 Open Access
 Total Downloads : 257
 Authors : Avinash D. Matre, Roshan P. Haste, Mrs. S. L. Shaikh
 Paper ID : IJERTV3IS052086
 Volume & Issue : Volume 03, Issue 05 (May 2014)
 Published (First Online): 09062014
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Voltage and Frequency Controller for Three Phase Four Wire Isolated Double Wind Energy Conversion System using Cage Generators
Avinash D. Matre
PG Student, Electrical Department Walchand College of Engineering.
Sangli, India.
Roshan P. Haste
PG Student, Electrical Department Walchand College of Engineering.
Sangli, India.
Mrs. S. L. Shaikh
Asst. Prof., Electrical Department Walchand College of Engineering.
Sangli, India.
AbstractThis paper presents a new voltage and frequency Controller for three phase four wire isolated double wind energy conversion system using one squirrel cage induction generator (SCIG) driven by a variablespeed wind turbine and another SCIG driven by a constant power wind turbine feeding three phase fourwire local loads. The proposed system consist two back to backconnected pulse width modulation controlled insulated gate bipolar transistor based voltage source converters (VSCs) with a battery energy storage system at their dc link. The main purpose of the control algorithm for the VSCs is to achieve control of the magnitude and the frequency of the load voltage. The proposed system has a capability of bidirectionalactive and reactive power flow, by which it controls the magnitude and the frequency of the load voltage. In this system wind turbineand a voltage and frequency controller are modeled and simulated in MATLAB using Simulink and Sim Power System set toolboxes and various aspects of the proposed system are studied for different types ofloads, and under varying wind speed conditions. The performance of the proposed system is presented todemonstrate its capability of voltage and frequency control (VFC) and load balancing.
Keywords Battery energy storage system (BESS), Wind energy conversion system, Squirrel cage induction generator (SCIG).
I.INTRODUCTION
Due to souring prizes of fossil fuels and increase in emission of greenhouse gases, the reasonableattention given to the renewable energy sources.Renewable energy sources are the natural energyresources that are inexhaustible, for example, wind, solar,geothermal, biomass, and small hydrogeneration.
As considering wind turbines, they are consisting of two types of wind turbine generators fixed speed and variable speed turbinein which rotational speedvaries inaccordance with wind speed. Theenergyconversion efficiency of fixed speed wind turbine is very lowfor widely varying wind speeds.In early years, windturbinetechnology has switched from fixed speed to variablespeed. The features ofvariable speed machines are they reducemechanical stresses, dynamically compensate for torque andPower pulsations, and improve power quality and systemefficiency [1].
When the renewable energy sources are connected to the grid, the total active power is fed to the grid. Forisolated
systems supplying local loads, if the extracted power ismore than the local loads (and losses), the excess power is supplied to a dump load orstored in the battery bank [1].
WhenSCIG is used for wind generation, its reactivepowerrequirement is met by a capacitor bank at its statorterminals. The SCIG has advantages like being simple, lowcost, rugged, maintenance free, absence of dc, brushless, etc.,
In this paper, a new threephase fourwire isolated wind energy conversion system is proposed for isolated locations, which cannot be connected to the grid. The proposed system utilizes variable speed
WindturbinedrivenSCIG (subscript vfor variable speed wind), and a constantspeed/constantpower windturbine
drivenSCIG (subscript c for constantspeed wind). For the rest of this paper, the subscript v is used to denote the
parameters and variables ofthe variable speed windturbine generator, and the subscript c is used to denote the parameters and variables of the constant power windturbine generator.A battery energy storagesystem (BESS) is used in the dc link, which performs thefunction of load leveling in the wake of uncertainty in thewind speed and variable loads. In order to remove the ripplesfrom the battery current an inductor isconnected in series with the BESS.
A new control algorithm is proposed for the double wind energy conversion systemit has the capability of loadleveling, load balancing, along with voltage andfrequency control (VFC).
For the proposed system, there are three modes of operation. In the first mode, the required active power of the load is less than the power generated by theSCIG , and the
excess power generated by the SCIG is transferred to the
BESS through the loadside converter. Moreover, the power
generated by the SCIG is transferred to the BESS.Second mode, the required active power of the load is morethan the
power generated by theSCIG but less than the total
power generated by SCIG and SCIG . Thus, portion of thepower generated by SCIG is supplied to the load through theloadside converter and remaining power is stored in
BESS. Inthe third mode, therequired active power of the
load is morethan the total power generated by SCIG and
SCIG . Thus,the deficit power is supplied by the BESS, and
thepowergenerated by
SCIG
and the deficit met by BESS
= 1 + ( ( ) –
are suppliedto the load through the loadside converter.

PRINCIPLE OF OPERATION
This system uses two back to backconnected PWM controlled IGBTbased VSCs. These VSCs are referred to
as the machine (SCIG ) side converterand loadside
( 1))+ ( ) (8)
( )
()
= (1) + ( ( ) ( 1))
+ ( ) (9)
The reference threephase SCIGC currents are thencompared with the sensed SCIGC currents ( , , and )
converter. The objectives of the machine(SCIG ) side converter are to convert AC to DC, and the objectiveof the
loadsideconverter is VFC at the load terminals
tocompute the SCIGC
current errors as
=
(10)
bymaintaining active and reactivepower balance..
= (11)
The loadside converter is controlled for theregulation
=
(12)
ofloadvoltage magnitude and loadfrequency. To maintain theloadfrequency constant, it is essential that any surplus
activepower in the system is diverted to the battery. Also, thebattery system should be able to supply any deficit in thegenerated power. Similarly, the magnitude of the load voltageis maintained constant in the system bybalancing the reactivepowerrequirement of the load through the load side converter.

CONTROL ALGORITHM

Control of Machine Side Converter
The main purpose of the loadside converter is to convert AC into DC. It is used as a rectifier.

Control of LoadSide Converter
The main purpose of the loadside converter is to maintain rated voltage and frequency at the load terminals irrespective of connected load.
Generation of Reference ThreePhase Currents:
The reference voltages ( , , and ) for the control of
These current errors are amplified and theamplifiedsignals are compared with a fixedfrequency (10 kHz)triangular carrier wave of unity amplitude to generate gatingsignals for IGBTs of the loadside converter.


DESIGN OF SCIGBASED DOUBLE WIND ENERGY CONERSION SYSTEM
The system is designed for an isolated location with theload varying from 30 to 90 kW at a lagging pwer factor (PF)of
0.8. The average load of thesystem is considered to be 60Kw.

Selection of Rating of SCIGs
The rating of the variable speed wind turbine is considered as 55Kwand that of constant speed wind turbineis taken as 35Kw.Both turbines arecoupled to SCIGs. Therating of the
the load voltages at time tare given as
SCIG is equal to the rating of the variable speedwind turbine,which is 55kW. The rating of the SCIG should be
= 2 sin(2) (1)
equal tothe rating of the constant speed wind turbine, which
(2)
is 35kW.
= 2 sin(2 120)
= 2 sin(2 + 120) (3)
wheref is the nominal frequency, which is considered as 50
Hz, and is the rms phaseto neutral load voltage, which is considered as 240 V.
The load voltages ( , , and ) aresensed andcompared with the reference voltages.The error voltages( ,
and ) at the nthsampling instant arecalculated as
Vanerr(n) ={V*an(n) Van(n)} (4)
Vbnerr(n) ={V*bn(n) Vbn(n)} (5)

Modeling of wind turbine
The mechanical power captured by the wind turbine is
= 0.5 2 3 (14)
Where =coefficient of performance, r=radius of turbine, =wind speed, =density of air.
C.Selection of voltage of dc link and battery design
Vcnerr(n) ={V*cn(n) Vcn(n)} (6)
For satisfactory PWM control, the dc busvoltage(
) must
The reference threephase SCIGC currents ( , , ) are
be more than the peak of the linevoltage [8]
generated by feeding the voltage error
= 2 2 (15)
= 1
+ (
– 1 ) 3
( )
( )
( ) ( )
where
is the modulation index normally with a
+ ( ) (7)
maximumvalue of one and is the rms value of the line
voltage on theac side of the PWM converter. The maximum
rms voltage atSCIG terminals as well as the rms value of the line voltage atthe load terminals is 415 V. Substitute the
value ofac=415V,
the value of Vdc should be obtained as 677.7 V. The voltage ofthe dc link and the battery bank is selected as 700 V. Battery is an energy storage unit, its energy isrepresented in kilowatthour, when a capacitor isused to modelthe battery
90 kW at 0.8 lagging PF. The reactive power of the load is supplied by the loadside converter. Hence, the reactive power flow through loadside converter ( ) is equal to
thereactive power demand of the load ( ). At a load of 90
kW at0.8 lagging power factor,
= = (90/0.8) Ã— 0.6 = 67.5kvar.
Therefore, the kVA rating of the loadside
converter( ) is
unit, the equivalentcapacitance
is given as[7].
=
= 156.5
= Ã—3600 Ã—1000
0.5 2 2
(18)
Where
3
is the rms voltage on the ac side of theload side
converter, which is 415 V.
Where and are the minimum and maximumopen circuit voltage of the battery under fully
discharged andcharged conditions. HereThevenins model is used fordescribing the battery in which the parallel combination ofcapacitance ( ) and resistance( ) in series
with internalresistance( ) and an ideal voltage source of
The maximum current through the switching devices in the loadside converter =1.25 Ã— (11.1 + 221.3) = 290.5 A.
The voltage rating of the switching devices is decided by the dclink voltage, whose maximumvalue is 750 V. Taking a 25% margin, the voltagerating of the switching devices of the loadsideconverter should be more than 1.25Ã—750 V,
voltage 700VTaking the values of 680V, andkW Â· h = 600, the value of
= 750V, =
i.e., 937.5 V.
The commercially available rating for switching device
obtained is 43156F.

Selection of Rating of Machine ( ) Side Converter
The maximum activepower flow through the machine side
converter = 55 kW, and the maximum reactive power flow provided from the machineside converter ( ) is calculated as
(IGBT) higher than 937.5 V and 290.5 A is 1200 V and 300
A.
F.Selection of rating of AC inductor and RC filter on ac side of loadside converter
An inductor is used on the ac side of the loadside converter for boost function. For 5% ripple in the current through the
inductive filter, inductance ( ) of the inductive filter can be
2
=
2
2
= 18.4 (19)
calculated as[8]
Where
is the maximum line voltage generated at the
= { 3 /(6 ( ) )} (19)
SCIG terminals, which is 415 V, at a frequency(f) of 50 Hz generated at a wind speed of 11.2 m/s.
The V A rating ( ) of the machinesideconverter is calculated as
Where
= switching frequency=10kHz
= 0.76
=(2 + 2 ) = (552 + 18.422) = 58kVA
A highpass firstorder filter tuned at half theswitching frequency is used to filter out the noise from the voltage at
and the maximum rms machineside convertercurrent as
the load terminals. The timeconstant of the filter should be very small compared with the fundamental time period (T), or RC <<T/10.When T = 20 ms, considering, C = 5F, R
=
3
= 80.7 .
can be chosen as 5.
The voltage rating of the switching devices is decided by the dclink voltage, whose maximum value is 750V. Taking a 25% margin,the voltage rating of the switching devices of the machineside
Converter should be more than 1.25 750 V, i.e., 937.5 V. The maximum current through the switching device is 1.25{0.05 (2) 80.7 + (2) 80.7}A =149.8 A.
The ratings of the commercially available device (IGBT) higher than these values are 1200 V and 200A, and the same are selected for the design purpose.

Selection of Rating of LoadSide Convertor

The rating of the loadside converter is determined by the case when the connected load is at its maximum value, i.e.,


MATLAB BASED MODELING
A simulation model is developed in MATLAB using Simulink and Sim Power System set toolboxes. The developed MATLAB model for the double windenergy conversion system is shown in Fig.1.
Fig.1. MATLAB simulation diagram of double wind energy conversion system.
Fig.2. Performance of double wind energy conversion system with balanced linear load (60Kw) at wind speed of 11.2 m/s.
Fig.3. Performance of double wind energy conversion system with balanced linear load(100Kw)at wind speed of 11.2 m/s.
Fig.4. Performance of double wind energy conversion system with balanced linear load (20Kw)at wind speed of 8 m/s.

SIMULATION RESULTS
The performance of the double wind energy conversionsystem with the proposed control algorithm is demonstrated under different dynamic conditions (various electrical conditions andmechanical conditions) as shown in Figs. 24. Moreover, performance of the double wind energy conversion system is studied with various electrical loads. Theperformance of the system is also studied under
varying SCIG rotor speeds due to wind speed variations
.The simulated transient waveforms of the three
phaseSCIG stator current(Isv), SCIG stator current(Isc),SCIG stator power( ),SCIG stator power( ),load voltage( ),load frequency( )are shown for different operatingconditions. Thus it verifies the three
modes of operation.

CONCLUSION
Among the renewable energy sources, wind energy conversion system is more reliable source of energy.A new threephase four ire autonomous double wind energy conversion system, using one cage generator driven by variable speed wind turbine andanother cage generator driven by constantspeed/constant power wind turbine along withBESS has been modeled and simulated in MATLAB usingSimulink and sim power system. Theperformance of thedouble wind energy conversion system has beendemonstrated under differentelectrical andmechanical dynamic conditions. It has beendemonstrated that the proposed double wind energy conversion system performssatisfactorily under different dynamicconditions whilemaintaining constant voltage and frequency. Moreover, it hasshown capability of load balancing.
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BIOGRAPHY
Avinash D. Matrehas obtained B.E. (Electrical)from B.M.I.T,Solapur India in 2011. Currently he is pursuing
M.Tech in Electrical Power System, from Walchand College of Engg. Sangli, India under the guidance of Prof. Mrs. S. L. Shaikh
Roshan P. Haste has obtained B.E. (Electrical) fromGovt College of Engg,
ChandrapurIndia in 2010. Currently he is pursuing M.Tech in Electrical Power System, from Walchand College of Engg. Sangli, India under the guidance of Prof. Mrs. S. L. Shaikh
Prof. Mrs. S. L. Shaikh is an Assistant Professor in Department of Electrical Engineering at Walchand college of Engineering, Sangli. Her area of interest is Power system Stability.