Behavioral analysis of a single-switch step up converter

This paper presents a detailed analysis of the behavior of a DC-DC boost-flyback converter which is a single-switch step up converter with a high voltage gain. The behavioral investigation of this converter is carried out supposing it consists of two converters, a boost and a flyback connected in series. The interesting characteristic of this boost-flyback converter is its modes of operation (continuous, discontinuous and mixed), which are depicted analytically. There are two different ways of operation: one in which the boost converter goes over first from the continuous conduction mode (CCM) to the discontinuous conduction mode (DCM) and another one in which the flyback goes over first from CCM to DCM. Each way of operation depends on the duty cycle δ and the ratio k_L of both boost´s and flyback´s magnetic components´ inductances. In this paper, all four different modes of operation are investigated and the output voltage characteristic curves are described as well. Finally, simulation and experimental results are compared to those from theory for different values of the duty cycle δ and the load to validate the theoretical analysis.