A High Step-Up DC-DC Converter Based on Three-State Switching Cell Grover V. Torrico-Bascopé (1) René P. Torrico-Bascopé (2) Demercil Souza de Oliveira Jr. (2) Samuel A.Vasconcelos (2) Fernando L. M. Antunes (2) Carlos G. C. Branco (3) (1) Eltek Energy AB Hammarbacken 4A, 4tr 191 24 Sollentuna Stockholm-Sweden grover.torrico@eltekenergy.com (2) Federal University of Ceará Electrical Engineering Department Energy Processing and Control Group Fortaleza – CE - Brazil rene@dee.ufc.br, demercil@dee.ufc.br (3) Technological Education Federal Center of Piauí Teresina – PI - Brazil cgustavo@ieee.org Abstract— A new non-isolated boost converter with high voltage gain is proposed on this work. This converter is suitable for applications with a high voltage gain between the input and the output. In this converter, for a given duty cycle, the output to input voltage ratio can be raised by adding transformer turns. Another important feature of this converter is the lower blocking voltage across the controlled switches compared to similar circuits, which allows the utilization of MOSFETs switches with lower conduction resistances R DS(on) . In order to verify the feasibility of this topology; principle of operation, theoretical analysis, and experimental waveforms are shown for a 1kW assembled prototype. I. INTRODUCTION When the desired application needs to raise a low-level input voltage, commonly presented in batteries and photovoltaic solar panels (12Vdc – 48Vdc), to high output DC bus voltage (300Vdc – 400Vdc), required to feed voltage source inverters-VSI utilized within UPS systems, motor drives, etc., the classical boost converter is not a good choice. An alternative might be the utilization of boost converters in cascade, but this solution achieves a low efficiency, due to the amount of power processing stages. To overcome this disadvantage some solutions using step-up converters capable of operating with high voltage gain ratio were proposed in the literature. Thus, in [1,2] several clamp-mode coupled-inductor boost converters operating with the advantages of high voltage gain ratio and half output voltage stress across the switches were presented. The disadvantages observed in these converters, were their pulsating input current and high currents stress through the clamping capacitors. A two-inductor boost converter with an auxiliary transformer was presented in [3]. It operates as an interleaved boost converter. To maximize the voltage gain of the converter, the output side of each circuit was configured as a voltage doubler rectifier using two diodes and two capacitors. This topology was connected without common input-output ground. As relevant features of both converters, it can be said that the input current drain of the voltage source is non-pulsating with low ripple and the maximum voltage stress across the switches is half of the output voltage. As difficulty on the converter, was observed the necessity to apply isolating sample output voltage or isolated gate drivers for the switches. Also, a non-isolated converter based on the interleaved boost converter, integrated with multiplier capacitors connected in series was proposed in [4]. These capacitors exhibit a similar behavior when compared with the series capacitor of the Sepic converter, but now allowing a high static gain. The converter presents the following advantages: the input current drain of the voltage source is non-pulsating with low ripple, and the maximum voltage stress across the switches is half of the output voltage. As drawback of the converter, it is observed the circulation of high current through the series capacitors when high levels of power are processed. Following the brief revision, in [5,6,7] were proposed several converters with high static gain, all based on boost-flyback. They are similar to the topologies proposed in [1,2]. They present the following advantage: the voltage stress across the switches is low and naturally clamped by the output filter capacitor. As disadvantages, it can be indicated that the input current is pulsating; therefore, a LC input filter is necessary to get continuous current on the input voltage source. Finally, in [8,9], switching capacitor techniques were used to elevate the input voltage up to the required output voltage level. This idea was adequate only for the development of low power converters, since many switches with several voltage stresses and many capacitors are necessary. The proposed converter, which is based on the three-state commutation cell [10,11], is shown in Fig. 1. As advantages, it can be emphasized that the input current is non-pulsating with low ripple; the input inductor operates within the double of the switching frequency allowing weight and volume reduction. It can be also observed that the voltage stress across the switches is lower than a half of the output voltage and naturally clamped by one output filter capacitor, so that a small snubber is necessary on each switch. Another benefit is that for a given duty cycle the output voltage can be elevated by incrementing the transformer turns ratio without compromising the voltage stress across the switches. The lower voltage across the IEEE ISIE 2006, July 9-12, 2006, Montréal, Québec, Canada 1-4244-0497-5/06/$20.00 © 2006 IEEE 998