Variable Switching Frequency Control Strategies for the SAB

Abstract

This paper explores control strategies based on variable switching frequency for the Single Active Bridge converter to expand its soft-switching capabilities without additional components. While the conduction mode and the soft-switching features of this converter can be maintained across the entire operational range using variable switching frequency with a constant duty cycle, this work demonstrates that the use of both as control variables provides additional degrees of freedom to optimize performance. Specifically, two control trajectory selection criteria are proposed: one focused on minimizing the switching frequency range while reducing rms currents, and another aimed at maintaining constant recirculating current to ensure adequate ZVS across all operating points. Additionally, comprehensive design guidelines that integrate both control variables are provided. The proposed strategies and design methodologies are validated through a comparative experimental analysis of four 800 V to 400 V, 2.2 kW prototypes, each designed for the same specifications and utilizing a different control strategy.