Plug-and-Play Control of the Virtual Infinite 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).