Frequency and Duty Ratio Control of Bidirectional Class-E2 Converter

Abstract

This paper presents a frequency and duty ratio control for a bidirectional class-E <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> dc-dc converter to provide a wide range of output voltage and current for small satellite power systems and energy storage applications. A class-E <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> resonant dc-dc converter consisting of the symmetrical design of a class-E inverter and a class-E rectifier using GaN FETs achieves high efficiency at MHz frequencies thanks to the soft-switching operation. Also, synchronous rectification in the converter produces a maximum 6% efficiency increase compared with a rectifier using a GaN FET as a diode. However, their operation is often limited to a narrow load range or small input and output voltage variations. Therefore, this paper proposes varying the switching frequency from 800 kHz to 1.5 MHz and the converter’s duty ratio to control the output current while varying the phase shift between the inverter and rectifier. We designed and implemented the bidirectional class-E <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> dc-dc converter prototype using GaN FETs and an FPGA to vary the output power levels and the direction of the power flow with a combination of frequency, duty ratio, and phase. The converter’s efficiency in the forward direction is 91.5% for 256 W output power and 89.1% in the reverse direction for 242 W output power at a nominal frequency of 1 MHz.