Analysis of Power Flow in UPQC during Voltage Sag and Swell Conditions for Selection of Device Ratings

Abstract

This paper deals with the steady state analysis of unified power quality conditioner (UPQC). The UPQC, a combination of shunt and series active power filter (APF), is one of the best solutions towards the mitigation of voltage sags and swells problems on distribution network. The mathematical analysis is based on active and reactive power flow through the shunt and series APF, wherein series APF can absorb or deliver the active power whereas the reactive power requirement is totally handle by shunt APF alone during all conditions. The derived relationship between source current and % of sag/swell variation shows shunt APF plays an important role in maintaining the overall power balance in the entire network. The digital simulation is carried out to verify the analysis done. The simulation results support the mathematical analysis. The effect of load VAR variation and the impact of % sag / swell on the kVA ratings of both shunt and series APF are also analyzed. This analysis can be very useful for selection of device ratings for both shunt and series APFs.

UPQC-S: A Novel Concept of Simultaneous Voltage Sag/Swell and Load Reactive Power Compensations Utilizing Series Inverter of UPQC

“…The rating of a UPQC is governed by the percentage of maximum amount of voltage sag/swell need to be compensated [19]. However, the voltage variation (sag/swell) is a short duration power quality issue.…”

“…The current I Sh represents the required current if the shunt inverter is used alone to compensate the total load reactive power demand. To achieve the voltage sag compensation through active power control approach the source should supply increased current I S [19]. Thus, to support the series inverter to inject the required voltage for load reactive power and sag compensations, the shunt inverter should now deliver the current I Sh .…”

“…The voltage fluctuation factor k f which is defined as the ratio of the difference of instantaneous supply voltage and rated load voltage magnitude to the rated load voltage magnitude is represented as [19] …”

Investigation on rating of shunt APF in unified power quality conditioner

“…The control of APFs are also achieved without the application of transformations using hysteresis and Sinusoidal Pulse Width Modulation (SPWM) control [4][5][6][7][8][9][10] . The steady state analysis of UPQC by applying Hysteresis controller to both shunt and series APF without using any transformation is presented in [6][7][8][9][10] . As both voltage and current are controlled using fi xed hysteresis band, this type of controller looks simple but the current fl owing through the shunt APF is almost 50% of the load current even during normal working condition 11 .…”

Digital feedback control based Dynamic Voltage Compensator for voltage sag mitigation: Simulation and experimental validation

“…The proposed controller is built using constant dc-link topology as recommended in [15]. The application of hysteresis control to the dynamic voltage compensator without using abc-dq0 transformations has been carried out in UPQC based systems [16][17][18][19]. A unique attempt is made in this paper by simulation and experimentation to apply hysteresis controller to DVC without using any transformations like symmetrical component / abc-dq0 for the computation of reference voltage.…”