A Study of PI Controller Based Unified Power Quality Conditioner

Volume 2, Issue 9, September 2012
ISSN: 2277 128X
International Journal of Advanced Research in

Computer Science and Software Engineering
Research Paper
Available online at: www.ijarcsse.com
A Study of PI Controller Based Unified Power Quality

Conditioner
Anil Bharti1,
Department of Electrical
Engineering, ,
M.M.M,E.C
Gorakhpur 273010, India
Rajat Varshney2
Department of Electronics
& Instrumentation
Engineering, INVERTIS UNIVERSITY,
Bareilly 243123, India
Dr S.K.Srivastva3
Department of Electrical
Engineering
M.M.M,E.C
Gorakhpur 273010, India
Abstract- The Unified Power Quality Conditioner is the combination of the STATCOM and SSSC, we can say it is the
most advanced controlling FACT device over the all basic power system parameter, transition voltage harmonics
compensation, impedance and phase angle held with the use of UPQC. It has been used very frequently amongst the
all other power flow techniques, but at the same time it is one of the most expensive controlling techniques. The
fundamental arrangement of UPQC is define as there is two voltage source inverter which are connected through a
common DC storage capacitor and it has been connect to the power system via a coupling transformer. First voltage
source inverter is used in shunt with the transmission system with the help of shunt transformer. On the other hand
second voltage source inverter is used in series with the help of series transformer.
Present work investigates PI controller as concerned to UPQC application for power quality improvement. The
UPQC is studied and its advantages over conventional APFs and UPFC are discussed in detail. The relevant
simulations are carried out using MATLAB/ Simulink.
KeywordsUPQC, Power Quality
I.
INTRODUCTION
Power electronics is playing an important role in transmission and utilization of electrical power due to its capability
of processing electric power in most efficient and cost-effective way. However, the nonlinear characteristics of power
electronic devices give rise to two important limitations; they generate harmonics and draw lagging current from the
utility. In recent years, UPQC is prove to be an all in one device for active power conditioning to compensate both
harmonics as well as reactive power. UPQC is an advanced version of unified power flow controller (UPFC). The
performance of UPQC mainly depends upon how quickly and accurately compensation signals are derived. The UPQC
mitigates harmonics and provides reactive power to the power systems network so as to improve the power factor close
to unity.[1],[4] ,[5]
The UPQC is a combination of shunt active and series active power filters connected through a dc bus.[2] The
shunt active filter of UPQC acts as a current source for injecting compensating current through a shunt transformer,
whereas, the series active filter acts as a voltage source for feeding compensating voltage through a series transformer.
Fig.1: Basic structure of UPQC using back to back
2012, IJARCSSE All Rights Reserved
Page | 85
Rajat et al., International Journal of Advanced Research in Computer Science and Software Engineering 2 (9),
September- 2012, pp. 85-88
II.
CIRCUIT DESCRIPTION
When PI based controller is used, the dc link voltage is sensed at regular intervals and is compared with a reference
value. The error signal thus derived is processed in a PI controller. A limit is put on the output of the controller to ensure
that the shunt active power filter supplies active power of the load through the series active power filter [3].
Fig. 2: showing simulation for UPQC
Page | 86
1. Shunt Controller/STATCOM in MATLAB
It is an integral part of the converter present in STATCOM to operate voltage control mode. Its function is to
operate the rectifier power switches so as to maintain a fixed dc voltage in the dc link and to generate a fundamental
output voltage waveform with demanded magnitude and phase angle in synchronism with the sinusoidal system which
forces the reactive power exchange required for compensation.[4][7]
2. Series Converter/SSSC Model in MATLAB

A SSSC is a solid-state voltage source inverter, which generates a controllable AC voltage source, and connected
in series to power Transmission lines in a power system. The injected voltage (vq) is in quadrature with the line current I,
and emulates an inductive or a capacitive reactance so as to influence the power flow in the transmission lines. The
compensation level can be controlled dynamically by changing the magnitude and polarity of vq and the device can be
operated both in capacitive and inductive mode. The main features of control system are:[6]
1. There is a phase-locked loop (PLL) which synchronizes measured positive-sequence component of the current with
self generated current. The quadrature axis and direct axis components Sequence of voltages va ,vb and the dc voltage
vdc of the AC 3- voltages and currents being used to compare with the help of output of the PLL.
2. The ac and dc voltage regulators which compute the both two components of the converter voltage (vdcnv and vqcnv)
required obtaining the desired dc voltage (vdcref) and the injected voltage (vqref).
3. The change in injected voltage is performed by the means of a Voltage-sourced converter (VSC) connected on the
secondary side of a coupling transformer. The VSC uses forced-commutated power electronic devices (e.g. IGBTs or
IGCTs, GTOs,) to synthesize a voltage vcnv from a dc voltage source. A capacitor connected on the dc side of the
VSC acts as a dc voltage source.
III. RESULT AND ANALYSIS

When the transmission line is without UPQC, the real and reactive power flow cannot be controlled. The active
power flow through line which is controlled by UPQC. Transmission capability of the existing transmission line is highly
improved with the presence of UPQC. The value of difference between the sending end real power and receiving end real
power is high in the transmission line without UPQC. This is due to the increase in transmission losses, which are
minimized with the help of UPQC. We have seen the improve result in Fig (a), (b), (c), and (d) where time is define from
0 to 0.4 in which for 0 to 0.1 the result are without UPQC and have great loses on the other hand 0.1 to 0.4 are with
UPQC which have improved result .It is also help to improving power factor of the transmission line. As shown in Fig. 6,
without UPQC, power factor of the transmission line is 0.83 but as UPQC switched, the power factor increases to 0.96.
Before compensation when UPQC not connected, source current THD is 30.70%, due to non linear RL load. The
dominant harmonic is 5th harmonic and its magnitude is 29.5% of fundamental component. Source current THD after
compensation when UPQC connected at 0.1s and PI controller used, source current THD is reduced to 3.94%
Source Voltage
x 10
Source Current
150
1
Current(A)
Voltage(v)
100
0
-1
50
0
-50
-100
-150
-2
0.05
0.1
0.15
0.2
Time (seconds)
0.25
0.3
0.35
-200
0.4
0.05
0.1
0.15
0.2
Time (seconds)
0.25
0.3
0.35
0.4
x 10
Current (A)
150
Voltage(v)
2
1
0
-1
100
50
0
-50
-100
-2
Fig.3:
0.05
0.1
Time(s) 0.2
0.15
0.25
0.3
0.35
0.4
-150
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Simulated results of UPQC (a) source voltage (b) source current (c) load voltage (d) load current
Page | 87
-50
-100
-150
0
Current (A)
0.05
0.1
0.15
0.2
Time (s)
0.25
0.3
0.35
0.4
Current (A)
Selected signal: 30 cycles.

50
Selected signal: 30 cycles. FFT window (in red): 5 cycles

50
0
-50
-100
-150
0
0.05
0.1
0.15
0.2
Time (s)
0.25
0.3
0.35
0.4
Fundamental (50Hz) = 32.79 , THD= 30.70%

Fundamental (50Hz) = 76.06 , THD= 3.94%
3.5
Mag (% of Fundamental)
Mag (% of Fundamental)
25
20
15
10
5
3
2.5
2
1.5
1
0.5
50
100
150
200
250
Frequency (Hz)
300
350
400
450
500
50
100
150
200
250
Frequency (Hz)
300
350
400
450
500
Fig.4: Total harmonic distortion (THD) distorted source current THDFig.5: Compensated source current THD
1
0.95
0.9
data
0.85
0.8
0.75
0.7
0.65
0.6
0.55
0.1
0.2
0.3
Time (se conds)
0.4
0.5
0.6
Fig.6: power factor

IV. CONCLUSION
This work presents control and performance of UPQC intended for installation on a transmission line with the
help of PI controller. A control system is simulated in switching and unbalanced condition with shunt inverter and series
inverter in open loop phase angle control mode. Simulation results show the effectiveness of UPQC in active filtering
and controlling real and reactive power through the line.AC voltage regulation and power factor of the transmission line
also improved. This work presents an improvement result in the real and reactive power flow via the transmission line
with UPQC using PI controller when compared to the system without UPQC.
V. REFERENCES
1.
2.
3.
4.
5.
6.
7.
IEEE standard 519-1992, IEEE recommended practices and requirement for harmonic control in electrical power
systems, IEEE, Inc. 1993.
L. Gyugi, Reactive power generation and control by thyristor circuit, IEEE Trans. Industrial Applications, pp.
1935- 1945, sept/oct 1979.
L. Gyugyi and E. C. Strycula, Active ac power filters, in Proc. 1976 IEEE/IAS Annual Meeting, 1976, pp. 529535.
L. Gyugi, Unified power flow control concept For flexible ac transmission system, IEE proc.-C, vol. 139, no. 4,
July 92, pp 323-332.
L. Gyugyi, et al, "The unified power flow controller a new approach for Transmission control " IEEE Trans.
Power System, 94 SM 474-7 PWRD.
K.K. Sen, E.J. Stacey, UPFC - unified power flow controller: theory, modeling, and application", PE-282PWR-0-12-1997, IEEE PES Winter Meeting, Tamp, FL.
H. Akagi, Performance and modeling of a shunt active filter for Installation on power distribution systems, to
be presented at the 1996 IEEE-PES International Conference on Harmonics and Quality of Power, Oct. 16-18,
1996.
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Volume 2, Issue 9, September 2012

ISSN: 2277 128X

International Journal of Advanced Research in

A Study of PI Controller Based Unified Power Quality

Fig.1: Basic structure of UPQC using back to back

2012, IJARCSSE All Rights Reserved

Fig. 2: showing simulation for UPQC

2012, IJARCSSE All Rights Reserved

2. Series Converter/SSSC Model in MATLAB

III. RESULT AND ANALYSIS

2012, IJARCSSE All Rights Reserved

Selected signal: 30 cycles.

Selected signal: 30 cycles. FFT window (in red): 5 cycles

Fundamental (50Hz) = 32.79 , THD= 30.70%

Fig.6: power factor

2012, IJARCSSE All Rights Reserved

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