Analytical design, modelling and simulation of an LLC resonant converter for an electric vehicle auxiliary power module

Abstract

This paper presents an analytical design, modelling, and simulation of an LLC resonant converter for an electric vehicle auxiliary power module (APM). The work contributes a complete LLC‑focused workflow that starts from design specifications and proceeds through: i) Resonant‑tank selection using normalized gain–frequency maps to choose the inductance ratio L_n and a quality factor Q_e with soft‑switching in mind; ii) Transformer sizing from core data and loss limits; and iii) Small‑signal‑based PI controller tuning those accounts for the plant’s inherent inversion. The workflow is implemented and validated in MATLAB Simulink and PLECS for input voltages of 235-265 V and load levels from 10% to 100%. The converter achieves a peak efficiency of 98.1% within an 80.6-128.3 kHz switching range, full‑load efficiency of 93.5%, and about ±1% output voltage regulation. The controller maintains stable output settling times of 0.42-0.44 ms during 100% to 80% load steps and the reverse transition. At the highest input voltage, the switching frequency drifts beyond the intended range, which indicates a clear target for controller refinement in future work. The results show that the proposed analytical workflow is practical for designing LLC converters that meet APM efficiency and regulation goals, with cross‑platform simulation providing consistent evidence of performance.