Low-Frequency Stability Analysis of Train-Grid System: A Perspective from DAB Converter

Despite the great potential of power electronic traction transformer (PETT) in high-speed train, the issue of lowfrequency oscillation (LFO) is a concern. Unfortunately, current studies assessing the low-frequency stability of the PETT often oversimplify the dual active bridge (DAB) converter as a passive circuit, which may lead to an unreliable analysis result. To clarify this issue, this letter examines the mechanism of LFO in the PETT-based train-grid system from the perspective of a DAB converter. Specifically, a complete impedance model of the PETT is first established by using the harmonic linearization method. Then, the stability differences between simplified PETT and complete PETT are investigated, and the impact mechanism of DAB converter on the LFO is thoroughly revealed. Experimental test results verify the correctness of modeling and analysis.