Simplified Discrete-Time Modeling for Convenient Stability Prediction of DAB Converter in Energy Storage System

This paper proposes a simplified discrete-time modeling approach capable of describing the global dynamic characteristics and predicting the stability conveniently of the dual active bridge (DAB) converter enabled energy storage system (ESS) within a DC microgrid. The proposed technique utilizes both the matrix exponential approximation and the simplification of the discrete iterative relationship, which is accurate and simple to obtain high-precision system stability boundary and fast-scale dynamic analysis. Compared with the accurate discrete-time model, the traditional reduced-order averaged model, and the bilinear discrete-time model, the proposed model significantly reduces the computational complexity and exhibits nearly equivalent reliability and accuracy in stability prediction in most practical scenarios. This simplified model is applicable for analyzing both steady-state and transient characteristics of the system. Moreover, using the simplified discrete-time model, a comprehensive and systematic investigation of all potential unstable behaviors is conducted for the constant voltage charging mode DAB converter. Accordingly, the corresponding multi-scale oscillations are revealed by correlation factor and sensitivity analysis. Therefore, a stability-oriented parameter design method is provided, offering effective means to select and tune the system parameters, guaranteeing the system's operation remains within the boundaries of the stable region. Finally, the theoretical analysis is validated by simulation and experimental results.