Design Considerations for Single-Phase Line Frequency Transformers Applied at Photovoltaic Systems

The issue of dc current injection at low voltage autonomous or interconnected grids as a result of photovoltaic (PV) systems integration is thoroughly discussed in this paper. This paper focuses on the sinusoidal pulsewidth modulation inverter with a low-frequency step-up transformer, as this was widely used in the past at PV grid connected applications, while nowadays, it is a favorable solution in standalone multisource residential applications. This paper highlights the fact that dc current injection is possible even at the presence of a low-frequency transformer. In addition, the impact of the dc current flow on the transformer efficiency is studied, and appropriate design considerations are extracted-thus limiting the dc current component in an efficient manner. The proposed design considerations are validated through experimental results accomplished on laboratory and commercial PV power conversion products.