Harmonic Suppression in DG Interface Converters in a Voltage-Controlled Network Based on a Two-Stage Virtual Impedance Strategy

Abstract

With the increasing penetration of distributed generation (DG) sources in power distribution networks, power quality issues particularly harmonic distortion caused by nonlinear loads have become a critical challenge. Conventional harmonic suppression methods, including passive and active filters, exhibit performance limitations under high-distortion conditions and are especially less effective in voltage-controlled DG systems. This paper proposes a novel two-stage virtual impedance-based strategy for harmonic suppression in DG-grid interface converters. In the proposed method, line and load harmonic current components are extracted using a Second-Order Generalized Integrator (SOGI) filter and injected into the voltage reference through two independent virtual impedance paths. This structure enables independent tuning between reducing DG current harmonics and improving voltage quality at the Point of Common Coupling (PCC). Simulation results in MATLAB demonstrate that the proposed method can reduce the Total Harmonic Distortion (THD) of DG current to below 5% under severe distortion conditions, while simultaneously improving PCC voltage quality. Furthermore, the method exhibits stable performance under unbalanced load conditions.