Application of a Parallel Virtual Infinite Capacitor to DC-link Voltage Filtering for a Doubly Fed Induction Wind Generator

We propose a parallel virtual infinite capacitor (PVIC) concept to replace the DC-link capacitor between two back-to-back converters for a DFIG (doubly fed induction generator) wind turbine for voltage filtering. The PVIC is composed of two virtual infinite capacitors (VICs) sharing one common capacitor: a LF (low-frequency)-VIC and a HF (high-frequency)VIC. The LF-VIC is controlled by a sliding mode controller to regulate low-frequency component of the DC-link voltage around its reference. We use a PI controller to maintain this VIC's state of charge in its desired operating range and achieve the 'plug-and-play' pattern of PVIC. The HF-VIC is controlled by another sliding mode controller to suppress high-frequency ripples of the DC-link voltage and simultaneously keep the VIC in its desired operating range. The simulation study indicates that PVIC performs much better than the equivalent DC-link capacitor in limiting the DC-link voltage fluctuations under different grid conditions.