Evaluation of commercial scale transformerless solar inverter technology

As the transformerless solar inverters have been pushed to an impressive 99% efficiency in residential and small commercial applications (less than 20 kW), high efficiency medium and large commercial scale (50-250 kW) transformerless solar inverters are gaining more and more attentions. However, due to the differences of inverter power ratings, grid voltages and standard requirements, there are new challenges and problems for the commercial scale photovoltaic system to eliminate the isolation transformers and achieve the competitive efficiency. This paper reviews and evaluates the state-of-art technologies of today's U.S. commercial scale PV inverters, and proposes the future trends for next generation commercial scale transformerless solar inverters. The transformerless inverter topologies, leakage current and existing standards are discussed and assessed. The goal of this paper is to address the new challenges of moving transformerless solar inverters into the commercial scale PV system with 99% efficiency.