PSIM Simulation Of Variable Duty Cycle Control DCM Boost PFC Converter to Achieve High Input Power Factor

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 04 Issue: 03 | Mar -2017 www.irjet.net p-ISSN: 2395-0072
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PSIM SIMULATION OF VARIABLE DUTY CYCLE CONTROL DCM BOOST
PFC CONVERTER TO ACHIEVE HIGH INPUT POWER FACTOR
Addagatla Nagaraju1, Akkela Krishnaveni2.
1 Lecturer in Electrical Engineering, Government Polytechnic, Station Ghanpur, Warangal, Telangana, India
2Lecturer in Electrical Engineering, Dr. B.R. Ambedkar Government Polytechnic, for Women, Karimnagar, Telangana, India
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Abstract - Power Factor Correction (PFC) converters have
been widely used in ac–dc power conversions to achieve high
power factor (PF) and low harmonic distortion. The methods
of achieving PFC can be classified intoactiveandpassivetypes.
Compared with a passive PFC converter, an active PFC
converter can achieve a high PF and a small size. There are
different topologies for implementing active PFC techniques,
among which the boost converter is the representingtopology
because it exhibits many advantages such as small input–
current ripple due to the series connection of the inductor at
the input side, high PF over the whole input–voltage range,
small size in the output capacitor due to its high voltage, and
simple circuit. WhenaboostPFCconverteroperatesinCCM,
the inductor current ripple is very small, leading to low root-
mean-square (RMS) currents on the inductor and switch and
to low electromagnetic interference (EMI). However, the
switch always operates at hard switching, and the diode
suffers from reverse recovery. A discontinuous-current-mode
(DCM) boost power factor correction (PFC)converterfeatures
zero-current turn-on for the switch, no reverse recovery in
diode, and constant– frequency operation. However, the input
power factor (PF) is relatively low when the duty cycle is
constant in a half line cycle. This thesis derives the expressions
of the input current and PF of the DCM boost PFC converter,
and based on that, variable-duty-cycle control is proposed so
as to improve the PF to nearly unity in the whole input–
voltage range. A method of fitting the duty cycle is further
proposed for simplifying the circuit implementation. Other
than a higher PF, the proposed variable-duty-cycle control
achieves a lower output–voltage ripple and a higherefficiency
over constant-duty-cycle control
Key Words: Discontinuous current mode (DCM), power
factor correction (PFC), variable-duty-cycle control.
INTRODUCTION
Most applications requiring ac-dc powerconvertersneed the
output dc voltage to be well regulated withgoodsteady-state
and transient performance.Thecircuittypicallyfavoreduntil
recently (diode rectifier-capacitor filter) for the utility
interface is cost effective, but it severely deteriorates the
quality of the utility supply thereby affecting the
performance of other loads connected to it besides causing
other well known problems. In order to maintain the quality
of the utility supply, several national and international
agencies have started imposing standards and
recommendationsfor electronicinstrumentconnectedtothe
utility. Since the mid-1980's power electronics engineers
have been developing new approaches for better utility
interface, to meet these standards. These new circuits have
been collectively called Power factor correction (PFC)
circuits.
With the increase of consumer electronics the power quality
becomes poor. The reactive power drawn from the supplyis
increasing. This is because of the use of rectification of the
AC input and the use of a bulk capacitor directly after the
diode bridge rectifier. Reducing the inputcurrentharmonics
to meet the agency standardsimpliesimprovementofpower
factor as well. For this reason the publications reported in
this area have used "Power factor correction methods" and
"Harmonic elimination/reduction methods" almost inter
changeably. Several techniques for PFC and harmonic
reduction have been reported and a few of themhavegained
greater acceptance over the others.
This chapter discusses the i) Nonlinear loads and their
effect on the electricity distribution network, ii) Standard
IEC and IEEE regulation for harmonics, iii) Power factor
correction and its benefits, iv) application of PFC both for
linear and non-linear loads, v) research background, vi) aim
of the dissertation.
I. NONLINEAR LOADS AND THEIR EFFECT ON THE
ELECTRICITY DISTRIBUTION NETWORK:
The instrument connected to an electricity distribution
network usually needs some kind of power conditioning,
typically rectification, which produces a non-sinusoidal line
current due to the non-linear input characteristic. Line-
frequency diode rectifiers convert AC input voltage into DC
output voltage in an uncontrolled manner. Single-phase
diode rectifiers are needed in relatively low power
instrument that needs some kind of power conditioning,
such as electronic instrument and householdappliances. For
higher power, three-phase diode rectifiers are used. In both
single and three-phase rectifiers, a largefilteringcapacitor is
connected across the rectifier output to obtain DC output
voltage with low ripple. As a consequence, the line currentis
non sinusoidal. In most of these cases, the amplitude of odd
harmonics of the line current is considerable with respect to
the fundamental. While the effect of a single low power

nonlinear load on the network can be considered negligible,
the cumulative effect of several nonlinearloadsisimportant.
Line current harmonics havea numberofundesirableeffects
on both the distribution network and consumers.
These effects include:
1. Losses and overheating in transformers shunt capacitors,
power cables, AC machines and Switchgear, leading to
premature aging and failure.
2. Excessive current in the neutral conductor of three-phase
four-wire systems, caused by odd Triple current harmonics
(triple-n: 3rd, 9th, 15th, etc.).
3. Reduced power factor, hence less active power available
from a wall outlet having a certain apparent power rating.
4. Electrical resonances in the power system, leading to
excessive peak voltages and RMS currents, and causing
premature aging and failure of capacitors and insulation.
5. The distorted line voltage may affect other consumers
connected to the electricity distribution network.
6. Telephone interference.
7. Errors in metering instrument.
8. Increased audio noise.
9. Cogging or crawling in induction motors, mechanical
oscillation in a turbine-generator combinationorina motor-
load system
II. POWER FACTOR CORRECTION:
Reduction of line current harmonics is needed in order to
comply with the standard. This is commonly referred to as
the Power Factor Correction -PFC,whichmaybemisleading.
When an electric load has a PF lower than 1, the apparent
power delivered to the load is greater than the real power
that the load consumes. Only the real power is capable of
doing work, but the apparent power determines theamount
of current that flows into the load, for a given load voltage.
Power factor correction (PFC) is a technique of
counteracting the undesirable effects of electric loads that
create a power factor PF that is less than 1.
The power factor is defined as the ratio of the activepowerP
to the apparent power S:
S
PPF 
(2.1)
For purely sinusoidal voltage and current, the classical
definition is obtained:
cospf (2.2)
Where cosΦ is the displacement factor of the voltage
and current. In classical sense, PFC means compensation of
the “displacement factor”.
The line current is non-sinusoidal when the load is
nonlinear. For sinusoidal voltageandnon-sinusoidal current
the PF can be expressed as.
 coscoscos 11
p
rms
rms
rmsrms
rmsrms
K
I
I
IV
IV
PF 
(2.3)
 1,0,1
 p
rms
rms
p K
I
I
K
(2.4)
Kp describes the harmonic content of the current with
respect to the fundamental.Hence,the powerfactordepends
on both harmonic content and displacement factor. Kp is
referred to as purity factor or distortion factor.
The total harmonic distortion factor THDi is defined as
rms
n
rmsn
i
I
I
THD
1
2
2
,



(2.5)
Hence the relation between Kp and THDi
2
1
1
THD
K p


(2.6)
Standard IEC 1000-3-2 sets limits on the harmonic content
of the current but does not specifically regulate the purity
factor Kp or the total harmonic distortion of the line current
THDi. The values of Kp and THDi for which compliance with
IEC 1000-3-2 is achieved depend on the powerlevel.Forlow
power level, even a relatively distorted line current may
comply with the standard. In addition to this, it can be seen
from (1.6) that the distortion factor Kp of a waveform with a
moderate THDi is close to unity (e.g. Kp=0.989 for
THDi=15%). Considering (2.3) as well, the following
statements can be made:
1. Power factor PF is not significantly degraded by
harmonics, unless their amplitude is quite large (low Kp,
very large THDi).
2. Low harmonic content does not guarantee high power
factor (Kp close to unity, but low cosΦ).
Benefits of Power Factor:
1. Voltage distortion is reduced.
2. All the power is active.
3. Smaller RMS current.
4. Higher number of loads can be fed.
Most of the research on PFC for nonlinear loads is actually
related to the reduction of the harmonic content of the line
current. There are several solutions to achieve PFC. The
shape of the input current can be further improved by using
a combination of low pass input and output filters
Depending on whether active switches (controllable by an

external control input) are used or not, PFC solutions can be
categorized as “Passive” or “Active”.
In passive PFC, only passive elements are used in addition to
the diode bridge rectifier, to improve the shape of the line
current. Obviously, the outputvoltageisnotcontrollable. For
active PFC, active switches are used in conjunction with
reactive elements in order to increase the effectiveness of
the line current shaping and to obtain controllable output
voltage. The switching frequency further differentiates the
active PFC solutions into two classes.Inlowfrequencyactive
PFC, switching takes place at low-order harmonics of the
line-frequency and it is synchronizedwiththelinevoltage.In
high-frequency active PFC, the switching frequency is much
higher than the line frequency.
III. OPERATION IN DISCONTINUOUS CURRENT MODE -
DCM:
These converters operating in CCM reduces the line current
harmonics, it also has Drawbacks, such as:
1) It increases the EMI, due to the high-frequency content of
the input current.
2) It introduces additional losses, thus reducing the overall
efficiency and
3) It increases the complexity of the circuit, with negative
effects on the reliability of the instrument, as well as on its
size, weight and cost.
The high frequency EMI can be eliminated by introducing an
EMI filter between AC
supply and diode bridge rectifier. The additional losses will
be reduced by using soft switching techniques such as ‘ZVS’,
‘ZCS’ and ‘ZVT’. Some of the basic EMI filter requirements
and a novel Zero Voltage Transition - ZVT technique, which
can be applied to boost converter used in the PFC
In this chapter, basic types of dc-dc converter topologies are
studied to investigate their self-PFC capabilities. Basic types
of dc-dc converters, when operating in discontinuous
inductor current mode, have self power factor correction
(PFC) property, that is, if these converters are connected to
the rectified ac line, they have the capability to give higher
power factor by the nature of their topologies. Input current
feedback is unnecessary when these converters are
employed to improve power factor. This property of DCM
input circuit can be called “self power factor correction”
because no control loop is required from its input side. This
is also the main advantage over a CCM power factor
correction circuit, in which multi-loop control strategy is
essential. The peak of the inductor current is sampling the
line voltage automatically.
However, the input inductor operating in DCM cannot hold
the excessive input energy because it must release all its
stored energy before the end of each switching cycle. As a
result, a bulky capacitor is used to balancetheinstantaneous
power between the input and output. In addition, if
discontinuous inductor current mode is applied, the input
current is normally a train of triangle pulse with nearly
constant duty ratio. In this case, an input filter is necessary
for smoothing the pulsating input current into a continuous
one. Obviously, to ensure high power factor, the average
current of the pulsating current should follow the input
voltage in both shape and phase. In this operating mode, the
inductor current varies from zero toa maximumandreturns
back to zero before the beginning of thenextswitchingcycle.
IV.DCM BOOST PFC CONVERTER WITH CONSTANT-DUTY-
CYCLE CONTROL
Fig. 4.1 boost PFC converter
Fig. 4.1 shows the main circuit of a boost PFC converter. For
simplicity, the following assumptions are made: 1) All the
devices and components are ideal; 2) therippleoftheoutput
voltage is too small to be neglected; and 3) the switching
frequency is much higher than the line frequency.
Supposing that the input voltage is purely sine waveform
and it has no distortion, the input voltage is defined as
tVtv min sin)( 
…………… (4.1)
Where Vm is the amplitude of the input voltage and ω is the
angular frequency of the input voltage.
Then, the rectified voltage is
tVv mg sin
………… (4.2)
Fig. Inductor current waveform in a switching cycle
Fig. 4.2 shows the inductor current waveform in a switching
cycle when the converter operates in DCM. In a switching
cycle, the inductor peak current iLb_pk is

sy
b
m
sy
b
g
pkLb TD
L
tV
TD
L
v
ti
sin
)(_ 
… (4.3)
Where Dy is the duty cycle and Ts is the switching cycle.
In each switching cycle, the inductor has a volt-second
balance, i.e.,
SRgosyg TDvVTDv )( 
…………. (4.4)
Where Vo is the output voltage and DR is the duty cycle
corresponding to the reset time of the inductor current..
Equation (4) can be rewritten as
y
mo
m
y
go
g
R D
tVV
tV
D
vV
v
D


sin
sin




(4.5)
From eq.(4.3) and (4.5), the average inductor current in a
switching cycle can be derived as
y
o
msb
ym
RypkLbavLb D
t
V
V
t
fL
DV
DDtiti


sin1
sin
2
))((
2
1
)(
2
__


… (4.6)
Where fs = 1/Ts is the switching frequency. Thus,the
input current is
t
V
V
t
fL
DV
ti
o
msb
ym
in


sin1
sin
2
)(
2


…… (4.7)
When Dy is constant, according to eq.(4.3) and eq.(4.6),
Fig.4.3 shows the instantaneous waveform, the peak value
envelope, and the ave rage value of the inductor current. It
can be seen that the shape of the peak inductor current is
sinusoidal; however, the shape of the average inductor
current is not sinusoidal, and there is distortion in it.
Fig. 4.3. Inductor current waveform in a half line cycle.
Fig. 4.4. Normalized input-current waveform in a half line
cycle.For analysis simplicity, the average inductor current is
nor-mailed with the base of
))/1/(1)(2/( 2
omsbym VVfLDV 
,soeq.(4.7)isrewrittenas
t
V
V
t
V
V
i
o
mo
m
in


sin1
sin
1*








……… (4.8)
According to eq.(4.8), the normalized average inductor
current is shown in Fig. 5.4, from which it can be seen that
the shape of the average inductor current is only dependent
on Vm/Vo, and the smaller the Vm/Vo is, the closer to
sinusoidal the current shape is. This can be explained as
follows. As the duty cycle is constant in a line cycle, the peak
value of the inductor current is in the sinusoidal shape, and
the average value of the inductor current in therisingperiod
is sinusoidal. However, the falling time of the inductor
current is dependent on the value of (Vo − vg ), and it varies
with vg , so the average value of the inductor current in the
falling period is not sinusoidal. Thus,theaveragevalueof the
inductor current in a switching cycle is not sinusoidal. The
smaller the Vm/Vo is, the shorter the falling time of the
inductor current is and, thus, the closer to sinusoidal shape
the average inductor current in a switching cycle is.
From eq.(4.1) and eq.(4.7), the average input power is
derived as

2
0
)()(
2/
1
lineT
inin
line
in dttitv
T
P
td
t
V
V
t
fL
DV
o
msb
ym








0
222
sin1
sin1
2
…. (4.9)
Where Tline is the line cycle.
Assuming that the efficiency of the converter is 100%, i.e.,
Pin = Po, the duty cycle is

td
t
V
V
t
PfL
V
D
o
m
osb
m
y








0
2
sin1
sin
21
…... (4.10)
From eq.(4.7) and eq.( 4.9), the input PF can be derived as
 



 0
2
_ )(
1
2
1
2
1
tdtiV
P
IV
P
PF
inm
in
rmsinm
in


























0
2
0
0
0
2
sin1
sin
sin1
sin2
td
t
V
V
t
td
t
V
V
t
m
m
…………. (4.11)
Where Iin_rms is the rms value of the input current.
V.DCMBOOSTPFCCONVERTERWITHCONSTANT-DUTY-
CYCLE CONTROL (OPEN LOOP)
Fig.5.3 DCM Boost PFC converter with constant-duty-
cycle control-R-L Load
Circuit specifications: Supply Voltage = 12 V
Filter inductor Lin = 7.6u , Filter capacitor Cin = 0.33u
Boost Capacitor = 470u , Boost Inductor = 9u
R=25ohm, L=0.09u,Pulse Generator Frequency = 10khz
Duty Ratio=0.7
Simulation waveforms
Fig.5.4 (a) input voltage and current (b) output voltage
waveforms with constant-duty-cycle control boost
converter-R-L Load
Comments:Fig.5.4 (a) Shows input voltage and current
waveform form in this we can observe that the input power
factor is .934 and the output voltage with constant-duty-
cycle control is 40VDC with the voltage ripple is 6%. In this
circuit the voltage boost up from 12VAC to 40VDC and the
line current harmonics are neglected.
VI. DCM BOOST PFC CONVERTER WITH VARIABLE-DUTY-
CYCLE CONTROL (CLOSED LOOP)
Fig.6.3 DCM Boost PFC converter with Variable-duty-cycle
control-R-L Load
Circuit specifications Supply Voltage = 12 V
Filter inductor Lin = 7.6u ,Filter capacitor Cin = 0.33u

Boost Capacitor = 470u, Boost Inductor = 9u, R=25ohm,
Reference wave frequency 100khz,
Switching Frequency = 100k
Fig.6.4 (a) input voltage and current (b) output voltage (c)
Boost inductor current waveforms with Variable-duty-cycle
control boost converter-R-L Load
Comments:
Fig.6.4 (a) Shows input voltage and current waveform
form in this we can observe that the input power factor is
0.9984, Fig.6.4 (b) Shows output voltage waveforms with
Variable-duty-cycle control in this the voltage ripple is 2%
Fig.6.4 (c) Shows Boostinductorcurrent waveformshere the
switching frequency is 100khz and the inductor
Current is zero for each switching interval.
Dc motor load
Fig.6.5 DCM Boost PFC converter with Variable-duty-cycle
control-DC Motor Load
Circuit specifications
Supply Voltage = 12 V, Filter inductor Lin = 7.6u
Filter capacitor Cin = 0.33u, Boost Capacitor = 470u
Boost Inductor = 9u,
Reference wave frequency 100khz
Switching Frequency = 100k,
DC Shunt motor parameters
Fig.6.5 (a) input voltage and current (b) output voltage (c)
load current (d) Boost inductor current waveforms with
Variable-duty-cycle control boost converter-DC motor Load
CONCLUSION
In DCM, the input inductor is no longer a state variable
since its state in a given switching cycle is independent on
the value in the previous switching cycle. The peak of the
inductor current is sampling the line voltage automatically.
This property of DCM input circuit can be called “self power
factor correction” because no control loop is required from
its input side.
It can conclude that the basic boost converter and buck-
boost converter have excellent self PFC capability naturally.
Among them, boost converter is especially suitable for DCM
PFC usage and buck-boost is not widely used because of the
drawbacks such as: the input voltage and the output voltage
don’t have a common ground due to the reversed output
voltage polarity, etc. Hence, this converter is the most
preferable by the designers for the power factor correction
purpose. Other converters may be used onlyiftheirinputV-I
characteristics have been modified (linear zed), or when
they operate in a continuous inductor conduction mode. To
conclude, a 500 W, 40 kHz variable duty cycle DCM boost

PFC converter has been analyzed, simulated and results are
presented in this thesis. The proposed converter gives
around 0.9977 (almostunity) powerfactorwithanefficiency
of around 98%.
REFERENCES
[1] O. Garcia, J. A. Cobos, R. Prieto, P. Alou, and J. Uceda,
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BIOGRAPHIES
Addagatla Nagaraju was born
in Warangal, India, in 1986. He
received the B.Tech. degree in
Electrical and Electronics from
Jawaharlal Nehru technological
university, Hyderabad, India, in
2009 and the M.Tech. degree in
Power Electronics from
2012, where he is currently
working as Lecturer in electrical
engineering at Department of
technical Education , Government of Telangana.
His main research interests include dc/dc converters,ac/dc
converters, and power supplies for LEDs.
Akkela krishnaveni was born in
karimnagar, India, in 1991. She
received the B.Tech degree in
electrical engineering from
2012, where she is currently
working as Lecturer in electrical
engineering at Department of
technical Education , Government
of Telangana. she is working
toward the M.Tech. degree in Power Electronics.
Her main research interests include dc/dc converters,ac/dc
converters, and electromagnetic interference filter designs.

PSIM Simulation Of Variable Duty Cycle Control DCM Boost PFC Converter to Achieve High Input Power Factor

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