1.
1

2.
MEHRAN
UNIVERSITY
OF
ENGINEERING
&
TECHNOLOGY
JAMSHORO
ACHIEVING HIGH INPUT POWER
FACTOR FOR DCM BUCK
CONVERTER BY VARIABLE DUTY
CYCLE CONTROL
MUHAMMAD OSAMA NIZAMANI (17 ME ELP 19)
SUPERVISOR: DR. ABDUL HAKEEM MEMON
CO-SUPERVISOR: PROF. DR. ZUBAIR AHMED MEMON
2

3.
3
Contents
 Introduction
 Literature Review
 Problem Statement
 Research Objectives
 Research Methodology
 Operating Principle of DCM Buck PFC Converter
 Variable Duty Cycle Control Scheme to Improve PF
 Fitting Duty Cycle
 Implementation of Control circuit
 Compression Analysis between CDCC and VDCC
 Simulation verification
 Conclusion
 Future work
 References

4.
 AC/DC power conversion is an important research area of power electronics technology.
 Harmonic pollution caused by increased number of electronic appliances has become a
serious issue
 To meet the international harmonic standards, e.g. IEC 61000-3-2 limit power factor
correction (PFC) converters had developed and adopted in the power systems, which can
attain low harmonic distortion and high power factor (PF).
Introduction
4

5.
Introduction (cont.)
 There are variety of topologies and control schemes to achieve PFC.
 The buck converter is one of the commonly used topology, especially in low power
applications due to its advantages of low voltages stress on semiconductor switch, low
dc output voltage, small conduction losses, low inrush current.
 As compared to other PFC converters, buck converter can achieved high efficiency in
entire universal input voltage range.
5

6.
 Hadley (1989) offer a solution where by controlling the pulse width modulation gradient through ac
module of the rectified input voltage a variable duty cycle could be achieved. Though, smallest
current alteration gained by this strategy is around about 10%, so additional change promotes near
unwanted increase in fifth or seventh harmonic component [1].
 D. Weng (1996) introduce solution, in which the operating system in controlled by second harmonic
of reference voltage. That technique needs complicate and expansive additional circuitry, for example
phase-locking-loop and phase-detecting but that is very effective for distortion reduction [2].
 schramm (1998) proposed peak current control in which with constant duty cycle a given harmonic
which is inserted to the assumed current for eliminating the third harmonic to reference current and
the power factor could be enhanced near unity [3].
Literature Review
6

7.
 Huber et al (2010) introduce design-oriented analysis, a significant optimization and execution
assessment on clamped current buck PFC converter [4].
 Kai Yao (2011) apply a variable duty cycle control on DCM boost PFC converter to improve PF [5].
 Wu et al (2012) present a variable on-time regulator into CRM mode buck PFC converter in high-
illumination LED application to meet the lighting system limitation and for current harmonic reduction
[6].
 X. Xie et al (2013) put forward to eliminate the dead zone of buck converter he added two diodes and
an auxiliary switch [7].
 D.D.-C. Lu (2013) evaluates a example of buck PFC and buck-boost dc/dc single step stage converter
and put forward a scheme of a low load power loss of reduction [8].
Literature Review ( Cont.)
7

8.
 Ohnuma (2014) adopt a small capacitor with active buffer for power decoupling in a buck PFC and
achieves a low output voltage ripple and high PF [9].
 kai Yao (2017) propose for improvement of PF by optimizing third harmonic. By compared with
sinusoidal current control the planned switch technique gains a large PF and minor output voltage
ripple in the worldwide input voltage choice [10].
 A. Hakeem Memon (2017) introduce a variable-on-time (VOT) control scheme designed for CRM
integrated buck and flyback PFC converter with high power factor (PF) and low total harmonic
distortion (THD). By utilizing input and output voltage to modulate the on-time of both buck and
flyback switches, the input current harmonic can be eliminated and high PF will be obtained [11].
Literature Review ( cont.)
8

9.
 A. Hakeem Memon (2018) propose an approach of unity PF control (UPC) for boundary
conduction mode (BCM) buck-buck/boost PFC. The control framework can secure high power
factor and low total harmonic distortion by applying input/output voltages to modulate the on-time
of both buck and buck/boost switches [12].
 A. Hakeem Memon (2018) proposed variable-on-time (VOT) control scheme for CRM buck-
buck/boost converter to realize high input PF [13].
 Memon et al., (2019) has introduce flyback converter to work with Buck converter for boundary
condition mode (BCM) to improve PF. [14]
Literature Review ( cont.)
9

10.
Literature Review ( cont.)
 Memon et al., (2019) has introduce buck/boost converter to work with buck converter for (BCM)
buck converter to improve PF. [15]
 Memon et al., (2019) has proposed control technique to improve input PF of integrated buck-
flyback converter. [16]
10

11.
“A buck PFC converter is widely used in low-power application for its many
applications. However, when duty cycle is kept constant in a line cycle, the average
input current is not proportional to the input voltage, so PF is not high and also
because of the inherent dead zone as shown in figure 1, the input PF is not high.
Therefore, it is essential for the buck converter to improve its PF, so that its average
input current can meet IEC limit”
Problem Statement
11

12.
12
Figure 2

13.
Research Objectives
 To propose variable duty cycle control scheme to improve Power
Factor (PF).
 To develop simulation model by using saber simulator to verify the
effectiveness of VDCC for DCM Buck PFC converter.
13

14.
1
• Literature survey along with collection of books and
equipment’s.
2
• Input PF analysis of tradition DCM buck converter.
3
• Introduction to variable duty-cycle control to improve the
input PF.
4
• Fitting duty-cycle by using Taylor’s series.
Research Methodology
14

15.
5 • Implementation of proposed control scheme.
6
• Comparison analysis between two control schemes in terms of input
PF.
7
• To develop simulation model by using Saber Simulator of DCM
buck PFC converter for constant duty cycle control (CDCC) and
variable duty cycle control (VDCC)
8 • Verifying result
9 • Thesis write up
Research Methodology ( cont.)
15

16.
Operating Principle of DCM Buck
PFC Converter
D1 D2
D3 D4
vin
iin
EMI
Filter
Co
Lb
Qb
Dfw Vo
RLd
Schematic diagram of a DCM buck PFC converter
Figure 2
16

17.
Operating Principle (cont.)
The instantaneous and rectified input voltage during half line cycle
can given as
sin
in g m
v v V 
 
The input current of Buck converter is given as
2
0 0
( sin )
2
m o y
in
b s
V V D
i
L f

   

   
Equations are derived in details in research paper and thesis
(1)
(2)
17

18.
The input PF of Buck converter is given as
0
0
2
_
2
sin ( sin 1)
1
( sin 1)
2
o
o
in
m in rms
a d
P
PF
V I a d
 

 

  

 



 



The input power with CDCC of Buck converter is
given as
0
2
/2
0
1
sin (V sin )
/ 2 2
line o
T m y
in in in m o
line b s
V D
P v i dt V d
T L f
 

  


  
 
Vm =Input
voltage
amplitude
θ = input voltage
angular
frequency
Dy =Duty cycle
(3)
(4)
18
Operating Principle (cont.)

19.
PF
Vm/Vo
2.766 3.111 3.457 3.803 4.148
0.970
0.975
0.980
0.985
0.990
Relation between the input PF and Vm/Vo
Vo=Voltage output
a= Vm/Vo
Figure 3
19
Operating Principle (cont.)

20.
Variable Duty Cycle Control Scheme
to Improve Input PF
For achieving unity PF , the variation rule for duty cycle is
0
0 0
sin
sin
m
y
m o
D V
D
V V

   

   

where Do is a co-efficient
By replacing the value of Dy in (2), we can get
0
0 0
sin
2
m
in
b s
D V
i
L f

   
   
Above equation shows that input current is pure sinusoidal and hence unity PF can be
achieved
(5)
(6)
20

21.
Variable Duty Cycle (cont.)
The average input power with proposed control scheme is given as
0
0
0 sin
1
sin
2
s m
in m o
b
D TV
P V d P
L
 


 


  

D0 can be obtained as
 
0 2
0 0
4
V 2 sin 2
b s o
m
L f P
D

  

 
   0 0
0 0
4 sin
V 2 sin 2 sin
o b s
y
m m o
P L f
D
V V
 
   
   
   
   (9)
(8)
(7)
21

22.
Fitting Duty Cycle
The subtraction, multiplication, division and root operation included, the duty-cycle expressed
in (9) is complicated to be realized by analog circuit. Therefore, it is necessary to simplify (9).
Defining a=Vm/Vo, y=sinθ, (5) can be rewritten ass
0
0 0
a 1
y
D ay
D
y
   
   

(10)
Talyor’s series
           
  
2
' ''
0 0 0 0 0 0 0
1 1
2! !
n
n
f x f x f x x x f x x x f x x x
n
         (11)
22

23.
By using Talyor’s series the simplified equation is
0 0 0
_ 1 0 0
2 2
0 0 0 0 0 0
2 1
1 (1 )
1 2( 1) 2 2
y fit
D ay ay y y
D D
ay ay ay y ay y
   
 

         
 
   
 
Where 0 0 0
1
0 0
2 1
1 2( 1)
D ay ay
D
ay ay

 
 
(12)
Therefore the input current and input Power for VDCC
2 2
1 2
0 0
_ 0 0
( sin 1)(1 )
2
2
o
in VDCC
b s
y
V D a
ay y
i
L f

   
 

   
(13)
23
Fitting Duty Cycle (cont.)

24.
0
2
2
1
_ 2
0 0
sin
sin ( sin 1)(1 )
2 2
o
m o
in VDCC o
b s
V V D
P P a d
L f ay y
 


  


   

 (14)
From (13) and (14), input PF is calculated as
0
0
0
2 2
0 0
2 4 2
_ _
0 0
2
sin (2 sin ) ( sin 1)
(2 sin ) ( sin 1)
o
in
in rms in rms
ay y a d
P
PF
V I
ay y a d
 

 

   

  


  
 
  


(15)
If input voltage range is 176-220 VAC output voltage is 90 V replacing a= into
(15), and differentiating (15) with y0, also setting it to zero, y0=0.75 is obtain
176 2 / 90
_ 1 0 0
1.125 0.75 sin
1.125 0.75
m o o
y fit
m o
V V V
D D
V V

   
 
    

(16)
24
Fitting Duty Cycle (cont.)

25.
Implementation of the Control Circuit
C
vEA
x y
z
v v
v

vx
vy
vz
R7
vo
R5
R6
R8
+
_
+
_
R15
R16
R17 C2
Vog
vof
+
_
+
_
2
1
9
R
S
Clock
PWM
Latch
Frequency
Divider
Comp
E/A
Qb
11
14
D2
D3
UC3525A
P
D
R9
R10
R13
R14
+
_
A
+
_
vg
R1
R2
vgf
D
R11
A of
B
v v
v

R3
D1
Feedforward Circuit
Multiplier
Multiplier
Error
Amplifier
+
_
B
C1 R4
0.75 1.125 sin
0.75 1.125
o m o
P EA
o m
V V V
v v
V V

 


Figure 4. Control circuit of the variable duty cycle control
25
(17)

26.
Comparison Analysis Between
CDCC and VDCC
From (4) and (15), the input PF curves with a CDCC and a VDCC are drawn and shown in
figure 5. it can be observed that VDCC improve the input PF. Once the input voltage is set
at 176 VAC, the PF is improved from 0.971 to 0.983.
constant duty
cycle control
variable duty
cycle control
176 198 220 242 264
Vm / 2
0.96
0.97
0.98
0.99
1.00
0.971
0.983
FIGURE 5 26

27.
Simulation Verification
For verifying the effectiveness of VDCC strategy, simulations are carried out.
The input voltage range is 176-264 VAC and the output voltage is 90 V. for ensuring the
current to be in DCM, UC3525A IC is used.
Figures show the simulation waveforms of vin, iin, and vo of buck converter with
CDCC and VDCC at 176-264 VAC inputs, respectively. It can be observed that the
input current with VDCC is more sinusoidal as compared with CDCC.
27

28.
v
o
/V
v
in
/V
i
in
/A 80
95
-1.5
1.5
0
400
0
90
90
Figure 6. vin, iin, and vo with CDCC on 176 VAC
v
o
/V
v
in
/V
i
in
/A
80
95
-1.5
1.5
0
400
0
90
90
Figure 7. vin, iin, and vo with VDCC on 176 VAC
28
Simulation Verification

29.
v
o
/V
v
in
/V
i
in
/A
80
95
-1.5
1.5
0
400
0
90
90
Figure 8. vin, iin, and vo with CDCC on 220 VAC
v
o
/V
v
in
/V
i
in
/A
80
95
-1.5
1.5
0
400
0
90
90
Figure 9. vin, iin, and vo with VDCC on 220 VAC
29
Simulation Verification

30.
v
o
/V
v
in
/V
i
in
/A
80
95
-1.5
1.5
0
400
0
90
90
Figure 10. vin, iin, and vo with CDCC on 264 VAC
v
o
/V
v
in
/V
i
in
/A
80
95
-1.5
1.5
0
400
0
90
90
Figure 11. vin, iin, and vo with VDCC on 264 VAC
30
Simulation Verification

31.
31
Conclusion
When the duty cycle is kept constant in a line cycle, the average input current is not
proportional to the input voltage, so the input PF is not high. In order to improve the
PF to near unity over whole input voltage range, a variable duty cycle control scheme
is proposed and furthermore a method of fitting the duty cycle has been proposed for
simplifying the circuit implementation.

32.
32
Future Work
1. Hardware implementation can be achieved for design model.
2. Digital circuit can be used for proposed model in place of analog
circuit.
3. Design model can be employed for 3-phase system

33.
33

34.
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circuits employing discontinuous-mode boost converters. In Power Electronics Specialists
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[2]. Weng, D., & Yuvarajan, S. (1995, March). Constant-switching-frequency AC-DC converter
using second-harmonic-injected PWM. In Applied Power Electronics Conference and Exposition,
1995. APEC'95. Conference Proceedings 1995., Tenth Annual (Vol. 2, pp. 642-646). IEEE.
[3]. Schramm, D. S., & Buss, M. O. (1998, May). Mathematical analysis of a new harmonic
cancellation technique of the input line current in DICM boost converters. In Power Electronics
Specialists Conference, 1998. PESC 98 Record. 29th Annual IEEE (Vol. 2, pp. 1337-1343). IEEE.
References
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[4]. Huber, L., Gang, L., & Jovanovic, M. M. (2010). Design-oriented analysis and performance
evaluation of buck PFC front end. IEEE Transactions on Power Electronics, 25(1), 85-94.
[5] Yao, K., Ruan, X., Mao, X., & Ye, Z. (2010). Variable-duty-cycle control to achieve high input power
factor for DCM boost PFC converter. IEEE Transactions on Industrial Electronics, 58(5), 1856-1865.
[6]. Wu, X., Yang, J., Zhang, J., & Qian, Z. (2012). Variable on-time (VOT)-controlled critical
conduction mode buck PFC converter for high-input AC/DC HB-LED lighting applications. IEEE
Transactions on power Electronics, 27(11), 4530-4539.
[7]. Xie, X., Zhao, C., Zheng, L., & Liu, S. (2013). An improved buck PFC converter with high
power factor. IEEE Transactions on power electronics, 28(5), 2277-2284.
[8]. Lu, D. D., & Ki, S. K. (2013). Light-load efficiency improvement in buck-derived single-stage
single-switch PFC converters. IEEE transactions on power electronics, 28(5), 2105-2110.
References
35

36.
[9]. Ohnuma, Y., & Itoh, J. I. (2014). A novel single-phase buck PFC AC–DC converter with power
decoupling capability using an active buffer. IEEE Transactions on Industry Applications, 50(3), 1905-
1914.
[10]. Yao, K., Zhou, X., Yang, F., Yang, S., Cao, C., & Mao, C. (2017). Optimum Third Current
Harmonic During Nondead Zone and Its Control Implementation to Improve PF for DCM Buck PFC
Converter. IEEE Transactions on Power Electronics, 32(12), 9238-9248.
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high input power factor for a CRM-integrated buck–flyback PFC converter. IEEE Trans. Power
Electron, 32(7).
References
36

37.
[12]. Memon, A. H., & Yao, K. (2018). UPC strategy and implementation for buck–
buck/boost PF correction converter. IET Power Electronics, 11(5), 884-894
[13]. Memon, A. H., Baloach, M. H., Sahito, A. A., Soomro, A. M., & Memon, Z. A. (2018).
Achieving High Input PF for CRM Buck-Buck/Boost PFC Converter. IEEE Access, 6,
79082-79093.
[14]. Memon, A. H., Pathan, A. A., Kumar, M., Sahito, A. A J., & Memon, Z. A (2019). Integrated
buck-flyback converter with simple structure and unity power factor. Indian Journal of Science and
Technology, 12(17), 1-5
References
37

38.
References
[15]. Memon, A. H., Memon, Z. A., Shaikh, N. N., Sahito, A. A & Hashmani, A. A (2019). Boundary
conduction mode modified buck converter with low input current total harmonic distortion. Indian
Journal of Science and Technology, 12(17), 1-5
[16] Memon, A. H., Memon, Z. A., Shaikh, N. N., Sahito, A. A & Hashmani, A. A (2019). buck-
buck/boost converter with high input power factor and non-floating output voltage. International
Journal of Computer Science and Network Security, 19(4), 1-5
38

39.
Thank You
39

40.
Relation between PF and THD
2
1
1
PF
THD


2
1
1
THD
PF
 
40