Controllable AC/DC Integration for Power Quality Improvement in Microgrids

Abstract

Renewable energy sources can be connected to utility grids by using AC and DC integration methods. The AC integration is a practical and cost-effective method thanks to its simple structure; however, its power quality protection is weak. The DC integration method provides high power quality to microgrids owing to extra AC/DC voltage conversion, but its power efficiency is lower than that of the AC integration method. This paper presents a controllable AC/DC integration method combining the advantages of both AC and DC integration methods. In the proposed method, AC integration is activated to provide high integration efficiency at times when the power quality of the utility grid is suitable. At other times when the power quality of the utility grid is unsuitable, DC integration is activated to improve the power quality of the microgrids. The proposed method was modeled and tested using Matlab/Simulink simulation environment. In the model, voltage sag and current harmonic distortion were used as destructive effects for the electrical energy of the utility grid. Results indicate that transitions between AC and DC integration modes are reliable in terms of voltage and current standards.