improve the system performance and reliability and reduce the system size and cost.