A Flexible Harmonic Control Approach Through Voltage-Controlled DG–Grid Interfacing Converters

TLDR

Nonlinear loads and power‑electronics DG systems can degrade distribution power quality, yet properly controlled DG‑grid interfacing converters—especially voltage‑controlled ones—can improve efficiency and maintain power quality. This paper develops a voltage‑controlled harmonic control scheme for DG‑grid converters and investigates harmonic circulating currents among multiple DG systems. The authors compare current‑controlled and voltage‑controlled DG units, design a voltage‑based harmonic compensation method, analyze inter‑DG harmonic currents, and validate the approach with simulations and experiments on a 5‑kVA laboratory prototype. The voltage‑based method eliminates the need for a harmonic current tracking loop, enabling seamless integration into voltage‑controlled DG units for direct voltage and frequency support, and its effectiveness is confirmed by simulations and experiments.

Abstract

The increased penetration of nonlinear loads and power-electronics-based distributed generation (DG) systems may introduce power quality issues to the distribution power system. However, if controlled and regulated properly, the DG–grid interfacing converters are able to improve the distribution system efficiency and power quality. This paper focuses on the distribution system harmonic control through the DG–grid interfacing converters. Two alternative DG systems, namely, current-controlled DG and voltage-controlled DG, are considered. While most of the previous works on harmonic compensation are based on the current-controlled method, a novel harmonic control scheme using a voltage-controlled method is developed in this paper. The voltage-controlled method is more flexible and has similar compensation performance compared to the conventional current-controlled method. In addition, by avoiding the implementation of a harmonic current tracking loop, the proposed voltage-based method can be seamlessly incorporated into a voltage-controlled DG unit, which is important to provide direct voltage and frequency support in a microgrid. Moreover, the possible harmonic circulating current among multiple DG systems is also investigated in this paper. Simulations and experimental results from a three-phase 5-kVA laboratory DG prototype are provided to validate the discussion.