Page 1 of 16

Journal for Studies in Management and Planning

Available at http://internationaljournalofresearch.org/index.php/JSMaP

e-ISSN: 2395-0463

Volume 01 Issue 02

March 2015

Available online: http://internationaljournalofresearch.org/ P a g e | 246

A New Model Wind Energy for a Stand Alone

Wind Energy System

Vijayakrishna Satyamsetti

E-mail: sdotvijay@gmail.com

Department of Power Electronics and Power Systems, School of Electrical Engineering,

Jawaharlal Nehru Technological University Kakinada, Kakinada , India

ABSTRACT:

This paper presents control scheme for a

stand-alone wind energy conversion system.

Present energy need heavily relies on the

conventional sources. But the limited

availability and steady increase in the price of

conventional sources has shifted the focus

toward renewable sources of energy. Of the

available alternative sources of energy, wind

energy is considered to be one of the proven

technologies.With a competitive cost for

electricity generation, wind energy

conversion system (WECS) is nowadays

deployed for meeting both grid-connected and

stand-alone load demands.However, wind

flowby nature is intermittent. In order to

ensure continuous supply ofpower suitable

storage technology is used as backup. In this

paper,the sustainability of a 4-kW hybrid of

wind and battery system isinvestigated for

meeting the requirements of a 3-kW stand- alonedc load representing a base telecom

station. A charge controller forbattery bank

based on turbine maximum power point

tracking andbattery state of charge is

developed to ensure controlled chargingand

discharging of battery. The mechanical safety

of the WECSis assured by means of pitch

control technique. Both the controlschemes

are integrated and the efficacy is validated by

testing itwith various load and wind profiles

in MATLAB/SIMULNIK.

INDEX TERMS

Maximum power point tracking (MPPT),

pitchcontrol, state ofcharge (SoC), wind

energy conversion system (WECS).

INTRODUCTION

Energy is the considered to be the pivotal

input for development.At present owing to the

depletion of availableconventional resources

and concern regarding

environmentaldegradation, the renewable

sources are being utilized to meetthe ever

increasing energy demand [1]. Due to a

relatively lowcost of electricity production [2]

wind energy is considered tobe one of the

potential sources of clean energy for the

future [3].But the nature of wind flow is

stochastic. So rigorous testing isto be carried

out in laboratory to develop efficient control

strategyfor wind energy conversion system

(WECS). The study ofWECS and the

associated controllers are, thus, becoming

moreand more significant with each passing

day. Nowadays, manystand-alone loads are

Page 2 of 16

Journal for Studies in Management and Planning

Available at http://internationaljournalofresearch.org/index.php/JSMaP

e-ISSN: 2395-0463

Volume 01 Issue 02

March 2015

Available online: http://internationaljournalofresearch.org/ P a g e | 247

powered by renewable source of energy.With

this renewed interest in wind technology for

stand-aloneapplications, a great deal of

research is being carried out forchoosing a

suitable generator for stand-alone WECS. A

detailedcomparison between asynchronous

and synchronous generatorsfor wind farm

application is made in [4]. The major

advantageof asynchronous machine is that the

variable speed operationallows extracting

maximum power from WECS and

reducingthe torque fluctuations [5]. Induction

generator with a lower unitcost, inherent

robustness, and operational simplicity is

consideredas the most viable option as wind

turbine generator (WTG)for off grid

application s [6]. However, the induction

generatorrequires capacitor banks for

excitation at isolated locations.The excitation

phenomenon of self-excited induction

generator(SEIG) is explained in [5]–[7]. The

power output of the SEIGdepends on the wind

flow which by nature is erratic. Both

amplitudeand frequency of the SEIG voltage

vary with wind speed.Such arbitrarily varying

voltage when interfaced directly withthe load

can give rise to flicker and instability at the

load end. So,the WECS are integrated with

the load by power electronic convertersin

order to ensure a regulated load voltage [8].

Again dueto the intermittent characteristics of

the wind power, a WECSneeds to have

energy storage system [9]. An analysis of the

availablestorage technologies for wind power

application is madein [9] and [10]. The

advantage of battery energy storage for

anisolated WECS is discussed in [10].With

battery energy storageit is possible to capture

maximum power [11] from the availablewind.

A comparison of several maximum power

point tracking(MPPT) algorithms for small

wind turbine (WT) is carried outin [12] and

[13]. In order to extract maximum power

form WECSthe turbine needs to be operated

at optimal angular speed [13].However, [11]

do not take into account the limit on

maximumallowable battery charging current

nor do they protect againstbattery

overcharging. In order to observe the charging

limitationof a battery a charge controller is

required. Such a chargecontrol scheme for

battery charging for a stand-alone

WECSusing MPPT is explained in [14].

However, in this paper alsothe maximum

battery charging current is not limited. The

discontinuousbattery charging current causes

harmonic heating ofthe battery. The terminal

voltage instead of state of charge (SoC)is used

for changeover from current mode to voltage

mode. Alsothe MPPT implementation is

Page 3 of 16

Journal for Studies in Management and Planning

Available at http://internationaljournalofresearch.org/index.php/JSMaP

e-ISSN: 2395-0463

Volume 01 Issue 02

March 2015

Available online: http://internationaljournalofresearch.org/ P a g e | 248

highly parameter dependent andwill be

affected by variation of these parameters with

operating conditions.Moreover, as the wind

speed exceeds its rated value,theWT power

and speed needs to be regulated for ensuring

mechanical and electrical safety [15]. This is

achieved by changingthe pitch angle to the

required value [16]. .From a study of the

aforementioned literature, it is observedthat

MPPT schemes with [14] and without [11]

battery chargingmode control and pitch

control technique [20] have been

implementedindependently for stand-alone

wind energy applications.However, none of

the control strategy proposed so far has

integratedall these three control objectives. In

this paper, a hybridwind-battery system is

considered to meet the load demand of

astand-alone base telecom station (BTS). The

BTS load requirementis modeled as a dc load

which requires a nominal regulatedvoltage of

50 V. The WECS is interfaced with the stand- alonedc load by means of ac–dc–dc power

converter to regulate theload voltage at the

desired level. The proposed control

schemeutilizes the turbine maximum power

tracking technique withthe battery SoC limit

logic to charge the battery in a

controlledmanner. Unlike [14], the MPPT

logic used here actually forcesthe turbine to

operate at optimum TSR and hence is

parameterindependent. The battery charging

current is always continuouswith very low

ripple thus avoiding harmonic heating.

Thechangeover between the modes for battery

charging is affectedbased on the actual value

of the SoC. Further it also providesprotection

against turbine over speed, over loading, and

overvoltage at the rectifier output by using

pitch control.

MODELLING OF CASE STUDY

HYBRID WIND-BATTERY SYSTEM

FOR AN ISOLATED DC LOAD:

The proposed hybrid system comprises of a 4-

kWWECS and400 Ah, C/10 lead acid battery

bank. The system is designedfor a 3-kW

stand-alone dc load. The layout of the entire

system along with the control strategy is

shown in Fig. 1. The specificationsof the WT,

SEIG, and battery bank are tabulated in

theAppendix. TheWECS consists of a 4.2-kW

horizontal axis WT, gear box with a gear ratio

of 1:8 and a 5.4 hp SEIG as theWTG.Since

the load is a stand-alone dc load the stator

terminals of theSEIG are connected to a

capacitor bank for self-excitation. The ac

output is rectified by three-phase uncontrolled

diode rectifier.However, there is a need for a

battery backup to meet the loaddemand

during the period of unavailability of