Boost Converter with Improved Voltage Conversion Ratio Using Bootstrap Capacitors and Boost Inductors

The International Journal Of Engineering And Science (IJES)
|| Volume || 5 || Issue || 8 || Pages || PP 51-56 || 2016 ||
ISSN (e): 2319 – 1813 ISSN (p): 2319 – 1805
www.theijes.com The IJES Page 51
Boost Converter with Improved Voltage Conversion Ratio Using
Bootstrap Capacitors and Boost Inductors
1
Vinny Babu, 2
Prof. Bindu Elias and 3
Dr. Bose Mathew Jose
1
PG Scholar, Department of Electrical and Electronics Engineering, Mar Athanasius College of Engineering,
Kothamangalam, Kerala
2,3
Professor, Department of Electrical and Electronics Engineering, Mar Athanasius College of Engineering,
Kothamangalam, Kerala
--------------------------------------------------------ABSTRACT-------------------------------------------------------------
In this paper, a high voltage boosting converter based on bootstrap capacitor and boost inductor is designed for
improving the voltage conversion ratio. This is based on the fact that the number of inductors and capacitors
are increased, and these inductors and capacitors are connected in series during the demagnetizing period,
thereby pumping the energy created by the input voltage and the energy stored in the inductors into the output
terminal. By changing the connection position of the anode of the diode and by using different pulse-width-
modulation control strategies, different voltage conversion ratios can be obtained. The boost converter is
controlled by PID controller. This makes a very high voltage conversion ratio than existing methods. Simulation
study has been carried out in MATLAB/Simulink.
Keywords: Boost converter, bootstrap capacitor, improved high voltage boosting converter, voltage conversion
ratio
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Date of Submission: 17 May 2016 Date of Accepted: 22 August 2016
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I. INTRODUCTION
As generally recognized, step-up converters have been widely used in many applications, such as battery
powering device, uninterruptible power supply (UPS), photovoltaic (PV) system, etc. requiring some circuits
transferring low voltages to high voltages used as input voltages for dc to ac converters. For the applications of
the power supply using the low voltage battery, analog circuits, such as RF ampliﬁer, audio ampliﬁer[2], etc.,
often need high voltage to obtain enough output power and voltage amplitude. This is achieved by boosting the
low voltage to the required high voltage. Therefore, in many 3C (consumer, communications, computer)
electronics, some converters are needed to supply one boosted voltage or more under a given low voltage,
especially for portable communications systems, such as MPEG-3 (MP3) players, Bluetooth devices, personal
digital assistant, etc.
A voltage-boosting converter, named as KY converter, provides low output voltage ripple and is very suitable
for supplying power to devices that must operate under low-ripple conditions [5]. In order to enlarge the output
voltages, additional components are added to KY converter. KY converter always operates in continuous
conduction mode (CCM). However, its ratio of the output voltage to the input voltage is one plus D, where D is
the duty cycle of the main switch. In certain converter topologies, a method of improving the voltage conversion
ratio is based on the fact that number of inductors is increased, and these inductors are connected in series
during the demagnetizing period, thereby pumping the energy created by the input voltage and the energy stored
in the inductors into the output terminal to obtain the high voltage conversion ratio [6].
II. IMPROVED HIGH VOLTAGE BOOSTING CONVERTER
A high voltage DC-DC boosting converters based on bootstrap capacitors and boost inductors with high voltage
conversion ratio. The converter based on the charge pump of the KY converter and the series boost converter.

Boost Converter With Improved Voltage Conversion Ratio Using Bootstrap Capacitors And Boost…
Fig.1. High Voltage Boosting Converter
Fig. 1.shows the high voltage boosting converter. In this circuit, diode D1 is connected to the cathode of diode
Db. The conversion ratio in CCM is (3+D)/(1-D). This converter contains three MOSFET switches S1, S2, S3,
two bootstrap capacitors Cb and Ce, three bootstrap diodes Db, D1, D2, One output diode Do, two inductors L1
and L2, one output capacitor Co, and one output resistor RL. Fig. 2. shows the improved high voltage boosting
converter. But in the case of improved high voltage boost converter contains five MOSFET switches S1, S2, S3,
S4 and S5, three bootstrap capacitors Cb1, Cb2 and Ce, four bootstrap diodes Db1, Db2, D1 and D2. The input and
output voltage is signified by Vi and Vo respectively. The voltage across Cb1, Cb2, Ce, D1 and D2 are shown by
Vcb1, Vcb2, Vce, VD1, and VD2, respectively. The currents flowing through L1, L2 and Do are denoted by iL1, iL2 and
iDo respectively.
Fig. 2. Improved High Voltage Boosting Converter
2.1. Basic Operating Principle
Mode 1 [t0-t1]: As shown in Fig.3. the switches S1, S3 and S5 are turned on, but S2 and S4 are turned oﬀ. Do is
reverse biased due to S5 being turned on but D1 and D2 are forward biased, thereby causing Ce to be abruptly
charged to Vi plus 2Vcb. Due to S1 being turned on, Db1 is reverse biased, thereby causing Cb1 to be discharged.
Db2 is reverse biased due to S3 being turned on, thereby causing Cb2 to be discharged. The voltages across L1 and
L2 are Vi plus Vcb, thereby causing L1,and L2 to be magnetized and Co releases energy to the output.
In this mode, the voltages across L1 and L2, VL1−ON and VL2−ON , can be written as
VL1−ON = Vi + VCb1 + VCb2 (1)
VL2−ON = Vi + VCb1 + VCb2 (2)

Fig. 3. Power flow of Improved High Voltage Boosting Converter operated in mode 1
Mode 2 [t1-t2]: As shown in fig.4.below, S1, S3 and S5 are turned off, but S2 and S4 are turned on. Due to S2
being turned on, Db1 is forward biased, thereby causing Cb1 to be abruptly charged to Vi. Due to S4 being turned
on, Db2 is forward biased, thereby causing Cb2 to be abruptly charged to Vi. At the same time, Vi plus the energy
stored in Ce, plus the energy stored in L1 and L2 supplies the load. The output voltage is boosted up and is much
higher than the input voltage.
Fig. 4. Power flow of Improved High Voltage Boosting Converter operated in mode 2
According to the voltage-second balance, the voltages VL1−OFF , VL2−OFF , and Vo in this mode can be expressed
to be
VL1−OFF =
−D
1−D
VL1−ON (3)
VL2−OFF =
−D
1−D
VL2−ON (4)
Vo = −VL1−OFF − VL2−OFF + Vi + VCe (5)
Since VCb and VCe are equal to Vi and 3Vi, respectively, (1), (2), and (5) can be rewritten as
VL1−ON = VL2−ON = 3Vi (6)
Vo = −VL1−OFF − VL2−OFF + 4Vi (7)
By substituting (6) into (3) and (4), VL1−OFF and VL2−OFF can be rewritten to be

VL1−OFF = VL2−OFF =
−D
1−D
3Vi (8)
Substituting (8) into (7) yields the following CCM voltage conversion ratio:
Vo
Vi
=
4+2D
1−D
(9)
III. SIMULATION MODELS AND RESULTS
Table1. Simulation Parameter of Improved High Voltage Boosting Converter
Fig.5. shows the simulation diagram of closed loop control of improved high voltage Boosting converter. in the
case of improved high voltage boost converter contains five MOSFET switches S1, S2, S3, S4 and S5, three
bootstrap capacitors Cb1, Cb2 and Ce, four bootstrap diodes Db1, Db2, D1 and D2. The input and output voltage is
signified by Vi and Vo respectively. The voltage across Cb1, Cb2, Ce, D1 and D2 are shown by Vcb1, Vcb2, Vce, VD1,
and VD2, respectively. The currents flowing through L1, L2 and Do are denoted by iL1, iL2 and iDo respectively. In
this circuit, PID control method is applied to control the duty ratio of switches. The input to the converter is fed
from 24 V DC supply. By using PID controller, output voltage is maintained at 280 V DC at duty ratio 0.6.
Fig. 5. Simulation Circuit of Improved High Voltage Boosting Converter

Fig.6.Input and Output Voltage waveform Fig.7.Inductor Current and Capacitor Voltage
waveform
Fig.8.Output Current waveform Fig.9.Output Power waveform
Fig.6. shows the input and output voltage waveforms. Input voltage applied to the converter is 24 V DC and the
output voltage obtained is 280.6 V DC. Fig.6(b). also shows the obtained output voltage when 24 V DC is
applied to the converter and it is clear that output voltage is exponentially increased up to 0.03 sec. After that
output voltage reaches a steady state value of 280 V DC. Fig.8. shows the waveforms of inductor current and
capacitor voltage with input gate pulse. Vgs1,Vgs2, Vgs3, Vgs4 and Vgs5 are the gate driving signals for S1, S2, S3, S4
and S5 respectively, iL1 and iL2 are the inductor current waveforms corresponding to inductors L1 and L2, Vcb1,
Vcb2 and Vce are the capacitor voltage waveforms corresponding to bootstrap capacitors and energizing
capacitor. Fig.8 shows the output current waveform. When switch is turned on, output current shoots the value,
after that it reaches steady state value of 0.701 A. Fig.9. shows the output power waveform up to 0.03 sec, it
follows a straight line path and approaches a constant value 196 W.
IV. CONCLUSIONS
The DC-DC boost converter has applications in the automotive, telecommunications, IT industries as well as in
renewable energy generation via fuel cells, photovoltaic arrays and wind turbines. The step-up power
conversion is continuously increasing its applications and power capability demands. In this paper, improved
high voltage boosting converter is designed. The converter is based on inductors connected in series with
bootstrap capacitors. The converter has high voltage conversion ratio than conventional boost converter. Two
inductors are connected in series during demagnetizing period. 39.74 percentage of output voltage is improved
by using modiﬁed circuit improved high voltage boosting converter. The conversion ratio is (4+2D)/(1-D).
Closed loop control is done using PID controller in order to maintain output voltage constant at 280 V, such a
converter is suitable for industrial application.

REFERENCES
[1]. D. Nicolae, C. Richards, and J. van Rensburg, ”Boost converter with improved transfer ratio”, in Proc. IEEE IPEC, 2010, pp. 7681.
[2]. C. E. Silva, R. P. Bascope, and D. S. Oliveira, ”Proposal of a new high voltage boosting converter for UPS application”, in Proc.
IEEE ISIE, 2006, pp. 12881292.
[3]. K. I. Hwu and Y. T. Yau, ”A KY boost converter”, IEEE Trans. Power Electron.,vol. 25, no. 11, pp. 26992703, Nov. 2010.
[4]. K. I. Hwu and Y. T. Yau, ”Voltage-boosting converter based on charge pump and coupling inductor withpassive voltage clamping”,
IEEE Trans.Ind. Electron., vol.57, no. 5, pp. 17191727, May 2010.
[5]. K. I. Hwu and Y. T. Yau, ”KY converter and its derivatives”, IEEE Trans.Power Electron., vol. 24, no. 1, pp. 128137, Jan. 2009.
[6]. K.I.Hwu, C. F. Chuang, and W. C. Tu, ”High voltage boosting converters based on bootstrap capacitors and boost inductors”,IEEE
Transactions on Industrial Electronics, vol. 60, no. 6, June 2013
[7]. H. Tao, J. L. Duarte, and M. A.M. Hendrix, ”Line-interactive UPS using a fuel cell as the primary source” IEEE Trans. Ind.
Electron., vol. 55, no. 8,pp. 30123021, Aug. 2008.

Boost Converter with Improved Voltage Conversion Ratio Using Bootstrap Capacitors and Boost Inductors

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