Impedance-Based Modeling and Stability Analysis of the Input-Series Output-Parallel DAB3 Converter with Decentralized Control

Input-series output-parallel (ISOP) dc-dc converter systems require a dedicated input-voltage-sharing (IVS) control strategy. A centralized IVS control typically reduces system modularity and reliability. Thus, this paper adopts a decentralized IVS control method to the ISOP-connected three-phase dual-active bridge (DAB3) converter. It contributes to exploring decentralized control methods for ISOP systems by linking the theory of the negative incremental-resistance behavior to the instability of the IVS-transfer function. For the stability assessment, closed-loop input impedance models of the DAB3 converter are derived that include the effects of the control and the output-parallel connection into a single-input single-output (SISO) model. The derived analytical models are verified via multitone analyses of a switching model in offline simulations. This way, the stability of the whole ISOP system can be predicted solely based on the SISO model. The model-based stability regions are validated on a real-time simulation system of a two-module system at a switching frequency of 10 kHz. Experimental results are presented for an eight-module system with an input voltage of 5 kV.