A Three-Phase Step-Up DC-DC Converter With a Three-Phase High-Frequency Transformer for DC Renewable Power Source Applications

This paper presents a new three-phase step-up dc-dc converter with a three-phase high-frequency (HF) isolation transformer in an average current-mode controlled closed loop. This converter was developed for industrial applications where the dc input voltage is lower than the output voltage, for instance, in installations fed by battery units, photovoltaic arrays, or fuel cell systems. The converter's main characteristics are reduced input ripple current, step-up voltage, HF transformer, reduced output-voltage ripple due to three-pulse output current, and the presence of only three active switches connected to the same reference, this being a main advantage of this converter. By means of a specific switch modulation, the converter allows two operational regions, each one depending upon the number of switches in overlapping conditions-if there are two switches, it is called R-2 region, and if there are three switches, it is called R-3 region. An average current-mode control strategy is applied to input-current and output-voltage regulation. Theoretical expressions and experimental results are presented for a 6.8-kW prototype, operating in the R-2 region, and for a 3.4-kW prototype, operating in the R-3 region, both in continuous conduction mode.