A comparative analysis of grid-tied single-phase transformerless five-level NPC-based inverters for photovoltaic applications

In recent years, photovoltaic systems designers have been started to pay attention in transformerless multilevel inverter topologies. This is due to they possess several advantages, such as, high efficiency, good performance, multiple voltage output levels and small size. In order to meet the safety requirement for transformerless grid-tied photovoltaic inverters, the leakage current has to be tackled carefully. To accomplish this requirement, common mode voltage has to be maintained in a constant value to avoid the current flow through the stray capacitances that appear between the photovoltaic array and the ground path. Due to the wide variety of available inverter topologies, in this paper a comparative analysis of efficiency between three neutral point clamped topologies is realized, besides modulations strategies are proposed to keep the common mode voltage constant to avoid leakage ground currents. Numerical results are performed in order to validate the analysis and modulation.