DC-Link Capacitor Optimization in AC–DC Converter by Load Current Prediction

Abstract

Alternating Current–Direct Current (AC–DC) converters require a high value bulk capacitor or a filter capacitor between the DC–DC conversion stages, which in turn causes many problems in the design of a AC–DC converter. The component package size for this capacitor is large due to its high voltage rating and capacitance value. In addition, the high charging current creates more problems during the product compliance testing phase. The shelf life of these specific high value capacitors is less than that of Multilayer Ceramic Capacitors (MLCC), which limits its use for the highly reliable applications. This paper presents a feasibility study to overcome these two problems by adding a few sensing mechanisms to the typical AC–DC converter topology. In majority of the AC–DC converter, Al-Elko capacitor takes approximately 3% to 5% of the converter size. The proposed method reduces this to approximately 50% size and so it effectively approximates 2% to 3% size reduction in converter size. The proposed method basically works based on the load current prediction method and hence it is highly suitable for the constant load application. Moreover, the converter response time increases in this method, which limit its application in high-speed systems. The high temperature application of Al-Elko capacitor is limited because of its poor performance, which is significantly rectified by replacing the Al-Elko with MLCC as it delivers good performance in high temperature.