Frequency modulation of a series resonant dual active bridge to minimize the circulating reactive currents in the high frequency link

Abstract

A frequency modulation scheme is proposed for a Capacitor-Inductor-Inductor-Capacitor (CLLC) Resonant Dual Active Bridge (RDAB) that relies on dynamic retuning of the resonant capacitors to the switching frequency as it is modulated. The proposed modulation scheme greatly reduces the circulating reactive currents in the High Frequency Link (HFL) by operating at a range of fixed discrete switching frequencies. A Triple Phase Shift (TPS) modulation scheme is used in between the discrete steps of switching frequencies and capacitances. In this paper, a mathematical analysis is presented of the RDAB and the proposed modulation scheme is compared to all of the existing modulation schemes. The CLLC RDAB is implemented in simulation and the simulation results demonstrate the effectiveness of the proposed modulation scheme at decreasing the circulating reactive currents, and therefore, greatly decreasing the conduction losses of the converter at light load, while maintaining its soft switching capability.