High Efficiency Single-Phase Transformer-less Inverter for Photovoltaic Applications

Abstract

Photovoltaic (PV) inverters have a very important role in the energy market, therefore they must possess excellent characteristics regarding cost and reliability. The PV structure most often used in the conversion stage of solar energy system includes a Low Frequency Transformer (LFT) which provides galvanic isolation, but on the other hand reduces the overall efficiency and increases the total size and cost of the system. An alternative to reduce the size of the system and the losses, is to use a High Frequency Transformer (HFT), the problem in this case is that additional power stages must be included in the system. The additional stages increase the power losses in the conversion process, as a consequence the efficiency of the system is reduced. Therefore the tendency is to remove the transformer in order to increase the efficiency and reduce the cost. A security problem regarding common mode currents arise when the LFT or HFT is omitted. In this paper an inverter topology to deal with the problem of the common mode currents is proposed. Numerical results are performed in order to prove the performance of the topology regarding efficiency and Common Mode Voltage (CMV) issues.