ENGINEERING ARTICLES

The shunt component is responsible for mitigating the power quality (PQ) problems caused by the consumer: poor power factor, load harmonic currents, load unbalance, DC offset, etc. The shunt active filter is responsible for power factor correction, compensation of load current harmonics and unbalances. It maintains constant average voltage across the dc storage capacitor C dc . The shunt part of UPQC consists of a VSI connected to the common dc storage capacitor C dc  on the dc side and on the ac side it is connected in parallel with the load through the shunt interface inductors L SH  and a star-connected three-phase shunt coupling auto-transformer T SH . The shunt interface inductors L SH  together with the shunt filter capacitors C SH  are used to filter out the switching frequency harmonics produced by the shunt VSI. T SH  is used for matching the network and VSI voltages. The series component of UPQC is responsible for mitigation of supply side distur...

The FACTS technology is not represented by a single high-power controlling device, but it is a collection of all the controllers, these individually or in coordination with the others give the possibility to fast control one or more of the interdependent parameters that influence the operation of transmission networks. These parameters include e.g. the line series impedance, the nodal voltage amplitude, the nodal voltage angular difference, then the shunt impedance and the line current. The design of the different schemes and configurations of FACTS devices is based on the combination of traditional power system components (such as transformers, reactors, switches, and capacitors) with power electronics elements (such as various types of transistors and Thyristors). The development of FACTS controllers is strictly related to the progress made by the power electronics. Over the last years, the current rating of thyristors has evolved into higher nominal values making power electronics ...