光伏逆變器

I. INTRODUCTION

P HOTOVOLTAIC （PV） ac modules may become a trend for future PV systems because of their greater flexibility in distributed system expansion， easier installation due to their “plug and play” nature， and higher system-level energy harnessing capabilities under shaded or PV manufacturing mismatch conditions as compared to the single or multistring inverters ［1］–［4］。 A number of inverter topologies for PV ac-module applications have been reported so far with respect to the number of power stages， location of power-decoupling capacitors， use of transformers， and types of grid interface ［5］–［15］。 Unfortunately， these solutions suffer from one or more of the following major drawbacks： 1） the limited-lifetime issue of electrolytic capacitors for power decoupling ［5］–［9］; 2） limited input voltage range for the available panels in the market ［10］–［12］; 3） high ground leakage current when the unipolar pulsewidth modulation （PWM） scheme is used in a transformerless PV system ［13］; 4） low-system efficiency if an additional high-frequency bidirectional converter is employed ［14］–［16］; and 5） increased cost

Manuscript received December 6， 2009; revised March 25， 2010 and July 12， 2010; accepted August 16， 2010. Date of current version June 10， 2011. The paper was presented in part at the 25th IEEE Applied Power Electronics Conference， Palm Springs， CA， February 21–25， 2010. Recommended for publication by Associate Editor T. Shimizu.

The authors are with the Bradley Department of Electrical and Computer Engineering， Virginia Polytechnic Institute and State University， Blacksburg， VA 24061-0111 USA （e-mail： wensong@vt.edu; jihshenglai@gmail.com; hqian@vt.edu; Hutchens@vt.edu）。

Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org.