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MODIFIED VARIABLE ON-TIME CONTROL SCHEME
TO REALIZE HIGH POWER FACTOR FOR AC/DC
INTEGRATED BUCK-BOOST CONVERTER
Abdul Hakeem Memon
Institute of Information and Communication Technologies (IICT),
Mehran UET, Jamshoro, Sindh, (Pakistan).
E-mail: hakeem.memon@faculty.muet.edu.pk
ORCID: https://orcid.org/0000-0001-8545-3823
Nazia Memon
Institute of Information and Communication Technologies (IICT),
Mehran UET, Jamshoro, Sindh, (Pakistan).
E-mail: naziamemon52@gmail.com
ORCID: https://orcid.org/0000-0003-2919-9220
Zubair Ahmed Memon
Institute of Information and Communication Technologies (IICT),
Mehran UET, Jamshoro, Sindh, (Pakistan).
E-mail: zubair.memon@faculty.muet.edu.pk
ORCID: https://orcid.org/0000-0001-5967-3152
Recepción:
09/12/2020
Aceptación:
10/03/2021
Publicación:
07/05/2021
Citación sugerida:
Memon, A. H., Memon, N., y Memon, Z. A. (2021). Modied variable on-time control scheme to
realize high power factor for AC/DC integrated buck-boost converter. 3C Tecnología. Glosas de innovación
aplicadas a la pyme, Edición Especial, (mayo 2021), 67-81. https://doi.org/10.17993/3ctecno.2021.
specialissue7.67-81
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ABSTRACT
In today’s modern era low power factor (PF) is major issue in the eld of power electronics
which has made our life, simpler, easier and comfortable. However, with this comfort and
easiness this technology brings power quality issues because it is centered on solid-state
devices. These issues introduce harmonic contained current or distorted current which
has several drawbacks like high power loss, voltage distortion and EMI compatibility issues
etc. The conventional boundary conduction mode (BCM) integrated buck-boost converter
(BBC) operating with constant on-time control (COT) control scheme have low PF with high
total harmonic distortion (THD) because of harmonic contained input current waveform.
So, in order to make the input current waveform as a sinusoidal by changing the on-time of
only buck switch, a modied variable-on-time (VOT) control scheme for Integrated BBC
is proposed in this paper. The VOT control scheme can achieve high PF with low THD
by utilizing the input and output voltage to modulate the on-time of only buck switch.
The theoretical analysis is given, and the simulation results conrm the advantages of
the proposed control scheme. The object of the research paper is to propose the control
scheme to realize unity PF for CRM buck converter by only modulating the on-time of
buck switch. The research methodology is based on: Input PF analysis of buck converter
with traditional control scheme; Introduction of proposed control scheme; comparative
analysis and simulation results to show the eectiveness of proposed control scheme.
KEYWORDS
Buck-Boost Converter (BBC), Constant On-Time Control (COT), Variable-On-Time
(VOT), Power Factor (PF), Total Harmonic Distortion (THD), Electromagnetic Interference
(EMI).
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1. INTRODUCTION
Power electronic technology is employed in various sorts of modern equipment’s which has
made our life, simpler, easier and comfortable. However, with this comfort and easiness
this technology brings power quality issues because it is centered on solid-state devices.
These issues introduce harmonic contained current or distorted current which has several
drawbacks like high power loss, voltage distortion and EMI compatibility issues etc.
Therefore, the standards are set by various industrious like IEC61000-3-2 limit and IEEE
519 (IEC Standard, 61000-3, n.d.); Langella, Testa, & Alii, 2014) to limit these harmonics.
In order to meet relevant harmonic standard and reducing input current distortion, various
researchers have proposed dierent types of power factor correction (PFC) converters
(García et al., 2003; Singh et al., 2011; Memon et al., 2016; Memon et al., 2018a, 2018b;
Memon et al., 2019a, 2019b, 2019c, 2019d, 2019e; Memon et al., 2020a, 2020b, 2020c).
The DC/DC converters or choppers such as buck, boost and buck-boost etc. are normally
employed for PFC application.
Each converter has its own advantages and disadvantages. The boost converter is good
selection for PFC due to various advantages like high PF, less current ripples and high
eciency (Yang et al., 2011), However, its eciency is low at low input line due to use
of more duty-cycle when the input is 90Vrms and the output is 400 V . The buck-boost
converter can step up or step down the input voltage and its characteristics are better as
compared to SEPIC, Flyback and CUK converter. However, its eciency is low, voltage
and current stress is more compared to boost and buck converter because the energy of
output is charged from inductor (Chen & Maksimović, 2010; Hwang & Park, 2012).
The buck converter now days have attracted the attention of the many researchers (Mahdavi
& Farzanehfard, 2010; Liu et al., 2014; Wu et al., 2011; Wu et al., 2012; Memon et al., 2016;
Memon et al., 2018a, 2018b; Memon et al., 2019a, 2019b, 2019c, 2019d, 2019e; Liu et al.,
2020). It can maintain high eciency at all input voltages. It also oers other advantages
like cost reduction, low output voltage, protection against inrush current, low stress on the
switch and life time improvement.
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The input PF of buck converter in low because of dead zone in the average input current
that is present until input voltage is more than output voltage. It causes the input current to
contain large harmonic disturbances.
For modifying the performance of buck converter, various researchers have proposed various
techniques and control schemes. Many research attempts have been conducted to improve
the performances of the conventional buck PFC converter (Mahdavi & Farzanehfard, 2010;
Liu et al., 2014; Wu et al., 2011; Wu et al., 2012; Memon et al., 2016; Memon et al., 2018a,
2018b; Memon et al., 2019a, 2019b, 2019c, 2019d, 2019e; Liu et al., 2020).
This paper is divided into six sections. In section 2, the operation states of BCM IBBC
are analyzed with traditional constant on-time control scheme (COTCS). The introduced
VOTCS is discussed in section 3. Then the comparative analysis is discussed in section 4 in
terms of PF. In section 5, the eectiveness of proposed topology is evaluated by simulation
results. Finally, some conclusions are drawn in section 6.
2. RESEARCH METHODOLOGY
The research methodology is based on:
1. Mathematical analysis of the operating principle of the traditional control scheme
for BCM IBBC with the help of MATHCAD software.
2. Analysis of input PF of BCM integrated BBC.
3. Introducing the proposed control scheme to obtain high PF with low THD.
4. Comparative analysis of the converter for COT control scheme and VOT control
scheme strategy in terms of input PF and THD.
5. Developing the simulation model of the converter with traditional and proposed
control scheme with the help of MATLAB software.
6. Conrming the results.
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3. CONVENTIONAL COTCS FOR BCM IBBC
Figure 1 shows the main circuit of the IBBC. It is a buck converter in series with a boost
converter with a common inductor. It works in buck mode with the boost switch opened
when the instantaneous input line voltage is higher than the boundary voltage and otherwise
in boost mode with buck switch closed. The boundary voltage is set a little higher than the
output voltage. The converter operates in BCM and its working principle can be analyzed
in two cases.
Figure 1. Schematic Diagram of IBBC.
Source: (Memon et al., 2019).
The input voltage and rectied input voltage is expressed as
(1)
(2)
where V
rms
is the rms value
The IBBC is working in buck mode until input voltage is more than boundary voltage.
Thus Q
buck
is operating while Q
boost
is o
When buck switch is on, the inductor voltage is expressed as
(3)
where
So its peak value is
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(4)
where t
on
is the on-time of the switch.
While Q
buck
is o, the inductor is discharged through load.
(5)
For each switching cycle, the value of o-time is calculated from inductor’s volt-second
balance
(6)
From (3) and (5), the following relation is obtained
(7)
In addition
(8)
Substituting (6) into (7)
(9)
The value of average input current for buck converter is got from
(10)
Substituting (3) and (8) into (9)
(11)
The IBBC is working in boost mode until input voltage is less than boundary voltage. Thus
Q
boost
is operating while Q
buck
is o
When boost switch is on, the inductor voltage is given as
(12)
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Same as (6), for each switching cycle, the value of o-time is calculated from inductor’s
volt-second balance
(13)
Substituting (13) into (8), we get
(14)
The value of average input current for boost converter is determined as
(15)
Combining (12) and (14), we get
(16)
Based on above analysis, the average input current of the IBBC with COTCS is as following.
(17)
Based on (1) and (16), The input power of the IBBC is expressed as
(18)
Now t
on
can be calculated by assuming the eciency of IBBC as 100%
(19)
And input power factor can be calculated as
(20)
Based on (16-20) and specication, the curve of the input PF can be drawn and is given in
Figure 2 from which it can be observed that the input PF is not unity for the wide range of
the input voltage.
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Figure 2. Input PF of COTCS [Eq: 17 to 20; Using Mathcad software].
4. PROPOSED VOTCS FOR BCM IBBC
For obtaining unity PF for the buck converter, the on-time of Q
buck
in (11) should vary as
(21)
where k
on1
is a constant
Substituting (21) into (11), the average input current of the buck converter is
(22)
From (22), it can be seen that if the on-time of the buck converter varies as (21), the input
current waveform looks like pure sinusoidal and the PF is unity
From (16), it is clear that the input current of the boost converter is already sinusoidal. So
there is no need of the variation of the on-time of the Q
boost
(23)
k
on2
is a constant.
The average input current of the IBBC with VOTCS is
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(24)
Because of the power balance of the input and output, the input current for the unity PF
can be expressed as
(25)
Based on (25-26), the input current at
can be written as
(26)
From (26), it can be concluded that
(27)
(28)
From (27-28) it can be summarized as k
on1
= k
on2
= k
on
Hence, the input current of the IBBC
with VOTCS is
(29)
Equation (29) demonstrates that input current of IBBC with VOTCS is pure sinusoidal.
Thus unity PF can be realized by using proposed control scheme.
5. COMPARATIVE ANALYSIS
From (14), the input PF curve with proposed control scheme is shown in Figure 3 which also
includes the PF values with traditional control scheme of Figure 2. It can be concluded that
the PF of the converter with proposed control is higher as compared to COTC. The values
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of input PF for COTCS & VOTCS along with percentage improvement is written in Table
1. It can conclude that improvement at low line is more as compared to high line.
Figure 3. Input PF comparison between COTCS & VOTCS [Eq: 17 to 20 & 22 to 29; Using Mathcad software].
Table 1. Input PF comparison between COTCS & VOTCS [Eq: 17 to 20 & 22 to 29; Using Mathcad software].
S. No Input Voltage PF(COTCS) PF(VOTCS) % Improvement
1 90 V
rms
0.755 1 32.499
2 110 V
rms
0.807 1 23.887
3 130 V
rms
0.852 1 17.309
4 150 V
rms
0.884 1 13.14
5 170 V
rms
0.905 1 10.485
6 190 V
rms
0.920 1 8.737
7 210 V
rms
0.93 1 7.55
8 230 V
rms
0.937 1 6.723
9 250 V
rms
0.942 1 6.136
10 264 V
rms
0.945 1 5.827
6. SIMULATION RESULTS
In order to verify the eectiveness of VOT control scheme, simulations results are given.
The range of input voltage is 90-264 V
rms
. The output voltage is selected as 90 V. The control
IC 6561 will ensure the current to be in BCM. Ideal components are used in simulation
Figure 4 illustrates the waveforms of input voltage and boundary voltage versus gate drive
signal of integrated BBC. It indicates only one converter is conducting at a time depending
on the boundary voltage.
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Figure 4. V
in
,V
d_buck
and V
d_boost
[Saber software].
Figure 5 and Figure 6 show the simulation waveforms of v
in
, & i
in
of integrated BBC with
COT control scheme and VOT control scheme at 220VAC inputs, respectively. It can be
conducted that current is almost sinusoidal in case of VOTCS as compared to COTCS.
Thus, VOTCS can attain unity PF.
Figure 5. Input voltage and current of IBBC with COTCS [Saber software].
Figure 6. Input voltages and current of IBBC with VOTCS [Saber software].
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7. CONCLUSIONS
In this paper, integrated BBC is presented and analyzed. It is composed of buck and boost
converter. With COT control scheme, the input PF of the IBBC is low. In order to attain
high input PF, VOT control scheme is proposed. Simulation results are presented for the
verication of the analysis.
REFERENCES
Chen, F. Z., & Maksimović, D. (2010). Digital control for improved eciency and reduced
harmonic distortion over wide load range in boost PFC rectiers. IEEE Transactions on
Power Electronics, 25(10), 2683-2692. https://doi.org/10.1109/TPEL.2010.2050702
IEC Standard, 61000-3. (n.d.). Electromagnetic compatibility (EMC). Limits for Harmonic Current
Emissions (Equipment input current≤ 16A per phase).
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.
https://doi.org/10.1109/TPEL.2003.810856
Hwang, T. S., & Park, S. Y. (2012). Seamless boost converter control under the critical
boundary condition for a fuel cell power conditioning system. IEEE Transactions on
Power Electronics, 27(8), 3616-3626. https://doi.org/10.1109/TPEL.2012.2185250
Langella, R., Testa, A., & Alii, E. (2014). IEEE recommended practice and requirements
for harmonic control in electric power systems. IEEE Std. 519-2014. IEEE.
Liu, X., Wan, Y., He, M., Zhou, Q., & Meng, X. (2020). Buck-Type Single-Switch
Integrated PFC Converter With Low Total Harmonic Distortion. IEEE Transactions
on Industrial Electronics, 6. http://doi.org/10.1109/TIE.2020.3007121
Liu, X., Xu, J., Chen, Z., & Wang, N. (2014). Single-inductor dual-output buck–boost
power factor correction converter. IEEE transactions on Industrial electronics, 62(2), 943-
952. https://doi.org/10.1109/TIE.2014.2334659
79
https://doi.org/10.17993/3ctecno.2021.specialissue7.67-81
3C Tecnología. Glosas de innovación aplicadas a la pyme. ISSN: 2254 – 4143 Edición Especial Special Issue Mayo 2021
Mahdavi, M., & Farzanehfard, H. (2010). Bridgeless SEPIC PFC rectier with reduced
components and conduction losses. IEEE Transactions on Industrial Electronics, 58(9),
4153-4160. https://doi.org/10.1109/TIE.2010.2095393
Memon, A. H., & Yao, K. (2018a). UPC strategy and implementation for buck–buck/
boost PF correction converter. IET Power Electronics, 11(5), 884-894. http://doi.
org/10.1049/iet-pel.2016.0919
Memon, A. H., Baloach, M. H., Sahito, A. A., Soomro, A. M., & Memon, Z. A.
(2018b). Achieving High Input PF for CRM Buck-Buck/Boost PFC Converter. IEEE
Access, 6, 79082-79093. http://doi.org/10.1109/ACCESS.2018.2879804
Memon, A. H., Memon, M. A., Memon, Z. A., & Hashmani, A. A. (2019a). 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. http://
dx.doi.org/10.17993/3ctecno.2019.specialissue3.201-219
Memon, A. H., Memon, Z. A., Shaikh, N. N., Sahito, A. A., & Hashmani, A. A.
(2019b). Boundary conduction mode modied buck converter with low input current
total harmonic distortion. Indian Journal of Science and Technology, 12. https://doi.
org/10.17485/ijst/2019/v12i17/144613
Memon, A. H., Nizamani, M. O., Memon, A. A., Memon, Z. A., & Soomro, A.
M. (2019c). 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. http://dx.doi.org/10.17993/3ctecno.2019.
specialissue3.185-199
Memon, A. H., Noonari, F. M., Memon, Z., Farooque, A., & Uqaili, M. A. (2020a).
AC/DC critical conduction mode buck-boost converter with unity power factor. 3C
Tecnología. Glosas de innovación aplicadas a la pyme. Edición Especial, Abril 2020, 93-105.
http://doi.org/10.17993/3ctecno.2020.specialissue5.93-105
Memon, A. H., Pathan, A. A., Kumar, M., & Sahito, A. J., & Memon, Z. A. (2019d).
Integrated buck-yback converter with simple structure and unity power factor.
80
https://doi.org/10.17993/3ctecno.2021.specialissue7.67-81
3C Tecnología. Glosas de innovación aplicadas a la pyme. ISSN: 2254 – 4143 Edición Especial Special Issue Mayo 2021
Indian Journal of Science and Technology, 12. https://doi.org/10.17485/ijst/2019/
v12i17/144612
Memon, A. H., Shaikh, N. N., Kumar, M., & Memon, Z. A. (2019e). 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. http://paper.ijcsns.
org/07_book/201904/20190442.pdf
Memon, A. H., Yao, K., Chen, Q., Guo, J., & Hu, W. (2016). 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. http://doi.org/10.1109/
TPEL.2016.2608839
Memon, A. H., Samejo, J. A., Memon, Z. A., & Hashmani, A. A. (2020b). Realization
Of Unity Power Factor For Ac/Dc Boundary Conduction Mode Flyback Converter
With Any Specic Turn’s Ratio. Journal of Mechanics Of Continua And Mathematical
Sciences, (spl6). 10.26782/jmcms.spl.6/2020.01.00014. https://doi.org/10.26782/
jmcms.spl.6/2020.01.00014
Memon, A. H., Shaikh, S. A., Memon, Z. A., Memon, A. A., & Memon, A. A. (2020c).
DCM Boost Converter with High Eciency. Journal Of Mechanics Of Continua And
Mathematical Sciences, (spl6). https://doi.org/10.26782/jmcms.spl.6/2020.01.00006
Singh, B., Singh, B. N., Chandra, A., Al-Haddad, K., Pandey, A., & Kothari, D. P.
(2003). A review of single-phase improved power quality AC-DC converters. IEEE
Transactions on industrial electronics, 50(5), 962-981. https://www.researchgate.net/
publication/3218193_A_review_of_single-phase_improved_power_quality_AC-
DC_converters
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. https://doi.
org/10.1109/TPEL.2011.2169812
81
https://doi.org/10.17993/3ctecno.2021.specialissue7.67-81
3C Tecnología. Glosas de innovación aplicadas a la pyme. ISSN: 2254 – 4143 Edición Especial Special Issue Mayo 2021
Wu, X., Yang, J., Zhang, J., & Xu, M. (2011). Design considerations of soft-switched
buck PFC converter with constant on-time (COT) control. IEEE transactions on power
electronics, 26(11), 3144-3152. https://doi.org/10.1109/TPEL.2011.2145391
Yang, F., Ruan, X., Yang, Y., & Ye, Z. (2011). Interleaved critical current mode boost
PFC converter with coupled inductor. IEEE Transactions on power electronics, 26(9),
2404-2413. https://doi.org/10.1109/TPEL.2011.2106165