Nonisolated High Step-up Stacked DC-DC Converter
Based on Boost Converter Elements for High Power
Application
Moises Tanca V. and Ivo Barbi
Federal University of Santa Catarina, UFSC
Power Electronics Institute, INEP
Florianopolis, SC Brazil
mtanca@inep.ufsc.br, ivobarbi@inep.ufsc.br
Abstract— Many application calls for high step-up dc-dc
converter that do not require isolation. To obtain a high step-up
gain with high efficiency in nonisolated application, a high stepup technique based on the stacking basic boost converter
elements is introduced in this paper. In this converter a high
step-up conversion ratio and distributed voltage stress can be
achieve and reduce reverse recovery on diodes. Based on a
conventional quadratics boost converter, the derived converter
satisfies all there feature, which make is suitable for high stepup application. The operational principle and characteristics of
proposed converter are presented, and verified experimentally
with a 1 kW, 100 V input, 400 V output prototype converter.
developed based on the classical boost converter, which utilize
as cascaded structure [6], a coupled–inductor [7] or a
multiplier cell of converter [3].
The proposed nonisolated high step-up DC-DC converter
is obtained from stacking basic boost converter elements with
some modifications as is presented in Fig. 1. is very suitable
for application that requires high power density level and high
efficiency. It is also intended to be used at higher switching
frequency than traditional topologies, since the reduced switch
voltage stress allows the use of faster semiconductor devices.
II.
I.
INTRODUCTION
Recently, the demand of high step-up conversion
technique is gradually increased according to the growth of
battery powered application and low voltage renewable
source, such as electric vehicles, the back-up energy system
for UPS, the frond-end stage for clean-energy source, the fuel
cell system, high-intensity discharge lamp for automotive
headlamp, a LED drive application and telecommunication
industry [4]-[7].
For nonisolated application, a conventional boost
converter has been normally chosen, because of a simple
structure and a continuous input current. But, when extreme
high voltage gain is required, however, it is hard for a boost
converter to achieve both high voltage conversion ratio and
high efficiency at once, due to the parasitic resistances,
associated with the inductor, filter capacitor, main power
switch and rectifier diode, which cause serious degradation in
the step-up ratio and efficiency as the operating duty cycle is
increased [1]. That is, a high voltage diode causes a severe
recovery problem requiring and additional current snubber and
high voltage switch increases conduction loss [2]. In addition,
the electromagnetic interference (EMI) problem is severe with
this condition. To achieve high step-up gain and low voltage
stress on devices, varies types of step-up converter have been
978-1-4244-9474-3/11/$26.00 ©2011 IEEE
PRINCIPLE OF OPERATION
The proposed step-up converter operating in continuous
conduction mode (CCM) is now considered. The equivalent
circuit of proposed topology is show in Fig. 1. Considering
all semiconductor ideal and the inductor large enough to be
treated as current sources, the stacked capacitors are assumed
to be long enough so that the voltage then are considered as
constant during the entire switching cycle. The main
waveforms are presented in Fig. 2. The two operation modes
are briefly described as follows:
Mode 1 (t0 – t1) [Fig. 1. (a)]
At time t = t0, all the switches simultaneously (S1, S2 and
S3) are turned on, the energy from the input power source and
the capacitors charged previously (C1 and C2) are stored in the
inductors L1, L2 and L3. The load is supplied by capacitor C3
according to Fig. 2.
A.
B. Mode 2 (t1 – t2) [Fig. 1. (b)]
At time t = t1, all the switches (S1, S2 and S3) are turned
off. At this time, the diodes (D1, D2 and D3) become forwardbiased to start conducting. The stored energy of the inductors
in Mode 1 are released to output load and to load the
capacitors C1, C2 and C3 for the next switching cycle.
249
io
C3
S 1, S2 , S3
D3
iL1,iL2 ,i L3
L3
C2
iL3
Vin
Ro
iL2
S2
i C1
Vo
D1
C1
iin
iin
S3
D2
iC2
L1
iL1
iC3
S1
Vi n
V L1,V l2 ,Vl3
a)
C3
-V.C1
io
V .S1,V.S2 ,V.S3
D3
Vi n /(1-D)
L3
C2
Vo
iL3
S3
D2
Vin
Ro
iL2
S2
V. C1 = V .C2 = V .C3
t1
Vo
Ts
D1
C1
t2
Fig. 2. Main waveforms of the proposed converter for CCM operation
L1
10
iin
iL1
9
S1
proposed converter
Voltage Gain(Vo/Vin)
8
b)
Fig. 1. Operation modes for a continuous conduction mode of proposed non
isolated high step-up stacked DC-DC converter: a) Mode 1 and b) Mode 2.
III.
STATIC ANALYSIS
To analyze the steady-state characteristics of the proposed
converter in CCM, the winding resistance and transient
characteristic as of the MOSFET are neglected, assuming
ideal power devices and all capacitors are extreme large, a
constant output voltage is ensured.
The ideal voltage gain of this proposed converter is given
by (1) and the total static gain as a function of duty cycle is
presented by Fig. 3.
Vo ⎡
D
D2
D3 ⎤
= ⎢1 +
+
+
⎥
Vin ⎣ (1 − D) (1 − D ) 2 (1 − D)3 ⎦
(1)
The high step-up DC-DC converter static analysis will be
performed to provide the fundamental equations that can be
used as a basis in design procedure elaboration. Thus, all
components in power stage can be correctly chosen in order to
meet all design specification.
7
6
5
4
boost converter
3
2
1
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
10
Duty ratio (D)
Fig. 3. Comparison of CCM static gain as function of duty cycle for
conventional and proposed converters
Performed the analysis yields a set of equations that
provide the converter’s output characteristics, depicted by
continuous lines in Fig. 4. The dashed lines shown in this
figure establish the boundaries operation.
In order to yield high power density level and high
efficiency, the inductances L1, L2 and L3 are given by (2), (3)
and (4).
250
M
DC
10
D=0.6
CCM
D=0.5
5
DC M
0
DCM
(Vo/V in)
DCM
CCM
CCM
D=0.4
DCM
CCM
D=0.3
CCM
D=0.2
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Fig. 5. The three-stacked converter simulation results in CCM
1
Io
Table 1 - Values of stresses in the components of de high step-up converter
Fig. 4. Output characteristics of proposed converter
L1 =
L2 =
L3 =
Vin D
(2)
Δ I L1 f s
Vin D 2
Δ I L 2 f s (1 − D )
Vin D 3
Δ I L3 f s (1 − D )
2
(3)
(4)
And the switch voltage stress in S1, S2 and S3 are given by
(5), (6) and (7).
VS1 = Vin
VS 2 = Vin
VS 3 = Vin
IV.
1
1− D
D
(1 − D )2
D2
(1 − D)3
Topologies of high step-up converter
3SC
2SC
1SC
7,5 A
7,51 A
7,5 A
--3,26 A
5,0 A
----2,5 A
8,64 A
13,28 A
15,10 A
--9,99 A
10,07 A
----5,03 A
400 V
230,28 V
200 V
--300,0 V
200 V
----200 V
7,5 A
7,51 A
7,5 A
--3,26 A
5,0 A
----2,5 A
4
4
4
50%
57%
75%
1,50 mH
0,85 mH
0,67 mH
--2,56 mH
1,00 mH
----2,00 mH
Stresses
IS1avg
IS2 avg
IS3 avg
IS1rms
IS2 rms
IS3 rms
VS1
VS2
VS3
IS1avg
IS2 avg
IS3 avg
Gain
D%
L1
L2
L3
(5)
(6)
V.
(7)
SIMULATION RESULTS
In order to validate the operation principles of the
proposed converter, the boost conventional converter, the
converter with two and three stacked DC-DC converter were
simulated to investigate their device stress. In Fig. 5
simulation results for proposed converter are showed. The
presented values were obtained by simulating all converters
with an input voltage of 100 V, output voltage equal to 400V
and output power equal 1000 W. The switching frequencies
for the three-stacked converter are 50 kHz. A summary of
these results is presented in table 1, where 3SC is the new
converter, 2SC is the two-stacked boost converter and 1SC is
a basic boost converter.
EXPERIMENTAL RESULTS
The proposed converter has been implemented to validate
its principle of operation for 100 V input voltage and 400 V
voltage. The maximum output power is 1000 W and the
chosen switching frequency is 50 kHz. The duty cycle for this
gain of converter is yielded equal to 0.5. A picture of
prototype is show by Fig. 6. The following semiconductors
were installed: three MOSFET IRFP460 from industry
International Rectifier, three diodes MUR1540 from Fairchild
Semiconductor.
The output voltage and the output current are being
presented by Fig. 7. Note that the output voltage is around 400
V. Since the converter is operating in CCM, the ripple current
is very small, what is interesting for clean energy source
application. If fewer ripples are required by the application the
input inductance could be increased, a capacitor could be
added to the input (operating as a filter by considering the
impedance of source).
251
Efficiency [%]
95
94
93
92
91
90
89
200
300
400
500
600
700
800
900
1000
Output power [W]
Fig. 9. Efficiency of the proposed converter as a function of the output
power for 100 V input voltage.
VI.
Fig. 6. A Picture of the prototype
The switches’ voltages of S1 are being presented in Fig. 8.
In this figure one can see that none of the switches are being
submitted to the highest output converter voltage. During the
turn off commutation, an overvoltage occurs, with justified by
the utilization of a non appropriate layout design for this
converter. Finally, Fig. 9 shows the efficiency of the converter
as a function of the output power, the proposed circuit
achieved one of the highest efficiency levels for the
considered power level.
CONCLUSION
An alternative structure to obtain high step-up gain for
nonisolated application is introduced in this paper. Based on
stacked basic boost converters and distribute voltage stress in
devices. The main advantage of the proposed topology, when
compared with conventional boost converter, is that the
voltages across the switches are lowers than the output
voltage. The cost and high efficiency are achieved by the low
RDS(on) and low voltage rating of the power switch device.
The presented converter can be interesting for application
where a high voltage ratio and high output power are
necessary, what can be case of clean energy source
application, but only when transformer isolation not required.
.
The new converter is there too for able to achieve high
overall efficiency, reduced voltage stress on the switching
element and suppression of the EMI to a minimum degree.
ACKNOWLEDGMENT
The author gratefully acknowledges to National Council
for Scientific and Technological Development (CNPq), the
Federal University of Santa Catarina (Brazil), and the National
University of San Agustin (Peru) all for financial support and
structure provided.
REFERENCES
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Fig. 7. Input voltages, output voltage, output current and input current of the
proposed converter.
[2]
[3]
[4]
[5]
[6]
[7]
Fig. 8. Experimental voltage curve of switch S1
252
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