A two-terminal active capacitor concept has been 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 increase power density or reduce 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-constraint applications is applied to size the active components and passive elements. A voltage feedforward 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 single-phase full-bridge rectifier is presented to demonstrate the theoretical analyses.

https://vbn.aau.dk/ws/files/308302874/On_the_Practical_Design_of_a_Two_terminal_Active_Capacitor.pdf

On the Practical Design of a Two-Terminal Active Capacitor

The virtual infinite capacitor (VIC) is a nonlinear active capacitor for dc voltage filtering (ripple elimination). It can replace large and unreliable electrolytic capacitors, and it is intended for dc systems where random fluctuations of the dc bus voltage may occur. We propose a plug-and-play (PnP) realization of the VIC, which can be connected directly to the dc bus like a passive capacitor without any extra connections. The proposed control algorithm automatically adjusts the reference voltage of the VIC so that it will be equal to the equilibrium voltage of the dc bus. For the stability of complex interconnected systems, it is recommended that the impedance of the components should be strictly positive real. By studying the output impedance of PnP VIC, we discuss how to achieve the strictly positive-real property of the overall dc bus by a careful choice of controllers and filters. The results were tested by simulations and experiments on a circuit comprising a commercial power factor compensator with an average of 390 V output and a variable resistive load (up to 345 W).

Plug-and-Play Control of the Virtual Infinite Capacitor

Single-phase rectifier systems often require simultaneously high power factor, efficiency, and power density but can be difficult to implement with conventional solutions. In this work, a 1.5 kW, universal (95 to 265 $\mathbf{V}_{rms}$ ) ac input, 400 V dc output power factor correction (PFC) rectifier with a flying capacitor multilevel (FCML) boost front-end and a series-stacked buffer (SSB) for twice-line frequency energy buffering is implemented to meet these stringent high performance design requirements. Specifically, a PLL-based SSB control method is proposed and characterized for system integration with a generalized PFC front-end. The impacts of the SSB on the PFC front-end performance as well as the impacts of the PFC front-end behavior on SSB performance are analyzed and discussed. The interdependence of this SSB control and the PFC control architecture are validated through appropriate system modeling and experimental verification.

A Digital Implementation of PLL-Based Control for the Series-Stacked Buffer in Front-End PFC Rectifiers

Resonant-type architectures for active power decoupling in grid-tied single-phase power electronics

H-bridge power modules can be used as Perturbation Injection Units (PIUs) for Impedance Measurement Unit (IMU) application However, DC side floating capacitors in the modules are subject to high voltage fluctuation due to the presence of reactive harmonic components during perturbation injections Utilizing large capacitors to compensate the ripple as in traditional methods makes the system bulky In this paper, an active capacitor is integrated with the floating H-bridge power module to remove the effect of ripple power on the DC-link voltage The auxiliary circuit, which is smaller in size compared to an equivalent passive capacitor, helps increase power density and improve the injection capability of the system The effectiveness of the active capacitor is verified through simulation results

Evaluation of Active Capacitor Bank for Floating H-bridge Power Modules

Conventional capacitors contribute to a considerable scale of system level size, cost and failure, and suffer from one or more issues on energy density, cost, and reliability. A two-terminal active capacitor, which has the same level of convenience as passive capacitors, is proposed recently to overcome the above issues. In this paper, the modeling of the active capacitor is investigated and a voltage feed-forward compensation scheme is proposed for overshoot reduction. Therefore, the impedance, equivalent capacitance, ESR, and ESL, of the active capacitor can be specified. A case study based on a single-phase full-bridge rectifier with an active capacitor demonstrates the theoretical analyses.

Haoran Wang

Papers

Impedance characteristics modeling of a two-terminal active capacitor