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Research ArticleModeling, Control, and Simulation of Battery StoragePhotovoltaic-Wave Energy Hybrid Renewable Power GenerationSystems for Island Electrification in Malaysia

Nahidul Hoque Samrat,1 Norhafizan Bin Ahmad,1

Imtiaz Ahmed Choudhury,1 and Zahari Bin Taha2

Centre for Product Design and Manufacturing (CPDM), Department of Mechanical Engineering,Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia

Innovative Manufacturing, Mechatronics and Sports Laboratory (iMAMS), Faculty of Manufacturing Engineering,Universiti Malaysia Pahang, Pekan, Pahang, Malaysia

Correspondence should be addressed to Norhazan Bin Ahmad; norhazan@um.edu.my

Received February ; Accepted March ; Published April

Academic Editors: P. Meyrueis and H. Zhou

Copyright Nahidul Hoque Samrat et al. Tis is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

oday, the whole world aces a great challenge to overcome the environmental problems related to global energy production. Mosto the islands throughout the world depend on ossil uel importation with respect to energy production. Recent development andresearch on green energy sources can assure sustainable power supply or the islands. Butunpredictable nature and high dependencyon weather conditions arethe mainlimitations o renewableenergy sources. o overcomethis drawback,different renewablesourcesand converters need to be integrated with each other. Tis paper proposes a standalone hybrid photovoltaic- (PV-) wave energyconversion system with energy storage. In the proposed hybrid system, control o the bidirectional buck-boost DC-DC converter(BBDC) is used to maintain the constant dc-link voltage. It also accumulates the excess hybrid power in the battery bank andsupplies this power to the system load during the shortage o hybrid power. A three-phase complex vector control scheme voltagesourceinverter (VSI)is used tocontrol theloadside voltage in terms othe requencyand voltageamplitude. Basedon thesimulationresults obtained rom Matlab/Simulink, it hasbeen oundthatthe overall hybridrameworkis capable o working under thevariableweather and load conditions.

1. Introduction

In developing countries like Malaysia, the development oislands is mostly related to the electric power availability,because there are many islands all over Malaysia whereelectric power grid is not available. Among these islandcommunities electricity is supplied by traditional energysources, but the uel cost increases signicantly with remote-ness. Furthermore, the energy produced by the conventionalsources raises the greenhouse gas emissions, which may bethe key source o global warming. It is projected that, by, Malaysia will release . million tons o CO2whichis an increase o .% compared to the amount o CO2emitted in the year . In Malaysia, electricity generation

alone contributes .% o the total CO2emission, which

is the largest among all sectors []. Malaysia signed theprevious Kyoto protocol on reduction o CO2 emission tothe atmosphere. For this reason, the Malaysian governmentis very much concerned about environmental issue andthe government wants the overall improvement o the CO2emission. As a result, island electrication in Malaysia byrenewable energy sources is the only way to overcome thechallenge.

Among the renewable energy sources, solar energy isan environmentally riendly and the astest growing greenenergy source. But the main drawback o the PV system isthat the power produced by this system is highly dependenton climatic conditions. For example, a PV system could

Hindawi Publishing Corporatione Scientific World JournalVolume 2014, Article ID 436376, 21 pageshttp://dx.doi.org/10.1155/2014/436376

http://dx.doi.org/10.1155/2014/436376http://dx.doi.org/10.1155/2014/436376

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not able to produce any power at night and during cloudyperiods. So the PV system intermittently produces power,which means that PV system may not totally satisy theload demand at each instant. Tis problem can be solved bycombining PV system with other renewable energy sourcesand/or energy storage systems (such wind, wave, uel cell,

battery bank, ultracapacitor bank, and hydrogen storagetank) in a suitable hybrid ramework []. As an islandsurrounded by sea, wave energy can be considered one o theenvironmentally riendly hybrid power generating sourcesor island communities.

Wave energy is a renewable energy generated by the orceo surace waves rom the ocean. Although many wave energyconversion techniques have been patented and new patentsare granted each month [], there are only nine basic tech-niques on which these conversions are based. Te nine basictechniques are cavity resonators or oscillating water column,pressure devices, heaving and pitching bodies, Salters duck,surging wave energy converters, particle motion converters,Russells rectier, Cockerells rafs, and wave ocusing tech-niques []. In this study, an OWC wave energy converterdevice is preerred because OWC is generally consideredone o the most promising wave energy conversion devicesamong the various wave energy converters []. However,assisting PV-wave hybrid system with battery banks makeseconomic sense when satisying the transients period or peakload demands. Battery based energy storage system is widelyused in standalone system because o its mature technology,high efficiency, quick response, and low cost [, ]. Withoutbattery bank, the PV-wave hybrid system must meet all loaddemands, thus increasing the cost and size o the hybridsystem.

An extensive review based on the solar and other relevantareas has been reported in the literature to model hybridrenewable energy system. Among them, Onar et al. [, ]described detail dynamic model, mathematical modeling,and simulation o both solar/uel cell/ultracapacitor andwind/uel cell/ultracapacitor hybrid system. In [], a wind,PV, and wave based large-scale hybrid system integration wasanalyzed and grid connection was discussed. Bhende et al.[] investigated a standalone uel cell based wind energysupply system. Power conditioning or hydrogen storagebased wind energy system has been reported in []. In[,,,,], the authors are silent about the wave energybased hybrid system design or island communities.

In this paper, detailed modeling, control, and simulation

o a PV-wave hybrid renewable power generation system aredeveloped or island communities. OWC wave energy deviceis used to generate the electrical power rom the sea wavesand PV model is used to generate power rom solar radiation.A control algorithm is developed using a BBDC between thebatterybank anddc-link, anda switch mode inverteris placedat the load side end. A simple passive L-C lter is placed aferthe inverter at load side end to eliminate the unwanted highrequency harmonics, which are generated by the load sideVSI based on the inverter switching requency.

Te simulation model can be used not only or analyzingthe battery storage based PV-wave hybrid system peror-mance, but also or designing and sizing the system HRES to

meet the consumer load demands or any available meteoro-logical condition. Te proposed standalone PV-wave hybridsystem model in this paper has been modeled, designed,and simulated using Matlab, Simulink, and SimPowerSys-tems sofware packages. In addition, simulation results arepresented to veriy the effectiveness o the proposed system

under variable weather conditions.Te sequential workow hints o this paper are as ol-lows. In Section the complete modeling process o PV-wave hybrid system has been described with the necessarymathematical equations. And also Section presents thecontrol algorithm o dc-link voltage and load side VSI. InSection, according to the meteorological data, PerhentianIsland is considered as a potential area or generating electricpower rom PV and wave energy sources. In Section allthe necessary simulation results and discussions are given tocheck theeasibilityo thehybrid system. Finally, a conclusionhas been drawn by combining all the important points o thestudy in Section.

2. System Description

In this section, the detailed simulation model o PV-wave hybrid renewable power generation system is brieydescribed. Figure shows the complete block diagram othe standalone PV-wave HRES. Te developed hybrid systemconsists o ve main parts: PV system, OWC system, batterybank, a BBDC with proportional integral (PI) control dutycycle, and a pulse width modulation (PWM) insulated-gatebipolar transistor (IGB) VSI located at the load side. Tesolar PV system consists o PV array and DC-DC converterwith maximum power point tracking (MPP) algorithm.

In PV system, MPP is used to increase the system effi-ciency by controlling DC-DC converter. Te OWC systemwas congured by the bidirectional Darrieus turbine drivenpermanent magnet synchronous generator (PMSG) and anAC-DC three-phase rectier.

In the HRES, the renewable PV and wave energy systemis considered as a main power generation source to meet thesystem load demand and battery bank is used as a backupenergy storage system. Te HRES is proposed to implementin island areas in Malaysia; hence, i generated power romHRES is not enough to meet the system load demands, thenbattery bank will deliver power to balance the system powerdemand. o interace PV, wave, and battery bank in hybrid

ramework, the dc-link voltage must be constant. Hence, aBBDC with PI controller is used in the HRES to maintainthe constantdc-link voltage. A three-phase VSI with relativelycomplex vector control scheme is used at load side to controlload side voltage in terms o the amplitude andrequency. Tedetailed description o each component o the overall HRESand controller is given in the ollowing parts.

.. Modeling and Characteristics of PV System. Solar PVsystems generate electric power by converting solar photonenergy into electrical energy in the orm o direct currentusing solar cell or PV cell. Crystalline or polycrystallinematerials are commonly used or solar cell []. Each o the

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DC

DC

MPPT

DC

DC

Emergency

backup

DC

DC

DC

DC

Dumpload

Photovoltaicarrays

DC bus

PWMinverter

Variable loads

AC voltage

OWC wave energyconverter

Battery bank

PV converter

DC-DCbuck-boostconverter

DC-DC

boost

converter

DC-DCbuck

converter

Permanent magnetsynchronous generator

Dioderectier

OWC

TurbineWave

PMSG

F : Block diagram o the proposed standalone PV-wave hybrid system.

Solarirradiation

Ideal PVcell

Diode

I0IphIPV

Rs

Rsh

F : Circuit diagram o single diode PV model.

PV cells produces around . V and it is the smallest unito the solar PV system. Cells are urther connected in seriesor/and parallel combination to orm a PV array. Figure shows widely used one diode equivalent circuit model or aPV cell []. PV cell equivalent circuit model consists o acurrent source parallel with a diode and the output terminalso the circuit are connected to the load through the shuntand series resistor. Te current-voltage characteristics o PVarray can be expressed using some nonlinear mathematicalexponentialequations. Te ideal relationship between voltageand current is given by []

PV= ph sh= ph 0 exp PV+ PV 1

PV+ PVsh ,()

wherePV is the output current o the PV cell (A),ph isthe photocurrent, is the diode current,sh is the currentthrough the shunt resistance,

0 is the reverse saturation

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0 5 10 15 20 250

1

2

3

4

5

6

PV module voltage (V)

PVmodulecurrent(A)

S = 1000W/m2

S = 800W/m2

S = 600W/m2

F : KOYCERA KC-W PV model I-V characteristics curve with varying irradiation.

PV module voltage (V)

0 5 10 15 20 250

10

20

30

40

50

60

70

80

90

PVmodulepow

er(W)

S = 1000W/m2

S = 800 W/m2

S = 600W/m2

F : KOYCERA KC-W PV model P-V characteristics curve with varying irradiation.

current,

, theBoltzmannconstant =

1.381023

(J

/K

),

,the

charge o electron = 1.61019 (), is the cell temperature(K),PVis the output terminal voltage o the PV cell (V),is the quality actor (lies between . and . or crystallinesilicon), is the series resistance (), andsh is the shuntresistance ().

Te output power rom solar PV array is given by

PV= PVPVconv, ()whereconvis the DC-DC converter efficiency (typically %). In this paper total ve KOYCERA KC-W PVmodels are used or W power generation and all theve models connected in series with one another. Te power-

voltage and current-voltage characteristics o KOYCERA

KC-W PV model are obtained according to the valueo the variablesph,0,sh, and. Te value o the variablescan be collected rom []; they usually provide values orPV andPV at open circuit, short circuit, and maximumpower point and nally the number o the PV cells. Tecurrent-voltage and power-voltage characteristics o a solarPV module operating at a standard temperature o C anddifferent solar irradiance are shown in Figuresand.

According to solar irradiation or load current, the max-imum output power o the PV module varies. Tereore,a proper control system is needed to use the PV modelmore efficiently as an electric power source by building aMPP. Tere are many different MPP methods discussed in

[, , ], among them perturbation and observation

method (P&O) is most widelyused becauseit is much simplerand needs ewer measured variables. In this paper rom [],P&O method is used or building MPP in Simulink envi-ronment. According to (), (), and the literature describedin [,], PV model with MPP is developed using MatlabSimulink, which is illustrated in Figures(a),(b), and(c).

.. Modeling of OWC. It should be noted that this paperocuses on the designing o a battery storage standalonePV-wave hybrid supply system or island communities and,thereore, the mathematical modeling or individualelementssuch as OWC wave chambers is simplied. Te detaileddesign and complete mathematical modeling o OWC wave

energy system can be ound in [], where more precisemodel is established.

Te operating principle o the OWC as shown in Figure is much like a wind energy system via the wave inducedair pressurization principle. In this system sea wave motioncauses the rise and all o the water level within the wavechamber. Tis causes pressure oscillations, which can be usedto drive a bidirectional air turbine. Te bidirectional turbineextracts the kinetic energy o sea wave and turned it intomechanical energy which is ed into the electrical generator.Te generator converts this mechanical energy into electricalenergy which will eed directly either to the load or in thegrid.

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T

Variable irradiations

S

30

S

T

IGBT

D

V

D P

I

PO MPPT PWM generator(DC-DC)

1

2

+

+

V+

V

CPV

LPV

CPV1

Vin

Iin

dc-link+

dc-link

(c)

F : Te Simulink diagram o the PV model with MPP. (a) PV Simulink model; (b) MPP model; (c) complete Simulink PV modelwith MPP.

Wave

Air direction

ShoreMean sea level

Darrieus turbine

VelocityV1PressureP1

1

Turbine inletareaA2

Inlet velocityV2Inlet pressureP2

Chamber inletareaA1

F : OWC chamber parameters.

In this section, a set o equations is present to describethe power generated by OWC system. As mentioned earlier,OWC wave energy operating principle is much like windturbine system, so the power available at the wave turbineconsists o two terms: air velocity term and air pressuretermpt. Tereore, the total inlet power can be describedusing the ollowing equation:

Inlet Powerin= + pt, ()where the power

acting on the turbine due to the air

velocity term is

=2322 . ()

Te available output power developed by the OWC is aunction o the turbine power coefficient, so the totaloutput power developed by the OWC is

total= + pt . ()Te power due to the air velocity term is straightorward andshown in (). But power due to the pressure term is more

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Wave progression

Wavelength

Chamber lengthLch= 1.5m

1(peak)

Wave heightH

F : OWC ull chamber arrangements [].

complex. It is mainly depending on the surace elevationin OWC chamber. But this wave surace elevation urtherdepends on the two major actors, namely, the turbine inlet

velocity and air pressureterm. Both o these actors are relatedto the OWC chamber length, water depth, and so orth. So,

in this paper, the mathematical modelling o OWC waveenergy system mainly ocuses on the air pressure term andits derivative rom the literature [], which is discussedhere.

Figures andillustrate the parameters related to theOWC. At rst, it assumed that the regular outer wave reesurace elevation can be stated as []

Outer wave surace elevation0=2 cos2 , ()

where is the wave height (m) and is the wave period(s). I the chamber length o OWC is

ch with respect to

the wavelength, then ree surace elevation in OWC can beapproximated as ollows:

1=in2 cos2

2 sin (/2) , ()

wherein is the averaged internal wave height (m) andit is calculated rom the literature in [, ]. Te angularchamber length(rad)is dened as

=2ch , ()where is the actual wave length; or calculating thiswavelength an equation can be ormulated [] as ollows:

1 30 , ()where is the water depth (m), is the gravitational constant(. ms2), and0 is the theoretical deep water wavelength,which is given by []

0=2

2. ()

Te velocity o the air adjacent to the internal ree surace isthe liner velocity o water height, where

1=1

= in

sin ()sin

2 ,

=2.()

Since the system is relatively low-pressure system, so the axialvelocity passage through the turbine is

2=121= 12

in sin ()sin2 , ()

where1 is the ow surace area o the chamber and2 isthe inlet turbine area. Te powerptavailable at the turbinedepends on the volume o air ow rateacross the turbineand the gradient o pressure. Hence, the power available atthe turbine due to the air pressure term (or completeness,this equation is derived in AppendixD) is

pt= 122in22 2 cos )2 1

sin2 2 +2 2 1 .

()

According to () and (), OWC model is developed usingMatlab Simulink, which is illustrated in Figures (a) and (b).

.. Modeling of Battery. A standard battery model presentedin [] is implemented in this paper. o avoid the battery

algebraic loop problem, this model uses only the state ocharge (SOC) o the battery as a state variable. Moreover,model in [] can precisely characterize our types o batterychemistries including lead-acid battery.

Te battery is modeled using a simple series connectedcontrolled voltage source with a constant resistive value, asshown in Figure , where the controlled voltage source isdescribed by

= 0 + exp , ()Battery= inBattery, ()

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Variable wave height

WH

Variable wave period

WP

Wavelength

T

T w

Matlab function

Matlab function

Chamber inletvelocity

Turbine inletvelocity

Q

A1/A2

V1

V2

A1/A2

A2

u(1) u(2)

Area ratio (A1/A2)

(a)

Pin

Matlab function

Matlab function

Air pressure term

Air velocity term

(Pa)

1.225

0.5

Density

Constant

Turbine inlet powerQ

Matlab subsystem

V1

V2

A1/A2

A2

++

Ppt

(b)

F : Te Simulink diagram o the OWC model.

where0 is the no load battery voltage (V), is thepolarization voltage (V),is the battery capacity (Ah),isthe exponential zone amplitude (V), is the exponentialzonetime constant inverse (Ah)1,Battery is the battery voltage(V),in is the battery internal resistance (),Battery is thebattery current (A), and is the charge supplied anddrawn by the battery (Ah).

Te battery model based on () is developed in Mat-lab Simulink environment and connected to a DC-DC

buck-boost bidirectional converter using controlled voltagesource as shown in Figure.

.. Control of dc-Link Voltage. Te circuit topology o theproposed PV-wave hybrid standalone system is shown inFigure . A neutral wire is placed between the capacitorsconnected beore the VSI or eeding single-phase as wellas three-phase loads to the proposed system, as shown inFigure.

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Controlled

voltage

source

E

Rinternal

V

battery

Ibattery

+

+

E = E0 K Q

Qi dti dt+ Aexp Bi dt

F : Nonlinear standard battery model [].

Controlled currentsource

Matlab functionMatlab function

Matlab functionQ

1.2

K

0.33

0.66

A

B

Eo 1/s

i

vS Vbattery

+

+

+

Rin

Rin1

F : Te Simulink diagram o the battery model.

In this paper, through BBDC the dc link side is connectedto batteries bank; the primary objective o the control o thisBBDC is to maintain constant dc-link voltage as a reerence

value in addition to discharge/charge current rom/to batter-ies bank according to the required load power. Te schematic

diagram o the battery bank BBDC controller is depicted inFigure. Te voltage o the battery bank can be kept loweras compared to the reerence dc-link voltage (dc) by usingBBDC and hence ewer numbers o batteries are required tobe connected in series. In the proposed standalone system,

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Solarirradiance

PV panel

MPPT

VPV IPV

IPV IPV

Duty cycle

Sea wave Turbine

OWC

PMSG

Diode rectier L1

C1

Boost converter

Boost converter

Buck converter

Dump load

Sd

Emergency backup

Ig

Se

Ig

Cdc

Cdc

IGBT PWM load sideinverter

Q1

Q2

C2

L2

Battery

Ibattery

Idc

Vdc

Controller

C3

L-C lterAC bus

Load1

Load2

Load3

Lf

Cf

+

F : Circuit topology o the proposed PV-wave hybrid standalone system with emergency backup and dump load.