Soft-Switched High Step-Up Quasi-Z-Source DC-DC Converter

A soft-switched nonisolated high step-up dc-dc converter based on the quasi-impedance-source structure is presented in this paper. In the proposed converter, a technique similar to the synchronous rectifier is applied such that the diode of the impedance network is replaced with an active switch. In this way, not only is conduction loss associated with the diode reduced but also zero-voltage-switching characteristics for power switches are provided. Also, output diodes of the proposed converter are switched under zero-voltage-zero-current-switching condition which extremely reduces their switching and reverse-recovery losses. It is shown that by correct design of the components, soft-switching performance is retained for all the semiconductor devices over the entire range of output load. All these factors together with simplicity of the proposed structure result in high efficiency over a wide range of output power. Moreover, the proposed converter benefits from continuous input current and a shared ground between input and output. Operating principles of the proposed converter along with its steady-state analysis are presented. Also, experimental results obtained from a laboratory prototype for 48 to 350 V voltage conversion and 100 W nominal power are provided to validate the feasibility of the proposed converter.