 Open Access
 Total Downloads : 877
 Authors : Rajan K. Detroja, Ronak V. Patel, Prof. Priyesh J. Chauhan
 Paper ID : IJERTV2IS3430
 Volume & Issue : Volume 02, Issue 03 (March 2013)
 Published (First Online): 21032013
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Operation And Modeling Of SelfExcited Induction Generator Based Standalone Wind Energy Conversion System
Rajan K. Detroja, Ronak V. Patel, Prof. Priyesh J. Chauhan Department of Electrical engineering
Marwadi education foundation, Rajkot, 360 003, Gujarat, India
Abstract
This paper concerns an application of a three phase cage induction machine (IM) as a self excited generator connected to the ac side of a voltagesource pulse width modulation bidirectional inverter. The generator is supposed to be driven by a wind turbine. The proposed system is intended to be applied in rural plants as a lowcost source of high quality ac sinusoidal regulated voltage with constant frequency. Selfexcited induction generator (SEIG) with Static var compensator (STATCOM) supported with battery energy storage system has been presented. As compared to dc link capacitor provided with the STATCOM, battery energy storage improves system stability and prevents power wastage.

Introduction
In the literature, it is well known that a threephase induction machine can be made to work as a selfexcited induction generator. When capacitors are connected across the stator terminals of an induction machine, driven by an external prime mover, voltage will be induced at its terminals. The induced electromotive force (EMF) and current in the stator windings will continue to rise until the steady state condition is attained, influenced by the magnetic saturation of the machine. There are two types of induction machine based on the rotor construction namely, squirrel cage type and wound rotor type. Squirrel cage rotor construction is popular because of its ruggedness, lower cost and simplicity of construction and is widely used in standalone wind power generation schemes. Wound rotor machine can produce high starting torque and is the preferred choice in gridconnected wind generation scheme [6].
The advantages of using standard three phase squirrel cage induction machine as a selfexcited induction generator, SEIG over synchronous alternator are the lower cost due to their simple construction, and the lower maintenance requirements due to their ruggedness and to avoid using brushes. Also, one does not need a separate source for dc excitation current which is required for synchronous alternator. The other advantage is the inherent over load protection. At the occurrence of fault, the current will be limited by the excitation, and the machine voltage will collapse immediately.
Due to the increasing demand on electrical energy and environmental concerns, a considerable amount of effort is being made to generate electricity from renewable sources of energy. The major advantages of using renewable sources are abundance and lack of harmful emissions. Wind is one of the most abundant renewable sources of energy in nature. The wind energy can be harnessed by a wind energy conversion system (WECS), composed of a wind turbine, an electric generator, a power electronic converter and the corresponding control system [1].

The Proposed Scheme
The increasing rate of depletion of conventional energy sources has given rise to increased emphasis on renewable energy sources such as wind, microhydro, biogas, etc. selfexcited induction generator(SEIG) are becoming popular because of their numerous advantages over alternators, specially for windgeneration of electricity in isolated places.
Important parts are available in this system configuration:

Wind turbine system

Selfexcited induction generator(SEIG)

Inverter(STATCOM)

Isolated load
In next part of this paper we will see the modeling of each part and see its important in this system configuration.
Fig.1 system configuration


Wind Turbine
The mechanical power generated by a wind turbine is given by Equation (5).
= = (1)
= 1 = 1 0.035 (2)
For using Equation (1) to (4) see the relationship between versus in Fig. 2.
In fig.2 to fig. 3 are graph of wind turbine generator using Equation (5) and (6). These graphs are generated in the matlab simulation for different different wind velocity.
0.5
0.45
0.4
0.35
0.3
Cp
Cp
0.25
0.2
0.15
0.1
0.05
0
0 1 2 3 4 5 6 7 8
lambda
Fig. 2 Relation between Cp versus
2200
V=12 m/s
V=12 m/s
2000
1800
1600
V=11 m/s
V=11 m/s
1400
POWER
POWER
1200
V=10 m/s
V=10 m/s
1000
800
600
400
= 21 (3)
200
0
0 10 20 30 40 50 60 70 80
SPEED(rad/s)
= 0.5176 116 5 + 0.0068
(4)
= 1 3 (5)
Fig. 3 Relation between wind power and speed
70
60
V=12 m/s
V=12 m/s
V=11 m/s
V=11 m/s
2 50
=
P = Mechanical output power of the turbine (W)
= Performance coefficient of the turbine
(6)
40
V=10 m/s
V=10 m/s
TORQUE
TORQUE
30
20
10
0
0 10 20 30 40 50 60
SPEED(rad/s)
= Air density (kg/m3)
A = Turbine swept area (m2) Vw = Wind speed (m/s)
= Tip speed ratio of the rotor blade tip speed to wind speed
= angular speed of the turbine shaft
Fig.4 Relation between torque and speed for wind turbine

Modeling of Integrated Generating System
The model of the integrated generating system has been developed which is having the following four salient components:
= 1
+

Induction Machine

Excitation system

Load and

STATCOM and its equivalent circuit.

Modeling of induction machine
The dq axes diagram of 3phase symmetrical SEIG with 3phase balance excitation capacitor and load across its terminals is shown in Fig. 5.
Fig. 5 Schematic dq axes diagram of SEIG.
The dq axes equivalent circuit of the 3 phase symmetrical SEIG with a 3phase balanced excitation capacitor and load across its terminals is shown in Fig. 6.
For the development of induction generator model, the dq arbitrary reference frame model of induction machine is transformed into stationary reference frame. Using dq component of the stator currents (isd & isq) and rotor currents (ird & irq) as state variables, the following differential equations are derived from the equivalent circuit shown in Fig. 6.
2
(10)
Fig. 6 Equivalent circuit of the Induction Generator in dq axes stationary reference frame
= + (11)
= + (12)
= + (13)
= + (14)
= 1
2
2
+
The electromagnetic torque can be computed as a function of q and d axes stator and rotor current as:
+ (7)
= 3 (15)
= 1
+ 2
2 2
+ +
2
+ (8)
Where,
= 1
+
+ +
Subscripts q and d are for quadrature and
2
direct axes;
(9)
Subscript l for lekage component;
Subscripts s and r are for stator and rotor variables;
v and i instantaneous voltage and current; im magnetizing current;
flux linkage;
r resistance;
M magnetizing inductance; L inductance;
P number of pole;
fundamental component of STATCOM and SEIG voltages. The output terminals of the STATCOM are connected through a coupling transformer having leakage inductance Xs forms the first order low pass filter, which minimizes the current harmonics inducted to SEIG terminals.
For the development of STATCOM model, the dq arbitrary reference frame model of STATCOM is transformed into stationary reference frame. Using dq component of the STATCOM currents as state variables, the following differential equations are derived from the circuit shown in Fig. 7.
=
sin +
(19)
r electrical rotor speed;

Modeling of Excitation System
=
cos +
(20)
The excitation system introduces the following state equations using dq components of stator voltage (vsd
Where,
& vsq) as state variables, from the circuit shown in Fig. 6.
ic subscripts for current through coupling
inductance;
=
(16)
VDC D.C battery voltage;
VAC SEIG per phase terminal voltage;
=
(17)
VPWM fundamental component of
STATCOM per phase voltage;
Where Ceq and Ced are the excitation capacitor values along with q and d axes.

Modeling of Load
The d and q axes current equations for balanced resistive load can be given by:
=
(18)
=
Where RL is load resistance.

Modeling of STATCOM
(19)
Fig. 7 STATCOM with battery energy storage system connected to SEIG terminals.
As mentioned earlier the STATCOM
consists of 3phase voltage source pulse width modulated bidirectional inverter having a bank of battery at the DC bus, which is used to absorb or supply active power between the AC bus and the STATCOM according to the value of modulation index m and phase angle between the
Rc resistance of coupling inductance; Lc coupling inductance;
m modulation index of the PWM inverter; k coupling transformer turns ratio;
phase angle between the voltages
At =0, the value of m, at which STATCOM does not draw any active and reactive power from the PCC. This value of m is called critical of mcril.
160
140
120
VOLTAGE
VOLTAGE
100
80
60
40
20
2 4 6 8 10 12 14 16 18
CURRENT
Fig. 9 Saturation graph of SEIG
1000
800
600
400
VOLTAGE
VOLTAGE
200
0
200
400
600
800
1000
0 0.5 1 1.5 2 2.5 3
TIME
(a)
5
x 10
Fig. 8 qd axis equivalent circuit of SEIG with STATCOM


Simulation Results
In Fig 10 are representing the waveform of generated voltage and machine torque at different value of capacitor bank. For SEIG capacitor bank
600
400
VOLTAGE
VOLTAGE
200
0
200
400
600
0 0.5 1 1.5 2 2.5 3
provide a reactive power to the machine to work as a generator and see the change in Fig 10. In this model induction machine is used. And saturation graph of the machine see in Fig 9. See the rating of induction machine in appendix.
400
300
200
(b)
TIME
5
x 10
Fig. 9 is relationship between no load voltage and current. In induction machine this saturation limit take as linear but in generator cannot take as linear.
100
VOLTAGE
VOLTAGE
0
100
200
300
400
0 0.5 1 1.5 2 2.5 3
In Fig.10 I conclude that the value of capacitance increases, generated voltage and torque
(c)
TIME
5
x 10
are decreases. And also change the time of generated voltage.
Fig. 10 Generated voltage of SEIG for (a) 200 ÂµF (b) 300 ÂµF (c) 400 ÂµF with no load
In Fig. 11 are representing the waveform of generated voltage and machine torque at different
value of rotor speed. In matlab speed model is used as a induction machine.
1000
800
600
400
VOLTAGE
VOLTAGE
200
0
200
400
600
800
1000
0 0.5 1 1.5 2 2.5 3
applied after 4 sec. I set the frequency is 50 Hz and generated voltage is set around 230 V rms. And specification and parameter of induction machine see in appendix.
500
400
300
200
VOLTAGE
VOLTAGE
100
0
100
200
300
TIME
(a)
5
x 10
400
500
0 1000 2000 3000 4000 5000 6000
TIME
1000
800
600
400
VOLTAGE
VOLTAGE
200
0
200
400
600
800
1000
0 0.5 1 1.5 2 2.5 3
2500
2000
SPEED
SPEED
1500
1000
500
0
0 1000 2000 3000 4000 5000 6000
TIME
1000
(b)
TIME
5
x 10
50.7
50.6
50.5
FREQUENCY
FREQUENCY
50.4
50.3
800
600
400
VOLTAGE
VOLTAGE
200
0
50.2
50.1
50
0 1000 2000 3000 4000 5000 6000
TIME
200
400
600
800
1000
0 0.5 1 1.5 2 2.5 3
Fig. 12 SEIG with proper RL load after 3 sec and STATCOM after 4 sec

Conclusions
TIME
(c)
5
x 10
Many important and interesting aspects of
Fig. 11 generated voltage of SEIG for (a) 1815 rpm
(b) 1830 rpm (c) 1845 rpm with no load
In Fig. 11 I conclude that the value of rotor speed increases, generated voltage and torque are decreases. And also change the time of generated voltage.
I used a open loop of control system so use proper control scheme the synchronization of converter and SEIG become near to ideal. No transients are produce see in Fig. 12 STATCOM
an isolated selfexcited induction generator have been discussed and presented in this paper. The study comprises theoretical analysis and simulation to induction generators. The modeling and characteristics of induction machines in general has been presented to provide an overall perspective of induction generator. Increasing the capacitance value can compensate for the voltage drop due to loading but drop in frequency can be compensated only by increasing the speed of the rotor. For an isolated self excited induction generator driven by a wind turbine the characteristics of the output power and torque of
the wind turbine are important. The output power and torque of a wind turbine drop at high turbine angular rotor speed.

Appendix
INDUCTION MACHINE1
Specification: – connected, squirrelcage, speed input, 5595 VA, 230 V, 4pole, 60 Hz
Parameters: – Rs=0.195, Rr=0.177, Lls=0.001313 H, Llr=0.001969 H
INDUCTION MACHINE2
Specification: – connected, squirrelcage, torque input, 5595 VA, 230 V, 4pole, 50 Hz
Parameters: – Rs=0.5 , Rr=0.5 , Lls=0.004 H, Llr=0.004 H

References
Godswill Ofualagba, Analysis of the Dynamic Characteristics of an Isolated SelfExcited Induction Generator Driven by a WindTurbine, International Journal of Scientific & Engineering Research Volume 2, Issue 2, February2012
ChingHuei Lee, Li Wang, a novel analysis of parallel operated selfexcited induction genepmtors, IEEE Transactions on Energy Conversion, Vol. 13, No. 2, June 1998.
Marcos S. Miranda, Renato 0. C. Lyra, Selenio R. Silva, an alternative isolated wind electric pumping system using induction machines, IEEE Transactions on Energy Conversion, Vol. 14, No. 4, December 1999.

Enes GonÂ¸calves Marra, Student Member, IEEE, and JosÂ´e Antenor Pomilio, Member, IEEE. "Self Excited Induction Generator Controlled by a VS PWM Bidirectional Converter for Rural Applications." IEEE TRANSACTIONS ON
INDUSTRY APPLICATIONS, VOL. 35, NO. 4,
JULY/AUGUST 1999.

Archer, C. L. and Jacobson, M. Z. (2007). "Supplying base load power and reducing transmission requirements by interconnecting wind farms." Journal of Applied Meteorology and Climatology.