Load-Independent Class E/EF Inverters and Rectifiers for MHz-Switching Applications

Abstract

This paper presents a unified framework for the modeling, analysis, and design of load-independent Class E and Class EF inverters and rectifiers. These circuits are able to maintain zero-voltage switching and, hence, high efficiency for a wide load range without requiring tuning or use of a feedback loop, and to simultaneously achieve a constant amplitude ac voltage or current in inversion and a constant dc output voltage or current in rectification. As switching frequencies are gradually stepping into the megahertz (MHz) region with the use of wide-bandgap (WBG) devices such as GaN and SiC, switching loss, implementing fast control loops, and current sensing become a challenge, which loadindependent operation is able to address, thus allowing exploitation of the high-frequency capability of WBG devices. The traditional Class E and EF topologies are first presented, and the conditions for load-independent operation are derived mathematically; then, a thorough analytical characterization of the circuit performance is carried out in terms of voltage and current stresses and the power-output capability. From this, design contours and tables are presented to enable the rapid implementation of these converters given particular power and load requirements. Three different design examples are used to showcase the capability of these converters in typical MHz power conversion applications using the design equations and methods presented in this paper. The design examples are chosen toward enabling efficient and high-power-density MHz converters for wireless power transfer (WPT) applications and dc/dc conversion. Specifically, a 150-W 13.56-MHz Class EF inverter for WPT, a 150-W 10-MHz miniature Class E boost converter, and a lightweight wirelessly powered drone using a 20-W 13.56-MHz Class E synchronous rectifier have been designed and are presented here. Index Terms-DC-AC power converters, resonant inverters, wireless power transmission, zero voltage switching. I. INTRODUCTION T HE full exploitation of wide-bandgap (WBG) devices is driving the design of ever higher frequency converters

Analysis and Comparison of Push–Pull Class-E Inverters With Magnetic Integration for Megahertz Wireless Power Transfer

“…As in Fig.1, the windings of the integrated inductor can be either coupled or uncoupled, thus the circuit design is different for the cases. If the windings are uncoupled, i.e., k in = 0, the circuit design is the same as a single-switch class-E inverter and has been well studied in existing literature [6], [8]. Note that the current amplitude of the inductor windings is kept large to satisfy ZVS when the load resistance varies from an optimal value to infinity.…”

“…A class-E inverter with finite DC-feed inductance is often used for the WPT of which the load varies in a wide range. The switch can naturally achieve zero-voltage-switching (ZVS) without using closed-loop control, but this expected feature is essentially based on using much lower input inductance [6]- [8]. It results in a large AC current through the input inductor and the DC source.…”

“…[15] introduces a design method to reduce the volume of inductors with significant AC current. However, by now, most existing literatures about class-E inverters focus on the circuit design and closed-loop control, but not the magnetic design [6], [8], [16]- [21].…”

Design of load-independent class-E inverter with MOSFET gate-to-drain and drain-to-source parasitic capacitances

“…In the class-E inverter, once the load varies from the desired value, the output-voltage waveform changes and the ZVS loses, which result in a degradation of the performance and efficiency. To solve the issue, a new design conception was shown in [29,30]. The circuit topologies of the class-E inverter with the new design conception introduced in [29] and [30] and the typical class-E inverter are identical.…”

“…To solve the issue, a new design conception was shown in [29,30]. The circuit topologies of the class-E inverter with the new design conception introduced in [29] and [30] and the typical class-E inverter are identical. The input inductor based on the load-independent design conception, however, works as a finite inductor instead of a RF bulk choke, which has the input current changed to provide a required amplitude and phase shift that the output-voltage waveform and the ZVS operation can be kept even the load varies.…”