Loss Characterization and Modeling of Class II Multilayer Ceramic Capacitors: A Synergic Material-Microstructure-Device Approach

This paper motivates the loss characterization and modeling of Class II multi-layer ceramic capacitors (MLCCs), which have been widely utilized owing to high energy density, in high-frequency resonant converters. In a resonant tank, MLCCs experience complex electrical operating conditions (e.g., large-signal, high-frequency, DC bias), but the incurred power loss has not been clearly characterized and modeled. This paper first proposes a novel resonant-Sawyer-Tower (Res-ST) circuit which can experimentally extracts the loss of a MLCC in real operation in a resonant tank. A general loss modeling approach named Steinmetz's Pre-electrified Graph (SPeG) is then proposed to correlate capacitor's loss to the peak value of excitation, frequency, and DC bias voltage. The SpeG model provides the material-specific volume loss density of common Class II dielectric materials and can be easily extrapolated to evaluate the loss of the MLCCs with different rated voltage $&$ capacitance but employing the same dielectric material. To generalize the material-specific SPeG model to device-level application, this paper also proposes an easy-to-follow tool, dielectric thickness observer (DTO), to estimate the internal microstructural geometry by tracking the $C$ - $V$ characteristic provided in product datasheet. The synergy of the proposed characterization circuit, SPeG loss model, and DTO establishes a toolkit that enables the estimation of MLCC losses in a manner similar to that of a ferromagnetic inductor/transformer core. This paper is accompanied by microscope images of the investigated MLCC samples and MATLAB scripts of the proposed DTO.