International Journal of
Emerging Research in Management &Technology
ISSN: 2278-9359 (Volume-4, Issue-12)
Research Article December
2015
Coupled Inductor and Voltage-Doubler Circuit for High Step-Up
DC-DC Converter
Uma S*, Mallanagowda N
Department of ECE, SJBIT,
Bangalore, India
Abstract—
I
n this paper, a novel high step-up dc–dcconverter with coupled-inductor and voltage-doublercircuits is proposed.
The converter achieves high step-upvoltage gain with appropriate duty ratio and low voltagestress on the power
switches. Also, the energy stored in theleakage inductor of the coupled inductor can be recycled tothe output.
The operating principles and the steady-stateanalyses of the proposed converter are discussed in detail.Finally, a
prototype circuit of the proposed converter isimplemented in the laboratory to verify the performance ofthe proposed
converter.
Keywords- step-up voltage gain, coupled-inductor, voltage doubler, step-up converter, low voltage stress
I. INTRODUCTION
A DC-DC converter converts directly from dc todc and is simply known as a DC converter. A dc convertercan be
considered as dc equivalent to an ac transformer witha continuously variable turn’s ratio. Like a transformer, itcan be
used to step down or step up a dc voltage source.
Dc converters are widely used for traction motorcontrol in electric automobiles, trolley cars, marine hoistsand mine
haulers. They provide smooth acceleration control,high efficiency and fast dynamic response. Dc converterscan be used
in regenerative braking of dc motors to returnenergy back into the supply and this feature results inenergy savings for
transportation systems with frequentstops.
Dc converters are used in dc voltage regulators; andalso used in conjunction with an inductor to generate a dccurrent
source, especially for the current source inverter.
A boost converter is generally used and it hasseveral advantages such as simple structure, continuousinput current, and
clamped switch voltage stress to theoutput voltage. However, it is very difficult to satisfy bothhigh voltage conversion
ratio and high efficiency at once.
This is primarily due to the parasitic resistances, whichcause serious degradation in the step-up ratio and efficiencyas
the operating duty increases. Moreover, in high outputsevere reverse recovery problem and it requires a snubber.
As a result, a general boost converter would not be acceptable for high step-up applications. To overcome
thislimitation, various types of step-up converters, utilizing thevoltage conversion ability of a transformer, can beadopted.
In order to provide such a large step-up/step-downvoltage gain, the non-isolation converters would have towork with
extreme duty ratios: in the case of boost-typeconverters, a large duty ratio would be necessary, but this isnot possible due
to the latch-up condition. Moreover, theshort conduction time of the rectifier switch determines ashort pulse current with
high amplitude flowing through it,and thus a severe rectifier-reverse-recovery problem.
Available solutions to the above problems include:a) The transformer-based converters (as flyback, forward), the transformer being an element that introduces many
losses, and the switch being submitted to high voltage stress (double the input voltage).
b) A cascade of two boost converters, with its two energy-processing steps, and two sets of active switches,
magnetic components and controllers that have to be synchronized to avoid the beat frequency.
c) Quadratic boost or buck converters, also presenting a too much complexity.
d) Much-phase and phase-shift buck converters as voltage regulator modules (VRMs).
e) Transformer less hybrid converters based on a defined switched capacitor/switched inductor cell and hard
switching basic converters with inserted switched capacitor structures, the last two solutions (d, e) still
presenting a limited DC gain.
A new parameter for increasing the DC ratio in step-up and step-down converters was introduced by the use of the
tapped-inductor: a tapped inductor replaces the output filter inductor in a buck converter. A coupled-inductor is used in a
boost or buck-boost converter instead of the input inductor. The choice of the turns-ratio N of the coupled DC gain.
The dc–dc flyback converter is adopted to achieve high step-up voltage gain by adjusting the turn’s ratio of the
transformer. This converter has the merits of simple topology, easy control, and low cost, but the fact that the leakageinductor energy of the transformer cannot be recycled results in low efficiency and high voltage stress on the active
switch. In order to reduce the voltage stress, an RCD snubber is used. However, this decreases the efficiency.
The transformerless dc–dc converters include the cascade boost type , the quadratic boost type the switched inductor
type , the voltage-lift type , the voltage-doubler type , the capacitor–diode voltage-multiplier type , and the boost type
that is integrated using a switched-capacitor technique.
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Uma et al., International Journal of Emerging Research in Management &Technology
ISSN: 2278-9359 (Volume-4, Issue-12)
These converters can provide higher voltage gain than the conventional dc–dc boost converter. However, the voltage
gain of these converters is only moderately high. If higher voltage gain is required, these converters must cascade more
power stages, which will result in low efficiency.
A conventional high step-up dc–dc converter with a coupled inductor technique is shown in Fig. 1.
The structure of this converter is very simple, and the leakage-inductor energy of the coupled inductor can be
recycled to the output. However, the voltage stresses on switch S1 and diode D1, which are equal to the output voltage,
are high.
This paper presents a novel high step-up dc–dc converter, as shown in Fig. 2
Fig: 2 Circuit configuration of proposed converter
The coupled-inductor and voltage-doubler techniques are integrated in the proposed converter to achieve high stepup voltage gain.
II. OPERATING PRINCIPLE OF THE PROPOSED CONVERTER
Fig. 2 shows the circuit configuration of the proposedconverter, which consists of two active switches S1, and S2,
one coupled inductor, four diodes D1−D4, and two output capacitors C1 and C2.
The simplified circuit model of the proposed converter is shown in Fig. 3.
Fig: 3 Simplified model of proposed converter
The coupled inductor is modeled as a magnetizing inductor Lm, a primary leakage inductor Lk1, a secondary
leakage inductor Lk2, and an ideal transformer. Capacitors CS1 and CS2 are the parasitic capacitors of S1 and S2,
respectively. In order to simplify the circuit analysis of the proposed converter, some conditions are assumed as follows.
First, all components are ideal. The ON-state resistance RDS (ON) of the active switches, the forward voltage drop of the
diodes, and the ESR of the coupled inductor and output capacitors are ignored. Second, output capacitors C1 and C2 are
sufficiently large, and the voltages across C1 and C2 are considered to be constant during one switching period.
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Uma et al., International Journal of Emerging Research in Management &Technology
ISSN: 2278-9359 (Volume-4, Issue-12)
III. MODES OF OPERATION
1) MODE 1:- [T0,T1]
(a) Mode 1
At t = t0, S1 and S2 are turned on. The current-flowpath is shown in Fig. (a). The dc-source energy istransferred to
Lm and Lk1 through D3, S1, and S2, socurrents iLm, iLk1, and iD3 are increased. The energystored in Lk2 is released to
Lm and Lk1 through D4, S1,and S2. Thus, iLk2 is decreased. Meanwhile, the energystored in Lk2 is recycled. The
energy stored in CS2 israpidly and completely discharged. The energies stored inC1 and C2 are discharged to the load.
This mode ends wheniLk2 is equal to zero at t = t1.
2) MODE 2:- [T1,T2]
In this mode, S1 and S2 are still turned on. The current flow path is shown in Fig. (b). The dc source energy is still
transferred to Lm and Lk1. Thus, iLmand iLk1 are still increased. The energies stored in C1 and C2 are still discharged
to the load.
3) MODE 3:- [T2, T3]
Current-flow path is shown in Fig. (c). The DC-sourceenergy is still transferred to Lm, Lk1, and CS1.Meanwhile,the
voltage across S1 is increased rapidly. The energiesstored in C1 and C2 are still discharged to the load.
4) Mode 4:- [T3, T4]
During this time interval, S1 is still turned off andS2 is still turned on. The current-flow path is shown in Fig.(d). The
DC source, Lm, and Lk1 are series connected totransfer their energies to Lk2, C1, and the load. Thus, iLmand iLk1 are
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Uma et al., International Journal of Emerging Research in Management &Technology
ISSN: 2278-9359 (Volume-4, Issue-12)
decreased and iLk2 is increased. Meanwhile,the energy stored in Lk1 is recycled to C1 and the load. Theenergy stored in
C2 is still discharged to the load. Thismode ends when iLk1 is equal to iLk2 at t = t4.
5) Mode 5:- [T4, T5]
During this period, S1 is still turned off and S2 is stillturned on. The current-flow path is shown in Fig.(e). TheDC
source, Lm, Lk1, and Lk2 are series-connected totransfer their energies to C1 and the load. Thus, iLm, iLk1,and iLk2 are
decreased. The energy stored in C2 is stilldischarged to the load.
6) MODE 6:- [T5, T6]
At t = t5, S1 and S2 are turned on. The currentflowpath is shown in Fig. (f). The DC-source energy istransferred to
Lm and Lk1 through D3, S1, and S2. Socurrents iLm, iLk1, and iD3 are increased. The energystored in Lk2 is released to
Lm and Lk1 through D4, S1,and S2. Thus, iLk2 is decreased. Meanwhile, the energystored in Lk2 is recycled. The
energy stored in CS1 israpidly and completely discharged. The energies stored inC1 and C2 are discharged to the load.
This mode ends wheniLk2 is equal to zero at t = t6.
7) Mode 7:- [T6, T7]
During this time interval, S1 and S2 are still turnedon. The current-flow path is shown in Fig. (g).The
DCsourceenergy is still transferred to Lm and Lk1. Thus, iLmand iLk1 are still increased. The energies stored in C1
andC2 are still discharged to the load.
8) Mode 8:- [T7, T8]
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Uma et al., International Journal of Emerging Research in Management &Technology
ISSN: 2278-9359 (Volume-4, Issue-12)
At t = t7, S1 is still turned on and S2 is turned off.The current-flow path is shown in Fig. (h). The DC-sourceis still
transferred to Lm, Lk1, and CS2.Meanwhile, thevoltage across S2 is increased rapidly. The energies storedin C1 and C2
are still discharged to the load.
9) Mode 9:- [T8, T9]
During this period, S1 is still turned on and S2 isstill turned off. The current-flow path is shown in Fig.(i).The DC
source, Lm, and Lk1 are series-connected totransfer their energies to Lk2, C2, and the load. Thus, iLmand iLk1 are
decreasedand iLk2 is increased. Meanwhile,the energy stored in Lk1 is recycled to C2 and the load. Theenergy stored in
C1 is still discharged to the load. Thismode ends when iLk1 is equal to iLk2 at t = t9.
10) Mode 10:- [T9, T10]
In this mode, S1 is still turned on and S2 is stillturned off. The current-flow path is shown in Fig. (j).TheDC source,
Lm, Lk1, and Lk2 are series-connected totransfer their energies to C2 and the load. Thus, iLm, iLk1,and iLk2 are
decreased. The energy stored in C1 is stilldischarged to the load. This mode ends when S1 and S2 areturned on at the
beginning of the next switching period.
Typical waveforms of the proposed converter
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Uma et al., International Journal of Emerging Research in Management &Technology
ISSN: 2278-9359 (Volume-4, Issue-12)
IV. SIMULATION CIRCUIT
Matlab simulated circuit for open loop circuit
Simulated circuit for closed loop
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Uma et al., International Journal of Emerging Research in Management &Technology
ISSN: 2278-9359 (Volume-4, Issue-12)
Gate pulses of switches
Voltage and current waveforms of switch
Output voltage
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Uma et al., International Journal of Emerging Research in Management &Technology
ISSN: 2278-9359 (Volume-4, Issue-12)
Voltage across capacitors C1 and C2
V. APPLICATIONS
The dc–dc converter with high step-up voltage gainis widely used for many applications, such as fuel-cellenergyconversion systems, solar-cell energy-conversionsystems, and high-intensity-discharge lamp ballasts
forautomobileheadlamps.
In the recent years, more and more industrialapplications have required DC-DC converters able toprovide a large
conversion ratio with a good efficiency andless electromagnetic interference noise. Just a few examplesshow the need of
a step-up or step-down of the input voltageof at least ten times: the 48V nominal telecom DC bus hasto be boosted at the
intermediate 380V DC bus needed forthe supply system of the servers for data processing whenthe telecom industry is
used to provide computer services.The 12V of a car’s battery voltage has to be boosted up to100Vduring the steady-state
operation and even up to 400Vat the start-up of the high-intensity discharge (HID) lampballasts used in the automotive
headlamp.
VI. ADVANTAGES
1) The leakage-inductor energy of the coupledinductor can be recycled.
2) The voltage stresses on the switches are half thelevel of the output voltage. Thus, the switches with lowvoltage
rating and low ON-state resistance RDS (ON) canbe selected.
3) The voltage gain achieved by the proposedconverter is double that of the conventional high step-upconverter.
Under thesame voltage gain and duty ratio, theturns ratio of the coupled inductor for the proposedconverter can
be designed to be less than the conventionalhigh step-up converter.
4) The frequency of the magnetizing-inductorcurrent for the proposed converter is double of the
switchingfrequency. Thus, the magnetizing-inductance of thecoupled- inductor for the proposed converter can
bedesigned to be less than the conventional high step-upconverter under same switching frequency.
VII. CONCLUSION
The novel high boost converter using the coupledinductor and voltage doubler was presented and theoperation and
features have been described. Experimentalresults were discussed with a 200W prototype using voltagedoublers. The
proposed method eliminates the problems ofextreme duty ratio or complexity of circuits in theconventional
topology.Also, the proposed circuit has the followingvarious advantages compared to the conventional boosterconverters:
low voltage stress, higher boost rate, higherefficiency, and several modified circuits for otherapplications. Therefore, the
proposed converter can beapplied to various high boost applications, such as a batteryback-up system, fuel cells, military
applications, etc.
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