Review of the Key Technology of Power Quality Improvement Device for Middle-Low Voltage Distribution Network

Under the background of new power system, distributed generation (DG) and new power electronic loads are connected to the distribution system, resulting in growing power quality problems. The paper presents the problems of harmonic, three-phase imbalance and voltage fluctuation existing in modern middle-low voltage distribution system. Different types of power quality improving devices are summarized. The operation principle and performance index of reactive power compensation device, active power filter (APF) and unified power quality conditioner (UPQC) are given. Next, the characteristics of some grid-connected inverters with power quality improvement ability are analyzed. It is considered that the inverter which can simultaneously output compensation voltage and current is one of the research focuses in the future.