Modeling, control and power management of hybrid photovoltaic fuel cells with battery bank supplying...

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Modeling, control and power management ofhybrid photovoltaic fuel cells with battery banksupplying electric vehicle

Zahra Mokrani, Djamila Rekioua, Toufik Rekioua*

Laboratoire LTII, Universite de Bejaia, 06000 Bejaia, Algeria

a r t i c l e i n f o

Article history:

Received 22 February 2014

Received in revised form

26 March 2014

Accepted 27 March 2014

Available online xxx

Keywords:

Hybrid power system

Photovoltaic

Fuel cells

Battery

Power management

Electric vehicle

* Corresponding author.E-mail addresses: [email protected], t_rek

Please cite this article in press as: Mokranwith battery bank supplying electric vj.ijhydene.2014.03.215

http://dx.doi.org/10.1016/j.ijhydene.2014.03.20360-3199/Copyright ª 2014, Hydrogen Ener

a b s t r a c t

In this paper, modeling, control and power management (PM) of hybrid Photovoltaic Fuel

cell/Battery bank system supplying electric vehicle is presented. The HPS is used to pro-

duce energy without interruption. It consists of a photovoltaic generator (PV), a proton

exchange membrane fuel cell (PEMFC), and a battery bank supplying an electric vehicle of

3 kW. In our work, PV and PEMFC systems work in parallel via DC/DC converter and the

battery bank is used to store the excess of energy. The mathematical model topology and it

power management of HPS with battery bank system supplying electric vehicle (EV) are the

significant contribution of this paper. Obtained results under Matlab/Simulink and some

experimental ones are presented and discussed.

Copyright ª 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

Introduction

Hybrid power systems are used to supply loads and ensure

load demand without interruption. We can use different

sources, conventional ones as coal, natural gazes, fossils

fuels,. or renewables ones as solar, wind, hydraulic,. [1e13].

In addition to energy, a hybrid system may also include a DC

or AC converters, a storage system, and a control system for

power management. All these components can be connected

in different architectures. The electric vehicle in the auto-

motive field is the cleanest andmost environmentally friendly

transport solution. Also, it overcomes the noise since there is

almost none noise. In fact, an electric car is really ecological if

the electrical energy consumed is produced from renewable

energy sources as solar, wind, hydro,.. However, these

[email protected] (T. Rekiou

i Z, et al., Modeling, conehicle, International Jo

15gy Publications, LLC. Publ

renewable sources are intermittent, why a storage system

must be inserted. Generally we use batteries. Electric vehicles

with batteries already exist and are have autonomy less than

200 km. These last years, manufacturers are interested to

hydrogen or fuel cell vehicle which can have autonomy of

400e800 km depending on car models, and which produces

less carbon dioxide (g/km). A fuel cell works as a battery. It

stores energy but as hydrogen. It react hydrogen with the

oxygen in the air to obtain water and energy. However,

extracting hydrogen from air or water requires twice as much

energy as the use of battery in electric vehicle, thus the cost of

hydrogen production is high. It will be interesting to use

another source of energy as solar.

The present work is dedicated to a study of hybrid photo-

voltaic/Fuel Cells system supplying an electric vehicle with bat-

terybank.Theadvantagesofeachsourceused, allowus toobtain

a).

trol and power management of hybrid photovoltaic fuel cellsurnal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/

ished by Elsevier Ltd. All rights reserved.

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http://dx.doi.org/10.1016/j.ijhydene.2014.03.215



Nomenclature

Af frontal surface area of the vehicle, m2

Cd aerodynamic drag coefficient

C10 rated capacity, A h

Eb voltage source, V

ENerst voltage Nerst, V

Fr total force, N m

fro rolling resistance force constant

Ftire rolling resistance force, N m

G solar radiation, W/m2

Ipv output-terminal current, A

Iph diode-current, A

Ish shunt-leakage current, A

Isc short circuit current, A

I0 saturation current of the diode, A

Impp maximum current at PPM, A

K Boltzmann constant, J/K

m vehicle total mass, kg

nb number of cells

Pmpp maximum power point, W

PPV photovoltaic power, W

q electron charge, C

r tire radius, m

Rb internal resistance, U

Rs series resistance, U

Rsh shunt resistance, U

Tj temperature cells, K

Tjref reference temperature of the PV cell, K

TPEMFC absolute operating temperature of the stack, K

Uact activation overvoltage, V

Uconc concentration or diffusion over-voltage, V

Uohm resistive or ohmic over-voltage, V

V vehicle speed, m/s

Vmpp maximum voltage at PPM, V

Voc open circuit voltage, V

VPEMFC fuel cell voltage, V

Greek letters

asc temperature coefficient of short-current, A/K

ai constants

b road slope angle, �

boc voltage temperature coefficient, V/K

DT heating of the accumulator, K

rair air density

Abbreviations

AC alternate current

DC direct current

DTC direct Torque control

EV electric vehicle

FC fuel cell

FLC fuzzy logic controller

HPS hybrid power system

IM induction motor

MPP maximum power point

PEMFC proton exchange membrane fuel cell

PM power management

PV photovoltaic panels

RFOC rotor flux oriented control

SFOC stator oriented control

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 4 ) 1e1 02

a cheaper and less polluting EV.We use in our case an induction

motor (IM) of 3 kW as propulsion of the EV. To kept the DC bus

voltage at a constant value when the speed of the rotor varies,

different control techniques can be used as stator oriented con-

trol (SFOC), rotor flux oriented control (RFOC), Direct Torque

Control (DTC), Fuzzy logic controller (FLC),.. In ourwork, the IM

Fig. 1 e Studied hybrid photovoltaic/fuel

Please cite this article in press as: Mokrani Z, et al., Modeling, conwith battery bank supplying electric vehicle, International Joj.ijhydene.2014.03.215

is controlled using DTC Strategy, which is a powerful control

method for motor drives. The global system is presented,

modeledandsimulatedunderMatlab/Simulink. Eachsubsystem

has been simulated separately, and then, the power manage-

ment of the proposed system is given. Obtained simulation re-

sults and some experimental ones are presented and discussed.

cells/battery bank for electric vehicle.




Fig. 2 e Different forces acting on a vehicle moving along a

slope.

Fig. 3 e Equivalent circuit of photovoltaic cell.

Table 1 e Parameter of the PV panel Siemens SM110-24[1].

PPV Photovoltaic power (W) 110 W

Impp Maximum current at PPM (A) 3.15 A

Vmpp Maximum voltage at PPM (V) 35 V

Isc Short circuit current (A) 3.45 A

Voc Open circuit voltage (V) 43.5 V

asc Temperature coefficient of short-current (A/K) 1.4 mA/�Cboc Voltage temperature coefficient (V/K) �152 mV/�CPmpp Maximum power point (W) 110 W

i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 4 ) 1e1 0 3

Studied system

The global system consists of a photovoltaic generator, a

proton exchange membrane fuel cell and a battery bank

supplying an electric vehicle of 3 kW (Fig. 1).

Electric vehicle description

The different forces acting on an EVwithm total massmoving

along a slope are represented in Fig. 2.

Fig. 4 e Bloc diagram of p


We have three forces:

- Rolling resistance force Ftire due to the friction of the

vehicle tires on the road. It is given as:

Ftire ¼ m� g� fro (1)

with: m is the vehicle total mass, g is the gravity acceleration,

fro is the rolling resistance force constant.

- Aerodynamic drag force Faero caused by the friction on the

body moving through the air. Its expression is:

Faero ¼ ð1=2Þ � rair � Af � Cd � V2 (2)

with: rair is the air density, Af is the frontal surface area of the

vehicle, Cd is the aerodynamic drag coefficient, V is the vehicle

speed.

- Climbing force Fslope which depends on the road slope.

Fslope ¼ m� g� sinðbÞ (3)

with: b is the road slope angle.

The total resistive force Fr is given as:

Fr ¼ Ftire þ Faero þ Fslope (4)

hotovoltaic module.




Fig. 5 e Electrical characteristics under experimental and simulation.


The load torque can be written as:

Tr ¼ Fr � r (5)

with: r is the tire radius, Fr is the total force.

Fig. 7 e Battery equivalent circuit.

Modeling of the studied system

Modeling of photovoltaic panels

The model studied in this work consists of a single diode for

the cell polarization function and two resistors for the losses

(Fig. 3).where: Ipv is the output-terminal current, Iph is the

light-generated current, Id is the diode-current, Ish is the

shunt-leakage current, Rs is the series resistance and repre-

sents the internal resistance to the current flows, and depends

on the p-n junction depth, the impurities and the contact

resistance, Rsh is the shunt resistance and it is inversely

related with leakage current to the ground, G solar radiation

(W/m2).

The Ipv(Vpv) characteristic of this model is given by

[1,4,9,13]:

Ipv ¼ Iph � Id � IRsh(6)

Ipv ¼ Iph � I0 ��exp

�q� �

Vpv þ Rs � Ipv�

A�Ns � K� Tj

�� 1

�� Vpv þ Rs � Ipv

Rsh

(7)

Fig. 6 e Electrical representation of a PEMFC.


The bloc diagram of PV module can be represented as

(Fig. 4):

The parameters of the solar module used (Siemens SM110-

24) are given in Table 1.

The electrical characteristics IpveVpv and PpveVpv are given

in Fig. 5 [1].

Modeling of fuel cell PEMFC

The electrical representation is as follows (Fig. 6).

Fig. 8 e Stator flux trajectory by appropriate voltage vectors

selection.




Fig. 9 e DTC general configuration.


The cell voltage VPEMFC is given as the summation of Nerst

voltage ENerst due to various irreversible loss mechanisms,

activation overvoltage Uact, concentration or diffusion over-

voltage Uconc and resistive or ohmic over-voltage Uohm [1,4,8].

VPEMFC ¼ ENernst þ Uact � Uohm � Uconc (8)

where:

Fig. 10 e Block diagram o


ENernst ¼ a1 þ a2 � ðTPEMFC � 298:15Þ þ a3� (9)
� TPEMFC � 0:5� ln P�O2
þ ln P�H2

Uact ¼ b1 þ b2 � TPEMFC þ b3 � TPEMFC � ln�j� 5� 10�3

�þ b4 � TPEMFC � ln C�

O2

(10)

f the overall system.




Uohm ¼ IpacScell

�

0B@181:6�

�1þ 0:03�

�IPEMFCScell

þ 0:06� �

T303

�2 � �IPEMFCScell

2:5�

hl� 0:634� 3�

�IPEMFCScell

iexp

�4:18

�T�303

T

�� IPEMFC þ Scell � Rc

1CA (11)


with C�O2

is the oxygen concentration in the cathode area

(mol/cm3), bi are constants, Scell: Area active cell (m2), Rc:

equivalent contact resistance of the electrodes conduction (U).

Uconc ¼ �B� ln

�1� j

jmax

�(12)

with: TPEMFC: absolute operating temperature of the stack (K),

ai are constants.

Battery modeling

Themodel used in this work is based on the electrical scheme

given in Fig. 7.

We have:

Ubatt ¼ nb � Eb � nb � Rbatt � Ibatt (13)

where: Eb the voltage source, Rb, an internal resistance, nbnumber of cells.

The battery capacity Cbatt is given as [1]:

Cbatt ¼ C10 � 1:67� ð1þ 0:005� DTÞ1þ 0:67�

�II10

0:9 (14)

where: DT is the heating of the accumulator, C10 is the rated

capacity (I10).

The state of battery charge can be written as:

SOC ¼ 1� QCbatt

(15)

with:

Q ¼ Ibatt � t (16)

where: t is the discharging time with a current Ibatt.

The battery voltage (charge and discharge) is function of

the internal components of the battery. It is written as:

Vbatt�charge ¼ nb � ½2þ 0:16� SOC� þ nb

� IbattC10

"6

1þ I1:3batt

þ 0:27SOC1:5

þ 0:002

#� ð1� 0:007$DTÞ

(17)

Table 2 e Parameters of the electric vehicle model.

Parameters Symbol Values Units

Vehicle total mass m 1300 kg

Rolling resistance force constant fr 0.01

Air density rair 1.20 kg m2

Frontal surface area of the vehicle Af 2.60 m2

Tire radius R 0.32 m

Aerodynamic drag coefficient Cd 0.32


Vbatt�discharge ¼ nb � ½1:965þ 0:12� SOC� � nb � IbattC10" #

� 4

1þ I1:3batt

þ 0:27SOC1:5

þ 0:002 � ð1� 0:007$DTÞ

(18)

Direct torque control strategy

In principle, direct torque control (D.T.C) strategy is based on

instantaneous space vector theory. By optimal selection of

the space voltage vectors in each sampling period, this

method archives effective control of the stator flux and

torque.

The stator flux can be estimated using measured current

and voltage vectors [14e17]:

fsðtÞ ¼Z t

0

ðVs � Rs � isÞ � dt (19)

The stator flux components fsa and fsb along a and b stator

axes can be estimated as:

fsaðtÞ ¼Z t

0

ðVsa � Rs � isaÞ � dt

fsbðtÞ ¼Z t

0

ðVsb � Rs � isbÞ � dt

(20)

The magnitude of the stator flux can then be estimated by:

fs ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffif2sa þ f2

sb

q(21)

And the electromagnetic torque can be calculated by:

Te ¼ 32� p� �

fsa � isb � fsb � isa�

(22)

Fig. 8 shows the voltage vectors which are usually

employed in DTC scheme [16].

A simplified block diagram of direct torque control is

shown in Fig. 9.

Table 3 e Parameters of the induction machine.

Parameters Symbols Values Units

Shaft power Pu 3 kW

Number of pole pairs P 2

Stator resistance Rs 1.76 U

Rotor resistance Rr 1.95 U

Mutual inductance M 0.183 H

Stator(rotor) self-inductance Ls ¼ Lr 0.194 H

Inertia moment J 0.02 kg m2

Viscous friction f 0.0001 N m s2




Fig. 11 e Power and vehicle speed.


Power management of the studied system

EV using batteries storage must be recharged regularly. Those

using fuel cells for feeding electrical energy, a supply for

hydrogen is necessary. And those equipped with PV panels,

solar energy provides them energy only during sunshine

period. Generally, EV uses batteries for storage, but due to the

less autonomy, hydrogen or fuel cell vehicle, solar vehicle or a

combination of solar, FC and battery bank can be a competi-

tive solution. Power management control is necessary to

make coordination between the different energy sources. In

our work, we choose to use the battery bank system to starts

producing energy. Then Hydrogen is used by the fuel cell to

produce energy and at least photovoltaic system works to

convert irradiation to electrical energy provided to a DC bus.

The total power is calculated as [9,10,17]:

Pload ¼ Pbatt þ PFC þ Ppv (23)

The bloc diagram of the overall studied system under

Matlab/Simulink is given (Fig. 10).

The motor and electric vehicle parameters used in simu-

lation are listed respectively in Tables 2 and 3.


The power and vehicle speed are given as follow (Fig. 11).

The obtained results are presented in Fig. 12(a, b, c, d, e).

We can note from the obtained results, that the proposed

hybrid system works as proposed by the power management

control. To test the robustness of DTC, we make a sudden

variation of rotational speed at t ¼ 2 s (Figs. 13e18).

The obtained results confirm the presented theory. We

note that even the rotation speed of the induction motor

changes, the flux kept constant.

Conclusion

In this paper, modeling, control and power management of

hybrid Photovoltaic/Fuel cells/Battery bank system supplying

an electric vehicle is presented. The different parts of the

proposed system have been firstly simulated separately and

then the power management control has been used to coor-

dinate between the three sources to supply the EV. The

simulation model of the hybrid system has been developed

using MATLAB/Simulink. The obtained results show the

feasibility of the hybrid system production for an electric

vehicle.




Fig. 12 e (a) Power delivered by photovoltaic generator; (b) Power delivered by battery bank; (c) Power delivered by fuel cells;

(d) Power delivered to the load by the three sources.


Please cite this article in press as: Mokrani Z, et al., Modeling, control and power management of hybrid photovoltaic fuel cellswith battery bank supplying electric vehicle, International Journal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/j.ijhydene.2014.03.215



Fig. 13 e Rotor speed waveform.

Fig. 14 e Stator current waveform.

Fig. 15 e Zoom on stator current waveform.

Fig. 16 e Electromagnetic torque waveform.

Please cite this article in press as: Mokrani Z, et al., Modeling, control and power management of hybrid photovoltaic fuel cellswith battery bank supplying electric vehicle, International Journal of Hydrogen Energy (2014), http://dx.doi.org/10.1016/j.ijhydene.2014.03.215

Fig. 17 e Zoom on electromagnetic torque waveform.

Fig. 18 e Stator flux circular trajectory.

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