Common-mode behavior study for transformerless PV inverter based on rl-load and grid-connected tests

With the elimination of the isolation transformer, such inverters are susceptible to high leakage current, so suppression techniques have been a popular research topic. Various topologies and modulation techniques for transformerless PV inverters have hence been introduced and published. Since transformerless PV inverters are mainly meant for grid-tied operation, their performance should only be validated via grid-connected tests. Nevertheless, there is much research that is only verified via simple RL-load tests. Moreover, due to laboratory equipment limitations, such validation is done at less stringent operating conditions, such as with reduced DC-link voltage and reduced power rating. While such validation gives an estimation of the converter's performance, it often raises doubts regarding the merits of the test inverter when connected to the actual grid. In this paper, the influence of test conditions on a transformerless PV inverter is investigated. Based on the analysis, a systematic approach for implementing lab-scale grid-connection is also explained, to allow a valid evaluation of the inverter's true characteristics.