Fuzzy control of a three-phase step-up DC-DC converter with a three-phase high frequency transformer

This paper presents a closed loop fuzzy logic control technique applied to three-phase step-up DC-DC converter with a three-phase high frequency isolation transformer. 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, high frequency isolating transformer, reduced output voltage ripple due to three pulsed output current and the presence of only three actives switches connected at the same reference, this being a main advantage of this converter. By means of a specific switch modulation, the converter allows two operational regions. A Fuzzy logic control strategy is applied to input-current and output- voltage regulation. The chosen controller algorithm is a PI-like fuzzy control based on the error and change of error of the reference signal. The Takagi-Sugeno inference process was choosen due to lower processing required to obtain the results. Theoretical expressions and simulations results are presented for a 6.8 kW prototype, operating in region R2 in continuous conduction mode.