Digital Control of Bidirectional Class-E² Converter with Dual ON-OFF Frequencies and Phase Shifts for Energy Storage Applications

This paper presents a digital control scheme using dual ON-OFF frequencies with phase shifts in a bidirectional class-E ² converter for energy storage applications. In bidirectional power transfer, an ON-OFF frequency of less than 100 Hz is necessary for the forward mode to improve battery life connected at the converter output, while a much higher ON-OFF frequency is beneficial for a fast dynamic response to power demands at the converter input in the reverse mode while discharging the battery. To address this requirement, we propose a digital control with dual ON-OFF frequencies and phase shifts for a bidirectional class-E ² converter. The phase shift is applied to achieve ZVS and maximum power in each direction of the power transfer, while the ON durations of the ON-OFF frequencies are varied to control the output power. Digital PI controllers and IIR filters are employed to regulate the current of the battery in the forward mode and the voltage of the input node in the reverse power transfer mode. The closed-loop performance of the converter was simulated and compared with a prototype of a 1-MHz, 250-W class-E ² dc-dc converter.