Frequency and Phase Modulation in a Bidirectional Class-E$^{2}$ Converter for Energy Storage Systems

Abstract

This paper presents frequency and phase-shift control in a class-E <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> DC-DC converter to provide a wide range of power levels for energy storage applications. The symmetrical design of a class-E inverter and a class-E rectifier in a class-E <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> DC-DC converter achieves high efficiency at MHz frequencies with GaN FETs. However, zero voltage switching (ZVS) requirements limit an output power range, especially in an infinite choke class-E <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> DC-DC converter. This paper proposes modulating the switching frequency from 800 kHz to 1.5 MHz along with a phase shift from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$57^{\circ }$</tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$295^{\circ }$</tex-math></inline-formula> to control the power flow. The converter's duty ratio is decreased from 60% to 18% with increasing frequency to maintain ZVS. We designed and implemented the proposed class-E <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> DC-DC converter prototype to control the output power above and below the nominal power level. Also, the direction of the power flow is changed by controlling the frequency and phase shift. At a nominal frequency of 1 MHz, the nominal output power is 224 W with an efficiency of 93.5%. In both directions of power flow, the converter's efficiency remains above 91.5% at a power level of 355 W at 800 kHz to 39 W at 1.5 MHz.