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

Abstract

This paper presents the circuit design and magnetic integration of push-pull class-E inverters for wireless power transfer (WPT) up to megahertz. The design criterion for achieving ZVS of a class-E inverter with coupled windings is derived mathematically. The approaches of magnetic integration for push-pull class-E inverters are analyzed and compared. Then, a new magnetic structure with hybrid magnetic materials is proposed to build the integrated inductors with either coupled windings or uncoupled windings. A 3 MHz WPT system is built to verify the analysis. The detailed comparison of the class-E inverters with magnetic integration is presented in terms of switch voltage, efficiency, harmonic currents and thermal distribution. In the optimized design example, the switches keep ZVS over the entire load range without using any closed-loop control. The system efficiency reaches 87.1% at 350 W output power.

Synchronous Push–Pull Class E Rectifiers With Load-Independent Operation for Megahertz Wireless Power Transfer

“…The push-pull class E rectifier, which comprises two switches operating differentially (i.e., interleaving with 180degree-shift switching), can naturally eliminate the odd-order harmonics at the output node. Thus, it is conducive to suppress the current ripples through the DC capacitor and reduce the electromagnetic interference [9], [28]. Combined with the load-independent operation, the synchronous push-pull class E rectifier can also achieve ZPA input impedance and softswitching over the entire load range.…”

“…However, the waveform of the switch voltage changes as the load varies, and resulting in an unexpected switching phase shift. This issue will be more troublesome in the differential (i.e., push-pull) class E topology due to the unbalance voltage waveforms [28]. In [9], the zero-current detection is implemented to generate the gate driving signal of several hundred kHz.…”

Load-Independent Push–Pull Class E$ ^2$ Topology With Coupled Inductors for MHz-WPT Applications

“…An investigation has been reported in [28] to integrate and couple the inductors of the push-pull Class E inverters. The coupled inductor was also implemented for active rectification [29].…”

Analysis and Design of Single-Ended Resonant Converter for Wireless Power Transfer Systems

“…Unfortunately, the auxiliary needs a high-side driver, which aggravates its complexity. In [ 21 ], a push–pull structure and coupled-choke inductors were introduced into the Class-E inverter to increase output power. In [ 22 ], a hybrid inverter named Class-EF was proposed.…”