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VARIABLE ON-TIME CONTROL SCHEME TO ACHIEVE
HIGH EFFICIENCY FOR AC/DC BORDER LINE CURRENT
MODE BUCK CONVERTER
Abdul Hakeem Memon
IICT, Mehran UET, Jamshoro, Sindh, (Pakistan).
E-mail: hakeem.memon@faculty.muet.edu.pk
ORCID: https://orcid.org/0000-0001-8545-3823
Asif Zahoor Shaikh
IICT, Mehran UET, Jamshoro, Sindh, (Pakistan).
E-mail: asifzahoorshaikh@gmail.com
ORCID: https://orcid.org/0000-0003-2999-6772
Zubair Ahmed Memon
IICT, Mehran UET, Jamshoro, Sindh, (Pakistan).
E-mail: zubair.memon@faculty.muet.edu.pk
ORCID: https://orcid.org/0000-0001-5967-3152
Anwar Ahmed Memon
IICT, Mehran UET, Jamshoro, Sindh, (Pakistan).
E-mail: anwar.memon@faculty.muet.edu.pk
ORCID: https://orcid.org/0000-0001-6600-204X
Recepción: 15/09/2021 Aceptación: 12/11/2021 Publicación: 14/02/2022
Citación sugerida:
Memon, A. H., Shaikh, A. Z., Memon, Z. A., y Memon, A. A. (2022). Variable on-time control
scheme to achieve high eciency for AC/DC border line current mode buck converter. 3C
Tecnología. Glosas de innovación aplicadas a la pyme, Edición Especial, (febrero 2022), 181-195. https://doi.
org/10.17993/3ctecno.2022.specialissue9.181-195
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ABSTRACT
The Buck power factor improvement converter (BPFIC) is much better topology because of
having advantages like less inrush current, less voltage gain ratio, gives less voltage output
ripple and steps down the voltage even with high input voltage, protection from short circuit
and its single active switch operation makes it attractive. However borderline current mode
(BCM) operated with xed on-time control technique (FOCT) results in its low eciency.
The main reason of low eciency is due to high conduction and switching losses which
occur due to high peak and rms inductor current. In this paper, varying on-time control
technique (VOCT) has been implemented that reduces the peak value of current which
results in improved eciency. In the proposed research, work is related to BPFIC operating
in BCM because BCM has many advantages like no reverse recovery of diode, and zero
current turning o the switch. To verify the eectiveness of proposed control technique,
comparative analysis is obtained between both the two control techniques using SABER
SIMULATOR. It is found that VOCT improves the converter’s eciency compared to
FOCT.
KEYWORDS
Buck Power Factor Improvement Converter (BPFIC), Borderline Current Mode (BCM),
Fixed On-Time Control Technique (FOCT), Varying On-Time Control Technique
(VOCT), Saber Simulation.
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1. INTRODUCTION
The increasing need of electronic devices (requires AC to DC conversion) have resulted
in harmonic content produced by non-linear elements (diodes and thyristors) of electronic
devices connected to AC supply system should be in such limit that it meets regulatory
standard. This requirement is fullled by using active power factor improvement (PFI) circuits
that shape the input phase current to be sinusoidal in nature and in phase with input phase
voltages. The combined eect of non-linear loads results in problem of serious harmonic
distortion in electrical distribution system and its result is poor Power Factor (PF) and power
quality, voltage distortion and low eciency (Azazi et al., 2010). PFI can be categorized into
active and passive types. Compared with a Passive Power Factor Improvement Converters
(PFIC), an active PFIC can achieve a high PF (Nagaraju & Krishnaveni, 2017). The PFIC
are being widely used in ac–dc power conversions to get power factor near to unity and to
reduce harmonic distortion so as to meet the standards like IEC61000-3-2 and IEEE 519
(Yao et al., 2011).
Amongst PFIC, buck Power Factor Improvement Converter (BPFIC) is much better
topology because of having advantages like less inrush current, less voltage gain ratio,
gives less voltage output ripple and steps down the voltage even with high input voltage,
protection from short circuit and its single active switch operation makes it attractive.
However, because of dead zone in the input current of (BPFIC) has resulted in poor PF
and other power quality issues
For enhancing the performance of BPFIC, dierent authors have proposed several control
techniques (Endo, Yamashita, & Sugiura, 1992; Memon et al., 2021).
In this paper, Variable On-Time Technique (VOCT) is implemented to reduce the
conduction and switching losses occurred in borderline current mode BPFIC caused by
peak and rms value of inductor current.
This paper is divided into six sections. First section gives detailed analysis of traditional
BPFIC. In, second section VOCT is implemented to improve converter’s eciency. Third
section represents loss analysis caused by conduction and switching losses. Fourth section
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shows simulation verication to conrm the eectiveness of proposed control technique. In
last section conclusion is discussed.
2. METHODOLOGY
The research methodology is based on:
1. Mathematical analysis of the operating principle of the control schemes for
Borderline Current Mode (BCM) Buck Power Factor Improvement Converter
(BPFIC) for FOCT with the help of MATHCAD converter.
2. Introducing the Varying On-Time Control Technique (VOCT) to obtain high
eciency.
3. Comparative analysis of the converter for FOCT and VOCT strategy.
4. Developing the simulation model of BCM Buck converter with the help of SABER
software.
5. Conrming the results.
2.1. WORKING ANALYSIS OF TRADITIONALLY USED BCM BPFIC
Figure 1 shows the circuit of Buck Power Factor Improvement Converter (BPFIC) that
can be operated in borderline current mode (BCM). The working of the BPFIC will be
analyzed in detail with the help of equations in order to nd out the expression of xed
on-time technique (FOCT).
Figure 1. Circuit Diagram of BPFIC.
Source: (Memon et al., 2021).
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The instantaneous value of source voltage at the input and output of bridge is expressed as
(1)
BPFIC operated with BCM has two switching cycles.
The inductor is charged from supply voltage when the buck switch is ON, as indicated in
Figure 2 (First switching cycle).
Figure 2. BPFIC when switch is on.
Source: (Memon et al., 2018).
The maximum current owing through inductor for BPFIC with FOCT is
(2)
The inductor is discharged through load when the buck switch is OFF, as showed in Figure
3 and the expression is given in (3) (Second switching cycle).
Figure 3. BPFIC when switch is off.
Source: own elaboration.
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(3)
The maximum current for charging and discharging is same as per energy conservation.
So, following relation is got
(4)
Similarly
(5)
By substituting (3) into (5) yields
(6)
The average input current for BPFIC with FOCT is calculated as
(7)
From (1) and (7), the input power of the BPFIC with FOCT is given
(8)
The value of ton_foct is expressed after supposing 100% eciency as
(9)
2.2. PROPOSED VOCT FOR BPFIC FOR ENHANCING EFFICIENCY
For improving the eciency for the BPFIC, the on-time of buck CMOS in (9) has to change
as
(10)
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where Mon is a constant
Replacing (10) into (7), the input current of the BPFIC is
(11)
The input power for BPFIC with VOCT is got as
(12)
Rearranging (12), we get
(13)
2.3. EFFICIENCY COMPARISON
2.3.1. POWER LOSS DUE TO BRIDGE RECTIFIER
The power loss due to bridge rectier in BPFIC with FOCT and VOCT is estimated as
(14(a))
(14(b))
The value of VFD for GBU 406 is 0.89.
2.3.2. CONDUCTED LOSSES BY CMOS (SWITCH)
The rms current owing through switch, when it is on is given as
(15)
The rms current of the o time period can be determined as
(16)
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The rms current due to switch on and o is calculated as
(17(a))
(17(b))
The losses due to conduction of switches can be got as
(18(a))
(18(b))
The resistance from drain to source is 0.188, which is from data sheet of 8N60.
2.3.3. SWITCH OFF LOSSES BY CMOS (SWITCH)
When the switch is o, the loss of BPFC with FOCT and VOCT is expressed as
(19(a))
(19(b))
Tf for 8N60 is 12ns.
2.3.4. COPPER LOSS OF THE BPFIC’S INDUCTOR
The inductor’s copper loss of BPFIC with FOCT and VOCT is given as
(20(a))
(20(b))
2.3.5. CORE LOSS OF BPFIC’S THE INDUCTOR
The inductor’s core loss of BPFIC with FOCT and VOCT is given as
(21(a))
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(21(b))
(21(c))
(21(d))
The value of core parameters can be found from Memon et al. (2018).
2.3.6. CONDUCTED LOSS BY FREEWHEELING DIODE
The conducted losses by freewheeling diode of BPFIC with FOCT and VOCT is got as
(22(a))
(22(b))
The forward voltage drop is 0.669 for MUR 860.
2.3.7. THE EFFICIENCY COMPARISON
The eciency of BCM BPFIC with FOCT and VOCT can be estimated as
(23(a))
(23(b))
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The calculated eciency of BCM BPFIC with FOCT and VOCT from (14-23) and
specication is depicted in Figure 4. It can be observed the eciency of BPFIC with VOCT
is more than FOCT.
Figure 4. Efciency at universal input voltage (Mathcad Graph from Eq. (14-23)).
Source: own elaboration.
3. SIMULATION RESULTS
In order to verify the eectiveness of VDCT, simulation verication is obtained using
MATLAB. 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.
In Figure 5, the peak of input current obtained in case of FOCT is more. The current
having more peak results in losses that degrades converter’s eciency whereas in Figure 6,
the peak of input current obtained in case of VOCT is less which reduces conduction and
switching losses hence converter’s performance is improved.
Figure 5. vin, and iin with FOCT (Simulation waveform).
Source: own elaboration.
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Figure 6. vin, and iin with VOCT (Simulation waveform).
Source: own elaboration.
4. CONCLUSIONS
The Buck Power Factor Improvement Converter (BPFIC) is much better topology because
of having many advantages. However Borderline Current Mode (BCM) operated with
Fixed On-Time Technique (FOCT) results in its low eciency. The main reason of low
eciency is due to high conduction and switching losses which occur due to high peak
and rms inductor current. In this paper, Varying On-Time Technique (VOCT) has been
implemented that reduces the peak value of current which results in improved eciency.
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