Design of a High-Power Filter Inductor for Variable-Switching-Frequency TCM-Based ZVS Inverters in EV Drive Systems

Abstract

Soft-switching inverters are essential for achieving high efficiency and low electromagnetic interference (EMI) in electric vehicle (EV) drive systems. However, designing filter inductors for such converters remains challenging. In sinusoidal triangular current mode (S-TCM)-based zero-voltage-switching (ZVS) inverters, the inductor is subjected to large triangular current ripple, intentional bidirectional current operation for ZVS, and variable switching frequency, making conventional fixed-frequency PWM inductor design approaches unsuitable. This paper presents a systematic design methodology for a high-power filter inductor specifically developed for S-TCM-based ZVS inverters. The proposed methodology combines analytical design calculations, experimental characterization of the magnetic material, and finite-element-method (FEM)-based electromagnetic and loss analysis. A 3C91 ferrite pot core and three winding configurations—Litz wire, copper foil, and solid copper wire—were investigated. The inductance of the designed inductors was validated experimentally and through FEMM and ANSYS simulations, while magnetic and winding losses were evaluated using FEM-based simulations in ANSYS. The core-loss coefficients of the 3C91 ferrite material were also experimentally determined for accurate loss estimation. Two parallel inductors per phase were employed to satisfy the required inductance and current-handling capability. The proposed methodology provides a practical framework for the systematic design and evaluation of high-power filter inductors by enabling accurate prediction of inductance, magnetic losses, winding losses, and thermal performance for S-TCM-based ZVS inverters used in EV powertrains and other high-frequency power conversion systems.