Second-Order Ripple Current Suppression Based on Virtual Impedance in the Application of Dynamic Voltage Restorer

In existing two-stage single-phase dynamic voltage restorer (DVR) voltage sag mitigation devices, the output-side power contains a pulsating component at twice the fundamental frequency (2f0), leading to the presence of second-order ripple currents (SRCs) on the DC input side. This, to some extent, affects the reliability of the system and has a significant impact on the lifespan of energy storage devices. In this study, the dual-loop control method of the buck/boost converter is combined with the virtual impedance auxiliary control strategy to suppress SRCs. Compared to existing solutions, this method offers the advantages of being fast, stable, and reliable, while the virtual impedance auxiliary control strategy is flexible and easy to implement. The feasibility and stability of this strategy were verified using a 3 kW DVR prototype. When applying the two virtual impedance methods, the second harmonic content was reduced from 39.64% to 1.74% and 1.78%, respectively. The proposed control strategy demonstrates significant effectiveness in suppressing second harmonic currents.