Double flux orientation control for a doubly fed induction generator based wind turbine

IJRET: International Journal of Research in Engineering and Technology ISSN: 2319-1163
__________________________________________________________________________________________
Volume: 02 Issue: 03 | Mar-2013, Available @ http://www.ijret.org 380
DOUBLE FLUX ORIENTATION CONTROL FOR A DOUBLY FED
INDUCTION GENERATOR BASED WIND TURBINE.
N. Hamdi1
, A. Bouzid 2
Electrical Laboratory of Constantine “LEC”, Department of Electrical Engineering, Mentouri University - Constantine,
25000 Constantine, ALGERIA, hamdi_naouel@yahoo.fr, you.bouzid@yahoo.fr
Abstract
Abstract In this paper we present a new strategy of vector control for variable speed wind turbines (WT) based on Doubly-Fed
Induction Generator (DFIG). It is based on the principle of a double flux orientation (DFOC) of stator and rotor at the same time.
This one creates the orthogonally between the two oriented fluxes, which must be strictly observed, and therefore leads to generate a
linear and decoupled control of the active and reactive powers. The simulation was performed using Simulink of Matlab to show the
effectiveness of the proposed control strategy.
Index Terms: Doubly fed induction generator (DFIG), wind turbine (WT), double flux Orientation control, vector control.
-----------------------------------------------------------------------***-----------------------------------------------------------------------
1. INTRODUCTION
Wind energy is the way of electrical generation from
renewable sources which uses wind turbines, concentrated in
wind farms, to convert the energy contained in flowing air into
electrical energy. Wind power is the world‘s fastest growing
energy source with a growing at an annual rate in excess of
30% and a foreseeable penetration equal to 12% of global
electricity demand by 2020 [1,2].
The DFIG has some advantages compared to the conventional
squirrel-cage machine. It can be controlled from the stator or
rotor by various possible combinations. Indeed, the input-
commands are done by means of four precise degrees of
control freedom relatively to the squirrel cage induction
machine where its control appears quite simpler [11]. The flux
orientation strategy can transform the non linear and coupled
DFIM-mathematical model to a linear model leading to one
attractive solution as well as under generating or motoring
operations [3,10].
The main idea behind all flux orientation control strategies is
that the machine flux position or vector flux components are
computed from the direct physic measurements. In DFIM,
both stator and rotor currents are easily measured [4].
The paper is organised as follows: In section II, the DFIG
model in an arbitrary reference-frame is presented. In section
III the turbine wind model is presented. In section IV the
control strategy for this system is proposed. Finally, the results
and conclusions are drawn.
2. MATHEMATICAL MODEL OF THE DFIG
The equivalent two-phase model of the symmetrical DFIG,
represented in an arbitrary rotating d-q reference frame is [3
,5,6,7]:
sd
ssq
sqssq
sq
ssd
sdssd
dt
d
dt
d
iRV
dt
d
dt
d
iRV






(1)
rd
rrq
rqrrq
rq
rrd
rdrrd
dt
d
dt
d
iRV
dt
d
dt
d
iRV






(2)
The Stator and rotor fluxes are given as:


















rd
sd
rrs
srs
rd
sd
i
i
LM
ML
.


(3)























rq
sq
rrs
srs
rq
sq
i
i
LM
ML
.


(4)
The electromagnetic torque is expressed as:
)(
2
3
sdsqsqsdem iiC  
(5)
sqsdsdsq
sqsqsdsd
iViVQ
iViVp


(6)

__________________________________________________________________________________________
3. WIND TURBINE MODEL
The air tube around a wind turbine is illustrated in Figure 1.
Assuming that the wind speed (V1) crossing the rotor is the
average value between the upstream speed (V0) and the
downstream speed (V2), the moving air mass of density ρ
crossing the surface S (S = πR2) per unit of time is given by
[9]:
2
)( 20
2
VVR
m



(7)
Fig -1: Air tube around the wind turbine
By applying the conservation of mass to the case of the Fig.1
we have:
221100V SVSVS  (8)
Where Vi is the wind speed at station i and iS is the cross
section area of station i. It is considered thereafter that 1VV 
et 1SS 
The pressure force of the turbine rotor is given by:
2
22
2
00 VSVSF  
(9)
Or equivalently, using Eq. (8):
 20 VVSVF   (10)
Assuming that the speed of the wind crossing the rotor is equal
to the average between the non-disturbed speed of the wind in
the front one the turbine 0V
and the speed of the wind after the
passage through the rotor 2V , that is to say:
2
20 VV
V


(11)
And customarily defining an axial induction (or interference)
factor, a, as the fractional decrease in wind velocity between
position 0 and position 1, by:
0
0
V
VV
a


(12)
Eq. (10) can be rewritten in a more useful manner:
 aaSVF  14
2
1 2
0
(13)
The wind power extracted by the rotor is the product of the
pressure forces the turbine rotor and the speed of the wind in
the plan of the rotor:
     23
00
2
0 14
2
1
114
2
1
aaSVaVaaSVFVPtu  
(14)
Theoretically, a non-disturbed wind crosses this same surface
S without reduction of the speed which is 0V , the
corresponding theoretical power thP would be then:
3
0
2
1
SVPth 
(15)
The ratio between thP and tuP , called the power coefficient Cp
is then:
 2
14 aa
P
P
C
th
tu
p 
(16)
The result is shown in Fig. 2.
The power coefficient has a maximum . This
theoretical value is well-known as ‗Betz limit‘ which
determines the maximum power that can be extracted from a
given wind speed. This limit cannot be reached in reality.
Therefore, each wind turbine is defined by its appropriate Cp
versus the tip-speed ratio λ, where:
v
Rturbine.

(17)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
a
Cp
Fig -2: Power coefficient versus wind speed ratio

__________________________________________________________________________________________
The mechanical power will be written then:
   
2
3
0
2
VR
CCPP ppthtu

 
(18)
This expression allows obtaining a set of characteristics
presenting the generator mechanical power depending both on
the wind and rotating speeds. The result is shown in Fig.3.
0 2 4 6 8 10 12 14 16 18 20
0
0.05
0.1
ratio of speed
powercoefficient(Cp)
Fig-3: Characteristics of mechanical power versus wind and
rotating speeds
3. DOUBLE FLUX ORIENTATION STRATEGY
This strategy consists to turn the rotor flux towards d axis, and
the stator flux towards q axis. After orientation the stator and
rotor fluxes are presented in Fig. 4
Fig-4: DFIG vector after orientation
Consequently, the two fluxes become orthogonal and we can
write:
ssq  
rrd  
0 rqsd 
(19)
If resistance is neglected we have:
0
dt
d
V sq
sq

(20)
ssd VV 
Introducing Using (19) in (6) the developed active power and
reactive power can be rewritten as follows:
sqs
sds
iVQ
iVP


(21)
Where:
rd
s
sr
sd i
L
M
i 
(22)
rq
sr
r
sq i
M
L
i 
(23)
Where:
rq
sr
r
s
rd
s
sr
s
i
M
L
VQ
i
L
M
VP


(24)
4. SIMULATION RESULTS
The system described above is simulated using Matlab -
SimulinkTM.
0 0.5 1 1.5 2 2.5 3
-2
-1
0
1
2
3
4
5
6
x 10
4
temps (S)
puissanceréactive(Var)
Qs-ref (Var)
Qs (Var)
Fig -5: Reactive power versus time.
0 0.5 1 1.5 2 2.5 3
0
0.5
1
1.5
2
temps (S)
fluxsrotorique(Web)
phirq (Web)
phird (Web)
Fig-6: Active power versus time

__________________________________________________________________________________________
0 0.5 1 1.5 2 2.5 3
0
0.5
1
1.5
2
temps (S)
fluxsrotorique(Web)
phirq (Web)
phird (Web)
Fig.7: Rotor fluxes versus time.
0 0.5 1 1.5 2 2.5 3
-1
-0.5
0
0.5
1
1.5
2
2.5
temps (S)
fluwsstatorique(Web)
phisd (Web)
phisq (Web)
Fig-8: Stator fluxes versus time.
We see in fig.5and Fig.6 that the corresponding power follows
the reference signal from 0.21s. In fig.7 and fig.8, the stator
and rotor fluxes are presented versus time and where we can
observe clearly the fluxes orientation strategy. Thus show the
effectiveness of the proposed control strategy.
CONCLUSIONS
Access to the stator and rotor windings is one of the
advantages of the wound rotor induction machine compared to
the conventional squirrel-cage machine. The DFIG offers the
possible control of the active and reactive powers. The
simulations results of this strategy control present clearly the
orientation of fluxes of the stator and rotor with respect to
time. The first advantage of this strategy is the transformation
of the nonlinear and coupled DFIG mathematical model to a
linear and decoupled one. The second advantage consists of
the non use of a controller. The simulation results prove that
the proposed wind power generator is feasible and has certain
advantages.
NOMENCLATURE
QP, Stator active and reactive powers.
sqsd VV ,
d- and q-axis components of the stator voltage.
rqrd VV ,
d-and q -axis components of the rotor voltage.
sqsq ii ,
d- and q-axis components of the stator current .
rqrd ii ,
d- and q-axis components of the rotor current.
sR Stator phase resistance.
rR Rotor phase resistance.
srM Mutual inductance between the stator and rotor.
sL Stator inductance.
rL Rotor inductance.
P Number of poles of the induction machine.
s Stator pulsation.
r Rotor pulsation.
emC Electromagnetic torque.
sqsd  ,
d- and q-axis components of the stator flux linkage.
rqrd  ,
d- and q-axis components of the rotor flux linkage.
REFERENCES:
[1]. C. Millais and S. Teske (2004, May). Wind Force 12: A
blueprint to achieve 12% of the world‘s electricity fromwind
power by 2020.Greenpeace and European Wind Energy
Association [Online].Avalable:
http://www.ewea.org/03publications/WindForce12.htm.
[2]. S. Muller, M. Deicke, and R. W. De Doncker., ―Doubly
fed induction generator systems for wind turbines,‖ IEEE
Industry Applications Magazine, pp. 26–33, May/June 2002.
[3]. M. G. Simões, B. K. Bose, and R. J. Spiegel, ―Fuzzy
logic based intelligent control of a variable speed cage
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Electron., vol. 12, pp. 87–95, Jan. 1997
[4]. Said Drid, Mohamed Tadjine, Mohamed-Said Nait-Said:
―Nonlinear feedback control and torque optimization of a
doubley fed induction motor‖ Journal of
ELECTRICALENGINEERING, VOL. 56, NO. 3-4, 2005,
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[5]. Herrera, J.I. and Reddoch, T.W.; ―Analysis of The
Electrical Characteristics of a Westinghouse Variable Speed
Generating System for Wind Turbine Applications‖
SERI/STR-217-3133, DE88001139, February 1988.
[6]. WANG, S.—DING, Y. : Stability Analysis of Field
Oriented Doubly Fed Induction Machine Drive Based on
Computed Simulation, Electrical Machines and Power
Systems (Taylor & Francis), 1993.Z. Chilengue,

__________________________________________________________________________________________
[7]. R. S. Peña, J. C. Clare, and G. M. Asher, ―Vector control
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[8].T. Tanaka, T. Toumiya, and T. Suzuki, ―Output control by
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Asynchrones pour l‘Utilisation de l‘Energie Eolienne‘‘ .Thèse
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BIOGRAPHIES:
N. Hamdi Was born in Constantine, Algeria, in 1976, in 2003
received the Engineer degree from the University of Montouri
Constantine. Algeria. In 2008 received the M.S. degrees in
electrical engineering, Option electrical machine. . In 2008
inscription in doctor's degree.
Aissa Bouzid was born in Constantine, Algeria, in1954. He
received the diploma of electrotechnology engineer in 1980 at
the science and Technology University of Algiers, Master
degree electronics, (1985) and his PhD in Electrotechnology
from Orsay University of Paris in France (1994). Since 1996
he has been a Professor, at the Faculty of Engineering,
University Mentouri of Constantine. His main scientific
interests are in the fields of circuit theory and applications and
power electronics, also his study is about the photovoltaic
systems and their applications

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Double flux orientation control for a doubly fed induction generator based wind turbine