International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 5, May 2014)
A Comparative Study and Analysis of Power Factor Correction
Methods
Khushboo Arora1, Vivek Saxena2, Sanjeev Saini3
1,2,3
Department of Electrical & Electronics Engineering (ABES Engineering College, Ghaziabad)
Also, in the conventional phase angle control technique
of ac voltage converters the input power factor is poor and
decreased with increasing the values of the firing angle.
The aim of power factor improvement techniques is to
cause the waveform of the supply current to be as close as
possible to the waveform of the supply terminal voltage. In
this paper, a performance analysis is presented between a
modified PAC & EAC to show which technique is better to
implement.
A modified phase-angle control technique controls both
the firing and the extinction angles by the make use of
forced commutations of switches and to introduce a
freewheeling path in parallel with the load terminals. In
modified PAC, ac voltage converter employs only two
controlled switches with the aid of two diode bridge
rectifier. Reducing the number of controlled switches is
essential for the control decreasing the switching losses [3].
The extinction-angle control (EAC) is similar to that of
phase-angle control where there is only one pulse per halfcycle. In the phase-angle control the conduction is started
at the required delay angle (α ) and continues until the
current reaches zero value naturally, while in the EAC
control the conduction is started at zero crossing of the
supply voltage and forced commutated at a certain angle
before the next zero crossing (β). A freewheeling path is
provided for the load current to discharge the stored energy
of the load inductance. The output voltage is controlled by
varying the extinction angle (β) [4]. The fundamental
component of input current leads the input voltage, and the
displacement factor (and power factor) is leading. In some
applications, this feature may be desirable to simulate a
capacitive load and to compensate for line voltage drops.
Therefore, the performance of ac voltage converters with
extinction-angle control is similar to that with phase-angle
control, except the power factor is leading while in phaseangle control, the power factor is lagging. AC voltage
controllers are compared using modified PAC technique &
EAC technique with static load & induction motor as a load
respectively. The operation as a variable voltage source of
this controller in modified PAC & EAC is compared with
conventional PAC from supply power factor improvement
point of view.
Abstract— This paper presents a study of the power factor
improvement in single phase ac voltage controllers through
various methods. The overall efficiency is improved by some
advanced methods. This analysis about power factor
correction can be utilized in learning process. On the basis of
power factor improvement, this paper compares two methods.
One method is a modified phase angle control (PAC)
technique & another is the extinction-angle control (EAC)
technique. PAC technique deals with reduced number of
controlled switches but EAC technique as applied to a singlephase voltage converter to verify the feasibility of the
proposed technique.
Keywords— AC voltage controller, phase angle control
(PAC), extinction angle control (EAC), power factor
improvement.
I. INTRODUCTION
The electric power, generation, transmission and
distribution systems are based on an alternating current and
voltage, which are sinusoidal in nature. When loads that
consist of inductances, capacitances and resistances, in any
combination, are connected to the system, the sine wave is
preserved and the system components are said to be Linear.
When non-linear devices are connected to the system, the
fundamental sinusoidal is changed. This is the problem
faced when non-linear static power converters (rectifiers
and thyristor power supplies) are connected to the system
[1].
In such cases, it is important to maintain the power
factor approaching towards unity otherwise power loss
would be large.
Phase-angle control (PAC) line commutated voltage
controllers and integral-cycle control of thyristors have
been extensively employed for many applications [2]. Such
techniques offer some advantages as simplicity and the
ability of controlling large amount of power economically,
but also suffer from inherent disadvantages such as;
retardation of the firing angle causes lagging power factor
at the input side especially at large firing angles and high
low order harmonic content in both of load and supply
sides Moreover, a discontinuity of power flow appears at
both input and output sides.
60
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 5, May 2014)
III. PERFORMANCE ANALYSIS OF CONVERTER
II. CIRCUIT & OPERATING PRINCIPLE
In this section, the performance evaluation of the ac
voltage converter with the modified PAC switching
technique and EAC technique are compared by simulation
using MATLAB /Simulink. The results are mentioned for
various load types and simulated variation of input power
factor with respect to the firing angle as well as extinction
angle is also shown. Here, power factor and total harmonic
distortion factor both are the performance analyzing
parameters for the ac converter. Static type load such as RL load is used for analyzing the converter with PAC and
EAC technique both. Induction motor is also used in case
of EAC technique controlled ac converter for calculating
power factor etc. Circuit parameters are considered as
maximum supply voltage (312 V), supply frequency (50
Hz), switching frequency (100 Hz), load resistance (18 Ω)
and load inductance (99 mH).
Loads can be resistive (Φ = 0ο) and inductive loads (Φ =
ο
45 , 60ο). For PAC technique, the simulated variation of the
input power factor versus the firing angle over the complete
range of control for three different load conditions has been
shown in figure 2. It is worth to mention that for
conventional phase-angle control, there is no control for the
firing angle a less than or equal to the load power factor
angle Φ and so the firing angle should exceed the load
power factor control. For modified phase-angle control, the
control will be all over the range of the firing angle from
zero to π irrespective to the load angle.
Figure 1: Circuit configuration of ac voltage converter
Fig. 1 shows the schematic representation of the power
circuit configuration which consists of an inductive load in
case of PAC and induction motor in case of EAC
connected to an ac source through an ac voltage converter.
The S1 (forward switch) is used periodically to connect and
disconnect the load to the supply, i.e. regulates the power
delivered to the load. The S2 (parallel switch) provides a
free-wheeling path for the load current to discharge the
stored energy of the load inductance when the forward
switch S1 is turned off.
In modified PAC technique, converter uses IGBT
devices as controlled switches as gating of these switches is
based on this modified PAC technique where the pulses are
synchronized with the supply voltage and the output
voltage is controlled by varying the firing angle of the
chopper switch S1 from 0 to π to vary the rms of the output
voltage from Vs to 0. The operation modes are divided into
three modes: active (on-state), dead time (in between state)
and freewheeling (off- state) modes [5].
The converter with EAC technique has been employed
with the same process except the output voltage is
controlled by varying the extinction angle β from 0 to π to
vary the rms value of the output voltage from rated input
voltage to zero [6].
The gating pulses of the freewheeling switch S2 are the
complement of the gating pulses of the forward S1. A dead
time is requisite to avoid commutation problem, for this a
by-pass capacitor Cb is added parallel to the load in order to
provide a path for the current during the dead time when
both switches are opened.
Figure 2: Simulated variation of input power factor versus firing
angle
61
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 5, May 2014)
For example, for output voltage equal to 80V, the input
power factor is improved for Φ = 45ο from 0.32 to 0.4 by
25% and for Φ=60ο from 0.11 to 0.22 by 100%. Also, for
output voltage equal to 160V, the input power factor is
improved for Φ=45ο from 0.58 to 0.63 by 9% and for
Φ=60ο from 0.31 to 0.42 by 35%. So, the proposed
modified phase-angle control technique is recommended
for poor power factor loads. It is seen that as the output
voltage decreases (i.e. increasing the firing angle), the THD
in the input current increases and also, as the load angle
increases, the THD increases. It is seen that the THD in
modified phase-angle control is more than that of
conventional phase-angle control.
For EAC technique, the input power factor is improved
gradually from its lagging value and becomes leading after
the extinction angle exceeds the load angle and as the
extinction angle increases, the input power factor gets more
improved and this feature gives more importance for EAC
technique. For RL load, in figure 3 simulated variation is
carried between input power factor and extinction angle for
Φ=45ο & Φ=60ο.
Figure 4: Simulated variation of input power factor versus extinction
angle for induction motor
If the output voltage decreases; the extinction angle
increases and hence the THDF in the supply current
increases. Also, as the load power factor decreases, the
THDF increases. Although the increase in THDF will
reduce the value of the supply power factor, however, it
will not affect its leading nature.
IV. CONCLUSION
In this paper a comprehensive summary of several
control techniques are analysed. The modified phase-angle
control technique for ac-ac voltage converters uses reduced
number of controlled switches (only two switches) and a
simple control circuit which not only reduces the
component count for low implementation cost but also
enhances the efficiency and reliability of the overall
system. The proposed modified phase-angle control
technique provides a considerable improvement in the input
power factor compared with conventional phase-angle
control technique. The proposed technique provides a full
control range of the ac output power whatever the load
power factor angle compared with conventional phaseangle control technique where the firing angle should
exceed the load power factor angle.
But the EAC technique provides a considerable
improvement in the input power factor. The ac voltage
controller with the EAC technique has been applied to a
static load and a dynamic load which is a squirrel cage
single-phase induction motor loaded by a fan.
Figure 3: Simulated variation of input power factor versus extinction
angle for RL load
For induction motor control, in figure 4, the graph is
drawn between input power factor versus extinction angle
to show the variation between simulated and measured
graph.
62
International Journal of Emerging Technology and Advanced Engineering
Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 5, May 2014)
[3 ] S. WilUiams, "'Redunion of the Voltage snd cumnt Harmonies
Introduced by a Single-phase Mac ae Camoller," IEEE Tm.
Ind EIecI~onG. mU. Instrum Vol. 28, ". 4, 1981.
[4 ] A-R A. M. Makky, G. M. Abdel-Rahim, and N. A. Ahmed, "A
Novel DC Chopper Drive for Single-Phase Induction Motors," IEEE
Trans. Ind. Electron., vol. 42, no. 1, pp. 33-39, Feb. 1995.
[5 ] G Roy, P. Poitevin and G. Olivier, "A Simple Topologies for SinglePhase AC Line Conditioning," IEEE Trans. Ind. Applicat., vol. IA30, no. 2, pp. 406-412, March./April 1994.
[6 ] Nabil A. Ahmed, Kenji Amei and Masaaki Sakui, "AC Chopper
Voltage Controller-Fed Single-Phase Induction Motor Employing
Symmetrical PWM Control Technique," Electrical Power Syslems
Research Journal, Vol. 55, no. 1, pp. 15-25, July 2000.
A full control range of the ac output power and a wide
control range of the motor speed can be achieved. Thus,
this technique is suitable for speed control of single-phase
induction motor as it is required a simple and less costly
technique.
REFERENCES
[1 ] E. El-Bidway, K. AL-Bidwsihy M. S. Mdwal!y and M. El.Eedwichy, "Power Factor of AC Controller for lnductive Loads,"
IEEE Trans. Ind Electron. be. Inmum. , vol. IEC1-27, no. 3, pp. 210212, June 1980.
[2 ] Nabil A Ahmeb K. Ami and M. S&, "A New Configurafion of
Single-Phase SynrmeUid PWM AC Chopper Voltage controller."
IEEE Trans. Inb Elect"., vol. 46, no. 5, pp. 942.952, (kt. 1999.
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