Power Quality Assessment for AC/DC Hybrid Network Based on New Modelling Methods and On-Site Measurements

Abstract

AC/DC hybrid network has become a new trend in power distribution and transmission system. It possesses the advantages like decreasing the power loss of AC/DC or DC/AC conversion by the direct power supply to AC and DC loads and increasing the reliability of network, etc. However, the power quality issues in this kind of grid have not been enough addressed and considered comparing to the individual AC network or DC network. How to evaluate power quality in DC grid and what’s the influence between DC part and AC part? Even more questions related to power quality and modelling methods in AC/DC hybrid network need to be answered and explored.The subject addressed in this paper is the power quality assessment which is carried out by new modelling methods and an experimental analysis of a real AC/DC hybrid network. DC voltage variation, voltage unbalance and harmonics (ripples in DC) in both AC and DC voltage are analysed in “grid-connected” mode or “islanding” mode. Furthermore, the dynamic impedance of battery converter is calculated during transient event, which is one of the key parameters to assess static power source behaviours and evaluate the potential power quality level when a new load is connected to the grid based on mainly power electronic interfaced supply sources. The simulated results are then validated by on-site measurements with very acceptable error.