antony

1. Design and Simulation of Boost Converter with Input
Ripple Cancellation Network
Sonima Antony
Dept. of Electrical and Electronics,
Karunya University
Coimbatore
Sonima13@gmail.com
Abstract-Ripples in the input current reduces the life span of
the fuel cell and overall performance of the converter, So in order
to reduce input current ripples, conventional boost converters
uses large value of LC filter in the input side, leads to worse
dynamic response and increase the overall weight. Open loop
control has poor voltage regulation. This paper proposes a closed
loop step up DC DC converter with reduced input current ripple.
In the proposed system, input inductor is tapped one and ripple
cancellation network(RCN) consist of a small inductor and
capacitor.The current through the ripple cancellation network
increases as main inductor current decreases and vice versa, thus
achieving input ripple cancellation in the proposed converter.
Typical application include fuel cell, electric vehicle,
SMPS,renewable energy conversion system etc. A comparative
study of conventional boost converter (CBC) and proposed boost
converter is performed by design and simulated in PSIM.
Keywords-DC DC converter, fuel cell, input current ripple,
tapped inductor, closed loop control, ripple cancellation
1. INTRODUCTION
Due to the shortage of global energy and ever increasing
atmospheric pollution, renewable energy sources such as
photovoltaic, fuel cells, wind energy, micro turbine generators,
etc., are becoming the most promising technology now a days.
Among them, fuel cell (FC) systems seem rather attractive
because it is truly a clean, emission free renewable electrical
generation technology with high reliability [1]-[2]. The main
application of fuel cell is in REVs due to their capability of
operating at higher efficiency than that of tradition internal
combustion engines [3]. But they have relatively low output
voltage.
Conventional converters used for converting low DC
voltage to high DC voltage require inverter, transformer and
rectifier. This results in increased size and cost of the
converter. So a high gain step up converter is required as an
interface to convert low DC voltage of fuel cell stack intohigh
DC link voltage for supplying standalone ac load or for
delivering energy to connected grid.
DC DC converters are the basic building block of modem
high frequency switching power supplies [4]. They convert dc
input voltage to another more desirable or usable output
voltage level. But it is important to create a steady dc output
voltage level, for different input dc voltage level. So a control
978-1-4799-6085-9/15/$31.00 ©2015 IEEE
S. Paul Sathiyan
Dept. of Electrical and Electronics,
Karunya University
Coimbatore
sathiyan@karunya.edu
circuit is used in power converter to compare the output
voltage against an internal reference voltage. Corrective action
is taken if the output drifts from its set value and is termed as
output regulation. The advantage of DC converter over AC
converter is they can simply be step up/step down and can
provide smooth acceleration control, high efficiency, and fast
dynamic response. Bidirectional converter can be used in
regenerating braking of DC motor to return energy back to the
supply and this feature results in energy saving for
transportation system with frequent stop.
Fig. 1. Typical fuel cell system
In general, a typical fuel cell system consist of fuel cell
stack, auxiliary battery, a high step up converter, DC/AC
converter etc., as shown in fig. I. The battery acts as an
auxiliary device that compensate dynamic characteristic of
slow fuel cell dynamics.
For FC based systems, it expected from DC DC converter
to have a low input current ripple as a high current ripple may
reduce life time of FC [5] and also decrease the overall system
performance. In order to minimize the input current ripple of
conventional boost converter (CBC), a large value of input
inductor is required [6]. This will results in worse dynamic
response and increased size of converter. Different input
current ripple cancellation and voltage regulation are discussed
in [7]-[10].
Fig. 2. Block diagram of proposed converter

2. In this paper, a closed loop step up converter with low input
current ripple for fuel cell system application is presented. The
block diagram of proposed converter consisting of boost
converter with tapped inductor ripple cancellation network and
closed loop system with PI controller is shown in fig. 2In the
proposed circuit, a ripple cancellation network consisting of a
small capacitor and inductor with tapped inductor is used.
Tapped inductor can be realized by adding extra tap to the
main inductor. Since the capacitor and inductor in RCN do not
need to handle main power as the conventional LC input filter,
size and weight of proposed converter are relatively small
comparing the CBC with the input LC filter. Also better
voltage regulation is achieved by the closed loop control of
boost converter. DC voltage regulation is achieved through
settling the PWM (Pulse Width Modulation)at certain
frequencies and switching devices using MOSFET or IGBT,
and by regulating the duty cycle. The operating principle and
theoretical analysis of proposed circuit is explained in later
sections.
II. PROPOSED CLOSED LOOP BOOST CONVERTER
A. Schematic diagram
Schematic of proposed closed loop boost converter with
ripple cancellation network is shown in fig.3.The inductors
Lpand Ls form the tapped inductor which is realized by
shorting two terminals of the transformer and the ripple
cancellation network comprises inductor Lrand capacitor Cr.
DC voltage regulation is achieved by the control circuit with
two PI controllers
Yin
Co
Ro
PI +2::)---4
1l
>
Fig.3. Schematic of closed loop boost converter with RCN
Tapped inductor with RCN in the proposed circuit can be
replaced by three equivalent non coupled inductor based on
kirchoff circuit law. The element representation of tapped
inductorLp,Ls and its equivalent non coupled inductor L11,L22
is shown in fig.4. The inductance can be represented as follows
(I)
b
(a) (b)
a Lll L22
b
�
(c)
Fig.4. Element representation (a) inductor (b) tapped inductor
(c) non coupled inductor
B. Modes ofoperation
The proposed converter has two stages in one operational
period, and the corresponding equivalent circuit and key
wavefonns for each operational stage are shown in figure
Cr
D
OFF
Co
ON
(a)
Cr
Co
OFF
(b)
Fig. 5.Equivalent circuit during one switching cycle (a)
Mode I[to - t1l (b) Mode 2[t1 - t2l
Mode l[to - td
The switch S is ONat to. Current through inductor L11 and
L22 increases linearly with different slopes. Output diode
remains OFF with the voltage stress equivalent to the output
voltage. The current through the ripple cancellation network
decreases linearly in order to achieve input current ripple
cancellation of proposed converter.
Ro
Ro
L = + +2M = +

3. The differential equation of proposed converter during on
state can be expressed as
L
di1-0n +-L
di2-on
-v:.
11 dt 22 dt
-
m
L
di1-on -L
di3-on
-v: v: v:
11 ----;;t + 33 ----;;t - in- Cr- 0
Mode 2[tl - t2l
(2)
(3)
Switch S is turn OFF at tb both inductors L11 and L22 start
to transfer their energy to the load Ro, so the inductor currents
i1 and i2 decreases linearly. The voltage stresses across switch
S are equal to the output voltage. The current through the RCN
increases linearly in order to achieve input ripple cancellation
in this mode.
The differential equation of proposed converter during off
state can be expressed as
L
di1-offf +-L
di2-off
=
v:. - v:
11 dt 22 dt m 0
di1-off di3-off
L11 -d-t- +-L33 -
d
- t - =
Vin- VCr-Va
(4)
(5)
The input current ripple LJlin of the proposed boost
converter with RCN can be expressed as
(6)
Under same operating condition, the current ripple of
conventional boost converter can be expressed as
(7)
Output voltage of proposed converter is same as that of
CBC and is given as
v:
- Vin
o
-l-D
(8)
The current ripple ratio of boost converter is as follows
(9)
Fig. 6. Key waveforms of proposed converter
The voltage gain of boost converter can be expressed as the
ratio of output voltage to the input voltage.
C. Control circuit statergy
In this a voltage sensor is used to sense output voltage and the
error signal obtained due to difference of output voltage and
reference voltage is given to PI controller.
To control over steady state and to improve the settling time
and overshoot on output voltage of boost converter, and also
to keep the boost converter output voltage to be constant,
despite the variation of load and input voltage, the
combination of P and I controller can be used. Coefficients of
P and I aim to accelerate respond of the system and eliminate
the offset. PI controller output is the sum of proportional and
integral controller output.
The controller output is given by
Kpe(t)+ Ki J e(t)dt (10)
Where e(t) is the error or deviation of actual measured value
from the set point, integral gain Ki = Kp.
T
The corrected signal is compared with a triangular pulse. The
output signal obtained from comparator is used to control the
switch S.
Ill. DESIGN PROCEDURE
A. Spec!fications 0.[proposed converter
Table 1 :Specifiations of proposed converter
PARAMETER DESCRIPTION
Vin Input voltage
Va Output voltage
is Switching
frequency
Po System capacity
Np:Ns Turns ratio
K Coupling
coefficient
B. Design ofL11, L22, L33
VALUES
36V
200V
100KHz
500W
2:3
0.7
For the boost converter in this paper, the maximum
average input current lin-max = 13.88A and the duty
ratio is 0.82.
V· DT
Tapped inductor, Lp'='� 53!lH
Lin
(II)
(12)
Mutual inductance, M = I<...[f;r:; = 55.65!lH (13)
Total inductance, L = Lp + Ls + 2M =283.55!lH (14)
The inductor Lr in the ripple cancellation network
should be equal to mutual inductor M inorder to achieve
input ripple cancellation.
(15)
= DT

4. The non coupled inductorL11= Lp+M, L22= Ls+M, L33=
Lr-M
C. Design ofCo andCr
The value of Co is designed so that the output voltage
ripples can be reduced. For the output voltage ripple L'lV of
0.4%,
So, Co = 4hlF
The value of capacitor, Cr can be expressed as
C
dVCr ..
rdt=-13
36
Table 2: component values
PARAMETER
Inductor L11
Inductor L22
Inductor L33
Auxiliary capacitor
Cr
Output capacitor Co
11 � 13.31747 283.55e.6
L
VALUE
108f.1H
175f.1H
0.25f.1H
3.3f.1F
47f.1F
(16)
(17)
Fig.7. Simulation diagram of conventional boost converter
C9 O.2SU 3_3u
Vo=199.40383
Fig.8. Simulation diagram of boost converter with RCN
Vo
"
PI 1------"(
Fig.9. Simulation diagram of closed loop boost
converter with RCN
IV. STMULATTON RESULTS
Three 36V to 200V converter (fig.7, fig.8, fig.9) with
output power rating 500W are simulated using PSIM and
specifications of the three converters are shown in table 2. The
waveform of input current ripple of CBC and proposed boost
converter is shown in fig. 10.In the simulation, input current
ripple of CBC is about 1.04A while in case of boost converter
with RCN input current ripples are reduced to 50mA.
Fig. 10. Waveform of gate pulses, input current ripple of
CBC and proposed boost converter

5. The current waveform through ripple cancellation network
of proposed converter is shown in fig. II. The peak to peak
value of this current waveform is about 0.85A . The diode
current waveforms of above three converters areshown in
fig.12and fig. l3.The diode current stress of boost converter
with RCN isl4.48Awhich is slightly higher than the current
stress of CBC of 14.37A. But in case of proposed closed loop
boost converter with RCN diode current stress is reduced by a
value of 13.72A. The input current ripple and current ripple
ratio of CBC and proposed converter is listed in table 3.
. . . . . . "
................. " . . . ...... 1'.." ....... . . . . ."'.... .
I J "
,,/
Fig. II Current waveform of ripple cancellation network
Fig.12 Diode current waveform of CBC and boost
converter with RCN
::::::::: ::: :::::::::::: ::: :::::::::'.
·�,LdJ����
Fig.l3 Diode current waveform of closed loop boost
converter with RCN
Table 3:Values of current ripple
PARAMETERS CONVENTIONAL BOOST
BOOST CONVERTER
CONVERTER WlTHRCN
Input current IA 0.05A
ripple
Current ripple 7.2% 0.36%
ratio
A comparative study of open loop system (fig.8) and closed
loop system (fig.9) is analyzed by varying input voltage
between 22V and 48V. The output waveforms of open loop
and closed loop boost converter with RCN are respectively
shown in fig.14and fig.15.
Fig. 140utput voltage of open loop system (Vin =
36V, Va = 200V, Po = 200W)
In case of open loop system, the average output voltage to
input variation is 178.79 and the average error is 21% (table 4)
whereas for closed loop system it is 200.54 and 0.335% (table
5) respectively.
Table 4: Open loop control
Vin Vref Va Absolute
error
22V 200V 115.78V 42%
26V 200V 136.83V 31.58%
28V 200V 147.36V 26.32%
32V 200V 168V 15.795%
34V 200V 178.9V 10.55%
36V 200V 199.9V 0.005%
44V 200V 231.56V 15.78%
48V 200V 252V 26%
Fig. 15. Output voltage of closed loop system(Vin =
36V, Va = 200V, Po = 200W)

6. Vin
22V
26V
28V
32V
34V
36V
44V
48V
Table 5: Closed loop control
Vref Va
200V 199.2V
200V 200.48V
200V 201V
200V 200.78V
200V 200.59V
200V 200.5V
200V 200.8V
200V 201V
V. CONCLUSION
Absolute
error
0.4%
0.24%
0.505%
0.09%
0.295%
0.25%
0.4%
0.5%
The boost converter with input current ripple reduction is
achieved by RCN including a small capacitor and inductor. The
simulation results show that current ripples are reduced to 95%
in the proposed converter. Thus a near zero ripple current is
achieved at the input side of the converter which improves fuel
cell stack life cycle that leads to the application of low input
current ripple. Also closed loop control of boost converter
provides a better voltage regulation than open loop control.
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