Comparison of SPS, DPS And CTPS Modulations with Full Consideration of Stability of DAB Converters with Input LC Filter

The cascaded systems composed of dual active bridge (DAB) converters and LC filters may suffer instability problems. The impedance-based criterion provides valid theoretical foundation to explore the instability issue of such cascaded systems. Although the input impedance of the DAB converter is highly dependent on the modulation methods, the impacts of these modulation methods on the DAB input impedances remain unclear. To investigate these impacts, three typical modulation methods of DAB converters, traditional single-phase-shift (SPS), dual-phase-shift (DPS) and the emerging cooperative triple-phase-shift (CTPS) modulation, are studied in this paper. The full-order input impedance models of the DAB converters with these modulation methods are originally derived. The impacts of the modulation methods on the DAB input impedances are compared for the first time. An interesting phenomenon is found that the open-loop impedances of SPS-DAB and DPS-DAB converters present the characteristics of the parallel-connected inductor and capacitor, while the open-loop impedance of CTPS-DAB converter presents the resistor characteristics. Therefore, the CTPS shows the best performance among these three modulation methods in terms of the stability of cascaded systems, which is further validated by hardware-in-the-loop experiments.