Low-Cost Transformerless Grid-Tie Inverter For Photovoltaic System

Transformerless grid-tie inverters are gaining wide spread in photovoltaic (PV) generation systems due to their benefits of high efficiency and low cost. However, usage of transformerless inverters that have no galvanic isolation from mains implies addressing specific problem with common-mode voltage which may be present on the PV panels with respect to mains. In order to meet the safety requirements of leakage currents, an original design of a non-isolated grid-tie inverter is proposed which eliminates any high-frequency common-mode voltage by directly connecting the negative PV array terminal to mains neutral. The proposed inverter circuit topology has only 4 power swithes, 2 of which are commutating on the mains frequency. The inverter have the ability to control the waveshape of the mains current ensuring high power factor as well as maximum power point tracking (MPPT) capability allowing maximum power draw from a PV panel array. An experimental grid-tie inverter prototype is built for concept proving.