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7/28/2019 High Step-Up Coupled-Inductor-based Converter Using Bi-Direction Energy Transmission
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High Step-up Coupled-inductor-based Converter Using Bi-direction Energy Transmission
Rong-Jong Wai, Member,IEEE
Department of Electrical Engineering, Yuan Ze University,Chung Li 32026, Taiwan, R.O.C.
E-mail: [email protected]
Rou-Yong Duan
Department of Industrial Safety & Health, Hung KuangUniversity, Tai Chung 433, Taiwan, R.O.C.
E-mail: [email protected]
AbstractIn this study, a high step-up converter with coupled-inductor by way of bi-direction energy transmission is
investigated. In the proposed strategy, a coupled inductor with a
lower-voltage-rated switch is used for raising the voltage gain
whether the switch is turned on or turned off. Moreover, a
passive regenerative snubber is utilized for absorbing the energy
of stray inductance so that the switch duty cycle can be operated
under a wide range, and the related voltage gain is higher than
other coupled-inductor-based converters. The capacity of the
magnetic core can be utilized completely by way of bi-direction
energy transmission. In addition, all devices in this scheme also
have voltage-clamped properties and their voltage stresses are
only related to the output voltage. Thus, it can select low-voltage
low-conduction-loss devices, and there are no reverse-recoverycurrents within the diodes in this circuit. Some experimental
results via an example of a proton exchange membrane fuel cell
(PEMFC) power source are given to demonstrate the
effectiveness of the proposed power conversion strategy.
I. INTRODUCTION
In recent, dc-dc converters with steep voltage ratio are
usually required in many industrial applications. Forexamples, the front-end stage for clean-energy sources, the dc
back-up energy system for an uninterruptible power supply
(UPS), high-intensity discharge lamps for automobile
headlamps, and telecommunication industry [1][3]. The
conventional boost converters cannot provide such a high dcvoltage gain, even for an extreme duty cycle. It also may
result in serious reverse-recovery problem and increase therating of all devices. As a result, the conversion efficiency is
degraded and the electromagnetic interference (EMI)
problem is severe under this situation [4]. In order to increase
the conversion efficiency and voltage gain, many modifiedboost converter topologies have been investigated in the past
decade [5][12].Although voltage-clamped techniques are manipulated in
the converter design to overcome the severe reverse-recovery
problem of the output diode in high-level voltageapplications, there still exists overlarge switch voltage
stresses and the voltage gain is limited by the turn-on time of
the auxiliary switch [5], [6]. Silva et al. [7] presented a boostsoft-single-switch converter, which has only one single active
switch. It is able to operate with soft switching in a pulse-
width-modulation (PWM) way without high voltage andcurrent stresses. Unfortunately, the voltage gain is limited
below four in order to achieve the function of soft switching.
In [8] and [9], coupled inductors were employed to provide ahigh step-up ratio and to reduce the switch voltage stress
substantially, and the reverse-recovery problem of the output
diode was also alleviated efficiently. In this case, the leakageenergy of the coupled inductor is another problem as the
switch was turned off. It will result in the high-voltage ripple
across the switch due to the resonant phenomenon induced bythe leakage current. In order to protect the switch devices,
either a high-voltage-rated device with higher )(onDSR or a
snubber circuit is usually adopted to deplete the leakage
energy. By these ways, the power conversion efficiency willbe degraded. Zhao and Lee [10] introduced a family of high-
efficiency, high step-up dc-dc converters by only adding oneaddition diode and a small capacitor. It can recycle the
leakage energy and alleviate the reverse-recovery problem. In
this scheme, the magnetic core can be regarded as a flyback
transformer and most of the energy was stored in themagnetic inductor. However, the leakage inductor of .the
coupled inductor and the parasitic capacitor of the outputdiode resonated after the switch was turned on, a proper
snubber is necessary to reduce the output rectifier peak
voltage. Moreover, the capacity of the magnetic core should
be increased substantially when the demand of high outputpower is required. The aim of this study is to design a high-
efficiency, high step-up converter with coupled-inductor byway of bi-direction energy transmission to regulate a stable
constant dc voltage.
II. CONVERTERDESIGN AND ANALYSES
The system configuration of the proposed converter
topology is depicted in Fig. 1, where it contains seven parts
including a dc input circuit, a primary-side circuit, a
secondary-side circuit, a passive regenerative snubber circuit,a filter circuit, a dc output circuit and a feedback control
mechanism. The major symbol representations are
summarized as follows. INV and II denote dc input voltage
and current, and INC is an input filter capacitor in the dc
input circuit. 1L and 2L represent individual inductors in
the primary and secondary sides of the coupled inductor ( rT ),
respectively. Q is a switch in the primary-side circuit and QTis a trigger signal in the feedback control mechanism. 1C ,
1D and 2D denote a clamped capacitor, a clamped diode
and a rectifier diode in the passive regenerative snubber
circuit. 2C is a high-voltage capacitor in the secondary-side
circuit. OD and OC are output diode and filter capacitor in
the filter circuit. OV and OI describe output voltage and
current; OR is an output load.
4060-7803-9033-4/05/$20.00 2005 IEEE.
7/28/2019 High Step-Up Coupled-Inductor-based Converter Using Bi-Direction Energy Transmission
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2L1L
1D
+
OC
2C
OV
rT
2DQ
1C
OD
OR
DC Input
Circuit
Primary-side
Circuit
Secondary-side
Circuit
Passive Regenerative
Snubber Circuit
Filter
Circuit
DC Output
Circuit
+
INV INC
2Li
II
O
I
Feedback Control Mechanism
Voltage Feedback
Proportional-
Integral Control
& PWM
Voltage CommandDriving Circuit
& Trigger Signal
QT
QT
Fig. 1. System configuration of high step-up converter.
The characteristic waveforms of the proposed high step-up converter are depicted in Fig. 2. Moreover, Fig. 3
illustrates the topological modes in one switching cycle andthe detailed operation stages are described in Section II-A.The coupled inductor in Fig. 1 is modeled as an ideal
transformer, a magnetizing inductor ( mL ), and a leakage
inductor ( kL ) in Fig. 3. The turn ratio (n) and coupling
coefficient (k) of this ideal transformer are defined as
12/ NNn = (1)
)(mkm
LLLk += (2)
where 1N and 2N are the winding turns in the primary and
secondary sides, respectively. For simplicity, the dc input
circuit in Fig. 1 is denoted as a constant voltage source, SV .
The voltages across the switch, the primary and secondary
winding of the ideal transformer, and the leakage inductor are
denoted as DSv , Lmv , 2Lv and Lkv , respectively. Moreover,
the primary current ( 1Li ) of the coupled inductor is composed
of the magnetizing current ( Lmi ) and the primary induced
current ( 1i ). The secondary current ( 2Li ) is formed by the
primary induced current ( 1i ) through the ideal transformer,
and its value is related to the turns ratio (n). In addition, the
conductive voltage drops of the switch (Q) and all diodes
( OD , 1D and 2D ) are neglected to simplify circuit analyses.
A. Operation Stages
Mode 1 (t0t1) [Fig. 3(a)]:In this mode, the switch (Q) was turned on for a span.
Because the magnetizing inductor ( mL ) is charged by the
input voltage source ( SV ), the magnetizing current ( Lmi )
increases gradually in an approximately linear way. The
secondary voltage ( 2Lv ) and the clamped capacitor voltage
( 1Cv ) are connected in series to charge the high-voltage
capacitor ( 2C ) through the switch (Q) and the rectifier diode
( 2D ). This behavior is the key path of bi-direction energy
transmission. Thus, the magnitude of the secondary current
( 2Li ) is decreased since the high-voltage capacitor voltage
( 2Cv ) is increased gradually. Since the primary current ( 1Li )
is the summation of the complementary currents ( Lmi and 1i ),the current curve of 1Li is similar to a square wave. At the
same reason, the switch current ( DSi ) is also close to a square
curve because the switch current ( DSi ) is equal to the current
summation of 1i , Lmi and 2Li . The square primary current
( 1Li ) will result in lower copper and core losses in the
coupled inductor, and the conduction loss of the switch also
can be alleviated by the square switch current ( DSi ).
Lmi
1Li
2Li
1Li
2Li
DSiDSv
DSi
DSv
2Di
1Dv
1Di
1Dv
Lmi1i
400V
2Dv
DOiDOv
400V
0t 1t 2t 3t 4t 5t 0t
GSv
1i
2Di
2Dv
DOi
DOv
Mode 1
1Di
Mode 4
Mode2
Mode3
Mode5
Mode6
Fig. 2. Characteristic waveforms.
Mode 2 (t1t2) [Fig. 3(b)]:At time
1tt= , the switch (Q) is turned off. At this time,
the primary and secondary currents ( 1Li and 2Li ) of the
coupled inductor starts to charge the parasitic capacitor of the
switch. After the switch voltage ( DSv ) is higher than the
clamped capacitor voltage ( 1Cv ), the clamped diode ( 1D )
conducts to transmit the energy of the primary-side leakage
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output diode ( OD ) decays to zero and starts to conduct, and
the rectifier diode ( 2D ) is cut off. At this time, the series
voltages of SV , Lkv , Lmv , 2Cv and 2Lv charges the output
capacitor ( OC ) and supplies the output load ( OR ) by way of
low current type. According to the conservation law of
magnetic energy, it still supplies currents in the primary andsecondary sides of the coupled inductor persistently after the
entire consumption of the leakage inductor energy. The
primary current ( 1Li ) charges the clamped capacitor ( 1C ) and
passes through the secondary side of the coupled inductor,
and the secondary current ( 2Li ) delivers to the output
terminal. In the middle stage of this mode, the high-voltage
capacitor ( 2C ) is discharged and its voltage ( 2Cv ) is
descended sustainability. Moreover, the clamped capacitor
voltage ( 1Cv ) is increased by electrifying for a long time, and
the primary current ( 1Li ) is equal to the secondary current
( 2Li ) when the clamped diode ( 1D ) is reverse-biased.
Mode 5 (t4t5) [Fig. 3(e)]:Since the clamped diode ( 1D ) is a low-voltage Schottky
diode, it will be cut off promptly without reverse-recovery
current when the switch (Q) is turned on at time 4tt= .
Because the raising rate of the primary current ( 1Li ) is limited
by the primary-side leakage inductor ( kL ), and the secondary
current ( 2Li ) needs time to decay to zero, these two currents
depends on each other. Because it can not derive any current
from these three paths including the primary-side circuit,
secondary-side circuit and passive regenerative snubber
circuit, the switch (Q) is turned on under zero-current-switching (ZCS) and this soft switching property is helpful
for alleviating the switching loss. In this mode, the circuitcurrent flow still directs to the output terminal, but its
magnitude decreases gradually.
Mode 6 (t5t0) [Fig. 3(f)]:After releasing the leakage energy, the secondary current
( 2Li ) decays to zero at time 5tt= and starts to pass through
the switch (Q) inversely. At the same time, the output currentprovides the reverse recovery current for the output diode
( OD ) to build its reverse-biased voltage ( DOv ), and the
secondary current ( 2Li ) leads the rectifier diode ( 2D ) to be
forward-biased. When the rectifier diode ( 2D ) is conducted
and the output diode ( OD ) is cut off ( 0tt= ), it begins the
next switching cycle and repeats the operation in mode 1.
B. Formula Derivation
When the switch (Q) is turned on, the voltages across the
magnetizing inductor ( mL ) can be denoted via (2) as
SLmkVv = (3)
Moreover, the voltage across the secondary winding of the
ideal transformer can be represented via (3) as
SLmLkVnnvv ==
2(4)
Because the series voltages of2L
v and1C
v charge the high-
voltage capacitor (2
C ), the voltage across2
C can be
described via (4) as
12 CSCvkVnv += (5)
When the switch (Q) is turned off, the current of the
leakage inductor (k
L ) in the primary side of the coupled
inductor flows persistently through the clamped capacitor
(1
C ) until the secondary current (2L
i ) reacts upon the energy
from the magnetizing inductor (m
L ). Due to the concept of
the zero average voltage across the leakage inductor (k
L )
over one period [10], the required cycle to release the energy
of the leakage inductor (k
L ) can be denoted as
13),1/()1(2 tttnDTtD
LSLL=+== (6)
whereS
T is the switching period, D is the duty cycle of the
switch (Q), andLt is the time from mode 2 to mode 3.
Moreover, the voltages ofLk
v andLm
v are given as
SLkV
D
knDv
)1(2
)1)(1(
+= (7)
)1/( DVkDvSLm
= (8)
Therefore, the clamped capacitor voltage ( 1Cv ) can be
represented via (7) and (8) as
DSS
S
SLmLkCvV
D
nkD
D
VVvvv =
+
=++=
)1(2
)1)(1(
11
(9)
Note that, the voltage of1C
v is equal to the switch voltage
( DSv ). According to (8) and (9), the voltages of 2Cv and 2Lvcan be rewritten as
SCV
D
nkDnkv ]
)1(2
)1)(1(2[
2
++= (10)
)1/(2
DnVkDvnvSLmL
== (11)
In the meantime, the voltages of1C
v ,2C
v and2L
v charge
the output capacitor (O
C ) and output load (O
R ); therefore,
the output voltage (O
V ) can be calculated as
SSLCCOV
D
nkDV
D
nkvvvV
+
+=++=
1
)1)(1(
1
2221
(12)
As a result, the voltage gain of the proposed high step-up
converter can be represented as
D
nkD
D
nk
V
VG
S
O
V
+
+==
1
)1)(1(
1
2(13)
Substituting 1=k and n=1,2,4,6,8 into (13), the curve of
the voltage gain (V
G ) with respect to the duty cycle (D) is
depicted in Fig. 4(a), where the line labeled with star denotes
the voltage gain curve of the newly designed converter and
the real line represents the one in [10]. As can be seen from
this figure, the voltage gain of the proposed high step-up
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converter is higher than a coupled-inductor-based converter
in [10], especially in the smaller duty cycle. For example, one
can obtain 40=V
G if the values of 1=k , 6=n and
8.0=D are selected. It can verify that the switch duty cycle
in the proposed converter can be operated under a wide range.
Moreover, the voltage gain curve by substituting 1~9.0=k
and 6=n into (13) is depicted in Fig. 4(b). By observingthis figure, the voltage gain (
VG ) is less sensitive to the
coupling coefficient, k. For simplicity, the coupling
coefficient (k) is set at one, then (9) and (13) can be rewrittenas
DSSCvDVv == )1/(
1(14)
D
n
V
VG
S
O
V
+==
1
2(15)
If the value of 5.0=D is selected, the voltage gain in (15) is
two times the ones in [10], [11]. According to (14) and (15),one can obtain
)2/( += nVvODS
(16)
By analyzing (16), the switch voltage ( DSv ) is not related to
the input power source ( SV ) and the switch duty cycle (D) if
the values of the output voltage ( OV ) and the turns ratio (n)
are fixed. Thus, it can ensure that the maximum sustainable
voltage of the switch (Q) is constant. As long as the inputvoltage is not higher than the switch voltage-rated, the
proposed high step-up converter can be applied well to low-
voltage power sources even with large voltage variations, e.g.photovoltaic cells, wind generator, fuel cells, batteries, etc.
Duty Cycle (D)
(a)
VoltageGain(Gv)
Coupling Coefficient k= 1
1* =n
2*=n
4
*
=n
6* =n
8* =n
1=n
8=n
6=n
2=n4=n
Coupled-inductor-based converter in [10]
* Proposed high step-up converter
9.0=k
1=k
VoltageGain(Gv)
Duty Cycle (D)
(b)
Turn Ratio n = 6
Fig. 4. Voltage gain curve: (a) Coupling coefficient k=1; (b) Turn ratio n=6.
III. EXPERIMENTAL RESULTS
In order to verify the effectiveness of the designed
topology, a PEMFC system is utilized for a low-voltagepower source in the proposed high step-up converter. The
PEMFC system used in this study is the PowerPEMTM-
PS250 manufactured by the Hpower Company. It is a dc
power source with 250 watts dc nominal power rating. The
system operates on ambient air and clean pressurizedhydrogen fuel. The fuel cell system consists of a (40) cell
stack of the PEM type, mechanical auxiliaries, and electroniccontrol module.
In experimentation, the high step-up converter is designedinitially to operate from the fuel cell variability dc input,
V3825 =IN
V , to deliver a constant dc output, V400=OV .
Assume that the maximum value of the switch voltage is
clamped at 50V, the turn ratio 62)/( (max) == DSO vVn
according to (16). From (15), the related duty cycle,
8.0=D , is reasonable in practical applications if theminimum input voltage is assumed to be 10V. In order to
solve the problem of the fuel cell output voltage varied with
the load variations, the proposed converter with dc voltage
feedback control is utilized to ensure the system stability, anda PWM control IC TL494 is adopted to achieve this goal of
feedback control. The prototype with the followingspecifications is designed in this section to illustrate thedesign procedure given in Section II.
Switching frequency: kHz100=Sf ;
Coupled-inductor: H131 =L ; H4702 =L ; 18:3: 21 =NN ;
98.0=k ; EE-55 core;
Capacitor: 2*V50/F3300=INC ; V100/F51 =C ;
V250/F8.62 =C ; V450/F47=OC ;
Switch Q: FQI90N08 (80V/71A, = m16)(onDS
R );
Diode: 1D : Schottky diode STPS20H100CT (100V/2*10A);
2D ,
OD : SFA1606G, TO-220AB (400V/16A).
The experimental voltage and current responses of theproposed high step-up converter operating at 300W-output
power is depicted in Fig. 5. From Fig. 5(a), the switch
voltage ( DSv ) is clamped at 50V that is much smaller than the
output voltage, V400=OV , and the curve of the switch
current ( DSi ) is similar to a square wave so that it can further
reduce the conduction loss of the switch (Q). By observing
Fig. 5(b) and (c), the primary current ( 1Li ) keeps about 20A,
thus only a smaller core capacity is necessary for H131
=L .
According to Fig. 5(d)(j), the reverse-recovery currents in
all diodes ( OD , 1D and 2D ) can be alleviated effectively,
and the voltages of the clamped capacitor ( 1C ) and the high-voltage capacitor ( 2C ) are close to constant values. Therefore,
it can alleviate the reverse-recovery problem and exhibit the
voltage-clamped effect for further raising the conversionefficiency. In order to examine the robust performance of the
proposed converter scheme, the experimental result of output
voltage ( OV ) and output current ( OI ) under the step load
variation between light-load (20W) and heavy-load (300W)
is depicted Fig. 5(k). As can be seen from this figure, the
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converter output voltage, V400=OV , is insensitive to the
load variations due to the utilization a small coupled-inductor
and a closed-loop control, and the output voltage ripple isalso slight extremely as a result of high switching frequency.
(c) (d)
(e) (f)
(b)
0V
(20V/div)
DSv
0A
DSi (10A/div)
0V
(50V/div)DSv
0A
1L
i(10A/div)
0A
2Li
(a)
0V
(20V/div)
INV
0A
1Li(10A/div)
0A
II
(2us/div) (2us/div)
(2us/div) 0V
0A
0A
1Di
2Di
1Cv
(5A/div)
(5A/div)
(50V/div)
(2us/div)
1Ci
0V
0A
0A
1Cv
(5A/div)
(10A/div)
(2us/div)(2us/div)
DSi
1Di
(50V/div) (50V/div)
(2A/div)
0V
0A
DSv
DSv
(10A/div)
(10A/div)
(g) (h)
(50V/div)
(5A/div)
(2us/div)
1Di
1Dv
(50V/div)DSv
(2A/div)
(2us/div)
2Di
2Dv (200V/div)
0V 0V
0A 0A
0A
(j)
0V
(200V/div)
0A
DOi(2A/div)
0V
(200V/div)2Cv
0A
22 , LC ii (2A/div)
(i)
(2us/div) (2us/div)
DOv210V
(k)
0
(200mA/div)
OV
(100V/div)
20W300W
(200ms/div)
OI
Fig. 5. Experimental voltage and current responses of high step-up converter
for PEMFC with W300=O
P and V400=O
V .
(b)(a)
0V
(20V/div)
0A
DSi (10A/div)
(2us/div)
DSv
0V
(20V/div)
0A
DSi (10A/div)
(2us/div)
DSv
WPO
32= WPO 120=
(c) (d)
0V
(20V/div)
0A
DSi (10A/div)
(2us/div)
DSv
0V
(20V/div)
0A
DSi(10A/div)
(2us/div)
DSv
WPO
210= WPO 272=
(e) (f)
0V
(20V/div)
0A
DSi(10A/div)
(2us/div)
DSv
0V
(20V/div)
0A
DSi(10A/div)
(2us/div)
DSv
WPO
332=
WPO 372=
Fig. 6. Experimental switch voltage and current curves of high step-up
converter for PEMFC with V400=O
V under different output powers.
Output Power (W)
ConversionEffici
ency(%)
InputVoltage(V)
* Conversion Efficiency-Output Power
oInput Voltage-Output Power
Fig. 7. Conversion efficiency and fuel cell voltage for PEMFC with
V400=O
V under different output powers.
For the sake of verifying the effectiveness of the proposed
converter for different output powers, the experimentalswitch voltage and current responses at 32W, 120W, 210W,272W, 332W and 372W-output powers are given in Fig. 6.
As can be seen from these results, it needs to raise the duty
cycle (D) to keep a constant output voltage ( V400=OV )
since the fuel cell voltage drops when the output power
increases. Moreover, the switch voltage ( DSv ) is still clamped
at 50V, and the curve of the switch current ( DSi ) is also close
to a square wave with low ripple. Note that, the oscillated
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switch voltage in Fig. 6(a) is caused by the resonance of the
leakage inductance ( kL ) and the switch parasitic capacitor at
low power output [12]. It is helpful to alleviate the switchingloss in mode 5. Fig. 7 summarizes the experimental
conversion efficiency of the proposed converter and fuel cell
voltage under different output powers. From the experimental
results, the output voltage of the fuel cell decreases as theoutput power increases, and it is varied easily with respect to
the load variations. In order to solve this phenomenon, theproposed high step-up converter with dc voltage feedback
control is utilized in this study to ensure the system stability.
In addition, the conversion efficiency at 40W-output power isover 94.5% and the maximum efficiency is over 97% at
210W-output power, which is comparatively higher than
conventional converters.
IV. CONCLUSIONS
This study has successfully developed a high step-up
converter with coupled-inductor by way of bi-direction
energy transmission, and this converter has been applied wellfor a PEMFC system. According to the experimental results,the maximum efficiency was measured to be over 97%,
which is comparatively higher than conventional converters
with the same voltage gain. This high-efficiency converter
topology provides designers with an alternative choice toconvert renewable energy efficiently, and it also can be
extended easily to other power conversion systems for
satisfying high-voltage demands.
ACKNOWLEDGMENTS
The authors acknowledge the financial support of theNational Science Council of Taiwan, R.O.C. through grant
number NSC 92-2623-7-155-014 and the Ministry of
Economic Affairs of Taiwan, R.O.C. through grant number
92-EC-17-A-05-S1-0012.
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