DESIGN AND SIMULATION OF DC-DC CONVERTER WITH HIGH … · dc-dc converter with high voltage gain...

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 8, August 2017, pp. 565–574, Article ID: IJMET_08_08_062

Available online at http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=8

ISSN Print: 0976-6340 and ISSN Online: 0976-6359

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DESIGN AND SIMULATION OF DC-DC

CONVERTER WITH HIGH VOLTAGE GAIN

FOR FUEL CELL BASED VEHICLES

J S V Siva Kumar and P Venkata sateesh

Department of Electrical and Electronics Engineering,

GMR Institute of Technology Rajam, AP. India.

ABSTRACT

The cost of petroleum based fuels are increasing because of its usage.so there is a

need to alternate these fuels. Fuel cell vehicles are best solution for this. A single fuel

cell gives a voltage nearly 1 to 1.5V. For getting more DC voltage we are connecting

the fuel cells are in series. After that the dc voltage can be boosted to high voltage by

using boost converter. In this paper we are concentrating on simulation of fuel cell

and dc to dc boost converter. By using this converter we are getting a dc output

voltage of 500V. This is more than enough to run an electrical vehicle. The simulation

results of fuel cell and boost converter are verified in PSIM 9.0.4 software.

Keywords: fuel cell, high gain, voltage doubler, current fed, high frequency

transformer, boost inductor and leakage inductance.

Cite this Article: J S V Siva Kumar and P Venkata sateesh, design and simulation of

dc-dc converter with high voltage gain for fuel cell based vehicles, International

Journal of Mechanical Engineering and Technology 8(8), 2017,pp. 565–574.

http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=8&IType=8

1. INTRODUCTION

In the recent years, the energy consumption from the renewable energy sources increases

when compared with the conventional energy sources in order to reduce the greenhouse gases

which causes global warming, acid rains, air, water, soil pollutions and ozone layer depletion.

According world environmental summit reports the conventional energy sources mainly fossil

fuels are may be completely vanished by the year 2050. So we have to reserve these

conventional energy sources for the next generation and give more importance to the

renewable energy sources to replace their applications. The renewable energy sources are

mainly solar energy system, wind energy system, biogas energy, geothermal energy, tidal

energy, fuel energy system and others. Among which fuel cell technology is the best suitable

for stationary and on board automobile applications because of more efficiency, reliable and

less weight. Architecture of an electrical vehicle powered with fuel cell shown in Figure 1.

The output voltage of single cell is very low which is not enough to run the electric motor

Design and simulation of dc-dc converter with high voltage gain for fuel cell based vehicles


Figure 1 Architecture of an electrical vehicle powered with fuel cell

So we have to place more number of cells in in order to get more dc voltage. But by using

above topology the efficiency of fuel cell will be decreases. So in order to overcome this

problem dc-dc converters having high voltage conversion ratio are used. These converters are

boosting the low voltage (22-65V) to very high voltage (300-600V).

This paper introduces the hybrid isolated dc-dc boost converter with high voltage

conversion ratio phenomenon for fuel cell based electrical vehicle applications. The present

paper because of the inductor with high frequency transformer responsible to boost up the

voltage.

2. DESIGN OF PEM FUEL CELL

Fuel cell is an electrochemical device that produces electricity by combining hydrogen and

oxygen without any combustion and produce water and heat as a byproducts. Fuel cell has

few moving parts so it requires less maintenance. They have not emitted any greenhouse

gases and produce zero and low emissions. A single fuel cell consists of a two electrodes and

in between them different types of electrolyte is sandwiched. The hydrogen gas is passed

through anode here the catalyst will separate hydrogen gas into protons and electrons. At

cathode the oxygen gas combined with protons and electrons produce heat and water as

byproducts. The electrons from anode will not pass through the membrane to reach cathode.

So they must travel around the electric circuit to reach another side of the cell. This movement

of electrons is cause electric current.

The amount of power produced by the cell will depends on the different factors such as

type of electrolyte sandwiched between the electrodes, fuel cell size, the operating

temperature, the hydrogen and oxygen gasses pressure at electrodes. A single cell will not

produce sufficient amount of electricity therefore, individual fuel cells are combined in series

to form a fuel cell stack. A typical fuel cell stack may consist of some hundreds of fuel cells

in series.

The different fuel cell technologies, their operating temperature, efficiency and

advantages are explained in below table1. Out of all fuel cell technologies PEM fuel cell

technology is most popular because of its low operating temperature range, smaller size, less

startup time and causes less corrosion.



Fuel cell type Type of electrolyte used Operating temperature

(0C)

System output

range efficiency

Polymer electrolyte

membrane (PEM)

Solid polymer poly

perfluorosulfonic acid 60-140

0C <1KW-250KW 54-59%

Alkaline(AFC)

40% of aqueous

potassium

hydroxide(KOH)

80-110 0C 10KW-100KW 59%

Phosphoric acid (PAFC) Liquid Phosphoric acid 160-190 0C

50KW-1MW >45%

Molten carbonate(MCFC)

Liquid solution of

lithium, sodium&

potassium carbonates

620-670 0C <1KW-1MW 45%

Table 1 different type of fuel cell technologies

The reactions of Polymer electrolyte membrane fuel cells (PEM) takes place at anode and

cathode are shown in be figure 2.

The output voltage of the fuel cell stack is given by the mathematical equation

2 2

2

0 0

.V N [ (ln )] ln(H I ) R

2

H O

FC FC ele FC

H O

P PRTE G I

F P= + − × −

(1)

The partial pressure of the hydrogen gas can be expressed as

2 2 2(P ) (q q 2 )in out

H H H r Fc

an

d RTK I

dt V= − −

(2)

By applying Laplace transform to the above equation we get

2

2

2

2

1( 2k I )

1

in

H r FC

H

H

H

qK

PSτ

−

=+

(3)

2

2

2

2

1( k I )

1

in

O r FC

O

O

O

qK

PSτ

−

=+

(4)

Figure 2 reactions take place at electrodes of PEM fuel cell



2

2

2

1(2 k I )

1

r FC

H O

H O

H O

KP

Sτ=

+ (5)

The fuel cell voltage is calculated as

cell act ohmicV E E E= + + (6)

The Nernst’s voltage equation is given as

2 2

2

0 0[ ln( )]2

H o

H O

P PRTE N E

F P= +

(7)

Where E0 is standard no load voltage is given by

3

0 1.229 0.85*10 (T 299.15)opE−

= − − (8)

Activation and ohmic losses can be expressed as following equations

ln(H*I )act FCE G= − (9)

5 50.01605 3.5 10 8 10ele op FCE T I

− −= − × + × (10)

Based on the load demand the fuel cell consumes hydrogen gas. The reformer supply

hydrogen gas to the fuel cell. The mathematical equation of the reformer is given as

2

2

1 2 1 2( )s 1

H

methanol

q CV

q sτ τ τ τ=

+ + + (11)

The amount of hydrogen available from the reformer can be used to control the methane

flow rate by using a PI controller can be expressed as

2

3 03

3

( )( )2

inFC

methanol H

k N Iq k q

s FUτ= + − (12)

Figure 3 Partial pressures of the gases Figure 4 Activation and ohmic losses of the fuel cell



Figure 4 simulation model of the PEM fuel cell.

Symbol Variable Value

N Number of cell in fuel cell stack 10

F Faraday’s constant 96484600 C/mol

R Universal gas constant 8314.47J/kmol2K

Kp=N/4F Constant 71.0883 10−× kmol/s

-1A

KH2 Valve molar constant for hydrogen 54.22 10−× kmol/s

-1atm

KO2 Valve molar constant for oxygen 52.11 10−× kmol/s

-1 atm

KH2O Valve molar constant for water 67.716 10 −× kmol/s

-1 atm

2 2 2, ,H O H Oτ τ τ

Response time for hydrogen, oxygen, water

flow 3.37,18,418,6.74sec

U Utilization factor 0.8

τ1, τ2 Reformer time constant 2 sec

CV Conversion factor 2

B Activation Voltage constant 0.04777

C Activation Voltage constant 0.0136

K3 PI gain constants 10

Table 2 Values used for design of PEM fuel cell



3. DESIGN OF HYBRID BOOST CONVERTER

3.1 Analysis of hybrid topology

When compared to non-renewable energy source based vehicles such as internal combustion

engines renewable energy based vehicles will give good vehicle performance lower fuel cost

and less pollution.in fuel cell vehicles the hydrogen gas is stored on board of vehicles. It

reacts with oxygen undergoes oxidation and give electricity, heat and water. The main

drawback of fuel cell vehicles is slow response to load variations due to their electrochemical,

thermal characteristics. Therefore, it needs energy storage that can deliver quick power such

as battery or capacitor bank.

The proposed converter consists of two cells with current fed full bridge connected in

parallel at low voltage side and half bridge voltage doubler connected in series at high voltage

side. The model diagram of the converter is shown in figure5. The proposed converter is

interleaved type which has more advantages then the single cell converter because of high

power handling capacity, high efficiency, reduced thermal requirements, reduced switch

ratings and turns ratio of the transformer. The upper and bottom cells was shares unequal

currents.

Merits of the proposed converter are switching losses are reduced greatly because of ZCS

of primary side switches and ZVS of secondary side switches, voltage across the primary side

devices is independent of duty cycle with varying input voltage, due to interleaved design the

power handling capacity and reliability will be increases. In case of failure of any one of the

cell it will supply 50% of the rated output power.it will satisfy bidirectional power flow that

means in forward direction it act as a current fed converter and during regenerative breaking

condition it will act as a voltage fed converter and charges the energy storage system.

Figure 4 simulation model of the hybrid boost converter.

3.2. Operation and analysis of the converter

In this section zero current switching of the primary side of the cells has been explained.

Before turn on the off switches (diagonal pair) (e.g. S2-S3) the already turned on switches

should be turned off (e.g. S1-S4). The total output voltage is the sum of two cells output

(V0).The output voltage of each cell is V0/2.The secondary side voltage of each HF

transformer is V0/4. This voltage is reflected to primary of transformer as V0/4n.where n is

turns ratio. This voltage will cause the current in one pair increases and finally reaches to

steady state value and current in other pair will decreases and finally reaches to zero. During

this period the body diodes of the respective switches will conducts.



The following assumptions are made in order to analysis the study state operation and

analysis of the proposed converter.1. The input boost inductor is assumed as large to make

constant current through it. 2. The output capacitors are assumed as large to make constant

voltage across it 3. By taking all the switches are assumed as ideal.4. Magnetizing inductance

of the transformer is assumed as very large.

In the proposed converter diagonal switch pairs of cell1 (S1-S4) and (S2-S3) are should be

operated with identical gate signals having phase shift of 1800.similarly diagonal switch pairs

of cell2 (S5-S8) and (S6-S7) are should be operated with identical gate signals having phase

shift of 1800.the phase shift between gating signals of (S1-S4) in cell1 and (S5-S8) in cell2 is

900. Similarly the phase shift between gating signals of (S2-S3) in cell1 and (S6-S7) in cell2 is

900. Maintain duty ratio of all the switches should be more than 50%. The gate signals of the

primary and secondary side switches are shown in figure 6.

3.2. Design of the proposed converter

The design of proposed converter is discussed in this section. The following parameters are

required to be designed for converter.

parameter symbol value

Input voltage Vin 12V

Output voltage Vout 300V

Switching frequency fsw 100KHz

Input boost inductors L1,L2 36uH

Snubber capacitors C1-C12 0.5pF

Turns ratio of transformer 1:k 1:2.5

Input capacitor Cin 4.7mF

Output filter capacitors C01- C04 680uF

Leakage inductance of T/F Llk 1.6uF

Duty ratio d% 0.8

Current ripple I∆ 1A

Table 3 Values used for design of boost converter.

A) Determine Boost Inductor Value:

While choosing the inductor, first the most basic parameter is the saturation current of the

inductor. In the event that the saturation current of the inductor is not as much as the converter

required peak current, at that point the converter won't ready to supply the fundamental output

power.

.(d 0.5)

.f

in

s

VL

I

−=

∆

%

(13)

By using above parameters, the inductor value can be calculated according to the

equation.

B) Voltage Gain:

According to volt-sec balance on inductor,

0

in

VM =

V (14)



The voltage conversion ratio is

0

2.k .V

1

inVd

=− %

. (15)

4. RESULTS AND DISCUSSIONS

The suggested converter was simulated by using PSIM 9.0.4 software. The fuel cell output

voltage is shown in figure5.with increase of temperature of the fuel cell stack the no-load

voltage, stack output voltage and output power are decreased. Input boost inductor currents i

(L1) and i (L2) are separated each other by 180 . Their ripple frequency is double the device

switching frequency. Input current ˆin

i in is the vector addition of i (L1) and i (L2) is shown in

figure7. The ripple frequency is four times the device switching frequency. So it reduces the

input capacitor filter Cin requirement. Voltage across output capacitors C01 and C02 are phase

shifted with each other by 180 shown in figure10.similarly for output capacitors C03 and C04

also is shown in figure10. The phase shift between voltage across C01 of CELL1 and C03 of

CELL2 is 90 . Due to the cancellation effect the output voltage contains lower ripple

magnitude, which eliminates the output filter requirement. The peak value of current through

the series inductors LLlk1and LLlk2 is greater than the constant value due to the extended

conduction of body diodes of corresponding primary switching devices ensuring their ZCS

turn-off. The maximum Voltage across the primary switches is very less, i.e., V0/4n.

Figure 5 fuel cell stack output voltage

Figure 6 Gating signals of all the switching devices of boost converter

0 5 10 15 20

Time (s)

12.001

12.002

12.003

12.004

12.005

12.006

12.007

Vfc

0

0.4

0.8

G1

0

0.4

0.8

G2

0

0.4

0.8

G5

0.2 0.20002 0.20004 0.20006 0.20008 0.2001

Time (s)

0

0.4

0.8

G6

0

0.4

0.8

G9

0

0.4

0.8

G10

0

0.4

0.8

G11

0.2 0.20002 0.20004 0.20006 0.20008 0.2001

Time (s)

0

0.4

0.8

G12



Figure 7 Simulation waveform of input boost inductor currents I(L1 ).

Figure 8 Simulation waveform of voltage Figure 9 Output voltage of boost converter

waveforms VAB and VCD

Figure 10 Voltages across output capacitors Figure 11 voltage waveforms of V (LLlk1), V (LLlk2)

Vco1, Vco1, Vco1 and Vco3.

5. CONCLUSION

The suggested converter is isolated based converter. The proposed converter operates ZCS

turn-off of primary side devices and ZVS turn-on of secondary side devices. Due to which the

switching losses of the converter is very low. Operating frequency of the converter is very

high so that size of the converter is reduces. With interleaved design power handling capacity

increases. The major advantage with this converter, the voltage across the power switches is

0.2 0.20002 0.20004 0.20006 0.20008 0.2001 0.20012

Time (s)

37

37.5

38

38.5

39

IL1

0 0.1 0.2 0.3 0.4 0.5

T ime (s)

0

-100

100

200

300

400

VO

78.2

78.21

78.22

78.23

78.24

VC01 VC02

0.19999 0.2 0.20001 0.20002

Time (s)

77.61

77.62

77.63

77.64

77.65

VC03 VC04

0

-20

20

VLK1

0.20002 0.20004 0.20006 0.20008

Time (s)

0

-20

-40

20

40

VLK2



very low. This converter is best for fuel cell based electric vehicle. The performance of the

presented converter will be studied with respect to closed loop control in future.

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DESIGN AND SIMULATION OF DC-DC CONVERTER WITH HIGH … · dc-dc converter with high voltage gain...

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