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

This article presents frequency and phase-shift control in a class-E $^{2}$ 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 $^{2}$ dc–dc converter achieves high efficiency at megahertz frequencies with GaN FETs. However, zero-voltage switching (ZVS) requirements limit an output power range, especially in an infinite choke class-E $^{2}$ dc–dc converter. This article proposes modulating the switching frequency from 800 kHz to 1.5 MHz along with a phase shift from 57 $^{\circ }$ to 295 $^{\circ }$ to control the power flow. The converter's duty ratio is decreased from 60% to 18% with increasing frequency to maintain ZVS. We design and implement the proposed class-E $^{2}$ 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 the 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.