12th International Conference on DEVELOPMENT AND APPLICATION SYSTEMS, Suceava, Romania, May 15-17, 2014
Experimental Analysis on a Self Excited Induction
Generator for Standalone Wind Electric Pumping
Stations
Mohamed Barara, Ahmed Abbou, Mohamed
Akherraz, Abderrahim Bennassar
University Mohamed V Agdal,
Mohammadia School’s of Engineering
Rabat Morocco
Mohamed-barara@hotmail.fr
Abstract—Self Excited Induction Generator (SIEG) has
become a focal point in the research of standalone renewable
energy sources. This paper investigates the capacity and the
applicability of self excited induction generator feeding an
isolated non linear load (induction motor coupled with variable
mechanical load) in order to exploited in the remote areas as
wind electric pump system for different application. The
performance characteristics are examined by experimental test,
the transient, steady state and limit of operating is also discussed
in this study.
Keywords— SIEG ; Excitation capacitance; wind pump.
I.
INTRODUCTION
The energy demand around the world increases the great
opposition facing the nuclear energy in some countries have
spur researchers attentions for renewable energy. The self
excited induction generator is a very popular machine used in
isolated location to generate electrical energy when the grid
connection is difficult due to difficult geographical conditions.
The use of squirrel-cage induction generators are a very
attractive choice because of its low price, mechanical
simplicity, robust structure.
When capacitors are connected across the stator terminals of
an induction machine, and driven at a given speed, the voltage
will be induced from a remnant magnetic flux in the core.
The induced electromagnetic field and current in the stator
windings will continue to rise until steady state is attained,
influenced by the magnetic saturation of the machine. At this
operating point the voltage and current will continue to
oscillate at a given peak value and frequency [1]. The reactive
power must be well provided in order to assure a successful
function of the induction generator [18], since for induction
machine working like generator the magnetizing inductance is
Silviu Ionita, Emilian Lefter, Bogdan Enache
University of Pitesti, Faculty of Electronics,
Communications and Computers
110040 Pitesti, Romania
the main factor for voltage buildup, for unloaded and loaded
conditions.
One of the major problem in the operation of SIEG is that the
value of allowable minimum capacitance is affected by
machine parameters, its speed and load condition. These
calculated values can be used to predict theoretically the
minimum value of terminal capacitance required for selfexcitation. Several papers have investigated the capacitance
requirements of the SEIG by different method [3],[8],[13],[19]
[20]. Also other major problem in the SIEG is that the
inability to control the output voltage under variable speed and
load. In order to solve this drawback, various researchers have
used different control strategy [2],[7],[11],[12],[15],[14],[16].
However this paper presents one of attractive application of
wind energy conversion, the proposed system based renewable
energy source is typically used such as wind power and the non
linear load (induction motor with variable mechanical load)
such a pump system used for different application as irrigation,
supply of drinking water and livestock in rural areas. The main
objective of this work is to examine all behavior of the self
excited induction generator for following main conclusions to a
good exploitation in isolated location.
The advantage of wind-electric pumping systems can be
placed where the wind resource is the best and connected to
the pump motor with an electric cable and we have possibility
to control it. In the other hand the mechanical windmills must
be placed directly above the well, which may not take the best
advantage of available wind resources [9]. An overview of
complete mechanical and electrical wind pumping as show in
Fig 1 and Fig 2 respectively.
978-1-4799-5094-2/14/$31.00 ©2014 IEEE
29
The transient behavior of self excited induction generator
machine is normally represented in the d-q reference as
illustrated in Fig. 4 [1].
Fig.1 Mechanical wind pump
Fig. 4 Self excited induction generator
The following differential equation is obtained for self
excitation induction generator is [1].
PI = AI + B
(1)
Where:
Fig. 2 Wind electric pump systems
.
II.
DESCRIPTION OF SYSTEM
The proposed topology in the laboratory test rig, depicted in
Fig. 3, contains, a three phase squirrel cage induction motor
controlled by variable frequency was coupled to an induction
generator as the prime mover, a capacitor bank and induction
motor coupled with variable mechanical load. The excitation
capacitors for reactive power necessary for the IG selfexcitation process and the auxiliary capacitance for keep the
system under excitation at application of a non linear load as
we well explain in this paper .The parameters of the global
system are given in Appendix.
⎡iqs ⎤
⎡Lm Kq − LrVcq ⎤
⎢ ⎥
⎢
⎥
isd ⎥
1 ⎢Lm Kd − LrVcd ⎥
⎢
;
(2)
;
I=
B=
⎢iqr ⎥
L ⎢LmVcq − Ls Kq ⎥
⎢ ⎥
⎢
⎥
⎢⎣idr ⎥⎦
⎢⎣LmVcd − Ls Kd ⎥⎦
⎡ − Lr Rs − L2mwr
Lm Rr
− Lmwr Lr ⎤
⎥
⎢ 2
Lm Rr ⎥
− Lr Rs Lmwr Lr
1 Lw
A= ⎢ m r
L ⎢ Lm Rs
Ls wr Lm − Ls Rr − Ls wr Lr ⎥
⎥
⎢
⎣⎢− Ls wr Lr Lm Rs − Ls wr Lr − Lr Rs ⎦⎥
(3)
Where
2
m
L = Lr Ls − L
(4)
The magnetizing inductance is determined experimentally
by driving the induction machine at synchronous speed and
taking measurements when the applied voltage was varied.
The saturated inductance (Lm) has been plotted against the
phase voltage.
The variation of magnetizing inductance increases until it
reaches a peak value and decreases until it attains saturated
value as is shown in Fig. 5.
Fig. 3. Proposed block system
A.
Self Exited Indution Generator
All the machine parameters in the equivalent circuit are
assumed to be constant except the magnetizing reactance
which is assumed to be affected by the magnetic saturation.
30
The admittance of global circuit:
0.26
magnetizing inductance(H)
Experiment
0.23
0.2
0.17
0.14
0.11
Fig. 7. Admittance of global circuit
0.08
0.05
0
10
20
30
40 50 60
voltage (V)
70
80
90
The loop equation involving the stator voltage Vs is written
as: Vs.(YG + YC + YM ) = 0
(8)
100
Fig. 5.Variation of magnetizing inductance with phase voltage
B. Excitation System Model
The stator windings of the induction generator are
connected to a triangle capacitive bank also it is important to
note that connected to the induction motor. The equations of
self excitation, at load conditions, are given by:
1
Vcq = ∫ (iqs − i sq )dt
c
1
Vcd = ∫ (ids − i sd )dt
c
The expression of admittance capacitive is giving by:
YC = j
(6)
where:
(7)
The capacitance will be having a value somewhat greater
than the minimum capacitance.
b) With non lineair load (induction motor)
From previous work [3], the minimal value of capacitance
is calculated based on the model depicted in Fig. 6 and Fig. 7
(9)
Yg1 (Yg 2 + Yg 3 )
Yg1 + Yg 2 + Yg 3
YG =
1) Design of Capacitor Bank
a) Without load
In case of the system in not loaded the minimum
capacitance (Cmin) required for building-up the stand-alone
induction generator is [2].
a
XC
The expression of The induction generator admittance is :
(5)
Where isd and isq are dq stator currents of induction motor.
1
C min =
Lm * w 2
where YG is a total admittance induction generator, YC is
admittance capacitive, YM is a total admittance induction
motor and: a P.U. frequency and b P.U. speed.
Yg 1 =
Yg 2 =
Yg 3 =
R sG
(10)
1
+ jaX sG
(11)
1
jaX mG
(12)
1
'
aRrG
'
+ jaX rG
a −b
(13)
The same method is used for calculation YM to motor, since
the total admittance must be equal zero:
Vs ≠ 0 So (YC + YC + YM ) = 0
(14)
Equation (14) is divided into real and into real and imaginary
parts:
ℜ(YG + YM + YM ) = 0
(15)
ℑ(YG + YC + YM ) = 0
(16)
YG =
1
R
X
= 2 G 2−j 2 G 2
RG ' + jX G ' RG ' + ( X G ' )
RG ' + ( X G ' )
(17)
where:
Fig. 6. Equivalent circuit of self excited induction generator feeding an
induction pumps motor
R G ' = R sG +
'
2
a ( a − b ) R rG
X mG
'
'
+ X mG ) 2 + R rG
( a − b ) 2 ( X rG
2
(18)
31
and
2
XG' = aXsG +
'
'
'
aXmG((a − b)2 XrG
(XmG + XrG
) + RrG
)
(19)
2
'
'
(a − b)2 ( XrG
+ XmG)2 + RrG
The nominal condition of the induction motor is given by:
1
RM '
XM'
=
−j 2
RM ' + jX M ' RM2 ' + ( X M ' ) 2
RM ' + ( X M ' ) 2
YM =
(20)
RM’ and XM: are expressed with the induction motor
parameters.
From Equations (15) and (16) we have:
RG '
2
RG '
RM '
+
=0
2
2
+ ( X G ')
RM ' + ( X M ')2
X G'
XM'
a
−
−
2
2
2
XC
RG ' + ( X G ')
RM ' + ( X
M '
(21)
•
Induction motor controlled by variable frequency
(prime mover)
•
Induction generator
•
Excitation capacitance
•
Auxiliary capacitance
•
Induction motor
mechanical load
coupled
with
variable
(22)
= 0
)2
of prime mover speed, excitation capacitance and non linear
load. The results data are determined by numerical scope type
Scopix OX7104-C, transferred to Excel and plotted by
Matlab®, the rms voltage and current are taken by the
measurement devices, the global experimental bench is
presented in Fig 8. It includes the following parts:
It is noted that (21) is independent of XC and the only variable
is the per unit frequency a.
Once the value of a has been determined then XC can be
determined using (22).
For no load operation RM’= ∞ and XM’=0
Substituting RM’= ∞ and XM’=0 in (21):
R sG +
'
2
a ( a − b ) R rG
X mG
On
following:
a
=
max
simplification,
b
−
b
2
⎡
1 −
⎢
⎢
R
⎢
⎢ 1 + R
⎣
(23)
=0
2
'
'
+ ( a − b ) 2 ( X rG
+ X mG ) 2
R rG
it
1 −
yields
(
b
(1 +
sG
'
rG
)
C
b
X
X
2
'
rG
)
2
mG
the
(24)
⎤
⎥
⎥
⎥
⎥
⎦
Fig. 8. Experimental bench
where bc is given by:
2 R sG
X Ms
bC =
R
R
'
rG
+ (1 +
sG
X
X
'
rG
)
(25)
2
mG
Substituting RM= ∞ and XM=0 in (23):
2
2
max
Xc = a
[ X sG +
'
'
'
( X mG + X rG
) + RrG
)
aX mG ((a − b)2 X rG
'
'
+ X mG ) 2 + RrG
(a − b) 2 ( X rG
2
(26)
]
Hence Cmin is given by:
(27)
1
Cmin =
2
2π 50.amax
( X sG +
2
'
rG
'
rG
' 2
rG
'
rG
aX mG ((a − b) X ( X mG + X ) + R )
'
(a − b)2 ( X + X mG )2 + RrG
2
)
Normally, the value of the excitation capacitance must be
greater than a minimum limit selected to ensure self-excitation.
III.
EXPERIMENTS RESULTS
Many example test cases have been studied to evaluate the
behavior of this system, different constraints such as variation
32
A. Step Change of Excitation Capacitance
The first experiment test aims to show the influence of
capacitance bank with no load in transient and steady state:
The system is driven by rotor speed of 1400 rpm and switched
capacitors bank of 27.5 μF.
15
250
200
10
100
s tator c urrent(A )
stator voltage(V)
150
50
0
-50
-100
-150
5
0
-5
-10
-200
-250
-15
0
5
10
15
time (s)
20
25
30
10
15
time (s)
20
25
30
This section investigates the response of the system with
same condition of prime mover 1400rpm by increasing the
value of capacitance up to 55µf.
5
4
3
stator current(A)
5
Fig. 12. Current build up at SEIG terminal with auxiliary capacitance and no
load
Fig. 9. Voltage builds up at SEIG terminal with no load
It well shows that the use of auxiliary capacitance provides a
rapid excitation and increase voltage and current as are shown
in Fig 11and Fig 12.
2
1
0
-1
-2
-3
-4
-5
0
5
10
15
time (s)
20
25
30
B. Sudden Application of non Linear Load(induction motor)
Initially SEIG is running under no load, the system
already excited by capacitance of 27.5µF and driven by
1400 rpm, suddenly a non linear load of induction motor
applied. We observed that the stator voltage and current
fall down and cause the demagnetization of the generator
due to the call of reactive energy.
300
Fig. 10. Current builds up at SEIG terminal with no load
400
300
200
200
s t a t o r v o lt a g e (V )
At the start-up the voltages and the currents generated
increase in exponential form, then they stabilize and it is the
moment when the magnetizing current reaches his so saturated
regime as shown in Fig. 9 and Fig. 10.
stator voltage(V)
0
100
0
-100
100
-200
0
-100
-300
-200
5
10
15
time (s)
-300
-400
0
Fig. 13. Voltage of SEIG terminal with sudden application of non linear load
0
5
10
15
time (s)
20
25
30
Fig. 11. Voltage builds up at SEIG terminal with auxiliary capacitance with no
load
33
4
10
3
5
1
stator current(A )
stator current(A)
2
0
-1
-2
0
-5
-3
-4
0
5
10
15
-10
0
5
10
time (s)
Fig. 14. Voltage of SEIG terminal with sudden application of non linear load
For the same condition of prime mover 1400 rpm with the
application of a non linear load and using the auxiliary
capacitance of 55µF in order to provide necessary reactive
energy. The voltage and current have dropped at time of the
application of a non linear load due to starting time of the
induction motor, and return to the normal condition of
operated without loss the excitation as are shown in Fig. 15
and Fig. 16.
20
25
Fig. 16. Current of SEIG terminal with sudden application of non linear load
and auxiliary capacitance
C. Step change of rotor speed with Sudden application of
non linear load.
The objective of this test is to maintain the system under
excitation without using the auxiliary capacitance but we
increasing the rotor speed until the system operate.
300
400
300
200
s ta to r v o lta g e (V )
200
s t a t o r v o lt a g e (V )
15
time (s)
100
0
-100
-200
100
0
-100
-200
-300
-300
-400
0
5
10
15
20
0
5
10
25
time (s)
Fig.15. Voltage of SEIG terminal with sudden application of non linear load
and auxiliary capacitance
15
time (s)
20
25
Fig. 17. Voltage SEIG terminal with sudden application of non linear and
variation of rotor speed
4
3
stator current(A)
2
1
0
-1
-2
-3
-4
0
5
10
15
time (s)
20
25
Fig. 18. Current SEIG terminal with sudden application of non linear and
variation of rotor speed
34
After the application of a non linear load the system starts to
loss excitation then we increase the speed to high value
between (1900-2200)rpm, after the system returns under
excitation.
From the previous results, the increase in load current should
be compensated either by thereby increasing the rotor speed or
by an increase in the reactive power to the generator.
While in induction generator based renewable energy
systems the energy source is typically a low-speed prime
mover such as hydropower or wind power [7].
It is necessary to investigate the speed limits between which
the machine is capable to build up, without large capacitance
value, the speed will be increased at high level in order to not
loss excitation but for reality is not possible to have this speed
from wind .The good solution is we increase the excitation
capacitance with respected the nominal operation of the
generator.
Fig 19 and Fig 20 show the variation of terminal stator
voltage and current against the excitation capacitance, rotor
speed and non linear load.
This analysis reveals that for a good operation of our system
with respecting the nominal current of induction motor and
generator .The system will be worked about (1250-1450) of
rotor speed with capacitance of 55µF. The increasing of the
capacitance or speed will be exceeded the nominal current of
generator, on the other hand the decreasing of the capacitance
or speed will produce the lost of the excitation of the
generator.
E. Evolution of the rms generator voltage and current
depending of variation of mechanical load of the
induction motor
In this section we fixed the value of excitation capacitance
in order to show the affect of non linear load.
300
275
V o lt a g e rm s
D. Evolution of the rms generator voltage depending on the
speed , excitation capacities and non lineair load
225
V oltage rm s
400
capacitance of 55µF without load
375
capacitance of 27.5F without load
350
capacitance of 55µF loaded by IM+Mechanical load of 1Nm
325
300
275
250
225
200
175
150
125
100
75
50
25
0
1000 1050 1100 1150 1200 1250 1300 1350 1400 1450 1500 1550 1600 1650 1700 1750 180
250
200
175
150
125
100
75
50
C:55µF speed 1500rpm
C:55µF speed 1400rpm
25
0
0
0.5
1
1.5
mecahnical torque (Nm)
2
2.5
Fig. 21. Voltages & currents of SEIG terminals with variation of to non linear
load
8
Fig. 19. Evolution of the rms generator voltage depending on the speed,
excitation capacities and non linear load
7
c u rre n t rm s
Fig. 20. Evolution of the rms generator current depending on the speed,
excitation capacities and load
c urrent rm s
6
10
capacitance of 55µF without load
9.5
9
capacitance of 27.5F without load
8.5
capacitance of 55µF loaded by IM+Mechanical load of 1Nm
8
7.5
7
6.5
6
5.5
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0
1000 1050 1100 1150 1200 1250 1300 1350 1400 1450 1500 1550 1600 1650 1700 1750 1800
d( )
5
4
3
2
1
0
C:55µF speed 1500rpm
C:55µF speed 1400rpm
0
0.5
1
1.5
mecahnical torque (Nm)
2
2.5
Fig. 22. Currents of SEIG terminals with variation of to non linear load
As can be seen form Fig. 21 and Fig. 22 the generated voltage
and current decrease, when the value of the load increases, and
its observed too when the SIEG driving by 1400 rmp the
maximal load operated about 1.5 Nm and with 1500 rpm can
operate at 2 Nm.
35
IV.
CONCLUSION
Accordingly the better applicability of our system as a
wind pump system for isolated applications has been
proposed. The SEIG system is analyzed during the initial selfexcitation, load switching, and reactive power switching. The
purpose of this study was experimentally verified by of the
self-excitation induction generator feeding an isolated non
linear load. In particular the tests were done on a small
available induction generator 1.5kw supplied induction motor
of 0.55kw where we present the behavior and the limit of
operating of this system under different condition. The main
contributions of this work are the successful analysis proposed
may be helpful for researchers to apply a several design and
new control technique for a good exploitation in rural location.
[8]
[9]
[10]
[11]
[12]
[13]
ACKNOWLEDGMENT
The author gratefully acknowledge the support and
facilities provided by the Agence Universitaire de la
Francophonie (AUF) to conduct this research work, and has
been carried out for University of Pitesti, Faculty of
Electronics, Communications and Computers Research Center
Electromet, Pitesti,ROMANIA, Special thanks to Mr Jumara
Ion for their valuable assistance in this work.
APPENDIX
[14]
[15]
[16]
The experimental setup includes no load test and blocked
rotor test in order to calculate the parameters of Self Excited
Induction Generator and Motor.
[17]
The data of the SIEG are indicated as follows:
1.5kW, Voltage=220V/380V, 6.6/3.8A, f=50Hz, 1405 tr/min,
P=4poles, Rs=5Ω, ls=lr=0.0234H, Rr=2.594Ω, lm=0.3725H.
[18]
The data of the induction motor are indicated as follows:
[19]
0.55kW, Voltage=220V/380V, 2.77/1.6A, F=50Hz, 1385
tr/min, P=4poles, Rs=14.6Ω, ls=lr=0.0495H, Rr =8.558Ω,
lm=0.587H.
[20]
REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
36
Seyoum D., Grantham C. and Rahman F,“Analysis of an Isolated SelfExcited Induction Generator Driven by Variable Speed Prime Mover”,
Proc.AUPEC‟01,pp. 49-54 , 2001.
Ahmed, T.; Nishida, K.; Nakaoka, M.; Tanaka „‟Advanced Control of a
Boost ACDC PWM Rectifier for Variable-Speed Induction
Generator‟‟K.Applied Power Electronics Conference and Exposition,
2006. APEC '06. Twenty First Annual IEEE 956-962 March 19, 2006.
A. abbou M. Barara, A. Ouchati, M. Akherraz, H. MahmoudiI’’
capacitance required analysis for selef excited induction genertor’’ 30th
September 2013. Vol. 55 No.3, 2013.
Samir Moulahoum and Nadir Kabache’’ Behaviour Analysis of Self
Excited Induction Gen erator Feeding Linear and No Linear Loads’’ J
Electr Eng Technol Vol. 8, No.: 742-?, 2013.
Dheeraj JOSHI, Kanwarjit Singh SANDHU, Mahender Kumar SONI’’
Voltage Control of Self-Excited Induction Generator using Genetic
Algorithm’’ Turk J Elec Eng & Comp Sci Vol.17, No.1, 2009.
A. M. Kassem A. A. Hassan and Yehia S. Mohamed,’’Adaptive Voltage
and frequency Control of an Isolated Wind-Generation System Using
Neural Networks’’.
M. Godoy Simões, Sudipta Chakraborty and Robert Wood, ’’Induction
Generators for Small Wind Energy Systems’’ IEEE Power Electronics
Society newsletter19, Third Quarter 2006.
S.N. Mahato a,*, S.P. Singh b, M.P. Sharma’’ Excitation capacitance
required for self excited single phase induction generator using three
phase machine’’ Energy Conversion and Management 49 pp. 1126–
1133, 2008.
http://www.windpoweringamerica.gov/pdfs/small_wind/small_wind_gui
de.pdf
Shakuntla BOORA’’On-Set Theory of Self-Excitation in Induction
Generator’’International Journal of Recent Trends in Engineering, Vol
2, No. 5, November 2009.
B. G. Ziter, “Electric Wind Pumping for Meeting Off-Grid Community
Water Demands,” Guelph Engineering Journal, Vol. 2, 2009, pp. 14-23.
Miranda, M.S.; Lyra, R.O.C.; Silva, S.R. "An alternative isolated wind
electric pumping system using induction machines", Energy Conversion,
IEEE Transactions on, On page(s): 1611 - 1616 Vol. 14, Issue: 4, Dec
1999 .
Karim H. Youssef, Manal A. Wahba, Hasan A. Yousef and Omar. A.
Sebakhy ‗‘A New Method for Voltage and Frequency Control of StandAlone Self-Excited Induction Generator Using PWM Converter with
Variable DC link Voltage‘‘2008 American Control Conference Westin
Seattle Hotel, Seattle, Washington, USA June 11-13, 2008 .
M. Ouali, M. Ben ali Kamoun, M. Chaabene,” Investigation on the
Excitation Capacitor for a Wind Pumping Plant Using Induction
Generator”, Smart Grid and Renewable Energy, 2, pp 116-125, 2011.
Mohamed barara and all ‘’ Modeling and Control Voltage of Wind
Pumping Systems using a Self Excited Induction Generator’’
International Journal on Electrical Engineering and Informatics Volume 5, Number 2, June 2013.
T. Ouchbel *, S. Zouggar †, M. Seddik, M. Oukili et M. El Hafyani‟‟
Régulation de la puissance d‟une éolienne asynchroneà vitesse variable
à l‟aide d‟un compensateur d‟énergie réactive (SVC) Revue des
Energies Renouvelables Vol. 15 N°3 (2012) 439 – 450 .
Mohammed Ali Elgendy, Bashar Zahawi’’Comparison of Directly
Connected and Constant Voltage Controlled Photovoltaic Pumping
Systems’’, IEEE TRANSACTIONS ON SUSTAINABLE ENERGY,
VOL. 1, NO. 3, OCTOBER 2010.
M.L. Elhafyani, S. Zouggar, Y. Zidani and M. Benkaddour, „Permanent
and Dynamic Behaviours of Selfexcited Induction Generator in
Balanced Mode‟, M. J. Condensed Mater, Vol. 7, pp. 49 - 53, 2006.
Avinash Kishore, G. Satish Kumar’’Dynamic modeling and analysis of
three phase self-excitedinduction generator using generalized state-space
approach ‘’,International Symposium on Power Electronics, Electrical
Drives, Automation and Motion , SPEEDAM 2006.
C. Chakraborty, S.N. Bhadra, A.K. Chattopadhyay,”Excitation
requirements for standalone three phase induction generator”, IEEE
Transactions on Energy Conversion, Vol. 13, No. 4, 1998, pp 358-365.