A Virtual-Rectifier AC/AC Converter-Based Dynamic Voltage Restorer

Dynamic Voltage Restorer (DVR) is widely employed to deal with the problems of the voltage sag or surge. The conventional two-stage-based converter uses the large electrolytic capacitor to act as the DC energy storage, which results in a large volume and poor reliability. The direct virtual-rectifier-based AC/AC converter employs the thyristors to realize the voltage compensation, whereas the reactive current will bring in serious commutation problems. Therefore, a virtual-rectifier with IGBT is proposed in this paper. The rectifier is driven with no dead-zone at the zero-crossing of the grid voltage, which facilitates to the continuous flowing of the reactive current. Further on, a low-cost digital control strategy is proposed, which consists of a phase-locked loop control based on the second-order generalized integrator (SOGI-based PLL), and the proportional-integral (PI) control. The zero-crossing point and the root-mean-square (RMS) of the grid voltage is correctly identified by the PLL under the polluted grid condition, and the steady-state error is minimized by the PI controller. Finally, simulation and experimental results validate the correctness of the working principle and the effectiveness of the proposed control strategy. Through the simulation, all the proposed operations are compatible with non-unity power factor loads and feature continuous input and output currents, and the experimental prototype is capable of efficient voltage compensation.