Comprehensive large-signal performance analysis of ceramic capacitors for power pulsation buffers

Abstract

In high power density single-phase PV inverter systems, active auxiliary circuits are installed, shifting the double line-frequency power pulsation away from the dc link to a dedicated buffer capacitor. Being relieved from strict voltage ripple requirements, a larger voltage ripple is allowed at the buffer capacitor, significantly reducing the capacitance requirements and consequently the overall volume of the converter system. Since the capacitance density of electrolytic capacitors must be derated because of imposed current limitations, ceramic capacitors become the preferred choice in power pulsation buffer applications. In particular, TDK's class II X6S MLCC with BaTiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ceramic and the recently launched CeraLink with PLZT ceramic are promising candidates due to their high energy density. The actual prevailing capacitance of these two types of ceramics, strongly depends on the operating point, that is, a dc bias voltage and a superimposed large-signal amplitude ac voltage. Unfortunately, the large-signal behavior and performance of these ceramic capacitors is not specified by the manufacturer. In this paper, a comprehensive characterization of the X6S MLCC and the CeraLink large-signal performance is carried out by means of experimental measurements. The acquired data enables an accurate dimensioning of the power pulsation buffer capacitor and an estimate of the capacitor losses during operation. Since the device temperature has a strong impact on the ceramic properties, results for 30 °C, 60 °C and 90 °C are presented.