Multi-Time-Scale Electromagnetic Modeling of A Battery-Integrated Solid-State Transformer

The increasing renewable energy demand accelerates the development of hybrid AC/DC distribution systems and the utilization of solid-state transformers. For better performance, solid-state transformers with embedded battery storage are introduced. Although integrating battery storage improves power routing capability, the electromagnetic simulation of these solid-state transformers becomes more complicated, requiring much larger computational overhead. In this paper, a multi-time-scale electromagnetic transient (EMT) modeling method is proposed for a dual-active-bridge(DAB)-based solid-state transformer with built-in energy storage. By analyzing the relationship between the state variables and the modulation indexes, The EMT model is divided into three partitions, each with independent simulating rates. The matrix solver dimension is largely reduced because the division of time scales naturally decouples the high-frequency AC conversion stage. The step-delay errors of the decoupled AC states are corrected by linear prediction utilizing the switch function. The battery dynamic model is simplified since the state of charge (SOC) variation has a small influence on EMT. The multi-time-scale EMT modeling is realized in MATLAB/Simulink without using parallel computing architecture. Compared with the detailed model and the single-rate EMT equivalent model, the simulation results prove the proposed method's high accuracy and high-speed simulation acceleration.