CRITICAL CONDUCTION MODE BUCK-
BUCK/BOOST CONVERTER WITH HIGH
EFFICIENCY
A. Hakeem Memon
IICT, Mehran UET, Jamshoro.
E-mail: hakeem.memon@faculty.muet.edu.pk
Mansoor A. Memon
IICT, Mehran UET, Jamshoro.
E-mail: mansoorjali74@gmail.com
Zubair A. Memon
IICT, Mehran UET, Jamshoro.
E-mail: zubair.memon@faculty.muet.edu.pk
Ashfaque A. Hashmani
IICT, Mehran UET, Jamshoro.
E-mail: ashfaque.hashmani@faculty.muet.edu.pk
Recepción: 31/07/2019 Aceptación: 23/09/2019 Publicación: 06/11/2019
Citación sugerida:
Memon, A.H., Memon, M.A., Memon, Z.A. y Hashmani, A.A. (2019). Critical
Conduction Mode Buck-Buck/Boost Converter with High Eciency. 3C Tecnología.
Glosas de innovación aplicadas a la pyme. Edición Especial, Noviembre 2019, 201-219. doi: http://
dx.doi.org/10.17993/3ctecno.2019.specialissue3.201-219
Suggested citation:
Memon, A.H., Memon, M.A., Memon, Z.A. & Hashmani, A.A. (2019). Critical
Conduction Mode Buck-Buck/Boost Converter with High Eciency. 3C Tecnología.
Glosas de innovación aplicadas a la pyme. Speciaal Issue, November 2019, 201-219. doi: http://
dx.doi.org/10.17993/3ctecno.2019.specialissue3.201-219
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ABSTRACT
The buck converter is commonly utilized in various low power applications because
of maintaining high eciency at universal input voltage and many other advantages.
On the other hand, when the on-time is constant, the conduction and switching losses
are more because the rms and peak value of the inductor current is more. So, the
eciency is low. For improving eciency, a variable on-time control (VOTC) strategy
has been proposed for buck-buck/boost topology with simple structure, minimum
losses and less component cost. For verifying the validity of proposed technique, the
simulation results are carried out by using saber simulator.
KEYWORDS
Variable on-time control (VOTC), Constant on-time control (COTC), Critical
conduction mode (CRM), Buck/boost converter, Buck converter.
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1. INTRODUCTION
Power electronic technology is used in various types of modern equipment’s which
has made our life easier, simpler and luxurious. However, this technology is based on
semiconductor devices, due to which the shape of average input current is distorted.
The distorted current has various drawbacks such as voltage distortion, increased
power loss and noise etc. So the industries have built various standards such as
IEC61000-3-2 limit and IEEE 519 (International Electrotechnical Commission,
2014; Langella, Testa, & Alii, 2014). Therefore, various types of power factor
correction (PFC) converters are put forward in the literature to improve the shape
of distorted current (García, Cobos, Prieto, Alou, & Uceda, 2003; Singh, Singh,
Chandra, & Al-Haddad, 2011) and the buck converter is one of them. Its advantages
include protection against short circuit, high eciency at universal input voltage, low
output voltage, and less voltage stress on the switch. However, its input power factor
(PF) is low due to dead zone in the average input current. Integrating buck converter
with buck/boost converters can solve the dead zone problem and enhance its PF. On
the other hand, when the on-time is constant, the conduction and switching losses
are more because the rms and peak value of the inductor current is more. So, the
eciency is low. Thus, it is necessary for the integrated buck-buck/boost converter
to propose the technique which can attain high eciency with simple structure and
minimum losses.
For modifying the performance of traditional buck converter, various researches
have proposed various control strategies and topologies.
Spiazzi and Buso (2000) have proposed a new solution for eliminating the dead zone
in the buck converter. It has proposed yback converter to work with buck converter
during dead zone period. Alonso, Dalla Costa, and Ordiz (2008) have implemented
integrated buck-yback converter (IBFC) for low cost, high PF and fast output voltage
regulations. Dalla Costa, Alonso, Miranda, García, and Lamar (2008) have presented
IBFC for single-stage electronic ballast with high PF. Gacio, Alonso, Calleja, Garcia,
and Rico-Secades (2011) have presented oine IBFC for high brightness light
emitting diode (HB-LED) to cover the application of LED in street light. Xie, Zhao,
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Lu, and Liu (2013) have put forward a new topology which combines buck and
yback converter to eliminate the dead zone. Zhang, Zhao, Zhao, and Wu (2017)
have proposed a topology which combines buck converter with yback converter.
Yao et al. (2017) have proposed an injecting third harmonic method to realize high
PF. Memon, Yao, Chen, Guo, and Hu (2017) have put forward a control scheme
is put forward to improve input PF. Memon et al., (2019) have introduced yback
converter to work with buck converter for boundary conduction mode (BCM) buck
converter to enhance PF. Memon et al., (2019) have introduced buck/boost converter
to work with buck converter for BCM buck converter to enhance PF. Memon et al.,
(2019) have proposed control technique to improve input PF of integrated buck-
yback converter.
In this paper, a variable on-time control (VOTC) strategy is introduced for critical
conduction mode (CRM) buck-buck/boost converter to attain high eciency with
simple structure, minimum losses and minimum component cost. It requires one
bridge rectier (BR) and for passing the low frequency current to reduce losses, EMI
lter is located after BR.
The analysis of the operating principle of buck converter is discussed with traditional
control (COTC) scheme in Section 2. The VOTC is put forward in Section 3 to attain
eciency. In Section 4, power loss analysis is given. Section 5 deals with simulation
results and the conclusion are given in Section 6.
2. OPERATION ANALYSIS OF CRM BUCKBUCK/BOOST
PFC CONVERTER
Figure 1 illustrates the schematic diagram of buck-buck/boost converter. The major
components in the power circuit are: Bridge rectier (BR); an inductor (L); a buck
switch (Q
b
); a buck/boost switch (Q
b/b
), a freewheeling diode (D
fw
), an output capacitor
(Co), etc.
The operating time period between buck and buck/boost converter depends on the
boundary voltage, whose value is little more as compared to output voltage (Vo). The
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converter operates in buck/boost mode as the input voltage (v
in
) is lower than V
o
and
in buck mode for opposite condition (i-e v
in
>V
boundary
). Thus, the operating principle of
the converter can be divided into two cases.
C
o
+
-
D
1
D
2
D
3
D
4
Q
b/b
D
fw
Q
b
i
in
v
in
L
R
L
LC
Filter
D
sk
v
g
+
-
R
1
R
2
sin
m
kV q
R
S_1
R
S_2
Figure 1. Schematic diagram of a CRM buck-buck/boost PFC converter.
The instantaneous and rectied input voltage during half line cycle can be given as:
(1)
Whereas V
m
represent the input voltage amplitude, θ represent the input voltage
angular frequency.
The converter is operating in buck mode when v
in
>V
boundary
. The buck/boost switch
(Q
b/b
) remain closed while buck switch (Q
b
) keeps switching.
The maximum value of the inductor current and the average value of input current
when the buck switch is conducting is respectively given as:
(2)
(3)
The converter is operating in buck/boost mode when v
in
<V
boundary
. The buck/boost
switch (Q
b/b
) keeps switching, while buck switch (Q
b
) remains closed.
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Same as (2-3), the peak value of primary inductor and the average value of input
current when Q
b/b
is switching is expressed respectively as:
(4)
(5)
By combining (3) and (5), the input current of the converter with traditional control
is expressed as:
(6)
The conducting angle of Q
b
and Q
b/b
respectively given as:
(7)
(8)
Where θ
0
is the boundary angle between buck and buck/boost converter and is equal
to arcsin V
boundary
/V
m.
The average input power can be calculated from (1) and (6) as:
(9)
From (9), t
on
can be determined by assuming the eciency to be 100% as:
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(10)
3. PROPOSED CONTROL SCHEME TO ATTAIN HIGH
EFFICIENCY
For high eciency and power balance, the input current must be:
(11)
By combining (6) and (11), we can get required on-time of both switches as:
(12(a))
(12(b))
The input power with put forward control scheme is given as:
(13)
The value of u
on
is got as by assuming eciency to be 100%
(14)
4. POWER LOSS ANALYSIS
The rms current of the on time period, i.e., the rms current of switch Q
b
and Q
b/b
can be got as:
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(15(a))
(15(b))
The rms current of the o time period can be determined as:
(15(c))
(15(d))
Where:
(16)
While Q
b
and Q
b/b
is on and o, the current ows through the winding of the inductor,
whose rms current is:
(17(a))
(17(b))
4.1. BRIDGE RECTIFIER LOSS
Bridge rectier loss can be calculated by using below formula:
(18(a))
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(18(b))
KBL10 is adopted as the rectier bridge, whose forward voltage drop V
FD
is 0.9 V.
The input current with traditional and proposed control scheme is given as:
(19(a))
(19(b))
4.2. CONDUCTION LOSSES OF THE SWITCHES
The losses due to conduction of switches can be got as:
(20(a))
(20(b))
R
DS(On)
for the switch 20N60C3 is 0.19 Ω and the value is found from datasheet.
4.3. TURN OFF LOSSES OF THE SWITCHES
The turn o losses of buck and buck/boost switch with traditional and proposed
control scheme can be determined as:
(21(a))
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(21(b))
The value of turn o fall time can be got from the datasheet which is 12ns for CMOS
20N60C.
The peak value of inductor current with both control scheme is given as:
(22(a))
(22(b))
The switching frequency in case of both control schemes can be found as:
(23(a))
(23(b))
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The value of switching frequency is got as:
(24(a))
(24(b))
4.4. COPPER LOSS OF THE INDUCTOR
The inductor’s copper loss with traditional and proposed control scheme is given as:
(25(a))
(25(b))
The equivalent resistance of the copper wire is 0.156Ω.
4.5. CORE LOSS OF THE INDUCTOR
The inductor’s core loss with traditional and proposed control scheme is calculated
as:
(26(a))
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(26(b))
(26(c))
(26(d))
4.6. CONDUCTION LOSS OF THE FREEWHEELING DIODE
The conduction loss caused by freewheeling diode is given as:
(27(a))
(27(b))
The forward voltage drop for freewheeling diode MUR 1560 is 0.67.
4.7. THE THEORETICAL EFFICIENCY
The theoretical eciency in case traditional and proposed control scheme can be
calculated by using below formula:
(28(a))
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(28(b))
Based on above analysis and parameter of the converter, loss distribution at
90VAC, 220VAC and theoretical eciency is illustrated in Figure 2-4 respectively.
It can be observed that by using proposed control scheme, the overall losses of the
converter are reduced, and the eciency is increased
Trad
Prop
0.0
1.5
3.0
4.5
6.0
0
1
2
3
4
5
6
Figure 2. Loss distributions at 90VAC.
0
1
2
3
4
5 6
0.0
0.9
1.8
2.7
3.6
Prop
Trad
Figure 3. Loss distributions at 220VAC.
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Figure 4. Efciency at universal input voltage.
5. SIMULATION VERIFICATION
For verifying the eectiveness of proposed strategy, simulations are carried out. The
input voltage range is 90-264VAC, and the output is 80V. For ensuring the current to
be in CRM, L6561 IC is used. All the components in the circuit are selected as idea.
Figure 5 and Figure 6 show the simulation waveforms of v
in
and i
in
of the converter
with traditional and proposed control scheme at 220VAC inputs, respectively. It can
be observed that the input current with proposed control scheme is less in magnitude
as compared to current with traditional control strategy. So the overall conduction
losses will be less in case of VOTC as compared to COTC.
Figure 7 shows the switches’ gate drive signals of the converter, from which in both
types of control schemes, the converter operates either in buck mode or in buck/
boost mode depending on the boundary voltage between them
Figure 5. v
in
& i
in
with traditional control.
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Figure 6. v
in
&i
in
with proposed control.
v
d_buck/boost
v
d_buck
v
in
V
boundary
Figure 7. Switches’ gate drive signals.
6. CONCLUSION
When the on-time is constant for buck-buck/boost converter, the conduction and
switching losses are more because the rms and peak value of the inductor current
is more. So, the eciency is low. Thus, in this paper a control scheme is proposed
to attain high eciency with simple structure, minimum losses and minimum
component cost. Simulation results are presented for the verication of the analysis.
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REFERENCES
Alonso, J. M., Dalla Costa, M. A., & Ordiz, C. (2008). Integrated buck-yback
converter as a high-power-factor o-line power supply. IEEE Transactions on Industrial
Electronics, 55(3), 1090-1100. doi: https://doi.org/10.1109/TIE.2007.908530
Dalla Costa, M. A., Alonso, J. M., Miranda, J. C., García, J., & Lamar, D.
G. (2008). A single-stage high-power-factor electronic ballast based on integrated
buck yback converter to supply metal halide lamps. IEEE Transactions on Industrial
Electronics, 55(3), 1112-1122. doi: https://doi.org/10.1109/TIE.2007.909729
Gacio, D., Alonso, J. M., Calleja, A. J., Garcia, J., & Rico-Secades, M. (2011). A
universal-input single-stage high-power-factor power supply for HB-LEDs based
on integrated buck-yback converter. IEEE Transactions on Industrial Electronics,
58(2), 589-599. doi: https://doi.org/10.1109/TIE.2010.2046578
Gacio, D., Alonso, J. M., Garcia, J., Campa, L., Crespo, M. J., & Rico-
Secades, M. (2012). PWM series dimming for slow-dynamics HPF LED drivers:
The high-frequency approach. IEEE Transactions on Industrial Electronics, 59(4),
1717-1727. doi: https://doi.org/10.1109/TIE.2011.2130503
García, O., Cobos, J. A., Prieto, R., Alou, P., & Uceda, J. (2003). Single phase
power factor correction: A survey. IEEE Transactions on Power Electronics, 18(3), 749-
755. doi: https://doi.org/10.1109/TPEL.2003.810856
Langella, R., Testa, A., & Alii, E. (2014). IEEE recommended practice and
requirements for harmonic control in electric power systems. In IEEE Std 519-
2014 (Revision of IEEE Std 519-1992), 1-29. doi: https://doi.org/10.1109/
IEEESTD.2014.6826459
Memon, A. H., Yao, K., Chen, Q., Guo, J., & Hu, W. (2017). Variable-on-time
control to achieve high input power factor for a CRM-integrated buck-yback
PFC converter. IEEE Transactions on Power Electronics, 32(7), 5312-5322. doi:
https://doi.org/10.1109/TPEL.2016.2608839
216
217
Edición Especial Special Issue Noviembre 2019
DOI: http://dx.doi.org/10.17993/3ctecno.2019.specialissue3.201-219
Memon, A. H., & Yao, K. (2018). UPC strategy and implementation for buck-
buck/boost PF correction converter. IET Power Electronics, 11(5), 884-894. doi:
https://doi.org/10.1049/iet-pel.2016.0919
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. doi: https://doi.org/10.1109/
ACCESS.2018.2879804
Memon, A. H., Pathan, A. A., Kumar, M., Sahito, A. A J., & Memon, Z. A.
(2019). Integrated buck-yback converter with simple structure and unity power
factor. Indian Journal of Science and Technology, 12(17). doi: https://doi.org/10.17485/
ijst/2019/v12i17/144612
Memon, A. H., Memon, Z. A., Shaikh, N. N., Sahito, A. A., & Hashmani, A.
A. (2019). Boundary conduction mode modied buck converter with low input
current total harmonic distortion. Indian Journal of Science and Technology, 12(17).
doi: https://doi.org/10.17485/ijst/2019/v12i17/144613
Memon, A. H., Shaikh, N. N., Kumar, M., & Memon, Z. A. (2019). Buck-buck/
boost converter with high input power factor and non-oating output voltage.
International Journal of Computer Science and Network Security, 19(4), 299-304. Retrieved
from: http://paper.ijcsns.org/07_book/201904/20190442.pdf
Singh, B., Singh, S., Chandra, A., & Al-Haddad, K. (2011). Comprehensive
study of single-phase AC-DC power factor corrected converters with high-
frequency isolation. IEEE transactions on Industrial Informatics, 7(4), 540-556. doi:
https://doi.org/10.1109/TII.2011.2166798
Spiazzi, G., & Buso, S. (2000). Power factor pre regulators based on combined
buck-yback topologies. IEEE transactions on Power Electronics, 15(2), 197-204. doi:
https://doi.org/10.1109/63.838091
Xie, X., Zhao, C., Lu, Q., & Liu, S. (2013). A novel integrated buck-yback
nonisolated PFC converter with high power factor. IEEE Transactions on Industrial
Electronics, 60(12), 5603-5612. doi: https://doi.org/10.1109/TIE.2012.2232256
218
219
3C Tecnología. Glosas de innovación aplicadas a la pyme.3C Tecnología. Glosas de innovación aplicadas a la pyme. ISSN: 2254–4143
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. doi: https://doi.org/10.1109/TPEL.2017.2657883
Zhang, J., Zhao, C., Zhao, S., & Wu, X. (2017). A family of single-phase hybrid
step-down PFC converters. IEEE Transactions on Power Electronics, 32(7), 5271-
5281. doi: https://doi.org/10.1109/TPEL.2016.2604845
International Electrotechnical Commission. (2014). Part 3-2: Limits-Limits
for harmonic current emissions (equipment input current≤16 A per phase).
International Standard IEC, 61000-3-2.
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219
Edición Especial Special Issue Noviembre 2019
DOI: http://dx.doi.org/10.17993/3ctecno.2019.specialissue3.201-219