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OPERATION OF THREE PHASE THREE WINDINGS UNIFIED POWER QUALITY CONDITIONER

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 Cdc. The shunt part of UPQC consists of a VSI connected to the common dc storage capacitor Cdc on the dc side and on the ac side it is connected in parallel with the load through the shunt interface inductors LSH and a star-connected three-phase shunt coupling auto-transformer TSH. The shunt interface inductors LSH together with the shunt filter capacitors CSH are used to filter out the switching frequency harmonics produced by the shunt VSI. TSH is used for matching the network and VSI voltages.
The series component of UPQC is responsible for mitigation of supply side disturbances: voltage sags/swells, flicker, voltage unbalance and harmonics. It inserts voltages so as to maintain the load voltages at a desired level balanced and distortion free. And also series active filter is responsible for voltage compensation during supply side disturbances. The series part of the UPQC also consists of a VSI connected on the dc side to the same energy storage capacitor Cdc and on the ac side, it is connected in series with the feeder through the series low-pass filter (LPF) and three individual single-phase series coupling transformers TSE.
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