Design and Comparative Analysis of LLC and LCC Resonant Converters for 800V/48V Electric Vehicle Auxiliary Power Modules (APM)

In modern electric vehicle (EVs), auxiliary power demand is rapidly increasing toward 5 kW due to advanced cabin electronics and autonomous driving systems. Combined with the transition from 400 V to 800 V voltage levels, this trend makes the design of high-efficiency and well-regulated 800 V/48V auxiliary power modules (APMs) increasingly challenging, particularly under wide input voltage variations and light-load conditions. This study presents a comparative analysis of full-bridge LLC and LCC resonant converters for a 5 kW EV APM. The analysis is based on First Harmonic Approximation (FHA), normalized gain curves obtained using MATLAB, and LTspice simulations, focusing on efficiency, loss distribution, magnetic performance, and frequency regulation behavior. The results show that the LLC converter achieves higher efficiency and a relatively flat efficiency profile; however, under wide input voltage and lightload conditions, it suffers from frequency runaway due to gain flattening in the buck region. In contrast, the LCC converter constrains the switching frequency within a narrower and more controllable range thanks to its a more pronounced gain characteristic, at the expense of increased circulating current and reduced efficiency. Overall, LLC is more suitable for applications prioritizing efficiency and power density, whereas LCC offers advantages in control stability and predictable operation under wide operating conditions in 800 V EV APM systems.