Cascaded structures reduce design repetition and improve modularity but risk system instability due to module interactions, making stability analysis crucial. This paper analyzes a two-stage DC/DC converter common in train auxiliary converters, focusing on control parameter effects on DC bus voltage via impedance matching. The open-loop front-stage Boost converter is modeled using state-space averaging, with its dual-loop controlled output impedance derived. The back-stage full-bridge LLC resonant converter’s input impedance model is derived using the fundamental wave approximation method. The detailed effects of each PI controller parameter on the Boost output impedance are analyzed and verified via Bode plots. A 150 kW simulation model is established. Experimental results, using theoretically calculated parameters as a control group and tenfold changes of specific parameters in other tests, show the current loop’s proportional factor has the greatest influence. Its increase causes the input current ripple to approximately double, aligning with theoretical analysis.