Class II Ceramic Capacitor Voltage Characteristic Modeling and Compensation for AC-Connected Applications

Abstract

Dielectrics used in class II multilayer ceramic capacitors offer vastly higher dielectric constants than class I ceramics or film capacitors, leading to large volumetric and cost savings. However, class II ceramic capacitors undesirably tend to have varying capacitance depending on the voltage applied across it, referred to as voltage characteristic of capacitance (VCC). When class II ceramic capacitors are connected to an ac-source, VCC can contribute large harmonic content, adversely impacting power quality. If left unmitigated, additional filtering may be required to meet electromagnetic compatibility (EMC) standards, thus, reducing volumetric benefits of class II ceramic capacitors. Furthermore, control systems relying on accurate feedforward require predictive control of such effects. This work introduces a compensation strategy to mitigate current distortions induced by VCC, leading to an enhancement in converter power quality without the need for additional filtering. To achieve satisfactory mitigation with minimal control burden, the article also proposes a mathematical model describing the voltage characteristic. A design application is used to demonstrate the relevant tradeoffs and the effectiveness of the proposed compensation approaches in enhancing power quality performance is validated through experimental testing.