Coupling Coefficient Tuning to Ensure Zero/Low Ripple in a QBC in a Wide Duty Cycle Range

Previous work showed the possibility of nulling the input current ripple of the Quadratic Boost Converter (QBC) at a selected duty cycle by coupling its two inductors, thus originating the coupled inductor-based QBC (CI-QBC). However, variations in load resistance, input voltage, and output voltage reference continuously cause deviations from the selected duty cycle. Therefore, this paper aims to analyze the sensitivity of the ripple reduction against duty cycle variations in a CI-QBC for different values of the CI's coupling coefficient k. For k>0.8, the sensitivity is extremely high, so the ripple can easily exceed that of a QBC. Since commercial CI often exhibit k>0.9, it is also shown how to tune the CI to obtain k≤0.8 using a suitably sized extra inductor. In this way, it is possible to ensure zero or low ripple in a wide duty cycle range. This feature, together with the high voltage gain, makes the CI-QBC a suitable DC/DC converter for FC and PV sources. The state-space model of the CI-QBC is devised, and the proposed techniques are assessed both in simulation and through experimental tests under open-loop and closed-loop control. A design procedure is also proposed to constrain the maximum ripple of the CI-QBC under a chosen level to increase the efficiency and lifespan of FC and PV sources.