40220130406009 2

International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print),
INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING &
ISSN 0976 – 6553(Online) Volume 4, Issue 6, November - December (2013), © IAEME
TECHNOLOGY (IJEET)
ISSN 0976 – 6545(Print)
ISSN 0976 – 6553(Online)
Volume 4, Issue 6, November - December (2013), pp. 83-93
© IAEME: www.iaeme.com/ijeet.asp
Journal Impact Factor (2013): 5.5028 (Calculated by GISI)

IJEET
©IAEME

www.jifactor.com

LOAD REACTIVE POWER COMPENSATION USING UPQC WITH
PAC - VDC CONTROL
1

SALOMIPUSHPARAJ,
1

2

Dr. D. MARY,

Research Scholar,

2

Professor,

3

C. JEGADESWARREDDY
3

PG Scholar

Arulmigu Meenakshi Amman College of Engineering, Sri Sapthagiri Institute of Technology

ABSTRACT
Power quality has become an important issue for several reasons e.g. modern society’s
growing dependence on electricity and the fact that the poor power quality may generate significant
economic losses in few moments. Probable power quality problems are harmonic, flicker, voltage
dips and supply interruptions. The power quality may be improved by using filters and
compensators. This thesis introduces a new concept of optimal utilization of a unified power quality
conditioner (UPQC). The series inverter of UPQC is controlled to perform simultaneous 1) voltage
sag/swell compensation and 2) load reactive power sharing with the shunt inverter. The active power
control approach is used to compensate voltage sag/swell and is integrated with theory of power
angle control (PAC) of UPQC to coordinate the load reactive power between the two inverters. Since
the series inverter simultaneously delivers active and reactive powers, this concept is named as
UPQC-S (S for complex power).Detailed mathematical analysis, to extend the PAC approach for
UPQC-S, is presented in this thesis. In PAC to analyze the voltage sag and voltage swell conditions.
Parameter estimation of series and shunt inverter also observed in voltage sag and swell conditions.
Phase angle and magnitudes also calculated. MATLAB/SIMULINK-based simulation results are
discussed to support the developed concept. Finally, the proposed concept is validated with a digital
signal processor-based experimental study.
Index Terms: Active Power Filter (APF), Power Angle Control(PAC), Power Quality, Reactive
Power Compensation, Unified Power Quality Conditioner (UPQC), Voltage Sag And Swell
Compensation.
I. INTRODUCTION
Power quality issues are becoming more and more significant in these days because of the
increasing number of power electronic devices that behave as nonlinear loads. A wide diversity of
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solutions to power quality problems is available for both the distribution network operator and the
end use. The power processing at source, load and for reactive and harmonic compensation by means
of power electronic devices is becoming more prevalent due to the vast advantages offered by them.
The shunt active power filter (APF) is usually connected across the loads to compensate for all
current related problems such as the reactive power compensation, power factor improvement,
current harmonic compensation and load unbalance compensation, whereas the series active power
filter is connected in a series with a line through series transformer. It acts as controlled voltage
source and can compensate all voltage related problems, such as voltage harmonics, voltage sag,
voltage swell, flicker, etc. UPQC is a Custom Power Device and consists of combined series active
power filter that compensates voltage harmonics, voltage unbalance, voltage flicker, voltage
sag/swell and shunt active power filter that compensates current harmonics, current unbalance and
reactive current Unified Power Quality Conditioner is also known as universal power quality
conditioning system, the universal active power line conditioner and universal active filte. UPQC
system can be divided into two sections: The control unit and the power circuit. Control unit includes
disturbance detection, reference signal generation, gate signal generation and voltage/current
measurements. Power circuit consists of two Voltage source converters, standby and system
protection system, harmonic filters and injection transformers.

Fig:1. Unified power quality conditioner (UPQC) system configuration
The voltage sag/swell on the system is one of the most important power quality problems.
The voltage sag/swell can be effectively compensated using a dynamic voltage restorer, series active
filter, Unified power quality conditioner, etc., among the available power quality enhancement
devices, the Unified power quality conditioner has better sag/swell compensation capability. Three
significant control approaches for Unified power quality conditioner can be found to control the sag
on the system: 1) active power control approach in which an in-phase voltage is injected through
series inverter, popularly known as UPQC-P; 2) reactive power control approach in which a
quadrature voltage is injected [4], [5], known as UPQC-Q; and 3) a minimum VA loading approach
in which a series voltage is injected at a certain angle, in this paper called as UPQC-VAmin. Among
the aforementioned three approaches, the quadrature voltage injection requires a maximum series
injection voltage, whereas the in-phase voltage injection requires the minimum voltage injection
magnitude. In a minimum VA loading approach, the series inverter voltage is injected at an optimal
angle with respect to the source current. Besides the series inverter injection, the current drawn by
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the shunt inverter, to maintain the dc link voltage and the overall power balance in the network, plays
an important role in determining the overall UPQC VA loading.
The reported paper on UPQC-VAmin is concentrated on the optimal VA load of the series
inverter of UPQC especially during voltage sag condition. Since an out of phase component is
required to be injected for voltage swell compensation, the suggested VA loading in UPQC-VAmin
determined on the basis of voltage sag, may not be at optimal value. A detailed investigation on VA
loading in UPQC-VAmin considering both voltage sag and swell scenarios is essential. In the paper,
the authors have proposed a concept of power angle control (PAC) of UPQC. The PAC concept
suggests that with proper control of series inverter voltage the series inverter successfully supports
part of the load reactive power demand, and thus reduces the required VA rating of the shunt
inverter. Most importantly, this coordinated reactive power sharing feature is achieved during normal
steady-state condition without affecting the resultant load voltage magnitude. The optimal angle of
series voltage injection in UPQC-VAmin is computed using lookup table or particle swarm
optimization technique. These iterative methods mostly rely on the online load power factor angle
estimation, and thus may result into tedious and slower estimation of optimal angle. On the other
hand, the PAC of UPQC concept determines the series injection angle by estimating the power angle
δ. The angle δ is computed in adaptive way by computing the instantaneous load active/reactive
power and thus, ensures fast and accurate estimation.
II. UNIFIED POWER FLOW CONTROLLER
The UPFC is a combination of a static compensator and static series compensation. It acts as
a shunt compensating and a phase shifting device simultaneously.

Fig: 2. Principle configuration of an UPFC
The UPFC consists of a shunt and a series transformer, which are connected via two voltage
source converters with a common DC-capacitor. The DC-circuit allows the active power exchange
between shunt and series transformer to control the phase shift of the series voltage. This setup, as
shown in Figure 4.13, provides the full controllability for voltage and power flow. The series
converter needs to be protected with a Thyristor bridge. Due to the high efforts for the Voltage
Source Converters and the protection, an UPFC is getting quite expensive, which limits the practical
applications where the voltage and power flow control is required simultaneously.
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III. OPERATING PRINCIPLE OF UPFC
The basic components of the UPFC are two voltage source inverters (VSIs) sharing a
common dc storage capacitor, and connected to the power system through coupling transformers.
One VSI is connected to in shunt to the transmission system via a shunt transformer, while the other
one is connected in series through a series transformer.

Fig :3. A basic UPFC functional scheme
The series inverter is controlled to inject a symmetrical three phase voltage system (Vse), of
controllable magnitude and phase angle in series with the line to control active and reactive power
flows on the transmission line. So, this inverter will exchange active and reactive power with the
line. The reactive power is electronically provided by the series inverter, and the active power is
transmitted to the dc terminals. The shunt inverter is operated in such a way as to demand this dc
terminal power (positive or negative) from the line keeping the voltage across the storage capacitor
Vdc constant. So, the net real power absorbed from the line by the UPFC is equal only to the losses
of the inverters and their transformers.
The remaining capacity of the shunt inverter can be used to exchange reactive power with the
line so to provide a voltage regulation at the connection point. The two VSI’s can work
independently of each other by separating the dc side. So in that case, the shunt inverter is operating
as a STATCOM that generates or absorbs reactive power to regulate the voltage magnitude at the
connection point. Instead, the series inverter is operating as SSSC that generates or absorbs reactive
power to regulate the current flow, and hence the power low on the transmission line. The UPFC has
many possible operating modes. In particular, the shunt inverter is operating in such a way to inject a
controllable current, ish into the transmission line. The shunt inverter can be controlled in two
different modes:
VAR Control Mode: The reference input is an inductive or capacitive VAR request. The shunt
inverter control translates the var reference into a corresponding shunt current request and adjusts
gating of the inverter to establish the desired current. For this mode of control a feedback signal
representing the dc bus voltage, Vdc, is also required.
Automatic Voltage Control Mode: The shunt inverter reactive current is automatically
regulated to maintain the transmission line voltage at the point of connection to a reference value.
For this mode of control, voltage feedback signals are obtained from the sending end bus feeding the
shunt coupling transformer. The series inverter controls the magnitude and angle of the voltage
injected in series with the line to influence the power flow on the line. The actual value of the
injected voltage can be obtained in several ways.
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Direct Voltage Injection Mode: The reference inputs are directly the magnitude and phase
angle of the series voltage.
Phase Angle Shifter Emulation mode: The reference input is phase displacement between the
sending end voltage and the receiving end voltage. Line Impedance Emulation mode: The reference
input is an impedance value to insert in series with the line impedance Automatic Power Flow
Control Mode: The reference inputs are values of P and Q to maintain on the transmission line
despite system changes.
III. SIMULATION RESULTS
The performance of the proposed concept of simultaneous load reactive power and voltage
sag/swell compensation has been evaluated by simulation. To analyse the performance of UPQC-S,
the source is assumed to be pure sinusoidal. Furthermore, for better visualization of results the load is
considered as highly inductive. The supply voltage which is available at UPQC terminal is considered
as three phase, 60 Hz, 600 V (line to line) with the maximum load power demand of 15 kW + j 15
kVAR (load power factor angle of 0.707 lagging).
The simulation results for the proposed UPQC-S approach under voltage sag and swell
conditions are given Before time t1, the UPQC-S system is working under steady state condition,
compensating the load reactive power using both the inverters. A power angle δ of 21◦ is maintained
between the resultant load and actual source voltages. The series inverter shares 1.96 kVAR per phase
(or 5.8 kVAR out of 15 kVAR) demanded by the load. Thus, the reactive power support from the
shunt inverter is reduced from 15 to 9.2 kVAR by utilizing the concept of PAC. In other words, the
shunt inverter rating is reduced by 25% of the total load kilovoltampere rating. At time t1 = 0.6 s, a
sag of 20% is introduced on the system (sag last till time t = 0.7 s). Between the time period t = 0.7
s and t = 0.8 s, the system is again in the steady state. A swell of 20% is imposed on the system for
a duration of t2 = 0.8–0.9 s.

Fig: 4. Simulation Block Diagram
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DVR CIRCUIT:

Fig:5. DVR sub circuit
Voltage and power factor angle:

Fig: 6. voltage and power factor angle sub circuit

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Simulation time period is 0.95secc.

Fig: 7. Supply voltage
In the above Supply Voltage The sag occurs in the time period of 0.6ssec to 0.7sec and
07.sec to 0.8sec stead state occurs. 0.8sec to 0.9sec the swell occurs. Here voltage decreases current
increases.

Fig:8. Load voltage
In the above simulation of Load voltage is pure sinusoidal wave foram occurs because any
faults occurs in the Load side the .UPQC compensate the faults.

Fig:9. Self supporting dc bus voltage
In the above dc bus voltage sag occurs 0.6sec to 0.7sec and swell occurs 0.8sec to 0.9sec.
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Fig: 10. Supply current
In the supply current swell occurs 0.6sec to 0.7sec.here first swell occurs because voltage
decreases and current increases. 0.8sec to 0.9sec swell occurs.

Fig: 11. Shunt inverter injected current
In shunt inverter injected current faults are Occurred.sag occurred in time period of 0.6sec to
0.7sec. swell occurred 0.8sec to 0.9sec.

Fig: 12. Series inverter P and Q
In series inverter active and reactive powers are increases in 0.6sec to 0.7sec due to increase
of the load current. Active and reactive powers are decreased in time period 0.8 sec to 0.9 sec.

90


Fig:13. Shunt Inverter P and Q
In the above shunt inverter and active and reactive powers are shown. In shunt inverter
reactive power is decreased at that time active power is increased.
With vdc controller Simulation results:

Fig:14. Self supporting dc bus voltage
In self supporting dc bus voltage using dc regulater transient response is decreased and
system dynamic performance increased.

Fig:15. Series inverter P and Q
using the dc regulater of series active and reactive powers are transient response is
decreased. System starting period also decreased.
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Fig:16. Shunt inverter P and Q
In shunt inverter active and reactive power are shunt reactive power is increased series active
power decreased. System dynamic performance increases.
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