Modeling and methodology

3.1.

Modeling and analysis

Unified 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 for

mitigation of voltage related power quality problems like: voltage sags and

swells, flicker, voltage unbalance and harmonics etc. It replaces voltages in

order to maintain the load voltages at a desired level, balanced and distortion

free. The shunt component is applicable for mitigating current relates power

quality problems caused by the non linear, sensitive loads such as: poor power

factor, load harmonic currents, loads unbalance etc. 11

The

integrated controller of the series APF and shunt APF of the UPQC to offer the

compensating voltage reference Vf and compensating current reference

If. UPQC combines of both a Distribution Static Compensator (DSTATCOM) and Dynamic

Voltage Restorer (DVR) together. The system configuration of a UPQC is shown in the

Figure 3.1 given below.

Figure3.1:

General topology of UPQC 11

3.2. Steady State Equivalent Analysis of UPQC 23

The equivalent circuit of UPQC is shown in

the figure 3.2. An ideal controlled voltage source is connected in series in

the circuit and

current source is connected in shunt of the circuit

so that the circuit works same as that of the UPQC. It is controlled in such a

way that the voltage at load bus is always

sinusoidal and at desired magnitude. Therefore the voltage injected by series

active power filter must be equal to the

difference between the supply voltage and the ideal load voltage. Thus the

series active power filter acts as controlled voltage

source. The function of shunt active power filter is to maintain the dc link

voltage at constant level. In addition to this the shunt active power filter provides the VAR required by the

load, such that the input power factor will be unity and only fundamental

active power will be supplied by the source 23

Figure 3.2: Equivalent circuit of the UPQC 11

3.3. Mathematical

analysis of UPQC IN Distribution system

The equivalent circuit of UPQC is shown in the Figure 3.2. In the UPQC representation it has two basic

configurations: series part in source side and shunt part in load side of

distribution system. From the equivalent circuit representation the ideal

controlled voltage source is connected in series in the circuit and current

source is connected in shunt of the circuit so that the circuit works. In the

mathematical analysis are the UPQC considering different assumption. Taking the

load voltage as a reference phasor and considering lagging power factor in the

load side.

i.

Voltage injected by series active power filter

must be equal to the difference between the supply voltage and reference load

voltage.

ii.

Series active power filter acts as controlled

voltage source.

iii.

The function of shunt active power filter is to

maintain the dc link voltage at constant level.

In addition to this the shunt active power filter provides

the VAR required by the load, such that the input power factor will be unity

and only fundamental active power will be supplied by the source.

Then write…

………………………………………………..

Assuming the lagging power

factor is the load side between voltage and current of the load side.

……………………………………………………………….

The quality of source voltage fluctuation which

subject 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 this

conduction to satisfy active power in demand equal to active power in input at

PCC nodes. In addition to this the unity

power factor in the series APF connected in source side.

…………………………………………………….

The complex apparent

power absorbed by the series APF can be expressed as,

……………………………………………………….

In lossless condition ?s=0, since UPQC

is maintaining unity power factor

…………………………………

…………………………………………………………

The complex

apparent power absorbed by the shunt APF can be expressed as,

…………………………………………………………………..

The current

provided by the shunt APF, is the difference between the input source current

and the load current, which includes the load harmonics current and the

reactive current.

………………………………………………………………

………………………………

………………………………………….