Modeling at a desired level, balanced and distortion free.

Modeling and methodology

3.1.
Modeling and analysis

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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.

………………………………………………………………

………………………………

………………………………………….