Luke Raymond

27.12 MHz large voltage gain resonant converter with low voltage stress

This paper presents the design and implementation of a high frequency switching power converter with a large voltage gain and air core inductors. Specifically, we demonstrate a 40 W, 30 V to 300 V dc-dc converter switching at 27.12 MHz. Operating at this frequency reduces bulk energy storage over conventional low frequency designs and allows for fast transient response. We implement a resonant converter based on the Φ2 inverter of [1]. In this paper, we evaluate and compare two rectifier topologies with lower voltage stress than the class E rectifiers described in [2], to get large voltage ratios. Unique to this design is the ability to provide short bursts of high voltage while promising excellent performance and high power density.

Performance evaluation of diodes in 27.12 MHz Class-D resonant rectifiers under high voltage and high slew rate conditions

This paper provides a performance review of select diodes for use in high frequency resonant rectifiers at modest power levels. Specifically, we evaluate the performance of several leading edge diodes for use in a 27.12 MHz Class-D type rectifier for output voltages from 170 V to 1000 V dc, and corresponding power levels between 8.5 W and 100 W. Previous work on resonant rectifiers at frequencies > 10 MHz [1] showed higher-than-expected losses in the diodes. These losses increased with increased output voltage and led to significant de-rating and poor utilization of the semiconductors. The authors suspect these losses are due in part to the high equation experienced by the Silicon Carbide (SiC) Schottky diodes used in that design. This paper provides an in depth comparison of select diodes to evaluate their performance for use at elevated voltages and frequencies. Further understanding of the losses involved in the design of high equation resonant rectifiers will lead to better de-rating guidelines for component selection of high frequency high voltage converters.

3-D-Printed Air-Core Inductors for High-Frequency Power Converters

This paper presents the design, modeling, and characterization of 3-D-printed air-core inductors for high-frequency power electronics circuits. The use of 3-D modeling techniques to make passive components extends the design flexibility and addresses some of the fabrication limitations of traditional processes. Recent work [1]- [9] has demonstrated the feasibility of incorporating air-core inductors in high-frequency (>10 MHz) switching power converters. These implementations have used discrete wire wound solenoids and toroids, and planar components that use printed circuit board traces or microfabrication techniques to make air-core inductors. However, realizations of such components have limitations in performance and applicability including open paths conducive to the flow of leakage fields, and difficulties in achieving optimal cross section to minimize loss. Along with the current effort of involving 3-D printing technology to make inductors [10], [11], we propose the use of 3-D printing and casting/plating techniques as a simple and accessible alternative that adds flexibility and functionality to the air-core inductor design for high-frequency power conversion at moderate to high-power (e.g., tens to thousands of watts) and high-voltage (greater than 100 V) levels. In this paper, we present several examples of air-core inductors realized using 3-D printing and casting/plating techniques to give an idea of the geometries that are possible to design. Moreover, we show that some of these designs can lead to improved electrical performance. This paper also describes the tools used by the authors to design, fabricate, and characterize the electromagnetic performance of the air-core inductors. The software used to generate the 3-D scaffolds for the inductors are freely available and easily accessible. Readers are encouraged to explore more possibilities of geometries that can lead to better performance with the ease of manufacturing. As progress in additive manufacturing continues, we envision 3-D printing of a complete scaffold structure that after plating (or casting) will contain all resonant passive components of an RF switching converter. Toward this goal, we present a 70-W prototype 27.12-MHz resonant inverter that incorporates some of the 3-D-printed components developed for this paper.

27.12MHz GaN resonant power converter with PCB embedded resonant air core inductors and capacitors

This paper presents the design and implementation of a 27.12 MHz, 320 W, 170 V to 28 V dc-dc resonant power converter with resonant inductors and capacitors embedded into the Printed Circuit Board (PCB). Operating at 27.12 MHz allows for small value and size resonant passive components to be implemented using traces on or within a PCB. Previous work [1]-[14] has demonstrated various ways of using PCBs to make inductors and capacitors. In this work, we evaluate a design with goals of achieving good power density, good EMI shielding, (relatively) low manufacturing cost, and the potential to operate in harsh environments (e.g. strong external magnetic field). Specifically, the proposed prototype converter consists of four vertically stacked PCBs. Two low cost 3.2 mm thick FR4 PCBs are used to make the air core toroidal inductors, and the resonant capacitors are implemented using two low-dielectric-loss thin Rogers PCBs and located in the middle of the stack. To help reduce leakage fields from inducing eddy current within the EMI shield, each resonant inductor is formed by the series/parallel combination of two vertically aligned opposite wound toroids placed in different PCBs. In this arrangement, the circumferential currents of the two inductors flow in opposite directions to cancel the axial “one turn” inductance. Capacitors are formed by two thin layers of high frequency laminates to minimize loss and avoid capacitive heating in the lossy FR4 material. A prototype dc-dc converter was built to verify the concept and it reaches an efficiency of 73.6%. A simulated loss analysis is also presented.

27.12 MHz isolated high voltage gain multi-level resonant DC-DC converter

This paper demonstrates a high efficiency, high power density, and fast transient response dc-dc converter design capable of providing a high-voltage isolated output from a low-voltage input. Specifically, we demonstrate two 100 W, 2000 Vdc proof of concept prototype dc-dc converters operating at a switching frequency of 27.12 MHz with input voltages of 40 V and 100 V respectively. Capacitive isolation provides an efficient means of allowing for multiple rectified outputs to be combined serially without exceeding semi-conductor device limits. Further, it can provide a more efficient means of impedance matching at frequencies of 10s of MHz than traditional methods such as passive matching networks or transformers by the reduction of or elimination of those stages altogether.

13.56 MHz high voltage multi-level resonant DC-DC converter

This paper demonstrates a dc-dc converter that combines resonant rectifiers in a way to achieve impedance matching and significant voltage gains without the need for a high quality factor (Q) impedance matching network. Multiple stages are stacked in a way that allows for higher output voltages without suffering efficiency penalties common to traditional serial type high-voltage converter topologies such as the Crockroft-Walton Multiplier. Application of this design results in an isolated resonant dc-dc converter design that promises high efficiency, fast transient response, and high power density while providing a high-voltage isolated output from a lower-voltage input. Specifically, we demonstrate a 2000 W, 2000 Vdc output proof of concept prototype dc-dc converter operating at a switching frequency of 13.56 MHz from an input voltage of 275 Vdc. Capacitive isolation provides an efficient means of allowing for multiple rectified outputs to be combined serially without exceeding semiconductor device limits. Further, it allows for implementation of a more efficient method of impedance matching at frequencies of 10s of MHz than traditional methods such as passive matching networks or transformers by the reduction of or elimination of those stages altogether.

3D printed air core inductors for high frequency power converters

This paper presents the design, modeling and characterization of 3D printed air core inductors for high frequency power electronics circuits. The use of additive manufacturing techniques in passive components design extends the design flexibility and offers ways to overcome some of the fabrication limitations of todays planar processes. Recent work [1]-[4] has demonstrated the feasibility of incorporating air core inductors in high frequency (>10 MHz) switching power converters. These implementations have used discrete wire wound solenoids and toroids, and planar components that use Printed Circuit Board (PCB) traces or photolithographic techniques to make air core inductors. However, realizations of such components have limitations in performance and applicability: wire wound and PCB devices leave open paths conducive to the flow of leakage fields, and photolithography yields devices with geometric constraints and limited cross section aspect ratios. We propose the use of 3D printing and molding techniques to add flexibility and functionality in the design as they allow the manufacturing of components with rounded edges and overhanging structures impossible for planar processes. In this paper, we present several examples of air core inductors designed using 3D printing and molding techniques to give an idea of the geometries that are possible to realize. Moreover, we show that some of these designs can lead to improved electrical performance. The paper also describes the tools used by the authors to design, fabricate and characterize the electromagnetic performance of the air core inductors. As progress in additive manufacturing continues, we envision a fully 3D printed power converter that obviates the need of printed circuits board. Toward this goal, we present a 70 W prototype 27.12 MHz resonant inverter that incorporates some of the 3D printed components developed for this work.

27.12MHz GaN Bi-directional resonant power converter

Resonant dc-dc converter regularly use Schottky diodes for high frequency rectification. Si Schottky diodes have relatively low voltage ratings and present reverse-recovery type losses when driven hard enough. SiC Schottky diodes can operate at high frequencies, but incur higher conduction losses. This paper presents a bidirectional dc-dc resonant converter having two ground referenced switches. The prototype converter delivers 400 W between a source of 170 V and a load of 50 V while delivering 250 W in the opposite direction. The converter presented herein can potentially be used in applications such as wireless power transfer, fuel cell and battery applications, bus converters, etc.

A High-Frequency Resonant Converter Based on the Class Phi2 Inverter for Wireless Power Transfer

This paper presents the design and implementation of high frequency resonant converter based on the Class Φ2 inverter for inductive power transfer. MHz frequency operation can allow for higher power density than conventional switching frequencies. The converter is based on the Class Φ2 inverter, reducing the voltage stress across the switch compared to other resonant topologies. A prototype of converter and a few cm airgap inductive coupling system with resistive load was implemented. We will demonstrate a greater than hundred Watt push-pull resonant converter for inductive power transfer at 13.56MHz.

Low mass RF power inverter for cubesat plasma thruster using 3D printed inductors

This paper presents the design of a low mass RF power inverter at moderate to high power levels (e.g. tens of watts and above) for weight critical applications such as cubesat plasma thrusters. Our approach for mass reduction includes resonant switching operation at tens of MHz, and the 3D printing of light-weight scaffolds that form air core inductors after plating with a thin layer of copper. Specifically, we present a 14.2 MHz 50 W resonant DC-RF power inverter implemented with 3D printed and plated air core toroidal inductors. As a demonstration of design flexibility of the 3D printing process, these toroidal inductors are designed and implemented with optimal cross sections [1] to improve quality factors. The weight of the proposed inverter is reduced by 50% when compared to a 40 W state-of-the-art counterpart in which all the inductors were implemented within the printed circuit board (PCB). The inverter achieves 90% electrical efficiency when operated on a 50 Ω resistive load at an input voltage of 50 V. Then the inverter was implemented with a low pass matching network to drive a helicon double layer (HDL) plasma intended for a cubesat thruster application. The combined inverter and matching network outputs 40 W and achieves 86% DC input to plasma efficiency at an input voltage of 40 V.