As to them. To mitigate voltage and current related

As
many power quality specialists offer regard for tackling power quality issues,
these issues are raised up because of the use of reactive loads and non-linear
loads. This load makes reactive power burden and harmonic issue. This harmonic
pollution deteriorates the quality of power at transmission side and
distribution side. Typically the term power quality imply keeping up a
sinusoidal waveform of bus voltages at evaluated voltage and frequency.
Electric power quality phenomenon basically incorporate unbalance voltage and
current flicker, harmonics, voltage sag, swell, and power interruption1, 2. One of the main
responsibilities of a utility system is to supply electric power in the form of
sinusoidal voltage and currents with appropriate magnitudes and frequency for
the customers at the points of common coupling (PCC). Although the generated
voltage of synchronous machines in power plants are almost sinusoidal, some
unsighted conditions such as lightning and short circuit faults and non linear
loads cause steady state error or transient voltages and current disturbances.
For example, electric arc furnaces, ASDs, etc causes voltage fluctuations,
power electronic converters generate current harmonics and distort voltage
waveforms, and short circuits faults result in voltage sags and swells 3-6. On the other hand most
customer loads such as office equipments, PLCs, microcontrollers, motor
starting, power electronics converters, and other industrial non linear and sensitive
loads are sensitive and unprotected to power quality disturbances and their
proper operation depends on the quality of the voltage that is supplied to
them.

To
mitigate voltage and current related problems various types of custom power
devices can be used. All custom power devices such as Dynamic
Voltage Regulator (DVR), Distribution Static Compensator (DSTATCOM), and UPQC
can mitigate voltage sag/swell, while compensation capability of UPQC is best.
The UPQC is a combination of series and shunt compensators, which are composed
of IGBT based VSIs act as active connected in cascade via a common DC link
capacitor. Both converters are fired by gating signals from PWM generator. The
gate pulses are generated by a dq0 based PWM control technique. It is the
control strategy which decides the efficiency of a particular system. By
using a unified power quality conditioner (UPQC) 1, it is possible to mitigate both the voltage quality related
problems and current quality issues by using the series and shunt compensators
for the load and from the utility grid respectively.

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 The main purpose of a UPQC is to compensate
for supply voltage and current related problems. The device UPQC has two active
power filters; series active power filter and shunt active power filter to
mitigate voltage and current related problems respectively. It has to be connected
in such a manner at the point of common coupling (PCC). These APFs are power
electronic devices based on IGBT based VSIs which are used to replace the
distorted wave coming from the load by injecting negative harmonics to the
network. The series active power filter can applied under non-sinusoidal supply
voltage at the PCC due to harmonics caused by non-linear loads. The shunt
active power filter is implemented to compensate harmonic current at supply and
load side and reactive power support

UPQC
can absorb active power or inject active power. The shunt APF can replace/ balance
the source currents by injecting negative and zero sequence components and
control the power factor by injecting the required reactive current. The series
connected APFF can replace/ balance the voltages at the load bus by injecting
negative and zero sequence voltages and maintain the magnitude of the load bus
voltage by injecting the required active and reactive components.

This
paper deals with the effectiveness of UPQC for distribution network with
nonlinear load under normal and faulted conditions. The proposed control
technique has been evaluated under different load conditions using MATLAB
software.