Single-stage single-phase three-level neutral-point-clamped transformerless grid-connected photovoltaic inverters: Topology review

Single-phase Transformerless (TRL) inverters (1-10 kW) are gaining more attention for grid-connected photovoltaic (PV) system because of their significant benefits such as less complexity, higher efficiency, smaller volume, weight, and lower cost compared to transformer (TR) galvanic isolations. One of the most interesting topologies for TRL grid-connected PV application is Three-Level Neutral-Point-Clamped Voltage Source Inverter (3L-NPC VSI) due to inherent feature of eliminating leakage current and other several dramatic benefits compared to classical two-level topologies. Therefore, in this paper, firstly, a leakage current model is represented for 3L-NPC topology. Then, more than 45 new / integrated single-stage single-phase 3L topologies, with the special focus on 3L-NPC VSI family are reviewed. Several aspects, such as leakage current problem, Shoot-Through (S-T) issue, complexity of modulation methods, component count, etc., are investigated for all topologies and more than 10 comparison tables are provided. Other advantages and disadvantages of topologies are represented as well. Then, discussion and future trends are highlighted. And finally, conclusion is represented.