CCM and DCM Analysis of Quasi-Z-Source Derived Push-Pull DC/DC Converter

This paper presents a steady state analysis of the operation modes of the quasi-Z-source (qZS) derived push-pull DC/DC converter topology. It was derived by the combination of the qZS network and coupled inductors. The output stage of the converter consists of a diode bridge rectifier and an LC-filter. This topology provides a wide regulation range of the input voltage and galvanic isolation. These features fit the requirements for the integration systems of renewable energy sources, such as PV panels, variable speed wind turbines, and fuel cells. A converter can operate in continuous (CCM) and discontinuous conduction mode (DCM). Switching period is divided into four and six intervals for CCM and DCM, respectively. Equivalent circuits and analytical expressions for each interval are presented. The DC gain factor for each mode is derived. To simplify our analysis, coupled inductors were substituted with a model that consists of an ideal transformer and magnetizing inductance. Leakage inductances are neglected because the coupling coefficient in this topology should be close to unity. In DCM the converter operation depends on the active duty cycle and the duty cycle of the zero current condition. Two solutions are possible for the DC gain factor in DCM. It is theoretically impossible to achieve the unity DC gain factor in DCM if the turns ratio of coupled inductors is equal to or more than one. The proposed topology was simulated with PSIM software in two operating points. Experimental verification proves our theoretical and simulation results.