Modulation-Independent Initial Current Control of DAB-Based Single-Stage AC–DC Converter for DC Bias Elimination

In the dual active bridge-based single-stage (DAB-1S) ac–dc converter, the varying input power causes a variation in the phase shift ratios, resulting in varying initial current and the generation of dc-bias current (DCBC). The DCBC will aggravate current stress and increase conduction loss, etc. This article introduces an initial current control method of DAB-1S ac–dc converter to eliminate the DCBC. The introduction of control degrees of freedom that are independent of power control enables the initial current of each switching cycle to be controlled to zero in any modulation mode. In this manner, the currents of neighboring switching cycles are decoupled, thereby eliminating the DCBC. Moreover, the impact of nonideal parameters in practical DAB 1S ac–dc converters is analyzed, and corresponding compensation methods are proposed. Meanwhile, mathematical analysis of the switching cycles and grid cycles indicates that this method only changes the initial phase angle of the voltage and current for each switching cycle, leaving the harmonic content of the port current unchanged and the total harmonic distortion of the grid current unaffected. The experimental prototype has confirmed the effectiveness of the dc bias elimination method. Comparative experimentation with various other existing modulation methods highlights the superiority of this method.