International Journal of Advance Engineering and Research Development (IJAERD)
ETCEE-2014 Issue, March 2014, e-ISSN: 2348 - 4470 , print-ISSN:2348-6406
Modelling of Reactive Power & Unity Power Factor
Control of Inductive Load
Nirvisha V. Vyas1, Nitin H. Adroja2, Ashish Doorwar3
1
PG student, 2,3Asst. Professor, Electrical Engineering Department,
Atmiya Institute of Technology & Science, Rajkot
1
nirvisha.vyas@gmail.com
2
nhadroja@aits.edu.in
3
ashish.doorwar@gmail.com
Abstract— TSC-TCR (SVC) is applied to control power factor of
system at unity & effectively regulate load voltage. Unity power
factor controller uses SVC technique, whose output is adjusted
to exchange capacitive or inductive current so as to maintain or
control specific power factor. In this proposed scheme simple
circuit model of thyristor switched capacitor & thyristor
controlled reactor is modeled. The number of capacitors to be
turned-on is decided according to the reactive power
requirement of load. The current delivered by the capacitor
depends on the reactive power requirement.
that cosᴓ2 is greater than cosᴓ1 and hence power factor of the
load is improved [1].
This is shown in the following phasor diagram.
Keywords - firing angle, reactive power, SVC, TSC-TCR.
I. INTRODUCTION
This paper deals with the description of power factor,
analysis and counter measures of power factor and mitigation
techniques are also explained. Modern power system is
complex and it is essential to fulfil the demand with better
power quality. Advanced technologies are now a day being
used for improving power system reliability, security and
profitability and due to this power quality is improved.
Voltage stability, voltage security and power profile
improvement are essential for power quality improvement.
Low power factor produces large copper losses, poor
voltage regulation and reduce handling capacity of the system.
At low power factor KVA rating of the equipment has to be
made more, making the equipment larger and expensive [1].
Power factor improvement is important because at high,
medium and low power factor the current distortion levels
tends to fall into low THD≤20%, medium (20%<THD≤50%)
and high (THD>50%) respectively [2].
Low power factor can be improved by static capacitors [4],
synchronous condenser, and phase advancers [1]. In this
paper power factor has been improved automatically by using
microcontroller with static capacitors & reactor.
II. POWER FACTOR IMPROVEMENT THEORY
The low power factor is mainly due to the fact that most of
the power loads are inductive and therefore, take lagging
currents, so capacitors are connected in shunt at the load end
for injecting leading power. It draws current I c which leads
the supply voltage by 90ᵒ. The resulting line current I1 is the
phasor sum of I and IC and at an angle of ᴓ2 as shown in fig.
1(c). It is clear that ᴓ2 is less than ᴓ1 from phasor diagram. So
@IJAERD-2014, All rights Reserved
Fig. 1 (a)-Inductive load (b)-Capacitor with load (c)-phasor diagram
A. Available Devices for Power Factor Correction
To achieve optimum performance of power system it is
required to control reactive power flow in the network.
Voltage collapse occurs in power system when system is
faulted, heavily loaded and there is a sudden increase in the
demand of reactive power. Reactive power balance can be
regained by connecting a device with the transmission line
which can inject or absorb reactive power based on system
requirement. FACTS are a family of devices which can be
inserted into power grids series, in shunt, and in some cases,
both in shunt and series for reactive power compensation &
hence for unity power factor control.
Available facts devices are:
1) Shunt Device
 Static VAR Compensator
 Static Synchronous Compensator (STATCOM)
2) Series Device
 Thyristor Controlled Series Compensator (TCSC)
 Static Synchronous Series Compensator (SSSC)
B. Different Methods for power Factor Correction
There are mainly three types of techniques for power factor
correction.
1) Synchronous Alternators
2) Static VAR Compensators (SVC)
1
International Journal of Advance Engineering and Research Development (IJAERD)
ETCEE-2014 Issue, March 2014, e-ISSN: 2348 - 4470 , print-ISSN:2348-6406
3) Banks of Static Capacitors
 Distributed power factor correction
 Group power factor correction
 Automatic power factor correction
In TSC capacitor is connected in series with anti-parallel
connected thyristor. By controlling turning ON & turning
OFF of the thyristor control reactive power delivered. This is
shown in fig 3.
III. PROPOSED SCHEME
Zero crossing of voltage & current of the system is
measured & it is given to micro-controller to generate
appropriate gate pulses as shown in fig.2. According to the
generated gate pulses, number of capacitor is on. To provide
proper compensation reactor is on after turning on number of
capacitor so that power factor can be maintain at unity [5].
Fig. 3 Switching of capacitor
Fig. 2 Basic unity power factor system
A. Switched capacitor
1) Switching Technique:
To avoid transients at the moments of connecting
capacitors, their voltage as well as sign must be equal to that
of the line. Moreover, the slope of variations of line voltage
must be equal to zero; that is, dVL(t)/d(t) = ic(t)/c = o , where
VL (t) is the line voltage (the series low impedance inductor is
ignored) and c is the capacity of a TSC branch. To disconnect
a capacitor from the line, sending firing signals to the relevant
thyristor gate will stop. When the current value through a
capacitor passes by zero, the thyristor turns off and leaves the
capacitor charged to the line peak voltage. To avoid the
capacitor to discharge in long periods of time due to its own
and also its peripheral circuit leakage, firing pulses are
sometime employed to the thyristor gate around the voltage
peak time.
Fig. 4 Voltage & Current waveforms of switched capacitor
B. Firing of Reactor
Firing of thyristor can be done according to the load
requirement & reactive power absorbed by the capacitor.
Here reactor is connected in series with anti-parallel thyristor
as shown in fig. 5[6].
2) Change of Polarity:
Technically and also economically considering, the best
capacitors for use in switching are AC capacitors. However
such capacitors cannot tolerate large DC voltages for a long
period of time [2]. In a TSC system, those capacitors that are
not connected to the line have fixed voltages and having
changed their polarity periodically, and therefore, put them
under a low frequency AC voltage. To achieve this, as shown
in fig. 3, connect the capacitor to the AC voltage line for only
half a cycle. Here inductor is connected in series with
capacitor to control high inrush current.
@IJAERD-2014, All rights Reserved
Fig. 5 Firing of reactor
IV. CONTROL STRATEGY
Basic scheme for power factor correction is shown in fig.6.
Here AC supply of load is fed to the transformer; this will
step down the voltage. Zero crossing of voltage & current is
2
International Journal of Advance Engineering and Research Development (IJAERD)
ETCEE-2014 Issue, March 2014, e-ISSN: 2348 - 4470 , print-ISSN:2348-6406
sensed by zero crossing voltage & current detector
respectively .This phase difference decide firing angle of
thyristor switched capacitor. This signal is generated by the
microcontroller. Reactor firing depends on the number of
capacitor to be on & reactive power required by the load.
Control scheme for generating switching signal &
maintaining power factor at unity.
Power
Supply
1) Simulation Results
Load
Voltage
Sensor
Current
Sensor
Control circuit
Zero Crossing
Detector
Micro Controller
Gate driver
Circuit
Capacitor
and
Inductor
Bank
Anti-parallel
Thyristor
Fig. 8 Waveforms of open loop system
The reactive power required to compensate the reactive
power & make power factor at unity can be calculated by
using the following equation [5].
Fig. 6 Control scheme for unity power factor
V. OPEN LOOP CONTROL
Inductive load is connected with power supply of 230
volt is shown in fig.7. Due to this inductive load power factor
of the system is 0.91 lagging and active power & reactive
power is 10000 watt & 4300 VAR.
A. Without TSC-TCR
+ -i
Vac
Cu
Continuous
powergui
Voltage Measurement
P,Q pf
+v
-
Scope5
Subsystem
V
1
PQ
pf
I
Scope2
Active & Reactive
Power
.........................................(1)
Where, VAR = capacitor unit VAR rating
C = capacitor (farads)
f = frequency (cycles/second)
Vr = capacitor unit rated voltage
From this equation, calculate the reactive power of
capacitor to compensate the lagging power factor of inductive
load. According to the theory of power factor controller the
capacitor add leading current to the lagging current and
resultant current phase is less than the phase angle of previous
inductive current. As power factor is cosine of this angle,
power factor is also increases. To correct power factor at
unity, capacitor of appropriate reactive power is fed using in
eq. (1). By calculation the value of capacitor is 4280 VAR.
B. Power Factor Correction With TSC
Power factor correction by placing capacitor in shunt with
load is shown in fig. 9.
Scope4
Fig. 7 Open loop control of power factor controller
@IJAERD-2014, All rights Reserved
3
International Journal of Advance Engineering and Research Development (IJAERD)
ETCEE-2014 Issue, March 2014, e-ISSN: 2348 - 4470 , print-ISSN:2348-6406
+ -i
+ -i
Cu2
Cu2
Scope1
Scope2
Scope2
V
V
PQ
PQ
Scope1
I
a
g
Sequence
Thy5
k
k
k
a
Active & Reactive
Power2
Thy4 Repeating
Thy3
g
k
Thy2
a
g
k
a
g
k
g
Vac
a
a
Thy1
Thy5
k
a
Thy3
g
Active & Reactive
Power2
a
g
Repeating
Thy4
Sequence
g
Thy2
k
a
g
Thy1
AC Voltage Source1
k
a
k
g
I
P,Q pf
P,Q pf
Scope4
Subsystem4
Scope4
Subsystem4
+v
-
+v
-
Voltage Measurement1
Voltage Measurement1
Continuous
C1
C1
powergui
Subsystem3
Continuous
Subsystem3
Logical
Operator1
Logical
Operator1
powergui
Fig. 9 Open loop system with capacitor
Fig. 11 Open loop system with capacitor & reactor
1) Simulation Results for Power Factor Corrector:
1)
Simulation Results for Power Factor Corrector &
Reactive Power Controller:
Fig.10 Waveform of close loop system
For variable load, reactive power requirement changes to
compensate the low power factor problem. So this circuit can
not be usefull for variable inductive load. For that continous
measurement & calculation of reactive power is required.
This is the limitation of this sheme. fig. 10 shows the
waveforms of corrected supply voltage and current & reactive
power when capacitor is connected in shunt with load.
C. Power factor & Reactive Power Correction With TSCTCR
@IJAERD-2014, All rights Reserved
Fig.12 Waveform of close loop system with reactive power
4
International Journal of Advance Engineering and Research Development (IJAERD)
ETCEE-2014 Issue, March 2014, e-ISSN: 2348 - 4470 , print-ISSN:2348-6406
VI. CLOSED LOOP CONTROL
For close loop system, continuous measurement of the
reactive power requirement of variable load is required. As
shown in fig. 12, power factor corrector that can supply
reactive power up to 6000 VAR is presented. Each capacitor
provides power of 2000 VAR
System is designed for variable load. According to the
requirement of the load number of capacitors is on. Here
working flow of the scheme is present for each capacitor
having capacity of providing 2000 VAR.
reactive power control shunt inductor is required. By using
TSC-TCR technique power factor & reactive power
consumption of load can be improved.
REFERENCES
[1].
[2].
[3].
[4].
[5].
[6].
V.K Metha and Rohit Mehata,“ Principles of power system”,S. Chand
& Company Ltd, Ramnagar, Newdelhi-110055,4th Edition,Chapter,6.
W.Mack Grady and Robert J. Gilleskie, “Harmonics and how they
relate to power factor”, Proc.Of the EPRI power quality issues &
opportunities conference (PQA’93), San Diego,CA,November 1993.
Coso, “Calculation of reactive power needed for the power factor of
given system.” a precise catalogue, published by khawaja electronics
pvt. ltd. manufacturing of fuji capacitors in lahore, pakistan, 1994.
Technical Application Paper No: 8, “Power FactorCorrection and
Harmonic Filtering in Electrical Plants”, ABB, Bangalore, 2010
Nader Barsoum,“Programming of pic microcontroller for power
factor correction.” School of Engineering, Curtin University of
Technology, Sarawak, Malaysia 2007
Md. Shohel Rana, Md. Naim Miah & Habibur Rahman, “Automatic
Power Factor Improvement by using Microcontroller” Double Blind
Peer Reviewed International Research Journal, Global Journals Inc.
(USA), Volume 13 Issue 6 Version 1.0 Year2013.
Fig. 13 Flow chart of proposed scheme
VII.
CONCLUSION
This paper shows an efficient & economic technique to
control power factor of the load. To improve power factor of
load, only shunt capacitor or static capacitor are used. But for
@IJAERD-2014, All rights Reserved
5