Input Stability Enhancement Strategies for Input-Series-Output-Parallel Dual-Active-Bridge Converter: Modeling, Reshaping, and Experiment

In input-series-output-parallel (ISOP) dual-active-bridge (DAB) converters, LC filters are employed for high-quality current into dc bus. However, with ISOP DAB converter operating as a constant power load (CPL), the LC filter will cause series resonance and bring oscillation in the input voltages of ISOP DAB converter and submodules. In addition, the previous strategies simplify the ISOP converter as a single-input-single-output (SISO) system in cascade with LC filter, causing the potential poor performance and impractical control of submodules. Thus, input stability enhancement strategies are proposed for ISOP DAB converter with LC filter. First, the input impedance model is established to reveal the input-voltage oscillation and difference of ISOP DAB converter and submodules. Second, a series of input stability enhancement strategies and practical implements are proposed, achieved as 1) series virtual impedances (SVIs) with inductor; 2) parallel virtual admittances (PVAs) with inductor; and 3) PVA with integrated capacitor in ISOP DAB converter, and 1) SVI with submodule input capacitor and 2) PVA with submodule input capacitor submodules. Third, the proposed input stability enhancement strategies are constructed, derived, and discussed from the perspectives of ISOP DAB converter and submodule each other, to achieve the proposed regulators. Moreover, the SVI with inductor, PVA with inductor, and PVA with integrated capacitor in ISOP DAB converter are verified by the input-voltage differences and oscillation of submodules; the SVI with submodule input capacitor and PVA with submodule input capacitor are verified by the input voltage oscillation of ISOP DAB converter. Compared to the conventional strategies, the proposed strategies achieve faster response time, fewer ripples, and less voltage oscillation in both ISOP DAB converter and submodules. Finally, an experiment is set up to verify the proposed strategies.