Power quality of DC microgrid: Index classification, definition, correlation analysis and cases study

DC microgrid has a promising future for its strong power supply capacity, good controllability, and high efficiency. The power quality of the DC microgrid is one of the core issues of planning, design, operation, and control. However, due to the zero-frequency characteristic of DC system, its power quality presents new characteristics. This paper analyzes the differences between AC and DC power quality and constructs the DC power quality index system. The DC harmonic, voltage fluctuation and flicker, voltage sag, voltage unbalances, and voltage deviations are defined according to the existing literature and standards. Moreover, the correlation between harmonics and fluctuations, voltage deviations and steady-state unbalances, voltage sags and transient unbalances are analyzed. Subsequently, the typical cases of the DC microgrids are selected to analyze the generation mechanism of each power quality phenomenon under different working conditions. According to the proposed index definition, the quantitative relationship between the indexes and the related parameters is obtained. The simulation cases are built to verify the generation mechanism and index relevance.