T HIS paper explores opportunities and challenges in power conversion in the VHF frequency range of 30-300 MHz. The scaling of magnetic component size with frequency is investigated, and it is shown that substantial miniaturization is possible with increased frequencies even considering material and heat transfer limitations. Likewise, dramatic frequency increases are possible with existing and emerging semiconductor devices, but necessitate circuit designs that either compensate for or utilize device parasitics. We outline the characteristics of topologies and control methods that can meet the requirements of VHF power conversion, and present supporting examples from power converters operating at frequencies of up to 110 MHz.

In this paper we present a vertical-cavity enhanced resonant thermal emitter-a highly directional, narrowband, tunable, partially coherent thermal source. This device enhances thermal emittance of a metallic or any other highly reflective structure to unity near a cavity resonant frequency. The structure consists of a planar metallic surface ͑e.g., silver, tungsten͒, a dielectric layer on top of the metal that forms a vertical cavity, followed by a multilayer dielectric stack acting as a partially transparent cavity mirror. The resonant frequency can easily be tuned by changing the cavity thickness ͑thus shifting resonant emission peak͒, while the angle at which the maximum emittance appears can be tuned as well by changing the number of dielectric stack layers. The thermal emission exhibits an extremely narrow angular emission lobe, suggesting increased spatial coherence. Furthermore, we show that we can enhance the thermal emission of an arbitrarily low-emittance material, choosing a properly designed thermal cavity, to near unity.

This paper presents a new switched-mode resonant inverter, which we term the 8 2 inverter, that is well suited to operation at very high frequencies and to rapid on/off control. Features of this inverter topology include low semiconductor voltage stress, small passive energy storage requirements, fast dynamic response, and good design flexibility. The structure and operation of the proposed topology are described, and a design procedure is introduced. Experimental results demonstrating the new topology are also presented. A prototype 8 2 inverter is described that switches at 30 MHz and provides over 500 W of radio frequency power at a drain efficiency above 92%. It is expected that the 8 2 inverter will find use as a building block in high-performance dc-dc converters among other applications. Index Terms-Class E inverter, class-F power amplifier, class 8 inverter, harmonic peaking, radio frequency inverter, very high frequency, VHF power converter.

Abstract-This paper explores the benefits of distributed power electronics in solar photovoltaic applications through the use of sub-module integrated maximum power point trackers (MPPT). We propose a system architecture that provides a substantial increase in captured energy during partial shading conditions, while at the same time enabling significant overall cost reductions. This is achieved through direct integration of miniature MPPT power converters into existing junction boxes. We describe the design and implementation of a high-efficiency (>98%) synchronous buck MPPT converter, along with digital control techniques that ensure both local and global maximum power extraction. Through detailed experimental measurements under real-world conditions, we verify the increase in energy capture and quantify the benefits of the architecture.

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This document describes several aspects relating to the design of dc-dc converters operating at frequencies in the VHF range (30-300 MHz). Design considerations are treated in the context of a dc-dc converter operating at a switching frequency of 100 MHz. Gate drive, rectifier and control designs are explored in detail, and experimental measurements of the complete converter are presented that verify the design approach. The gate drive, a self-oscillating multi-resonant circuit, dramatically reduces the gating power while ensuring fast onoff transitions of the semiconductor switch. The rectifier is a resonant topology that absorbs diode parasitic capacitance and is designed to appear resistive at the switching frequency. The small sizes of the energy storage elements (inductors and capacitors) in this circuit permit rapid start-up and shutdown and a correspondingly high control bandwidth. These characteristics are exploited in a high bandwidth hysteretic control scheme that modulates the converter on and off at frequencies as high as 200 kHz.

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