Modelling of DC-DC converters with continuous input current for high power PV applications

Renewable Energy sources integration to the grid is becoming more vital due to the market share increase. The integration of PV farms, for instance, usually requires a DC-DC conversion stage to boost up the source voltage. In addition, DC-DC converters with continuous input current reduce the bulky input capacitor requirements. This saves the cost, and enhances the reliability of the system since these capacitors exhibit short life time. This paper presents a complete mathematical modeling of two appropriate converters for such application, namely the Cuk and SEPIC DC-DC converters. The parasitic non-idealities are included to account for gain deterioration at high duty cycles, which is a vital point in high power applications especially when high gains are required. The performance of both converters is then compared and their small signal models are derived and presented in terms of both the input voltage and duty cycle, which provides an additional path for performance assessment. The theoretical models are verified practically.