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). This feature, together with the high voltage gain, makes the CI-QBC suitable as a DC/DC converter for photovoltaic and fuel cell systems. However, variations in load resistance, input voltage, and output voltage reference continuously cause deviations from the selected duty cycle. Therefore, this paper aims at analyzing 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 high values of k, the sensitivity is extremely high, so the ripple can easily exceed the value obtained in a QBC without CI. A suitable sensitivity is achieved if k is not higher than 0.8. Since commercial CI often exhibit k>0.9, it is also shown how to tune the coupling coefficient to the desired value using a suitably-sized extra inductor. The proposed techniques were assessed both in simulation and through experimental tests.