Integration of Isolation for Grid-Tied Photovoltaic Inverters

摘要

Photovoltaic (PV) industry has been enjoying great growth over the past few years, mostly driven byrnhigh oil price and environmental concerns. However, PV cost remains to be the greatest barrier forrnfurther expansion, and it needs to come down further to compete with traditional coal based gridrnelectricity. Besides solar panels, the electronic components such as PV inverters are the major costrncomponents. For safety and operational concerns, grid-tied PV converters need to have harvested DCrnbe isolated from AC grid. Isolation is usually required to satisfy safety regulation to prevent DCrninjection into the AC grid that may impact distribution transformers and traditional watt-hour meters.rnTraditional isolation solution such as opto-couplers can’t satisfy the 25 year warranty typical for PVrnpanels. Micro-inverters also become the trend where the system availability is improved andrnperformance under shading condition is also dramatically improved. In those cases, the PV inverter isrninstalled at the back of the PV panel where the high temperature there can accelerate the degradationrnof the opto-couplers. This paper discusses the signal and power isolation needs in PV inverters, andrnhow integration of isolation functions using micro-transformers can improve the system performancernand reliability, reduce the system size and cost.