I- Introduction

II- Two-Terminal Active Capacitor Concept

III- Component Sizing of the Active Capacitor for Cost-Constraint Applications

IV- Impedance Characteristics of the Active Capacitor

V- Start-Up Solutions for the Active Capacitor

VI- A Case Study for A Capacitive Dc Link Application And Experimental Verifications

VII- Conclusions

References

Abstract

A two-terminal active capacitor concept is proposed recently based on an active power electronic circuit with a voltage control method and self-power scheme. It retains the convenience of use as a passive capacitor with two power terminals only without any additional required connections, and has the potential to either increased power density or reduced design cost depending on the applications. Based on the previously proof-of-concept study, this paper addresses the design constraints, impedance modeling, and start-up solutions of two-terminal active capacitors. A design method for functionality, efficiency, lifetime and cost constraints application is applied to size the active components and passive elements. A voltage feed-forward control scheme is implemented to improve its dynamic response. Two start-up solutions are proposed to overcome the issues brought by the self-power scheme. A case study of an active capacitor for the DC link of a singlephase full-bridge rectifier is presented to demonstrate the theoretical analyses.

INTRODUCTION

The applications of power electronics consume unprecedented quantities of capacitors for harmonic filtering, power balancing, and/or short-term energy storage. In a singlephase voltage-source rectifier or inverter system, the capacitive DC link needs to filter low-frequency current components while limiting the voltage variation within a specific range. In a three-phase system, possible unbalances appearing in line voltages and/or loads introduce low-frequency harmonics in the DC link [1]. Therefore, a bulky capacitor bank is required for the capacitive DC links in most single-phase and three-phase applications. Moreover, large capacitor banks are also necessary for the AC filters in MW-level highpower inverter applications [2]. Electrolytic capacitors, film capacitors, and ceramic capacitors have been applied for one or more of those applications by considering their respective electrical characteristics, cost, volumetric efficiency, and reliability performance. Capacitor technology advancements have introduced to the market high-performance products, such as high-density, long-lifetime, low Equivalent Series Resistance (ESR), or high-temperature series. However, capacitors are still one of the highest failure components in power electronic systems, and the design constraints in cost and/or power density compromised with electrical and reliability performance still impose a great challenge even with the state-of-the-art capacitor technologies [3].