seminar code
07-08-2014, 02:16 PM
Performance of UPQC for Power Quality Improvement
[attachment=66705]
Abstract
This paper deals with a Unified Power Quality
Conditioner (UPQC) for load balancing, power factor-correction,
voltage regulation, voltage and current harmonics mitigation,
mitigation of voltage sag, swell and voltage dip in a three-phase
three-wire distribution system for different combinations of
linear and non-linear loads. The unit template technique (UTT) is
used to get the reference signals for series APF, whereas the
control algorithm for shunt APF utilizes two closed loop PI
controllers. The control algorithm for shunt APF is made flexible
so that it can correct supply power factor, eliminate harmonics,
provide load balancing and also improve the load terminal
voltage at point of common coupling (PCC).MATLAB/Simulink
based simulation results are presented, which support the
functionality of the UPQC
INTRODUCTION
O supply uninterrupted sinusoidal voltage of constant
magnitude to their consumers is the main objective of
electric utility companies. But, this is becoming tedious
day by day because of the increased applications of power
electronics based appliances at domestic and industrial
purposes. These nonlinear loads draw non-linear current and
degrade electric power quality. The quality degradation leads
to low power-factor, low efficiency, overheating of
transformers and so on [1]. Apart from this, on a distribution
system the over all loads is hardly found balanced. Because of
increased applications of sophisticated and more advanced
software and hardware for the control systems, the power
quality has figured out the most important issue for power
engineers.
In the past, passive filters were used to mitigate these
identified power quality problems. But the limitations
associated with passive filter such as, fixed compensation,
resonance with the source impedance and the difficulty in
tuning, time dependence of filter parameters have forced the
need of active and hybrid filters[2-4]. These filters address
only few identified power quality problems of the present
distribution networks. Relating to power quality issues
SYSTEM DISCRIPTION
The system under consideration is shown in Fig.1.The
UPQC is connected before the load to protect the load from
any voltage based distortions and at the same time, to make
the source currents sinusoidal, balanced and in phase with the
source voltages. Provisions are made to realize voltage
harmonics, voltage sag and swell in source voltage by
switching on/off the three-phase rectifier load, R-L load and
R-C load, respectively. In order to create a voltage dip in
source voltage an induction motor is connected suddenly on
the load side. The UPQC is realized by using two voltage
source inverters (VSIs) connected back to back with a
common DC link voltage, is shown in Fig.2. One VSI acting
as a shunt APF, while the other as series APF. Each APF is
realized by using six Insulated Gate Bipolar Transistors
(IGBT) switches. The (isa, isb , isc) ,(ila, ilb , ilc) and (ifa, ifb ,
ifc,),represent the source currents, load currents and shunt APF
currents in phase a, b and c respectively. The injected voltages
by the series APF in phase a, b and c is represented by (vinja,
vinjb and vinjc), respectively
Reference current signal generation for shunt APF
The control strategy for shunt APF utilizes two closed loop
PI controllers. One controller is used to get the amplitude of
the in-phase components of reference supply currents (Ispdr),
while the other PI controller is exploited to calculate the
amplitude of the quadrature components of reference supply
currents (Ispqr).The first PI controller is realized on the sensed
and reference values of DC bus voltage of back-back VSI
capacitor of UPQC, while the second PI controller is realized
on sensed and reference peak value of voltage at PCC (Vtmn).
To regulate the voltage at PCC the three-phase reference
supply currents have two components. The first component of
reference supply currents in-phase with the voltage at PCC. It
is required to feed active power to the load and the losses of
UPQC. The second component
RESULT AND DISCUSSION
The developed model of UPQC and the proposed control
scheme in the MATLAB/ SIMULINK enviournment is shown
in Fig.4. The performance of UPQC is evaluated in terms of
voltage and current harmonics mitigation, load balancing,
power-factor correction and mitigation of voltage sag, swell
and voltage dip under different load conditions.
Performance of UPQC for load balancing, power-factor
correction and current harmonic mitigation
In order to show the response of UPQC for load balancing,
power factor correction and current harmonic mitigation, the
load under consideration is a combination of a three-phase
diode bridge rectifier with resistive load on dc side and
unbalanced R-L load in phase ‘a’ and ‘b’ only. It is observed
that the supply currents are balanced, sinusoidal and in-phase
with the voltages as is shown in Fig
CONCLUSION
The performance of UPQC has been investigated under
various practical situations. A configuration of UPQC using
UTT based control has demonstrated satisfactory working.
The performance of the UPQC has been evaluated in terms of
various power quality improvements like load balancing,
power-factor correction, voltage and current harmonics
mitigation, voltage regulation at PCC, mitigation of voltage
sag, swell and voltage dip. The source current THD is
improved form 27. 81 % to 4.54 %, while load voltage THD is
improved form 7.04 % to 0.62 %.In addition to this the
performance of UPQC was found satisfactory during transient
conditions. The result of this study may be useful for potential
applications of UPQC under wide practical situations. The
performance of UPQC can be further improved by suitable
tuning of PI controllers
[attachment=66705]
Abstract
This paper deals with a Unified Power Quality
Conditioner (UPQC) for load balancing, power factor-correction,
voltage regulation, voltage and current harmonics mitigation,
mitigation of voltage sag, swell and voltage dip in a three-phase
three-wire distribution system for different combinations of
linear and non-linear loads. The unit template technique (UTT) is
used to get the reference signals for series APF, whereas the
control algorithm for shunt APF utilizes two closed loop PI
controllers. The control algorithm for shunt APF is made flexible
so that it can correct supply power factor, eliminate harmonics,
provide load balancing and also improve the load terminal
voltage at point of common coupling (PCC).MATLAB/Simulink
based simulation results are presented, which support the
functionality of the UPQC
INTRODUCTION
O supply uninterrupted sinusoidal voltage of constant
magnitude to their consumers is the main objective of
electric utility companies. But, this is becoming tedious
day by day because of the increased applications of power
electronics based appliances at domestic and industrial
purposes. These nonlinear loads draw non-linear current and
degrade electric power quality. The quality degradation leads
to low power-factor, low efficiency, overheating of
transformers and so on [1]. Apart from this, on a distribution
system the over all loads is hardly found balanced. Because of
increased applications of sophisticated and more advanced
software and hardware for the control systems, the power
quality has figured out the most important issue for power
engineers.
In the past, passive filters were used to mitigate these
identified power quality problems. But the limitations
associated with passive filter such as, fixed compensation,
resonance with the source impedance and the difficulty in
tuning, time dependence of filter parameters have forced the
need of active and hybrid filters[2-4]. These filters address
only few identified power quality problems of the present
distribution networks. Relating to power quality issues
SYSTEM DISCRIPTION
The system under consideration is shown in Fig.1.The
UPQC is connected before the load to protect the load from
any voltage based distortions and at the same time, to make
the source currents sinusoidal, balanced and in phase with the
source voltages. Provisions are made to realize voltage
harmonics, voltage sag and swell in source voltage by
switching on/off the three-phase rectifier load, R-L load and
R-C load, respectively. In order to create a voltage dip in
source voltage an induction motor is connected suddenly on
the load side. The UPQC is realized by using two voltage
source inverters (VSIs) connected back to back with a
common DC link voltage, is shown in Fig.2. One VSI acting
as a shunt APF, while the other as series APF. Each APF is
realized by using six Insulated Gate Bipolar Transistors
(IGBT) switches. The (isa, isb , isc) ,(ila, ilb , ilc) and (ifa, ifb ,
ifc,),represent the source currents, load currents and shunt APF
currents in phase a, b and c respectively. The injected voltages
by the series APF in phase a, b and c is represented by (vinja,
vinjb and vinjc), respectively
Reference current signal generation for shunt APF
The control strategy for shunt APF utilizes two closed loop
PI controllers. One controller is used to get the amplitude of
the in-phase components of reference supply currents (Ispdr),
while the other PI controller is exploited to calculate the
amplitude of the quadrature components of reference supply
currents (Ispqr).The first PI controller is realized on the sensed
and reference values of DC bus voltage of back-back VSI
capacitor of UPQC, while the second PI controller is realized
on sensed and reference peak value of voltage at PCC (Vtmn).
To regulate the voltage at PCC the three-phase reference
supply currents have two components. The first component of
reference supply currents in-phase with the voltage at PCC. It
is required to feed active power to the load and the losses of
UPQC. The second component
RESULT AND DISCUSSION
The developed model of UPQC and the proposed control
scheme in the MATLAB/ SIMULINK enviournment is shown
in Fig.4. The performance of UPQC is evaluated in terms of
voltage and current harmonics mitigation, load balancing,
power-factor correction and mitigation of voltage sag, swell
and voltage dip under different load conditions.
Performance of UPQC for load balancing, power-factor
correction and current harmonic mitigation
In order to show the response of UPQC for load balancing,
power factor correction and current harmonic mitigation, the
load under consideration is a combination of a three-phase
diode bridge rectifier with resistive load on dc side and
unbalanced R-L load in phase ‘a’ and ‘b’ only. It is observed
that the supply currents are balanced, sinusoidal and in-phase
with the voltages as is shown in Fig
CONCLUSION
The performance of UPQC has been investigated under
various practical situations. A configuration of UPQC using
UTT based control has demonstrated satisfactory working.
The performance of the UPQC has been evaluated in terms of
various power quality improvements like load balancing,
power-factor correction, voltage and current harmonics
mitigation, voltage regulation at PCC, mitigation of voltage
sag, swell and voltage dip. The source current THD is
improved form 27. 81 % to 4.54 %, while load voltage THD is
improved form 7.04 % to 0.62 %.In addition to this the
performance of UPQC was found satisfactory during transient
conditions. The result of this study may be useful for potential
applications of UPQC under wide practical situations. The
performance of UPQC can be further improved by suitable
tuning of PI controllers