A control algorithm for power converters in the field of photovoltaic applications

An improved digital control for SEPIC converter has been designed and implemented in order to extract the maximum power from a photovoltaic system. A maximum power point tracking (MPPT) algorithm has been used to increase the energy extracted from the source in a microcontroller based environment. Analyses of the electric behavior of the photovoltaic modules have been performed looking to create a mathematical model that has been represented by a lumped parameters circuit. Such a model is suitable for simulation runs with commercial software packages. The model parameters have been identified by means of measurements performed onto two different photovoltaic module technologies (crystalline and amorphous silicon). A V² control algorithm was also implemented to establish a performance comparison with more common MPP strategies. The V² algorithm allows evaluating the input power of the converter without current sensing devices being sufficient the knowledge of some converter parameters. The experimental system has been tested with both a low-power amorphous panel and a crystalline one. The obtained results by means of the used algorithms demonstrate good performances with high efficiency values in several working conditions and a shorter searching time of the MPP in comparison to other ones. The experimental converter has been tested with an output power of 100 W (5A, 20 V). The resonant operations allowed also achieving very low values of the converter power losses.