Contents I. Introduction
In recent years, electrified railway has a rapid development. Because of advantages of high speed, heavy load, high energy utilization and lower air pollution, it is widely accepted in many countries. However, its access to grid will bring about power quality issues[1]which have received wide attention for researchers. Power quality refers to a wide range of aspects, such as voltage deviation, voltage and current imbalance, harmonics, reactive power and voltage sag, etc. among which the main problems caused by electrified railway are voltage imbalance, harmonics and reactive power[2]. These problems will affect each link of power system [3]−[5]. To improve power quality and minimize harms on power system, researchers have devoted themselves to power quality improvement methods. Papers dealing with improvements and compensation devices with aspects to harmonics[6], [7], negative-sequence currents[8], [9] and the combination of harmonics, negative-sequence currents and reactive power[10]−[12] are discussed.
