High Accuracy Calorimetric Measurements and Modeling of Ceramic Capacitor Losses Under Large Ripple Operation

Recent work on hybrid and resonant switched-capacitor converters, as well as on flying capacitor multi-level converters, have demonstrated exceptionally high efficiencies and power densities, through the use of multilayer ceramic capacitors (MLCCs). However, when used in such converters as the main energy transfer components, the capacitors experience high voltage and current ripple, under large dc bias. Yet, capacitor characterization today is typically done only with small signal excitation, and under low or no dc bias, yielding highly inaccurate loss models when the capacitor is used as the main energy transfer element. This work presents a technique for obtaining detailed loss characterizations of MLCCs under more realistic operating conditions, and presents experimental results from a number of different capacitors. Finally, several simple loss models are presented and compared which helps guide practicing engineers in the design of capacitor-based power converters.

I. Introduction

Recent work has shown the advantages of using multilayer ceramic capacitors (MLCCs) as the primary energy storage/transfer device in hybrid [1] and resonant switched capacitor converters [2]–[4]. These capacitors are energy-dense and allow for the efficient transfer of energy; however, the performance of these devices are dependent upon a number of operating conditions, making it challenging to accurately capture and model their behavior. To fully capitalize on the potential benefits of MLCCs, it is important to understand and model their energy storage and loss characteristics. Past work [5], [6] has characterized MLCCs under low-frequency (i.e., 50-60 Hz) sinusoidal excitation, but to date, only [7] has performed high frequency, square-wave excitation experiments, for a small number of capacitors under a narrow range of frequencies, with constant excitation amplitude. In this work, we seek to expand the survey of MLCC capacitors, and evaluate them for a wide range of frequencies and amplitudes. Moreover, based on the empirical data, we propose a relatively simple loss model that can be used for circuit designers that seek to utilize MLCCs capacitors as energy transfer components under large signal swings.