Closed-Loop Adaptive Frequency and Phase-Shift Control of Bidirectional Class-E² Converter for Energy Storage Applications

This paper presents discrete frequency and phase-shift control for a bidirectional class-E2 converter, enabling a wide range of output power in energy storage applications. Class-E² converters typically operate within a narrow power range to achieve zero voltage switching (ZVS) across the switching devices and ensure high efficiency. To address this limitation, we propose an adaptive frequency control algorithm that utilizes multiple frequency steps to reduce output ripple and minimize output capacitor requirements. Our adaptive frequency control algorithm ensures high efficiency across a wide output power range by using 16 discrete switching frequency steps ranging from 800 kHz to 1.6 MHz. Duty ratios are pre-computed and stored in a lookup table to provide ZVS at each frequency. We also apply a variable phase shift between the switching devices to maintain ZVS and control the power flow direction. By directly selecting and applying the appropriate frequency from the lookup table instead of sequential searching, our proposed algorithm enables faster dynamic response with minimal undershoot and overshoot. Through simulation and implementation of closed-loop control of the bidirectional class-E2 converter prototype using an MCU, we achieved bidirectional output power level variation from 13 W to 350 W with a maximum efficiency of 93.5%.