Three-level quadratic non-insulated basic DC-DC converters

This paper presents a family of three transformerless converters (buck, boost and buck-boost) with two specific characteristics: the quadratic static gain as a function of the duty cycle ratio, and the division of the higher voltage level between the two switches. Because of that they are called "three-level quadratic converters", or TLQ converters. All of them are composed by two diodes, two active switches, two inductors and two capacitors. A specific modulation strategy based on concentric pulses is presented. Based on it, they are able to convert the input voltage with a ratio that the basic converters could not. The proposed converters are mostly attractive for applications in which a wide voltage ratio is desired, like fuel cells, for instance. The commutation cell common to them is shown, as the main waveforms, equations and output characteristics. Experimental results are presented to confirm the theory.