Due to electronic design constraints, most DC-DC (or MPPT) converters operate on a "step-down" principle. HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. This means that without a transformer, they cannot deliver a voltage greater than the input voltage. Therefore, in a pumping system, the PV-array MPP voltage must be higher than the voltage. There, transformerless topologies, like the H5 and Heric, can reach very high levels of efficiency and allow the best cost–benefit ratio for low-power grid-tied systems. The available inverter models are now very efficient (over 95% power conversion.
[PDF Version]