ACHIEVING HIGH INPUT POWER FACTOR
FOR DCM BUCK PFC CONVERTER BY
VARIABLE DUTY-CYCLE CONTROL
A. Hakeem Memon
IICT, Mehran UET, Jamshoro.
E-mail: hakeem.memon@faculty.muet.edu.pk
M. Osama Nizamani
IICT, Mehran UET, Jamshoro.
E-mail: osama12el118@gmail.com
Anwar A. Memon
IICT, Mehran UET, Jamshoro.
E-mail: anwar.memon@faculty.muet.edu.pk
Zubair A. Memon
IICT, Mehran UET, Jamshoro.
E-mail: zubair.memon@faculty.muet.edu.pk
Amir M. Soomro
IICT, Mehran UET, Jamshoro.
E-mail: amir.soomro@faculty.muet.edu.pk
Recepción: 31/07/2019 Aceptación: 20/09/2019 Publicación: 06/11/2019
Citación sugerida:
Memon, A.H., Nizamani, M.O., Memon, A.A., Memon, Z.A. y Soomro, A.M. (2019).
Achieving high input power factor for DCM Buck PFC converter by variable Duty-Cycle
Control. 3C Tecnología. Glosas de innovación aplicadas a la pyme. Edición Especial, Noviembre
2019, 185-199. doi: http://dx.doi.org/10.17993/3ctecno.2019.specialissue3.185-199
Suggested citation:
Memon, A.H., Nizamani, M.O., Memon, A.A., Memon, Z.A. & Soomro, A.M. (2019).
Achieving high input power factor for DCM Buck PFC converter by variable Duty-Cycle
Control. 3C Tecnología. Glosas de innovación aplicadas a la pyme. Speciaal Issue, November 2019,
185-199. doi: http://dx.doi.org/10.17993/3ctecno.2019.specialissue3.185-199
186
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ABSTRACT
Buck power factor correction (PFC) converter is widely used for a broad range of
AC/DC applications because of its many advantages However, the traditional
discontinuous conduction mode (DCM) buck power factor correction converter
(PFC) operates on constant duty-cycle control (CDCC) scheme, due to which its input
power factor (PF) is low. For improving PF near to unity, a variable-duty-cycle control
(VDCC) method has been proposed. Fitting duty-cycle method is also introduced to
make circuit implementation easier. For verifying the validity of proposed technique,
the simulation results are carried out.
KEYWORDS
Variable duty-cycle control (VDCC), Constant duty-cycle control (CDCC),
Discontinuous conduction mode (DCM), Power factor correction (PFC).
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DOI: http://dx.doi.org/10.17993/3ctecno.2019.specialissue3.185-199
1. INTRODUCTION
For achieving high power factor (PF) and low total harmonic distortion (THD),
power factor correction (PFC) converters are normally used in most of ac-dc power
conversion applications. PFC converters may be divided into active and passive
types. Active PFC converters have more advantages as compared to passive ones in
terms of high PF and small size (Memon, Yao, Chen, Guo, & Hu, 2017). Various
types of topologies and control schemes are available to implement the active PFC
techniques. Amongst them, buck PFC converter is a good choice especially for a
broad range of ac/dc applications due to its several advantages like high eciency,
cost reduction, low output voltage, and life time improvement. In literature, many
researchers (Memon et al., 2017-2019) have introduced buck PFC converter as a pre-
regulator. The buck ac-dc converter can overcome the disadvantages of the universal
input condition. On the other hand, if this converter works in hard switching mode,
switching losses will be higher especially at high input voltage that deteriorates
the advantages of buck converter (Chiang & Chen, 2009). The problem of hard
switching mode can be overcome by operating it in critical conduction mode (CRM)
or discontinuous conduction mode (DCM), which can provide zero voltage switching
(ZVS) and reduce reverse recovery losses in diode (Yang, Wu, Zhang, & Qian, 2010).
For modifying the performance of traditional buck converter, various researches
have proposed various techniques and control schemes.
Endo, Yamashita, and Sugiura (1992) have introduced a high PF buck converter.
Lee, Wang, and Hui (1997) have discussed modeling, analysis, and applications of
buck converter in discontinuous input voltage mode operation. Huber, Gang, and
Jovanovic (2010) have presented the performance evaluation on a clamped-current
buck PFC converter. Jang and Jovanović (2011) have introduced a bridgeless buck PFC
converter that substantially improves the eciency at low line. Wu et al. (2011) have
presented soft switched buck PFC converter operating with constant on-time control.
Lamar, Fernandez, Arias, Hernando, and Sebastian (2012) have presented a tapped-
inductor high-brightness light-emitting diode (HB-LED) AC/DC driver operating
in boundary conduction mode (BCM) for replacing incandescent bulb lamps. Wu et
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al. (2012) have put forward variable on-time control strategy to enhance the PF of
buck converter. Xie, Zhao, Zheng, and Liu (2013) have proposed a new topology to
enhance the PF. Yao et al., (2017) have proposed an injecting third harmonic method
to realize high PF. Memon et al. (2017) have proposed a variable control scheme for
integrated buck-yback converter to enhance input PF.
In this paper, a variable duty-cycle control (VDCC) strategy is introduced for
discontinuous conduction mode (DCM) buck converter to realize high input PF.
The analysis of the operating principle of buck converter is discussed with traditional
control (CDCC) scheme in Section 2. The VDCC is put forward in Section 3 to
attain high PF. In Section 4, simulation results are discussed, and the conclusion is
given in Section 5.
2. OPERATION ANALYSIS OF DCM BUCK PFC
CONVERTER
The gure 1 illustrates the schematic diagram of a DCM buck PFC converter.
D
1
D
2
D
3
D
4
v
in
i
in
EMI
Filter
C
o
L
b
Q
b
D
fw
V
o
R
Ld
Figure 1. Schematic diagram of a DCM buck PFC converter.
The instantaneous and rectied input voltage during half line cycle can be given as:
(1)
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Whereas V
m
represent the input voltage amplitude, θ represent the input voltage
angular frequency.
In switching cycle, peak current of inductor i
Lb_pk
is:
(2)
According to volt-second balance in the inductor:
(3)
Whereas D
y
represents duty-cycle, and T
s
represents switching cycle, V
o
represents
voltage output and D
R
represents duty-cycle during turn o time of switch.
Re arranging Eq. no (3) we get:
(4)
The average value of inductor current is:
(5)
The input current of the buck converter can be expressed as:
(6)
where θ0=arcsin Vo/Vm and Dy is constant.
The average input power with constant duty-cycle control (CDCC) is given as:
(7)
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Whereas, T
line
represent the line cycle.
Suppose the converter’s eciency is 100%, at that moment
the duty-cycle is:
(8)
The input power factor (PF) can be calculated from (6-8)
as:
(9)
PF
V
m
/V
o
2.766 3.111 3.457 3.803 4.148
0.970
0.975
0.980
0.985
0.990
Figure 2. Relationship among the input PF and a.
Where a=V
m
/V
o
The curve of input PF is drawn from (9) and is depicted in Figure 2. It can be
observed that when the V
m
/V
o
is greater, the PF is higher. When input voltage is
176VAC and output voltage is 90 V, at that time PF is 0.971. So, for achieving high
PF, a new control technique must be proposed.
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3. PROPOSE CONTROL SCHEME TO ENHANCE INPUT PF
3.1. VARIABLE DUTYCYCLE CONTROL TO REALIZE HIGH PF
For realizing unity PF, the variation rule for duty-cycle must be:
(10)
where D
o
is a co-ecient,
By replacing the value of D
y
in (7), we get:
(11)
Eq. (11) shows that input current is pure sinusoidal and hence unity PF can be
realized.
The average input power with proposed control scheme is given as:
(12)
From (13), D
0
can be obtained as:
(13)
By putting (13) into (11) leads to:
(14)