Modeling and methodology 3.1.

Modeling and analysisUnified Power Quality Conditioner(UPQC) contains shunt active power filter and series active power filter and sharing a common DC capacitor. The series component of the UPQC is used formitigation of voltage related power quality problems like: voltage sags andswells, flicker, voltage unbalance and harmonics etc. It replaces voltages inorder to maintain the load voltages at a desired level, balanced and distortionfree. The shunt component is applicable for mitigating current relates powerquality problems caused by the non linear, sensitive loads such as: poor powerfactor, load harmonic currents, loads unbalance etc.

11Theintegrated controller of the series APF and shunt APF of the UPQC to offer thecompensating voltage reference Vf and compensating current referenceIf. UPQC combines of both a Distribution Static Compensator (DSTATCOM) and DynamicVoltage Restorer (DVR) together. The system configuration of a UPQC is shown in theFigure 3.1 given below.Figure3.1:General topology of UPQC 113.2. Steady State Equivalent Analysis of UPQC 23The equivalent circuit of UPQC is shown inthe figure 3.

2. An ideal controlled voltage source is connected in series inthe circuit andcurrent source is connected in shunt of the circuitso that the circuit works same as that of the UPQC. It is controlled in such away that the voltage at load bus is alwayssinusoidal and at desired magnitude. Therefore the voltage injected by seriesactive power filter must be equal to thedifference between the supply voltage and the ideal load voltage. Thus theseries active power filter acts as controlled voltagesource. The function of shunt active power filter is to maintain the dc linkvoltage at constant level.

In addition to this the shunt active power filter provides the VAR required by theload, such that the input power factor will be unity and only fundamentalactive power will be supplied by the source 23Figure 3.2: Equivalent circuit of the UPQC 113.3. Mathematicalanalysis of UPQC IN Distribution system The equivalent circuit of UPQC is shown in the Figure 3.2.

In the UPQC representation it has two basicconfigurations: series part in source side and shunt part in load side ofdistribution system. From the equivalent circuit representation the idealcontrolled voltage source is connected in series in the circuit and currentsource is connected in shunt of the circuit so that the circuit works. In themathematical analysis are the UPQC considering different assumption.

Taking theload voltage as a reference phasor and considering lagging power factor in theload side. i. Voltage injected by series active power filtermust be equal to the difference between the supply voltage and reference loadvoltage. ii. Series active power filter acts as controlledvoltage source. iii.

The function of shunt active power filter is tomaintain the dc link voltage at constant level. In addition to this the shunt active power filter providesthe VAR required by the load, such that the input power factor will be unityand only fundamental active power will be supplied by the source.Then write..

.………………………………………………..Assuming the lagging powerfactor is the load side between voltage and current of the load side.……………………………………………………………….

The quality of source voltage fluctuation whichsubject to change to formulate voltage regulation between vt and vl……………………………………………………..Then… …………………………………………..The voltage injected by series APF formulate as ……………………………………………………………The UPQC is assumed to be lossless in case of thisconduction to satisfy active power in demand equal to active power in input atPCC nodes. In addition to this the unitypower factor in the series APF connected in source side.……………………………………………………. The complex apparentpower absorbed by the series APF can be expressed as,……………………………………………………….

In lossless condition ?s=0, since UPQCis maintaining unity power factor……………………………………………………………………………………………The complexapparent power absorbed by the shunt APF can be expressed as,…………………………………………………………………..The currentprovided by the shunt APF, is the difference between the input source currentand the load current, which includes the load harmonics current and thereactive current. ………………………………………………………………………………………………………………………………………….