New design methdology for megahertz-frequency resonant dc-dc converters using impedance control network architecture

This paper introduces a new design methodology for high-frequency resonant dc-dc converters utilizing the recently proposed impedance control network (ICN) converter architecture. This design methodology guarantees zero voltage switching (ZVS) and near zero current switching (ZCS) of all transistors across the entire operating range of the converter. As compared to previous ICN converter design techniques, the new methodology does not require frequency adjustment to achieve ZVS. In addition, it uses a rigorous analytical approach to minimize the phase lag required for ZVS, thus ensuring near-ZCS operation. The advantages gained from the proposed design methodology are validated using a prototype 1-MHz 90-W ICN resonant converter designed to operate over an input voltage range of 36 V to 60 V and output voltage of 1.8 V. This prototype ICN resonant converter employs a stacked inverter structure to further enhance performance.

I. Introduction

The ever increasing demand on the compactness of power electronic converters necessitates high-frequency operation. Achieving high efficiency at high frequencies requires soft-switching in the form of zero voltage switching (ZVS) and/or zero current switching (ZCS) to reduce transistor switching losses. In addition, many applications such as power supplies and large step-down point-of-load converters also require large conversion ratios, isolation, and efficient operation under wide variations in input voltage and output power. Therefore, there is a need for isolated high-frequency converters that can provide large conversion ratios and achieve soft-switching across wide operating ranges. Unfortunately, most soft-switching converters can only maintain high efficiency under specific operating conditions, and lose ZVS or ZCS capability when input voltage or output power change. For example, in the case of resonant converters operated under frequency control [1]–[3], output voltage can be regulated in the face of wide variations in input voltage by substantially increasing the switching frequency (frequency is increased rather than decreased in order to maintain ZVS); however, this exacerbates switching losses. Furthermore, wide frequency range operation presents difficulties in optimizing magnetics and EMI filters [4]. Several fixed-frequency techniques have also been proposed for resonant converter control. Conventional resonant converters using phase-shift control suffer from asymmetric current in the two inverter legs [4], [5]. Under partial loads, the leading inverter leg turns off at large current, while the lagging leg loses ZVS capability. Other fixed frequency control techniques also lose ZVS capability under low output power conditions [6]–[8]. Therefore, there is a requirement for converter architectures and associated design and control methods that can achieve soft-switching across wide input voltage and power ranges, and provide large voltage conversion ratios. One such architecture, the impedance control network (ICN) resonant converter, was recently proposed in [9].