Exploring the Concept of Active DC Capacitor for Power Conditioning Systems

In today’s eco-conscious world, the rapid pace of advancement in smart grid technology has a positive effect on the electricity industry reforms. The trend is shifting from large centralized to small distributed power generation units utilizing new and renewable energies. The goal is to use smarter control of distributed energy sources combined with intelligent demand side management to improve the overall efficiency and reliability of the power grid.Regardless of the type of the distributed power generation unit, the electricity generated by the renewable energy source is processed through a power conditioning system that contains multiple power converters. Those converters are interconnected through a DC link. The DC-link voltage is stabilized by a capacitor bank, which is sometimes the dominant part in terms of both volume and cost. Electrolytic capacitors are a popular choice for the capacitor bank, due to their high capacitances in a small form factor. However, their life expectancy is comparatively short and is reduced dramatically with elevated ambient temperatures. Statistics reveal that up to 30% of electronic system failures are caused by malfunctions of capacitors. Thus, capacitors are usually a reliability bottleneck.For high-voltage high-power conversion systems, DC-link capacitors are usually periodically replaced and monitored for reliable and safe operation, leading to substantial maintenance costs and electronic waste. To enhance reliability and lifetime, some high-performance capacitors have been used as replacements for electrolytic capacitors. However, the benefits of using those capacitors are to some degree compromised by their reduced volumetric efficiency.To lessen the dependency of the DC-link capacitors, many prior-art methods have been proposed to minimize the DC-link capacitance. However, the methodology is often circuit-structure-dependent. Many methods also suffer from performance degradation or are not well justified in terms of the reduction of the capacitance that can be achieved.This project aims at making a breakthrough in the architecture of power conditioning systems by exploring a new technology named “active DC capacitor” as a direct substitute for the capacitor bank. The results of a preliminary investigation indicate that the technology allows a significant reduction of the output capacitance in a power factor pre-regulator without performance degradation. This project will be working towards formulating a theory to generalize the technology for different classes of power converters, investigating the potential of the technology in enhancing the static, dynamic, and transient behaviors of the entire power conditioning system, and performing a cost-benefit analysis of the new technology.